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

• Published in: Antarctic Science
• Main 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.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 2001
• Subjects: Antarc*; Antarctic Science; Antarctica
• Online Access: http://dx.doi.org/10.1017/s0954102001000608; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0954102001000608

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 ( 210 Pb and 137 Cs), radiocarbon (AMS 14 C) and uranium series ( 238 U) 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 210 Pb levels below acceptable detection limits. However, a relatively well-defined peak in 137 Cs gave a date marker which corresponds to the fallout maximum from the atmospheric testing of atomic weapons in 1964/65. Radiocarbon (AMS 14 C) 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 14 CO 2 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 128 U 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 ...