Assessing the suitability of brGMGTs as temperature indicators since the last deglaciation: Insights from Sihailongwan Maar Lake, northeastern China

Reconstructing past temperature variations is essential for predicting future trends under global warming. The recently developed biomarker, branched glycerol monoalkyl glycerol tetraethers (brGMGTs), has emerged as a promising proxy for continental paleotemperatures. However, lake water physicochemical conditions may influence brGMGT distributions, limiting their reliability as temperature indicators. Here, we analyzed brGMGT distributions in Sihailongwan Maar Lake (Lake SHL) in northeastern China. Results show that brGMGTs are abundant in downcore sediments and differ from those in catchment soils, indicating that they are primarily produced in situ. Further analyses demonstrate that, among the brGMGT-derived proxies, %brGMGTs exhibits a significant positive correlation with the mean lake water temperature reconstructed for Lake SHL since the last deglaciation (15.3 kyr BP), indicating that it effectively captures overall temperature variations. In contrast, the other proxies correlate significantly with precipitation, highlighting their susceptibility to precipitation influence in this lake. This divergence likely arises because brGMGT-producing bacteria may adjust their membrane composition to maintain stability in response to variations in ambient temperature—a signal effectively preserved by %brGMGTs—whereas the other proxies depend on weighted ratios among different brGMGT compounds, which can mask this temperature sensitivity when individual compounds are influenced by precipitation.