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Building Ocean Science Partnerships: The United States and Mexico Working Together (1999)

Chapter: 2 Examples of Promising Science Programs and Projects

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Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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2
Examples of Promising Science Programs and Projects

This chapter describes a set of potential programs and projects that are of binational interest and scientific significance. Each topic was developed by a team of Mexican and U.S. ocean scientists. The studies described below are designed both to illustrate the existence of a wide range of possible projects of common interest and binational importance and to show the wealth of important questions that could benefit from (or require) collaboration between U.S. and Mexican scientists. The projects presented are not an exhaustive list of scientific issues and admittedly reflect the interests and expertise of members of the Academia Mexicana de Ciencias-National Research Council (AMC-NRC) Joint Working Group on Ocean Sciences (JWG). Concrete proposals, implementation plans, and other details required to initiate new research related to these and other topics depend on consultation and inclusion of scientists beyond the JWG, for example, through focused workshops. In the development of other binational ocean science activities, they should pass the test of being studies that are (1) of unique scientific concern to scientists in the United States and Mexico in waters adjacent to or significantly influenced by these nations and (2) best done collaboratively. Another source of ideas for binational research is the plan of the Southwest Regional Marine Research Program (1996). The JWG identifies here projects that should be done cooperatively because scarce resources from both countries could be used more effectively and the scientists of each nation have knowledge (not all of which has been published) unavailable to the other nation. It is possible that either nation could conduct the research alone, but the research would be more efficient if knowledgeable scientists from both nations could be involved.

An effective binational collaboration in ocean science between the United

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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States and Mexico will require sufficient human and economic resources from both nations to make the collaboration meaningful and equitable. In this regard, and given the limited resources available, only a few binational projects can be promoted at any given time, after a peer-review process to select projects that address specific binational oceanographic topics, contribute to answering interesting scientific questions, and help solve marine-related problems shared by the two nations. Project size should not be the determining factor. Some binational collaboration has been initiated with small projects involving few scientists and graduate students. Other projects, for example, those requiring regional oceanographic observations, must be larger, requiring proportionately larger budgets and involving a larger number of scientists and students. Project administration, regardless of size, does not automatically promote bureaucracy. The expeditious channeling of economic resources, minimization of binational political barriers, and granting of project organization and administration independence minimize bureaucratic barriers.

The studies described below include both single-discipline and multi-disciplinary projects, classified by geographic region. In planning research on these topics, it should be recognized that insights can be gained not only by research within individual regions, but also by comparative studies among the three regions.

PACIFIC OCEAN AND GULF OF CALIFORNIA REGIONS

Oceanographic Setting

Pacific Ocean

The Pacific Ocean region shared by the United States and Mexico is dominated by the California Current, which flows southward as the eastern boundary current of the subtropical North Pacific Ocean (Figure 2.1). This surface current overlies a poleward subsurface flow. Wind-driven coastal upwelling is prevalent, especially in the summer season. The California Current is punctuated by upwelling of nutrient-rich cool waters and current jets that can extend 100 or more kilometers (km) offshore (Batteen, 1997). These features depend on coastal wind patterns that vary with climate (Bakun, 1990) and on other factors such as topography, interior ocean circulation, and instabilities of the currents. Batteen (1997) has shown that the meridional variability of the Coriolis parameter (ß effect), irregularities in the coastline geometry, and the longshore component of wind stress are key ingredients for generating the vertical and horizontal structures of the California Current System. Such structures render the currents unstable, resulting in the generation of meanders, filaments, and eddies.

The coastal seafloor topography off the Californias (California and Baja California) features a narrow continental shelf, submarine canyons, basins, and is-

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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FIGURE 2.1 Important features of the Californias and Gulf of California.

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
×

lands that greatly affect regional circulation, sediment transport, and biology. This region is called the California Borderland (Figure 2.1). The coast of the Californias is also the site of many bays that provide shallow-water coastal habitats missing from the exposed outer coast. For the purposes of this report, the region of proposed cooperative activities extends from Point Conception in California to the southern tip of Baja California and the Gulf of California.

There have been both extensive, long-term studies (e.g., the California Cooperative Oceanic Fisheries Investigations [CalCOFI]) and intensive studies (e.g., Coastal Upwelling Experiment [CUE], Coastal Ocean Dynamics Experiment [CODE], Ocean Prediction Through Observation, Modeling, and Analysis [OPTOMA], Coastal Transition Zone [CTZ] experiment, and Eastern Boundary Currents [EBC] experiment) of the California Current and the inshore coastal upwelling systems farther north. The U.S. Global Ocean Ecosystems Dynamics (GLOBEC) program is developing a scientific study focused on the ecosystem dynamics of the California Current System (GLOBEC, 1994). In 1997, the Center of Scientific Investigation and Higher Education of Ensenada (Centro de Investigación Científica y de Educación Superior de Ensenada [CICESE]) initiated a new program for the long-term monitoring of the waters off Baja California: Investigaciones Mexicanas en la Corriente de California [IMECOCAL], as a counterpart to the CalCOFI program, using similar methodology and occupying stations in Mexican waters that include stations of the old CalCOFI network that had been abandoned.

In terms of physical oceanography, a great deal has been learned in the past three decades about the physical processes characteristic of eastern boundary currents over the continental shelf in regions where the shelf is long and straight, particularly regarding coastal upwelling, upwelling fronts, coastal jets, undercurrents, response to transient (day-to-day) winds, seasonal wind-driven shelf circulation, coastal trapped waves (periods of days to weeks), local and remote forcing, waves propagating from the equatorial Pacific Ocean, perturbations associated with the El Niño-Southern Oscillation (ENSO), and interannual variations (Huyer, 1983, 1990; Neshyba et al., 1989; Batteen, 1997).

More recently, there has been progress in studying more complex phenomena such as

  • the nature of the upwelling front and associated jets and eddies in the case where the front lies seaward of the edge of the continental shelf;

  • the relation between coastal upwelling jets and the core of the California Current;

  • the evolution of jets and eddies through an upwelling season;

  • the circulation in regions of more complex bottom topography (see the special issue of the Journal of Geophysical Research, 1991); and

  • the influence that wind forcing, coastal irregularities, and the variation of the Coriolis parameter have on the generation of many of the observed features of the California Current System (Batteen, 1997).

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
×

South of the U.S.-Mexico border there has been some sampling of the California Current by CalCOFI, which was interrupted in the late 1970s. Although the CalCOFI program covered latitudes north and south of the U.S.-Mexican border, the sampling has been more intense and continuous in U.S. waters. Many important gaps persist at the southern (tropical) limit of the California Current System along Baja California and in the Gulf of California.

One example of a large-scale feature that has not been sampled adequately is the California Undercurrent. This is a narrow ribbon of water from the south, approximately 20 km wide, flowing poleward, with its core located at a depth of approximately 200 meters (Batteen, 1997). This current is almost always found hugging the continental slope but occasionally intrudes onto the shelf. There is a distinct thermohaline signature of the waters within this ribbon (i.e., the Subtropical Subsurface Water) that distinguishes them continuously to the south, somewhat beyond the Gulf of Tehuantepec. The presence of poleward undercurrents is a common phenomenon along eastern ocean boundaries (see Neshyba et al., 1989; Batteen, 1997).

Another large-scale feature that deserves more intensive study is the confluence of the California and Costa Rica Currents, which occurs near the latitude of Cabo Corrientes. The surface flows from north and south merge and turn westward, forming the North Equatorial Current. The seasonal shift and modulation in the position of this confluence is known only vaguely. A similar feature deserving study is the mixture of subarctic waters of the California Current, tropical waters of the Costa Rica Current, and waters outflowing from the Gulf of California in the vicinity of the mouth of the gulf.

Analysis of large-scale marine wind observations (Parrish et al., 1983; Bakun and Nelson, 1991) shows that the wind-driven or Ekman transport* of water off-shore occurs year-round to at least the southern tip of Baja California. Variations—convergences and divergences—of this transport imply upwelling and downwelling in different regions along the coast.** The regions of convergence

*  

According to Ekman's theory, the steady-state wind-driven transport of water in the ocean surface layer is proportional to the wind stress at the sea surface, is directed 90 degrees to the right (left) of the wind in the Northern (Southern) Hemisphere, and takes place in a layer (the Ekman layer) some tens of meters deep. The depth of this layer and the distribution of currents within it depend on poorly known frictional processes in the layer, but the total transport integrated over the layer depends only on the surface wind stress and the Coriolis parameter in the Ekman theory, and so can be calculated without any direct measurement of ocean currents.

**  

If the Ekman layer transport is convergent at a particular place, more water flows into that location than flows out, so there must be a compensating downwelling out of the layer to conserve the mass of water. Conversely, a divergent Ekman transport implies upwelling of deeper water into the Ekman layer. Since there can be no flow through a coastal boundary, equatorward winds on the West Coast produce a coastal Ekman divergence, and thus, coastal upwelling. The curl of the wind stress (a physical property involving east-west [north-south] gradients of north-south [east-west] wind stress) yields the estimate of open-ocean upwelling or downwelling in the Ekman theory. Since the equatorward winds off the West Coast have an offshore maximum, there is cyclonic wind stress curl over the shoreward side of the California Current, and thus, open-ocean upwelling there.

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
×

seem to separate populations of fish such as anchovies, sardines, and mackerel. The 1982–1983 and 1997–1998 El Niño events have had dramatic impacts on the eastern Pacific Ocean off Mexico and the United States in relation to the current systems, ocean properties, marine biological systems and fisheries, and local climate. The scientific questions raised by the 1997–1998 El Niño and the data that have been generated will contribute significantly to the research agenda in the years ahead. The phenomenon affects all of the scientific problems discussed here.

Gulf of California

The virtually land-locked Gulf of California is an extreme physical and geological environment, characterized by such major features and processes as

  • large tidal range, reaching 10 m during spring tides, causing extensive drying and flooding of the nearshore regions;

  • relatively pristine and arid land areas;

  • strong tidal streams and strong vertical mixing forced by them;

  • wide shallow-water deposits of fine sediments in the Colorado River delta;

  • local wind forcing of both drift currents and wave-induced mixing;

  • strong resuspension of seabed material, probably correlated with tidal and wind-induced mixing; and

  • circulation that may distribute particulate matter across the shelf, reaching the deeper basins near the middle of the gulf.

Variability of Fisheries

The social and economic concerns related to studies of the California Current System are obvious. An improved ability to monitor and predict primary and secondary productivity has potential value for improving the management of coastal fisheries and possibly allowing forecasting of catch. Forecasting the onset of ENSO events could enable the prediction of their effects on coastal ecosystems. A better understanding of the California Current System and its variations may also be useful in mitigating the effects of pollution (e.g., oil spills or pollutants from coastal communities).

Fish populations in this region fluctuate considerably, apparently under the influence of global-scale climatic and oceanic variations (Figure 2.2), and are also affected by the coastal physical conditions described in the previous section, and, of course, by human fishing activities and predation by other marine organisms. Fluctuations in the abundances of organisms found in the California Current System parallel those of other stocks of the same (or similar) species in other areas of the world (Lluch-Belda et al., 1992). The specific mechanisms through which the environment provokes these significant changes are unclear, but this is one of the most important questions to be answered if proper management of

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
×

FIGURE 2.2 Cycles of abundance of sardine and anchovy species worldwide, showing the coincidence of fish abundance (panels A, C, D) and sea surface temperature (SST) and air temperature (panel B). Type I and Type II fishes tend to have different cycles. Thus, Type I fish species (sardines + Benguela anchovy) have higher abundance during periods of high SST and Type II fish species (anchovies + Benguela sardine) have higher abundance during times of lower air and sea temperatures. Source: Lluch-Belda et al. (1992) (used with permission from Blackwell Scientific Publications). Note: mmt = million metric tons.

fisheries is to be achieved. Working Group 98 of the Scientific Committee on Oceanic Research (Worldwide Large-Scale Fluctuations of Sardine and Anchovy Populations) (Lluch-Belda et al., unpublished report) stated:

  • Coherent fluctuations on a decadal scale affect fish populations and the structure of their ecosystems; transitions between stages typically are abrupt. Cycles of high and low abundance of certain species—mainly evident in the temperate sardines Sardinops—alternate with abundances of other groups of species, most clearly anchovies.

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
×
  • Worldwide coincidences of such regime shifts imply links to global climate variability.

  • There are regime shifts (Steele, 1996) presently occurring in several major oceanic ecosystems.

  • These large-scale variations pose severe challenges to sustainable economic development and to fisheries management.

  • Regime shifts are now hypothesized to be of far greater magnitude than interannual variation and present fundamentally different problems than usually considered by fisheries science. Existing approaches are inadequate for the management of sardine and anchovy fisheries and associated economic development because they do not account for regime shifts that occur on time scales of decades.

Environmental variations seem to affect marine organisms directly through several locally different mechanisms. Indeed, many local events are related simultaneously to large-scale climatic and oceanic changes. An understanding of how climate affects fish population abundances is important not only in the Californias, but also in all of the eastern boundary current systems in the world, which are fueled by coastal upwelling and are particularly vulnerable to climate variations such as ENSO. The effectiveness of fisheries management will depend significantly on how well we understand and predict such effects. This is true not only for sardines and anchovies (which account for more than 10% of world landings), but also for many other species. Climate changes affect not merely a few fish species, but exert effects on the physical and biological characteristics of entire ecosystems, as revealed by fluctuations of other commercial fish populations (e.g., see Bakun, 1996) and of other components such as thermocline depth (Polovina et al., 1995), zooplankton volumes (Roemmich and McGowan, 1995a,b), and the abundance of marine organisms such as fish (Bakun, 1996), abalone, and other benthic species (Phillips et al., 1994; Vega et al., 1997).

Regime shifts and the associated changes in abundance and distribution of critical prey species such as sardines and anchovies have profound influences on the population dynamics and status of marine mammals and seabirds. The most notable example of such effects is the drastic changes in populations of marine mammal and seabird populations associated with ENSO events (Trillmich and Ono, 1991). These long-lived species have adapted to withstand annual and decadal variations in food resources over large spatial and temporal scales. However, many species are now at historically low population levels, at least partially due to overfishing, pollution, disturbance, and habitat degradation, and may not be able to accommodate future changes in prey species and composition resulting from regime shifts.

The Pacific coast of the Californias offers a unique opportunity to learn how the environment acts on both populations and ecosystems in upwelling regions. It includes several distinct upwelling zones (Southern California Bight, Pt. Banda, Pt. Eugenia, Bahia Magdalena, and larger islands of the Gulf of California) with year-round high productivity, controlled by different mechanisms in each zone.

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
×

There are two arguments to support the common interest of both the United States and Mexico in studies of the physics and biology of the California Current System. First, the California Current constitutes a continuous major ecosystem fully shared by the two countries. As such, intense interdependence of populations through migratory patterns, advection, genetic interchange, and trophic relations is widely recognized. Second, the need for cooperation is increasing because the demand for marine living resources is growing. Societal concern for the environment has created a movement toward sustainable management practices, requiting new approaches for wise management. Natural and anthropogenic events and processes induce fluctuations, and possibly long-term changes in the abundance and availability of marine species, that may be as strong as those induced by harvesting.

The problem of fluctuating fish populations extends well beyond scientific interest. Managing shared, uncontrollably fluctuating resources is not a trivial challenge. Further, human fishery activities profoundly influence and are in turn influenced by marine mammals and seabirds. In the face of major natural changes in abundance and availability, the management of human activities becomes considerably more complex and must extend beyond the mere assurance of sustainability. Marine harvesting needs to be managed to avoid exerting too much fishing pressure during natural collapses, yet be able to detect and exploit population booms. Switching target species during regime shifts to avoid wasting fishing infrastructure and attempting to allocate fishing effort temporally and geographically to improve efficiency will not be easy tasks without deeper insight into the fundamental ecosystem processes. Answers to some of these fundamental questions will be found most readily by comparative studies among regions around the world that exhibit similar physical and biological processes. Comparative studies can be conducted most efficiently and with the most insight if carried out cooperatively, rather than unilaterally.

Binational cooperation could lead to greater progress in understanding the effects of the physical environment on fisheries in the California Current System (e.g., fish and shellfish population fluctuations caused by ENSO phenomenon [Phillips et al., 1994; Vega et al., 1997]. Studies must include socioeconomic aspects—Fisheries resources and their exploitation—and should document the enormous losses that result from unpredictable, major fluctuations in natural systems. More specifically, there are a number of important scientific questions related to the physical dynamics of the California Current System and how the physical system affects the population dynamics of commercially important fish species. The following are some examples:

  • What is the nature of the climatic and oceanic variations, and what drives them?

  • Are these variations predictable? Scientists have gained some degree of ability in predicting the timing and magnitude of ENSO events, even though the

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
×

biological outcomes of these events, such as the relative abundance of sardines and anchovies, are less predictable (Lynn et al., 1995; Smith, 1995; Chavez, 1996).

  • How should we expect climatic and oceanic variability to change if global warming occurs?

  • What is the dynamic behavior of eddies and upwelling that allows for the maintenance of large sardine and anchovy populations throughout the year in areas ranging from subarctic to subtropical?

  • How do these major changes affect population abundances, and by which specific mechanisms? Why do anchovy populations increase when sardine populations are scarce?

  • Where are sardine and anchovy populations located near the southern limit of the California Current System, and do these populations vary coherently with others elsewhere?

  • What is the offshore structure of the California Current at its southern extent, given the fairly steady Ekman transport throughout the region?

  1. Does the California Current have a relatively narrow (<100 km), highvelocity (approximately 50 centimeters per second [cm/s]) core off the Baja California coast, as it does off northern California, or is it broad and weak as described by Wooster and Reid (1963)?

  2. How do the California Current's strength and position vary with season?

  • Is there a near-shore (i.e., over or near the shelf) coastal jet flowing toward the equator at southern latitudes, as there is in midlatitude coastal upwelling regions (e.g., Oregon, northern California)?

  • How do the strength and position of the poleward undercurrent or countercurrent over the continental slope vary with season?

  • Are the dynamics of this system governed primarily by coastal upwelling (i.e., offshore Ekman transport), open-ocean upwelling due to wind-stress curl (i.e., Ekman pumping), or ring/eddy dynamics?

Study of the California Current's regime shifts presents a binational challenge because of the limitations of resources for such a large-scale, long-term (decadal-scale) task. The only way regime shifts in the California Current System can be studied is within the context of a larger regional or global program, for example, through the establishment of a regional ocean observing system or through links with the Climate Variability and Predictability (CLIVAR) program or other international programs designed to study decadal-scale changes and comparisons among eastern boundary current systems.

The causes and effects of short-term climate variability in coastal areas of the United States and Mexico is another important topic for collaborative research. Short-term climate variability is dominated by ENSO events (on a 2- to 10-year time scale) in the Pacific Ocean and by North Atlantic Oscillation (NAO) events (on a 10- to 20-year time scale) in the Atlantic Ocean (with repercussions in the Caribbean Sea and Gulf of Mexico). The impacts of ENSO events are relatively

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
×

well understood and intensively studied on the Pacific coasts of the United States and Mexico compared to those of NAO events on the Atlantic/Caribbean/Gulf of Mexico coasts of the two countries, but much remains to be understood on both coasts. The severity of the 1997–1998 ENSO event highlights the importance of improving U.S.-Mexican interactions on this topic. The scientific questions raised by the 1997–1998 ENSO event and the data that have been generated from it will contribute significantly to the research agenda in the years ahead. The phenomenon affects all of the scientific problems discussed here.

The impacts of ENSO events on the Pacific Coast involve anomalous currents, surface temperatures, and runoff; increased storm damage, especially due to excessive rainfall; and the displacement of biota, including fish, beyond their normal ranges. Furthermore, ENSO events are known to impact the Caribbean Sea and Gulf of Mexico through anomalous atmospheric forcing, especially changes in surface winds and precipitation due to altered weather cycles and storm tracks. The coastal impacts of NAO events are basically unexplored; however, it has been established that sea surface temperature (SST) variability in the Caribbean Sea and Gulf of Mexico is linked to anomalous SSTs in the tropical Atlantic Ocean associated with the NAO.

Climate fluctuations of the Caribbean, southern meso-America, and northern South America are associated with anomalous SST variability in both the tropical Pacific and tropical Atlantic (Enfield, 1996). The effect of ENSO is to produce rainfall deficits along the Pacific coast of meso-America during the rainy season following the period of maximum Pacific SST anomalies. However, with the possible exception of strong ENSO events, non-ENSO SST warmings in the tropical North Atlantic, especially when the South Atlantic is cool, has a stronger association with rainfall in this region, increasing it (Enfield and Alfaro, 1998). These are manifestations of the NAO.

Collaborative studies of regional, short-term climate variability, including its impact on coastal circulation and ecosystems, associated with ENSO and NAO events will have obvious societal benefits (including predictability of climate). Additionally, climate variability will serve as a natural test of our understanding of the response of circulation systems and ecosystems under differing atmospheric forcing conditions. To achieve maximum effect, such collaborative studies will require cooperation among hydrologists, meteorologists, and oceanographers in multi-year investigations.

Marine Mammals and Seabirds

Seabirds and marine mammals rely on regional patches of high productivity that result from localized sources of nutrient influx associated with upwelling or tide-induced vertical mixing regions, bottom topography, or divergence zones (Schoenherr, 1991; Kenney et al., 1995; Macaulay, 1995). As endotherms with high metabolic rates, seabirds and marine mammals are the dominant consumers

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
×

of zooplankton and fish biomass and can influence the community structure of marine habitats (Estes et al., 1978; Huntley et al., 1991). Their populations are distributed in patches and their distributions are usually good predictors of areas of high productivity and prey abundance (Fraser et al., 1989; van Franeker, 1992). The population centers or breeding locations of many marine mammals and seabirds are located in close proximity to such areas of high productivity (Hui, 1979, 1985; Winn et al., 1986; Reilly, 1990; Mullin et al., 1991; Whitehead et al., 1992; Kenney et al., 1995). For example, the highest densities of brown pelican, brown-and blue-footed boobies, and California sea lions are associated with the highly productive waters of the mid-region of the Gulf of California (Breese and Tershy, 1993; Tershy et al., 1993; Velarde and Anderson, 1994).

Many seabirds breed exclusively or primarily in the Pacific Ocean and Gulf of California regions (e.g., yellow-footed gull, Townsend shearwater, blackvented shearwater, Caveri's murrelet, black storm petrels, least storm petrels, Heermans gull, elegant tern, and possibly Xantu's murrelet). Many of these species are endangered or threatened, and although their population status and distribuffon are relatively well known in the United States, very little is known about their status in Mexican waters (Velarde and Anderson, 1994).

Four species of pinnipeds breed in this region (harbor seal, northern elephant seal, California sea lion, and Guadalupe fur seal) and three are resident. The region is a critical feeding and breeding ground for 26 whale species. The 30 species of marine mammals found in these waters represent 25% of all species of marine mammals in the world (Vidal et al., 1993). Some of these species exist nowhere else in the world or have breeding colonies that are located exclusively in the waters off Baja California (Barlow et al., 1997). For example, the highly endangered vaquita, a small porpoise, is limited to less than a few hundred individuals living exclusively in the northern region of the Gulf of California. The sole breeding site of the Guadalupe fur seal is limited to one island. The calving grounds of the entire California gray whale population (approximately 22,000 individuals) are situated exclusively in the coastal lagoons and embayments of the Pacific coast of Baja California. In addition, populations of other species, such as humpback and blue whales, remain quite low and continue to receive protection under national and international agreements for endangered species. Populations of both blue and humpback whales migrate between their winter and spring breeding grounds of the Pacific coast of Mexico and in the Gulf of California to their summer feeding grounds off the west coast of the United States (Urban et al., 1987). Importantly, the population of blue whales that inhabits the regional waters between the United States and Mexico is the only one in the world that appears to be increasing.

A wealth of information exists for some species with regard to their population status, general biology, feeding ecology, and migratory patterns; such information is totally lacking for other species. Application of new technologies, such as satellite telemetry, recoverable data loggers, molecular markers, acoustic track-

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
×

ing, and remote sensing, combined with dedicated research vessels, holds significant promise to increase our understanding of the ecology and biology of these important marine predators (Greene and Wiebe, 1990; Costa, 1993; Hoelzel, 1993). These new tools have already provided significant insights into the lives of a few species (Boyd, 1993). The potential exists to link marine mammal and seabird studies with investigations of commercially important prey species such as anchovies, sardines, and squid. The relatively calm waters and the high concentrations of marine mammals and seabirds in the Pacific Ocean and Gulf of California provide a unique opportunity to apply these new techniques to pelagic species that have been difficult to study.

Significant insights into the ability of marine mammals and seabirds to adjust to climate-driven changes in food availability and abundance (e.g., El Niño effects) would be gained from inclusion of these top predators into integrated studies of fisheries biology and biophysical interactions. Fledgling efforts are under way at a number of institutions in the United States and Mexico. Researchers at the University of California at Santa Cruz and Davis have collaborated with colleagues at the Autonomous University of Baja California and the Interdisciplinary Center of Marine Sciences (CICIMAR-La Paz) of the National Polytechnic Institute (IPN), to study marine mammal and seabird populations and foraging ecology in the Gulf of California and Pacific Ocean. Texas A&M University at Galveston is carrying out a major research effort funded by the U.S. Minerals Management Service to understand the relationship between marine mammal abundance and the physical and biological oceanography of the Gulf of Mexico (Davis and Fargion, 1996).

Pinnipeds and seabirds require isolated and predator-free islands to rear their young successfully and are thus extremely susceptible to the short-term negative impacts of human disturbance (Anderson et al., 1976) and the long-term negative impacts of introduced terrestrial mammals (Burger and Gochfeld, 1994; Velarde and Anderson, 1994). In the past 30 years, a 175% increase in the human population of the Pacific coast and Gulf of California areas and road construction along much of the coast have increased the accessibility and attractiveness of the region's islands to commercial fishers, tourists, and other potential visitors. Together with the increased human disturbance there has been introduction of non-indigenous mammals. Currently, one species of seabird, the Townsend shearwater, is threatened with extinction due to the presence of introduced mammals on all known breeding colonies, and other species are endangered. Most of the important breeding islands are legally protected as natural areas. Thus, the development and application of effective techniques to eradicate introduced mammals from such islands are possible and can have long-term conservation benefits for breeding seabirds in the region.

Human development of estuarine habitats also may impact both seabirds and marine mammals through the direct loss of foraging and breeding habitat and the indirect loss of areas important in the life history of prey species. For example,

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
×

the destruction of the Colorado River delta due to the collapse of freshwater flow directly and indirectly threatens the vaquita as well as regional populations of many species of seabirds that breed and winter in the upper Gulf of California. Similar to what has already occurred in the United States, the smaller-scale destruction of wetland habitat through increasing marina and aquaculture development further threatens seabird and marine mammal populations in Mexico.

Climate-Controlled Laminated Sediments

Finely laminated sediments in periodically or permanently anoxic basins of the California Borderland and the Gulf of California carry a detailed record of the ocean's response to global climate change over at least the past 100,000 years, as shown in the Santa Barbara Basin by correlation to the isotopic temperature records of the Greenland ice cores and to events in the North Atlantic Ocean (Kennett and Ingram, 1995). Certain oceanic sites, such as the Santa Barbara Basin, apparently amplify the climate-ocean coupling signal. The laminations are alternately dominated by oceanic and terrestrial components and by oxygenated, bioturbated sediments versus undisturbed sediments.

Studies by Baumgartner et al. (1992) of fish scales in laminated sediments show a 2,000-year record of fluctuations of the populations of the Pacific sardine and the northern anchovy over periods of about 60 and 100 years, respectively. Recent changes in these populations resemble fluctuations of the past. Studies of anoxic sediments off western Baja California and in the Gulf of California (e.g., Holmgren-Urba and Baumgartner, 1993) show a similar long time series of fish population fluctuations. Observations of laminated sediments could help answer questions regarding the physical and biological factors that control long-period variations of the marine environment. Preliminary work on the subject has been carried out by Broenko et al. (1983), Devol and Christensen (1993), and Ayala-López and Molina-Cruz (1994), but further work could provide new insights.

Collaborative research on laminated sediments by Mexican and U.S. scientists could be quite productive as a means of refining estimates of past climate changes and the response to such changes by the ocean's physical and biological systems. Such collaborative research is already occurring in the Gulf of California—for example, on slope basins northeast of La Paz—involving the Autonomous University of Baja California Sur and the University of Southern California, but similar research should also be conducted in the California Borderland. Comparative studies of processes occurring in these two regions would improve our understanding and use of these sensitive climatic indices.

Marine Pollution

Reports of beach closures, bans on shellfishing, health warnings to seafood consumers, waste discharge to the sea, ocean dumping, and habitat losses have

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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increased public concern about the quality and health of the coastal environment in the Mexico-U.S. border areas (Botello et al., 1996). Consequently, the public is becoming increasingly aware of pollution problems in the coastal marine environment, particularly on beaches and adjacent waters.

The marine environment in the Mexico-U.S. border area is used heavily for transportation, recreation, and commercial fishing and is the final repository of many pollutants, threatening both marine ecosystems and coastal human populations. The impacts of pollution include contamination and disease in fish and shellfish populations, changes in kelp beds and other ecosystems, changes in plankton populations due to nutrient enrichment by wastewater, and contamination of sediments and organisms with toxic material and bacteria in wastewater and storm runoff. These effects can accumulate as local and regional inputs continue over time.

The range of contaminants introduced into the marine environment surrounding the U.S.-Mexico border region is extensive. Among the contaminants that should be studied are bacteria and pathogens, particulate organic matter and solids, trace metals, synthetic organic chemicals, and products of oil exploration and production. Among the regional pollution topics that need to be studied are the following:

  • the biogeochemistry related to inputs, pathways of transport, and fates of various pollutants;

  • the usefulness of regularly acquired coastal environmental quality data as a foundation for resource management and policy (there are many monitoring programs presently operating; are they effective?);

  • the role of bivalve sentinel organisms in monitoring chemical contaminants;

  • the effectiveness of sewage outfall monitoring: and

  • the biological effects of chemical contamination.

Standardized bioassay protocols and bioaccumulation tests should be required, to assess (1) the toxicity of effluents to marine life, (2) the hazards of human consumption of fishery products from coastal areas affected by such effluents, and (3) habitat changes resulting from human activities. As a foundation for such studies, the following steps will be necessary:

  • Develop an inventory of harmful chemicals and bacteria in the border coastal environment.

  • Identify sources of environmental pollutants.

  • Develop basic descriptions of the geography, hydrology, water quality, nearshore circulation patterns, climate, habitats, and natural resources of areas prone to pollution, including land-use patterns and economic activities.

In the near future, monitoring and research related to marine pollution must assess the degree of exposure and sensitivity of marine ecosystems to contaminants, as well as the cumulative effects of these agents.

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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Sediment Transport in the Upper Gulf of California

The waters of the northern Gulf of California (less than 40 m deep) are mixed vertically by tidal currents, resulting in large amounts of sediment in suspension, particularly in the channels within river deltas, for example, at the mouth of the Colorado River. Concentrations of suspended particulate matter reach 130 milligrams per liter (mg/L) near the Baja California side of the upper gulf, decreasing to 5 mg/L toward the center of the northern gulf (García de Ballesteros and Larroque, 1974). Extreme values of 10 g/L have been reported at the mouth of delta channels. Sediments originating in the delta region have been observed 250 km to the south, near Ángel de la Guarda Island. Whether resuspension and widespread sediment transport take place over the remainder of the northern gulf or other local areas is not yet known. It has been shown that when sediments are resuspended, nutrients are released with the interstitial water, so sediment transport could have a direct impact on food chains through stimulation of phytoplankton growth (Hernández-Ayón et al., 1993).

Ongoing research at CICESE involves detailed measurement of suspended sediment and velocity profiles. It is known that the tidal influence on turbidity is large; advection and resuspension signals are both important, but the former seems to dominate during neap tides (Cupul-Magaña, 1994; Alvarez and Ramírez, 1996). Off Baja California, concentrations of suspended sediments were about 5 mg/L near the surface and about 80 mg/L near the seafloor during spring tides.

There are studies of the circulation (Godínez, 1997), hydrography (Alvarez Borrego et al., 1973; Alvarez Borrego and Galindo-Bect, 1974; Alvarez Borrego et al., 1975), biomass, nutrients, seston (Farfán and Alvarez Borrego, 1992; Hernandez-Ayón et al., 1993; Zamora-Casas, 1993) and hydrodynamical modeling (Carbajal et al., 1997; Marinone, 1997; Argote et al., 1997) of the area, but a comprehensive understanding of sediment transport has not been achieved. Most of the knowledge we have gained about suspended sediments and turbidity in the upper gulf comes from observations. As a result, changes taking place at tidal and lower frequencies are unexplained and unpredictable. Frequent measurements of these properties over time are required to gain understanding and predictive abilities. Measurements of turbidity should be connected to circulation and sediment transport modeling for maximum value and potentially to achieve predictive ability. Measurements capable of revealing small residual circulation in the presence of large tidal variations are needed in the upper gulf. New observations are planned, primarily by CICESE and Autonomous University of Baja California personnel with the aid of funding from CONACyT.

The vertical distribution of suspended particulate matter and changes of distributions caused by tidal and wind forcing have not been explained. Consequently, the more difficult task of explaining the horizontal distribution of suspended material has not been achieved. Difficulties in developing predictive models are due in part to rapid changes in turbidity resulting from the semidiurnal

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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tidal frequency that dominates this environment. Several turbid water patterns (bands, front-like structures, small eddy-like structures, cross-shore plumes) have been observed in satellite images (Lepley, 1973), but their origin is unknown. These phenomena have to be explained in terms of the dynamics involving tides, wind, and the interaction of currents with seafloor morphology.

Now that the Colorado River input of terrigeneous sediment and water is negligible, the sediment budget of the delta and adjacent regions depends mainly on tide-induced transport (both as bed load and suspended load). It is important to determine if the delta or specific areas of this region are being destroyed by dominant erosive processes over time or if these areas are being filled in by depositional mechanisms. Answers to this question have significant implications both for the future of natural marine habitats and for the future of human activities on the Gulf of California coast.

Tectonic Development of the California Borderland and the Gulf of California

The Continental Borderland to the west of Baja California and Southern California occupies a unique and strategic location critical to understanding the crustal evolution of the Californias and the Pacific Plate-North American Plate boundary (Krause, 1965). Acquiring such an understanding will require new collaborative research between Mexican and U.S. scientists. The Borderland is an underwater region of high ridges, deep basins, and a few islands that extends 900 km from Point Conception on the north to Bahía Vizcaíno on the south and is up to 300 km wide (Krause, 1965). The geologic structure of the Borderland consists of displaced continental blocks, unroofed lower crustal and subducted oceanic rock, extensive basaltic volcanism, and sedimentary facies of various ages (Greene and Kennedy, 1987). The region has experienced significant elements of Tertiary subduction, Miocene extension, and post-Miocene compression, in addition to major components of strike-slip deformation. The Borderland is nearly twice as wide as any other analogous location along the western edge of North America and was the result of extreme continental extension in Miocene time, estimated to be as much as 250 km.

Recent conceptual advances (e.g., Legg, 1991; Bohannon et al., 1993; Crouch and Suppe, 1993; Nicholson et al., 1994) have provided, for the first time, coherent and testable models for the tectonic* development of the Borderland and its relationship to the tectonics of the Californias. Presently, all of Baja California and the western part of Southern California are being carried northwestward with the Pacific Plate, relative to the North American Plate. However, prior to mid-Tertiary time (20 million years ago), the Pacific Plate was separated from the continent by the Farallon Plate, which was subducting at an oceanic trench along

*  

 Tectonic refers to the regional structural and deformational features of Earth's crust.

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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the margin of the Californias. A spreading rift separated the two oceanic plates. Eventually, almost complete subduction of the Farallon Plate brought the oceanic rift near to the North American Plate at the trench, whereupon the Farallon Plate began to break up and the resultant microplates were captured by the Pacific Plate together with portions of the continental margin. The motion between the oceanic plate and the North American Plate then changed from subduction to the present right lateral strike-slip motion of the San Andreas Fault and its ancestral analogues, followed later by the oblique opening of the Gulf of California. Off Southern California, this event occurred 20 million years ago with the welding of the Monterey Microplate remnant of the Farallon Plate to the continental margin; it initiated

  1. a splitting off and northward shift of some segments of the continental margin upon their capture by the Pacific Plate;

  2. a rotation of 90 degrees of one of these segments over the present area of the northern Borderland to become the present east-west trending western Transverse Ranges, as the western end of the range moved northward faster than the eastern end; and

  3. a reorganization of the tectonics of the region that resulted in the present structure of the Borderland and the Californias, the opening of the Gulf of California, and the capture by the Pacific Plate of Baja California and all of Southern California west of the San Andreas Fault.

A major debate, however, concerns

  • whether extension in the Borderland continued until seafloor spreading was reached in the thinned basins;

  • how this process of extension was accommodated at different levels in the crust;

  • how this extension was related to the evolving transform plate boundary; and

  • how closely related the timing of extension was to motions of the oceanic plates or to predictions from proposed tectonic models.

Much geological and geophysical research has been carried out in the northern Borderland, especially by oil companies. However, few studies, and no modern deep seismic studies, have been made in the southern Borderland off Baja California, where the prime targets for testing the new tectonic model are located. The most significant recent research development has been the drilling of cores in Borderland basins during the Ocean Drilling Program (ODP) Leg 167 in 1996. The drill hole in the Southern Borderland bottomed in relatively young basalt of late Miocene age (9 million years ago; Lyle et al., 1997). The drill cores carry a rich history of climate change with warm and cool periods, changes in the California Current and marine flora and fauna, and influences of tectonic reorganiza-

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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tion such as the uplift of Baja California. Further study of the cores will be fruitful in revealing this history.

Scientists from the United States and Mexico have shown considerable interest in conducting research in the Borderland area. A binational program on this topic could be pursued involving several ships and institutions, using

  1. shipboard multichannel seismic measurements, swath sounding, and other marine geophysical techniques to image the three-dimensional geological structure at shallow to deep crustal levels;

  2. detailed offshore-onshore refraction to assess velocity structure of the crust and upper mantle and to help relate offshore structure to onshore geology; and

  3. seafloor sampling, core analysis, isotope dating, and petrologic studies to assess offshore and nearshore rock composition, stratigraphy, and the rates and dates of sedimentation, volcanism, and Borderland deformation and breakup, as well as changes in the climate and the California Current System.

Observations of these three types would provide an integrated data set to allow detailed interpretation of the fundamental processes involved in crustal evolution, crustal extension, and plate boundary development of this critical segment of the continental margin of the Californias. Scientific objectives should include the determination of sedimentary facies in the area and the processes of their deposition, such as the relative roles of land-derived versus marine sediments and the effects of climate change. As an initial step, a workshop of Mexican and U.S. scientists interested in these problems should review the state of knowledge in detail and identify suitable joint scientific and environmental research problems, both disciplinary and interdisciplinary.

A natural corollary of the above activity would be a detailed study of the present interaction of the oceanic Rivera Microplate with the continental margin of the State of Jalisco, mainland Mexico. This interaction may be a modern analogue of the tectonic interaction 20 million years ago, when the Monterey Microplate was about to be captured by the Pacific Plate, with all of the consequences described above.

The history of plate reorganization to the west of the peninsula of Baja California is known with some detail; however, with respect to the Gulf of California, there are inadequate data to allow us to discern the beginning of oceanic rifting and transform faulting or the history of the movements in the region linking Baja California to continental Mexico. A recent study of the North American Plate boundary was conducted by Spanish and Mexican scientists and ships in the southern Gulf of California and southward along the Pacific coast of the Mexican mainland (Dañobeita et al., 1997). This study documents the transition of the tectonic setting from an entirely subduction to entirely transform plate boundary and could lead to better understanding and prediction of earthquakes in the region.

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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From about 5 million years ago until the present, the system of transform faults and spreading centers in the Gulf of California has been formed as a result of changes in the plate boundary of this region. This system of transform faults and basins developed to the north, joining itself to the San Andreas Fault system in California.

In the following paragraphs, some questions are suggested with regard to the geology and geophysics of the Gulf of California. These questions are of interest to scientists because they help to define the history of the gulf and its adjacent land area and their geology and geophysics (Umhoefer et al., 1996).

Some local studies seem to support the model in which the gulf is divided into segments of spreading rifts offset from one another by transform faults, similar to orthogonal rifts of the California Borderland. There are, however, many unanswered questions. For example, is the peninsula the result of a migration in time from Sonora to the northwest, such as it appears today? If so, when did it start? Is segmentation a widely distributed feature in the gulf? Is this structural pattern responsible for the formation of the protogulf in the time that has been proposed for the orthogonal extension?

Some primary geological aspects relevant to the formation of the gulf are possible influences on the gulf's location and development: the batholith* in Baja California may have controlled the definition of the western margin of the rift by acting as a rigid block; perhaps the Cretaceous trans-arc environment occupied the position of the modern gulf, and/or the later Miocene volcanic arc helped to determine the present position of the gulf. Data from the extreme south of the San Andreas Fault system still must be integrated with data from the mouth of the gulf to determine the importance of Miocene volcanism.

Knowledge of plate movements suggests a difference in the history of rifting and volcanism between the northern and southern parts of the gulf, but this contrast is not clear from petrologic data; therefore, additional isotopic studies are needed to define the temporal evolution of the lithospheric composition in both ends of the gulf.

Micro- and macrofossil data suggest that the first marine incursion in the modern gulf occurred between 12 and 15 million years ago and was characterized as a transgressive process in shallow coastal environments. Two questions related to marine incursions are (1) could paleontologic data help in determining if there are synchronous discordances on a regional scale in the gulf? and (2) when and in which regions were there links between the gulf and the Pacific Ocean, as suggested by some paleontologic data?

*  

 A batholith is a body of igneous rock formed at considerable depth and spanning at least 100 square kilometers.

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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Sediment-Smothered Hydrothermal Vents

Seafloor hydrothermal environments in the Gulf of California are premier sites for interdisciplinary studies of ecological, biogeochemical, and geophysical processes important for understanding the global significance of processes that occur at ocean spreading centers. Unlike most open-ocean spreading centers, some vents in the Gulf of California are buried by a thick cover of sediments that are characterized by extreme physical and chemical gradients. Sediment temperatures can range from bottom water values of 2 to 4 °C at the sediment-water interface to more than 200 °C at <1 m depth in the sediment column. Hydrothermal fluids whose temperatures exceed 350 °C exit chimneys located on mineralized mounds (Von Damm et al., 1985). Petroleum, found in association with the mounds and in surrounding sediments, is created from biological detritus by thermal alteration, followed by quenching during hydrothermal removal and condensation at the seafloor (Simoneit and Lonsdale, 1982; Peter et al., 1991). Light hydrocarbons dissolved in the hydrothermal fluids of the Guaymas Basin have a thermogenic rather than a biogenic origin (Welhan and Lupton, 1987).

Hydrothermally altered sediments on the seafloor of the Guaymas Basin provide unique opportunities for research; these systems have attracted scientists from many countries to the gulf area. Heat flow to overlying waters (Lonsdale and Becker, 1985) is slowed not only by thick sediment cover, but also by an extensive system of subsurface dikes and sills that interrupt the hydrothermal circulation (Einsele et al., 1980). No other deep-sea area is known to have a comparable variety of physical contrasts influencing ecological relationships. Chemical distributions are dominated by complex interactions between migrating hydrothermal fluids and both inorganic and organic sedimentary materials (Gieskes et al., 1982). In addition to the deep sediment-smothered basins of the gulf, there are numerous nearby shallow-water areas such as Punta Banda, Baja California, where hydrothermal activity and the microbiology of thermophilic marine bacteria can be studied at depths of approximately 30 m (Vidal, 1980; Vidal and Vidal, 1980; Vidal et al., 1982: Vidal et al., 1978, 1981).

In contrast to open-ocean spreading centers where the heat flux is concentrated in discrete vents along the rift zone, a majority of the heat flux from Guaymas sediments may be carried by solutions flowing through a myriad of small-diameter (<2 cm) holes in the sediment. Such venting occurs continuously over many areas of more than 100 m2 and thus has major implications for chemical mass transport and reactions within the sediment column.

Chemical distributions in the rapidly accumulating, diatomaceous muds of the Guaymas Basin also are dominated by complex interactions between hydrothermal fluids and both inorganic and organic materials (Gieskes et al., 1982; Von Damm et al., 1985; Simoneit et al., 1990). High concentrations of sulfide and short-chain organic acids resulting from thermal degradation of sedimentary organic matter (Martens, 1990) occur both in pore waters and in fluids exiting

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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vent holes in sediments that support luxuriant mats of Beggiatoa bacteria. The generation of toxic and carcinogenic polycyclic aromatic hydrocarbons (PAHs) during seafloor petroleum formation (Kawka and Simoneit, 1990) at concentrations similar to levels found in typical crude oils or at contaminated industrial sites suggests that these vent sites may be interesting ''natural laboratories'' for the study of the effects of such compounds on both individual organisms and benthic ecosystems.

Sediment-smothered vents provide unique opportunities for the study of microbiological processes occurring at extremely high temperatures. Massive mats of Beggiatoa may exceed 3 cm in thickness on surface sediments and up to 30 cm on hydrothermal mounds (Jannasch et al., 1989). Beggiatoa are lithoautotrophic* primary producers (Nelson et al., 1989). Studies by Jørgensen et al. (1992) using sulfur 35 (35S) as a radioactive tracer have revealed the presence of sulfate-reducing bacteria within the mats, with a temperature optimum between 103 and 106 °C and activity up to 110 °C. These observations extend the known upper temperature limit of bacterial sulfate reduction by 20 °C and have potential implications for high-temperature biotechnological applications.

The role of bacterial communities in vent environments has been studied by Jørgensen et al. (1990) and Romero et al. (1996), who documented the importance of diverse groups in the degradation of organic matter produced in the vent environment. Additional studies should be carried out related to the functional aspects of the bacteria in vent food webs. Knowledge of the ecology of the benthic fauna associated with the Guaymas hydrothermal vents is recent and still minimal. Most studies have focused on the taxonomy and description of new species of polychaete worms and crustaceans (Grassle, 1984, 1991; Grassle et al., 1985; Soto and Grassle, 1988). There are few published papers that focus on the megafauna (Soto et al., 1996; Escobar et al., 1996) and macrozooplankton at and near deep-sea hydrothermal vents, their strategies of dispersion in the water column, and the potential effect of vent plumes on their distribution patterns (Grassle, 1986; Berg and van Dover, 1987). Paleoceanographic studies conducted by Ayala-López and Molina-Cruz (1994) revealed the presence of living benthic foraminifera in the Guaymas Basin hydrothermal vents. Studies of sedimentsmothered vents in the Gulf of California offer opportunities for significant new findings and provide a natural impetus for interdisciplinary and multinational oceanographic research. The vent sites are attractive because of their proximity to shore and their accessibility.

Examples of Significant Study Topics

Investigators from Mexico, the United States, Denmark, Germany, France, and other countries have been actively involved in studies of the Guaymas Basin

*  

 Lithoautotrophic organisms are those that rely on minerals derived directly from rocks.

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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for more than two decades. However, because Mexico lacks the equipment and infrastructure needed to conduct these studies, very few Mexican scientists have had the opportunity to participate in the investigations of the Guaymas hydrothermal vents. Mexican participation generally has been limited to playing a modest role aboard foreign vessels and with foreign funds. This primarily foreign research has led to important discoveries in a number of areas and has indicated a need for additional investigation of many exciting new topics including the examples listed below. This is an area of research that is ripe for Mexican leadership. Scientific disciplines likely to be centrally involved include microbiology and benthic ecology, biogeochemistry, geology and geophysics, and biotechnology and toxicology.

Microbiology and Vent Ecology: Sediment-smothered vents in the Gulf of California offer opportunities for studies of unique communities of microorganisms and deep-sea fauna. Potential research topics include temperature and substrate regulation of metabolism and microbial degradation rates; chemical gradient controls on microbial processes; effects of thermal and chemical perturbations on community structure along gradients from the active vent environment to the abyssal plain; major biogeochemical pathways that support microbial food webs; comparison of animal-sediment interactions in hydrothermally altered versus abyssal sedimentary environments; colonization of vents; genetics of bacterial consortia and larger organisms; and biodiversity paradigms in the deep sea.

Biogeochemistry: Studies of the interactions of hydrothermal fluids with sediment organic matter in these unique environments can elucidate novel biogeochemical processes that may have been common on ancient Earth. Examples of promising research topics include degradation of organic matter by thermal versus microbial pathways; mechanisms of chemical transport (advection versus diffusion); role of mineral surface composition; interactions between organic and inorganic materials at elevated temperatures; and mineral formation and dissolution.

Geology and Geophysics: The geology and geophysics of vent zones and resulting heat flux variations are major factors controlling the biological and chemical cycling in vent zones. Potential studies related to geology and geophysics include formation of massive sulfide ore bodies; petroleum formation from recently produced organic matter; hydrothermal fluid migration through thick sediments; controls on temporal variability of venting processes; and comparison of seismic activity at sediment-smothered versus open-ocean vents.

Biotechnology and Toxicology: Sediment-smothered vents may harbor unique organisms that could have useful commercial properties or could help in the study of the effects of toxic materials on marine organisms. Important scientific activities include isolation of extreme thermophilic bacteria with potential for industrial applications, thermal generation of toxic and carcinogenic organic materials, and isolation of novel compounds.

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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Such studies in the Guaymas Basin could yield a number of social and economic benefits that might derive from new investigations of sediment-smothered vents and shallow water hot springs. Potential benefits include the following:

  • development of a biotechnology industry based on novel characteristics of extreme thermophilic organisms from environments featuring extreme chemical gradients combined with high temperatures;

  • use of Guaymas Basin-type environments as "natural laboratories" for studies of the effects on benthic communities of naturally produced toxic and carcinogenic compounds such as PAHs found in highly polluted sediments;

  • better understanding of processes leading to the production and transport of petroleum and natural gas; and

  • better understanding of hydrothermal fluid and groundwater migration processes along the land-ocean margin, origins of hydrothermal systems, and determinants of their chemical composition.

THE INTRA-AMERICAS SEA*

Introduction

The Intra-Americas Sea (IAS) is a coherent geographical unit bounded primarily by the islands of the Caribbean Sea and the continental land masses of the United States, Mexico, and Central and South America. Offshore oil and gas resources are economically important off the Gulf of Mexico coasts of the United States and Mexico, with exploration and production persistently moving into deeper water (Figure 2.3). Valuable fisheries include commercial fishing for shrimp and finfish in the Gulf of Mexico (Figure 2.3); subsistence and small-scale fishing in much of the Caribbean Sea, a variety of sportfishing activities, and a growing investment in marine aquaculture. Coastal tourism is increasingly important. The economic importance and, to a large degree, the nature and biological composition of the ecosystems of the IAS are functions of its unique physical attributes. Physical oceanographers and meteorologists have suspected for decades that regional climate, weather, and hydrological cycles are affected significantly by the IAS. Examples well known to the general public are tropical

*  

 Although the Gulf of Mexico is the focus of this section, both Mexico and the United States have significant coastal oceans in the Caribbean Sea (or the Antillean Sea according to the popular Mexican usage). In addition, scientific evidence indicates essential physical and biological linkages between the Caribbean Sea and the Gulf of Mexico. Thus, the geographic scope of the Gulf of Mexico and adjacent waters of concern here includes the region that has begun to be referred to as the Intra-Americas Sea (IAS), a term that originated with an IOCARIBE working group of the Sub-Commission for the Caribbean and Adjacent Regions of the Intergovernmental Oceanographic Commission and encompasses the Caribbean Sea, the Gulf of Mexico, Straits of Florida, Antilles and Guyana Currents, and because of biogeographic considerations, even Bermuda. Consequently, the expression "Intra-Americas Sea" is conveniently used here to refer to this linked system.

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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FIGURE 2.3 Distribution of oil and gas fields, urban centers (populations greater than 100,000), and fishing activities in the IAS region. Because of the semi-closed nature of the IAS basin and the circulation pattern observed, human activities in one part of the IAS can affect other areas. Actual currents are substantially more complex and vary on all time scales. Fishing areas (shaded on map) are the overlay of fisheries for conch, demersal fish, lobster, and shrimp. The circulation in the IAS links coastal regions and populations of commercially important species. Source: Adapted from Maul (1993).

storms and hurricanes. Air-sea transfers of heat, moisture, and trace gases are also suspected to be affected by such events and processes but are less well understood.

The upper ocean waters of the IAS are uniquely warm, clear, and pristine, flowing from east to west into the Caribbean Sea from the tropical and subtropical Atlantic Ocean on its eastern boundary. This water transits the Caribbean Sea basins from east to west and exits the Caribbean Sea through the Yucatan Strait into the Gulf of Mexico. From there, water moves north through the eastern Gulf of Mexico as the Loop Current, which turns south along the west Florida shelf and subsequently exits into the Atlantic Ocean through the Straits of Florida between the coast of Cuba, Florida, and the Bahamas, east of the Florida Keys. The western Gulf of Mexico is impacted by warm-core eddies (rings) shed by the

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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Loop Current and by fresh water supplied by the Mississippi and Atchafalaya Rivers and smaller U.S. rivers, and by 25 Mexican rivers from nine hydrological drainage systems. No synoptic observations of IAS-wide circulation are available, although modeling studies (Figure 2.4) and temporally diffuse observations of areas within the IAS (Figure 2.5) provide insight into the flow through the region.

FIGURE 2.4 The IAS near-surface flow field on Day 670 and Day 740 of a model simulation. The Gulf Stream System (A, B, and C) flowing through the IAS is the predominant feature. In the Caribbean Sea, the Panama-Colombia Gyre (D) was a persistent and dominant feature, which varied from Day 670 to Day 740. In the Gulf of Mexico, the large anticyclone (E) was separating from the Loop Current on Day 670; it moved about 300 km west-southwest by Day 740, and interacted with another anticyclone (F) shed prior to Day 670. A conceptual schematic of the major features is shown in Figure 2.3. Source: cf. Mooers and Maul (1998).

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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FIGURE 2.5 Western boundary currents and baroclinic circulation in the western surface Gulf of Mexico during (a) March 1985 and (b) July-August 1995, relative to 500 decibars (dbar). Source: Modified from Vidal, V.M.V. et al. (1994d).

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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This section assumes that the nature and variability of the living resources of the IAS depend on the coupling of physical and biological processes of the IAS. Thus, it is presumed that the natural variability of living resources can be better understood, predicted, and managed by documenting and verifying how currents transport larvae; how smaller-scale phenomena control primary production; and how temperatures and salinities, both low and high, affect physiological tolerances. The discussion below centers on the way in which variations in a large marine ecosystem can be understood on the basis of a better understanding of physical transport and mixing processes, which is especially relevant to the IAS because of its unique features.

A better understanding of the biophysical coupling of the IAS is also important because of potential threats to environmental quality, degradation of which would diminish the economic worth of the IAS and the habitability of coastal areas. Such threats, discussed below, include habitat loss from urban and industrial development, toxic pollutant release from industrial development and intensive shipping, and inadequate fisheries management.

Because of its location, the Gulf of Mexico is readily accessible to U.S. and Mexican scientists. Major research efforts, some of them carried out jointly, have been conducted by Mexico and the United States in the gulf during the past three decades. The IAS provides an excellent physical laboratory within which major oceanographic processes can be studied and extrapolated to other parts of the global ocean. The Gulf of Mexico portion of the IAS covers a surface area measuring 1.5 × 106 km2 and encloses a water volume of 2.3 × 106 km3. The central gulf, encompassed by the Sigsbee Deep, has an average depth of 3,000 m. Twenty-seven percent of the Mexican coastline borders the IAS. The Gulf of Mexico is a major producer of finfish (e.g., Gulf menhaden), shrimp, crabs, and oysters (NMFS, 1996). It contains 50% of U.S. and 70% of Mexico's coastal wetlands, providing critical wetland habitats for fish and shellfish spawning and feeding areas for migratory waterfowl. Approximately two-thirds of the continental areas of Mexico and the United States drain into the Gulf of Mexico. The coastal areas are fringed by barrier islands throughout and by coral reefs in southern areas (see NRC, 1996, for additional information).

There are several important potential topics for future binational ocean science in the IAS. These focus on the physics, geology, geochemistry, biology, and environmental quality of the coastal zone, continental shelf-slope, and abyssal plain ecosystems of the IAS (including oil, gas, and brine seeps). Such studies would be facilitated by the development of a regional observing system. Given the terms of the United Nations Convention on the Law of the Sea (UN, 1983), which entered into force in 1994, that require a nation to conduct certain studies in order to make full use of the provisions for extended continental shelves, it is important for both governments to undertake these studies promptly in the relevant Gulf of Mexico regions.

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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Physics of the Intra-Americas Sea

The physics of the IAS features a persistent general circulation overlaid with seasonal variations due to atmospheric forcing and river runoff, plus mesoscale variability associated with Loop Current intrusions into the Gulf of Mexico, shedding of rings by the Loop Current, mesoscale eddies entering the Caribbean Sea from the Atlantic Ocean, and other elements of mesoscale variability intrinsic to the Caribbean Sea and the Gulf of Mexico.

General Circulation of the IAS

General circulation of the IAS is dominated by the throughflow of the Gulf Stream system, which is derived from the equatorial and subtropical Atlantic Ocean areas and discharged to the subtropical Atlantic Ocean (Wüst, 1963, 1964; Gordon, 1965; Mooers and Maul, 1998). This throughflow is described largely as a series of named currents: the Caribbean, Yucatan, Loop, and Florida Currents; the Guayana Current, which flows (in part) to the IAS, and the Antilles Current, which bypasses the interior IAS, are also components (Gallegos, 1996). Secondary factors are interannual, seasonal, and episodic atmospheric forcing from storms and runoff from four major river systems: the Mississippi, Orinoco, Magdalena, and Amazon Rivers. A tertiary factor is tidal forcing that produces strong currents only on the inner shelf and in estuaries.

Exchanges of water between the continental shelf and the open ocean are present along the shelfbreak, probably at discrete points associated with topographic features (e.g., submarine canyons) and at discrete times associated with transient (wind-driven and eddy-driven) events. The character of these exchanges varies geographically, depending on the juxtaposition of the Gulf Stream system, shelfbreak topography, and synoptic meteorology. For example, (1), along the Antilles archipelago, the principal phenomena are associated with flow through island passages (i.e., across isobaths*); (2) in the Yucatan Strait and Straits of Florida, the principal phenomena are associated predominantly with flow along isobaths; (3) along the coast of Belize and the West Florida Shelf, the flow is also predominantly along isobaths; and (4) other regions are not directly dominated by the throughflow.

Where a strong current primarily parallels isobaths, cross-shelf exchanges are dominated by meanders of the mean flow and small mesoscale eddies (tens to a hundred kilometers in diameter) shed by the currents. Where there is no strong current paralleling isobaths, cross-shelf exchanges are generally dominated by interactions of large mesoscale eddies (a few hundred kilometers in diameter) with bottom topography, for example, along the northern, western, and southwestern edges of the Gulf of Mexico (Vidal et al., 1992, 1994b,c,d), and by wind-

*  

 Isobaths are lines of constant depth.

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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driven coastal upwelling and downwelling. The southwestern Caribbean Sea has more localized seasonally modulated cyclonic (counter clockwise) circulations (Mooers and Maul, 1998). Conversely, the cyclonic circulation within the Bay of Campeche (southwestern Gulf of Mexico) is influenced strongly by colliding Loop Current rings. Circulation in virtually all of these regimes is modulated by coastal upwelling and downwelling cycles on seasonal (especially along the coasts of Venezuela, Colombia, Cuba, and Yucatán) and weather-cycle time scales (Gallegos and Czitrom, 1997).

In the Gulf of Mexico, it is well known that mesoscale variability is ubiquitous and intense, ranging from large (a few hundreds of kilometers in diameter) anticyclonic eddies (Kirwan et al., 1984a,b; Lewis and Kirwan, 1985) to small (a few tens of kilometers in diameter) cyclonic eddies (Vidal et al., 1988, 1990, 1994d); most are derived from the Loop Current (SAIC, 1988). Some cyclonic eddies may also be induced by stalled or slowly moving hurricanes. Recently, it has been determined that the Caribbean Sea is also rich in mesoscale variability (Mooers and Maul, 1998). There is growing evidence for the east-to-west propagation of topographic Rossby waves in the Gulf of Mexico (Hamilton, 1990).

A central question related to IAS circulation is the nature and importance of the interactions of the throughflow and mesoscale eddies with continental margin topography, especially their role in exchanges across the continental shelf through entrainment of shelf waters and detrainment of oceanic waters. In numerous cases, the boundary currents and large anticyclonic eddies interact with bottom topography to generate small cyclonic eddies, upwelling, and downwelling (Vidal et al., 1992, 1994a,b,c,d). Such features are extremely important in influencing coastal ecosystems because they affect the flux of fresh water, nutrients, heat, pollutants, sediment, and phytoplankton across the shelf into deeper waters. Conversely, the flux of oceanic water onto the continental shelf, driven by the collision of Loop Current rings, has been shown to be the precursor of intense vertical mixing and the formation of Gulf Common Water in the western Gulf of Mexico (Vidal et al., 1988, 1992, 1994b,c).

The superposition of mean throughflow, mesoscale variability, and the seasonal and transient responses to atmospheric forcing (including mixed layerthermocline evolution as well as upwelling-downwelling cycles) yields a complex environment for the transport of nutrients, organisms, and pollutants. Thus, from a marine ecosystems perspective, an understanding of physical processes is critical to characterize the transport pathways and rates of materials in the IAS; equally critical is the determination of retention zones where physical transports are minimal.

A number of mesoscale, time-dependent circulation phenomena exist in the Gulf of Mexico and are important to successful modeling, forecasting biological interactions, and basic understanding of the dynamics of the system (see special issue of the Journal of Geophysical Research , 1992). Specific topics of interest include the following:

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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  • spatial and temporal distributions of hydrographic features and currents in the Gulf of Mexico and the Yucatan and Florida Straits;

  • factors that control the northward intrusion of the Loop Current;

  • factors that control Loop Current ring shedding. Shedding is known to be aperiodic, with a broadband between 6 and 20 months and peaks between 10 and 14 months. Loop Current ring shedding does not have an annual cycle, although its associated transport does;

  • ring movements and the distribution of potential vorticity due to the fluid's velocity shear and stratification within the gulf;

  • ring-continental slope and ring-ring interactions;

  • ring collisions with the continental margin and the formation of along-shelf currents;

  • origin of the gulf's western boundary current (is it wind-driven or does it result from the decay of colliding Loop Current rings in the western gulf or both?);

  • ring bifurcations and angular momentum conservation; the proliferation of cyclonic-anticyclonic pairs and their influence on mass-volume exchanges between the gulf's continental shelf and oceanic waters;

  • water mass formation and mixing in the gulf, including the influence of wind-driven mixing versus ring-slope and ring-ring interactions; and

  • vertical transport balance associated with the distribution of relative potential vorticity and its influence on the intermediate and deep mean circulation of the gulf.

Although these research issues are focused on processes occurring in the IAS, they are also relevant to understanding physical phenomena genetic to the global ocean (e.g., eddy shedding, carbon dioxide [CO2] removal and climate change, western boundary current generation in response to weather events, and sea-level rise). Indeed, the IAS represents a natural laboratory where numerous oceanic processes can be observed and modeled. Given the location of the IAS, the United States, Mexico, and other Latin American and Caribbean countries benefit from it; thus, they have the responsibility to conduct joint scientific studies to protect the IAS and use its resources wisely, through advancing the understanding of IAS oceanography. A brief discussion of some of the regional studies listed above follows.

The spatial and temporal distributions of major hydrographic features and currents in the IAS should be monitored on a continuous basis (Vidal et al., 1989). This knowledge is crucial to validate satellite altimetry measurements and to calibrate, validate, and verify numerical models of the gulf's circulation. Ultimately it is from such models, suitably calibrated and kept "on track" by regularly assimilated data, that regular updates and even forecasts of the time-dependent circulation of the gulf will be obtained. This step would constitute the precursor for a much needed ability to use regular observations of IAS conditions to improve the efficiency and safety of shipping, fishing, and oil and gas exploitation in the IAS.

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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Mexico and the United States have cooperated in the past in studies of physical features of the IAS (SAIC, 1988; Lewis, 1992). Recently (1992 to 1995), the Louisiana-Texas Shelf Circulation and Transport Processes (LATEX) program, sponsored by the U.S. Minerals Management Service, could have provided an excellent platform for binational cooperation. A program structured similarly, but sponsored jointly by Mexico and the United States and providing full coverage of the key components of circulation in the IAS, would yield valuable information required to manage the Gulf of Mexico and other portions of the IAS more effectively.

Factors That Control the Northward Intrusion of the Loop Current and Its Ring-Shedding Periodicity

The hydrodynamic character of the Gulf of Mexico, including its two connecting straits, is predominantly baroclinic,* which is particularly true within the Loop Current as well as within the gulf's ring-dominated upper (0 to 1,000 dbar**) layer (SAIC, 1988). Below 1,000 dbar the hydrodynamic character, although strongly influenced by ring translations and the propagation of topographically trapped Rossby waves (Hamilton, 1990), is overwhelmingly barotropic.*** Both the upper and the lower layers in the gulf are strongly affected by fluctuations of the Loop Current, and there is evidence that the deep-water fluctuations become progressively more decoupled from upper layer currents as the topographically trapped Rossby waves and warm eddies propagate into the western gulf basin (Hamilton, 1990; Vidal et al., 1990, 1994b,d). Therefore, it becomes essential for proper understanding and modeling of the gulfs basin-wide hydrodynamics to investigate factors that control the Loop Current's northward penetration into the gulf, its variability, and its ring-shedding periodicity. This knowledge is crucial to define adequately the initial conditions for numerical models and to understand the gulf's basin-wide hydrodynamic response to the propagation of topographically trapped Rossby waves.

Ring Movements and Distribution of Potential Vorticity Within the Gulf; Ring-Slope and Ring-Ring Interactions; Ring Collisions and Formation of Along-Shelf Current Jets

Circulation in the Gulf of Mexico is dominated by anticyclonic rings shed from the Loop Current (Ichiye, 1962; Cochrane, 1972; Elliott, 1982; Lewis and

*  

 A baroclinic fluid is one in which surfaces of constant pressure intersect surfaces of constant density, resulting in vertically sheared flows.

**  

One decibar (dbar) is a unit of pressure equal to 104 pascals, about equivalent to seawater pressure at 1 m depth.

***  

A barotropic fluid is one in which surfaces of constant density (or temperature) are coincident with surfaces of constant pressure, resulting in vertically uniform flows.

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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Kirwan, 1985). Elliott (1982) used historic, quasi-synoptic data sets to establish the separation and movement of three anticyclonic rings into the western gulf and calculated westward translation speeds of 2.1 km per day, ring radii of 183 km, and ring lifetimes of about 1 year. A typical ring inputs approximately 7 × 105 joules (J) per square centimeter of heat and 17 g/cm2 of salt into the western gulf (Elliott, 1982). The intensity of their anticyclonic circulations, with swirl velocities of 50 to 75 cm/s, indicates that Loop Current rings also transport a considerable amount of angular momentum into the western gulf (Kirwan et al., 1984a,b).

Measurements by Brooks (1984) of the currents over the continental shelf and slope in the northwestern gulf indicate that the influence of hurricane-induced currents (which depends on the attributes of individual hurricanes) on the hydrographic and current variability in the western gulf is considerably less than that contributed by a ring migrating northward along the western gulf boundary. Ongoing studies of the circulation of the western gulf have incorporated numerical modeling of Loop Current intrusions and eddy shedding (Hurlburt and Thompson, 1980, 1982; Dietrich and Lin, 1994); interactions of Loop Current anticyclones with bottom topography and the western gulf boundary (Smith and O'Brien, 1983; Smith, 1986; Shi and Nof, 1993, 1994); satellite infrared imagery and hydrography (Vukovich et al., 1979; Brooks and Legeckis, 1982; Vukovich and Crissman, 1986; Biggs and Muller-Karger, 1994); satellite positioning of surface drifters seeded within Loop Current rings (Kirwan et al., 1984a,b; Lewis and Kirwan, 1985; SAIC, 1988; Lewis et al., 1989); regional hydrography and baroclinic circulation studies (Nowlin, 1972; Molinari et al., 1978; Elliott, 1979, 1982; Merrell and Morrison, 1983; Merrell and Vázquez, 1983; Hofmann and Worley, 1986; Vidal et al., 1988, 1990, 1992, 1994a,b,c); and satellite altimetry measurements (Forristall et al., 1990; Leben et al., 1990; Biggs and Sanchez, 1997).

The studies listed above have described the tracks of anticyclonic rings within the eastern, central, and western gulf, including their hydrography, baroclinic circulations, ring-ring interactions, and ring interactions with topography. Despite the new information provided by these studies, much remains to be learned about the nature of anticyclonic Loop Current rings and their influence on the hydrography and circulation of the central and western gulf; for example:

  • What is the hydrodynamic response of the gulf's water masses to ring-shelf collisions?

  • How do these ring-shelf interactions affect the gulf's local, regional, and basin-wide circulations?

  • To what extent are rings responsible for the conversion of 30 sverdrups (Sv, 1 Sv = 106 m3/s) of Caribbean Subtropical Underwater to Gulf Common Water (Vidal et al., 1992, 1994b,c)?

  • On their westward travel, do rings transfer angular momentum to the surrounding water, induce geostrophic turbulence, and generate cyclonic circulations and vortex pairs on their peripheries?

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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  • Do rings coalesce?

  • Do Loop Current rings dominate the surface and deep circulation of the central and western gulf and control its surface, intermediate, and deep-water mass exchanges and residence times?

  • How do rings affect the vertical and horizontal distribution of hydrographic properties, micronutrients, and planktonic organisms?

  • Does the coupled translation and vorticity of anticyclonic and cyclonic rings determine the location of topographic upwelling and downwelling regions in the gulf and constitute a natural pumping mechanism that controls the primary productivity and CO2 exchange between the ocean and atmosphere and between surface and deep waters?

  • When anticyclonic Loop Current rings collide with the western gulf boundary, do they generate western boundary currents and current jets parallel and normal to the shelf break, respectively?

  • If these current jets exist, do they constitute a primary and efficient exchange mechanism between the western gulfs continental shelf and offshore waters?

Origin of the Gulf's Western Boundary Current: Is It Wind Driven or Does It Result from Decay of Colliding Loop Current Rings in the Western Gulf?

Sturges and Blaha (1976) and Blaha and Sturges (1981) have postulated that the curl of the wind stress should drive the mean circulation in the gulf and that the net result of this wind forcing should be a Gulf Stream-like western boundary current. A recent paper by Sturges (1993) examined the relative importance of the wind-stress curl and detached Loop Current rings as precursors of the gulf's western boundary current. Sturges' work focused on the annual cycle of the estimated flow as deduced from a compilation of ships' drift data. He concludes that given the loss of fluid from rings as they interact with the western boundary of the gulf, they tend to dissipate rapidly (characteristic decay time is about 70 days); hence rings do not contribute significantly to the formation of the western gulf anticyclonic current. Sturges also concludes that Elliott's (1979, 1982) reported ring lifetimes (1 year) are important within the gulf's interior but are not applicable once the rings interact with the shelf-slope boundary (Sturges, 1993). Furthermore, because the rings shed from the Loop Current have no significant annual periodicity, they make no significant contribution to the long-term annual signal (Sturges, 1993).

Contrary to Sturges' (1993) deductions, Elliott's (1979, 1982) fundamental work on anticyclonic rings and the energetics of the circulation of the gulf established the dominant role of Loop Current rings in the general circulation of the gulf, including the western gulf. Elliot's analyses of Loop Current rings versus wind energy sources indicate that although the energy contribution by wind stress and Loop Current rings is about the same, the wind-stress energy is a basin-wide

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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value, whereas the rings' available potential energy is concentrated into a smaller length scale similar to that of the north-south scale of the western boundary flow anticyclone. Thus, Elliott (1979) concluded that although the work done by the wind stress may generate part of the available potential energy of the western boundary flow anticyclone, the primary source of available potential energy must be the western-moving anticyclonic rings that separate from the Loop Current.

Vidal et al. (1988, 1989, 1990, 1992, 1994a,b,c,d) have reported field measurements and studies providing clear evidence that the principal decay process of anticyclonic rings in the western gulf is via mass-volume shedding associated with their collisions with the continental slope. These collisions give rise to a western boundary current and cyclonic-anticyclonic triads whose decay times are greater than 150 days (Vidal et al., 1989, 1994a,d). This result is in agreement with the observed residence time of colliding anticyclones in the western gulf, which exceeds 6 months (Lewis and Kirwan, 1985; SAIC, 1988).

From the previous discussion it is evident that controversy exists regarding the origin of the western boundary current in the Gulf of Mexico. Is it primarily wind-driven or ring-driven, or is it a combination of the two? Detailed measurements on the evolution of ring-slope interactions, as well as of long-term currents in the western gulf, are crucial to resolve this important question that has analogues in other oceanic regions of the world.

Biophysical Coupling

Studies of the dependence of biological and chemical phenomena on physical forcing are an important new area for scientific collaboration between Mexico and the United States. An understanding of the physical oceanography of the IAS is fundamental to understanding the biology of this region, because the physics of water movements strongly influence larval transport and primary productivity (Biggs et al., 1996).

Mesoscale circulation measurements and numerical simulations of IAS circulation illustrate the potential coupling of physical and biological processes over extensive space scales (Vidal et al., 1988, 1989, 1990, 1992, 1994a,b,c,d; Mooers and Maul, 1998). Water masses entering the southeast sector of the IAS control conditions throughout the region to a large degree. These water masses exert considerable influence on the entire downstream environment, affecting productivity, fisheries, and regional ecology. The east-to-west (and south-to-north) pattern of flow and its potential control of the entire IAS ecosystem pose a large set of important, interrelated questions. Primary productivity, seasonal pulses, the success of regional and local fisheries, and regional biodiversity in continental shelf (Soto and Escobar, 1995, Escobar and Soto, 1997; Escobar et al., 1997) and coral reef communities are all related to physical forcing processes along the path of IAS circulation.

Can fisheries productivity, recruitment, and landings be explained on the

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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basis of physics? Fisheries depend on production and survival of fish larvae to a size that can reproduce or be caught (called recruitment); recruitment can be affected by physical factors (Cushing, 1995). The relationship of IAS physical flow patterns to recruitment could be important to regional fisheries. The physical continuity among regions of the IAS suggests that the health of particular fisheries may also be coupled on large spatial and temporal scales. For example, Roberts (1997) has estimated the impact of surface currents on dispersal of marine larvae, with the implication that island nations must cooperate with each other to protect upcurrent reef areas that supply larvae to downcurrent reefs.

Collaborative efforts by physical oceanographers and biologists may provide new understanding of variations in fisheries recruitment throughout the IAS, based on determining the degree to which variations in physical processes affect larval transport and recruitment. Variations in species distributions in the IAS, both as larvae and as adults, could be studied using molecular approaches to identify subtle taxonomic differences, and the unidirectional flow and diversity gradients could provide an opportune situation in which to apply these new approaches to zoogeography and systematics.

The distribution of biogenic particles and concentrations of quasi-conservative chemicals can be used as ''tracers'' in the physical flow fields to refine the IAS physical model. Development of a composite biophysical model could be a long-term goal of a binational effort. Such a model could be initiated immediately using what is known, and validated and updated later through joint field work.

Fronts

Frontal regions are sites of intensified primary and secondary production and are the habitat for certain pelagic fish and their larvae. By providing physical and biological cues that can be sensed by migrating organisms, fronts can concentrate such organisms (Olson and Podesta, 1987). Satellite color and thermal images of the western Gulf of Mexico and the coast of Florida confirm that the major features of phytoplankton chlorophyll distribution are associated with boundary regions of major currents such as the Loop Current and the Florida Current. Assemblages of larval fish, copepods, and phytoplankton in the Gulf of Mexico seem unique to these frontal regions. Phytoplankton growth is supported in these systems by the upward flux of nutrients associated with areas of higher productivity in the Gulf of Mexico (Grimes and Finucane, 1991). In the region of the Loop Current the major source of energy for vertical mixing is believed to be supplied by the winds. The major source of energy for vertical mixing in the western gulf is believed to be supplied by ring-slope and ring-ring interactions (Vidal et al., 1990, 1992, and 1994b,c,d). Tuna larvae (Thunnus thynnus) are associated with the boundary of the Loop Current in surface waters having temperatures of 24 to 26 °C and large numbers of myctophid fish larvae, especially

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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Myctophum nitidulum (Richards et al., 1988). Catch per unit effort data for T. thynnus indicate that adult fish are also concentrated along the temperature front of the Loop Current. Fronts are not complete barriers to plankton, and there is a considerable advection of organisms such as fish larvae across the Mississippi River plume frontal boundary (Govoni, 1993).

Mississippi River Plume

Biological productivity in the northern gulf is significantly affected by the Mississippi River. Its freshwater discharge contains high concentrations of dissolved nutrients, which results in high primary production. The phytoplankton are ultimately grazed by zooplankton or decomposed by bacteria, fueling the annual development of a region of hypoxic water along the Louisiana coast (Rabalais et al., 1994). The Mississippi River plume and plume front are associated with high densities of nutrients, phytoplankton, zooplankton, larval fish, and predators (Govoni et al., 1989; Ortner et al., 1989; Cowan and Shaw, 1991; Dagg and Whitledge, 1991). Stratification caused by the inflowing low-salinity water is hypothesized to produce small-scale patches with high abundance of copepods (Dagg et al., 1988). In addition to the seasonal rainfall and subsequent river outflow, winter storms redistribute nutrients and phytoplankton, significantly affecting the productivity of higher trophic levels in the inner shelf waters of the northern Gulf of Mexico (Dagg, 1988). A number of important Mexican rivers drain into the Gulf of Mexico (e.g., the Grijalva-Usumacinta River), but their plumes have yet to be studied comprehensively.

Loop Current

The Loop Current and the rings it sheds impact continental shelf areas bordering the Gulf of Mexico (Vidal et al., 1992, 1994c,d). The Loop Current in its northernmost position affects shelf processes to the east of the Mississippi River Delta. Rings deriving from meanders of the Loop Current have marked differences in nutrient concentrations (Vidal et al., 1989, 1990, 1994b,d), primary production, and phytoplankton and zooplankton biomass from ambient shelf waters (Biggs, 1992). Anticyclonic rings derived from the Loop Current occasionally impact the Louisiana shelf west of the delta but usually drift to the western gulf where they collide with the continental shelf slope, resulting in an exchange of about 18 × 106 m3 per ring of oceanic and shelf waters (Vidal et al., 1994b) and a large input of particulate organic carbon available to benthic organisms (Escobar and Soto, 1997). The Loop Current-Florida Current-Gulf Stream System is an important mechanism for transporting planktonic animals, petroleum products (Vleet et al., 1983), and toxic dinoflagellate blooms out of the gulf (Tester et al., 1991).

Cyclonic gyres formed by the Loop Current are significant components of the mechanism for the retention of larval fish in the waters surrounding the Florida Keys (Lee et al., 1992, 1994). The Loop Current flow can overshoot the entrance

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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to the Straits of Florida, causing the formation of a cool, cyclonic gyre recirculation between the Florida Current and the Dry Tortugas that persists for about 100 days. Cyclonic gyre formation provides enhanced food supply, as well as retention and shoreward transports of snapper and grouper larvae for successful recruitment in the western and lower Florida Keys.

Other reasons for studying the physical-biological coupling in the IAS include the following:

  1. The hydrodynamics of the water column seems to have major effects on benthic organisms and on the distribution of their larvae (Soto, 1991; Soto and Escobar, 1995; Escobar and Soto, 1997).

  2. The large spatial heterogeneity in carbon sources around the IAS offer exceptional possibilities for comparisons of pelagic-benthic coupling at different sites in the IAS (Escobar et al., 1997).

  3. Improved biophysical models will yield more realistic predictions of ecosystem characteristics that will benefit countries bordering the IAS, including Mexico and the United States, and allow more effective management. Except for a model at the large marine ecosystem scale (Birkett and Rapport, 1996), no models have been generated for integrated management in the IAS.

Interdisciplinary research will be needed to study the following topics as a basis for new biophysical models:

  • Effects of deep-sea circulation, including bottom boundary layers, on deep-sea organisms.

  • Impact of circulation patterns on the distribution of larvae and the association of larvae with the distribution of marine organisms.

  • Habitability in shelf, slope, and abyssal seafloor areas and their relation to hydrodynamics in the water column and the geology and geochemistry of sediments.

  • Primary productivity in the water column and processes that allow it to contribute to benthic productivity.

  • Anthropogenic effects on food chains and pathways, and the modes of temporal response by the benthic components.

  • Integrated ecosystem approaches in studying and evaluating damage to ecosystems; quantification of biological processes and formulation of models.

Biology of the Intra-Americas Sea

For the most part, the waters of the IAS can be characterized as oligotrophic, having low nutrient concentrations and low standing stocks of phytoplankton. The low supply of inorganic nutrients vital to phytoplankton primary production is related to IAS boundary conditions. At the southern entrance to the Caribbean Sea, beginning about 10°N, the entering coastal flow contains fresh water from the Amazon and Orinoco Rivers. The Amazon's nutrients are mostly depleted

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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before its waters enter the IAS. The opposite is true for the Orinoco, whose unmixed discharge enters the Caribbean Sea through the Gulf of Paria (Vidal et al., 1986). Productivity in the IAS is thus limited to regional upwelling or to local river runoff. The latter can be intense, however, as in the case of the Orinoco River (Vidal et al., 1996) and the Mississippi River (el Sayed, 1972; Biggs and Sanchez, 1997).

A highly diverse series of coral reef ecosystems characterizes the entire IAS up to about 27°N, where they become limited by low (about 20 °C) temperatures. A southeast-to-northwest decline in the species richness of the major reef-building corals and associated finfish and invertebrates has been described (Stehli and Wells, 1971), proceeding from the Caribbean basins northwestward along the generalized path of the upper ocean currents. This gradient extends into the northern Gulf of Mexico, with the most species-poor coral banks being the offshore assemblages on salt diapirs or other topographic features along the Texas coast. The degree of biological diversity decreases from the source of the IAS to its ultimate fate at the northwest margin of the Gulf of Mexico, but needs further study. This biodiversity gradient may occur because larval transport is primarily unidirectional in the IAS from east to west and nutrients become depleted along this path, and because of habitat variability. Linking the biodiversity gradient of the marine ecosystems to physical transport processes at the spatial scale of the IAS is a formidable task, but one worth pursuing by the various nations bordering the IAS, especially the United States and Mexico.

The ecology of the benthic infauna in the IAS is not well known. On the broad shelves of the Caribbean Sea the sediments are predominately carbonate sands containing highly diverse invertebrate assemblages of relatively low biomass. The species composition of a "Caribbean Fauna" is bounded on the north by a series of faunal boundaries such as the northern boundary of reef-forming corals in the Gulf of Mexico. Benthic primary production of attached algae such as Lithothamnion and microalgae is relatively high because of high light transmission, but its relative importance compared to water column productivity is unknown. Coral reef communities are very productive, but net export of production to surrounding shelf environments may be modest at best.

Mariculture is becoming increasingly important in countries bordering the IAS. In most cases, mariculture is carried out by constructing ponds adjacent to an estuary or to the open ocean. The IAS serves as a source of water, nutrients, and perhaps larvae. If and when the water in the ponds become excessively contaminated with waste products, it is exchanged with adjacent water masses. This could cause deleterious effects to the natural environment outside the ponds.

There are a variety of mesoscale features that have significant impacts on gulf ecosystems, creating distributions that vary significantly over space and time. The Gulf of Mexico is the site of some of the most economically valuable fisheries in the world. The remarkable diversity of mesoscale features that are established by the combined presence of the Loop Current and the Mississippi River

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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outflow, plus that of 25 Mexican rivers from nine hydrologic basins may make this a uniquely productive habitat for marine species. The significance of the throughflow and mesoscale variability for the functioning and robustness of the basin-scale ecosystem—including recruitment sources, sinks, and variability; genetic flow; and biodiversity—has yet to be determined.

The carrying capacity of an ecosystem may be determined by the availability of food, space, or some other limiting factor in the system (as described by Odum, 1971). Human intervention in the IAS may reduce its carrying capacity for commercial fish stocks. Anthropogenic effects on carrying capacity can be illustrated by a species whose territorial range shrinks because it cannot tolerate low dissolved oxygen concentrations, low salinity, high sediment concentrations, and/or warm water caused by inputs from rivers. Populations of shrimp, fish, and other animals can be forced into a smaller geographical area by hypoxia, increasing the density of the populations until their needs exceed some other resource that is often related to food supply, food quality, environmental quality, or in the case of sessile benthic organisms, benthic habitat. After this range contraction occurs, the number of organisms decreases, approaching or oscillating around a new, lower carrying capacity.

Understanding large-scale and long-term IAS processes requires ample measurements over a large geographic area for a long time. Efforts should continue at two levels:

  1. Process Studies: Specific processes should be elucidated through studies of cause-and-effect linkages using intensive experiments, for example, relating food supply to carrying capacity.

  2. Monitoring: Long-term monitoring should be designed for observing variability among a suite of correlated variables. Such monitoring is necessary to discover linkages among biological components of ecosystems and between the ecosystem and the environment. For example, little is known about deep-sea communities, so they have not been integrated into a whole-ecosystem view. Funding for long-term monitoring is difficult to sustain and examples of long-term, regular monitoring are rare in the United States and virtually non-existent in Mexico. Such monitoring is crucial for documenting trends in environmental conditions and for understanding processes that vary on interannual and decadal time scales.

The National Autonomous University of Mexico's (Universidad Nacional Autónoma de México, UNAM) Institute for Ocean Science and Limnology (Instituto de Ciencias del Mar y Limnología [ICMyL]) and Texas A&M University's (TAMU's) Department of Oceanography have established a collaboration comparing the benthic food chains of the continental shelves of the northern and the southern Gulf of Mexico. This study has utilized the research vessels Gyre (TAMU) and Justo Sierra (UNAM). A basic theme of the research is to gain better understanding of carbon cycling in relation to continental shelf shrimp

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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and finfish fisheries. Although rather simplified models can now be constructed based on the information collected by this group (Soto and Escobar, 1995; Rowe et al., 1997), much remains to be learned about how physics and primary production limit or control these important fisheries. Regional studies such as those described here differ to some degree from a broader, large-scale IAS study of biophysical coupling because the economically important target species depend on more localized estuaries as nursery grounds. A natural extension of this research would be to make it more interdisciplinary and to involve a larger number of investigators. Necessary expertise in the areas of phytoplankton ecology, benthic ecology, and physical oceanography is available at many U.S. and Mexican institutions throughout the region. The mesoscale features of meanders, rings, and fronts associated with the Loop Current, together with seasonally varying inflow of the Mississippi River and 25 Mexican rivers, shape much of the biological oceanography of this region (Vidal and Vidal, 1997).

Sedimentary Dynamics and Environmental Impacts on the Coastal and Oceanic Zones of the Gulf of Mexico

Land-ocean interactions affecting the marine sedimentary environment in the western Gulf of Mexico are complex and vary among regions of the coastal ocean. These variations are due to differences in (1) river discharges of sediments and contaminants from both Mexico and the United States; (2) collision of Loop Current anticyclonic tings against the continental slope and shelf; (3) longshore currents and waves; and (4) human activities such as sewage discharge, dam building, coastal urban development, tourism, oil and gas exploration and extraction, and fisheries. These factors have contributed to short- and long-term changes in the marine sedimentary environment (Aguayo and Estavillo, 1985; Aguayo, 1988; Aguayo and Gutiérrez-Estrada, 1993; Gutiérrez-Estrada and Aguayo, 1993).

The Gulf of Mexico can serve as a natural laboratory, offering the opportunity to understand the dynamics of several marine geological environments, from tidal flat to abyssal plain, subject to distinctive climate conditions along the margin of the gulf. The observable geology results from the continuous subsidence of the continental margin and sea-level changes due to variations in climate and continental ice sheets; both factors control sedimentary cycles and the suite of resulting sedimentary structures (Aguayo and Marín, 1987; Aguayo and Carranza-Edwards, 1991). However, to understand regional and local sedimentary environments in detail and to develop predictive models, systematic, fundamental research is necessary to describe and quantify (1) river discharges of sediments to the coastal zone; (2) riverine input versus coastal erosion and redistribution; and (3) role of the collision of Loop Current anticyclonic rings against the continental slope-shelf in sediment transport, dispersion, and deposit. The following are some of the questions that arise:

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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  • How does geography (climate, physiography, and hydrology) control sediment load, flow regime, and water quality?

  • How are sedimentary settings affected by erosional, depositional, and nondepositional processes?

  • How do tectonic settings (local or regional) affect the dynamics of the sedimentary environments (subsidence, emergence, or stationary)?

Oil- and Gas-Associated Seeps in the Southern Gulf of Mexico

The southern Gulf of Mexico has the same geologic history as the northern gulf; it is underlain by thick salt deposits that extrude through bottom sediments as mountainous structures called diapirs. These structures often have oil and gas deposits associated with them, as demonstrated by the extensive oil and gas resources now being developed offshore in both Mexico and the United States.

Unique communities of organisms utilizing energy sources associated with the oil or gas deposits and brine pools have been observed over a broad range of depths in the northern Gulf of Mexico. These communities have a large biomass and a composition resembling in form—and to some degree in function—those surrounding hydrothermal vents. Such communities have not been observed in the southern Gulf of Mexico, but it is logical that they should occur there also. This is supported by records of oil slicks on the water surface in Campeche Bank and the discontinuities in bathymetric profiles that suggest the existence of gas seepage.

An obvious new area of collaboration among biologists, geochemists, geologists, and geophysicists would be to look for and describe the distribution of the oil and gas seep communities, if they exist, in the southern Gulf of Mexico. The study of hydrocarbons as alternate carbon sources to slope communities is an interesting question that needs to be answered. This would assist the Mexican Petroleum Corporation (Petroleos Mexicanos [PEMEX]) in finding potential oil and gas deposits, as it has assisted oil and gas exploration in the offshore waters of the United States. Such information would also aid the study of the physiological ecology of deep-sea organisms.

Marine Environmental Quality

Binational research and monitoring could contribute to reducing the effects of marine pollution in the IAS, including pollution from nutrients, toxic materials, oil, and debris from land and marine sources. The northern Gulf of Mexico has been studied extensively with respect to its chemical constituents. For 10 years, the Status and Trends Program of the National Oceanic and Atmospheric Administration (NOAA) has monitored pollutant levels in oysters (Crassostrea virginica ) and sediments (Long and Morgan, 1990; Sericano et al., 1995). More recently, the U.S. Environmental Protection Agency (EPA) started the Environ-

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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mental Monitoring and Assessment Program (EMAP) (Summers et al., 1992), a more ambitious effort that is attempting to develop and validate indicators of environmental health including, but not limited to, pollutant levels. One of the environmental indicators proposed by EMAP is the "Benthic Index" (Engle et al., 1994), which discriminates between healthy and degraded conditions. A similar level of study does not exist on the Mexican side of the gulf, and there is not much basic information regarding levels and trends of pollutants on an IAS-wide scale.

International monitoring efforts exist in the IAS on a wider scale, mainly under the auspices of the Sub-Commission for the Caribbean and Adjacent Regions (IOCARIBE) of the Intergovernmental Oceanographic Commission (IOC) of the United Nations Educational, Scientific and Cultural Organization (UNESCO). IOCARIBE's Pollution Monitoring Programme in the Caribbean (CARIPOL) was a productive program (Atwood et al., 1987a). A database with thousands of records of floating and stranded tar and of dissolved or dispersed hydrocarbons has been compiled and is now archived at NOAA (Atwood et al., 1987b). One important conclusion is that approximately 50% of the oil in the IAS comes from the Atlantic Ocean. Regretfully, this program was terminated. A new program, Caribbean Environmental Program-Pollution (CEP-POL), is administered jointly by IOCARIBE and the United Nations Environmental Programme (UNEP).

Another international effort was the first phase of the International Mussel Watch, which was designed to assess the levels of organochlorine compounds in bivalves (Sericano et al., 1995). Samples of bivalves were collected from 76 locations along the coastlines of the Americas, excluding the United States and Canada, and the results were compared with those of NOAA's Status and Trends program. The idea behind this project was that the use of organochlorine pesticides, primarily for antimalaria campaigns, was more widespread in the southern portion of the continent and that pollution by organochlorine compounds would be more serious in the southern Gulf of Mexico. However, one of the major findings was that "contamination is significantly higher along the northern coast of the Gulf of Mexico" (Sericano et al., 1995).

The search for reliable indicators of environmental health has focused on the use of "biomarkers," that is, "a biological response that can be specified in terms of a molecular or cellular event, measured with precision and confidently yielding information on either the degree of exposure to a chemical and/or its effect upon the organism or both" (GESAMP, 1995). Various environmental indicators have been proposed, including some for tropical coastal ecosystems, such as the frequency of mutations in red mangroves, Rhizophora mangle (Klekowsky et al., 1994); histopathological lesions in oysters, Crassostrea virginica (Gold et al., 1995); and oxygenases associated with cytochrome P-450 and metallothioneins (GESAMP, 1995). The variability between sexes and changes associated with

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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gonadal development or spawning are generally unknown, complicating the use of such biomarkers.

In contrast to the Sericano et al. (1995) study, some published results indicate that the levels of pollutants along the southern coast of the Gulf of Mexico are of the same magnitude or even higher than those in the northern gulf, for example in the Coatzacoalcos River (Gallegos, 1986; Botello et al., 1996), Laguna de Terminos (Gold-Bouchot et al., 1995; Botello et al., 1996), and Tampico (Sericano et al., 1995). This is particularly true for petroleum hydrocarbons (Gold et al., 1995a,b; Botello et al., 1996).

The Gulf of Mexico is an ideal place for binational pollution studies, including fates and effects of pollutants and transport mechanisms. Many of the same species live in the estuaries and bays throughout the region, but there are enough differences in climate, the presence of other species, overall diversity, and other factors to allow for the generalization and validation of existing environmental indicators. The existence of binational monitoring programs is highly desirable and would contribute to scientific goals. Joint research on biomarkers and validation of environmental indicators in tropical marine ecosystems, which are more diverse and more stable climatically, is also highly desirable. This kind of information would be very valuable for coastal zone management.

Oil, Hazardous Materials, and Marine Debris

Oil production, refining, and transport occur in the IAS at high levels, and the petroleum industry is a major contributor to the economies of many countries bordering the IAS (Botello et al., 1996). To place the environmental importance of the petroleum industry in perspective, the Yucatan Strait (between Cuba and Mexico) is considered to be one of the three straits in the world most likely to have a tanker accident, and the IAS is considered the second most likely region in the world to have such an accident (Reinberg, 1984). A study conducted for the U.S. Coast Guard (Reinberg, 1984) concluded that the Gulf of Mexico and the Caribbean have the most intricate pattern of tanker traffic and declined to designate any part of these bodies of water as low-risk areas (Botello et al., 1996; Figure 2.6). Pollution by oil has been identified by the IOC (1992) as one of the major potential environmental problems in the IAS. It can particularly affect the small island states that depend on tourism as their main economic activity, yet do not themselves gain a direct benefit from petroleum production (IOC, 1992).

Marine debris is becoming a major concern in the IAS because the economies of many countries in the region depend on tourism. A committee co-sponsored by several state Sea Grant programs in the United States and by IOCARIBE organizes biannual workshops with participation from many countries in the IAS. The CEP-POL program has as one of its components a marine debris monitoring program, under whose auspices a pilot study was conducted in Puerto Rico, Colombia, and Mexico and is being expanded to include additional countries.

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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FIGURE 2.6

Principal oil tanker routes in the IAS. Source: Adapted from Botello (1996).

Land-Based Sources of Pollution

Land-based sources account for approximately 80% of all pollutants entering the ocean (UNEP, 1995), including contaminants such as persistent organic pollutants (pesticides and petroleum hydrocarbons), sewage, and trace metals. A United Nations protocol recently has been adopted to control and diminish the quantity of pollutants entering the ocean from sources on land (UNEP, 1995). Reduction of land-based sources of pollution is extremely difficult to accomplish because of the widely dispersed sources related to virtually all sectors of the land-based national economies (Botello et al., 1996).

There is very little information about present levels and trends of persistent pollutants in the IAS region. The status of oil pollution has been reviewed by IOCARIBE (IOC, 1992; Botello et al., 1996). CEP-POL has promoted a number of pilot studies of point sources of pollution, including concentrations of organochlorine pesticides and hydrocarbons. What is lacking are systematic observations that will, if sustained over time, lead to valid conclusions about IAS-wide levels and trends. Because inputs to the ocean are diffuse and the dispersal is so dependent on time-variable ocean circulation, only long-term, systematic measurements can reveal significant trends and large-scale patterns of pollutant levels. There is a need to evaluate the sources, fates, and effects of persistent pollut-

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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ants throughout the region and to link these observations with circulation models, so as to enable the predictions that are crucial for coastal zone management and planning.

MARINE NATURAL PRODUCTS

A good basis exists for collaboration between Mexico and the United States in the area of marine natural products chemistry. Both countries have strong academic programs in chemistry, pharmacology, marine biology, and marine ecology, which are the primary disciplines required for this multidisciplinary field. Differences between the two countries result primarily from the way science is practiced and funded. In the United States, research programs tend to be goal-oriented whereas in Mexico research programs are discipline oriented. For example, U.S. funding agencies such as the National Cancer Institute and the National Sea Grant College Program have provided financial support to foster interdisciplinary goal-oriented research programs in the United States that reward chemists and pharmacologists for collaborating to discover new pharmaceuticals. These programs are not without their problems, but when properly managed they can be very effective in fostering both basic and applied research in marine natural products chemistry, pharmacology, and marine biology.

One of the more surprising results of drug discovery programs has been the degree to which they have stimulated advances in marine science disciplines. Examples included basic studies of symbiosis and the role of symbiotic microorganisms in the biosynthesis of pharmacologically active compounds, actions of bioactive compounds to protect the producing organism from predation (chemical ecology), basic studies in marine ecology that must precede a major harvesting program, aquaculture research, and studies in marine biodiversity. Mexican researchers and funding agencies might wish to examine the feasibility of interdisciplinary research programs related to marine natural products chemistry, learning from the successes and mistakes experienced by U.S. programs. The strength of both Mexico and the United States in the area of biotechnology offers the potential for substantial collaborative efforts on this topic. Pharmaceutical companies often play a considerable role in drug discovery and commercialization. With this in mind, any academic drug discovery program, particularly a program based on international cooperation, should clearly address the legal issues of patent rights and the sharing of potential financial rewards before the program starts. Few academic discoveries have led to pharmaceuticals, however, largely because pharmaceutical companies prefer to develop their own discoveries. Academic groups should place good research above commercial application while acknowledging that the latter might result from the former. For collaboration in marine biotechnology and drug development to work, it is important that use of natural products derived from U.S. and Mexican organisms receive equitable patent protection and distribution of royalties.

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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Conservation of Marine Biological Diversity*

The conservation of biological diversity has become both a scientific and a political goal of the 1990s. Whereas this concept seems well defined when applied to tropical rain forests, its application to marine environments is poorly understood. It is absolutely certain that we have described only a small percentage of the marine organisms in the intertidal zone and that our knowledge of deep- and midwater organisms is even more sparse. Because we do not know what exists, we cannot know what to conserve.

Current efforts in Mexico in the area of marine biological diversity include the definition of priority areas along the coast and open-ocean environments, based on criteria of the highest diversity. Large databases are being created primarily with the major taxa represented in formal collections of museums and research institutions. Criteria proposed by Sullivan (1997) are also being applied. Documents that have recognized the status of marine biological diversity by regions and habitats were published by Salazar-Vallejo and González (1993). At this moment, the National System of Protected Areas (Sistema Nacional de Areas Protegidas [SINAP]) recognizes 59 protected areas along all coasts of Mexico, representing different levels of protection (e.g., Biosphere Reserves, national parks, refuges, protected areas, and reserves) in habitats such as dunes, beaches, reefs, coastal lagoons, mangroves, marshes, and islands. A major effort is still needed to consider the real value of habitats integrated in Large Marine Ecosystems. A joint effort is required to unify the efforts started in the United States with the existing efforts in Mexico.

Many people believe that the rain forests provide a habitat for many species that may contain important pharmaceutical agents and that destruction of the rain forests will deprive science of the opportunity to discover these agents. Yet the invertebrates found on tropical and subtropical reefs are known to be a far more productive source of pharmacologically active compounds, according to statistics accumulated by the National Cancer Institute (data from J.H. Cardellina and P.T. Murphy, quoted in Gatson, 1994). Research on marine biodiversity, with an eventual goal of conservation, is an area of U.S.-Mexico cooperation that would receive both political and popular support. However, such research has its detractors because commercial fishing and destruction of marine habitats for urban and industrial development are among the principal factors contributing to the reduction of marine biodiversity.

Research on marine biodiversity requires significant financial support for taxonomic studies on both sides of the border. It requires collaboration between marine biologists, marine ecologists, and biological oceanographers, which is strangely lacking in some areas because of the competition among these disciplines for scarce resources. Ultimately, it will require the involvement of scientists from other fields to evaluate the potential value of newly described organ-

*  

 See also NRC (1995).

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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isms as resources for drag discovery and biotechnology. The conservation of biodiversity will require cooperation among nations that share common ocean areas to ensure that actions by one nation do not cause detrimental effects in the shared area. An open border for such scientific research, subject to strict reporting requirements, should be a primary goal of a U.S.-Mexico binational marine science collaboration.

Marine Biotechnology*

Marine biotechnology, which may be defined as the search for commercial uses of marine biology, biochemistry, and biophysics, is a fledgling field of study having substantial potential. At the simplest level, there is a sense that organisms living in a saline medium, often at high pressures or temperatures, contain biochemical agents that may be of use to industry in marine biotechnology. Neither the United States nor Mexico can match Japan's investment in this field (Rinehart et al., 1981; Faulkner, 1983), and there is evidence that the European Union is accelerating its investment in marine biotechnology. A research collaboration between the United States and Mexico could yield considerable benefits for both countries, because the United States is experiencing a boom in biotechnology while some of the most promising locations in which to perform marine biotechnology field research are in Mexico.

The microbial and invertebrate biodiversity found in the Gulf of California makes it a prime target for ''bioprospecting.'' From 1970 to 1985, studies of the chemistry of a rather limited selection of marine algae and invertebrates from the Gulf of California resulted in the discovery of several antimicrobial, antineoplastic, and anti-inflammatory agents (Rinehart et al. 1981; Faulkner, 1983). A reinvestigation of these sources using modem mechanism-based bioassays may lead to the discovery of new biomedical agents.

The opportunity to sample marine microorganisms, including extreme thermophilic bacteria from the geothermal vent systems and extreme halophiles from salt ponds, can significantly expand the biomedical potential of Gulf of California organisms. The fledgling marine biotechnology industry has shown considerable interest in extreme thermophilic marine bacteria because they produce enzymes that are stable and efficient at high temperatures and pressures and are therefore attractive for use in industrial processes. The hydrothermal vent systems in the Guaymas Basin are known to be an excellent source of extreme thermophiles (Vidal, 1980; Jørgensen et al., 1992), but there are also many shallow-water seeps, salt ponds, mangrove swamps, and other unique marine microenvironments that could provide a diversity of microorganisms useful to the biotechnology industry.

It is almost impossible to predict the future directions of marine biotechnology research or the benefits that could accrue. It is safe to say, however, that

*  

 See also NRC (1994a).

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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marine biotechnology is lagging behind the leading edge of biotechnology but that this situation will improve as the field becomes better organized. For example, an initial meeting of California researchers interested in marine biotechnology resulted in an unexpectedly broad array of research topics being presented. Both the organizers and the participants were surprised at the diversity of existing research. A similar U.S.-Mexico conference on marine biotechnology could be used to initiate binational collaborations in this field.

REGIONAL CLIMATE CHANGE

Of the several modules of IOC's proposed global ocean observing system (GOOS) (see Chapter 3), perhaps the most mature is the climate module for reasons of technical readiness and scientific urgency. Fundamental understanding of climate change must ultimately be global, but efforts to document changes and to make climate change and impact predictions of practical use to society must be done region by region. If global warming occurs, no individual nation will be affected primarily by the global average temperature rise; rather, nations will be affected by the temperature rise and associated effects in their region.

It is certain that atmospheric CO2 concentration has risen during the industrial age, and that global temperatures have risen about 0.5 °C in the past century. The relative importance of natural variation versus human activity in forcing the temperature change is subject to ongoing study. Model predictions of global warming are beset by uncertainty, particularly if one tries to predict regional patterns of change instead of global averages (Speranza et al., 1995, p. 425).

The ocean plays a major role in the climate system. It is an enormous thermal flywheel because of its huge heat capacity relative to that of the atmosphere, and it is a key reservoir of carbon. Exchange of CO2 gas across the sea surface depends on physical processes, some of which are poorly known for the full range of complex conditions (from calms to hurricanes) to which the surface is subject. In ocean surface waters, biological processes take up CO2 (e.g., photosynthesis by phytoplankton and carbonate removal by corals), and carbon falls to the sea-floor and is sequestered in sediments. These biological processes or "pumps" may both affect and be affected by the changing state of the atmospheric climate and carbon systems. The effectiveness of the ocean in removing CO2 directly affects forecasts of atmospheric buildup; similarly, if the climate changes in the future and forces a different ocean circulation, the distribution and effectiveness of these biological processes may change.

Joint U.S.-Mexican contributions to solutions of these questions in the form of (1) careful, high-quality, long-term measurements of key carbon and climate system variables in the region of common interest and (2) scientific efforts designed to interpret such measurements and place them in global context can be important parts of the worldwide effort to understand climate change.

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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The area of joint U.S.-Mexican interest spans extensive tropical and subtropical regions, where it is naturally easier to detect trends in long time series of some ocean variables because of the reduced synoptic-scale and seasonal noise relative to the situation at high latitudes. This advantage should be used in the selection of sites and variables to be studied.

Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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Suggested Citation:"2 Examples of Promising Science Programs and Projects." National Research Council. 1999. Building Ocean Science Partnerships: The United States and Mexico Working Together. Washington, DC: The National Academies Press. doi: 10.17226/5874.
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Building Ocean Science Partnerships describes a set of potential ocean science projects for cooperative research between scientists from the United States and Mexico, particularly focused on the Pacific Coast of California and Baja California, the Gulf of California, and the Gulf of Mexico. Barriers to cooperation between scientists of the two nations are identified, and methods to overcome such barriers are recommended.

The book describes how interactions can be promoted by enhancing opportunities for education and training, building and sharing scientific infrastructure, participating together in large-scale marine research programs and regional ocean observing systems, planning joint science events and publications, and developing sources of binational funding. Building Ocean Science Partnerships will be published in English and Spanish to make its contents widely accessible in the United States and Mexico.

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