Comparison and implication of TEX86 and U37Kʹ temperature records over the last 356 kyr of ODP Site 1147 from the northern South China Sea

Proxy records from the South China Sea (SCS) have played an important role in understanding late Quaternary SCS environmental changes and the East Asian Monsoon (EAM) variations, but few long sea surface temperature (SST) records have been generated from the SCS. The recently established TEX86 index provides an opportunity to generate long SST records, especially for tropical oceans, but the applicability and climatic interpretation of the TEX86 index for the SCS need further study. We report and compare orbital scale resolution (ca. 5.3 kyr) TEX86 and U37Kʹ temperature records of the past 356 kyr for ODP Site 1147 from the northern SCS. Both records display clear and similar glacial–interglacial patterns. The U37Kʹ SST fluctuated between 22.3 °C and 28.3 °C, with a glacial–interglacial difference of 4–5 °C; while the TEX86 temperature fluctuated between 20.3 °C and 25.4 °C, with a slightly smaller glacial–interglacial difference of ca. 4 °C. The TEX86 temperature has been consistently lower than the U37Kʹ temperature over the past 356 kyr, consistent with previous studies suggesting that the U37Kʹ index is a proxy for SST but the TEX86 index is a proxy for subsurface temperature. Thus, it is proposed that the temperature difference (ΔT) between the U37Kʹ and TEX86 records reflects mixed layer depth (MLD) changes in the northern SCS, which fluctuated between 0.3 and 4.0 °C with high values mostly during interglacials and lower values mostly during glacial stages. MLD changes in the northern SCS are interpreted to be driven by EAM changes, with stronger winter monsoon resulting in a deeper MLD and a smaller ΔT. Thus, the combination of U37Kʹ and TEX86 records and their ΔT can be used to reconstruct East Asian winter monsoon variations, as well as their influences on the hydrographic structure of the SCS.