Disentangling effects of sea surface temperature and water depth on hydroxylated isoprenoid GDGTs: Insights from the hadal zone and global sediments

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 (2560 – 9560 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 dataset, 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