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. The West Antarctic Ice Sheet (WAIS) is one of the largest potential sourcesof future sea-level rise, with glaciers draining the WAIS thinning at anaccelerating rate over the past 40 years. Due to complexities in calibratingpalaeoceanographic proxies for the Southern Ocean, it remains difficult toassess whether similar changes have occurred earlier during the Holocene orwhether there is underlying centennial- to millennial-scale forcing inoceanic variability. Archaeal lipid-based proxies, specifically glyceroldialkyl glycerol tetraether (GDGT; e.g. TEX86 and TEX86L), arepowerful tools for reconstructing ocean temperature, but these proxies havebeen shown previously to be difficult to apply to the Southern Ocean. Agreater understanding of the parameters that control Southern Ocean GDGTdistributions would improve the application of these biomarker proxies andthus help provide a longer-term perspective on ocean forcing of Antarcticice sheet changes. In this study, we characterised intact polar lipid (IPL)-GDGTs, representing (recently) living archaeal populations in suspendedparticulate matter (SPM) from the Amundsen Sea and the Scotia Sea. SPMsamples from the Amundsen Sea were collected from up to four water columndepths representing the surface waters through to Circumpolar Deep Water(CDW), whereas the Scotia Sea samples were collected along a transectencompassing the sub-Antarctic front through to the southern boundary of theAntarctic Circumpolar Current. IPL-GDGTs with low cyclic diversity weredetected throughout the water column with high relative abundances ofhydroxylated IPL-GDGTs identified in both the Amundsen and Scotia seas.Results from the Scotia Sea show shifts in IPL-GDGT signatures acrosswell-defined fronts of the Southern Ocean. Indicating that thephysicochemical parameters of these water masses determine changes inIPL-GDGT distributions. The Amundsen Sea results identified GDGTs withhexose-phosphohexose head groups in the CDW, suggesting active GDGT synthesisat these depths. These results suggest that GDGTs synthesised at CDW depthsmay be a significant source of GDGTs exported to the sedimentary record andthat temperature reconstructions based on TEX86 or TEX86Lproxies may be significantly influenced by the warmer waters of the CDW.

Archaeal intact polar lipids in polar waters: a comparison between the Amundsen and Scotia seas