%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Chabert, P.
%A d'Ovidio, F.
%A Echevin, Vincent
%A Stukel, M. R.
%A Ohman, M. D.
%T Cross-shore flow and implications for carbon export in the California current ecosystem : a Lagrangian analysis
%D 2021
%L fdi:010081114
%G ENG
%J Journal of Geophysical Research : Oceans
%@ 2169-9275
%K PACIFIQUE
%K CALIFORNIE COURANT
%M ISI:000624429800046
%N 2
%P e2020JC016611 [14 ]
%R 10.1029/2020jc016611
%U https://www.documentation.ird.fr/hor/fdi:010081114
%> https://www.documentation.ird.fr/intranet/publi/2021-05/010081114.pdf
%V 126
%W Horizon (IRD)
%X Eastern Boundary Current Upwelling Systems are regions of elevated primary production and carbon export and thus play a central role in the global carbon cycle. In these regions, nutrient upwelling occurs in a narrow region close to the coast, but primary production and carbon export are typically observed across a broader region. The fact that productive waters reach the open ocean has important consequences for the biological carbon pump, because such transport connects nutrient sources close to the coast to the deep carbon sinks of the offshore ocean. However, many aspects of this offshore transport are still not known. Here we address seasonal and interannual variability of upwelling-related cross-shore flows in the California current ecosystem (CCE) by employing Lagrangian diagnostics of horizontal transport inferred from satellite data. We define an advective age as the time a water parcel flowed offshore of the 500 m isobath. We find that the offshore extension of high Chl-a waters covaries with the age of a coastal water parcel, and is consistent with mesoscale circulation. Interannual variability in the offshore extent of older waters is primarily driven by mesoscale variability and covaries with large scale forcing by both ENSO and the NPGO. The measured ratio of in-situ new production: carbon export also covaries with water age, and tends to be 1 in younger and more balanced in older waters. Our results may help to parameterize the role of the finescale on the export of carbon in upwelling regions for climate resolving models. Plain Language Summary The California current ecosystem (CCE) is a region of strong coastal upwelling, elevated organic matter production and high carbon flux into the deep ocean, and potentially influential in the global carbon cycle. Previous studies have suggested that production and sinking are not balanced in the CCE: there is more production than sinking close to the coast and more sinking than production offshore. Our study uses satellite measurements to analyze cross-shore flows in the CCE and assess whether horizontal transport of water, nutrients, and plankton can reconcile this spatial imbalance. By following water parcel trajectories, we find that the time since a water parcel is transported from the coast to the offshore is a predictor of whether the water parcel is a net source of organic matter (greater new production than sinking) or a net sink (greater sinking than new production). We find that the offshore distance of water transport varies strongly from year to year and is related to known sources of climate forcing, including El Nino-Southern Oscillation and the North Pacific Gyre Oscillation. Future organic matter exchanges between the coast and the offshore can be estimated thanks to covariability with these climate indices.
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