Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 13, 4111-4133, 2016
https://doi.org/10.5194/bg-13-4111-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
18 Jul 2016
Role of zooplankton dynamics for Southern Ocean phytoplankton biomass and global biogeochemical cycles
Corinne Le Quéré1, Erik T. Buitenhuis1, Róisín Moriarty1, Séverine Alvain2, Olivier Aumont3, Laurent Bopp4, Sophie Chollet5, Clare Enright1, Daniel J. Franklin6, Richard J. Geider7, Sandy P. Harrison8, Andrew G. Hirst9,10, Stuart Larsen11, Louis Legendre12, Trevor Platt13, I. Colin Prentice14, Richard B. Rivkin15, Sévrine Sailley13, Shubha Sathyendranath13, Nick Stephens13, Meike Vogt16, and Sergio M. Vallina17 1Tyndall Centre for Climate Change Research, School of Environmental Sciences, University of East Anglia, Norwich Research Park, NR4 7TJ, Norwich, UK
2Laboratoire d'Océanologie et de Géosciences – UMR LOG 8187, Université Lille Nord de France, BP 8062930 Wimereux, France
3Laboratoire d'Océanographie et de Climatologie: Expérimentation et Approches Numériques, IRD/IPSL, Plouzané, France
4Lab. des Sciences du Climat et de l'Environnement, Orme des Merisiers, Bat. 709, 91191 Gif-sur-Yvette, France
5School of Environmental Sciences, University of East Anglia, Norwich Research Park, NR4 7TJ, Norwich, UK
6Faculty of Science & Technology, Bournemouth University, Talbot Campus, Poole, BH12 5BB, UK
7School of Biological Sciences, University of Essex, Colchester CO4 3SQ, UK
8Department of Biological Sciences, Macquarie University, North Ryde, NSW 2109, Australia and School of Archaeology, Geography and Environmental Sciences (SAGES), University of Reading, Whiteknights, Reading, RG6 6AB, UK
9School of Biological and Chemical Sciences, Queen Mary University of London, London, E1 4NS, UK
10Centre for Ocean Life, National Institute for Aquatic Resources, Technical University of Denmark, Kavalergården 6, 2920 Charlottenlund, Denmark
11Norwegian Institute of Marine Research, Nye Flødevigveien 20, His, 4817, Norway
12Sorbonne Universités, UPMC Univ Paris 06, CNRS, Laboratoire d'Océanographie de Villefranche (LOV), Observatoire océanologique, 181 Chemin du Lazaret, 06230, Villefranche-sur-Mer, France
13Plymouth Marine Laboratory, Prospect Place, Plymouth, PL1 3DH, UK
14AXA Chair of Biosphere and Climate Impacts, Grand Challenges in Ecosystems and the Environment and Grantham Institute – Climate Change and the Environment, Department of Life Sciences, Silwood Park Campus, Buckhurst Road, Ascot, SL5 7PY, UK
15Department of Ocean Sciences, Memorial University of Newfoundland, St. John's, NL A1C 5S7 Canada
16Institute for Biogeochemistry and Pollutant Dynamics, ETH Zürich, Universitätsstraße 16, 8092 Zürich, Switzerland
17Institute of marine Sciences (CSIC), Department Marine Biology and Oceanography, 08003 Barcelona, Spain
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.

Citation: Le Quéré, C., Buitenhuis, E. T., Moriarty, R., Alvain, S., Aumont, O., Bopp, L., Chollet, S., Enright, C., Franklin, D. J., Geider, R. J., Harrison, S. P., Hirst, A. G., Larsen, S., Legendre, L., Platt, T., Prentice, I. C., Rivkin, R. B., Sailley, S., Sathyendranath, S., Stephens, N., Vogt, M., and Vallina, S. M.: Role of zooplankton dynamics for Southern Ocean phytoplankton biomass and global biogeochemical cycles, Biogeosciences, 13, 4111-4133, https://doi.org/10.5194/bg-13-4111-2016, 2016.
Publications Copernicus
Download
Short summary
We present a global biogeochemical model which incorporates ecosystem dynamics based on the representation of ten plankton functional types, and use the model to assess the relative roles of iron vs. grazing in determining phytoplankton biomass in the Southern Ocean. Our results suggest that 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 growth.
We present a global biogeochemical model which incorporates ecosystem dynamics based on the...
Share