Jean-Pascal Van Ypersele

For decades, the surface of the polar Southern Ocean (south of 50°S) has been freshening—an expected response to a warming climate. This freshening enhanced upper-ocean stratification, reducing the upward transport of subsurface heat and possibly contributing to sea ice expansion. It also limited the formation of open-ocean polynyas. Using satellite observations, we reveal a marked increase in surface salinity across the circumpolar Southern Ocean since 2015. This shift has weakened upper-ocean stratification, coinciding with a dramatic decline in Antarctic sea ice coverage. Additionally, rising salinity facilitated the reemergence of the Maud Rise polynya in the Weddell Sea, a phenomenon last observed in the mid-1970s.

The Antarctic Circumpolar Current (ACC) is the world's strongest ocean current and plays a disproportionate role in the climate system due to its role as a conduit for major ocean basins. This current system is linked to the ocean's vertical overturning circulation, and is thus pivotal to the uptake of heat and CO2 in the ocean. The strength of the ACC has varied substantially across warm and cold climates in Earth's past, but the exact dynamical drivers of this change remain elusive. This is in part because ocean models have historically been unable to adequately resolve the small-scale processes that control current strength. Here, we assess a global ocean model simulation which resolves such processes to diagnose the impact of changing thermal, haline and wind conditions on the strength of the ACC. Our results show that, by 2050, the strength of the ACC declines by ∼20% for a high-emissions scenario. This decline is driven by meltwater from ice shelves around Antarctica, which is exported to lower latit

Le climat de l'Arctique change rapidement. En témoigne le déclin dramatique de la calotte polaire depuis 40 ans. Les modèles climatiques suggèrent d'ailleurs que l'océan Arctique pourrait être totalement libre de glace de façon saisonnière d'ici quelques décennies. Or, l'arrivée massive d'eau douce, en modifiant la stratification de l'océan, pourrait avoir des conséquences non négligeables sur la productivité biologique, impactant de fait toute la faune marine locale.

Une nouvelle étude confirme que la Terre réagit bien plus vite à sa fièvre que ce que les scientifiques n’osaient encore imaginer. Celle-ci concerne le réchauffement des océans, pouvant de plus en plus perturber la circulation des courants propices à la vie, favoriser les tempêtes les plus violentes, et accélérer « naturellement » le dérèglement climatique, y compris de manière brutale.