A Microscale View of Mixing and Overturning Across the Antarctic Circumpolar Current

Thursday, 18 December 2014: 9:45 AM
Alberto Naveira Garabato1, Kurt L Polzin2, Raffaele M Ferrari3, Jan David Zika1 and Alexander Forryan4, (1)University of Southampton, Southampton, SO14, United Kingdom, (2)WHOI, Woods Hole, MA, United States, (3)Massachusetts Institute of Technology, Cambridge, MA, United States, (4)University of Southampton, Southampton, United Kingdom
The meridional overturning circulation and strati cation of the global ocean are shaped critically by processes in the Southern Ocean. The zonally unblocked nature of the Antarctic Circumpolar Current (ACC) confers the region with a set of special dynamics that ultimately results in the focussing therein of large vertical exchanges between layers spanning the global ocean pycnocline. These vertical exchanges are thought to be mediated by oceanic turbulent motions (associated with mesoscale eddies and small-scale turbulence), yet the vastness of the Southern Ocean and the sparse and intermittent nature of turbulent processes make their relative roles and large-scale impacts extremely difficult to assess.

Here, we address the problem from a new angle, and use measurements of the centimetre-scale signatures of mesoscale eddies and small-scale turbulence obtained during the DIMES experiment to determine the contributions of those processes to sustaining large-scale meridional overturning across the ACC. We find that mesoscale eddies and small-scale turbulence play complementary roles in forcing a meridional circulation of O(1 mm / s) across the Southern Ocean, and that their roles are underpinned by distinct and abrupt variations in the rates at which they mix water parcels. The implications for our understanding of the Southern Ocean circulation's sensitivity to climatic change will be discussed.