Application potential of UK′37 and TEX86H palaeothermometers in high-energy strait-type marginal seas: a case study in the Taiwan Strait

Abstract

U^K’₃₇ and TEX₈₆^H palaeothermometers are widely applied to sea surface temperature (SST) reconstructions in global oceans. However, their applications in marginal seas often yields biased results due to regional environmental factors. This study investigated the applicability and controlling factors of these proxies in the subtropical, high-energy Taiwan Strait (TS). Utilizing a 35-year dataset (1982–2016) of AVHRR and MODIS-derived annual and seasonal average SST archives, we conducted regression analyses on U^K’₃₇ and TEX₈₆^H proxies of 58 surface sediment samples from the study area. Additionally, we employed Empirical Orthogonal Function (EOF) analysis to elucidate the physical processes influencing the index reliability. TEX₈₆^H-reconstructed SSTs exhibit a cold bias of −5.5–0.3 °C compared to observed SSTs, largely due to seasonal upwelling and terrestrial inputs. Conversely, U^K’₃₇-reconstructed SST in the muddy sediment zone of the northern TS shows a warm bias of 1.8–6.3 °C, relative to observed SST, attributable to lateral transport processes in the said environment. By accounting for terrestrial influences as the main non-temperature factor, we developed an improved regional calibration equation for TEX₈₆^H-SST in the TS. These results highlight the necessity of considering hydrodynamic effects when applying U^K’₃₇ index in such marginal seas. Through modern calibration using surface suspended particulate matter (SPM) and hydrodynamic correction, this study effectively mitigates lateral transport interference, providing a robust framework for palaeotemperature reconstruction in strong hydrodynamic strait-type marginal sea environments.