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Relative contributions of sinking and non-sinking carbon to the downward carbon flux
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  • Wei-Lei Wang,
  • Frederic Andre Corentin Le Moigne,
  • Robert T. Letscher,
  • Francois W. Primeau,
  • Jefferson Keith Moore
Wei-Lei Wang
UC Irvine

Corresponding Author:[email protected]

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Frederic Andre Corentin Le Moigne
Mediterranean Institute of Oceanography
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Robert T. Letscher
University of Hampshire
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Francois W. Primeau
University of California, Irvine
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Jefferson Keith Moore
University of California, Irvine
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The downward flux of organic carbon exported from the surface ocean is of great importance to the Earth’s climate because it represents the major pathway for transporting CO from the surface ocean and atmosphere into the deep ocean and sediments where it can be sequestered for a long time. Here we present global-scale estimates for the export fluxes of total, dissolved, and particulate organic carbon (TOC, DOC, and POC, respectively) constrained by observed thorium-234 (Th) activity and dissolved phosphorus (DIP) concentration in a global inverse biogeochemical model for the cycling of phosphorus and Th. We find that POC export flux is low in the subtropical oceans, indicating that a projected expansion of the subtropical gyres due to global warming will weaken the gravitational biological carbon pump. We also find that DOC export flux is low in the tropical oceans, intermediate in the upwelling Antarctic zone and subtropical south Pacific, and high in the subtropical Atlantic, subtropical north Pacific, and productive subantarctic zone (SAZ). The horizontal distribution of DOC export ratio (F/F) increases from tropical to polar regions, possibly due to the detrainment of DOC rich surface water during mixing events into subsurface waters (increasing the strength of the mixed layer pump poleward due to stronger seasonality). Large contribution to the export flux from DOC implies that the efficiency with which photosynthetically fixed carbon is exported as particles may not be as large as currently assumed by widely used global export algorithms.