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Hydroxylated glycerol dialkyl glycerol tetraethers (OH-GDGTs) have been recently proposed as novel proxies for sea surface temperature (SST) estimation. However, it is still unclear whether these proxies are applicable to the tropical South China Sea (SCS). We assessed the possible impact of extraction methods on the OH-GDGT distribution in marine sediments. A batch of marine sediments from the SCS was subjected to lipid extraction using a modified Bligh/Dyer method (BDM) and an ultrasonic extraction (UE) method, respectively. A systematic difference in the concentration and distribution of OH-GDGTs was observed between the two methods. Sample-by-sample comparison also demonstrated that the BDM had a higher extraction efficiency for OH-GDGTs than UE. The concentration of OH-GDGTs for the BDM dataset was generally higher than that for the UE dataset. The fractional abundance of OH-GDGTs with one cyclopentyl ring was higher for the BDM, resulting in a different OH-GDGT distribution between the BDM and UE datasets. The BDM dataset was thus further used to explore the potential of OH-GDGTs as a proxy for SST in the SCS. OH-2/OHs, the ratio of OH-GDGTs with two cyclopentyl moieties to total OH-GDGTs, exhibited a negative correlation with annual SST when SST was > 25 °C, as opposed to the positive correlation between them when SST was < 25 °C. This suggests that OH-2/OHs holds promise for the reconstruction of SST in the SCS where the SST is close to the warm threshold and proxies, like U K' 37 and TEX 86 H , do not work well. [ABSTRACT FROM AUTHOR]

To shed more light on the applicability of glycerol dialkyl glycerol tetraether (GDGT) based proxies for reconstructing environmental change in shallow marginal seas, we analyzed the GDGT composition of surface sediments from the east coastal sea of China (ECSC). The GDGT distribution in 58 surface sediment samples from the ECSC shows that the isoprenoid GDGTs ( i GDGTs) are mainly from autochthonous planktonic Thaumarchaeota and that the relative abundance of the acyclic GDGT (GDGT-0) in the ECSC increases with latitude, whereas that of cyclic GDGTs decreases. The fractional abundances of i GDGTs correlated significantly with annual and seasonal sea surface temperature (SST), especially with summer SST. Based on this, we propose a new calibration of the TEX 86 H proxy to reconstruct past SST in the ECSC. The new calibration shows a higher calibration coefficient ( R 2 0.84, p < 0.001), leading to a more robust reconstruction of temperature in China marginal seas. The 90 yr SST record derived with the new calibration for a sediment core from the ECSC is consistent with climate data from NOAA, demonstrating the applicability of the new calibration for summer SST reconstruction in this shallow marginal sea [ABSTRACT FROM AUTHOR]