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The Scientific Potential of Seafloor Observatories
Pages 25-70

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From page 25...
... These processes include hydrothermal activity and biomass variability in vent communities along portions of the mid-ocean ridge system, air-sea interactions in the Southern Ocean, and biological and chemical variability of the water column at both coastal and oceanic sites. · Obser7)
From page 26...
... decadal report themes based on the "Futures" workshops (Baker and McNutt, 1996; Jumars and Hay, 1999; Mayer and Druffel, 1999; Royer and Young, 1999~. Each section addresses future directions and major scientific problems, the role of sustained time-series observations, and technical requirements for seafloor observatories.
From page 27...
... A substantially improved observational basis for determining the needed model enhancements is required. Specific ocean science challenges include quantifying and understanding turbulent mixing; convection; water-mass formation and destruction; thermohaline circulation and its coupling to the wind-driven circulation; the generation, maintenance, and destruction of climatic anomalies; climatic oscillations and the extratropical coupling of the ocean and atmosphere on seasonal, decadal, and interdecadal timescales; and the physics of exchange processes between the ocean and the atmosphere (Royer and Young, 1999~.
From page 28...
... Established: HOT was established in late 1988 with National Science Foundation funding under the auspices of the Joint Global Ocean Flux Study (JGOFS) and World Ocean Circulation Experiment (WOCE)
From page 29...
... Fixed site observatories would primarily consist of moorings, which are best suited for vertical and temporal sampling. Moorings also provide the means to sample scientifically critical regions, such as the upper few tens of meters of the ocean under ice cover in confined current systems and in abyssal layers (including bottom boundary layers; see "Turbulent Mixing and Biophysical Interaction" section in this chapter)
From page 30...
... Joint Global Ocean Flux Study (JGOFS) program in 1988.
From page 31...
... OOPC and other groups representing climate research interests hosted a major international conference, OceanObs99, in St. Raphael, France, in October 1999 (OCEANOBS99, 1999~; the conference gathered broad input from the ocean science and climate communities and helped further the scientific rationale for sustained observations.
From page 32...
... Observatory science is USEFUL in investigating the following: · Water mass formation and destruction; and · The relationship of heat and freshwater fluxes to wind and buoyancy forcing.
From page 33...
... , to the implementation of a sustained global ocean-observing system. TECHNICAL REQUIREMENTS The technical requirements of the climate and turbulent mixing communities have an important overlap, and there are compatible needs for platforms.
From page 34...
... Different types of relocatable observatories should be considered for investigating specific science questions. These could be repositioned for one or more years at different locations around the globe as needed, such as proposed for surveying turbulence parameter space in the "Technical Requirements" of the "Turbulent Mixing and Biophysical Interaction" section.
From page 35...
... Similarly, the dynamics of gas hydrate formation and dissociation, especially in response to perturbations produced by tectonic cycles or global warming, is a problem of current interest that could be addressed by observatory science. FUTURE DIRECTIONS AND MAJOR SCIENTIFIC PROBLEMS Four different oceanic environments are important for research on fluids and life in the ocean crust: ridge crests, ridge flanks, convergent margins, and coastal areas on passive margins.
From page 36...
... A seafloor observatory system near a volcanically active site would provide an important platform for characterizing the early stages of an event while also monitoring longer-term changes. For instance, once an eruptive event has been detected (acoustically or otherwise)
From page 37...
... Location: Axial seamount (summit caldera at 1,520 m water depth) on the Juan de Fuca Ridge, approximately 250 mi off the coast of Oregon and Washington Established: Autumn 1997 FIGURE 2-3 Axial Volcano, Juan de Fuca Ridge the first place where new tube worms were found on the site of the 1998 Axial Volcano seafloor eruption.
From page 38...
... form and assess their global importance; · directly observe how biological productivity and diversity change in response to fluctuations in fluid and chemical fluxes at vents and seeps on ridge crests, ridge flanks, and at convergent margins; assess the extent to which sediment cover and spreading rate or subduction rate affect fluid chemistry and biological diversity at ridge crests, ridge flanks, and subduction zones and assess the impact of these chemical systems on the overlying ocean; · quantify the importance of chemosynthetic productivity on the seafloor; understand the relations between tectonic and fluid processes in subduction zones; · determine rates of gas hydrate formation and dissociation in response to perturbations of pressure, temperature, and fluid chemistry and flow rate and determine the influence on ocean chemistry, biology, and climate.
From page 39...
... Seafloor observatories could also provide valuable real-time control of experiments and allow in situ process studies in which intervention or perturbation experiments could be conducted. On a broader scale, a more ambitious goal would be to design an observatory that could provide simultaneous observations on the ridge crest, ridge flank, and convergent margins.
From page 40...
... Building on these successes, a new generation of advanced CORKs has been developed, incorporating a capability to separately seal and isolate multiple zones in the sub-seafloor formation, so the observatory configurations correspond much more closely to natural hydrogeological structures. This new generation will also accept an enhanced range of sensors and auxiliary experiments, allowing customized sub-seafloor observatories for studying a variety of fluids-related problems (e.g., sub-seafloor microbiological communities and processes, gas hydrate processes)
From page 41...
... Biological studies within the crustal and vent environments will necessitate a wide range of experiment types that in turn will require different observatory approaches. To study the biological response to transient events, such as the colonization of newly formed vent fields, relocatable observatories that can be rapidly deployed are essential.
From page 42...
... . The CMB is compositionally and perhaps dynamically the most dramatic boundary within the earth and it has been proposed as the origin of hot spots and the graveyard of subduction zones.
From page 43...
... (Montagner and Lancelot, 1995) that would also include ~8 seafloor magnetic observatory sites identified by a task group of the U.S.
From page 44...
... The H20 junction box is a "smart" design that incorporates redundancy to protect against failure and with full control of instrument functionality from shore. Initial instrumentation at the observatory site includes broadband seismometer and hydrophore packages.
From page 45...
... This gunman box is designed to be removed for servicing and relnstaHed by a research vessel and a remotely operated vehicle (R~. SOURCE: Alan Chow Woods Hole Oceanographlc Instltutlon.
From page 46...
... Possible experiments include seismometers, hydrophores, and pressure sensors, as well as systems to monitor biological activity, chemical variations, hydrothermal venting, and motion of the unstable flank of Kilauea volcano (Plate l\/. The observatory junction box is located at a depth of 1,200 m and has excellent acoustic visibility of approximately 1/4 of the world's oceans.
From page 47...
... The scientific strategy employed by SEIZE involves a combination of geophysical imaging, drilling, and long-term monitoring over an earthquake cycle (a few years to several decades) at a few representative subduction zones.
From page 48...
... ILLUMINATING THE HIDDEN PLANET Cal 48 at/ con
From page 49...
... This area will be a major focus of a new program in the earth sciences community known as Earth Scope, and its subprograms the USArray and the Plate Boundary Observatory. A seafloor observatory program would complement these land-based studies by providing the capability to monitor deformation and faulting seaward of major active fault systems, like the San Andreas, in tectonic settings where fault systems may have less complex structures than on the continent.
From page 50...
... Seafloor observatories provide an opportunity to advance the embryonic science of monitoring geodetic motions on the seafloor. It will finally be possible to continuously observe motion near plate boundaries.
From page 51...
... TECHNICAL REQUIREMENTS The diverse solid-earth applications for seafloor observatories result in a range of technical requirements that argue for a flexible observatory infrastructure using both cabled-based and moored-buoy systems. The technical requirements for the global OSN sites are comparatively simple: a broadband seismometer with a sensor mounted in a borehole or buried in sediment, and a seafloor magnetometer.
From page 52...
... For certain applications, photography and real-time video will be required. In addition, remotely controlled seafloor rovers and AUVs will be needed to collect data and samples in a broader area around each FIGURE 2-8 Schematic drawing of a seafloor geodetic experiment showing the buoy, seafloor transponders, global positioning system, and acoustic transmitter.
From page 53...
... COASTAL OCEAN PROCESSES The coastal ocean includes estuaries, the surf zone, the Laurentian Great Lakes, the continental shelf, and the continental slope. This definition incorporates a great deal of environmental diversity.
From page 54...
... Large algal blooms that occur offshore provide a pulse of organic matter to deep environments, affecting population dynamics and seasonality in bottom-dwelling organisms. A seafloor observatory positioned in a location where blooms occur could contribute substantially to our understanding of processes initiating algal blooms, and the effect of these blooms on marine communities and food webs.
From page 55...
... · A number of coastal management issues will require long, highresolution time series of coastal ocean processes. Fisheries applications are an obvious example, but there are numerous other concerns, such as coastal eutrophication, impacts of transportation, and the effects of nearshore minerals exploitation.
From page 56...
... To address the science where observatories are essential, development or improvement of the following sensors is needed: · Increased duration, speed, and long-term reliability for AUVs; · In situ nutrient and chemical sensors; and · In situ zooplankton sensors. The coastal ocean is often typified by relatively short spatial scales and by strong anisotropy.
From page 57...
... TURBULENT MIXING AND BIOPHYSICAL INTERACTION Turbulent mixing occurs over a broad spectrum of timescales and space scales, strongly affecting the distribution of momentum, heat, chemical compounds, and living organisms in the ocean. Modeling of the physics of turbulent flows is a major limitation in our ability to simulate observed ocean circulation features.
From page 58...
... 't? 're of Physical Oceanography, this is concisely expressed: Past achievements in quantifying small-scale turbulent mixing in the main thermocline, coupled with exciting recent measurements in the deep ocean, suggest that a description and an understanding of the spatial distribution of turbulent mixing in the global ocean is achievable in the next decade.
From page 59...
... THE ROLE OF SUSTAINED TIME-SERIES OBSERVATIONS The main challenge for the parameterization of turbulent mixing is in obtaining high-quality turbulence statistics and their variation, along with sufficiently dense temporal and spatial information about the oceanic processes that modulate the turbulence. To develop a universal parameterization it is necessary to conduct observational studies in a broad range of environmental conditions (Table 2-5~.
From page 60...
... and velocity profilers is now possible, and such an array can be used to examine mixing issues independent of a seafloor observatory program. To add value to these arrays, the seafloor observatory concept must provide the needed horizontal resolution over much finer scales than presently possible.
From page 61...
... Flow over bottom roughness that extends into the stratified water column can excite internal waves that propagate and break. Special cases are: a)
From page 62...
... This, in turn, would have an important impact on biogeochemical models. The seafloor observatory concept is of limited value to the turbulent mixing community without the ability to implement the strategy of acquiring data in four dimensions while executing dedicated process studies.
From page 63...
... Technical requirements in common with the ocean climate objectives are given in the section titled "Role of the Ocean in Climate" earlier in this chapter. ECOSYSTEM DYNAM INS AN D BIODIVERSITY Seafloor observatories are crucial for addressing many of the major scientific problems identified by the NSF Futures report on biological oceanography, Report of the OEWRE Workshop (lumars and Hay, 1999; Table 2-6~.
From page 64...
... . Observatory science is USEFUL to accomplish the following: · Characterize changes in biodiversity and community structure; · Determine the spatial scales of the connection between marine populations via dispersal of early life stages (e.g., local population isolation, barriers to dispersal, and linkages in the epidemiology of disease)
From page 65...
... In some cases, observatories will be most effective when used with more traditional approaches, such as drifters, ROVs, manned submersibles, and surface ships. The following are scientific questions well suited for study using seafloor observatories along with a description of the most compatible facility to address the particular scientific problem.
From page 66...
... Relocatable observatories will also be a useful approach when addressing ecological questions where shorter-term time series are sufficient (as with the study of hydrothermal vent communities)
From page 67...
... The satellite data received in New Brunswick provides information about sea surface temperature, water quality, and phytoplankton content over a huge area (40 deg. latitude x 50 deg.
From page 68...
... Data collected from the sensors listed above should be correlated with satellite data providing optical information and radar imaging for current flow. It is anticipated that perturbation experiments, such as the controlled release of chemicals or tracers into the water column, or manipulations of seafloor communities using colonization surfaces, faunal clearances, faunal transplants, and predator inclusion and exclusions, will be conducted as part of the observatory activities, and that ecosystem responses will be recorded with sensors and by sampling.
From page 69...
... Specific scientific problems include encounter rates of predators and prey, long-term variations in population abundances, and detection of processes generating large-scale patterns in ecosystems. Both long-term and relocatable observatories are essential to address this question.
From page 70...
... Long-term studies are likely to require a cabled network with a series of moorings with cameras, active omnidirectional acoustic sonars, and environmental sensors measuring physical, chemical, and biological properties. Because identification, genetic, and chemical analyses of organisms will be a component of the studies, procedures for in situ sample processing and sample collection will be needed.


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