Southern Ocean anthropogenic carbon sink constrained by sea surface salinity

• Published in: Science Advances
• Main Authors: Terhaar, Jens, Frölicher, Thomas, Joos, Fortunat
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Association for the Advancement of Science 2021
• Subjects: 530 Physics; Southern Ocean
• Online Access: https://boris.unibe.ch/156125/1/terhaar21sciadv_eabd5964.full.pdf; https://boris.unibe.ch/156125/

The ocean attenuates global warming by taking up about one quarter of global anthropogenic carbon emissions. Around 40% of this carbon sink is located in the Southern Ocean. However, Earth system models struggle to reproduce the Southern Ocean circulation and carbon fluxes. We identify a tight relationship across two multimodel ensembles between present-day sea surface salinity in the subtropical-polar frontal zone and the anthropogenic carbon sink in the Southern Ocean. Observations and model results constrain the cumulative Southern Ocean sink over 1850-2100 to 158 ± 6 petagrams of carbon under the low-emissions scenario Shared Socioeconomic Pathway 1-2.6 (SSP1-2.6) and to 279 ± 14 petagrams of carbon under the high-emissions scenario SSP5-8.5. The constrained anthropogenic carbon sink is 14 to 18% larger and 46 to 54% less uncertain than estimated by the unconstrained estimates. The identified constraint demonstrates the importance of the freshwater cycle for the Southern Ocean circulation and carbon cycle.