A paleolimnological reconstruction of mid and late holocene climate change in South Georgia

South Georgia is located at the barrier between Antarctica and the mid-latitudes which makes it a key location to determine the main drivers of past and present-day climate variability and to assess whether the climate in the South Atlantic was synchronous with Antarctica or South America. Here we performed a sedimentological, high resolution (ITRAX) geochemical, and fossil diatom and pigment analysis of a 5.41 m long, ca. 8000 cal yr BP, sediment core from Fan Lake, Annenkov Island, South Georgia (54°29U+20190U+2019U+2019S, 37°5U+20190U+2019U+2019W) in an attempt to separate the influence of Holocene palaeoclimatic variability from changes in catchment stability and glacier activity. While radiocarbon ages of events in the top 250 cm (c. 4 ka) of this core appear to be broadly in line with some other studies on South Georgia, the chronology of the lower half still poses several questions. The main lithological division in the profile is marked by the establishment of finely laminated sedimentation at c. 250 cm (4000 yrs BP) and is also picked out by the diatom and pigment analysis. This change is characterized by a reduction to low stable magnetic susceptibility values and a step-change increase in organic matter, and is most likely related to deglaciation of the lake catchment during the U+2018Mid Holocene HypsithermalU+2019. Although the diatom composition is dominated by a single species (i.e., Cyclotella stelligera), relatively minor, but sometimes significant, fluctuations in other diatom species occur in the top 250 cm (mid-late Holocene). Interestingly, the most remarkable change in the diatom record occurs at c. 100 cm (1000 cal yr BP) and coincides with an increase in general lake productivity. We link these changes to increased catchment disturbance at c. 1000 cal yr BP, which is possibly associated with deglaciation following one of four relatively minor U+2018post-cooling eventsU+2019 during the late Holocene.

Jaar van publicatie:2010