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Production of particulate organic carbon (POC) in nutrient-rich coastal waters over continental shelves, its export to depth, and its transport to deeper ocean waters is a poorly quantified component of the global carbon cycle. A critical step in quantifying this vertical transport is identifying shelf processes that export phytoplankton out of the euphotic zone. During cruises of the Santa Barbara Coastal Long Term Ecological Research project, we discovered substantial chlorophylla(chla)below the euphotic zone in the Santa Barbara Channel, a part of the southern California Current System. Observations from towed, undulating vehicles revealed deep chlorophyll layers near fronts where upwelled waters from central California converged with lower-density waters from the Southern California Bight. The mean fraction ± 1 standard deviation (SD) of chlorophyll biomass below the euphotic zone spanning the entire Santa Barbara Channel was ~7 ± 9% during 13 cruises averaged across all seasons. In one spring cruise, the fraction was ~30%, and in other cruises the layers were absent. Phytoplankton export out of the euphotic zone by subduction was indicated by spatial coherence between chlaand sloping density surfaces. Vertical plumes of chlacrossing density surfaces indicated enhanced gravitational export within cyclonic eddies. Chlain water samples below the euphotic zone, away from fronts and cyclonic flows, suggested additional phytoplankton export. Our results emphasize the importance of subduction in the export of phytoplankton and POC out of the euphotic zone in coastal upwelling systems.
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Offshore transport of particulate organic carbon in the California Current System by mesoscale eddies
Abstract The California Current System is characterized by upwelling and rich mesoscale eddy activity. Cyclonic eddies generally pinch off from meanders in the California Current, potentially trapping upwelled water along the coast and transporting it offshore. Here, we use satellite-derived measurements of particulate organic carbon (POC) as a tracer of coastal water to show that cyclones located offshore that were generated near the coast contain higher carbon concentrations in their interior than cyclones of the same amplitude generated offshore. This indicates that eddies are in fact trapping and transporting coastal water offshore, resulting in an offshore POC enrichment of 20.9 ± 11 Gg year−1. This POC enrichment due to the coastally-generated eddies extends for 1000 km from shore. This analysis provides large-scale observational-based evidence that eddies play a quantitatively important role in the offshore transport of coastal water, substantially widening the area influenced by highly productive upwelled waters in the California Current System.
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- Award ID(s):
- 1643468
- PAR ID:
- 10153772
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 10
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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