Satellite color observations of spring blooming in Bering Sea shelf waters during the ice edge retreat in 1980

Abstract

Coastal Zone Color Scanner (CZCS) images of the eastern Bering Sea between April 27 and July 22, 1980, were analyzed in a study of the biological response of the Bering Sea system to the 1000‐km retreat of the ice edge across the shelf and to the subsequent establishment of the highly stratified water column characteristic of spring and early summer. Images from the Norton Sound area showed seasonal changes both in an ice edge bloom near the sound and in the Yukon River sediment plume inside the sound. Three spring images revealed details of several stages of the classic spring bloom development over the shelf which typically begins inshore and progresses offshore. High pigment concentrations were observed over the inner shelf domain in early spring and developing across the middle shelf domain in May. A band of high chlorophyll concentration seaward of the 100‐m isobath in the approximate area of the outer domain, thought to have been caused by periodic offshore movements of shelf waters, was seen in late July. The phytoplankton pigment concentrations derived from the satellite data appeared to be much lower than those observed by the Processes and Resources of the Bering Sea Shelf group, but the spatial and temporal distributions agreed well with trends identified during that experiment. While it is clear that the ice edge and open water spring bloom events together make up the most important component of the seasonal Bering production cycle, the extraordinary spatial and temporal extent of the classic spring bloom over the shelf underscores the significance of the contribution made by this phenomenon to the annual production budget of the eastern Bering shelf.