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Size-differentiated Export Flux in Different Dynamical Regimes in the Ocean
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  • Mathieu Dever,
  • D Nicholson,
  • M M Omand,
  • A Mahadevan
Mathieu Dever
Wood Hole Oceanographic Institution

Corresponding Author:[email protected]

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D Nicholson
Woods Hole Oceanographic Institution
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M M Omand
University of Rhode Island
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A Mahadevan
Woods Hole Oceanographic Institution
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Export of Particulate Organic Carbon (POC) is mainly driven by gravitational sinking. Thus, traditionally, it is thought that larger, faster-sinking particles make up most of the POC export flux. However, this need not be the case for particles whose sinking speeds are comparable to the vertical velocities of a dynamic flow field that can influence the descent rate of particles. Particles with different settling speeds are released in two process-oriented model simulations of an upper ocean eddying flow in the Northeast Pacific to evaluate the impact of (1) ocean dynamics on the respective contribution of the different sinking-velocity classes to POC export, and (2) the particle number size-spectrum slope. The analysis reveals that the leading export mechanism changes from gravitationally-driven to advectively-driven as submesoscale dynamics become more active in the region. The vertical velocity associated with submesoscale dynamics enhances the contribution of slower-sinking particles to POC export flux by a factor ranging from 3 to 10, especially where the relative abundance of small particles is large, (i.e., steep particle size-spectrum slope). Remineralization generally decreases the total amount of biomass exported, but its impact is weaker in dynamical regimes where submesoscale dynamics are present and export is advectively-driven.
Mar 2021Published in Global Biogeochemical Cycles volume 35 issue 3. 10.1029/2020GB006764