Deep Ocean Currents Slowing Earlier than Predicted in Southern Ocean

Nature Climate Change, 25 May 2023

In a major basin south of Australia, increased meltwater runoff from Antarctica has decreased deep ocean oxygen levels and slowed overturning circulation by one-third over the past three decades. This region serves as an early-warning signal for global deep ocean changes due to its downstream position from the Antarctic ice sheet. Melting of the ice sheet releases freshwater into the surrounding ocean. This “freshening” reduces the formation of cold, oxygen-rich bottom water that flows off the continental shelf and sinks to the sea floor before rising thousands of kilometers away. Antarctic bottom water powers a global network of ocean currents that redistribute heat, carbon and nutrients around the world. Researchers found that slowing of this overturning, that was predicted to occur by 2050, already is under way today. This will have widespread consequences well beyond the Southern Hemisphere. The study underscores the sensitivity of Antarctic bottom water to influxes of freshwater from the melting of Antarctica. Reducing greenhouse gas emissions is essential to prevent additional ice sheet loss; limit freshening along the Antarctic continental shelf; and maintain stable ocean currents, weather patterns, and nutrient-rich marine environments across the globe.

https://www.nature.com/articles/s41558-023-01667-8