Darwin / Hatherton glacial system: preliminary results of geomorophological mapping and cosmogenic sampling in 2009/10.

The role that Antarctica played in post-glacial global sea level rise and the configuration of the LGM ice margins are poorly understood and are the subject of much debate. The Darwin / Hatherton Glacial System (79.5° S, 158° E) in the Transantarctic Mountains contains an important archive of glacial recession during this period in the form of well-preserved glacial landforms. These represent the former extent of ice masses and have been previously used to support numeric models of Antarctic ice volume. By using this glacial system as a proxy for the East and West Antarctic Ice Sheets, the timing and magnitude of the LGM recession can be quantified. In situ cosmogenic nuclide dating combined with detailed geomorphological mapping of glacial landforms is being used at a number of sites along the downstream profile of the glaciers to create isochronous surfaces. These represent the ice sheet margins post LGM. Aluminum-26 and Beryllium-10 are two common radionuclides produced within quartz from the interaction of high energy cosmic particles with atoms of Oxygen and Silicon in the rocks. The production rate of these nuclides is known under given conditions, allowing an “exposure” age to be calculated based on their measured concentration. As the age of various glacial landforms and the retreat of ice can be correlated, cosmogenic dating allows the temporal and spatial distribution of ice to be analysed. During the 2009/10 field season, a series of well preserved moraines was mapped and several cosmogenic sampling transects were carried out in the Dubris/Bibra valleys area on the southern side of the Hatherton Glacier. This work confirmed the general distribution of known drift sheets and moraines mapped by Bockheim et al (1989) but also recognised that cold based glaciers have produced a subtle and complex glacial record due to simultaneous deposition and /or reworking of some drifts and in some cases protection and preservation of relict surfaces. These previously unrecognised cold based glacial events have significant implications for interpreting cosmogenic ages of deposits and glacial history of the area. The use of cosmogenic dating viewed through the lens of cold based ice will provide new data about the size and behaviour of the Antarctic ice sheets. Combined with numeric modelling, a new understanding of how Antarctica reacted to a warming climate post LGM may be gained. This in turn may lead to predictions of ice sheet response to current and future climate change and its effect on sea level rise.Antarctica New Zealan