On the temporal variability of the physical environment over the south-eastern Bering Sea

During 1997 and 1998, unusual physical conditions occurred in the Bering Se a: strong May storms and calm conditions in July; record high sea surface t emperature; a shallow wind mixed layer; a fresher-than-normal water column; and abnormal cross-shelf currents. Accompanying these conditions were chan ges in the dominant phytoplankton, a die-off of seabirds, increased sightin gs of large whales and diminished returns of salmon. Changes to the physica l environment during 1997 and 1998 are placed in context of historical mete orological and oceanographic data sets. Although 1997 had the warmest sea s urface temperature ever observed on the south-east Bering Sea shelf, the he at content of the water column was cooler than average. In contrast, during 1998, the sea surface temperature was cooler than in 1997 but the water co lumn had significantly higher heat content. During recent years, the water column has freshened over the middle shelf because of increased sea ice and reduction of on-shelf transport of the saline, high-nutrient water from th e slope. The timing of the spring bloom is directly related to the presence of ice. When ice is advected over the south-east shelf during March/April an early, sharp phytoplankton bloom occurs. The absence of ice during this critical time is associated with a May/June bloom.