Influence of Seasonal Temperature Variation and pH Disparity on bGDGTs Thermometers in Soils

To better understand the seasonal variation of bGDGTs in soils, we collected samples time{\hyphen{}}serially from several Chinese alkaline soils over 1 year. On the seasonal scale, the composition of bGDGTs is the result of a long{\hyphen{}}time adaption to temperature variation rather than a short{\hyphen{}}time adjustment. bGDGTs{\hyphen{}}derived temperatures in soils from cold and high altitude of Tibet Plateau are likely to reflect the temperature of spring/summer transition period. However, in other sites, the distribution and proxies of bGDGTs don’t show significant seasonal variation or bias. Furthermore, soil pH appears to be the main reason for discrepancy in slopes of different calibrations, which can result in distinct calibration formulas in soils. Combining with the previously published datasets, our results demonstrate that the responses of MBT index to temperature are different in alkaline and acidic soils. Here, we propose an MBT{\hyphen{}}MAAT calibration in neutral to alkaline soils: MAAT = 20.78 $\times$ MBT + 5.92 ({\it R}\textsuperscript{2} = 0.88, {\it p} \textless{} 0.001) (5$\sim$25 $^\circ$C). This calibration partially amends the impact of soil pH on MBT{\hyphen{}}MAAT relationship, which provides more accurate calibration for paleotemperature reconstruction in specific regions of~China.