GFI/BCCR Seminar | Lea Toska Oppedal: Cirque glacier on South Georgia shows repeated centennial variability over the last 7000 years
Lea Oppedal (Department of Earth Science, UiB)
Cirque glacier on South Georgia shows repeated centennial variability over the last 7000 years
A 7000 year-long cirque glacier reconstruction from South Georgia, based on detailed analysis of fine-16 grained sediments deposited downstream in a bog and a lake, suggests continued presence during most of the Holocene. Glacier activity is inferred from various sedimentary properties including magnetic susceptibility (MS), dry bulk density (DBD), loss-on-ignition (LOI) and geochemical elements (XRF), and matched to a set of terminal moraines. The two independently dated sediment records document concurring events of enhanced glacigenic sediment influx to the bog and lake, whereas the upstream marginal moraines afford the opportunity to calculate past Equilibrium Line Altitudes (ELA) which has varied in the order of 100 m altitude. Combined, the records provide new evidence of cirque glacier fluctuations on South Georgia. Based on the onset of peat formation, the study site was deglaciated prior to 9900 years ago when a local tidewater glacier retreated up-fjord. The continuous sedimentary records indicate five major centennial scaled glacier advances centered around 7000 cal BP, 5700 cal BP, 3600 cal BP, 2400 cal BP, 400 cal BP, and during the 1960-70s. These glacier events are largely in-phase with reconstructed Patagonian glaciers, implying that they respond to centennial climate variability possibly connected to corresponding modulations of the Southern Westerly Winds.