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Impact of Spatial Variability in Zooplankton Grazing Rates on Carbon Export Flux

Published version
Peer-reviewed

Repository DOI


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Abstract

jats:titleAbstract</jats:title>jats:pThe 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 parameterized greatly influences biomass and subsequent carbon export estimates. The half‐saturation constant, or jats:italick</jats:italic> value, is central to the Holling functional response. Empirical studies show jats:italick</jats:italic> 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 jats:italick</jats:italic>. The impact of these spatially varying jats:italick</jats:italic> values on model skill and carbon export flux estimates is then considered. This study finds large spatial variation in jats:italick</jats:italic> 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 parameterization is found to be critical in reproducing satellite‐derived distributions of small phytoplankton 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 fecal 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 modeling marine carbon sequestration under future climate scenarios.</jats:p>

Description

Publication status: Published

Keywords

Journal Title

Global Biogeochemical Cycles

Conference Name

Journal ISSN

0886-6236
1944-9224

Volume Title

38

Publisher

American Geophysical Union (AGU)
Sponsorship
Natural Environment Research Council (NE/S007164/1, NE/P018319/1)
National Oceanic and Atmospheric Administration (NA20OAR4310438, NA20OAR4310441, NA20OAR43‐10442)
Australian Government (DE240100115)
ONR (N00014‐22‐1‐2082)