Physical and Biogeochemical Variability of Upwelling Events Measured by Long-Term, Multi-Disciplinary Moorings in the California Current System

The two moorings of the California Current Ecosystem (CCE) project are located in the upwelling regime and at the core of the southward-flowing California Current System. They are co-located with stations of the CalCOFI quarterly hydrographic program, and have collected more than 5 and 7 years of hourly data for the nearshore and offshore moorings, respectively. Satellite telemetry provides near-real time measurements of physical and biogeochemical variables. This provides for long-term studies of event-scale forcing (weeks to days) of the upwelling and of eddy events which dominate the highly productive region.

For example, in situ nitrate measurements provide an appropriate proxy for upwelling events, during which the effect on other variables is observed. Following an event characterized by increased nitrate, a chlorophyll bloom develops in the upper layer measured using a bio-optical algorithm applied to paired radiometers. During this time, new production estimates using nitrate deficits from the nitrate-temperature relationship match the chlorophyll variability on selected timescales. The initial bloom eventually shuts down, usually followed by a secondary chlorophyll peak during the relaxation period after upwelling weakens or ceases.

The CCE Moorings resolve the upwelling and eddy time scales over several years. When these data are averaged over the full time series, the cross-shelf transport of biogeochemical quantities can be estimated, including the mean and fluctuating components. Taken together with CalCOFI observations for historical and spatial context, these observations are meant to provide new insights into the processes that drive biogeochemical fluxes in the California Current System.