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Impact of spatial variability in zooplankton grazing rates on carbon export flux
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  • Sophie Alexandra Meyjes,
  • Colleen M Petrik,
  • Tyler Weaver Rohr,
  • B. B. Cael,
  • Ali Mashayek
Sophie Alexandra Meyjes
University of Cambridge

Corresponding Author:[email protected]

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Colleen M Petrik
UC San Diego
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Tyler Weaver Rohr
University of Tasmania
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B. B. Cael
National Oceanography Centre
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Ali Mashayek
University of Cambridge
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The biological carbon pump is a key controller of how much carbon is stored within the global ocean. This pathway is influenced by food web interactions between zooplankton and their prey. In global biogeochemical models, Holling Type functional responses are frequently used to represent grazing interactions. How these responses are parameterised greatly influences biomass and subsequent carbon export estimates. The half-saturation constant, or k value, is central to the Holling functional response. Empirical studies show k can vary over three orders of magnitude, however, this variation is poorly represented in global models. This study derives zooplankton grazing dynamics from remote sensing products of phytoplankton biomass, resulting in global distribution maps of the grazing parameter k. The impact of these spatially varying k values on model skill and carbon export flux estimates is then considered. This study finds large spatial variation in k values across the global ocean, with distinct distributions for micro- and mesozooplankton. High half-saturation constants, which drive slower grazing, are generally associated with areas of high productivity. Grazing rate parameterisation is found to be critical in reproducing satellite-derived distributions of nanophytoplankton biomass, highlighting the importance of top-down drivers for this size class. Spatially varying grazing dynamics decrease mean total carbon export by >17% compared to globally homogeneous dynamics, with increases in faecal pellet export and decreases in export from algal aggregates. This study highlights the importance of grazing dynamics to both community structure and carbon export, with implications for modelling marine carbon sequestration under future climate scenarios.
02 Jan 2024Submitted to ESS Open Archive
03 Jan 2024Published in ESS Open Archive