Did the Signy Ice Cap Melt During the Mid-Holocene?

Philippa E. Noon¹, Adrian P. Palmer², Vivienne J. Jones³ & H. John Birks⁴

¹British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK peno@bas.ac.uk
²Department of Geography, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK. A.Palmer@rhul.ac.uk
³Environmental Change Research Centre, Department of Geography, University College London, 26 Bedford Way, London WC1H 0AP, UK. v.jones@geog.ucl.ac.uk
⁴Botanical Institute, University of Bergen, Allégaten 41, N-5007 Bergen, Norway. John.Birks@bot.uib.no

So, the mid-Holocene was warm and balmy. The terrestrial environment enjoyed a well-earned break from ice-scour and howling winds. Mosses blossomed. Seals played and shed hairs everywhere. Penguins crooned and preened themselves on land once too slippery for a foot-hold. But how much ice melt-back was there during this 2100 year period of idyll before it became chilly again?

At Signy Island in the South Orkneys (lat. 60°43'S, long. 45°38'W) there are a series of glacier formed lakes in valleys draining the central ice cap. Two lakes on opposing sides of the ice cap - evocatively named Sombre and Emerald lakes - have full sediment sequences from the immediate post-glacial period to the present. Radiometric chronologies (137Cs, 210Pb, 14C) provide time scales for landscape evolution. Basal lake sediments indicate deglaciation on the west coast (8500 cal. yr BP) a little earlier than the east coast (7050 cal. yr BP).

Three simple measured parameters of the lake sediments - water content, organic content and particle size - can be used to reconstruct past glacier extent and activity using an inverse regression technique (Noon et al., 2001). Noon and Palmer have been slaving over the SediGraph particle size analyzer for the last 2 years and are ready to break this news to you:

the ice did not melt completely during the mid-Holocene at Signy Island

Smith (1990) predicted past ice coverages at Signy Island based on radiocarbon dates of terrestrial mosses and came to a similar conclusion.

For information:

Smith, R.I. Lewis, 1990. Signy Island as a paradigm of biological and environmental change in Antarctic terrestrial ecosystems. In K.R. Kerry and G. Hempel (eds.) Antarctic Ecosystems Ecological Change and Conservation. Springer Verlag Berlin Heidelberg, 32-50.

Noon, P.E., Birks, H.J.B., Jones, V.J. & Ellis-Evans, J.C. 2001. Quantitative models for reconstructing catchment ice-extent using physical-chemical characteristics of lake sediments. Journal of Palaeolimnology, 25, 375-392.