Oxygen-isotope (delta18O) evidence of Holocene hydrological changes at Signy Island, maritime Antarctica
A record of Holocene hydrological changes has been produced from variations in oxygen-isotope composition (delta(18)O) preserved in freshwater lake sediments from maritime Antarctica. Small amounts (<5%) of authigenic carbonate have been extracted from a non-marl sediment core from Sombre Lake, Signy Island (60 degrees 43'S, 45 degrees 38'W). Oxygen-isotope and particle-size analysis provide a sensitive record of hydrological events in the lake arising from local and regional climate phenomena. The climate affects delta O-18 through snowpack volume and glacier activity in the catchment, lakewater temperatures, the input versus evaporation balance and the duration of seasonal lake ice cover. The most depleted (negative) delta O-18 values are associated with influxes of meltwater at times of glacier advance or retreat. Enriched (positive) delta O-18 values occur during more arid, warmer conditions with longer periods of open water in summer. This isotope record can be used to determine century-scale to decadal variability in air circulation and moisture origin. Strong similarities with other Holocene proxy records from the Weddell Sea and Antarctic Peninsula Region are apparent, including the mid-Holocene climate optimum followed by the Neoglacial and, most recently, late twentieth-century climatic warming. The oxygen-isotope record from Sombre Lake illustrates the importance of remote islands in contributing to our understanding of teleconnections in atmospheric and oceanographic circulation, sea-ice extent, air temperatures and precipitation in the Southern Ocean.