Empirical Orthogonal Function (EOF) analysis of sea-surface temperature and chlorophyll in the eastern Bering Sea

Empirical orthogonal function (EOF) analysis was used to study spatio-temporal variability of the Moderate Resolution Imaging Spectroradiometer (MODIS) imagery of sea surface temperature (SST (oC)) and chlorophyll (mg m(-3)) for the eastern Bering Sea for May, June, July, August, September (MJJAS) for a period of 7 years (2003 - 2009). The EOF analysis was conducted on SST and chlorophyll monthly composites that were normalized by subtracting the spatial and temporal means with cloud, ice and land cover masked out. The SST in eastern Bering Sea showed a transition from a warm period (2003-2005) to cooler period (2006-2009). The first 3 EOF modes of SST were retained as they explained 76.7% of the spatio-temporal variability, with the first SST EOF mode explaining 59.5% of the total variation of SST in the study area during the study period. For the chlorophyll dataset, the first 3 EOF modes explained greater than 58.5% of the spatio-temporal variability, with the first chlorophyll EOF explaining 28.14% of total variance in chlorophyll. The decreasing amplitude of first SST EOF and switching from mostly positive to negative amplitude of the third chlorophyll EOF mode in 2006 was consistent with the May SST Index, Ice Cover Index and Bering Sea Pressure Index (BSPI).