Compared to the present-day climate, the cold period of the Last Glacial Maximum was characterized by an expanded sea-ice cover in the Southern Ocean, a shoaled Atlantic deep ocean circulation and a lower atmospheric CO₂ concentration. These changes are well-documented by indirect observations but difficult to represent in simulations of climate models.

Indeed, these models tend to simulate a too high atmospheric CO₂ concentration, a too deep Atlantic deep ocean circulation, and a sea-ice cover with a too circular distribution in the Southern Ocean and a too small winter extent and seasonal amplitude. The model-data discrepancies observed at the Last Glacial Maximum call into question the model representation of some important climate processes.

Several studies have underlined the crucial role of the Southern Ocean sea ice on ocean carbon storage capacity and deep circulation. I have therefore focussed on this region to improve our understanding of the processes associated with this storage. Thanks to simulations performed with the Earth System Model iLOVECLIM, I have demonstrated that the uncertainties related to ice sheet reconstructions have a limited impact on the variables examined in this study.

In contrast, other choices of boundary conditions (influencing the ocean volume and alkalinity adjustment) can yield large changes of carbon sequestration in the ocean. I also show that a simple parameterization of the sinking of brines consequent to sea-ice formation significantly improves the simulated Southern Ocean sea ice, deep ocean circulation and atmospheric CO₂ concentration.

A set of simulations including the effects of diverse ocean parameterizations is used to show that the too deep ocean circulation simulated by our model cannot be attributed to an insufficient sea-ice cover, whereas convection processes in the Southern Ocean seem crucial to improve both the Southern Ocean sea ice, the deep ocean circulation and the atmospheric CO₂ concentration at the Last Glacial Maximum.

Informations pratiques

La soutenance de thèse aura lieu en présentiel au LSCE (salle 118, accès restreint), en ligne par visioconférence. Lien public pour obtenir l’accès à la salle virtuelle de soutenance : https://cnrs.zoom.us/j/98214083691

ID de réunion : 982 1408 3691

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