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Hydroxylated isoprenoid GDGTs (OH‐GDGTs) have emerged as a novel tool for reconstructing sea surface temperatures. However, when using marine OH‐GDGT calibration in lacustrine settings, it leads to a significant overestimation of temperatures, emphasizing the necessity for a thorough examination of OH‐GDGTs in lakes. Here, we investigated OH‐GDGT distributions in surface sediments from 65 lakes in West China and compiled published Asian lake and global marine OH‐GDGT data sets. Among all GDGT‐based indices, RI‐OH showed the strongest correlation with temperature across Asian lakes. The RI‐OH value was higher in lakes than in marine sediments, likely due to differences in the composition of Group 1.1a thaumarchaeotal species between the two settings. The first RI‐OH temperature calibration for lakes was developed and it addressed the issue of temperature overestimation when applied to both water column and sediment core, highlighting the potential of OH‐GDGTs as a new terrestrial paleothermometer. Plain Language Summary: Reconstruction of past terrestrial temperatures plays a crucial role in understanding modern global warming and projecting future climate patterns, yet reliable terrestrial temperature proxies remain limited. In this study, we present compelling evidence that the ring index of OH‐GDGTs, expressed as RI‐OH, is predominantly influenced by temperature in lacustrine settings, regardless of the wide range of physical and chemical characteristics of the lakes. We developed the first lacustrine RI‐OH‐temperature calibration and successfully applied it to a water column and a sediment core. These findings suggest that RI‐OH can be used as a novel paleothermometer in lacustrine settings. Key Points: OH‐GDGTs were first investigated in lacustrine settings along a wide temperature gradientTemperature was the most important factor affecting OH‐GDGT distributions in lacustrine settingsThe first calibration in lacustrine settings was established and successfully applied to a water column and a sediment core [ABSTRACT FROM AUTHOR]

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]

Hydroxylated isoprenoid glycerol dialkyl glycerol tetraethers (OH-GDGTs), with one or two hydroxyl groups in one of the biphytanyl moieties, are major compounds in planktonic Thaumarchaeota , and occur widely in marine and lacustrine sediments. In order to examine their potential as an indicator of local variation in sea surface temperature (SST), we collected 70 surface sediments from the Chinese coastal seas (CCSs), including 16 from the Yangtze Estuary, to determine their tetraether lipid composition. The proportion of OH-GDGTs relative to total isoprenoid GDGTs increased with latitude from 1.8% to 12.8% and correlated strongly with SST, as indicated from redundancy analysis. The variation in OH-GDGT composition was best captured by the weighted average number of cyclopentane moieties in OH-GDGT-1 and -2 (RI-OH), which correlated significantly with both summer and autumn SST and was associated with minimum residual SST relative to remote sensing data. The large input of terrigenous organic matter to the Yangtze Estuary appears to have no significant influence on the OH-GDGT based proxy. Our study suggests that RI-OH could serve as a useful proxy for recording warm seasonal SST in the CCSs. A global surface sediment compilation further indicates that RI-OH and its derivative, RI-OH′, which additionally contains OH-GDGT-0, may be used to estimate SST in warm (ca. > 15 °C annual mean SST) and cold (ca. < 15 °C) environments, respectively. [ABSTRACT FROM AUTHOR]