Late Holocene climate variability and fire history from Deepwater Lake sediments, Fraser Island, South Queensland.

Abstract

Lake sediments are an important resource that can be used to reconstruct past climate and environmental conditions from all over the world. Understanding past climate changes is extremely important to help understand what’s happening to climate in Australia today and potentially into the future. The perched lake systems on Fraser Island in subtropical Queensland, Australia, act as natural rainfall gauges, allowing them to be highly sensitive to environmental changes which, through a variety of indicators, are recorded in the sediments.

Deepwater Lake, a small perched lake on Fraser Island, was investigated using a range of environmental proxies. A detailed chronology was created using a range of accelerator mass spectrometry radiocarbon dates and 210Pb dates on cores taken to a depth of 4.7 m. The chronology indicates an age range of 4800 cal BP to present.

The lake sediments were analysed for carbon isotope ratios, carbon/nitrogen ratio variation, macro-charcoal changes, sediment organic content, magnetic susceptibility, XRF based element geochemistry, 210Pb, and radiocarbon dating. These proxies are used to reflect the changes of catchment processes within the lake environment over the mid to late-Holocene.

The proxies reflect a transition from a dry, fire-prone environment, with very low organic content from 4800-3800 cal BP, to a more rainfall-erosional based environment from 3800-300 cal BP. During the period from 3800-3000 cal BP, it was determined there was a high influx of detrital sediments, organic content, and a transition from an algal based source to a more terrestrial based organic source. Environmental conditions have remained consistent from 3000 cal BP to present day with very little variation observed in the proxies indicating a stabilisation of climate into the late Holocene.