Climatological phytoplankton chlorophyll and sea surface temperature patterns in continental shelf and slope waters off the northeast U.S. coast

Abstract

Satellite‐derived chlorophyll estimates from the Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) and Coastal Zone Color Scanner (CZCS), a large archive of in situ near‐surface chlorophyll data, and satellite sea surface temperature (SST) measurements were used to quantify spatial and seasonal variability of near‐surface chlorophyll and SST in middle shelf to slope waters off the coast of the U.S. Northeast. The results of empirical orthogonal function (EOF) analysis on normalized monthly fields (after temporal and spatial means were removed) show that all three chlorophyll climatologies have similar mode 1 temporal and spatial patterns in these waters. Mode 1, which explains about half of the total variability in monthly climatological images, shows that shelf waters in the Gulf of Maine (GOM) are out of phase with the mid‐Atlantic bight (MAB), with seasonally high chlorophyll concentrations in winter in the MAB and in summer in the GOM. The three chlorophyll climatologies begin to differ at higher modes (modes 2 and 3), although SeaWiFS and in situ climatologies keep similar features through mode 3. Higher modes in both SST and chlorophyll are related to the effects of tidal mixing on Georges Bank, differences in seasonal stratification between the southwestern and northeastern GOM, and the importance of the spring bloom in MAB outer shelf waters and western GOM. SST patterns during the CZCS and SeaWiFS eras are very similar, and this indicates that the observed differences between results obtained with these two sensors are probably not caused by differences in physical processes during the two satellite eras.