Glacial history of the King Haakon Trough System, sub-Antarctic South Georgia

In an effort to elucidate an important part of the Quaternary evolution of sub-Antarctic South Georgia, hydroacoustic data from its southern continental shelf are presented. The island with its surrounding shelf is of key interest for climate reconstructions, because it is located within the core belt of the Southern Westerlies and between the main fronts of the Antarctic Circumpolar Current in the Southern Ocean. This makes it particularly susceptible to changes in climate conditions on a local, regional, but also Southern Hemisphere-wide scale. The data provide new insights into the glacial evolution of the King Haakon Trough, one of several cross-shelf trough systems around the island. Numerous landforms, identified from high-resolution bathymetry data, document phases of ice advance and retreat. They are interpreted to be related to the confluence of two major trunk glaciers fed by an extended, possibly warm-based, South Georgia Ice Cap. Linear bedforms become progressively elongated towards the shelf and imply accelerated ice flow and/or softer sediment substrate towards the shelf edge. In contrast, recessional moraines and large morainal banks not only evidence shelf-wide ice extent during a peak glaciation, but also attest to staggered retreat, at least during the initial phase of deglaciation. The establishment of a complex bottom-current system around the onset of the last deglaciation is implied by the presence of moats and contourite drifts, which are mainly recorded in sub-bottom profiler data from the trough system. These data also show an acoustically semi-transparent facies of variable thickness present on the mid- and outer shelf as basal trough fill, which, on the basis of its acoustic appearance and the presence of several strong internal reflectors, is interpreted as a sequence of stacked glacial tills. These are similar to stacked tills previously documented from the Antarctic Peninsula and probably document a minimum of three extensive ice advances around South Georgia. Because the tills in the King Haakon Trough occur over a distance of ~26 km across the shelf, it is postulated that they derive from a minimum of three separate glaciations, rather than from re-advances within one glaciation period. Accordingly, the new findings from the combined bathymetry and sub-bottom profiler data show that the marine-geological archives around South Georgia offer unique potential to constrain how ice masses in the Southern Ocean responded to Quaternary climate change.