Temporal and spatial variability of chlorophyll concentrations in the Bering Sea using empirical orthogonal function (EOF) analysis of remote sensing data

Seasonal and interannual variability of surface chlorophyll concentration in the Bering Sea was examined using Empirical Orthogonal Function (EOF) analysis of data obtained by the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) from 1998 to 2002. The analysis of normalized monthly fields (removing temporal and spatial monthly means) shows that different temporal and spatial patterns are evident in the eastern and western Bering Sea during the spring bloom period. The first EOF mode explains 30% of the variability and shows how the eastern shelf break region and the western Bering Sea are out of phase during the spring bloom. The second EOF mode (17.6%) indicates a pattern involving the eastern shelf break region and the Kamchatka Basin. This strong east–west signal is linked by both surface winds and light. EOF modes of wind-speed anomalies, derived from Special Sensor Microwave Imager (SSM/I), and photosynthetically active radiance (PAR) from SeaWiFS, show a similar dipole feature where the east–west pattern is related to the position and strength of the Aleutian Low pressure system. In years when the Aleutian Low shifts from west to east, weaker wind stress facilitates the development of stratification resulting in a strong spring bloom in the western Bering Sea. The variability of spring chlorophyll has a strong connection with variability in atmospheric forcing in the Bering Sea.