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- Title
The California Undercurrent as a Source of Upwelled Waters in a Coastal Filament.
- Authors
Zaba, Katherine D.; Franks, Peter J. S.; Ohman, Mark D.
- Abstract
In the California Current System, cross-shore transport of upwelled, nutrient-rich waters from the coastal margin to the open ocean can occur within intermittent, submesoscale-to-mesoscale features such as filaments. Time-varying spatial gradients within filaments affect net cross-shore fluxes of physical, biological, and chemical tracers but require high-resolution measurements to accurately estimate. In June 2017, the California Current Ecosystem Long Term Ecological Research program process cruise (P1706) conducted repeat sections by an autonomous Spray glider and a towed SeaSoar to investigate the role of one such coastal upwelling feature, the Morro Bay filament, which was characterized by enhanced cross-filament gradients (both physical and biological) and an along-filament jet. Within the jet, speeds were up to 0.78 m/s and the offshore transport was 1.5 Sverdrups (3.8 Sverdrups) in the upper 100 m (500 m). A climatological data product from the sustained California Underwater Glider Network provided necessary information for water mass differentiation. The analysis revealed that the cold, salty side of the filament carried recently upwelled California Undercurrent water and corresponded to higher chlorophyll-a fluorescence than the warm, fresh side, which carried California Current water. Thus, there was a convergence of heterogeneous water masses within the core of the filament's offshore-flowing jet. These water masses have different geographic origins and thermohaline characteristics, which has implications for filament-related cross-shore fluxes and submesoscale-tomesoscale biological community structure gradients. Plain Language Summary In the California Current System, slow broad currents move water in the alongshore direction but fast narrow flow features, such as filaments, can move water from the coast to the open ocean. Water at the coast tends to be cold, dense, and nutrient-rich, thus filaments serve as an important mechanism for biogeochemical supply to nutrient-poor offshore waters. In June 2017, an oceanographic experiment was conducted to measure a filament off the coast of Morro Bay, California. This study presents results from that experiment, specifically data from an autonomous underwater glider, Spray, and a ship-towed platform, SeaSoar. The high-resolution measurements reveal that there was a confluence of warm, fresh and cold, salty water within the filament, which originated far offshore and at the coast, respectively. The cold, salty side corresponded to more phytoplankton.
- Subjects
CALIFORNIA Current; PACIFIC Ocean currents; UPWELLING (Oceanography); OCEAN circulation; OCEANOGRAPHY
- Publication
Journal of Geophysical Research. Oceans, 2021, Vol 126, Issue 2, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2020JC016602