Antarctic melting disrupts global ocean circulation

If it seemed to have weathered climate change for so long, Antarctica’s ice is now being hit harder and harder. An obvious consequence of the melting of glaciers in Antarctica is sea level rise. But the freshwater supply from this melt will also perturb local and global ocean circulation, as evidenced by the latest work by Qian Li, of the Massachusetts Institute of Technology (MIT), in the US, and colleagues.

The planet’s oceans pass large, interconnected currents that transport heat and nutrients as well as gases such as oxygen and carbon dioxide. This ocean circulation plays an important role in climate regulation and allows the oceans to absorb most (93%) of the additional heat energy trapped in the atmosphere due to the increased concentration of greenhouse gases. One such current forms in the Southern Ocean, off Antarctica. Closer to the continent, this cold current becomes more intense (because its salinity increases during the formation of pack ice, which rejects the salt contained in sea water) and sinks along the continental slope, to a depth of more than 4,000 meters. Then it moves away from the mainland, refreshing the waters of the abyssal plain.

But the rise in temperatures in the southern abyss for several years suggests that this dynamic is disturbed. To shed light on this question, Qian Li and colleagues used a computer model that represents ocean circulation in this region of the globe and ran two simulations: one integrating measured data over the period 1991-2019, and the other integrating data estimated for the period 2020-2050 in the case of greenhouse gas emissions in general. big. Their model specifically takes into account the effect of melting Antarctic ice.

The first simulation results are consistent with historical measurements of ocean circulation. In the second simulation, the researchers observed a slowdown in the formation and sinking of the thick cold water current at the level of the Antarctic continental shelf. They also found Warming of the southern abyssal waters consistent with observations that do not appear when meltwater is not taken into account.

According to the researchers, this slowdown would be driven by fresh water from melting ice in Antarctica, which reduces salinity and thus the density of cold water that sinks along the continental slope into the abyss. Thus, this deceleration is slowing down — something Qian Li and colleagues observed in their model of Abyss of 2030.

The researchers’ model predicts that with increased ice melt associated with climate change, the slowing of this downward cold water current could reach 42% by 2050. With consequences on a global scale: reduced capacity of the ocean to store carbon dioxide, limited nutrient supply to certain ecosystems, And even modify the distribution of precipitation in the tropics.