Ronnie N. Glud

Hydroxylated isoprenoid glycerol dialkyl glycerol tetraethers (OH‐GDGTs) preserved in marine sediments are thought to be controlled by sea surface temperature (SST). However, water depth may also exert a significant influence on OH‐GDGTs. Here, we investigated sedimentary OH‐GDGTs in the Kermadec and Atacama trench regions (2,560–9,560 m water depth). Sedimentary OH‐GDGTs in hadal trenches were dominated by OH‐GDGT‐0 (72 ± 8%), potentially reflecting an adaption of source organisms to ambient cold deep water. This result, combined with global data set, revealed that the predominance of OH‐GDGT‐0 is a ubiquitous phenomenon in deep‐sea sediments, leading to a considerable underestimation of RI‐OH′‐derived SSTs. By considering both SST and water depth effects, we developed more accurate OH‐GDGT‐based paleothermometers for both shallow regions and the global ocean, encompassing the full‐ocean‐depth range. Our findings highlight the importance of accounting for the effect of water depth on OH‐GDGTs and provide improved tools for reconstructing paleo‐SSTs.