Temperature and water depth effects on brGDGT distributions in sub-alpine lakes of mid-latitude North America

Calibration and Application of Branched GDGTs to Tibetan Lake Sediments: The Influence of Temperature on the Fall of the Guge Kingdom in Western Tibet, China

“…We calculated the degrees of methylation of 5‐ and 6‐methyl brGDGTs (MBT′ 5Me and MBT′ 6Me ) from our new samples combined with previously published Chinese surface sediment samples (Dang et al., 2018; Table S1 in Supporting Information ) and regressed with measured temperatures to develop a new brGDGT‐temperature calibration (Figures 3a–3f). We compare applications using our new temperature calibrations with those from previously published calibrations from global lakes (Martínez‐Sosa et al., 2021; Raberg et al., 2021), and regional lake calibrations (Dang et al., 2018 [China]; Dugerdil et al., 2021 [Mongolian and Baikal]; Feng et al., 2019 [Southwestern China]; Harning et al., 2020 [Iceland]; Russell et al., 2018 [East African]; Stefanescu et al., 2021 [North America]; Zhao et al., 2021 [South Greenland]) to evaluate the performance of our calibration (Figures 3g and 3h).…”

“…While there is substantial agreement for the relationship between brGDGT distributions and temperature, there is little understanding of how accurately the brGDGT-temperature relationship represents the transition between lake and air temperatures. Stefanescu et al (2021) found that in both shallow and deep lake surface sediments from North America, the MBT′ 5Me index is strongly correlated to lake bottom water temperatures. Similarly, brGDGTs in the Dagze Co surface sediment reflect lake bottom water temperatures (Table 2; 2.36°C in surface sediment MBT′ 6Me -MAAT; 0.17°C in observed station MAAT, 2.86°C in observed annual bottom water temperatures according to Wang et al [2021]).…”

“…Previous studies suggest that lake depth, seasonality, salinity, and dissolved oxygen content were important variables controlling the brGDGT production in many (Dang et al, 2018;Raberg et al, 2021;Stefanescu et al, 2021;Wu et al, 2021) though not in all lake sediments (Russell et al, 2018). To determine if lake depth influences brGDGT-derived temperatures, we selected three lakes with similar MAAT (∼0.2°C) and different lake depths: Dagze Co (0.31°C, 38 m), Laguo Co (0.14°C, 18 m), and Bieruoze Co (0.13°C, 2 m).…”

“…In addition, we find more 6-methyl brGDGTs in our studied lake sediments than 5-methyl brGDGTs (Figure 2a) and Dang et al (2018) also found that 6-methyl brGDGTs are correlated with temperature in Chinese lakes. Therefore, we developed the following new brGDGT-derived calibrations to MAAT, summer temperature (Summer T), and mean temperature of MAF T based on MBT′ 6Me : (Dang et al, 2018;Dugerdil et al, 2021;Feng et al, 2019;Harning et al, 2020;Martínez-Sosa et al, 2021;Raberg et al, 2021;Russell et al, 2018;Stefanescu et al, 2021;Zhao et al, 2021). (a-c) The relationship between MBT′ 5Me and MAAT, summer and MAF temperatures based on the study sites and previously published sites in China according to (Dang et al, 2018)…”

“…We calculated the MAAT, Summer T, and MAF T bias of settling particles from traps (Dagze Co and Lake 578) to evaluate the performance of our calibrations (Figure 3g). Estimated biases of temperatures in Dagze Co and Lake 578 settling particles from traps revealed that bias ranges from −3.97°C to 12.65°C based on global lake calibrations (Martínez-Sosa et al, 2021;Raberg et al, 2021), from −34.02°C to 27.86°C based on site-specific calibrations (Feng et al, 2019;Harning et al, 2020;Zhao et al, 2021), and from −12.56°C to 32.81°C based on regional calibrations (Dang et al, 2018;Dugerdil et al, 2021;Russell et al, 2018;Stefanescu et al, 2021).…”