Nature Communications, 14 June 2022

Increased ice loss appears to be reducing the Southern Ocean’s ability to absorb and store atmospheric carbon. The surface waters surrounding Antarctica have been absorbing much of human CO2 emissions from the atmosphere, sequestering the carbon in deep ocean layers. This has slowed the increase in atmospheric CO2 concentrations and related atmospheric warming. Rising global temperatures have however increased the flow of warm ocean water onto the Antarctic continental shelf. This accelerates glacial ice loss, reduces the formation of sea ice, and decreases the production of dense water in key regions such as the Weddell Sea in West Antarctica. All these factors slow the movement of carbon-rich surface waters into deep ocean layers, preventing long-term carbon storage. Under a high emissions scenario, reduced deep layer circulation in the Southern Ocean will greatly decrease its capacity for additional carbon storage by the end of this century. The Southern Ocean is one of the Earth’s most important carbon sinks; it has absorbed 40% of anthropogenic carbon dioxide emissions taken up by global oceans, as well as 75% of human-created excess heat. Authors underscore the importance of reducing emissions to avoid sudden system shifts in Southern Ocean circulation, maintain the stability of the West Antarctic Ice Sheet and related sea-level rise, and curb the long-term trajectory of climate change.