Global calibration of a novel,branched GDGT-based soil pH proxy |
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| Institution: | 1. MOE Key Laboratory for Earth Surface Process, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China;2. Hadal Science and Technology Research Center, College of Marine Sciences, Shanghai Ocean University, Shanghai 201306, China;3. Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China;4. Department of Environmental Science and Engineering, College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China;5. Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085, China;1. State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;2. Organic Geochemistry Unit, Bristol Biogeochemistry Research Centre and The Cabot Institute, School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK;1. Max Planck Institute for Biogeochemistry, Hans-Knöll-Str. 10, 07745 Jena, Germany;2. TEL, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, 100085 Beijing, China;3. NIOZ Royal Netherlands Institute for Sea Research, Department of Marine Organic Biogeochemistry, 1790 AB Den Burg (Texel), The Netherlands;4. Faculty of Geosciences, University of Utrecht, Utrecht, The Netherlands;1. CNRS, UMR 7619, METIS, F-75005 Paris, France;2. Sorbonne Universités, UPMC Univ. Paris 06, UMR 7619, METIS, F-75005 Paris, France;3. Institut de Recherche pour le Développement, UMR 7159, LOCEAN, Centre IRD France Nord, F-93143 Bondy Cedex, France;4. CNRS-UPS UMR 8148, GEOPS, F-91405 Orsay, France;5. Institute of Resource Assessment, University of Dar Es Salaam, PO Box 35097, Dar Es Salaam, Tanzania;1. State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;2. Organic Geochemistry Unit, School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK;3. University of Bristol Cabot Institute, University of Bristol, Bristol BS8 1UJ, UK |
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| Abstract: | Recently, 6-methyl branched glycerol dialkyl glycerol tetraethers (brGDGTs) were separated from 5-methyl brGDGTs, which are used in brGDGT-based proxies. Here we analyzed brGDGTs in 27 soil samples along the 400 mm isoline of mean annual precipitation in China by using tandem 2D liquid chromatography. The fractional abundance of 6-methyl brGDGTs showed a positive correlation with soil pH, while that of 5-methyl brGDGTs decreased with increasing soil pH. The abundance ratio of 6-/5-methyl brGDGTs, namely the isomerization of branched tetraethers (IBT), was calculated. The correlation of IBT with pH (pH = 6.33 ? 1.28 × IBT; R2 0.89; root mean squared error, RMSE, 0.24) was much stronger than that of the traditionally used cyclization index of branched tetraethers (CBT) with pH (R2 0.52; RMSE 0.49) and comparable with that of CBT′ with pH (R2 0.88; RMSE 0.25). Compiling all available data from 319 soil samples resulted in a global calibration: pH = 6.53 ? 1.55 × IBT (R2 0.72; RMSE 0.65), which has a better correlation than the CBT5ME-pH proxy (R2 0.63; RMSE 0.78), but a weaker correlation than the CBT′-pH proxy (R2 0.85; RMSE 0.52). Our result suggests that the IBT is a promising indicator for soil pH, particularly in cases when some compounds in the CBT′ index cannot be determined. |
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| Keywords: | 6-Methyl brGDGTs Soil pH CBT IBT GDGTs |
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