Reconstructing mid-late Holocene climate and environmental change in Antarctica using Glycerol Dialkyl Glycerol Tetraethers (GDGTs) and pigments in lake sediments

Abstract

Assessing the impact of past phases of natural warming on climatically sensitive areas, such as Antarctic and sub-Antarctic regions, will help us better understand the impact that climate warming may have in the future. In recent decades, the Antarctic Peninsula has been one of the fastest warming regions on Earth, warming at a rate of 3.4 °C per century, five times the global mean. Several phases of marked environmental change have occurred on the Antarctic Peninsula during the mid-late Holocene nonetheless, to date quantitative temperature reconstructions of terrestrial climates are not possible. GDGTs are one of few existing quantitative temperature proxies and recent developments of their use in lakes indicates their potential as a temperature proxy. Prior to application the relationship between GDGT-composition and several environmental factors, such as temperature, pH and conductivity, in Antarctic and sub-Antarctic lakes was assessed. Temperature explained a statistically significant independent control on the composition of branched GDGTs in the lakes and a new regional Antarctic and sub-Antarctic GDGT-temperature calibration was developed. Within this calibration, GDGT-IIIb was a statistically significant component indicating its importance in these environments. Applying the new GDGT-temperature calibration to sediment cores from Fan Lake, South Georgia and Yanou Lake, South Shetland Islands allowed the quantitative reconstruction of past temperatures during the Mid to Late-Holocene. The reconstructions showed varied temperatures throughout the records, evidencing the mid-Holocene warm period, and potentially the Medieval Climate Anomaly and Little Ice Age. Neither record, however, reconstructed the recent rapid warming seen in the glacial meltwater and instrumental records. A comparison of Fan Lake and Yanou Lake with other records from Antarctica and Chile showed periods of coherence between records alongside periods of inconsistency. This comparison also enabled potential changes in the PFZ to be considered, suggesting a more poleward position of the PFZ during warmer climates.