Isabelle Durand (LOCEAN, Université Paris 6, France); Christine Provost (LOCEAN, Université Paris 6, France)

The Southern Ocean lies at the heart of the global thermohaline circulation controlling the long-term variations of the Earth’s climate. The subpolar ocean south of the Antarctic Circumpolar Current (ACC) is known to loose heat to the atmosphere at a rate of 0.2-0.4 PW (1 PW = 1015 W). However, the exact mechanism by which heat is transmitted poleward across the powerful near-zonal ACC is still in debate, although recent studies suggest the mean current as a plausible candidate especially in the poleward flank of the ACC, as opposed to the traditional theory involving only mesoscale eddy activity. In order to verify the novel idea of the time-mean current-controlled poleward heat transport in comparison to eddy-induced transport, three lines of current meter moorings were installed through the ACC vein across the Udintsev Fracture Zone, which reveals the most restricted ACC flow controlled by bottom topography of the fracture zone. These moorings were made along a CTD section covering the quasi-totality of the ACC breadth and laid mostly along an altimetric ground track in order to use the altimetry in combination with direct current measurements for monitoring the ACC transport during the altimetric era started since more than 20 years ago. On waiting for the recovery of the moorings planned for early 2018, we will present the preliminary results of frontal circulation inferred from the cruise data, which can be compared with a circulation pattern derived from Aviso altimetric data and a high-resolution OGCM from MERCATOR. Dynamic parameters from both altimetry and the model will be critically intercompared in order to prepare the basis for using the model outputs for validating the point estimates of heart flux at the mooring sites and for estimating eventually the net poleward heat flux across the entire circumpolar extent.