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Constraining the ocean’s biological pump with in situ optical observations and supervised learning. Part 2: Carbon Flux
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  • Daniel J Clements,
  • Simon Yang,
  • Thomas Weber,
  • Andrew Mcdonnell,
  • Rainer Kiko,
  • Lars Stemmann,
  • Daniele Bianchi
Daniel J Clements
University of California, Los Angeles, University of California, Los Angeles, University of California, Los Angeles

Corresponding Author:[email protected]

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Simon Yang
University of California Los Angeles, University of California Los Angeles, University of California Los Angeles
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Thomas Weber
University of Rochester, University of Rochester, University of Rochester
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Andrew Mcdonnell
University of Alaska Fairbanks, University of Alaska Fairbanks, University of Alaska Fairbanks
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Rainer Kiko
Sorbonne Université, Sorbonne Université, Sorbonne Université
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Lars Stemmann
Sorbonne Université, Sorbonne Université, Sorbonne Université
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Daniele Bianchi
University of California Los Angeles, University of California Los Angeles, University of California Los Angeles
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Abstract

Export of sinking particles from the surface ocean is critical for carbon sequestration and for providing energy to the deep-ocean biosphere. The magnitude and spatial patterns of this flux have been estimated in the past by in situ flux observations, satellite-based algorithms, and ocean biogeochemical models; however, these estimates remain uncertain. Here, we use a novel machine learning reconstruction of global in situ ocean particle size spectra from Underwater Vision Profiler 5 (UVP5) measurements, to determine particulate carbon fluxes. We combine global maps of particle size distribution parameters for large sinking particles with observationally-constrained empirical relationships to calculate the sinking carbon flux from the euphotic zone and the wintertime mixed layer depth. Our flux reconstructions are comparable to prior estimates, but suggest a less variable seasonal cycle in the tropical ocean, and a more persistent export in the Southern Ocean than previously thought. Because our estimates are not bounded by a specific depth horizon, we reconstruct export at multiple depths, and find that export from the wintertime mixed layer globally exceeds that from the euphotic zone. Our estimates provide a baseline for more accurate understanding of particle cycles in the ocean, and open the way to fully three-dimensional global reconstructions of particle size spectra and fluxes in the ocean, supported by the growing database of optical observations.