Séminaire
The Southern Ocean is home to some of largest of the world's ocean currents, with in particular the Antarctic circumpolar current (ACC) and its ~130Sv flowing through Drake passage. These current systems are also highly variable in time over a broad range of time scales. Understanding the nature and the causes of the interannual to decadal variability of large scale volume transport in the Southern Ocean is essential for both detecting climate trends and attributing the observed changes. High resolution ocean model simulations as performed by the DRAKKAR consortium (http://www.drakkar-ocean.eu/) are providing useful information for this purpose.
In this talk, we will discuss two new mechanisms contributing to large scale volume transport at interannual time scale in the Southern Ocean and discuss their relevance on the basis of a series of DRAKKAR eddy resolving numerical simulations. First, we will show how local wind curl variations in the western South Atlantic can drive year to year fluctuations of ACC transport at Drake passage as efficiently as zonal wind stress at latitudes of Drake passage. Second, we will show how the intense fluctuations of the Zapiola anticyclone volume transport in the Argentine basin results from the integration of the white noise forcing of oceanic eddies.
These results advocates that the explicit representation of mesoscale eddy dynamics and the reduction of error in wind stress curl in atmospheric reanalyses are essential for improving the interannual variability of Southern Ocean currents in ocean models.