[ES_JOBS_NET] Postdoc on global ocean ventilation and climate change at Sorbonne University (France)

[IAPSO ECS]

Human influence on global ocean ventilation

The World Ocean has crucial climatic and life-supporting roles. We know
that these roles depend critically on the ventilation of the deep ocean,
i.e., the transport of tracers (heat, carbon, oxygen, nutrients) between
the surface and the deep seas. However, too little is known about the
processes shaping deep-ocean ventilation and its changes. The Southern
Ocean is thought to have an outsized role in connecting surface and deep
waters: about 60% of the total global ocean volume had its last surface
contact or will have its next surface contact south of 40S (DeVries and
Primeau, 2011). A key unknown of the ventilation puzzle concerns the return
path from the interior ocean to the Southern Ocean surface, which involves
wind-driven vertical circulation as well as mixing processes, and which
controls the rate at which the large carbon and nutrient deep-ocean
reservoirs communicate with the surface (e.g. Le Quere et al., 2009;
DeVries et al., 2017). **The central objective of the project is to
understand the drivers of this return path from the global deep ocean to
the Southern Ocean surface, and their ability to change under on-going
climate change.**

Ocean ventilation can occur either through advection of material as part of
the global ocean overturning circulation, or through diffusive mixing.
While the resurfacing of deep waters in the Southern Ocean has been
described as primarily driven by winds (Marshall and Speer, 2012), the
local and large-scale impacts of interior mixing hotspots remain unclear.
**The first objective of this project will be to quantify the impact of
varying interior mixing intensity versus winds on the resurfacing of deep
waters in the Southern Ocean.** This will be addressed by sensitivity
experiments using varying mixing schemes in an existing configuration of
the NEMO global ocean model (used in the IPSL climate model).

**The second objective of the project will be to delineate the processes
driving Southern Ocean overturning circulation change in the context of
ongoing climate change.** The ocean responds to climate change through
modifications of heat, freshwater and momentum fluxes at its boundaries.
Recent work has started to highlight the potential important contribution
of thermodynamic drivers (change in air-sea heat fluxes) over mechanical
drivers (change in momentum fluxes) in impacting some large horizontal
current systems worldwide (Shi et al., 2021; Peng et al., 2022). But the
relative importance of these drivers on the vertical circulation, as well
as the time evolution of the respective role of each driver under past and
future climate change remains a knowledge gap. This gap will be addressed
in this project from a newly developed modeling framework, allowing to
isolate the contributions of heat, freshwater and momentum fluxes at the
ocean surface to drive ocean change (Silvy et al., 2022a). We will leverage
existing simulations that have been run based on a large ensemble
experiment (historical+SSP2-4.5) developed for CMIP6 with the IPSL climate
model (Silvy et al., 2022a,b).

APPLICATION:

Please contact Jean-Baptiste Sallee (jean-baptiste.sallee at locean.ipsl.fr)
and Casimir de Lavergne (casimir.delavergne at locean.ipsl.fr) with a CV, as
soon as possible.

STARTING DATE:

As soon as possible

DURATION:

Depending on the starting date. End of the postdoc in October 2024 (due to
funding availability). There are good prospects to continue employment
through an alternative research position.

SUPERVISORS:

J.-B. Sallee and Casimir de Lavergne (LOCEAN, Sorbonne University)

Collaborators:

Y. Silvy (Uni. Berne), J. Mignot (LOCEAN), E. Guilyardi (LOCEAN)
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