Kilpatrick, T., S.-P. Xie, A. J. Miller and N. Schneider, 2018:
Satellite observations of enhanced chlorophyll variability in the
Southern California Bight
Journal of Geophysical Research-Oceans, sub judice.
Satellite observations from the Moderate-resolution Imaging Spectroradiometer (MODIS)
and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) 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 SST indicates that
non-seasonal chlorophyll variability in the bight is closely related to SST, but the spatial
patterns of SST influence vary by time scale: sub-annual 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.