Field Process Studies

Understanding the coupling of physical and biological processes in the sea is the core of U.S. GLOBEC. This understanding has been limited by our ability to sample, process, and analyze biological data on scales commensurate with physical data. To accomplish this, U.S. GLOBEC emphasizes improved rapid discrete sampling, continuous in situ measurement, and remote sensing in ongoing and future field studies. The emphasis is on sampling marine populations on appropriate time scales and with sufficient spatial resolution to compare with the concomitant physical data. In addition, process studies are necessary to elucidate the actual mechanisms coupling biology and physics. Only by understanding mechanism can we extrapolate, generalize, and make predictions about the influences of global climate change on marine ecosystems.

Banks, Shelves and Shallow Seas

These environments are the home of many of the world's most important fisheries. The first U.S. GLOBEC field study is occurring in the Northwest Atlantic on Georges Bank-the site of oceanographic and fisheries studies for more than a century (Backus, 1987). The cod, haddock and other groundfish stocks of Georges Bank have historically been important to the economy of New England. In recent years the stocks of these species have declined, in part due to overfishing. One challenge that U.S. GLOBEC faces on Georges Bank (and elsewhere) is that of deciphering natural population fluctuations from anthropogenic impacts. Georges Bank is thought to be highly sensitive to climatic change because it is positioned in a faunal, climatic, and oceanic boundary region. Moreover, model results indicate that the Georges Bank region will be more heavily impacted by climate change than other areas in the North Atlantic Ocean (Manabe et al. 1991). Finally, Georges Bank is an excellent site for a study of the population biology of marine animals because it is of sufficient size and has a physical circulation pattern resulting in distinct, trackable populations that persist for long periods amenable to time-series study. The focus of the Georges Bank study is to determine how biological and physical processes interact to control the population dynamics and retention of specified target species on the Bank (see Appendix A.1). The information provided by the Georges Bank field studies will permit assessment of the potential fate of these zooplankton and fish populations under various plausible global climate change scenarios. More information can be found in U.S. GLOBEC reports Nos. 2 and 6 and Appendix A.1.

Eastern Boundary Currents

Eastern boundary current (EBC) systems are particularly appropriate for examining both high and low frequency components of climate variability. Biological and physical responses to forcing at interannual (e.g., ENSO events) to decadal time scales (e.g., regime shifts) are known to be very strong. The local biological response almost certainly involves coupling to a variety of physical processes. Some of these prominent physical processes are: wind speed, direction and wind stress curl; pycnocline depth; alongshore and cross-shore advection; and buoyancy inputs. These are influenced by larger-scale (basin-wide) oceanic and atmospheric circulation. Lower frequency components of biological variability (decades to centuries) are clearly evident in reconstructions from historical and sedimentary data. Equally important, several EBCs, including the California Current System (CCS), have long biological and physical records, making them ideal for examination of long-term changes, such as might occur due to gradual global climate change. In the CCS, quantitative surveys of zooplankton and fish have been conducted off British Columbia, Washington, Oregon, California, and Baja California (Mexico). The best of these is perhaps the CalCOFI investigations of the past 40 years. Data and scientific insights developed from one EBC may be applicable to others, providing global significance to such studies. EBCs are oceanographically and ecologically distinctive; the dominant life history patterns and trophic pathways contrast with those of other continental shelf ecosystems. Moreover, in the CCS, some species extend over a broad latitudinal range and are exposed to large differences in the intensity and timing of seasonal circulation patterns. Conversely, other planktonic, benthic and fish species are restricted to smaller regions, perhaps due to the population's responses to the differing mesoscale physical variability in different regions. Finally, eastern boundary current systems are important economically-approximately 35% of the global marine fish catch is taken from the EBC systems of the Atlantic and Pacific, and the U.S. west coast fishery in 1992 produced an impact of $4 billion on the economies of California, Oregon and Washington (U.S. Department of Commerce, 1992). More information can be obtained from U.S. GLOBEC Reports No. 7 and No. 11 (U.S. GLOBEC 1992, 1994) and Appendix A.2.

Southern Ocean

Global climate change is predicted to be greatest at high latitudes, with dominant effects being increased temperature and changes in ocean circulation. The Antarctic has a high negative radiation budget; its immense masses of continental ice and annual sea-ice act as a refrigerator buffering seasonal and multiannual changes in temperature. The extent of sea-ice in the Southern Ocean is not, however, constant from year to year. The fluctuations in sea-ice extent may represent one of the most dramatic manifestations of climate change in the Southern Hemisphere. Recent paleoclimate studies indicate that changes in atmospheric greenhouse gas concentrations may have already affected the extent of sea-ice.

Were atmospheric warming in the Antarctic to reduce the areal extent of sea-ice, this would almost certainly reduce photosynthetic carbon fixation, destroy habitats, and disrupt the life cycles of marine animals. Marine zooplankton, like krill, and higher trophic level animals, whose present-day biogeographic ranges are directly related to the extent of sea-ice coverage, might be most seriously impacted. On the other hand, increased meltwater input from the continental ice sheet might have a compensatory effect by altering water column stability, stratification, and extending the high production zone further from shore. It has been suggested that because of the tight linkages between trophic levels (producer–herbivore–carnivore) in the Antarctic, long-term studies focusing on predator-prey relationships and their environment are an efficient way to monitor the effects of man-induced perturbations on the entire regional ecosystem (Croxall et al. 1988). The focus of a U.S. GLOBEC Southern Ocean study will be how variability in sea-ice extent determines variability in the population dynamics of the target species. To understand the mechanisms responsible for changes in resource levels for the higher trophic level consumers requires knowledge of the many inter-related factors affecting krill abundance and availability. These include water mass distribution, reproductive and recruitment success, and food availability, which may depend directly or indirectly on ice cover. Further information about the Southern Ocean GLOBEC study can be found in U.S. GLOBEC Report No. 5, GLOBEC International Report No. 5, and Appendix A.3.

Open Ocean

The physical and biological environment in the open ocean differs dramatically from that found in coastal, polar, and marginal seas. So too may the coupling of physical and biological processes. We presently do not know whether open ocean ecosystems will be resistant to climatic variations, or shift dramatically under such potential forcing. For example, there may be less variability in physical forcing over time scales of days to several months and over both small (e.g., meters to km) and large (10's to 1000's of km) spatial scales in the open ocean than is commonly found in the coastal ocean. Further, the frequency distribution of numbers of individuals in a species in much of the open ocean appears to be more stable year-to-year than in coastal environments. If the apparent stability of open ocean biological communities is due to internal biological checks and balances, then the biomass and food-web relations of oceanic communities might be relatively resistant to changing physics caused by climate change. Conversely, if the stability of the open ocean biological communities is due to the near constancy of the physical environment, then oceanic communities may be more susceptible to physical perturbations resulting from global climate change. Some open ocean environments, for example the Arabian Sea (U.S. GLOBEC Report 9), do not fit the paradigm. The Arabian Sea is subject to extremely strong physical forcing due to seasonal reverses of monsoonal winds. Quite likely the biological community is also strongly seasonally variable.

Comparison of zooplankton vital rates and population dynamics of various oceanic and coastal habitats will be essential. In fact, several circumglobally distributed species might be targeted for study. In this way some of the inherent variability associated with different habitats in different regions of the world's oceans might be minimized and the biological responses to global climate change extracted from records of seasonal and interannual variability. Possible U.S. GLOBEC studies in the open ocean were discussed at a workshop held in September 1993 and a report of the workshop discussions and recommendations is under review. Possible U.S. GLOBEC studies in the Arabian Sea were discussed at a workshop in June 1992. Recommendations and further information can be found in U.S. GLOBEC Report 9.