Ocean and Climate group

Increasing anthropogenic greenhouse gas emissions into the atmosphere are modifying the balance of the climate system. This climate change is reflected in an increase in atmospheric surface temperature, which global average is the emblematic metric of global warming, but also in ocean acidification and the melting of ice caps and sea ice. In this headlong rush, the ocean acts as a modulator. It stores and redistributes excess heat. This storage and redistribution is not uniform across the globe. Ocean circulation shapes them.
In this change of climatic equilibrium, ocean circulation is modified both directly and indirectly. Winds, evaporation and precipitation zones, and heat fluxes all change and shift, impacting ocean circulation. In the Arctic Basin, the melting of sea ice and ice caps modifies the properties of the water formed, and the ice no longer acts as a buffer between the ocean and the atmosphere. All this has an impact on ocean circulation, such as the North Atlantic meridional overturning circulation, leading to changes in the ocean's capacity to store heat, as well as on sea levels. The oceanic carbon pump and thus ocean acidification are also affected, deregulating biogeochemical cycles. But the ocean is not passive in this change. The ocean's surface temperature controls its capacity to absorb atmospheric carbon. Similarly, meridional heat transport by ocean circulation has a regional impact on global warming and rising sea levels.
All these changes are coupled to one another and are not monotonous. They sometimes appear in a series of stages, or as a highly non-linear threshold effect. Understanding ocean dynamics is crucial to understanding and quantifying these modulations of climate change. It is therefore necessary to better understand how the ocean varies on interannual time scales and spatial scales of the order of the ocean basin, in order to anticipate its effect on climate and its current changes.
In this context, the team's two main objectives are:

• Diagnose the baseline, variability and trends in the state of the ocean (e.g., ocean circulation, water mass properties, sea level, biogeochemistry and floating wastes) ;
• Improve understanding and quantification of ocean processes and variability mechanisms in the ocean-atmosphere-sea-ice system.

In addition to the tools traditionally used within the team (the traditional triptych of observation - modeling - theory), we are increasingly relying on technical and methodological advances, and in particular:

• The development of Artificial Intelligence (AI) methods, which are used, for example, for the validation of Argo data and the production of products constrained by observations, the reconstruction of long time series and the improvement and understanding of climate forecasts.
• Advances in deep ocean observation, through the Deep-Argo program and the development and improvement of platform reliability.
• The existence of long observation time series, which are now capable of capturing both mesoscale and large-scale.
• The availability of CMIP6 simulations, which now include high-resolution coupled models capable of representing eddies on long time scales.
• The ability to run simulations representing the (sub-)mesoscale over an entire ocean basin.

The group is led by Florian Sevellec and Pascale Lherminier, and structured in 7 thematics:

• Improving our understanding of the carbon cycle in the ocean
• Ocean convection and water cycle
• Arctic Ocean dynamics and its role in the climate system
• Past, present and future climate
• Variation of ocean heat content and sea level
• observation of variability of the Atlanric Meridional Overturning Circulation
• oceanic plastic waste and surface circulation.