The banks of the Northwest Atlantic such as the Grand Banks and Georges Bank have been exploited for fisheries resources since at least the 1500's. This trend has continued to the present, with 1988 New England landings of cod, scallops, and pollock amounting to $133.4 million dollars. Combined, this is approximately equal to the value of the lobster harvest for that period. Of the three species, the groundfish are at their lowest stock size on Georges Bank since estimates were begun. A rise in populations of elasmobranch species such as dogfish and skates suggests the possibility of a major shift in ecosystem structure. In a similar vein the most recent National Marine Fisheries Service report on the status of fishery resources off the northeastern United States concludes in the case of scallops the "current fishing effort is far beyond what the resource can sustain". Much of the stock decline is due to the effects of overexploitation. The effects of fishing on stocks are, however, strongly influenced by variations in the physical and biological environment within which the fishery exists.
Climatic effects on fisheries have been reasonably well established in a number of regions, although the exact processes by which these effects take place are not well understood in any situation. It is also well established that climate variations can substantially modulate the influence of exploitation and, within the extremes suggested in the recent climate record, can completely eliminate regional fisheries. These climatic variations range from the effects of the last ice age, which probably reduced the viable habitat for the species mentioned above by up to 90% through a combination of lowering temperature, salinity, and sea level, and increases in sea ice cover; to historically documented decadal time scale fluctuations in winds, sea temperature, and salinity that have a marked correlation with cod stock declines in recent decades. There is ample evidence for a broad range of climatic fluctuations in the past and some grave concerns about future variations tied to natural cycles, the effects of man through greenhouse warming, and modification to the marine environment tied to pollution. The GLOBEC steering committee suggests the following components of the U.S. portion of the Northwest Atlantic Study as a product of the Halifax workshop.
Target zooplankton species should emphasize Calanus finmarchicus and include Pseudocalanus spp. and Centropages spp. Local populations of Calanus are thought to overwinter in the nearby Gulf of Maine; the dynamics of their springtime advection onto Georges Bank should be studied in detail. Population dynamics studies should focus on understanding reproduction, growth, and mortality in relation to physical transport processes. Process studies should be aimed at understanding how local physics controls the distribution of zooplankton, and what processes control overwintering. Historical data are not as abundant as for fish, but are sufficient to determine the magnitude of signal required to detect effects of climate change. Modeling studies could make new sampling technology (e.g., acoustics and optics) more effective by helping to understand the relation between animal size and physiology; population dynamics could be better understood through coupled biological/physical numerical modeling. New technology is needed to rapidly assess physiological state, and to rapidly sample distributions of zooplankton from both moored and mobile platforms.
Target benthic species should include sea scallops (Placopecten magellanicus), but the focus might best be on contrasting different types of meroplanktonic larvae and evaluating the relationships between cod feeding success and benthic habitat character. Local populations could be studied by comparing how a variety of larval types (e.g., feeding vs. non-feeding larvae, spring vs. fall spawners) respond differently to physical processes. Population dynamics studies should focus on larval dynamics of any species which might produce distinguishable cohorts of easily identifiable larvae from a well defined adult population, and should not necessarily be restricted to scallops. Process studies should focus on understanding the relation between fundamental population dynamics parameters (e.g., growth, reproduction) and physical and biological forcing such as tides, storms, food availability, and temperature change. Historical data are less abundant than for other groups, but efforts should be undertaken to use what data do exist. Modeling studies could help to understand how local physical processes favor different reproductive strategies, what causes interannual variation in scallop recruitment, and how changing physical and biological factors affect larval life histories. New technology is acutely needed to rapidly sample and identify larvae of different species.
These sites each individually satisfy many or all of the selection criteria established previously. Each would also strongly complement the planned North Atlantic program by emphasizing a distinct but broadly relevant subset of physical/biological linkages, forcing time scales, and dominant life history pattems. The following paragraphs outline the planning status and some of the major opportunities (and disadvantages) we have identified for each of these regions.
Several features of eastern boundary current ecosystems make them attractive as GLOBEC study sites. First, they are quantitatively significant both to human populations and in the global biogeochemical balance. Many of the world's most productive fisheries are found in and near coastal upwelling regions. Particularly for adjoining developing nations, these ecosystems have great economic and sociologic importance and their demonstrated and potential biotic variability is a major concern. In the United States, the California Current is also the "backyard ocean" for a concentrated, affluent, and environmentally-conscious human population. This group places considerable aesthetic and moral value on understanding and preserving the health of the local marine environment.
Second, eastern boundary currents are oceanographically and ecologically distinctive. The dominant life history and energy transfer pattems contrast with those in higher latitude continental shelf ecosystems: most species are holoplanktonic/pelagic rather than meroplanktonic/demersal and often have relatively short life spans (e.g., anchovies, sardines, and scombrids vs. gadids, herring, and flatfish). Flow fields and their effects on organisms are also distinctive. Mean wind stress is typically alongshore with large temporal variability. Surface-layer flow is on average divergent from the coast. This divergence is often particularly intense in the vicinity of major headlands. Continental shelves are usually narrow and large offshore bathymetric features are rare. The resulting current pattems provide strong temporal and spatial patchiness but few geographically fixed and predictable opportunities for horizontal recirculation and retention. Perhaps in consequence, higher trophic levels are often strongly migratory. For planktonic and larval organisms, advective input and loss rates are large. Behavioral orientation to, and utilization of, small-scale shears and convergences appears to play an extremely important role in reseeding and population persistence.
Third, eastern boundary current systems are particularly appropriate for examining the higher frequency components of global climate variability. Biological and physical response to forcing at interannual to decadal time scales (e.g., ENSO events) is known to be very strong (Chelton et al., 1982). The local response almost certainly involves a variety of proximate physical coupling mechanisms (e.g., altered wind speed and direction, pycnocline depth, alongshore and cross-shore advection, buoyancy inputs). Important lower frequency components of biological variability (decades to centuries) are also clearly evident in reconstructions from historical and sedimentary data.
Fourth, many of the dominant species extend over a broad latitudinal range and are exposed to large differences in the intensity and timing of seasonal circulation patterns. Particularly for the nearshore benthic community, strong spatial gradients in probability of successful recruitment appear to be linked to differences in upwelling intensity (Ebert and Russell, 1988; Roughgarden et al., 1988). There is clear potential for within-region comparative studies of the controlling mechanisms.
The historical knowledge base for the California Current is excellent. This is one of the few oceanographic regions for which there is a long time series of archived plankton and larval fish samples (the CalCOFI program, 1949-date). Commercial catch statistics are available from the early part of this century. Sediments from anoxic basins (e.g., Soutar and Isaacs, 1974) provide a longer record of changes in relative abundance for major fish species. There have also been a number of major shorter term studies of the physical and biological oceanography of this region. Recent examples include the CODE, OPTOMA, NCCCS, FRONTS, and CTZ programs.
Subarctic, Transition Zone, and Subtropical faunal groups are all represented within the California Current system; field and modeling studies will probably have to examine a relatively large number of species and trophic linkages. Some candidates include:
Potential for international and interagency collaboration is good. Canada and Mexico adjoin the region and share some of the migratory stocks. Other Latin American countries (especially Peru and Chile) have an interest in Pacific coastal upwelling ecosystems and especially in the effects of ENSO events. The Soviet Union and Poland have major joint-venture hake fisheries in U.S and Canadian waters. The same or similar species are present in northern Japanese waters. Within the U.S., ONR, MMS, NOAA, DOE, Cal. Fish and Game, and other NSF programs (e.g., COOP and JGOFS) have overlapping interests.
Probably the major weakness of a California Current study site is the practical difficulty of tracking populations in such an advective system. Ship time and technology commitments (especially acoustics and genetics) will have to be substantial to do a good job.
We know that large coastal inputs of fresh water have strong effects on both the alongshore and cross-shore circulation of major estuaries and the adjoining continental shelf. One common and important situation is the interaction with Coriolis force to produce an intense baroclinic current that hugs the coastline and is maintained or intensified by additional downstream freshwater inputs (Royer, 1981 a,b). These buoyancy-driven coastal currents are relatively narrow, fast, often seasonal (depending on the timing of precipitation and snowmelt) and typically have a sharp front along their seaward margin. In addition to the expected salinity and temperature gradients across this front, there is often a strong contrast in nutrient content, water color, and plankton biomass and species composition. Nursery areas and migration routes of both juvenile and adult fish parallel the frontal boundary; the coastal current may be both a "conduit" for alongshore transport and migration and a "barrier" to cross-shore motion (Thomson et al., 1988).
Freshwater input to the coastal ocean reflects the balance between precipitation, storage, and evapo-transpiration on the continental shelf and from the adjoining drainage basins. Climate models and empirical analyses suggest that all of these processes will be sensitive to generalized global climate change (e.g., Bolin et al., 1986). Seasonality of both weather and biology is strong at high latitudes. If key life cycle events are "tuned" to the past average seasonality of the physical environment, the phasing as well as the amplitude of runoff and resulting coastal circulation may be critical. Seasonal ice cover is an important variable north of the Alaska Peninsula and in many inlets along the Gulf of Alaska.
A large fraction of the Pacific coast is strongly influenced by coastal freshwater input, roughly from the Columbia River north to the Bering Strait. The southern end of this range overlaps at least seasonally with the California Current upwelling system. Dominant species are mostly from the Subarctic faunal group. Although there are important homologies with the North Atlantic study area (herring, cod, euphausiids, and large and small calanoid copepods), there are also important and interesting additions (all of the Pacific salmon, halibut, walleye, pollock, pandalid shrimps, several crab species, large "zonal migrating" copepods).
The historical knowledge base is good for commercially harvested species. Other taxa have been studied intensively but intermittently. Most major studies (with the exception of the DOE Columbia River program off Washington and Oregon) have less than a 10 year time base. Examples include ISHTAR, PROBES, and FOCI in Alaska, the La Perouse and MASS projects in Canadian waters.
Unlike the California and Oregon coasts, the Washington, British Columbia and Alaska coasts include many deep water embayments that could serve as semi-enclosed isolates for some of the population and process studies. This is a very important practical advantage because it reduces the scale of essential but relatively tedious boundary monitoring.
International collaboration is likely with Canada, and perhaps with Japan, Norway, and/or the Soviet Union. Within the U.S., interagency collaboration is likely with NOAA, ONR, MMS, DOE, and the NSF CoOP program.
Biologically, the system is truly pelagic. The subarctic zooplankton are dominated by large copepods with distinctive seasonal migrations (e.g., Miller and Clemons, 1988), euphausiids, and salps. The nekton are dominated by the Pacific salmonids, saury, myctophids, and gonatid squids. For GLOBEC purposes, there is no significant benthic component. However, there are potentially interesting and important links between the epipelagic and migratory mesopelagic communities. The southern boundary of the gyre is highly variable, and Transition Zone fauna are also frequently locally important. The real or potential bycatch from the high seas drift net fishery (primarily by Japan, Korea and Taiwan) is an important international issue, and is aggravated by the discrepancy between mapped fishing zone boundaries, and the meandering frontal boundaries that appear to actually control fish distributions.
The Alaska Gyre is bordered on the south by the North Pacific Current, and on the northeast, north, and west by the Alaska mainland and the Aleutian Islands. The wind-driven circulation is broadly divergent. Water from beneath the pycnocline mixes with and is diluted by freshwater inputs (probably mostly direct precipitation but including some coastal runoff) to the surface layer. There is good evidence for teleconnection of weather pattems between the Subarctic and Tropical Pacific (Philander, 1983; Rasmusson and Wallace, 1983), and winter/spring storm activity shows considerable interannual variation.
The Canadian weathership sampling program (1956-80) provided a long and relatively detailed time series of zooplankton and water properties for the southern part of the gyre. Strong interannual variability has been noted in zooplankton biomass and in fish distributions, but mechanistic causes (mixing vs. advection) remain poorly understood. Project SUPER (1984-88) examined in detail the processes controlling lower trophic levels; results highlighted the role of microzooplankton and the importance of late winter storm events.
As a GLOBEC study site, the Alaska Gyre presents major practical difficulties in long-term measurement of demographic parameters. Adequate sampling will be particularly difficult for the larger migratory species. However, ship-mounted ADCP, bioacoustics, and new satellite remote sensing technologies may allow valuable "feature-oriented" studies over shorter time scales.
International collaboration is likely with many of the Pacific Rim nations, as this is a region with substantial shared use by migratory fish stocks. The steering committee felt that planning of any "high seas" Pacific site needs to be closely coordinated with future open ocean activities in the Atlantic, Indian, and Southern Oceans.
Before going on to more specific questions concerning the northwestern Indian Ocean and the Arabian Sea, it is worthwhile to put this region in perspective with other areas of the globe. Here we will consider the differences in two high latitude sites, the Alaska Gyre and the North Atlantic in the same latitude belt, and two low latitude regimes, the equatorial Pacific and Arabian Sea. All four of these areas experience seasonally variable atmospheric forcing which produces responses in biological production and biogeochemical cycles. The resulting response is quite different in the four regimes, however, with comparatively higher but less variable biomass concentrations occurring in the Alaska Gyre compared to the Atlantic, which experiences pronounced bloom phenomenon. The low latitude regimes have similar contrasts: the Arabian Sea undergoes pronounced bloom cycles as opposed to the Pacific where both the maximum biomass and its variations are much smaller.
The different responses in these strongly forced regimes can be attributed to a combination of the type of physical forcing, the nature of the mixed layers and underlying stratification, and the nature of the biological/chemical response. The current rationale for the difference between the high latitude Pacific and Atlantic is the strong vertical stratification in the Pacific that limits deep mixed layer formation and therefore does not allow convective deepening to mix phytoplankton below their critical depth as occurs in the Atlantic. Differences in species composition in both the phytoplankton and zooplankton in the two regions further amplify this effect. It is possible to hypothesize a similar physical connection to explain the difference between the equatorial Pacific and the Indian Ocean. Here one can suggest that it is both the nature of the mixed layer development and the seasonal variation of the forcing with respect to the capabilities of organisms to withstand the changing environment that determines the contrasting conditions.
Three of the regions contrasted here have been extensively studied as part of past efforts such as SUPER, MLML, JGOFS Atlantic Bloom, or in upcoming efforts such as the JGOFS Equatorial Pacific Experiment. Planning on the part of various global initiatives (WOCE, JGOFS, GLOBEC) has suggested the Arabian Sea as an important site with respect to air-sea interaction and its role in determining the nature of the ecosystem. Specifically both JGOFS and GLOBEC have suggested the Arabian Sea as a priority experiment site. This U.S. interest is complemented by a sizable commitment to the region by the Germans and expressed interest in cooperation by Pakistan, India, Holland, France, and Great Britain. This system thus provides an opportunity for a joint JGOFS-GLOBEC study (perhaps including WOCE also) that could be greatly beneficial to the U.S. Global Change Program. GLOBEC collaboration could help assess the degree to which prediction of carbon fluxes by JGOFS requires specific knowledge of ecosystem composition and processes. JGOFS participation could help GLOBEC incorporate a much better understanding of the nature of primary production and its role in ecosystem dynamics.
In summary, the Arabian Sea provides a unique site to study air-sea interaction in relation to the marine ecosystem both in terms of intercomparison with other regions and in several unique aspects of the region including the following:
The proposed effort will seek to address the following sets of questions:
The continental ice sheet contains 90% of the world's fresh water, representing a potential sea level rise of approximately 60 meters. Major portions of the ice sheet grounded below sea level, such as the current West Antarctic ice sheet, have undergone disintegration on time scales of the order 100 years during past northern hemisphere glaciations. Whether the ice sheet is currently growing or shrinking is unknown.
Seasonal sea ice coverage in the Southern Ocean increases from approximately 4 x 10^6 km2 in summer to 20 x 10^6 km2 in winter (Zwally et al., 1983). During the austral summer the sea ice melts back almost to the edge of the Antarctic continent. During the last glacial maximum the sea ice in the Antarctic extended outward an additional 15 x 10^6 km2 and its retreat in the summer was much reduced (CLIMAP, 1981). These fluctuations in sea ice extent represent one of the most dramatic manifestations of climate change in the Southern Hemisphere. Recent paleoclimate studies (e.g., Crowley and Parkinson, 1988 a, b) have indicated that changes in atmospheric C02 may be a major factor in regulating the sea ice extent in the Southern Ocean.
Pack ice modifies the marine environment in other fundamental ways. It creates habitats with biotic and abiotic characteristics that differ from those of open water habitats and the extent of these habitats varies seasonally. Furthermore, in the winter it forms a barrier between the atmosphere and water and thereby dampens wind-forced motions. Interannual cycles and/or trends in the annual extent of pack ice may also have significant effects on all levels of the Antarctic food web, from total annual primary production to breeding success in seabirds.
The timing and maximum extent of the sea ice in the Southern Ocean is forced to a large extent by large-scale atmospheric processes. The same processes also influence the position of the major frontal systems and the strength of the various currents in the Southern Ocean. Since the type and abundance of species can differ on opposite sides of fronts (or in different water masses) a shift in the circulation or change in the intensity of a current can change the type and abundance of prey and predators.
The effect of atmospheric warming in the Southern Ocean may be to reduce the areal extent of annual sea ice, which could reduce total annual photosynthetic carbon fixation (Walsh, 1990), destroy habitats, and disrupt the life cycles of marine zooplankton and animals at higher trophic levels, whose present-day biogeographic ranges are directly related to the extent of sea ice coverage. Increased meltwater input from the continental ice sheet might have a compensatory effect, further extending the coastal production zone.
At the base of the Antarctic food web are the phytoplankton, or primary producers. The phytoplankton are eaten by herbivorous zooplankton such as copepods, salps, and Antarctic krill (Euphausia superba). In most oceanic food webs copepods are the dominant macrozooplankton grazers, but the Antarctic planktonic ecosystem is unique - its biomass can often be dominated by Antarctic krill. The krill in turn are a major component of the diets of birds, fish, many species of seals and baleen whales, and represent about half the total animal biomass available as food to the larger carnivores. In fact, in the food web of the Southern Ocean, all the vertebrates either directly or indirectly depend on krill as a food source (Laws, 1985). The dominant consumers serve as good indicators of ecosystem processes and of second order effects of decreases in key species because they show the cumulative effect of changes in ecosystem dynamics. For example, Adelie penguins comprise 60 to 70% of the entire Antarctic avian biomass (Prevost, 1981). Because their diets are dominated by krill (Emison, 1968; Volkman et al., 1980; Trivelpiece et al., 1987), aspects of the reproductive biology of the Adelie penguins have been proposed as sensitive indices of krill abundance and availability (CCAMLR, 1987).
Although consumers can serve as indices of local krill abundance and availability, to understand the mechanisms behind changes in resource levels for the consumers requires knowledge of many other factors affecting krill abundance and availability, such as changes in pack ice extent, water mass distribution, reproductive and recruitment success, and food availability. Food availability, or primary production, in turn depends on other environmental factors such as light, turbulence, and nutrients. Many of these biotic and abiotic parameters are directly or indirectly related to or affected by ice cover.
Even the immense spatial extent of the Antarctic marine ecosystem does not provide sufficient buffer against departures caused by global changes in environmental conditions, the stress of pollution or exploitation of renewable resources. If stress on any segment of the ecosystem continues for long periods of time, the system may be permanently altered. Documentation of natural population cycles and the mechanisms underlying these cycles of natural variability is important if we are to predict how changes in the environment due to such things as global warming impact the biology of the Antarctic ecosystem.
Numerous countries are interested in this region and international groups such as CCAMLR (Convention for the Conservation of Antarctic Marine Living Resources) have an active interest in Antarctic marine studies. Presently the U.S. has several agencies with strong interests or ongoing programs in the Antarctic, including NSF-Division of Polar Programs and NOAA (which holds the responsibility for carrying out U.S. CCAMLR activities). Other global geoscience initiatives such as WOCE and JGOFS have planned, or are now planning, research components in the Southern Ocean. It is expected that JGOFS field studies there will begin in 1992, although the precise locations of the research have not yet been finally agreed upon. The GLOBEC steering committee plans to hold a community workshop in 1991 to initiate planning for a potential GLOBEC study in Antarctic waters.
Coral reef ecosystems are widely recognized as among the most diverse ecosystems on earth. In addition, tropical reef systems are characterized by extensive and often intricate webs of complex biological interactions among resident biota. Because many reef systems are found on islands at varying degrees of isolation from other reefs, interesting questions arise about how reef animals successfully complete recruitment and maintain populations. For example, Lobel and Robinson (1986) evaluated the role of island eddies in retaining larvae of reef fishes and thereby promoting successful recruitment. Sammarco and Andrews (1989) demonstrated how relatively large-scale circulation patterns influence recruitment of corals themselves on the Australian Great Barrier Reef. The impact of changing global climate on recruitment and dynamics of coral reef ecosystems is unknown and likely to be substantial. This could threaten maintenance of diversity of a highly diverse ecosystem.
The Great Lakes share many of the physical and biological characteristics of the oceans. Nevertheless, sufficient differences in both physics and biology may exist to justify establishment of a GLOBEC study within one or more of the Lawrentian Great Lakes. The bounded nature of even large lakes, the potential for substantial change in their physical dynamics with variation in rainfall regime, and various specific attributes of lacustrine biota imply that understanding the impact of global change on the dynamics of ecosystems of the Great Lakes may require a lacustrine field study.