Christian K. Wilson

A new bathymetric compilation highlighting extensive paleo–ice sheet drainage on the continental shelf, South Georgia, sub‐Antarctica

A grid derived from a new compilation of marine echo-sounding data sets has allowed us to visualize and map the geomorphology of the entire continental shelf around South Georgia at an unprecedented level of detail. The grid is the first continuous bathymetric data set covering South Georgia to include multibeam swath bathymetry and represent them at a subkilometer resolution. Large and previously undescribed glacially eroded troughs, linked to South Georgias modern-day fjords, radiate from the island, marking the former pathways of large outlet glaciers and ice streams. A tectonic or geological influence is apparent for the major troughs, where glaciers have exploited structural weaknesses on the continental block. Bed forms lining the troughs give some first insights into glacial dynamics within the troughs, suggesting arteries of fast flowing ice occupied these topographic depressions in the past and operated over both bedrock and sedimentary substrates. On the outer shelf and within the troughs, large ridges and banks are also common, interpreted as terminal, lateral, and recessional moraines marking former positions of ice sheets on the shelf and their subsequent reorganization during deglaciation. A small trough mouth fan has developed at the mouth of at least one of the cross-shelf troughs, demonstrating a focused sediment delivery to the margin. Slides and slide scars are also present on parts of the margin, showing that margin stability, perhaps also related to glaciation, has been an important factor in depositional processes on the continental slope. Implications of the new observations are that ice sheets have been more extensive on South Georgia than any previous studies have reported. Their age may date back to late Miocene times, and evolution of the shelf system has probably involved numerous late Cenozoic glacial episodes. However, relatively fresh seafloor geomorphology coupled with evidence from other maritime-Antarctic islands (Heard Island and Kerguelen Island) indicating extensive glaciation at the Last Glacial Maximum raises the possibility that the extent of sub-Antarctic glaciation for the Last Glacial period has, until now, been underestimated.

Pristine fjord landsystem revealed on the sea bed in the Summer Isles region, NW Scotland

Synopsis We present new multibeam bathymetry and boomer seismic profiles from 200 km2 of sea floor around the Summer Isles in NW Scotland. The data reveal an undisturbed marine landscape comprising overdeepened basins, grooves, moraines, pockmarks and slide scars. Collectively these features represent a Late Devensian fjord landsystem. In more detail, the basins and grooves represent focused subglacial erosion during successive ice-sheet cycles. A suite of moraines charts the retreat of a marine-terminating ice sheet at the end of the last glaciation (c. 15–18 000 bp). Pockmarks attest to the release of shallow gas from organic-rich proglacial sediments. Finally, slumps and slide scars demonstrate slope evolution following the retreat of the fjord glaciers. This slope instability, both onshore and offshore, continues to the present day. Ongoing work aims to unravel the detailed sequence of events in the Summer Isles region at the end of the last glaciation, with particular emphasis on the glaciology of The Minch palaeo-ice stream.

Slope Failures in the Faroe — Shetland Channel

Submarine slides varying from 0.002km3 to more than 360km3 have been identified in the Faroe — Shetland Channel using a wide range of surveys. Although not a major constraint to seabed use slides need to be considered as a potential geohazard. Dynamic loading of contouritic horizons is considered the triggering mechanism of these thin layer failures.

The Afen Slide — A Multistaged Slope Failure in the Faroeshetland Channel

The Afen slide submarine slope failure has comprehensive 2D and 3D seismic coverage as well as geotechnical data from sediment cores. This allows a detailed assessment of the phases, modes and characteristics of failure. These findings can be applied to the recognition and understanding of other submarine slope failures.