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Ocean Surface Topography from Space
Southern Ocean Mixed-LayEr interannual variability and BarOtropic DYnamics from ocean surface topography and gravimeter data (SOMeBoDY)


Frédéric Vivier - (LOCEAN)

  Park Young-Hyang
Boutin Jacqueline
Sallée Jean-Baptiste

Southern Ocean Mixed-LayEr interannual variability and BarOtropic DYnamics from ocean surface topography and gravimeter data
Top: Skill of barotropic SSH in accounting the variance of the monthly climatology of satellite SSH, for the model of Vivier et al. [2005] (left) and for GRACE eqH2O data (right). Bottom: same as above except for annual mean anomaly.
The Southern Ocean is a major ventilation window of the World Ocean, and a pivotal element of the meridional overturning circulation (MOC). There, isopycnals outcrop and upwelled waters are exposed to intense buoyancy forcing, to form intermediate and mode waters, as well as bottom water. The rate of formation and properties of these waters depend on exchanges with the atmosphere through ocean mixed-layer (ML) processes. Profound changes have occurred in the past decades both in the southern hemisphere’s atmospheric circulation, with and intensification of the winds, and in the water masses forming in the Southern Ocean. There is therefore a high motivation to analyze the ML variability at interannual time scales, its interplay with subsurface layers, and to gain insight into the dominant mechanisms driving its response.

The way the Southern Ocean currents respond to climate variability may also ultimately affect water mass transformation, as this process occurs in localized injection windows along the Antarctic Circumpolar Current (ACC) pathway. There is thus great interest to investigate the dynamical response of the ocean jointly with upper ocean thermodynamics. We will focus on the Kerguelen region as a test case, where we benefit from a 20-year long time series of transport derived from altimetry, of the branch of the ACC crossing the Kerguelen Plateau. The dynamical response of the current will be analyzed from a recent long barotropic simulation and GRACE data. ML temperature and salinity budgets will be investigated at the scale of the entire ice-free Southern Ocean from a relatively simple model relying on altimeter data, atmospheric forcings, and hydrographic observations.

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