Thesis supervisor
M Julien Lesommer,
Research Officer, CNRS, Supervisor
Abstract
Recent climate trends show a warming and freshening of the surface layers in the region of the Antarctic Circumpolar Current (ACC). Over the same period, the westerlies driving
the circulation of the Southern Ocean have significantly increased. This increase is partly due to the intensification of the Southern Annular Mode (SAM), the main mode of atmospheric variability south of 20°S.
In this thesis, we are interested in understanding the effects of the positive trend of the SAM onto the properties of water masses formed in the region of the ACC. To do so,
we implement a strategy of regional coupled ocean-sea ice simulations forced by a series of atmospheric disturbance scenarios. These scenarios are constructed from atmospheric reanalyses in order to describe the various components (dynamic and thermodynamic) of the changes related to the SAM.
In response to the increase of the SAM, the simulations show a significant salinification of the ocean mixed layer and of the mode water (SAMW) and intermediate water (AAIW). Most of these changes can be attributed to the dynamic components of the SAM. In Seasonal Ice Zone, the thermodynamic components of the SAM can play an important part (especially in Amundsen Sea and Weddell Sea). The simulations also show the key role played by sea ice in mediating atmospheric changes toward the interior ocean. These simulation results suggest that SAM is not the only driver of recent climate trends in the Southern Ocean.
Keywords
Southern Ocean, air-sea heat flux, air-sea freshwater flux, Southern Annular Mode, oceanic water masses, regional numerical sea ice-ocean coupled model