University of Bordeaux

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A Postdoctoral position is available at University of Bordeaux to work within the UK ARIA project named SORTED led by the National Oceanographic Center (NOC) in Southampton. This proposed position aims at better understanding and anticipating the risk of a tipping point of the North Atlantic subpolar gyre in the near future.

The North Atlantic subpolar gyre (SPG) plays a key role in global ocean circulation through the process of convection, resulting in the transfer of heat and carbon to the deep ocean. However, some CMIP6 climate models project a collapse of this convection before 2100, causing sudden cooling and changes in the mixed layer. It is linked to the lightening of the surface waters of the North Atlantic, caused by warming, the melting of the Greenland ice sheet, the increase in atmospheric precipitation, which are increasing stratification of the ocean. However, the exact mechanisms leading to such a tipping point remain debated. To better understand these processes and anticipate possible early warning signals, an in-depth analysis of heat, volume and salinity budgets in CMIP6 models is required as well as the quantification of water mass transformation in the SPG and its evolution through time. The work proposed to the postdoctoral fellow is to identify the processes leading to the critical stratification that prevents convection, by examining the ocean’s spatial density, temperature and salinity budgets. The aim is to isolate the factors responsible for the formation of dense water and to assess their role in the collapse of the SPG. The study will integrate air-sea fluxes, horizontal and vertical advection and climate feedbacks specific to the SPG. A comparison with observations and high-resolution experiments will make it possible to test the representation of these processes in CMIP6 models.
The postdoctoral fellow will therefore determine the respective roles played by each component of the upper ocean budget in the development of a critical stratification before the SPG collapse. The postdoctoral fellow will additionally assess the links between these processes and changes in large-scale dynamics, such as atmospheric water vapour (moisture) transport, remote anomalies of heat and salinity transported by North Atlantic drift as well as internal feedback specific to the SPG. By comparing the budget analysis in CMIP6 models and observations notably provided by our partner the NOC, the postdoctoral fellow will strengthen our understanding of the drivers of deep convection over the SPG and of their sensitivity to different emission scenarios, which will be further tested through dedicated experiments in higher resolution models. Finally, the work will focus on the quantification of the positive salt advection feedback from the SPG system using a methodology that evaluates the origin of density changes in convection sites for the AMOC, adapted here for the SPG system. Such an approach is crucial in our understanding of the interconnected dynamics at play in different climate models. From the comparison with observations, we will be able to evaluate the proximity of the real system to a tipping point and develop an early warning system based on observation.
This project is being carried out at the EPOC laboratory at the University of Bordeaux, under the supervision of Didier Swingedouw and in collaboration with the NOC in Southampton. The EPOC laboratory is just two hours by train from Paris where some collaborations could be built with IPSL laboratories. Some short stays in Southampton could be also envisaged to strengthen interactions within the project.

We are searching for an expert in physical oceanography and climate dynamics profile. The position is offered for 24 months, potentially renewable once. Payment will be in accordance with French public service salaries (between 2500 and 4000 Euros before taxes, depending on experience). The starting date is as soon as possible. Application will close the 18th of July 2025.

The postdoctoral fellowship will be primarily supervised by Didier Swingedouw. Applications will be accepted by e-mail only. They should comprise: a CV with scientific experience, a letter of motivation with an availability date, and some referee name(s). Applications and queries should be sent to the following e-mail addresses: didier.swingedouw@u-bordeaux.fr