Browsing by Author "Atkins, C"

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    A 2 million year glacial chronology of the Hatherton Glacier, Antarctica and implications for the size of the East Antarctic Ice Sheet at the Last Glacial Maximum
    (Pergamon-Elsevier Science Ltd, 2014-01-01) Joy, K; Fink, D; Storey, BC; Atkins, C
    A series of distinct glacial deposits flanking the margins of the upper Hatherton Glacier, an outlet glacier in the central Transantarctic Mountains, are used to constrain the behaviour of the Antarctic ice-sheets. Cosmogenic exposure ages of 18 erratics from four glacial drifts covering the ice free Dubris and Bibra valleys, range in age from 5 to 1997 ka. Our results document four glacial advance and retreat events superimposed on an overall long-term ice thickness reduction of about 500 m since the mid-Pleistocene. The lack of field evidence and absence of LGM exposure ages in the glacial deposits of the Hatherton Glacier supports our conclusion that at the LGM the East Antarctic Ice Sheet was of similar size, or may have been slightly smaller, than present. Minimum exposure ages from the oldest two glacial events, represented by the Isca and Danum drifts, are similar to 1-2 Ma and similar to 0.5 Ma respectively. The Britannia-II Drift, previously assumed to mark the maximum extent of the Last Glacial Maximum advance, has a mean Be-10 age of 126 +/- 3.2 ka (n = 5). Ages from the younger Britannia-I Drift suggest that since the mid-Holocene (6.5 +/- 1.2 ka, n = 5), approximately 200 m of additional ice has been lost. © 2014, Elsevier Ltd.
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    Darwin / Hatherton glacial system: preliminary results of geomorophological mapping and cosmogenic sampling in 2009/10.
    (University of Canterbury, 2010-07-05) Joy, K; Atkins, C; Storey, BC; Fink, D
    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.