oa Assessing Water Depth Effects on Archaeal Lipids and Refining the TEX86 Proxy: From Hadal Trenches to Global Perspectives

The TEX86 proxy, based on archaeal isoGDGTs, is widely used for reconstructing past sea surface temperatures (SSTs), yet the impact of water depth on its reliability remains unclear. To address this, we analyzed sediments from five hadal trench regions alongside a global dataset. Our findings show that as water depth increases, low-ring-number isoGDGTs become more abundant, while high-ring-number isoGDGTs decrease. Despite these shifts, isoGDGT compositions and TEX86 remain strongly correlated with SST, even in the ocean’s deepest regions, suggesting that sedimentary isoGDGT pools are largely dominated by shallow-water-derived signals. The impact of water depth on TEX86 is further minimized by compensatory changes in GDGT-2 and GDGT-3 and TEX86’s inherent ratio structure. Notably, TEX86 provides more reliable SST estimations in deep-sea sediments than in coastal sediments. We also observed an unusually high abundance of the crenarchaeol regio-isomer (Cren’) in deep-sea sediments, suggesting a distinct source or history compared to other isoGDGTs. By excluding Cren’ from TEX86, the resulting TEX*86 proxy shows stronger correlations with SST, reduced sensitivity to water depth, and improved performance in polar regions. We further establish new TEX*86-SST calibration models, improving SST reconstructions globally and across diverse water depths.