EGU21-1834
https://doi.org/10.5194/egusphere-egu21-1834
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

The Southern Ocean carbon sink 1985-2018: first results of the RECCAP2 project

Judith Hauck1, Luke Gregor2, Cara Nissen1, Eric Mortenson3, Seth Bushinsky4, Scott Doney5, Nicolas Gruber2, Andrew Lenton3, Corinne LeQuere6, Matt Mazloff7, Pedro M. S. Monteiro8, and Lavinia Patara9
Judith Hauck et al.
  • 1Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung, Marine Biogeosciences, Bremerhaven, Germany (judith.hauck@awi.de)
  • 2Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, Zürich, Switzerland
  • 3CSIRO Oceans and Atmosphere, Hobart, Australia
  • 4Department of Oceanography, University of Hawai`i at Manoa, USA
  • 5Department of Environmental Sciences, University of Virginia, Charlottesville, VA, USA
  • 6School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TH, UK
  • 7Scripps Institution of Oceanography, La Jolla, CA, USA
  • 8CSIR-SOCCO, 15 Lwr Hope Rd., Rosebank, Cape Town 7700, South Africa
  • 9GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany

The Southern Ocean is the main gateway for anthropogenic CO2 into the ocean owing to the upwelling of old water masses with low anthropogenic CO2 concentration, and the transport of the newly equilibrated surface waters into the ocean interior through intermediate, deep and bottom water formation. Here we present first results of the Southern Ocean chapter of RECCAP2, which is the Global Carbon Project’s second systematic study on Regional Carbon Cycle Assessment and Processes. In the Southern Ocean chapter, we aim to assess the Southern Ocean carbon sink 1985-2018 from a wide range of available models and data sets, and to identify patterns of regional and temporal variability, model limitations and future challenges.

We gathered global and regional estimates of the air-sea CO2 flux over the period 1985-2018 from global ocean biogeochemical models, surface pCO2-based data products, and data-assimilated models. The analysis on the Southern Ocean quantified geographical patterns in the annual mean and seasonal amplitude of air-sea CO2 flux, with results presented here aggregated to the level of large-scale ocean biomes.

Considering the suite of observed and modelled estimates, we found that the subtropical seasonally stratified (STSS) biome stands out with the largest air-sea CO2 flux per area and a seasonal cycle with largest ocean uptake of CO2 in winter, whereas the ice (ICE) biome is characterized by a large ensemble spread and a pronounced seasonal cycle with the largest ocean uptake of CO2 in summer. Connecting these two, the subpolar seasonally stratified (SPSS) biome has intermediate flux densities (flux per area), and most models have difficulties simulating the seasonal cycle with strongest uptake during the summer months.

Our analysis also reveals distinct differences between the Atlantic, Pacific and Indian sectors of the aforementioned biomes. In the STSS, the Indian sector contributes most to the ocean carbon sink, followed by the Atlantic and then Pacific sectors. This hierarchy is less pronounced in the models than in the data-products. In the SPSS, only the Atlantic sector exhibits net CO2 uptake in all years, likely linked to strong biological production. In the ICE biome, the Atlantic and Pacific sectors take up more CO2 than the Indian sector, suggesting a potential role of the Weddell and Ross Gyres.

These first results confirm the global relevance of the Southern Ocean carbon sink and highlight the strong regional and interannual variability of the Southern Ocean carbon uptake in connection to physical and biogeochemical processes.

How to cite: Hauck, J., Gregor, L., Nissen, C., Mortenson, E., Bushinsky, S., Doney, S., Gruber, N., Lenton, A., LeQuere, C., Mazloff, M., Monteiro, P. M. S., and Patara, L.: The Southern Ocean carbon sink 1985-2018: first results of the RECCAP2 project, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1834, https://doi.org/10.5194/egusphere-egu21-1834, 2021.

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