Role of zooplankton dynamics for Southern Ocean phytoplankton biomass and global biogeochemical cycles

Le Quéré, Corinne ORCID: https://orcid.org/0000-0003-2319-0452, Buitenhuis, Erik T. ORCID: https://orcid.org/0000-0001-6274-5583, Moriarty, Róisín, Alvain, Séverine, Aumont, Olivier, Bopp, Laurent, Chollet, Sophie, Enright, Clare, Franklin, Daniel J., Geider, Richard J., Harrison, Sandy P., Hirst, Andrew G., Larsen, Stuart, Legendre, Louis, Platt, Trevor, Prentice, I. Colin, Rivkin, Richard B., Sailley, Sévrine, Sathyendranath, Shubha, Stephens, Nick, Vogt, Meike and Vallina, Sergio M. (2016) Role of zooplankton dynamics for Southern Ocean phytoplankton biomass and global biogeochemical cycles. Biogeosciences, 13. pp. 4111-4133. ISSN 1726-4189

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Abstract

Global ocean biogeochemistry models currently employed in climate change projections use highly simplified representations of pelagic food webs. These food webs do not necessarily include critical pathways by which ecosystems interact with ocean biogeochemistry and climate. Here we present a global biogeochemical model which incorporates ecosystem dynamics based on the representation of ten plankton functional types (PFTs): six types of phytoplankton, three types of zooplankton, and heterotrophic procaryotes. We improved the representation of zooplankton dynamics in our model through (a) the explicit inclusion of large, slow-growing macrozooplankton (e.g. krill), and (b) the introduction of trophic cascades among the three zooplankton types. We use the model to quantitatively assess the relative roles of iron vs. grazing in determining phytoplankton biomass in the Southern Ocean high-nutrient low-chlorophyll (HNLC) region during summer. When model simulations do not include macrozooplankton grazing explicitly, they systematically overestimate Southern Ocean chlorophyll biomass during the summer, even when there is no iron deposition from dust. When model simulations include a slow-growing macrozooplankton and trophic cascades among three zooplankton types, the high-chlorophyll summer bias in the Southern Ocean HNLC region largely disappears. Our model results suggest that the observed low phytoplankton biomass in the Southern Ocean during summer is primarily explained by the dynamics of the Southern Ocean zooplankton community, despite iron limitation of phytoplankton community growth rates. This result has implications for the representation of global biogeochemical cycles in models as zooplankton faecal pellets sink rapidly and partly control the carbon export to the intermediate and deep ocean.

Item Type: Article
Uncontrolled Keywords: sdg 13 - climate action,sdg 14 - life below water ,/dk/atira/pure/sustainabledevelopmentgoals/climate_action
Faculty \ School: Faculty of Science > School of Environmental Sciences
Faculty of Science
University of East Anglia Research Groups/Centres > Theme - ClimateUEA
UEA Research Groups: Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences
University of East Anglia Schools > Faculty of Science > Tyndall Centre for Climate Change Research
Faculty of Science > Research Centres > Tyndall Centre for Climate Change Research
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Depositing User: Pure Connector
Date Deposited: 24 Sep 2016 00:06
Last Modified: 13 Apr 2023 13:49
URI: https://ueaeprints.uea.ac.uk/id/eprint/59829
DOI: 10.5194/bg-13-4111-2016

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