Spatial and temporal characteristics of sediment plumes and phytoplankton blooms in the Santa Barbara Channel

Satellite ocean-color and sea-surface temperature (SST) imagery are used to assess the occurrence, extent and duration of surface sediment plumes from discharged stormwaters and phytoplankton blooms in the Santa Barbara Channel (SBC), California. Nearly four years (October 1997–June 2001) of Advanced Very High Resolution Radiometer and Sea-viewing Wide Field-of-view Sensor local area coverage imagery, in situ measurements, and supporting data are analyzed. Monthly mean annual cycles of SST, chlorophyll (Chl) and the water-leaving radiance at 555 nm (LwN(555)), an index for sediment-affected waters, show plumes associated with runoff in winter, while blooms occur in the late spring–early summer and are associated with cool SST and upwelling favorable winds. Interannual variations are consistent with remote forcing by El Niño cycles. During the 1997–1998 El Niño, Chl concentrations are moderate, and El Niño-induced floodwater discharges result in high LwN(555) values throughout the SBC. However, a correspondence between El Niño–La Niña state and Chl is not found for the SBC due to what appears to be the advection of nutrient-depleted waters from the east. Empirical plume and bloom indices show that plumes occur episodically in response to discharge events whereas blooms occur more regularly and can cover up to 95% of the SBC. Empirical orthogonal function analysis is used to spatially and temporally deconvolve processes regulating SST, Chl and LwN(555). The first Chl mode contains 43% of the temporal variance and is associated with wind-driven upwelling in spring and summer. The first LwN(555) mode contains 51% of the temporal variance and is associated with episodic terrestrial runoff events in February and March. The second modes for both Chl and LwN(555) represent the transition from runoff-dominated processes in winter to upwelling and bloom-dominated processes in summer.