Nearsurface pattern in the California Current: coupling between physical and biological structure

The results of a four-year program of continuous nearsurface mapping and a 12-year time series of nearsurface chlorophyll measurements, both made by the CalCOFI program, are interpreted in the context of the CalCOFI hydrographic time series. There are consistent regional differences in the mechanisms affecting nutrient input to the upper layers, and these result in different spatial and temporal patterns of chlorophyll concentration. We define three regimes in which nearsurface ecosystem structure appears to be regulated differently. A sharp physical and biological front at the inner edge of the low-salinity California Current jet separates offshore and inshore regions. The inshore area is further divided into northern and southern regions based upon the intensity of isopycnal shoaling, which alters the relationship between physical structure and chlorophyll concentration. These observations indicate that even on the scale of the CalCOFI area a regional approach to developing models and interpreting mesoscale structure will improve our understanding of important physical–biological interactions.