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Were the Larsemann Hills ice-free through the Last Glacial Maximum?

Published online by Cambridge University Press:  27 April 2004

D.A. Hodgson
Affiliation:
British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK
P.E. Noon
Affiliation:
British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK
W. Vyverman
Affiliation:
Laboratory of Protistology & Aquatic Ecology, Department of Biology, University of Gent, K.L. Ledeganckstraat 35, B-9000 Gent, Belgium
C.L. Bryant
Affiliation:
Natural Environment Research Council Radiocarbon Laboratory, Scottish Enterprise Technology Park, Rankine Avenue, East Kilbride G75 0QF, UK
D.B. Gore
Affiliation:
Department of Physical Geography, Macquarie University, NSW 2109, Australia
P. Appleby
Affiliation:
Environmental Radioactivity Research Centre, Department of Mathematical Sciences, University of Liverpool, Liverpool L69 3BX, UK
M. Gilmour
Affiliation:
Natural Environment Research Council Uranium Series Facility, Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA, UK
E. Verleyen
Affiliation:
Laboratory of Protistology & Aquatic Ecology, Department of Biology, University of Gent, K.L. Ledeganckstraat 35, B-9000 Gent, Belgium
K. Sabbe
Affiliation:
Laboratory of Protistology & Aquatic Ecology, Department of Biology, University of Gent, K.L. Ledeganckstraat 35, B-9000 Gent, Belgium
V.J. Jones
Affiliation:
Environmental Change Research Centre, University College London, 26 Bedford Way, London WC1H OAP, UK
J.C. Ellis-Evans
Affiliation:
British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK
P.B. Wood
Affiliation:
Department of Geography, Royal Holloway, University of London, Egham TW20 OEX, UK

Abstract

Lake sediments in the Larsemann Hills contain a great diversity of biological and physical markers from which past environments can be inferred. In order to determine the timing of environmental changes it is essential to have accurate dating of sediments. We used radiometric (210Pb and 137Cs), radiocarbon (AMS 14C) and uranium series (238U) methods to date cores from eleven lakes. These were sampled on coastal to inland transects across the two main peninsulas, Broknes and Stornes, together with a single sample from the Bolingen Islands. Radiometric dating of recent sediments yielded 210Pb levels below acceptable detection limits. However, a relatively well-defined peak in 137Cs gave a date marker which corresponds to the fallout maximum from the atmospheric testing of atomic weapons in 1964/65. Radiocarbon (AMS 14C) measurements showed stratigraphical consistency in the age-depth sequences and undisturbed laminae in some cores provides evidence that the sediments have remained undisturbed by glacial action. In addition, freshwater surface sediments were found to be in near-equilibrium with modern 14CO2 and not influenced by radiocarbon contamination processes. This dating program, together with geomorphological records of ice flow directions and glacial sediments, indicates that parts of Broknes were ice-free throughout the Last Glacial Maximum and that some lakes have existed continuously since at least 44 ka bp. Attempts to date sediments older than 44 ka bp using 128U dating were inconclusive. However, supporting evidence for Broknes being ice-free is provided by an Optically Stimulated Luminescence date from a glaciofluvial deposit. In contrast, Stornes only became ice-free in the mid to late Holocene. This contrasting glacial history results from the Dålk Glacier which diverts ice around Broknes. Lakes on Broknes and some offshore islands therefore contain the oldest known lacustrine sediment records from eastern Antarctica, with the area providing an ice-free oasis and refuge for plants and animals throughout the Last Glacial Maximum. These sediments are therefore well placed to unravel a unique limnological sequence of environmental and climate changes in East Antarctica from the late Pleistocene to the present. This information may help better constrain models of current climate changes and ensure the adequate protection of these lakes and their catchments from the impacts of recent human occupation.

Type
Papers—Earth Sciences and Glaciology
Copyright
© Antarctic Science Ltd 2001

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