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How the source depth of coastal upwelling relates to stratification and wind
  • Jing He,
  • Amala Mahadevan
Jing He
Massachusetts Institute of Technology

Corresponding Author:jinghe@mit.edu

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Amala Mahadevan
Woods Hole Oceanographic Institute
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Wind-driven coastal upwelling is an important process that transports nutrients from the deep ocean to the surface, fueling biological productivity. To better understand what affects the upward transport of nutrients (and many other properties such as temperature, salinity, oxygen, and carbon), it is necessary to know the depth of source waters (i.e. “source depth’) or the density of source waters (“source density’). Here, we focus on the upwelling driven by offshore Ekman transport and present a scaling relation for the source depth and density by considering a balance between the wind-driven upwelling and eddy-driven restratification processes. The scaling suggests that the source depth varies as $(\tau/N)^{1/2}$, while the source density goes as $(\tau^{1/2} N^{3/2})$. We test these relations using numerical simulations of an idealized coastal upwelling front with varying constant wind forcing and initial vertically-uniform stratification, and we find good agreement between the theory and numerical experiments. This highlights the importance of considering stratification in wind-driven upwelling dynamics, especially when thinking about how nutrient transport and primary production of coastal upwelling regions might change with increased ocean warming and stratification.
Dec 2021Published in Journal of Geophysical Research: Oceans volume 126 issue 12. 10.1029/2021JC017621