Abstract Trough mouth fans (TMFs) are sediment depocentres that form along high-latitude continental margins at the mouths of some cross-shelf troughs. They reflect the dynamics of past ice sheets over multiple glacial cycles and processes operating on (formerly) glaciated continental shelves and slopes, such as erosion, reworking, transport and deposition. The similarities and differences in TMF morphology and formation processes in the Arctic and Antarctic regions remain poorly constrained. We analyse the dimensions and geometries of 15 TMFs from Arctic and Antarctic margins and the grain size distribution of 82 sediment cores centred on them. We compare the grain size composition of sub- and proglacial diamictons deposited on the shelves and glacigenic debris flows deposited on the adjacent TMFs and find a significant difference between Arctic and Antarctic margins. Antarctic margins show a coarser grain size composition for both glacigenic debris flows and shelf diamictons. This significant difference provides insight into high-latitude sediment input, transportation and glacial–interglacial regimes. We suggest that surface runoff and river discharge are responsible for enhanced fine-grained sediment input in the Arctic compared with the Antarctic.

Abstract The behaviour of ice caps and glaciers on sub-Antarctic islands during previous periods of warming provide key empirical evidence for understanding the behaviour of marine ice sheets in the future. However, the extent of ice on sub-Antarctic islands during the last 100 kyr is poorly constrained. Here, we investigate the past glacial extents on South Georgia, where previous Last Glacial Maximum (LGM) reconstructions vary between small fjord-terminating glaciers and a large marine-based ice sheet. To help resolve this uncertainty, we apply Schmidt hammer relative-age dating to measure rock hardness and, thus, exposure age of a range of glacial deposits. Applying a hardness–age calibration curve constructed from well-dated Holocene, late-glacial deposits and terminal LGM deposits, we determine that deglaciation of the approximately 600 m-high peaks on the outer Lewin Peninsula occurred during the latter half of the last glacial stage, and probably the end of the LGM. We infer that South Georgia was covered by a marine-based ice cap during the latter part of the last glacial stage.