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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]

Microbial glycerol dialkyl glycerol tetraethers (GDGTs) in lacustrine sediments are widely used to reconstruct terrestrial paleoenvironments. However, lipids of diverse origin in lakes make it difficult to decipher environmental information, appealing for the necessity to evaluate the impact of terrigenous input on the distribution of GDGTs through long-term monitoring. In this study, we conducted two-year monitoring of GDGTs along the river, estuary, near shore, to the center of Lake Liangzi in central China. By comparing the spatiotemporal changes of GDGT distribution in suspended particulate matter (SPM) and surface sediments, we found that the archaeal isoprenoid GDGTs (isoGDGTs) were mainly produced in situ in the river-lake systems, and not affected by the soil input. In contrast, the bacterial branched GDGTs (brGDGTs) were affected, to some extent, by soil input, depending on the distance to the lakeshore. The soil input of brGDGTs was enhanced during an episode of abnormal rainfall (flood). Moreover, the large variation of isoGDGTs indicates the in situ production under the anoxic condition in lake water. The paired increase in the GDGT-0/Cren ratio and GDGT concentration might be diagnostic of flooding events in ancient times. [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]

Highlights: [•] GDDs and GDGTs in surface soil and a loess–paleosol sequence investigated. [•] iGDDs and bGDDs followed same distribution pattern as corresponding GDGTs, suggesting common source. [•] GDGTs/(GDGTs+GDDs) ratio decreased exponentially with depth. [•] GDDs in soils may be degradation products of GDGTs. [Copyright &y& Elsevier]

Abstract: Lipid biomarkers in stalagmites have potential in palaeoenvironmental reconstruction, but glycerol dialkyl glycerol tetraethers (GDGTs) in stalagmites have rarely been investigated. We report the occurrence of archaeal isoprenoid GDGTs and bacterial branched GDGTs in Heshang Cave stalagmites in central China. The archaeal component, crenarchaeol, dominated bacterial branched GDGTs in the stalagmites and on the weathered parent rock surface collected inside the cave. In contrast, the distribution of GDGTs in the overlying soil shows that branched GDGTs dominated archaeal GDGTs. Hence, the majority of archaeal GDGTs in stalagmites may be produced by Crenarchaeota inhabiting the cave rather than being inherited from the overlying soil. Bacterial branched GDGT distributions, expressed as MBT and CBT indices, showed remarkable differences between stalagmite and soil samples, implying that most branched GDGTs may also be produced in situ in the cave. The TEX86 or values were found to increase with more depleted δ 18O values representing much stronger monsoon and therefore usually higher temperatures, in the study region. However, the MBT/CBT index in stalagmites may be influenced by a variety of factors besides palaeotemperature. [ABSTRACT FROM AUTHOR]

The distribution of archaeal ether lipids is thought to be governed by salinity in hypersaline and marine environments due to differences in their biological sources. However, little is known about their source and relationship with salinity in lacustrine environments. To explore this, we analyzed the distribution of specific archaeal lipids (isoprenoid GDGTs and diethers) of 11 ponds along a salinity gradient (0.8‰ to 279‰) in Inner Mongolia, NE China. Functional gene mcrA and compound-specific stable carbon isotope data were used to explore the biological source(s) of archaeal diether and tetraether lipids. Both lipid- and DNA-based methods showed methanogens to be abundant in ponds, which is consistent with the dominance of GDGT-0 relative to other isoprenoid GDGTs as well as the occurrence of archaeol (C 20 /C 20 DGD), hydroxyarchaeol and the mcrA gene. However, the occurrence of the extended archaeol (C 20 /C 25 DGD) also suggests the presence of Halobacteriales, non-halophilic methanogens and halophilic methanogens. This means that the biological sources of archaeal diethers and tetraethers are complicated. We subsequently evaluated the applicability of TEX 86 temperature and ACE salinity proxies in these settings; however, due to the mixed sources of archaeal diethers and tetraethers, these proxies are not applicable in these ponds and it appears that salinity is not the dominant control on archaeal ether lipid distributions in these saline ponds. [ABSTRACT FROM AUTHOR]