What's New.............
Recent NOAA/University of Alaska Research on the Green Belt in the Eastern Bering Sea
In their call for research to improve understanding of the ecosystem of the Bering Sea (NRC Report on the Bering Sea Ecosystem, 1996), The National Research Council identified the Green Belt as a critical feature. The importance of the Green Belt to the ecosystem is well established (GLOBEC, Report #16). It is a vital feature of the Bering Sea (Springer et al., 1996). Annual primary production in the Green Belt may be 60% greater than over adjacent outer shelf domain and 270% greater than in the oceanic domain. To address this research need, the Arctic Research Initiative funded a scientific partnership between NOAA and the University of Alaska-Fairbanks to investigate the basis for the rich productivity of the eastern Bering Sea. Physical processes at the shelf edge, including tidal mixing and/or instabilities and eddies in the Bering Slope Current, bring nutrients to the euphotic zone and contribute to enhanced primary and secondary production and elevated biomass. Fishes and squids concentrate in this region due to favorable feeding conditions and because it is a thermal refuge from the cold shelf-bottom water temperatures. The abundance of zooplankton, fishes and squids, in turn, attracts huge numbers of marine birds and mammals. In aggregate, the observations suggest that sustained primary production, intense food web exchange, and high transfer efficiency in the Green Belt are important to biomass yield at numerous trophic levels and to the ecosystem production of the Bering Sea.
Until a recent research cruise, however, a thorough mapping of water properties, currents, nutrients and primary production had never been undertaken. Even the nature of the currents over the slope has not been well described or understood (Schumacher and Stabeno, 1998). Yet, it is this feature which is the source of nutrients for primary production and may seed the outer shelf with pollock larvae and other plankton. Under the direction of Dr. Ned Cokelet (PMEL), Chief Scientist, the NOAA ship MILLER FREEMAN conducted a research cruise (March 28 to April 13, 1997) along the Bering Sea shelf break crossing the Green Belt on seven transects from the United States-Russia Convention Line in the north to the Aleutian Islands in the south (Figure 1). Water density observations analyzed aboard ship gave the scientists a preliminary indication of the Bering Slope Current's location and strength. It was flowing just seaward of the shelf break transporting 4-7 Sverdrups (Sverdrup=1,000,000 cu. m per sec) northwestward. Modern Acoustic Doppler Current Profiler (ADCP) and Global Positioning System (GPS) measurements will be used to reference water-density-based geostrophic currents and provide much more accurate current data in this region than has been possible in the past. Chlorophyll measurements revealed heightened photosynthetic activity seaward of the shelf break. These await further analysis in conjunction with nutrient and primary productivity observations in order to map the location of the Green Belt and its relationship to the Bering Slope Current.
Related Information:
ADCP Velocity Vectors from Cruise MF97-04 (March 28 to April 13, 1997)
>Cooperative Institute for Arctic Research (CIFAR), University of Alaska Fairbanks. Ecosystem Foundation for the Green Belt: Observations of Velocity, Water Properties and Nutrients in the Green Belt. PI: Peter McRoy (UAF), Co-PIs: Jim Schumacher (PMEL), and Alan Springer (UAF).
References:
National Research Council, 1996. The Bering Sea Ecosystem, National Academy Press, Washington, D.C., 307 pp.
Schumacher, J.D., and P.J. Stabeno, 1998. The continental shelf of the Bering Sea. In: The Sea, Vol. 11 - The Global Coastal Ocean: Regional Studies and Synthesis. J. Wiley & Sons, Inc., New York, in press.
>Springer, A,M., P. McRoy and M.V. Flint, 1996. The Bering Sea Green Belt: shelf-edge processes and ecosystem production. Fish. Oceangr., 5, 205-223.
U.S. GLOBEC, 1996. North Pacific Climate Change and Carrying capacity (CCCC) science plan. U.S. Global Ocean Ecosystems Dynamics Report # 16, Univ. of Calif., Berkeley, CA, 44 pp.