Interannual-interdecadal variations in zooplankton biomass, chlorophyll concentration and physical environment in the subarctic Pacific and Bering Sea

Interannual, decadal and interdecadal variations in summer plankton biomass during 1954-1994 in the whole subarctic Pacific and Bering Sea were compared among regions as well as with climatic and oceanographic conditions. The zooplankton biomass and chlorophyll concentration during the mid 1960s to early 1970s in the central and western subarctic Pacific were a few times higher than those in the preceding and following decades. The values in the eastern Bering Sea and eastern subarctic Pacific also increased in the mid 1960s, but remained at an elevated level until the end of the 1980s. These decades of higher and mid plankton biomass levels during the mid 1960s to early 1970s and mid 1970s to late 1980s correspond to the period of positive and negative values of the Northern Hemisphere zonal index (NHZI), respectively. in the decadal scale, one can see a significant positive correlation between the summer plankton biomass and the wind speed during winters in the eastern Bering Sea. The effect of grazing by biennially fluctuating Asian pink salmon on zooplankton biomass and its effect on chlorophyll concentration in the central subarctic Pacific is also significant.