Temporal modulation of biogeochemical cycles and phytoplankton biomass by submesoscale circulation in the California Current System

Seasonal wind-driven upwelling supports phytoplankton blooms that turn the California Current into one of the most productive ecosystems of the ocean. This upwelling is confined to a narrow near-shore band that is poorly resolved by current physical-biogeochemical models. Further offshore, mesoscale eddies counteract the upwelling by removing surface nutrients through subduction. However, the impact of submesoscale motions on upwelling and subduction of productivity has not yet been quantified. Here, we present results from three sets of simulations with a regional physical-biogeochemical model of the California Current run at the resolutions of 4 km, 1 km and 300 m respectively. The 300m focuses only on the Southern California Bight (SCB). We will demonstrate the role of the submesoscale dynamics via three processes: First, submesoscale eddies generated by increased frontogenesis during spring, controls up to 50% the vertical eddy transport of nutrients across the euphotic layer, reducing plankton productivity, and exporting biomass out of the euphotic layer during the post-upwelling period. Second, in the offshore oligotrophic region, submesoscale eddies intensify the vertical velocities in winter, driving injection of nutrients from enriched thermocline to the depleted mixed layer and maintain productivity in the deep chlorophyll depth. Lastly, we will demonstrate how submesoscale eddies emphasizing the generation of topographic wakes in Channel Islands and strong vertical turbulence in coastal regions of the SCB promoting very high productivity, low omega aragonite and low oxygen all year around previously observed during local surveys and confirmed by remote sensing data.