Dominant role of eddies and filaments in the offshore transport of carbon and nutrients in the C alifornia C urrent S ystem
Abstract
The coastal upwelling region of the California Current System (CalCS) is a well‐known site of high productivity and lateral export of nutrients and organic matter, yet neither the magnitude nor the governing processes of this offshore transport are well quantified. Here we address this gap using a high‐resolution (5 km) coupled physical‐biogeochemical numerical simulation (ROMS). The results reveal (i) that the offshore transport is a very substantial component of any material budget in this region, (ii) that it reaches more than 800 km into the offshore domain, and (iii) that this transport is largely controlled by mesoscale processes, involving filaments and westward propagating eddies. The process starts in the nearshore areas, where nutrient and organic matter‐rich upwelled waters pushed offshore by Ekman transport are subducted at the sharp lateral density gradients of upwelling fronts and filaments located at ∼25–100 km from the coast. The filaments are very effective in transporting the subducted material further offshore until they form eddies at their tips at about 100–200 km from the shore. The cyclonic eddies tend to trap the cold, nutrient, and organic matter‐rich waters of the filaments, whereas the anticyclones formed nearby encapsulate the low nutrient and low organic matter waters around the filament. After their detachment, both types of eddies propagate further in offshore direction, with a speed similar to that of the first baroclinic mode Rossby waves, pro…
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Diagnostics of the eddy-induced circulation in realistic simulations for this upwelling sector tend to confirm our estimates.
“Diagnostics of the eddy-induced circulation in realistic simulations for this upwelling sector tend to confirm our estimates.”
From Competition between Baroclinic Instability and Ekman Transport under Varying Buoyancy Forcings in Upwelling Systems: An Idealized Analog to the Southern Ocean (2021) · cites this paper as Nagai et al. (2015)
Two estimations of the eddy cancellation strength in the California Current System can be drawn from Nagai et al. (2015) and Colas et al. (2013).
“Two estimations of the eddy cancellation strength in the California current system can be drawn from Nagai et al. (2015) and Colas et al. (2013).”
From Competition between Baroclinic Instability and Ekman Transport under Varying Buoyancy Forcings in Upwelling Systems: An Idealized Analog to the Southern Ocean (2021) · cites this paper as Nagai et al. (2015)
The two studies (Nagai et al. 2015 and Colas et al. 2013) use very similar numerical configurations.
“Note that the two studies use very similar numerical configurations.”
From Competition between Baroclinic Instability and Ekman Transport under Varying Buoyancy Forcings in Upwelling Systems: An Idealized Analog to the Southern Ocean (2021) · cites this paper as Nagai et al. (2015)
Counting streamfunction contours in Nagai et al. (2015) gives an annual mean eddy cancellation intensity of about 25% of the Ekman flow at 50-m depth and 100 km from shore for central California.
“Counting streamfunction contours in Figs.5a and 5b of Nagai et al. (2015) gives an annual mean eddy cancellation intensity ;2/8 5 25% of the Ekman flow at 50-m depth and 100 km from shore for central California.”
From Competition between Baroclinic Instability and Ekman Transport under Varying Buoyancy Forcings in Upwelling Systems: An Idealized Analog to the Southern Ocean (2021) · cites this paper as Nagai et al. (2015)
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References 80 · Cited by 163
- Authors
- Nagai, T., Gruber, N., Frenzel, H., Lachkar, Z., McWilliams, J. C., & Plattner, G.
- Affiliations
- Tokyo University of Marine Science and Technology (JP)
- ETH Zurich (CH)
- University of Washington (US)
- New York University Abu Dhabi (AE)
- University of California, Los Angeles (US)
- University of Bern (CH)
- Corresponding author
- Nagai, Takeyoshi
- ORCID
- Venue
- Journal of Geophysical Research: Oceans
- Publisher
- American Geophysical Union (AGU)
- Published
- 2015-08
- Volume
- 120
- Issue
- 8
- Pages
- 5318-5341
- ISSN
- 2169-9275 (ISSN-L)
- 2169-9291
- OpenAlex
- W2120904082
- Cited by
- 163
- References
- 80
- Citations by year
- 2026: 15 · 2025: 8 · 2024: 11 · 2023: 20 · 2022: 19 · 2021: 21 · 2020: 16 · 2019: 8 · 2018: 16 · 2017: 15 · 2016: 14
- FWCI
- 12.49
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Journal of Geophysical Research Oceans (publishedVersion)
- Funders
- JSPS (KAKENHI 24684036)
- “The Study of Kuroshio Ecosystem Dynamics for Sustainable Fisheries (SKED)”
- MEXT, and MIT-Hayashi Seed Fund
- NASA, U.S. NSF ITR
- Swiss National Science Foundation
- EU FP7 project CARBOCHANGE (264879)
- Topics
- Physical Sciences › Earth and Planetary Sciences › Oceanography › Oceanographic and Atmospheric Processes
- Physical Sciences › Earth and Planetary Sciences › Oceanography › Marine and coastal ecosystems
- Physical Sciences › Earth and Planetary Sciences › Atmospheric Science › Meteorological Phenomena and Simulations
- Keywords
- California Current System, coastal upwelling, mesoscale eddies, filaments, offshore transport, nutrient transport, organic matter transport, carbon export, Ekman transport, upwelling front, cyclonic eddies, anticyclonic eddies, Rossby waves, nitrate, coupled physical-biogeochemical modeling
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