The Contemporary System
The depth, breadth, and complexity of the global ocean, covering more than 70 percent of Earth's surface, have challenged our ability to explore, measure, and comprehend its controlling processes and to predict its behavior. Technology has evolved to the point where we can study the ocean on a global scale and study its interactions with the land and the atmosphere. Such studies have gained increased importance because expanding populations and development, and an increase in atmospheric carbon dioxide and other greenhouse gases, will impact the physical, chemical, biological, and geological processes in the global ocean. Interactions among these processes are responsible for the distribution and abundance of plants and animals in the ocean and also produce our climate.
Changes in climate are a critical factor governing life on Earth, and the ocean plays a significant role in climate control. An understanding of short-term, coupled atmosphere-ocean effects like the El Niño-Southern Oscillation (ENSO) can have immediate economic and societal impacts. Agricultural production, and therefore food supplies and economies, is directly affected by climate variations. Changes in climate and the response of the ocean will greatly affect coastal areas resulting in rising or falling sea-level, changes in coastal upwelling, and seawater intrusion into freshwater aquifers. We must understand the role of the ocean and sea ice in climate change, particularly changes in atmospheric gases like carbon dioxide, in order to make predictions and minimize adverse effects on humankind.
The ocean and the atmosphere store heat derived from solar radiation and redistribute the heat from equatorial to polar regions. The thermal inertia of the ocean may reduce the speed of transition from one climate regime to another, as the slow overturning of the deep-ocean limits heat absorption and release at the ocean surface. The ocean is also a major source and sink for gases and chemicals that effect climate, such as carbon dioxide, water vapor, and dimethyl sulfide. Evaporation from the ocean is the main source of water for the global hydrological cycle, in which moisture is distributed by atmospheric motions and returned through precipitation, either directly to the ocean or indirectly as runoff from the continents. The deep circulation of the ocean is strongly coupled to surface processes in polar regions. Most water that flows to the ocean bottom is formed in these regions as surface water becomes colder (through interaction with cold overlying air) and saltier (through ice formation). The sinking of this dense water can have a large effect on global climate because it carries greenhouse gases and heat with it to the ocean bottom, out of contact with the atmosphere for hundreds of years. Formation of deep water in the North Atlantic Ocean can be diminished and reestablished over decadal time scales. There is increasing evidence that anomalously hot summers or cold winters in the United States are related to particular ocean conditions that cause distortions in weather patterns across the country for weeks at a time.
At certain times, developments in basic understanding and technology coalesce to produce dramatic advances. Such a breakthrough is now possible in ocean science with new observational tools and techniques, such as remotely operated vehicles, satellite-borne sensors, trace chemical measurement, acoustic techniques, long-life buoys and floats, and seafloor seismometers. Progress in electronics has provided supercomputers and work stations that can facilitate the processing and analysis of data and the construction of detailed models. The new technology and innovative ideas now available have provided the basis for developing scientific programs on a scale that has not been attainable previously. Successful initiation and completion of the inter-disciplinary global experiments described in this report could produce a tremendous increase in our understanding of how Earth works as a system.
The World Climate Research Program (WCRP) began in the early 1980s, using new in situ and satellite measurement techniques. It is aimed at understanding long-term weather variability and climate change. In recognition of the central role of the ocean in these processes, WCRP has focused on understanding the interaction of the ocean and the atmosphere. Programs falling
under the aegis of WCRP include the Tropical Ocean-Global Atmosphere (TOGA) program and the World Ocean Circulation Experiment (WOCE). In addition, WCRP will continue to study the processes that control the exchange and transport of energy and water within the global climate system. These programs, for which the United States is providing considerable resources, furnish a context for much of U.S. ocean science research.
The International Geosphere-Biosphere Program (IGBP) is aimed at describing and understanding the interactive physical, chemical, and biological processes that regulate the total Earth system, the unique environment it provides for life, the changes that are occurring in that system, and the manner in which these changes are influenced by human actions. The Joint Global Ocean Flux Study (JGOFS), Marine Aspects of Earth System History (MESH), and Land-Ocean Interactions in the Coastal Zone (LOICZ) programs, which are described in this report, are elements within the IGBP. [The Past Global Climate (PAGES) program is also an IGBP element, though it is not included here.]
Global Ocean Observing System
The Global Ocean Observing System (GOOS) program will initially emphasize those observations needed for prediction of the El Niño-Southern Oscillation (ENSO), the consequent rainfall and temperature patterns, and observations needed for detection of global change due to greenhouse warming, such as absolute sea-level and average ocean temperatures. GOOS is planned to have five application modules, including climate, living marine resources, marine weather and operational ocean services, health of the ocean, and the coastal zone. The climate module of GOOS provides the oceanic component of the Global Climate Observing System (GCOS) and includes the efforts related to global long-term climate change. GOOS will be based in so far as possible on operational measurements (i.e., observations made routinely, essentially permanently, and with societal needs in mind). GOOS is led by the Intergovernmental Oceanographic Commission (IOC) in cooperation with the World Meteorological Organization (WMO), the International Council of Scientific Unions (ICSU), and the United Nations Environment Program (UNEP).
Drawing strongly upon the successes of the TOGA program, the main observational systems for GOOS will initially be moored buoys, primarily in the tropical Pacific; volunteer observing ships; drifting buoys; island tide gauges; and satellites to measure sea-surface temperature and determine surface topography. Future instrument systems might include autonomous profilers [e.g., Autonomous Lagrangian Circulation Explorer (ALACE)], acoustic sensing of average ocean temperature, and in situ biogeochemical measurements. Overlaid on the measurement systems will be satellite telemetry, quality control, and data management, all of which exist now but need improvement and expansion. The design and enhancements of GOOS are based on the current research programs described in this report, planned future programs, and close cooperation between the research and operational communities. Several of the programs described in this report will also furnish important contributions to the development and operation of GOOS.
Tropical Ocean-Global Atmosphere Program
The Tropical Ocean-Global Atmosphere (TOGA) program was designed as the first major World Climate Research Program (WCRP) project and concentrates on the study of the ENSO cycle. The Southern Oscillation is a seesaw-like variation, over several-year intervals, of barometric pressure differences between the South Pacific Ocean and the western Pacific/eastern Indian Ocean. El Niño is a manifestation of the warm phase of the cycle, in which the pool of warm water normally observed in the western Pacific Ocean shifts eastward, diminishing upwelling of cold water along the coast of western South America and along the equator and shifting rainfall patterns away from Australia and Indonesia and eastward into the Pacific. The economic impacts of excess rainfall and flooding in South America and droughts in Australia alone are estimated to be in the billions of dollars.
The U.S. TOGA program has been concerned primarily with studies of the ENSO cycle in the tropical Pacific Ocean and its effect on global climate. The observational phase of TOGA started in 1985 and runs through the end of 1994.
The TOGA program was designed to (1) describe the interactions between the tropical oceans and the global atmosphere in sufficient detail to determine the predictability of the global climate system on seasonal to interannual time scales, (2) understand how and why these ocean-atmosphere interactions occur,
(3) model the coupled system for the purpose of predicting its variations, and (4) design a data collection and distribution system sufficient to achieve the first three objectives. The program includes process studies, long-term observations (over several ENSO cycles), and modeling. Modeling efforts aim to provide a quantitative description of ocean and atmosphere characteristics and to explain why and how these characteristics change over time and space. Coupled TOGA models, used for both simulation and prediction, require data on windstress (which drives surface ocean currents) and sea-surface temperature, in addition to the thermal structure of the upper tropical Pacific.
At present, data are collected regularly from the TOGA Observing System consisting of: (1) the TOGA Tropical Atmosphere Ocean (TAO) array—approximately 65 moored buoys that incorporate instruments to measure the surface winds and the thermal structure of the upper ocean and telemeter the information instantaneously to satellites for immediate distribution through the Global Telecommunications System (GTS), where it is used for research and weather prediction; (2) a network of several equatorial moorings that measure the vertical structure of currents; (3) the TOGA sea-level network—sea-level gauges in the Pacific and Indian Ocean; (4) a Voluntary Observing Ship (VOS) network that measures upper ocean temperature from expendable instruments dropped from merchant vessels in all three tropical oceans; (5) a drifting buoy array that measures tropical sea-surface temperatures and near surface currents; (6) a drifting buoy array that measures sea-surface temperature and sea-level pressure over all three tropical southern oceans; and (7) a Trans Pacific Profiler Network consisting of eight radar sites that measure atmospheric wind profiles.
The TOGA Coupled Ocean-Atmosphere Response Experiment (TOGA COARE), a major process experiment in the eastern Pacific, has just been completed (Box 2). This experiment measured processes influencing interactions between the atmosphere and the warm-water pool in the western Pacific Ocean, including measuring the convective processes in both the atmosphere and ocean that influence these interactions.
The TOGA Program on Seasonal to Interannual Prediction (T-POP), a research program, has been instituted to develop the models and methods needed to provide socially useful predictions of aspects of ENSO a month to a year in advance using data provided by the TOGA Observing System (Box 2). Program participants include scientists from the National Atmospheric and Oceanic Administration (NOAA) and National Aeronautics and Space Administration
(NASA) laboratories, the National Center for Atmospheric Research, and several U.S. universities working on coupled dynamic models for prediction. Informal participation by international colleagues is encouraged.
Planning is under way to form a multinational center, the International Research Institute for Climate Prediction (IRICP), with the following goals: (1) to institutionalize and regionalize short-term climate predictions for the benefit of those nations affected by ENSO variations and (2) to train people from those countries to make, understand, and use these predictions for social and economic benefit. The operating concepts embodied in the IRICP are being demonstrated in a pilot project currently in operation at Lamont-Doherty Earth Observatory.
Because the observational phase of TOGA is drawing to a close, a planning process has been under way both nationally and internationally for programs to maintain and expand the TOGA Observing System as appropriate and to use and expand the prediction results of TOGA. Internationally, the World Climate Research Program is planning the Climate Variability and Predictability (CLIVAR) program whose designated Focus 1 will be on seasonal to interannual global variations and predictability. Nationally, the United States is planning the Global Ocean-Atmosphere-Land System (GOALS) program, a contribution to CLIVAR Focus 1. Efforts are also under way to transfer parts or all of the TOGA Observing System, developed initially as a research observing system, to a permanent observing system in support of the Global Ocean Observing System for use in regular and systematic prediction.
The U.S. component of TOGA is a coordinated effort among NOAA, NASA, the National Science Foundation (NSF), and the Office of Naval Research (ONR). Nationally, the TOGA program was managed by the U.S. TOGA Office which coordinated interagency funding and was advised by the NRC/TOGA Advisory Panel. Internationally, the program was managed by the International TOGA Office, funded by the Intergovernmental TOGA Board, and advised by the TOGA Scientific Steering Group.
Box 2—Major TOGA Accomplishments
The original aims of the TOGA program were to investigate the feasibility of predicting interannual variations in the tropics characteristic of ENSO, to design an observing system to understand the ENSO phenomenon, and to initialize predictions of ENSO. A TOGA Observing System has been established in the tropical Pacific to relay surface and subsurface information to the GTS in real-time. Data collected with the TOGA Observing System has helped develop coupled atmosphere-ocean models for the simulation of ENSO events. Using these models and data collected continuously by the TOGA Observing System, researchers have demonstrated that there is significant skill in predicting some aspects of ENSO a year or so in advance (the prediction is a noticable improvement over a prediction that relies solely on the seasonal cycle). The first real-time ENSO forecast using coupled models was made in early 1986, and this ability has since been demonstrated by a number of coupled prediction systems. Today, experimental ENSO forecasts are published routinely.
As a result of TOGA, scientists are now close to establishing a regular and systematic climate prediction capability, using coupled models and sophisticated data assimilation systems, and an operational observing network to support this capability. Accomplishments in these areas have been substantial (Box 2). Predictions have been used advantageously by numerous countries, including the United States, Peru, Brazil, and Australia, for agricultural and water resources planning. Although few studies of the economic impact of ENSO events have been carried out, it has been estimated that the ability to predict an El Niño event at least 6 months in advance with a 60 percent probability, could save the U.S. agricultural sector alone between $0.5 and 1.1 billion per event—the average annual savings would be $183 million per year over a 12-year period (Workshop on the Economic Impact of ENSO Forecasts on the American, Australian, and Asian Continents, 1993). Assuming that forecasts continue to become more skillful, the ability to anticipate climate and mitigate its effects in the United States and other nations could result in even larger savings in the agricultural, fisheries, and water resources sectors of the economies.
World Ocean Circulation Experiment
Ocean circulation is related to climate on a decades-to-centuries scale, through the transfer of heat, momentum, and greenhouse gases between the atmosphere and the ocean. Thus, in order to understand and predict global climate change, on these time scales improved understanding of ocean circulation is crucial. To that end, the WCRP established the World Ocean Circulation Experiment (WOCE).
WOCE studies surface and subsurface circulation of the global ocean. The field program began in 1990 and extends through 1997; it is anticipated that the synthesis phase will continue until 2005. The primary WOCE goal is to understand ocean circulation well enough to model its present state, to predict its future state under a variety of assumptions, and to predict feedback between climate change and ocean circulation. This goal will be met by describing (1) present ocean circulation and variability, (2) air-sea boundary layer processes, (3) the role of exchange among different ocean basins in global circulation, and (4) the effect of oceanic heat storage and transport on the global heat balance.
The WOCE program consists of several related parts, the largest of which is a global survey called Core Project 1 (Box 3). This cooperative international
project integrates measurements from satellites, voluntary observing ships (VOSs), moorings, subsurface floats, surface drifters, tide gauges, and research vessels. This global hydrographic survey measures (1) water density; (2) various natural tracers, such as salinity, oxygen and nutrients; and (3) man-made tracers of water motions, such as chlorofluorocarbons (CFCs). Subsurface floats and current meter moorings augment the global survey with direct observations of ocean current velocity. Objectives of the survey are to (1) quantify oceanic transport of heat and the pathways of downward water movement by which atmospheric gases are transported into the deep ocean and (2) provide data to model observed circulation patterns. An upper ocean program will focus on the atmosphere-ocean fluxes that drive the ocean, feedback to the atmosphere, and variations in upper ocean temperature and heat storage.
The U.S. contribution to Core Project 1 began in 1991 in the Pacific Ocean and will be completed by mid-1994. Unfortunately, there will likely be a large gap in coverage in the western North Pacific, where commitments of other nations will not be met. Following the Pacific, U.S. attention will turn to the Indian Ocean, where a major international effort is planned to begin in late 1994 and continue into 1996. U.S. Core Project 1 work in the Atlantic, other than expendable bathythermograph deployments that began in 1990, is still undecided but is scheduled to begin in 1996.
Work in the Southern Ocean (Core Project 2) concentrates on the Antarctic Circumpolar Current (ACC), which connects the Atlantic, Pacific, and Indian oceans, and its interaction with the waters to the north and south. This program includes studies of the formation and spread of cold, dense, high-latitude water masses, as well as measurement of surface temperature, pressure, and velocity from surface drifters. Time series and repeat hydrographic measurements in the areas south of America, Africa, and Australia, together with altimetric measurements from satellites, will give insight into the variability of the ACC. Unfortunately, at present there is little chance of long-term absolute measurements of the transports because of the expense associated with setting up large enough mooring arrays.
Core Project 3 focuses on specific processes important to ocean circulation and modeling. The Subduction Experiment (1991–93) examined the process by which surface water is conditioned and mixed downward into the thermocline. The Tracer Release Experiment (1992–93) has provided the first direct open ocean measurements of vertical and lateral diffusivity of a tracer (the inert,
anthropogenic substance, sulfur hexafluoride). The Deep Basin Experiment is examining deep and abyssal flow in the Brazil Basin. These three process studies have been carried out principally by U.S. scientists with assistance from scientists from the United Kingdom, Germany, and France. Enhanced sampling of the North Atlantic Ocean (especially with repeat hydrography, floats, and drifters) is planned through international cooperation and joint work with the Atlantic Climate Change Program (ACCP). However, the full suite of planned Core Project 3 studies is not likely to be implemented because of budgetary constraints.
Progress toward WOCE objectives has resulted in part from a series of technological improvements including: (1) improved meteorological observations from ships and buoys, (2) a new accelerator mass spectrometry facility for measuring radioactive carbon (14C), (3) improved methods for extracting and measuring CFC and helium/tritium, (4) a new type of acoustic Doppler current profiler, (5) autonomous pop-up floats that report their position via Argos satellites at intervals of several weeks for periods up to 5 years, (6) better surface drifters fitted with surface pressure sensors, and (7) an automatic XBT launcher. New procedures for quality control and storage of data have been developed. These will ensure that the WOCE data set remains internally coherent and will be of use for many years in the future.
Despite setbacks, there has been considerable progress toward a better description of general ocean circulation and improvements in modeling ocean circulation. The incorporation of CFC, helium/tritium, and 14C sampling into the hydrographic program is providing a global ocean inventory of these tracers for the first time—an important environmental baseline for the global change research community. Also, the first heat transport analyses addressing the role of the global ocean are being completed currently and will be refined as WOCE proceeds. There has also been steady progress toward improved surface specification of boundary conditions and model-based estimates of surface flux. Major advances have been made in our ability to establish a truly global model of the ocean, with realistic time and space scales. U.S. support for the program comes from NSF, NOAA, ONR, NASA, and the Department of Energy (DOE).
Box 3—Major WOCE Accomplishments
The WOCE program's primary purpose is to model long-term climate change. Decade-long variations in ocean climatology that affect economic activities such as fisheries and agriculture are known, but the causes of these changes are not understood. The first goal of WOCE is to develop models to predict climate change on decadal scales and to collect the data necessary to test them. WOCE is already making significant strides in this area (Box 3). However, field programs to date have concentrated primarily on the Pacific and South Atlantic oceans. U.S. work in the Indian Ocean is scheduled to begin only in late 1994. A major initiative for the North Atlantic is proposed to begin in 1996, and studies of variability elsewhere will continue for some time. WOCE's second goal is to determine whether specific WOCE data sets are representative of the long-term behavior of the ocean and to find methods for quantifying decadal changes in ocean circulation. This goal will be fulfilled only if appropriate resources are supplied to long-term programs such as climate variability and predictability and global ocean observing system. The research conducted under WOCE is providing indications of what should be measured and where such measurements should be taken to monitor ocean circulation. Process studies are providing new views on small-scale oceanographic processes
Box 4—Future Plans for WOCE
such as vertical diffusivity and subduction, and processes within deep-ocean basins. Additionally, WOCE research is leading to continued improvements in global ocean modeling as scientists begin to use the largest computers at fine model scales. While providing new insights into ocean circulation, these data and models will also form the large-scale physical framework for studies of chemistry and biology being carried out through programs such as Joint Global Ocean Flux Study (JGOFS) and Global Ocean Ecosystem Dynamics (GLOBEC). Following the WOCE field program, a synthesis phase is being planned to provide improved operational models of the global ocean and atmosphere as well as a new understanding of how the ocean works in terms of large-scale circulation. Specific products will include: (1) an ocean climatology for the
WOCE period; (2) estimates of ocean variability such as Ekman transport, meridional heat, mass and property transports, interbasin transport, and ocean surface fluxes and fields; and (3) a mid-depth ocean reference level with horizontal velocity estimates.
Joint Global Ocean Flux Study
Observations demonstrating a continuing increase in the concentration of atmospheric CO2, linked with numerous model-based forecasts, have led the nations of the world to consider controlling of CO2 emissions. Since the Industrial Revolution, humankind has been altering the partitioning of carbon in the Earth system and hence altering environmental biogeochemical cycles. Unfortunately, scientists cannot accurately assess the relative roles of the land and ocean system in taking up atmospheric CO2. Neither do scientists understand the ocean's role in moderating atmospheric carbon dioxide and other radiatively active gases well enough to quantify its impact and to predict future atmospheric concentrations.
The need to understand biological utilization, regeneration, transport, and sediment burial of bio-active elements such as carbon, nitrogen, and phosphorus in the ocean has led to a number of studies and advances in measurement capability in the 1970s and 1980s. The capability for global satellite measurement of ocean color, which is related to the abundance of phytoplankton in surface waters, has provided new impetus to these studies. In situ techniques have also been developed for direct measurements of the amount of sinking organic debris in the water column, as well as high-precision measurements of chemicals present in minute concentrations. The new understanding of ocean biology and chemistry, and the capabilities provided by new techniques, led to the development of the international Joint Global Ocean Flux Study (JGOFS).
The U.S. JGOFS program was initiated in 1984 and the international JGOFS was established by the Scientific Committee on Oceanic Research (SCOR) in 1987. JGOFS provided the first coordinated planning for studies of biogeochemical cycles in the ocean. A major goal of JGOFS is to gain a better understanding of how carbon dioxide is exchanged between the atmosphere and the surface ocean and of how calcium carbonate and organic debris are transferred to the deep-sea. In the deep-sea, carbon—originally derived from carbon dioxide in the atmosphere—is removed from the short-term carbon cycle.
Objectives of the JGOFS program are to (1) understand the global scale processes that control carbon, nitrogen, oxygen, phosphorus, and sulfur exchanges in the ocean over time; (2) understand how, and at what rates, gases, salts, and water are transferred within the ocean and across the boundaries between the ocean and the atmosphere, seafloor sediments, and the continents; (3) determine how well productivity can be measured remotely by satellite-or aircraft-borne sensors; (4) determine the dependence of particle production and sinking on physical, chemical, and biological processes; and (5) develop mathematical simulations that predict chemical transfers within the ocean and across ocean boundaries and the effects of these transfers on global environmental changes. The program is using several approaches for data collection, including research vessels, satellites, aircraft, and deep-ocean moorings.
The first JGOFS process study, of the spring phytoplankton bloom in the North Atlantic, was conducted by a group of nations in the spring and summer of 1989 (Box 5). The second process study was carried out in the equatorial Pacific Ocean in 1991 and 1992. Process studies are scheduled for the Arabian Sea (1994–95) and the Southern Ocean (1994–96). In addition to process studies, U.S. JGOFS maintains two long time-series stations located near Hawaii and Bermuda (Box 5). Data collected at these sites on regular ship visits and permanent moorings will allow JGOFS scientists to assess the variability of the ocean environment on a range of time scales. U.S. JGOFS has a global survey component that presently has two major components: (1) a large-scale survey of oceanic CO2 parameters measured in collaboration with the WOCE Hydrographic Program series of cruises and (2) a large-scale survey of surface ocean chlorophyll/productivity by observations of ocean color from the new Sea-Viewing, Wide Field Sensor (SeaWiFS) due to be launched in 1994.
U.S. federal agencies have coordinated their involvement in U.S. JGOFS experiments as part of the biogeochemical dynamics section of the U.S. Global Change Research Program. NSF, NOAA, NASA, ONR, and DOE are all involved with U.S. JGOFS. JGOFS also has a liaison with WOCE. JGOFS is now a fully international effort and has been designated as a core project of the IGBP with WOCE and GLOBEC.
Box 5—Major JGOFS Accomplishments
The JGOFS program seeks to quantify the oceanic fluxes of bio-active elements in particular carbon. An increases understanding of carbon, including exchanges with the atmosphere, will reduce the uncertainties associated with the ocean's role in the global carbon cycle and will provide improvements in coupled models which permit prediction of the carbon system in the future. It is important to understand how the ocean carbon cycle responds to perturbations of global temperature. This knowledge will be of immense value to policymakers trying to craft economic and environmental policies based on the best scientific knowledge available.
A list of JGOFS accomplishments (Box 5) reveals progress toward reaching these goals. The time-series studies at Bermuda and Hawaii provide a sense of the range of seasonal and interannual variability in carbon cycle processes characteristic of the cast oligotrophic areas of the world oceans. The various process studies have provided and will continue to reveal details of key carbon cycle controls in globally significant ocean areas. The large-scale surveys of ocean color and carbon dioxide system parameters will reduce our uncertainty about the global atmosphere-ocean fluxes of carbon and their temporal variability.
Global Ocean Ecosystem Dynamics
The goal of the Global Ocean Ecosystem Dynamics (GLOBEC) program is to predict the effects of changes in the global environment on the abundance, variation in abundance, and production of marine animals. The program aims to understand the fundamental physical and biological mechanisms that determine how marine animal populations vary over time and space, with an emphasis on discovering how changing climate alters the physical environment of the ocean and how this in turn affects marine animals, especially zooplankton and fish. The GLOBEC approach is to determine which fundamental physical and biological oceanographic processes control populations, how the controls operate, and how variations in the abundance of organisms can be attributed to natural or anthropogenic causes. Finally, once the linkages among atmospheric forcing and physical and biological processes are elucidated, this understanding can be translated into assessments and predictions of the impact of climate change on marine ecosystems. These goals will be accomplished through an inter-disciplinary effort involving physical and biological oceanographers and
fisheries biologists, who will conduct modeling studies, field investigations, retrospective data analysis and long-term observations.
The abundance of marine organisms is related in part to factors other than man's influence. For example, sardine and anchovy abundances, estimated from the abundance of scales in layered sedimentary records, have varied by factors of 3 to 10 over the past 1,700 years—long before intense exploitation by man. Phytoplankton and zooplankton also display substantial year-to-year and longer-term variability, suggesting that the physical environment controls populations to some extent. For example, northerly winds in the North Atlantic intensified from the 1950s to the 1970s and were correlated with a decrease in the biomass of phytoplankton and zooplankton. The decline in phytoplankton might have been due to dilution in their concentration that resulted from deeper wind-driven mixing in the euphotic zone. In turn, this may have resulted in poorer feeding conditions for zooplankton and higher trophic level organisms. Thus, relatively small changes in the physical environment can cascade throughout marine food webs.
The early phases of U.S. GLOBEC concentrated on (1) the development of coupled physical and biological models, (2) the development and application of improved sampling and measurement systems, and (3) the planning of sitespecific process studies. Toward that end, several modeling investigations and projects to develop molecular techniques were funded, and a process study on the Georges Bank ecosystem in the northwest Atlantic Ocean was planned (Box 6). U.S. GLOBEC is funding physical and biological research (including modeling) retrospective data analysis and process research in the Georges Bank ecosystem. Key processes that will be investigated include: stratification (water column stabilization) and its relation to feeding success, to growth, and to survival of zooplankton and fish larvae; episodic exchanges of water and organisms with the coast due to storms and interactions with warm core rings; and cross-frontal exchanges of plankton and nutrients. The goal is to obtain an understanding of how physical processes control vital rates (e.g., birth, growth, and survival) of key zooplankton and fish species in the Georges Bank ecosystem particularly and in retentive gyre banks generally. In this way, predictions can be made of the biological and ecological impact of likely climate change scenarios.
U.S. GLOBEC is continuing to develop plans for a study of ocean physics and biology off the West Coast of the United States. Planning activities for investigations in the California Current system have identified four components of study. First, a large-scale component to include satellite studies, nested
regional numerical modeling, and comparative studies from Baja California to Washington. Second, mesoscale studies that investigate biophysical interactions at the larval stages, with emphasis on processes involving transport, retention, aggregation, and vital rates as functions of location within mesoscale features. Third, retrospective studies that quantify the natural modes of variability in the marine ecosystem, with a specific focus on the linkages between climate, ocean, ecosystem, and population variability. And fourth, modeling activities, including models with various spatial and temporal resolution, data assimilative models, ecosystem structure models, and nested regional and basin-scale models.
U.S. GLOBEC is a component of the U.S. Global Change Research Program and receives funding from NSF and NOAA. In cooperation with GLOBEC-International, U.S. GLOBEC is proceeding with planning for a study of ocean physics, sea ice dynamics, and marine animal population dynamics in the Southern Ocean.
GLOBEC-International focuses on fundamental scientific issues associated with zooplankton population dynamics and their variability. The stated goal of GLOBEC-International is ''to understand the effects of physical processes on predator-prey interactions and population dynamics of zooplankton, and their relation to ocean ecosystems in the context of the global climate system and anthropogenic change.'' GLOBEC is endorsed by Scientific Committee on Oceanic Research, Intergovernmental Oceanographic Commission, International Council for the Exploration of the Sea (ICES), and Pacific ICES (PICES).
GLOBEC-International has established a research strategy articulated in the GLOBEC Core Program (GCP). The GCP strategy provides a framework by which international and regional programs can join together toward a common goal of understanding zooplankton dynamics in a physical and ecosystem setting. The GCP is evolving into separate but coordinated activities, with working groups meeting throughout the past year to articulate different aspects of the GCP and to prepare for the full implementation of GLOBEC-International. To date, six scientific planning meetings have been completed.
The GCP is being developed in two complementary directions. The general scientific approach is being generated by four working groups: Population Dynamics and Physical Variability, Numerical Modeling, Sampling and Observation System, and GLOBEC Prudence, which will be reviewing historical data to determine its applicability to GLOBEC problems. The results will be applied to specific ecosystems, the other line of GLOBEC investigation.
The development of the scientific approach so far indicates that the GLOBEC-International mission will involve two components. The first involves the population dynamics of zooplankton and is fairly straightforward. The second involves the development of coupled numerical, physical-biological models and observational systems that will involve a significant planning effort and international cooperation. Coupled models and observations are central to determining present oceanic conditions and predicting future conditions. Both have important applications in global-change and fisheries management issues. The modeling-observation systems would attempt to estimate realistic physical and biological fields with mesoscale resolution since these are thought to be the most energetic (and hence, physically variable) and the most biologically demanding.
Box 6—Major GLOBEC Accomplishments
The goal of the U.S. GLOBEC program is to conduct scientific investigation into the linkages among climate, ocean physics, and marine animal populations. If these linkages are understood, then the responses of marine ecosystems to potential future climate changes, whether anthropologically induced or natural, can be predicted, assessed, and better managed. In addition, GLOBEC supports the development of new technologies (i.e., acoustic, optic, and molecular) that promise higher resolution or more cost effective ways to measure the structure and condition of ocean ecosystems and the status of living marine resources.
The first GLOBEC field programs have just begun and accomplishments to date are preliminary (Box 6). A pilot study of the role of water column stratification on the feeding and behavior of larval cod and haddock on Georges Bank suggests that vertical migratory behavior plays an important role in retaining the larval stages of these commercially important species in favorable environments for growth, survival, and recruitment. Eventually, U.S. GLOBEC research on groundfish species (cod, haddock) on Georges Bank may provide the scientific underpinnings for a rational rebuilding of these historically important commercial stocks and of the fishing industry that is dependent upon them.
Finally, U.S. GLOBEC emphasizes the development of coupled physical and biological diagnostic models to understand existing conditions, with the goal of then using them as prognostic tools to assess potential conditions and responses in the future. These prognostic tools will permit better management of marine ecosystems providing stability, profit, and sustainability.
Atlantic Climate Change Program
The Atlantic Climate Change Program (ACCP) is aimed at understanding large-scale air-sea interaction between the Atlantic Ocean and the global atmosphere. Much of the early emphasis of ACCP is directed at middle and high latitudes of the North Atlantic for several reasons. First, the subarctic North Atlantic is the only site in the northern hemisphere where convection in the ocean extends from the surface to deeper levels, providing a mechanism for creating persistent sea-surface temperature anomalies one decade to century time scales. Second, there is a good correlation between sea-surface temperature in
the northwestern Atlantic and atmospheric surface temperatures averaged over the entire northern hemisphere. For example, the "dust bowl" in the western United States in the 1930s was accompanied by pronounced warmth over the northern North Atlantic. Similarly, the relatively cool climate of the late 1960s and early 1970s was associated with very low sea-surface temperature in the western Subarctic North Atlantic. Finally, in the context of assessing global climate change due to anthropogenic causes, understanding the very low frequency, apparently natural variability 'of climate will help answer the question: Can we discriminate natural climate variability of very long time scale from the possible effects of human-induced greenhouse warming?
To study these phenomena, ACCP has adopted a three-pronged approach—analysis of historical data, modeling, and direct observation and monitoring of the ocean. The first step in ACCP has been to assemble and examine Atlantic Ocean data collected in the past. The second element of the program is an attempt to validate a whole hierarchy of atmospheric and ocean models using these data. The model hierarchy is intended to range from simple conceptual models to numerical models that link the global ocean and atmosphere. These models are aimed to better understand high-latitude air-sea interactions and to help design an effective system for monitoring low-frequency changes in water mass properties and in the heat balance, which may be linked to persistent sea-surface temperature anomalies. The final element of the program will be to test and deploy instruments for monitoring winds, seasurface temperature, sea ice, and water mass properties and to combine that information with other measurements from satellites, drifting instruments, and ships of opportunity. ACCP will coordinate closely with WOCE in North Atlantic studies.
ACCP analysis of historical data has indicated two types of low-frequency climate variability over the North Atlantic. One type has a period of about a decade with marked observational signatures in surface winds, sea-ice coverage, and sea-surface temperature. A second type has a period of four to six decades and appears to be associated with polar-amplified climate variations affecting the entire northern hemisphere. Its observational signature is in the ocean temperature and salinity fields, both at the surface and at depth. The accompanying atmospheric anomalies are weaker than those of the decadal mode and show a markedly different structure. Why this difference should exist between the decadal and the multidecadal time-scale climate fluctuations is an open question being investigated by ACCP modelers.
An abrupt change in the climate regime of the Atlantic Ocean occurred in the late 1960s and early 1970s. This was associated with the formation of a very large patch of low salinity water in the northwest Atlantic, which has been dubbed "The Great Salinity Anomaly." This anomaly drifted off to the east after a few years, but while it was in the Labrador Sea it apparently caused a major disruption of normal wintertime convection in the ocean, leaving a clear signal in surface, as well as deepwater mass properties. Though historical record is incomplete, there is evidence to indicate that a similar event may have taken place around 1910 in the Labrador Sea. It is not clear whether these extreme surface salinity events are associated with the decadal or multidecadal climate variations.
Some of the most important accomplishments of the ACCP have been in the area of modeling. Atmospheric models have shown that the response to high-latitude sea-surface temperature anomalies is much more complicated than, and fundamentally different from, the response to tropical sea-surface anomalies. The chaotic nature of middle and high latitude flows prevent any simple, linear response patterns from emerging, in which cause and effect could easily be identified. This insight explains the confusing results obtained in previous studies of atmospheric response to high-latitude sea-surface temperature patterns.
Ocean models with boundary conditions which mimic the effects of air-sea interaction provide the simplest illustration of how changes in the ocean's thermohaline circulation and in high-latitude ocean convection provide an explanation for low-frequency climate variability in the North Atlantic. Rapid progress has been made in clarifying the early results obtained with these models, which showed that two very different solutions could exist for the same boundary conditions. These results show how the different salinity patterns that may have existed during the last Ice Age could lead to a very different, and greatly amplified, type of climate variability than has existed over the past few thousand years.
Perhaps the single most important accomplishment in modeling has been the simulation of multidecadal Atlantic climate variability by the Geophysical Fluid Dynamics Laboratory (GFDL) global coupled ocean-atmosphere model (Box 7). In 1,000-year-long integration, multidecadal variability associated with changes in strength of the thermohaline circulation comes out clearly. The sea-surface temperature anomalies produced by the model also match the decadal time-scale anomalies observed in the North Atlantic. This successful simulation provides
an important building block for future ACCP modeling studies and for the design of practical monitoring systems in the Atlantic.
In planning ACCP, it was recognized that the instrumental record is too short to adequately sample decade-to-century time scales. For this reason the program contains an effort to analyze proxy data for the ocean—ice caps on land. These data can be used to constrain the models and to provide a perspective on the limited climate data available in the instrument record, which may already be contaminated by anthropogenic effects. The records from the Greenland ice cap appear to have enormous potential for the study of North Atlantic climate variability.
Plans for field activities in ACCP are guided by the results of the data analysis and modeling elements of the program. Thus, an original strategy of ACCP was to concentrate attention on the poleward transport of heat by the ocean circulation into the northern North Atlantic. In its early stages the field component of the program focused on continuation of long-term monitoring at 24°N in the Atlantic. In coordination with WOCE, a repeat section was made at 24°N in 1992 along with two shorter parallel sections in the vicinity of the western boundary. Measurements extending over nearly a decade are gradually providing details of the boundary flows near the Bahamas and in the Florida Straits. ACCP will coordinate with WOCE to continue monitoring heat transport at 24°N and to extend monitoring to higher latitudes. One of the most valuable data sources for ACCP has been the time series of hydrographic measurements taken at Bermuda and from the weather ships. While the Bermuda time series is being maintained, the weather ships no longer exist. One of the long-term goals of ACCP is to develop the instrumentation to reinstate the time series of temperature and salinity at weather ship sites in the northwestern Atlantic relying on measurements made by WOCE and other programs for the interior of the ocean.
ACCP has achieved a close working relationship with Canadian oceanographers also studying the decade-to-century climate variability in the Atlantic. Phase II of Climate Variability and Predictability, the new program of the WCRP, is focused on decade-to-century climate variability, and many of the early research accomplishments of ACCP have been incorporated in the early planning of CLIVAR. In the future CLIVAR is expected to play a major
role in coordinating ACCP efforts with that of a larger international community interested in the role of the Atlantic in climate variability and climate change.
Box 7—Major ACCP Accomplishments
Arctic Systems Science
The Arctic region has gained a prominent role in the current debate regarding global change. The Arctic comprises a mosaic of precariously balanced ecosystems that interact intimately with climate. Global climate models have shown that the largest temperature changes may occur in the Arctic. In addition the Arctic has been identified as a potentially key source of global greenhouse gases, especially methane. The recognition of the importance and sensibility of the polar regions in a changing global environment led to the creation of a new program called Arctic Systems Science (ARCSS).
The ARCSS program has two goals: (1) to understand the physical, chemical, biological, and social processes of the Arctic system that interact with the total Earth system and thus contribute to or are influenced by global change
and (2) to improve the scientific basis for predicting environmental change on a decade-to-centuries time scale and for formulating corresponding policy options in response to the anticipated impacts of this change on humans and social systems.
Oceanographic research is a crucial component of ARCSS, although the initiative spans terrestrial, marine, and atmospheric research. The marine environment of the Arctic is an interactive system, comprising the water, ice, biota, dissolved chemicals, and sediments. Several key research areas have been identified, including the effects of energy exchange (for example, from wind or the sun) on temperature, salinity, and density distributions in the water column and carbon removal from the atmosphere and surface waters to the deep ocean and sediments via plant material. These goals are shared with WOCE and JGOFS, and in order for them to give a complete global assessment of ocean processes interrelated with climate, WOCE and JGOFS must have the knowledge of high latitudes that can be supplied through the ARCSS initiative. Because of the remoteness and inaccessibility of much of the Arctic Ocean, satellite sensors play a key role in data gathering.
ARCSS has included three components: (1) Paleoenvironmental Studies, (2) Ocean-Atmosphere-Ice Interactions (OAII), and (3) Land-Atmosphere-Ice Interactions (LAII) (Box 8). The Paleoenvironmental Studies component is, in turn, made up of two activities, the Greenland Ice Sheet Project Two (GISP2) and the Paleoclimates of Arctic Lakes and Estuaries (PALE) project.
The ARCSS Executive Committee has also identified research priorities for the future. The current categories of paleoenvironmental studies (GISP2, PALE) and studies of the contemporary environment (OAII, LAII) are expanded to include archaeology and human-environment interactions, respectively. ARCSS is funded by NSF as part of their contribution to the U.S. Global Change Research Program.
Box 8—Major ARCSS Accomplishments
Acoustic Thermometry of Ocean Climate Project
The Acoustic Thermometry of Ocean Climate (ATOC) project is designed to characterize global climatic trends in the ocean by measuring the changes in the speed of sound along long-distance undersea paths. It rests on two principles: (i) sound speed increases with temperature, and (ii) acoustic transmissions can be monitored over gyre and basin scale ranges. This makes it possible to form synoptic horizontal temperature averages that are well suited for measuring climate change. Following a successful 1991 demonstration of the viability of acoustic travel time measurements over trans-oceanic paths (the Heard Island Experiment), ATOC was funded in early 1993 to establish a Pacific Ocean network of sound path measurements to test the feasibility of a future global network for monitoring ocean climate trends.
The advantage of using acoustical measurements is one of scale. Timing sound travel across ocean basins removes small-scale (mesoscale) variability in local temperature to reveal large spatial and temporal scale changes. ATOC has developed a plan to install mid-and eastern Pacific sound sources in the deep-ocean sound channel to establish pathways from California to New Zealand. These sources will transmit low-frequency signals to generate precise timing for sound traveling to Navy and ATOC receivers.
In the first 6 months of project activity, ATOC has established a configuration for the planned network, started construction of the sources and receivers, and developed detailed plans for their installation and operation (Box 9). The initial network will begin operational activities in early 1994 to connect North Pacific paths. Trans-equatorial paths will be established by late spring, and the network will become fully operational by late summer. To date, ATOC has met all of its planned engineering milestones and has developed contingency plans in case of changing circumstances.
Acoustic propogation studies have developed new insights into "ocean weather" effects on acoustic travel time, which will be important to the processing of ATOC data for climate trend direction. Coupled ocean climate models from the Princeton, Hamburg, and Massachusetts Institute of Technology research groups are being integrated with ATOC to provide better insights into the expected scales and distribution of global ocean change. ATOC is being funded by the Advanced Research Projects Agency (ARPA) from the Strategic
Environmental Research and Development Projects (SERDP) through a grant to Scripps Institution of Oceanography.
Box 9—Major ATOC Accomplishments
A Global Ocean-Atmosphere-Land System for Seasonal-to-Interannual Climate Prediction Program
A Global Ocean-Atmosphere-Land System (GOALS) for Seasonal-to-Interannual Climate Prediction Program was conceived as the U.S. contribution to the Climate Variability and Predictability (CLIVAR). CLIVAR is the WCRP's major new seasonal-to-interannual focused initiative. Planning for GOALS is being overseen by the National Research Council Climate Research Committee (CRC). The CRC has already completed a number of important steps, including producing a scientific background document and holding a major national scientific meeting with international representation. The CRC intends to establish a GOALS advisory panel in 1994, and GOALS will proceed with implementation plans during that year.
The ultimate scientific objectives of the GOALS program are to (1) understand global climate change variability on seasonal-to-interannual time scales; (2) to determine the extent to which this variability is predictable over time and space; and (3) to develop the observational, theoretical, and computational means to predict this variability, if feasible. A skillful forecast of average temperature and precipitation, a season to a year in advance, has
already proven valuable in the countries in and around the tropical Pacific; an extension of predictions to the industrialized countries at higher latitudes would be of enormous economic benefit for agricultural planning, resource allocation, price support policies, and flood and drought mitigation.
The central hypothesis of GOALS is that variations in the forcing characteristics of sea-surface temperature, soil moisture, sea ice, and snow at the global boundary exert a significant influence on the seasonal-to-interannual variability of atmospheric circulation. Therefore, understanding variability and predicting climate at seasonal-to-interannual time scales requires understanding the processes that control these boundary conditions. Predicting the evolution of these boundary conditions will undoubtedly require improved models and observations.
The first phase of GOALS will augment the original prediction goals of TOGA by improving coupled models and by incorporating the data produced by the TOGA Observing System, especially the TAO Array, into predictions. Expansion into the global tropics will be based on the hypothesis that seasonal-to-interannual variability is related to variations in the locations, interactions, and effects of the major thermal sources and sinks. Expansion to higher latitudes will be guided by insights gained in studies of seasonal-to-interannual variability in the extratropical atmosphere, upper ocean, and land surfaces.
Following the successful example of the TOGA program, GOALS will be composed of four major program elements: modeling, observations, empirical studies, and process studies. The process studies will concentrate on the monsoonal forcing of the atmosphere in the eastern Pacific and Indian oceans and the transmission of these signals to higher latitudes. It is anticipated that two major ongoing TOGA activities, the TOGA Observing System and the TOGA Program on Seasonal to Interannual Prediction (T-POP) will be maintained during transition to the GOALS program. As GOALS matures, its programs can be expected to evolve and expand.
The success of GOALS will be measured in several ways: by the enhanced understanding of global climate variability and predictability on seasonal-to-interannual time scales, by the effectiveness of the observing system developed for describing and predicting the climate system, by the increased ability to model the processes involved in seasonal-to-interannual variations, and by the skill developed in predicting these variations.
Land-Ocean Interactions in the Coastal Zone
Coastal areas of the world are zones of increasing competition between the needs of human populations and the limited resilience of natural ecosystems. Human activities exert a tremendous burden on the coastal zone on both a global scale (e.g., sea-level rise and climate change) and a local scale (e.g., land use practices and overfishing). Because existing global change research lacks strong components focused specifically on the coastal zone, the International Geosphere-Biosphere Program developed the Land-Ocean Interactions in the Coastal Zone (LOICZ) program. LOICZ defines the coastal zone as extending from the coastal plains to the edge of the continental shelf. LOICZ is based on the premise that the current use of the coastal zone will inevitably affect its use by future generations. The creation of long-term, sustainable policies for coastal management will require an understanding of the many impacts derived from changes in climate, sea-level, and land use and in the functioning of the ecosystems themselves. A LOICZ science plan has been published, and the implementation plan is scheduled for publication in late 1994.
The goals of LOICZ are: (1) to determine the fluxes of materials between land, sea, and atmosphere in the coastal zone, the capacity of coastal systems to transform and store particulate and dissolved matter, and the effects of changes in external forcing conditions on the structure and functioning of coastal ecosystems on global and regional scales; (2) to determine how changes in land use, climate, sea-level, and human activities alter the fluxes and retention of particulate matter in the coastal zone and affect coastal morphodynamics; (3) to determine how changes in coastal systems, including responses to varying terrestrial and oceanic inputs of organic matter and nutrients, will affect the global carbon cycle and the trace gas composition of the atmosphere; and (4) to assess how the responses of coastal systems to global change will affect human use and habitation of coastal areas and to develop further the scientific and socioeconomic bases for the integrated management of the coastal environment.
U.S. involvement in the LOICZ program to date has been informal. Three U.S. scientists are members of the Scientific Steering Committee, but there is no official federal agency representation or program office in the United States. Efforts continue to determine appropriate U.S. participation.