Archaeal Intact Polar Lipids in Polar Waters: A Comparison Between the Amundsen and Scotia Seas

Abstract. The West Antarctic Ice Sheet (WAIS) is one of the largest potential sources of future sea-level rise, with glaciers draining the WAIS thinning at an accelerating rate over the past 40 years. Due to difficulties in calibrating palaeoceanographic proxies for the Southern Ocean, it remains difficult to assess whether similar changes have occurred earlier during the Holocene or whether there is underlying centennial to millennial scale forcing in oceanic variability. Archaeal lipid – based proxies, specifically Glycerol Dialkyl Glycerol Tetraether (GDGT) (e.g. TEX86 and TEX86L) are powerful tools for reconstructing ocean temperature, but these proxies have been shown previously to be difficult to apply to the Southern Ocean. A greater understanding of the parameters that control Southern Ocean GDGT distributions would improve the application of these biomarker proxies and thus help provide a longer-term perspective on ocean forcing of Antarctic ice sheet changes. In this study, we characterised intact polar lipid (IPL) - GDGTs, representing (recently) living archaeal population in suspended particulate matter from the Amundsen Sea and the Scotia Sea. Shifts in IPL-GDGT signatures across well-defined fronts of the Southern Ocean revealed a correlation between the physicochemical parameters of these water masses and IPL-GDGT distributions. Further analysis is required to elucidate the additional role of productivity and nutrient availability on Southern Ocean IPL-GDGT distributions. Of particular note for proxy development in the Amundsen Sea is that IPL-GDGTs are likely actively synthesised at Circumpolar Deep Water depths and may be a significant source of GDGTs exported to the sedimentary record in this region.