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Abstract

The TetraEther indeX of 86 carbon atoms (TEX86) proxy, which is based on isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) produced by Thaumarchaeota in marine environments, is widely used to reconstruct past sea surface temperatures (SSTs). However, evidence suggests that this proxy often instead reflects subsurface conditions, particularly in dynamic marginal seas. Therefore, we conducted a cross-seasonal study of glycerol dialkyl glycerol tetraether (GDGT) distributions in the southern East China Sea (ECS), which is characterized by strong monsoonal and current-driven hydrographic variability. We analyzed surface sediments and the high-resolution vertical profiles of suspended particulate matter (SPM) collected from 2016 to 2022. Our results indicate that the sedimentary TEX86 values correlated more closely with annual mean subsurface temperatures (subT) than with SSTs. The concentrations of isoGDGTs consistently peaked between 100 and 150 m, with limited seasonal variation. Linear regression overestimated SSTs, with BAYSPAR Bayesian calibration yielding values matching the observed subT, particularly at isoGDGT production depths. These findings suggest that the TEX86 calculations integrate a stable subsurface signal rather than capture transient surface variability. This study observed a resemblance between SPM and sediment TEX86, indicating that vertical transport dominates the delivery of GDGTs to the seafloor. Overall, our findings underscore the importance of identifying the subsurface origin of TEX86 signals and indicate that BAYSPAR calibration should be used in marginal sea environments. This study provides key cross-seasonal evidence of GDGT stratification in the ECS and refines TEX86-based paleotemperature reconstructions in climatically sensitive western Pacific settings.

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