The Arctic is undergoing rapid climate change, warming nearly four times faster than the global average, leading to increasingly ice-free conditions and significant changes in biogeochemical feedbacks in the Arctic Ocean. Understanding past climate variability in this region is crucial for constraining the effects of ongoing climate change. Glycerol Dialkyl Glycerol Tetraethers (GDGTs) are microbial membrane lipids widely used to reconstruct past ocean temperatures from sediment archives. However, proxy-temperature relationships based on GDGTs in the Arctic Ocean differ from those observed in global calibration datasets. In high-latitude environments, GDGT-based proxies display reduced sensitivity and increased variability, potentially limiting their reliability for temperature reconstructions. These inconsistencies may be due to distinct processes governing GDGT distributions in these regions, highlighting the need for further investigation of their spatial and temporal variability. This study determines concentrations and relative abundances of relevant GDGT groups (isoprenoid, hydroxylated, and branched) in sediment cores and surface sediments from the Arctic Ocean. We observe larger than expected variability in downcore records of the temperature proxies TEX 86 and those based on hydroxylated GDGTs (e.g., TEX 86 OH or RI-OH’), exceeding spatial variability observed in Arctic Ocean surface sediments or as expected due to past climate change. GDGT concentrations in downcore sediments are an order of magnitude lower than at the sediment surface and more than two orders of magnitude lower than in surface sediments from more productive outer shelf and slope environments. These differences in concentrations suggest that GDGT records in central Arctic sediments may be highly influenced by shifts in terrestrial input and lateral transport of allochthonous GDGTs, as well as possible in situ production of GDGTs. Substantial and consistent subsurface temperature excursions in downcore records are potentially linked to in situ GDGT production by methanotrophic archaea. Furthermore, the abundance of hydroxylated GDGTs may depend on microbial community changes, potentially signifying past changes in biological productivity alongside calcareous microfossils. These complexities contribute to large variability and systematic temperature misrepresentation in GDGT-based temperature estimates. Our findings emphasize the need for a refined understanding of GDGT sources when interpreting GDGT-derived climate records in complex environments such as the Arctic Ocean.
Martens et al. (Wed,) studied this question.