Were the Larsemann Hills ice-free through the Last Glacial Maximum?
Lake sediments in the Larsemann Hills contain a great diversity ofbiological 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 (*loPb and I3'Cs), radiocarbon (AMS "C)
and uranium series (2'*U) methods to date cores from eleven lakes. These were sampled on coastal to inland
transects across the two mainpeninsulas, Broknes and Stornes, together with a single sample from the Bolingen
Islands. Radiometric dating of recent sediments yielded *"Pb levels below acceptable detection limits.
However, a relatively well-defined peak in I3'Cs gave a date marker which corresponds to the fallout maximum
from the atmospheric testing of atomic weapons in 1964/65. Radiocarbon (AMS I4C) 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 I4CO, and not influenced by radiocarbon contaminationprocesses.
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 than44 ka BP usingZ3*Ud ating 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 D%lk Glacier which diverts ice around Broknes.
Lakes onBroknes 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 throughoutthe Last
Glacial Maximum. These sediments are therefore well placed to unravel a unique lirnnological 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.
Authors: Hodgson, D.A., Noon, P.E., Vyverman, W., Bryant, C.L., Gore, D.B., Appleby, P., Gilmour, M., Verleyen, E., Sabbe, K., Jones, V.J., Ellis-Evans, J.C., Wood, P.B.