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Abstract Eastern boundary upwelling systems (EBUSs) are among the most productive regions in the ocean because deep, nutrient‐rich waters are brought up to the surface. Previous studies have identified winds, mesoscale eddies and offshore nutrient distributions as key influences on the net primary production in EBUSs. However uncertainties remain regarding their roles in setting cross‐shore primary productivity and ecosystem diversity. Here, we use a quasi‐two‐dimensional (2D) model that combines ocean circulation with a spectrum of planktonic sizes to investigate the impact of winds, eddies, and offshore nutrient distributions in shaping EBUS ecosystems. A key finding is that variations in the strength of the wind stress and the nutrient concentration in the upwelled waters control the distribution and characteristics of the planktonic ecosystem. Specifically, a strengthening of the wind stress maximum, driving upwelling, increases the average planktonic size in the coastal upwelling zone, whereas the planktonic ecosystem is relatively insensitive to variations in the wind stress curl. Likewise, a deepening nutricline shifts the location of phytoplankton blooms shore‐ward, shoals the deep chlorophyll maximum offshore, and supports larger phytoplankton across the entire domain. Additionally, increased eddy stirring of nutrients suppresses coastal primary productivity via “eddy quenching,” whereas increased eddy restratification has relatively little impact on the coastal nutrient supply. These findings identify the wind stress maximum, isopycnal eddy diffusion, and nutricline depth as particularly influential on the coastal ecosystem, suggesting that variations in these quantities could help explain the observed differences between EBUSs, and influence the responses of EBUS ecosystems to climate shifts.
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This content will become publicly available on January 1, 2026
The Importance of Eddy Stirring in Wind-Driven Coastal Upwelling
Abstract Coastal upwelling systems play a key role in sustaining productive coastal ecosystems in the global ocean by transporting nutrients to surface waters. However, the fundamental mechanisms and pathways responsible for nutrient upwelling are not fully understood, largely due to the historically employed two-dimensional frameworks in which coastal upwelling systems have long been studied. Using both observations and idealized numerical simulations, we identify and quantify two primary routes of nutrient upwelling: the residual circulation, resulting from a significant cancellation between Eulerian-mean and eddy-induced circulations, and along-isopycnal eddy stirring. Our analysis demonstrates that their relative contributions depend on two distinct parameters: 1) the slope Burger number S, defined here as S=αN/f, whereαis the topographic slope angle and Nandfare the buoyancy and Coriolis frequencies, and 2) the surface nutrient uptake rate by biological activities. Specifically, we propose that wind forcing induces isopycnal tilting and surface outcropping, which creates favorable conditions for along-isopycnal nutrient gradients to develop in regions of strong biological activity at the surface. The magnitude of these gradients depends on both the slope Burger number S, which influences the strength of the residual circulation bringing nutrients from depths, and the surface biological uptake rate, which consumes nutrients. Our diagnostics provide insights into the intricate pathways for nutrient upwelling and underscore the significance of eddy stirring in coastal upwelling systems.
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- Award ID(s):
- 2343008
- PAR ID:
- 10581095
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of Physical Oceanography
- Volume:
- 55
- Issue:
- 1
- ISSN:
- 0022-3670
- Page Range / eLocation ID:
- 29 to 42
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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