Article Dans Une Revue Biogeosciences Année : 2016

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

Sophie Chollet
  • Fonction : Auteur
Clare Enright
  • Fonction : Auteur
Daniel J. Franklin
  • Fonction : Auteur
Andrew G. Hirst
  • Fonction : Auteur
Stuart Larsen
  • Fonction : Auteur
Louis Legendre
Trevor Platt
  • Fonction : Auteur
Ian C. Prentice
  • Fonction : Auteur
Nick Stephens
  • Fonction : Auteur

Résumé

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. Herewe 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 zooplanktondynamics 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 lowchlorophyll (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 thereis 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 lowphytoplankton 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 biogeochemicalcycles in models as zooplankton faecal pellets sink rapidly and partly control the carbon export to the intermediate and deep ocean.

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hal-01504558 , version 1 (27-10-2020)

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Corinne Le Quéré, Erik T. Buitenhuis, Róisín Moriarty, Séverine Alvain, Olivier Aumont, et al.. Role of zooplankton dynamics for Southern Ocean phytoplankton biomass and global biogeochemical cycles. Biogeosciences, 2016, 13 (14), pp.4111 - 4133. ⟨10.5194/bg-13-4111-2016⟩. ⟨hal-01504558⟩
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