Abstract
Bacterial branched glycerol dialkyl glycerol tetraethers (brGDGTs) have been successfully used as quantitative climate proxies for reconstructing annual mean air temperature (MAT) and soil pH from sediments. However, reconstructions derived from brGDGTs in regions with diverse hydrological and atmospheric conditions require further refinement. In this study, we investigated the suitability of brGDGTs as temperature and precipitation proxies from surface soils on opposite slopes of Mount Fanjing in subtropical China. The results show a clear altitudinal lapse rate of MBT′5ME-derived MAT and between-slope differences in MAT at given altitude. Moreover, the MBT′5ME-derived MAT values are more strongly related to the MAT from March to November than that of the whole year. A turning point is also observed from the measured pH and CBT′-derived pH gradients at altitude of 1400 m~1500 m, in accordance with the fog horizon, where precipitation reaches the maximum value. The findings prove that brGDGTs from soil transects can be used as indicators for reconstructions of climate parameters from subtropical regions of China.
Highlights
Glycerol dialkyl glycerol tetraethers (GDGTs) are membrane lipids that are ubiquitous in diverse environments[1]
In order to examine the suitability of branched glycerol dialkyl glycerol tetraethers (brGDGTs)-derived proxies, local temperature, precipitation, soil pH value and water content are measured or estimated for each sampling location
What’s more, the uncertainty of the global soil calibration (RMSE = ± 4.8 °C) is one of the reasons attributed to the temperature differences between methylation index of branched tetraethers (MBT)′5ME derived and measured mean air temperature (MAT) values
Summary
Glycerol dialkyl glycerol tetraethers (GDGTs) are membrane lipids that are ubiquitous in diverse environments[1]. To further improve understanding of the correlations between the two new brGDGT proxies (CBT′ and MBT′5ME), and both hydrological and temperature climatic parameters, we have investigated brGDGTs in surface soils along two altitudinal gradients from 579 m to 2314 m on Mount Fanjing of the Wuling Range, Guizhou Province, subtropical China (Fig. 2). This region of central-south China area is strongly influenced by the Summer Monsoon and receives more than 1100 mm precipitation per year. We assume that an analysis of altitudinal changes in brGDGTs from this mountain can enhance understanding of their potential utility as palaeo-climate proxies, especially for precipitation and temperature, in subtropical China
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