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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-352
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-352
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 09 Sep 2019

Submitted as: research article | 09 Sep 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Coccolithophore biodiversity controls carbonate export in the Southern Ocean

Andrés S. Rigual Hernández1, Thomas W. Trull2,3, Scott D. Nodder4, José A. Flores1, Helen Bostock4,5, Fátima Abrantes6,7, Ruth S. Eriksen2,8, Francisco J. Sierro1, Diana M. Davies2,3, Anne-Marie Ballegeer9, Miguel A. Fuertes9, and Lisa C. Northcote4 Andrés S. Rigual Hernández et al.
  • 1Área de Paleontología, Departamento de Geología, Universidad de Salamanca, 370085 Salamanca, Spain
  • 2CSIRO Oceans and Atmosphere Flagship, Hobart, Tasmania 7001, Australia
  • 3Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, Tasmania 7001, Australia
  • 4National Institute of Water and Atmospheric Research, Wellington 6021, New Zealand
  • 5University of Queensland, Brisbane, Queensland 4072, Australia
  • 6Portuguese Institute for Sea and Atmosphere (IPMA), Divisão de Geologia Marinha (DivGM), Rua Alferedo Magalhães Ramalho 6, Lisboa, Portugal
  • 7CCMAR, Centro de Ciências do Mar, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
  • 8Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 129, Hobart, Tasmania 7001, Australia
  • 9Departamento de Didáctica de las Matemáticas y de las Ciencias Experimentales, Universidad de Salamanca, 37008 Salamanca, Spain

Abstract. Southern Ocean waters are projected to undergo profound changes in their physical and chemical properties in the coming decades. Coccolithophore blooms in the Southern Ocean are thought to account for a major fraction of the global marine calcium carbonate (CaCO3) production and export to the deep sea. Therefore, changes in the composition and abundance of Southern Ocean coccolithophore populations are likely to alter the marine carbon cycle, with feedbacks to the rate of global climate change. However, the contribution of coccolithophores to CaCO3 export in the Southern Ocean is uncertain, particularly in the circumpolar Subantarctic Zone that represents about half of the areal extent of the Southern Ocean and where coccolithophores are most abundant. Here, we present measurements of annual CaCO3 flux and quantitatively partition them amongst coccolithophore species and heterotrophic calcifiers at two sites representative of a large portion of the Subantarctic Zone. We find that coccolithophores account for a major fraction of the annual CaCO3 export with highest contributions in waters with low algal biomass accumulations. Notably, our analysis reveals that although Emiliania huxleyi is an important vector for CaCO3 export to the deep sea, less abundant but larger species account for most of the annual coccolithophore CaCO3 flux. This observation contrasts with satellite remote sensing images that mostly reflect E. huxleyi blooms as a result of its higher cell abundance and detachment of its relatively small liths. It appears likely that the climate-induced migration of oceanic fronts will initially result in the poleward expansion of large coccolithophore species increasing CaCO3 production. However, subantarctic coccolithophore populations will eventually diminish as acidification overwhelms those changes. Overall, our analysis emphasizes the need for species-centred studies to improve our ability to project future changes in phytoplankton communities and their influence on marine biogeochemical cycles.

Andrés S. Rigual Hernández et al.
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Andrés S. Rigual Hernández et al.
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Short summary
Coccolithophores account for a major fraction of the carbonate produced in the world's oceans. However, their contribution in the subantarctic Southern Ocean remains undocumented. We quantitatively partition calcium carbonate fluxes amongst coccolithophore species in the Australian-New Zealand sector of the Southern Ocean. We provide new insights into the importance of species other than Emiliania huxleyi in the carbon cycle and assess their possible response to projected environmental change.
Coccolithophores account for a major fraction of the carbonate produced in the world's oceans....
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