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

Abstract

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 complexities 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 populations in suspended particulate matter (SPM) from the Amundsen Sea and the Scotia Sea. SPM samples from the Amundsen Sea were collected from up to four water column depths representing the surface waters through to Circumpolar Deep Water (CDW), whereas the Scotia Sea samples were collected along a transect encompassing the sub-Antarctic front through to the southern boundary of the Antarctic Circumpolar Current. IPL-GDGTs with low cyclic diversity were detected throughout the water column with high relative abundances of hydroxylated IPL-GDGTs identified in both the Amundsen and Scotia seas. Results from the Scotia Sea show shifts in IPL-GDGT signatures across well-defined fronts of the Southern Ocean. Indicating that the physicochemical parameters of these water masses determine changes in IPL-GDGT distributions. The Amundsen Sea results identified GDGTs with hexose-phosphohexose head groups in the CDW, suggesting active GDGT synthesis at these depths. These results suggest that GDGTs synthesised at CDW depths may be a significant source of GDGTs exported to the sedimentary record and that temperature reconstructions based on TEX86 or TEX86L proxies may be significantly influenced by the warmer waters of the CDW.

Evaluation of lipid biomarkers as proxies for sea ice and ocean temperatures along the Antarctic continental margin

“…There is an emerging consensus that GDGTs predominantly reflect subsurface ocean temperatures (SOT) along the Antarctic margin (Kim et al, 2012;Etourneau et al, 2019;Liu et al, 2020). This is supported by observations of elevated archaeal abundances (and GDGTs) in warmer subsurface waters (Liu et al, 2020;Spencer-Jones et al, 2021). Archaea adapt their membrane in cold waters by adding hydroxyl groups and changing the number of rings, OH-GDGTs (Fietz et al, 2020).…”

Constraining Water Depth Influence on Organic Paleotemperature Proxies Using Sedimentary Archives

“…GDGT contributions from >500 m from deep water Thaumarchaeotal communities are observed in the Mediterranean and near the Portugal margin influenced by deep Mediterranean Outflow Waters (Besseling et al, 2019;Kim et al, 2015Kim et al, , 2016. For the Southern Ocean, it has been suggested that a significant amount of GDGTs from depths of >1,400 m might be reaching the underlying sediments (Spencer-Jones et al, 2021). Hence, regional studies are required to constrain the source depth of the TEX 86 signal at different locations.…”

Biomarker proxies for reconstructing Quaternary climate and environmental change

“…The accuracy and precision of the temperature proxies vary, especially at the upper and lower ends of the calibrations or close to detection limits, and not all proxies are found in all settings. Many of the proxies are calibrated to mean annual surface water temperature (Table 1), but if the producers have preferred seasons or water depths, a seasonal or subsurface temperature signal may be reconstructed (D'Andrea et al, 2005(D'Andrea et al, , 2011Jaeschke et al, 2017;Tierney and Tingley, 2018;Inglis and Tierney, 2020;Theroux et al, 2020;Spencer-Jones et al, 2021). Although marine biomarkers have global calibrations (Table 1), there can also be local controls over the biomarker-temperature relationship in all aquatic settings (e.g.…”