Varied contribution of the Southern Ocean to deglacial atmospheric CO2 rise

Abstract

Glacial–interglacial changes in atmospheric CO2 are generally attributed to changes in seawater carbon chemistry in response to large-scale shifts in the ocean’s biogeochemistry and general circulation. The Southern Ocean currently takes up more CO2 than any other and it is likely to have played a crucial role in regulating past atmospheric CO2. However, the physical, biological and chemical variables that control ocean–atmosphere CO2 exchange during glacial–interglacial cycles are not completely understood. Here we use boron isotopes and carbon isotopes in planktonic foraminifera and an alkenone-based proxy of temperature to reconstruct seawater pH and CO2 partial pressure in sub-Antarctic surface waters south of Tasmania over the past 25,000 years, and investigate the mechanisms that regulate seawater CO2. The new record shows that surface waters in this region were a sink for atmospheric CO2 during the Last Glacial Maximum. Our reconstruction suggests changes in the strength of the biological pump and the release of deep-ocean CO2 to surface waters contributed to the last deglacial rise in atmospheric CO2. These findings demonstrate that variations in upwelling intensity and the distribution of Southern Ocean water masses in this sector played a key role in regulating atmospheric CO2 during the last glacial–interglacial cycle.

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Fig. 1: Location of sediment core MD972106 and modern positions of the Southern Ocean water masses and fronts.
Fig. 2: δ18O, δ13C, shell weight and δ11B for the planktonic foraminifer, G. bulloides and SST estimates from alkenones in sediment core MD972106.
Fig. 3: Reconstructed surface water pH and \(p_{{\rm{CO}}_2}\) at the MD972106 site and atmospheric CO2 over the past 25,000 years.
Fig. 4: Planktonic and benthic foraminiferal δ13C, Δδ13C gradient, alkenone concentrations and \(\Delta p_{{\rm{CO}}_2}\) over the past 25,000 years.
Fig. 5: Reconstructed surface water carbonate ion concentration.

Data availability

All data are archived at the Australian Antarctic Data Centre (https://data.aad.gov.au/) and are publicly accessible at https://doi.org/10.26179/5d5df822acf6c.

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Acknowledgements

This work was supported by the Australian Antarctic Division (AAS 4061) and the Australian Government’s Cooperative Research Centres Programme through the Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC). The boron isotope analyses were supported by the European Union 5th Framework Programme project 6C (Project ID: EVK2-CT-2002-00135 6 C). E.C. and C.P. acknowledge Graham Logan and Geoscience Australia for providing analytical facilities for alkenone analyses. We thank the French Polar Institute and the crew of the RV Marion Dufresne for their efforts in recovering sediment core MD972106.

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A.D.M. and W.R.H. designed the study with input from M.R.P. and J.B. The manuscript was written by A.D.M., W.R.H., M.R.P. and J.B. with contributions from M.J.C., E.C., C.P., M.K.G. and T.B.C. Analysis and interpretation of the measurements were completed by A.D.M., W.R.H., M.R.P., J.B., M.J.C., E.C., C.P., M.K.G. and T.B.C. All authors contributed to improving the final manuscript.

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Correspondence to Andrew D. Moy.

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Moy, A.D., Palmer, M.R., Howard, W.R. et al. Varied contribution of the Southern Ocean to deglacial atmospheric CO2 rise. Nat. Geosci. 12, 1006–1011 (2019). https://doi.org/10.1038/s41561-019-0473-9

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