A description of temporal and spatial variability in the Bering Sea spring phytoplankton blooms (1997–1999) using satelite multi-sensor remote sensing

The Bering Sea is well known as a highly productive marginal sea. The objectives of this study were to clarify the interannual variability of spring bloom dynamics of the Bering Sea and to describe the spatial variability of this highly productive area using satellite multi-sensor remote sensing. We used multi-sensor remote sensing data sets of ocean color (OCTS and SeaWiFS), sea surface temperature (AVHRR), sea ice (SSM/I) and sea wind (SSM/I) to understand the complexity of the Bering Sea ecosystem. Phytoplankton biomass depends on the timing of sea ice melting and tends to increase when the melting is delayed. Wind stress is one of the important factors controlling the timing of the spring bloom. In 1997 and 1998, the east–west distribution of phytoplankton biomass exhibited a seesaw pattern, either high in west and low in east or low in west and high in east. We hypothesize that this seesaw pattern results from changes in the position and intensity of the Aleutian Low during spring and its relation to the El Niño–La Niña phenomena. During the El Niño period of 1998, the Aleutian Low shifted to the east of its normal position, and weak wind stresses facilitated the development of stratification and enhancement of spring bloom in the west. Conversely, when the Aleutian Low moved over into the western region in spring 1997, the same situation occurred in the east. Thus, the movements of the Aleutian Low promote a west-east seesaw pattern of sea surface wind stress, and consequently a corresponding seesaw pattern in phytoplankton biomass resulting from the subsequent variations in the depth of the mixed layer.