The Reconstruction of Climate in Beringia by analysis of Glycerol Dialkyl Glycerol Tetraether (GDGT) Distributions using High Performance Liquid Chromatography – Mass Spectrometry (HPLC-MS).

Abstract

The reconstruction of past environments, including temperatures, aids in the production of climate models which predict how the Earth will respond to future climatic changes that are occurring at an accelerated rate, due to global warming. High-latitude seas, including the Bering Sea, are sensitive to changes in global climate, across both glacial and interglacial timescales. Membrane lipids synthesised by archaea and bacteria are retained within the sediment and when extracted give evidence to the environmental conditions present during the organism’s lifetime. The membrane lipids are structured in a way that is chemically favourable to their environment, and calibrations derived in other works were used to reconstruct paleoclimates herein. Thirty polar sediment extracts were analysed by high-performance liquid chromatography coupled via atmospheric pressure chemical ionisation to mass spectrometric detection (HPLC-APCI-MS). Glycerol dialkyl glycerol tetraether (GDGT) ratios within the extracts were used to reconstruct sea surface temperatures (SSTs), mean air temperatures (MATs) and pH. Climatic and environmental parameters were successfully assessed and reconstructed using isoprenoid GDGTs (isoGDGTs), finding that GDGT distributions were characteristic of the open marine environment in most cases. Temperatures were found to be lowest on the transition from marine isotope stage (MIS) 6 to 5, while they peaked as MIS 5 closed. SSTs appeared to get cooler throughout glacial periods, while interglacial times were much more variable, particularly within MIS 5. Consideration was also given to the origin of the isoGDGTs, with the deep-water contribution found to be greatest across the 160-thousand-year (kya) period investigated. Branched GDGTs (brGDGTs) were also present, in lesser quantities and were used to determine MAT (between -5.8 and 10.4 °C) and pH (6.7 – 8.2) The findings showed a significant relationship between the GDGT distributions and numerous environmental proxies.