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The Southern Ocean carbon cycle 1985-2018: Mean, seasonal cycle, trends and storage
  • +11
  • Judith Hauck,
  • Luke Gregor,
  • Cara Nissen,
  • Lavinia Patara,
  • Mark Hague,
  • Precious Mongwe,
  • Seth M Bushinsky,
  • Scott C. Doney,
  • Nicolas Gruber,
  • Corinne Le Quéré,
  • Manfredi Manizza,
  • Matthew R. Mazloff,
  • Pedro M. S. Monteiro,
  • Jens Terhaar
Judith Hauck
Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research

Corresponding Author:[email protected]

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Luke Gregor
ETH Zurich
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Cara Nissen
University of Colorado Boulder
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Lavinia Patara
GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel
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Mark Hague
Environmental Physics, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zuric
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Precious Mongwe
Council for Scientific and Industrial Research (CSIR)
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Seth M Bushinsky
University of Hawaiʻi at Mānoa
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Scott C. Doney
University of Virginia
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Nicolas Gruber
ETH Zürich
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Corinne Le Quéré
School of Environmental Sciences, University of East Anglia, UK
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Manfredi Manizza
Scripps Institution of Oceanography
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Matthew R. Mazloff
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Pedro M. S. Monteiro
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Jens Terhaar
Climate and Environmental Physics - University of Bern
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We assess the Southern Ocean CO2 uptake (1985-2018) using data sets gathered in the REgional Carbon Cycle Assessment and Processes Project phase 2 (RECCAP2). The Southern Ocean acted as a sink for CO2 with close agreement between simulation results from global ocean biogeochemistry models (GOBMs, 0.75±0.28 PgCyr-1) and pCO2-observation-based products (0.73±0.07 PgCyr-1). This sink is only half that reported by RECCAP1. The present-day net uptake is to first order a response to rising atmospheric CO2, driving large amounts of anthropogenic CO2 (Cant) into the ocean, thereby overcompensating the loss of natural CO2 to the atmosphere. An apparent knowledge gap is the increase of the sink since 2000, with pCO2-products suggesting a growth that is more than twice as strong and uncertain as that of GOBMs (0.26±0.06 and 0.11±0.03 PgCyr-1 decade-1 respectively). This is despite nearly identical pCO2 trends in GOBMs and pCO2-products when both products are compared only at the locations where pCO2 was measured. Seasonal analyses revealed agreement in driving processes in winter with uncertainty in the magnitude of outgassing, whereas discrepancies are more fundamental in summer, when GOBMs exhibit difficulties in simulating the effects of the non-thermal processes of biology and mixing/circulation. Ocean interior accumulation of Cant points to an underestimate of Cant uptake and storage in GOBMs. Future work needs to link surface fluxes and interior ocean transport, build long overdue systematic observation networks and push towards better process understanding of drivers of the carbon cycle.
23 May 2023Submitted to ESS Open Archive
25 May 2023Published in ESS Open Archive