Distribution of phytoplankton abundance and physical properties on the southeastern shelf of the Bering Sea in summer

Oceanographic structure, nutrient concentration, and chlorophyll a concentration were surveyed from 55°N to 59°N along 166°W on the southeastern shelf of the Bering Sea during mid to late July of 1994,1995,and 1996. The present results show a consistent trend that, in every year, high chlorophyll a concentration occurred in the outer shelf domain around 55°00\u27N, as well as the coastal shelf domain, and that the concentrations were usually low in the central shelf domain although large yearly variation occurred. The high phytoplankton abundance in the southern outer shelf domain related to relatively high salinity water, which contained more nitrate than the central shelf domain water. It is suggested that the high abundance is maintained by a continuous supply of nutrients caused by interaction between the ocean current from the open water of the North Pacific and the bottom topography in the vicinity of Unimak Pass. On the other hand, alternative high chlorophyll a stock was observed in the coastal shelf domain, where the sea floor depth was about 40m and vertically homogenous water properties occurred. This suggests that the nutrient supply from the bottom maintains the high phytoplankton abundance. In the central shelf domain, chlorophyll a concentrations less than 1.0μg l^ were usually observed between 55°30\u27N and 58°30\u27N in 1995 and 1996. In 1994,however, chlorophyll a concentrations of 1.0 to 2.0 μg l^ were widely distributed. The slightly high concentrations coincided with a weak pycnocline and occurrence of cold bottom water, which contained high nitrate. It is suggested that phytoplankton abundance may be low when the pycnocline is well developed or the cold bottom water does not transport a large amount of nutrients in the central shelf domain of the southeastern Bering Sea

3. Satellite and Ship Observations of Coastal Upwelling in the St. Lawrence Island Polynya (SLIP) Area in Summer, 1994 and 1995

Ⅰ. Physical, Chemical Environment, Primary Production, Zooplankton and Their Coupling Model Studie