Sack Lunch Seminar (SLS)

The structure of the Antarctic Circumpolar Current around the Kerguelen Plateau



Due to its great meridional extent and relatively shallow depth, the Kerguelen Plateau constitutes a major barrier to the eastward flowing Antarctic Circumpolar Current (ACC) in the Indian sector of the Southern Ocean. While most of the ACC transport is deflected north of the Kerguelen Islands, the remainder (30-40%) must pass south of the islands, most probably through the Fawn and Princess Elizabeth deep troughs. However, our knowledge of the circulation around the Kerguelen Plateau has long been hampered by the lack of observations in this remote area.

The analysis of hydrographic data collected by instrumented elephant seals together with satellite and in situ data-sets has recently confirmed the existence of a strong northeastward current through the Fawn Trough, a deep passage (sill depth: 2650 m) splitting the plateau in two parts. The Fawn Trough appeared to act as a veritable bottleneck, channelling the quasi-totality of the cold Antarctic Surface Water found south of the Ice Limit (58°S) and the Circumpolar Deep Water transiting the Enderby Basin toward the Australian-Antarctic Basin. The TRACK cruise across the Fawn Trough recently confirmed that it concentrates ~30% of the ACC transport (43 Sv).

The new circulation scheme obtained from observation analysis has then been used to assess the overall quality of a state-of-the-art eddy-permitting numerical simulation in the Southern Indian Ocean. It was found that the two main sources of large-scale circulation biases were related to 1) the bathymetry and 2) the representation of bottom water formation processes.