Year: 2025
Type: article
Abstract: The Southern Ocean critically mitigates global surface warming by taking up a large portion of the carbon released to the climate system by human activities. While models suggest this carbon sink should weaken with human-induced climate change due to an increased upwelling of carbon-rich deep water, such a strong decline has not been observed over the past decades. Here, using circumpolar hydrographic observations, we reveal that the freshening of the Southern Ocean since the 1990s has prevented the weakening of its carbon sink by trapping the upwelled carbon-rich deep water in the subsurface. The enhanced density stratification has prevented these CO2-enriched waters from reaching the surface, and, thus hindered a saturation of the carbon sink in this period. Meanwhile, the surface layer became thinner, allowing the CO2-rich circumpolar deep water to get closer to the surface, replacing winter water between 100 and 200 m. In this layer, the CO2 fugacity increased by ~ 10 µatm since the 1990s. Consequently, our findings imply that the model-predicted weakening of the Southern Ocean carbon sink has been delayed by the surface freshening and might emerge when the stratification weakens.
Source: Nature Climate Change
Authors: Léa Olivier, F. Alexander Haumann
Language: English
Subfield: Oceanography
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $12,690
Awards: G1058552491, G5253141131
OpenAlex ID: W4415300688