Changement climatique et Arctique et circulation océanique globale

Anthropogenic climate change is affecting major components of the Earth’s climate system. Its impacts are pronounced at high latitudes, where the decline of Arctic sea ice is evident. Likewise, they are clear in low latitudes, as exemplified by the enhanced warming of the tropical Indian Ocean. Accordingly, the overarching goal of this project is to investigate climatic links between the key element of global ocean circulation, the Atlantic meridional overturning circulation (AMOC), and changes in other ocean basins in the context of global warming. The project is led by Drs. Alexey Fedorov, Eric Guilyardi, and Juliette Mignot of the Laboratoire D'Oceanographie Et Du Climat Experimentations Et Approches Numeriques (LOCEAN). In 2022 the project also involved postdoctoral associates Drs. Brady Ferster and Yona Silvy, PhD student Yoania Povea-Perez, collaborators Drs. Leonard Borchert and Matthew Menary at LOCEAN, and international collaborators in the US. During the past year, we focused on several problems related to the ocean inter-basin connections. Dr. Ferster continued working on the problem of how Arctic sea ice decline affects the North Atlantic climate and the AMOC on decadal to centennial timescales. We showed that the accumulation of freshwater in the Arctic, caused by the seasonal melting of sea ice, could strengthen ocean vertical stratification, thus suppressing deep-water formation and weakening the AMOC. In the model we used, IPSL-cm5, this weakening is maximum after 70 years but then the AMOC gradually recovers. Surprisingly, we find that Arctic sea ice decline also leads to the formation of the so-called North Atlantic warming hole (NAWH) – a large area in the North Atlantic south of Greenland with a cooling anomaly of about 2ºC. The NAWH persists even after the AMOC recovers. This warming hole is expected to increase storminess, leading to large temperature swings during European winters. These results are described in a paper published in Geophysical Research Letters. Further, Dr. Ferster and other members of the team continued modelling the remote impacts of the tropical Indian Ocean (TIO) on the AMOC. Specifically, we discovered that a large fraction of climate variability in the North Atlantic could be attributed to the observed multi-decadal variations in TIO temperature over the past century or so (manuscript submitted to npj Journal of Climate and Atmospheric Sciences). Dr. Yona Silvy continued her study on the emergence of anthropogenic climate warming signal in the deep ocean and published a manuscript based on her work in Journal of Climate. As part of her PhD study, Yoania Povea-Perez submitted a manuscript titled “The central role of the Atlantic meridional overturning circulation in the Bjerknes compensation in a climate model” to Climate Dynamics. The Bjerknes compensation is a fundamental mechanism regulating global climate, such that changes in oceanic poleward heat transport can be compensated by changes in atmospheric heat transport. In addition, Dr. Fedorov and collaborators conducted research on the problem of climate change in the tropical Pacific. In total, in 2022 this project supported 11 publications, including in Nature Geoscience, Nature Climate Change, and Nature Communications. Finally, Dr. Fedorov attended, and gave a presentation at the MOPGA conference in Berlin (December 2022).