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

Le Quéré, C; Buitenhuis, ET; Moriarty, R; Alvain, S; Aumont, O; Bopp, L; Chollet, S; Enright, C; Franklin, DJ; Geider, RJ; Harrison, SP; Hirst, AG; Larsen, S; Legendre, L; Platt, T; Prentice, IC; Rivkin, RB; Sathyendranath, S; Stephens, N; Vogt, M; Sailley, SF; Vallina, SM. 2015 Role of zooplankton dynamics for Southern Ocean phytoplankton biomass and global biogeochemical cycles. Biogeosciences Discussions, 12 (14). 11935-11985. 10.5194/bgd-12-11935-2015 (Submitted)

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Official URL: http://dx.doi.org/10.5194/bgd-12-11935-2015

Abstract/Summary

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 bacteria. We improved the representation of zooplankton dynamics in our model through (a) the explicit inclusion of large, slow-growing zooplankton, 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 represent crustacean macrozooplankton grazing, they systematically overestimate Southern Ocean chlorophyll biomass during the summer, even when there was no iron deposition from dust. When model simulations included the developments of the zooplankton component, the simulation of phytoplankton biomass improved and the high chlorophyll summer bias in the Southern Ocean HNLC region largely disappeared. 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 rather than iron limitation. 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: Publication - Article
Subjects: Earth Sciences
Marine Sciences
Oceanography
Divisions: Plymouth Marine Laboratory > Science Areas > Marine Ecosystem Models and Predictions
Depositing User: Sevrine Sailley
Date made live: 29 Mar 2016 10:41
Last Modified: 06 Jun 2017 16:15
URI: http://plymsea.ac.uk/id/eprint/6923

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