Low Primary Productivity in the Chukchi Sea Controlled by Warm Pacific Water: A Data-Model Fusion Study

The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) has identified a broad low chlorophyll-a (chl-a) area in the Chukchi Sea since 2002. High sea surface temperature from 2002 (more than 5°C), which resulted in a long duration of open water, was also detected by satellite. An intensified ocean color front at the southwest Chukchi Sea near the Siberian Coast indicates nutrient depletion in the Alaska Coastal Current and its branches. A low chl-a area started to emerge in the Hope Valley in June, and then expanded to the Herald Shoal and Hanna Shoal during July and August. The evolution pattern of low chl-a area is consistent with the variability of the pathway of the Pacific water simulated by a Coupled Ice-Ocean Model (CIOM). These results suggest that the summer phytoplankton bloom from 2002 to 2005 was suppressed by the dominance of warm nutrient-poor water from the Pacific, and by the deepening of the surface mixed layer by strong wind stress. During the summer of 2004, a phytoplankton bloom was detected at the ice edge when the sea surface wind field was relatively calm. Our results imply that the ice-edge bloom was induced due to weak wind speeds, which produce shallower upper mixed layer, favoring the ice-edge bloom.