Cross‐Shore Flow and Implications for Carbon Export in the California Current Ecosystem: A Lagrangian Analysis

Abstract

In Eastern boundary upwelling systems (EBUS), winds blow alongshore during the upwelling season, causing nutrient-replete deep waters to come to the euphotic zone through divergence of Ekman transport at the coast, stimulating elevated net primary production (NPP) and inorganic carbon uptake. This primary production induces secondary production, the recycling of nutrients, and export of organic carbon into the aphotic zone. EBUSs are strongly advective systems: Ekman currents, as well as intense geostrophic mesoscale eddies and filaments, transport nearshore surface water offshore. The transport of organic matter (OM) from formation sites to export sites, occurs in three-dimensional space: the location of carbon export may be offset spatially from the region of elevated PP (

Monthly to Decadal Variability of Mesoscale Stirring in the California Current System: Links to Upwelling, Climate Forcing, and Chlorophyll Transport

“…We found positive correlations in some areas of the central CCS although the correlations in the CCS region were largely nonsignificant. The negative correlation between lagged FSLE intensity and the ONI index in the CCS is consistent with prior studies, showing that mesoscale activity is lower in the CCS during El Niño events (strongly positive ONI values) and higher during La Niña events (strongly negative ONI values) (Chabert et al, 2021).…”

“…We found persistent spatial variability in the correlations between horizontal stirring, chlorophyll a , and climate forcing. Consistent with the hypothesis that horizontal stirring increases primary productivity in offshore waters (Chabert et al., 2021; Chenillat et al., 2016), chlorophyll a was positively correlated with FSLE intensity in a meridional band approximately 200–600 km offshore. This band of high positive correlation is apparent both with and without the annual cycles of FSLE and chlorophyll a , consistent with stronger offshore advection of chlorophyll a during times of intense FSLE activity.…”

“…Flow into the CCS from the NPC is predicted to increase by 2100 (Toste et al., 2019); if transport into the CCS is related to the intensity of horizontal stirring, we would likewise expect an increase in FSLE intensity and horizontal stirring in the CCS over time. An increase in horizontal stirring could lead to an increase in carbon export from the coastal ocean as nutrient‐rich waters are advected away from coastal upwelling zones (Chabert et al., 2021). Research is required to determine what influence, if any, the volume of transport has on horizontal stirring and mesoscale activity in the CCS.…”

“…Fluctuations in the NPGO are associated with changes in physical and biological parameters in the CCS, such as salinity, nutrient concertation, and chlorophyll a (Di Lorenzo et al, 2008). A recent study by Chabert et al (2021) found that the NPGO was positively correlated with the advection of upwelled water offshore in the central CCS, which they hypothesized was due to the influence of climate forcing on mesoscale activity. We found positive correlations in some areas of the central CCS although the correlations in the CCS region were largely nonsignificant.…”

“…Recently upwelled water does not remain isolated in the narrow band along the coast in which it was upwelled. Instead, horizontal stirring moves the water offshore, increasing the offshore influence of coastally upwelled water (Chabert et al., 2021). Fronts of upwelled water in the CCS tend to be baroclinically unstable and frequently form both cyclonic and anticyclonic eddies that propagate westward at a speed of approximately 2 km/day (Kurian et al., 2011).…”