T. Deen

Subglacial bedforms reveal complex basal regime in a zone of paleo- ice stream convergence, Amundsen Sea embayment, West Antarctica

The flow of ice streams, which account for most discharge from large ice sheets, is controlled by processes operating at the ice stream bed. Data from modern ice stream beds are difficult to obtain, but where ice advanced onto continental shelves during glacial periods, extensive areas of the former bed can be imaged using modern swath sonar tools. We present new multibeam swath bathymetry data analyzed alongside sparse preexisting data from the Amundsen Sea embayment. The compilation is the most extensive, continuous area of multi-beam data coverage yet obtained on the inner continental shelf of Antarctica. The data reveal streamlined subglacial bedforms that define a zone of paleo–ice stream convergence, but, in contrast to previous models, do not show a simple downflow progression of bedform types along paleo–ice stream troughs. We interpret high spatial variability of bedforms as indicating a complex mechanical and hydrodynamic regime at the former ice stream beds, consistent with observations from some modern ice streams. We conclude that care must be taken when using bedforms to infer paleo–ice stream velocities.

West Antarctic ice sheet change since the Last Glacial Period

The potential for rapid deglaciation, or collapse, of the 2–million–square–kilometer West Antarctic Ice Sheet (WAIS) in response to climate change is one of the most serious environmental threats facing mankind. The WAIS is a marine ice sheet with large parts of its ice grounded below sea level. Complete collapse would result in a global sea level rise of approximately 5 meters, with immense social, economic, and ecological consequences.

Compilation of a new bathymetric dataset of South Georgia

Abstract We introduce a new bathymetric compilation of the area around South Georgia in the Southern Ocean. Using a variety of data sources including multi and single-beam swath bathymetry we have constructed a gridded bathymetric dataset of the shelf and near-shelf sea-floor areas. The grid has been constructed using a layered hierarchy dependent upon accuracy of each dataset. The spikes and errors have been checked both manually and with a novel semi-automated process. We discuss the resulting bathymetry and the potential uses of the new dataset.

3-D tomographic seismic inversion of a paleochannel system in central New South Wales, Australia

Buried paleochannels are of significant interest for understanding hydrological mechanisms and their potential as alluvial gold deposits. Seismic tomographic methods are a suitable solution for resolving the vertical and horizontal structure of such features. We assess a method for seismic 3‐D tomographic inversion from refraction arrivals with reflection control over a suspected paleochannel adjacent to the Wyalong gold fields in the Lachlan fold belt of central New South Wales, Australia. A standard multichannel engineering seismic recording and cable–receiver system was used on a 3‐D field geometry of multiple linear arrays. More than 3000 P‐wave first‐arrival traveltime values were inverted using a regularized inversion scheme for which simplified 2‐D models served as initial velocity–depth models for the complete 3‐D inversion. Seismic reflection arrivals provided additional depth estimates to the bedrock and compensated for a lack of refraction phases at that depth. Correlating the 3‐D seismic veloc...

Establishing lichenometric ages for nineteenth- and twentieth-century glacier fluctuations on South Georgia (South Atlantic).

Abstract. Glaciers in small mountain cirques on South Georgia respond rapidly and sensitively to changes in South Atlantic climate. The timing and rate of their deglaciation can be used to examine the impact that nineteenth‐ and twentieth‐century climate change has had on the glacial dynamics and terrestrial ecosystems of South Georgia. As part of a reconnaissance study in Prince Olav Harbour (POH), South Georgia, we measured the size of lichens (Rhizocarpon Ram. em Th. Fr. subgenus. Rhizocarpon group) on ice‐free moraine ridges around two small mountain cirques. Our aims were twofold: first, to provide age estimates for lichen colonization, and hence, deglaciation of the moraine ridges, and second, to examine the potential of applying lichenometry more widely to provide deglacial age constraints on South Georgia. In the absence of lichen age‐size (dating) curves for South Georgia, we use long‐term Rhizocarpon lichen growth‐rates from recent studies on sub‐Antarctic Islands and the western Antarctic Peninsula to calculate likely age estimates. These data suggest ice retreat from the two outermost moraines occurred between the end of the ‘Little Ice Age’ (post c. 1870) and the early twentieth century on South Georgia. Lichen colonization of the innermost moraines is probably related to glacier retreat during the second half of the twentieth century, which has been linked to a well‐defined warming trend since c. 1950. Patterns of possible nineteenth‐ and twentieth‐century glacial retreat identified in POH need to be tested further by establishing species‐ and site‐specific lichen age‐size (dating) curves for South Georgia, and by applying lichenometry to other mountain cirques across South Georgia.