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2 General Objectives and Program Summary I. INTRODUCTION As we move closer to an understanding of global environmental phenomena, the important role of the polar regions in long-term atmosphere and ocean dynamics becomes more apparent. An adequate understanding of the physics and dynamics of polar regions is essential to the prediction of global environmental processes that are required for eventual rational manage- ment of the earth for the benefit of man. The goal of this report is to consider the future role of oceanography in the Southern Ocean in light of the above statement. Three general ques- tions are addressed in this chapter: what is the scientific and practical rationale, why is a program being recommended now, and are the existing and projected manpower and scientific resources adequate to carry out the recom- mended program? The great distances and high logistics costs involved in mounting pro- grams in the antarctic regions require a strong justification for U.S. participa- tion. For oceanography, we believe that it is appropriate for the United States to give first consideration to matters of global rather than strictly regional significance. Therefore, the recommended dynamics experiments in the Southern Ocean have two major scientific goals. The first is to use the Southern Ocean as a unique geophysical laboratory for process-oriented studies of the time- dependent dynamics and air-sea interaction of large-scale ocean currents and frontal zones. The second is to use monitoring experiments and theory to understand the role of this part of the ocean in the global ocean-atmosphere circulation, in the global interaction of the sea and the atmosphere, and in the dynamics of climate. Although we have some understanding of the problems studied in other latitudes, and the grossest features of the circulation can be ra- tionalized, little fundamental progress has been made in actually elucidating 3
4 Southern Ocean Dynamics the dynamics of processes sufficiently to understand their essential aspects. Both experiment and theory are required to solve these problems. We presently lack both global observational data on the relevant time and space scales and sufficient theoretical understanding. Global observations are inadequate because it is difficult to make oceanographic measurements: the technology is complex and the time scales relating to energy exchanges are relatively short compared with the global scales. Theories are inadequate because we have not yet been able to isolate essential processes from the many parameters of fluid motions inherent in the conservation equations. We believe that the proper course for solution of these problems is to plan and execute a set of sharply defined ocean experiments that utilize existing reliable technology. The data from these experiments and from ex- isting data can form a basis for a set of theoretical numerical experiments designed to isolate processes and understand them. The essential role of the theoretical experiments is to provide the feedback between theoretical ideas and the design and interpretation of the field experiments. As a firm under- standing of physical processes emerges, their essential aspects can be param- eterized into larger models. A balance among monitoring, numerical models, and process-oriented experiments will be required in order properly to couple the ocean to the atmosphere for models that adequately represent long-term climate variability. The above remarks are general. The specific scientific goals are discus- sed below. II. SPECIFIC SCIENTIFIC GOALS A. OCEAN DYNAMICS The circumpolar current systemâthe zonal flow, the meridional flow, and the source of deep water in the Weddell Seaâis the heart of the deep- ocean circulation. The antarctic currents link the world's major oceans, and deep antarctic convection sends both slowly moving water and swifter western boundary currents equatorward. The main thermocline in the ocean is maintained by the resulting gentle upward flow. Processes occurring in the Antarctic affect the global distribution of properties in the oceans; only by exploring these processes and their consequences, first regionally, then globally, can we eventually gain an understanding of the ocean as it operates on climatic time scales. The variability of physical properties and nutrient chemicals is also intimately tied to the circulation. The dynamics of the circumpolar currents are nonlinear and time-dependent and apparently similar to dynamics in temperate latitudes. Therefore, the circumpolar currents will
General Objectives and Program Summary 5 be no easier, and probably more difficult because of logistics, to study than other major current systems. The geography of the region provides a unique opportunity to monitor certain averaged properties of the circumpolar flow. The current is funneled through the Drake Passage; the total transport here represents the flow that is recirculated around the continent. With the proper set of measurements, one might determine a major ocean current response to large- scale atmospheric forcing. Thus the Drake Passage is a natural geophysical fluid-dynamics laboratory for large ocean currents. In spite of the increased logistics problems, the possible achievements could be a major step in under- standing large-scale ocean currents. The specific problems are to measure and understand the vorticity balance and variability of the strong surface flows and the deeper abyssal flows and to understand the interaction of the source flow and the abyssal currents. There is a strong frontal zone around the Antarctic continent. The processes that maintain this polar front are fundamental in the formation of intermediate water masses. The polar front is closely coupled to the cir- cumpolar current. The specific problems are to delineate the processes occur- ring at the front and to understand the interaction between the front and the circumpolar current. B. AIR-SEA INTERACTION Strong atmospheric cooling of the Weddell Sea water causes it to be the largest source of bottom water in the global ocean. Air-sea interaction also is probably closely related to the circumpolar frontal zones. Processes of heat exchange between the ocean and the atmosphere and of heat redis- tribution in the Southern Ocean are only very generally known. The specific goals here are to measure, isolate, and understand the air-sea processes responsible for bottom-water formation and to monitor the amount of bottom water formed as a function of time in order to determine its input to the general abyssal circulation. In addition, we need to isolate the air-sea exchange processes at the polar frontal zones in order to parameterize these into large-scale air-sea interaction models. Finally, the requirements of global climate dynamics models include a knowledge of the annual and longer-term trends of separate heat-balance components in the Southern Ocean. C. SEA-ICE-AIR INTERACTION The formation and dynamics of sea ice are fundamental to the dynam- ics of Antarctic Bottom Water formation and to exchange processes and
6 Southern Ocean Dynamics budgets. In an earlier version of this report, a chapter on sea-ice dynamics was included; that chapter is now Appendix D of the report Guidelines for Antarctic Glaciology (by the ad hoc Glaciology Working Group of the CPR [1974]). The change in location of that chapter in no way diminishes the Working Group's opinion of the fundamental importance of sea-ice-air in- teractions in polar regions; in fact, the Working Group notes that proper ice-dynamics studies will be an essential part of an Antarctic Bottom Water formation experiment and of the overall budget studies. Certain aspects of ice interaction are included in Chapters 4 and 5 on Antarctic Bottom Water formation and on exchange processes and overall budgets, respectively. D. ATMOSPHERIC DYNAMICS The Global Atmospheric Research Program (GARP) has set specific requirements for atmospheric measurements in the southern hemisphere during the First Global GARP Experiment (FGGE) scheduled for 1977. The first goal of this program is the improvement of short-term atmospheric prediction. The related meteorological requirements include measurement of sea-surface temperature [because the sensible heat transfer to and from the oceans is a major heat source (or sink) for the atmosphere] and atmospheric pressure. This requirement will involve obtaining measurements from drifting buoys and input from oceanographers to see that the information obtained will be of maximum value to both disciplines. The specific quantity of interest to oceanographers here is Lagrangian information, i.e., paths of sur- face currents around the continent. The second goal of the program is the understanding of the physical basis of climate. This longer-term atmospheric prediction capability requires information on the motions and thermal structure of the upper ocean layer. Thus a second quantity of interest is heat-storage information along the path of the drifting buoys. This could be obtained, for example, by measurement of near-surface temperature profiles. III. ULTIMATE PRACTICAL GOALS Studies on the physical oceanography of the Southern Ocean can contribute significantly to our understanding of four areas of global societal concern. They are (1) weather and climate modification; (2) an ecologically efficient long-term use of the region's fisheries; (3) an ecologically sound strategy for the disposal of waste and radioactive by-products; and (4) the improved prediction of local weather, sea, and ice conditions. The National Academy of Sciences report on weather and climate modification [Committee on Atmospheric Sciences, 1973] states that "con-
General Objectives and Program Summary 7 cern for man's impact on the worldwide climate has been sharply increased by the exponentially growing capacity to utilize global resources to produce goods and servicesâa capacity that within decades may begin to approximate the natural forces influencing the atmosphere and the ocean. Alterations to the atmosphere are assuming a place of prominence in worldwide concern over the human environment." The polar regions play a major role in climatic variability. Through polar meteorological experiments like POLEX (a sub- program of GARP), interaction experiments like AIDJEX, and oceanographic experiments like the ones recommended here, oceanographers and meteor- ologists hope to define more clearly the role of the polar regions in oceanic and atmospheric climate. Biological productivity is high in the Southern Ocean. The large regions of summer plankton growth at high latitudes, brought on by the long days of sunlight, are a source of food for animals from small krill to large whales. The monitoring of the physical oceanographic environment will be a necessary adjunct if man is to harvest efficiently but not exhaust the renew- able organic resources of this richly productive region. The disposal of waste and radioactive by-products is a major environ- mental concern today. If the practice of dumping such by-products in the ocean were to be seriously advocated, an ecologically sound strategy would be required. Such a strategy awaits our understanding of the deep circulation of the ocean. The Southern Ocean plays a major role in the abyssal circula- tion, which is in turn responsible for the distribution of materials in the deep ocean. Overturning rates and processes must be understood and monitored before we can predict the residence times for these man-made pollutants. Finally, understanding of the physical environmental processes in the atmosphere and ocean surrounding the Antarctic continent could eventually lead to an economically and ecologically sound development of the region. With improved local weather, ice, and sea condition predictions, and improve- ment in navigational aids, a rational development of the potential resources of the continent and its ocean can be planned. IV. HISTORICAL BACKGROUND A clear view of the next steps in physical oceanography programs in the Southern Ocean and their time frame is now emerging from recent sci- entific literature and a number of international meetings. The region has revealed a variety of strong, transient dynamical phenomena involved in the formation of large water masses and abyssal circulation. Vigorous exchanges of heat and momentum with the atmosphere suggest the importance of south- ern hemisphere air-sea interactions in the global atmospheric circulation. In November 1970, the coordination group on the Southern Ocean of
8 Southern Ocean Dynamics the International Oceanographic Commission (IOC) noted that significant progress had been made in describing the hydrography of the Southern Ocean and in delineating the gross exchanges of physical properties with the adjacent parts of the World Ocean. They noted that data required for proper understanding of phenomena, however, were still lacking. Especially empha- sized was the serious lack of data on (1) variability in the distribution of prop- erties and of the large-scale circulation, (2) the direct measurements of deep- water movements in the Southern Ocean, (3) the origin and dynamics of frontal zones, and (4) the formation of water masses. They noted that winter data in particular are needed and that the heat budget should be refined on the basis of direct measurements. Furthermore, the concept of an integrated global observing program is currently being extended to the IGOSS by the IOC. The IGOSS pilot project is now under way with the ultimate objective of providing comprehensive monitoring of the oceans and atmosphere through an integrated system involving the common use of facilities, sensors, and plat- forms such as ocean buoys, ships, and space satellites. The U.S. contribution to this advancement of knowledge of antarctic oceanography has been substantial. The collection of a network of modern data in the Southern Ocean carried out from the USNS Eltanin from 1962 to 1972 has provided a firm but incomplete base for future research there in a number of oceanographic disciplines. The Working Group notes that the termination, due to budgetary limitations, of the USNS Eltanin program in 1972, before its circumpolar survey was completed, is the cause of the in- complete data base and recommends that every effort be made to complete the survey, either from the Eltanin or from some other ship. The existing data base and recent developments in ocean engineering do, however, allow us to consider now a new phase of observation: long-term monitoring of the dynamics and specific experiments designed to probe the basic physics and interaction processes. We recommend in the chapters that follow a series of experiments designed to explore in depth three major areas: the dynamics of the Antarctic Circumpolar Current; the mechanisms and variability of Antarctic Bottom Water formation; and the role of exchange processes in strong frontal zones and overall budgets. The steady advances in experimental and theoretical oceanography achieved during the past decade have provided a pool of sophisticated yet reliable instrumentation and expertise that can be applied to any ocean. With the use of these techniques, scientists are beginning to be able to ask and answer the relevant dynamical questions. Some of the recommended experiments can be done with existing technology, and these should be implemented as soon as reasonably possible in order to minimize ever-rising support costs. Others will require develop-
General Objectives and Program Summary 9 ment of automatic data buoys and other remote technology. In view of the importance of such technology in long-term monitoring, pilot experiments and development should begin as soon as possible. The plans for GARP also show the need for prompt inception of this program of exploration. It is clear that the goals of the oceanographic studies are closely related to ultimate goals of GARP. The second objective of GARP is to study those physical processes in the atmosphere that are essential for an understanding of the factors that determine the statistical properties of the general circulation of the atmosphere, which would lead to better under- standing of the physical basis of climate. Knowledge of ocean circulation and its interaction with the atmosphere will be an essential input to this objective. The Polar Experiment subprograms POLEX-GARP (North) and POLEX- GARP (South) of FGGE will require monitoring of oceanic dynamical processes, but the detailed experiments have not yet been defined. The Working Group emphasizes the opportunities for fruitful simul- taneous experimentation with FGGE and POLEX-GARP (South) in 1977and urges that an experimental plan be developed as soon as possible so that scientific interaction can be achieved and adequate monitoring systems made operable by then. Finally, we turn to the question of logistics and resource allocation. Can a program be structured so that it is scientifically sound but does not stretch the available resources (manpower, equipment, and funds) beyond their projected limits? We believe that it is possible to do so provided that the activities are a sequence of well-defined, sharply focused experiments rather than a parallel broad effort toward a diffuse and ill-defined goal. Activities in several areas can be carried forward simultaneously, but expensive field pro- grams should be staggered so that the project as a whole remains of manage- able size. Therefore, we recommend that a sequence of sharply focused ocean monitoring and dynamics experiments be begun as soon as possible in the Southern Ocean for the purpose of contributing to the goal of understanding long-term, large-scale ocean and climate dynamics. In order to do this, continual review and planning must be part of the scientific management of the program. Therefore, we recommend that the management of such a program include a continuing effort to review con- ceptual design, strategy, and interaction among Southern Ocean experiments and on collaboration between this regional and other global oceanographic and meteorological programs. We note that the international interest in antarctic oceanography sug- gests that these experiments could be done together with national oceanog- raphy organizations of other countries. The existing international coopera-
10 Southern Ocean Dynamics tion of several countries in antarctic research is a firm basis for this collab- oration, which would maximize the information flow. Therefore, we recom- mend that the National Science Foundation actively seek cooperation of scientists and sponsoring institutions of other nations in planning and carrying out these investigations. Such a sequence of experiments could form the U.S. nucleus of a program of International Southern Ocean Studies (ISOS) on ocean dynamics and monitoring. This program could contribute directly to research in physi- cal oceanography and climate variation sponsored by the International Decade of Oceanographic Exploration (IDOE), the Division of Environmental Sciences (DBS), and the Research Applied to National Needs (RANN) pro- gram. Monitoring should be carried out in cooperation with the Intergovern- mental Oceanographic Commission's (IOC) Integrated Global Ocean Station System (IGOSS), the United Nations Environmental Program (UNEP) "Earthwatch," and other such international global programs. V. PROG RAM SUMMARY We have recommended the planning of a sequence of ocean dynamics and monitoring experiments in the Southern Ocean with maximum inter- action with the FGGE. The specific areas of study for these experiments is discussed in detail in the following chapters. In summary, the Working Group, noting that data should be gathered through an integrated program of manned and unmanned stations and that the development of technology of remote sensing is to be encouraged, recom- mends three specific areas of study: 1. A program emphasizing presently available measurement tech- niques for the study of the large-scale transient dynamics of the Antarctic Circumpolar Current and its role in the general ocean circulation; 2. A program for direct observation of the processes involved in the formation of Antarctic Bottom Water and the determination of the amounts and variability of this formation; 3. A program to elucidate the structure of the strong frontal zones and their role in the formation of intermediate water masses and to monitor, with existing stations, exchange processes for overall budgets of heat, mass, and momentum in the region. A summary time-phased chart is shown in Table 2.1. As noted above, we do not recommend here a specific program in Sea Ice Dynamics. This subject is already covered in Appendix D of the report
General Objectives and Program Summary 11 TABLE 2.1 RECOMMENDED GENERAL PROGRAM STRUCTURE Activlty rTime Frame | CONTINUAL PLANNING AND REVIEW 1973 - 1976 1976 - 1979 1979 - 1982 Dynan.ics of the Circumpolar Current Begin Field » Monitoring Experiment Antarctic Bottom , Begin Field â - *- Monitoring Experiment Merge into International Water Formation 1 Climate Research Effort Overall Budgets Experiment GARP PLANNING I AIDJEX FGGE Antarctic Glaciology, Guidelines for U.S. Program Planning, 1973-1983, by the ad hoc Glaciology Working Group of the CPR (National Academy of Sciences, 1974). The interaction of oceanography with sea ice is discussed in Chapter 5.
