Vertical distribution of isoprenoid GDGTs in suspended particles from the East China Sea shelf and implications for sedimentary [formula omitted] records

Abstract

The TEX86H (or TEX86) paleothermometer has been widely applied for reconstructing water temperature in marine settings, particularly in marginal seas which often archive paleoclimate records with high temporal resolution. Yet debate remains regarding the water depth at which the TEX86H signal is imparted in these settings. In this study, East China Sea (ECS) surface sediments and suspended particulate matter (SPM) from different water depths (0–60 m) were analyzed for lipid biomarkers to better constrain the depth to which the sedimentary TEX86H signal corresponds. Our data showed divergent vertical distributions between archaeal lipids and phytoplankton lipids. The maximum concentration of core lipid isoprenoid glycerol dialkyl glycerol tetraethers (core iGDGTs) appeared in bottom waters (2–5 m above the sea floor) at all sites, whereas phytoplankton lipids showed highest abundance in surface waters (0 m). Consistent with the maximum core iGDGTs concentration in bottom waters, the best correlation was observed between SPM TEX86H values and 2–4 weeks averaged water temperatures from the bottom waters. Moreover, the SPM core iGDGTs content was higher in bottom waters than in surface sediments, implying that in situ production rather than sediment resuspension leads to the maximum concentration of core iGDGTs in bottom waters. By compiling published surface sediment data from water depths < 100 m we find that the correlation of TEX86H with bottom water temperature (BWT) exceeds that with sea surface temperature (SST). Therefore, it is proposed that sedimentary TEX86H is a BWT proxy in the shallow ECS.