Satellite Observations of Enhanced Chlorophyll Variability in the Southern California Bight

Abstract

AbstractSatellite observations from the Moderate Resolution Imaging Spectroradiometer and Sea‐viewing Wide Field‐of‐view Sensor reveal a “tongue” of elevated near‐surface chlorophyll that extends into the Southern California Bight from Point Conception. A local chlorophyll maximum at the western edge of the bight, near the Santa Rosa Ridge, indicates that the chlorophyll is not solely due to advection from Point Conception but is enhanced by local upwelling. Chlorophyll in the bight peaks in May and June, in phase with the seasonal cycle of wind stress curl. The spatial structure and seasonal variability suggest that the local chlorophyll maximum is due to a combination of bathymetric influence from the Santa Rosa Ridge and orographic influence from the coastline bend at Point Conception, which causes sharp wind stress curl in the bight. High‐resolution glider observations show thermocline doming in May–June, in support of the local upwelling effect. Despite the evidence for local wind stress curl‐forced upwelling in the bight, we cannot rule out alternative mechanisms for the local chlorophyll maximum, such as iron supply from the ridge. Covariability between chlorophyll, surface wind stress, and sea surface temperature (SST) indicates that nonseasonal chlorophyll variability in the bight is closely related to SST, but the spatial patterns of SST influence vary by time scale: Subannual chlorophyll variability is linked to local wind‐forced upwelling, while interannual chlorophyll variability is linked to large‐scale SST variations over the northeast Pacific. This suggests a greater role for nonlocal processes in the bight's low‐frequency chlorophyll variability.