Distribution of branched glycerol dialkyl glycerol tetraethers in surface soils of the Qinghai-Tibetan Plateau: implications of brGDGTs-based proxies in cold and dry regions

The methylation index of branched tetraethers (MBT) and cyclization ratio of branched tetraethers (CBT) based on the distribution of branched glycerol dialkyl glycerol tetraethers (brGDGT) are useful proxies for the reconstruction of mean annual air temperature (MAT) and soil pH. Recently, a series...

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Bibliographic Details
Published in:Biogeosciences
Main Authors: Ding, S., Xu, Y., Wang, Y., He, Y., Hou, J., Chen, L., He, J.S.
Other Authors: Xu, Y (reprint author), Peking Univ, Coll Urban & Environm Sci, MOE Key Lab Earth Surface Proc, Beijing 100871, Peoples R China., Peking Univ, Coll Urban & Environm Sci, MOE Key Lab Earth Surface Proc, Beijing 100871, Peoples R China., Chinese Acad Sci, Inst Tibetan Plateau Res, Key Lab Tibetan Environm Changes & Land Surface P, Beijing 100085, Peoples R China., Chinese Acad Sci, Northwest Inst Plateau Biol, Key Lab Adaptat & Evolut Plateau Biota, Xining 810008, Peoples R China.
Format: Journal/Newspaper
Language:English
Published: BIOGEOSCIENCES 2015
Subjects:
CHAIN ALKENONE DISTRIBUTIONS
GDGT-BASED PROXIES
LAST DEGLACIATION
MEMBRANE-LIPIDS
LATE MIOCENE
ICE CORE
TEMPERATURE
SEDIMENTS
LAKE
WATER
ice core
Online Access:https://hdl.handle.net/20.500.11897/421179
https://doi.org/10.5194/bg-12-3141-2015
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Summary:The methylation index of branched tetraethers (MBT) and cyclization ratio of branched tetraethers (CBT) based on the distribution of branched glycerol dialkyl glycerol tetraethers (brGDGT) are useful proxies for the reconstruction of mean annual air temperature (MAT) and soil pH. Recently, a series of 6-methyl brGDGTs were identified which were previously co-eluted with 5-methyl brGDGTs. However, little is known about 6-methyl brGDGTs in the Qinghai-Tibetan Plateau (QTP), a critical region of the global climate system. Here, we analyze 30 surface soils covering a large area of the QTP, among which 6-methyl brGDGTs were the most abundant components (average 53 +/- 17% of total brGDGT). The fractional abundance of 6-methyl brGDGTs showed a good correlation with soil pH, while the global MBT'(5ME) calibration overestimates MAT in the QTP. We therefore proposed a MBT5/6 index including both 5- and 6-methyl brGDGTs, presenting a strong correlation with MAT in QTP: MAT = -20.14 + 39.51 x MBT5/6 (n = 27; r(2) = 0.82; RMSE=1.3 degrees C). Another index, namely IBT (isomerization of branched tetraether), based on carbon skeleton isomerization of the 5-methyl to 6-methyl brGDGTs, is dependent on soil pH: pH = 6 .77-1.56 x IBT (n = 27; r(2) = 0.74; RMSE = 0.32). Our study suggests that changing the position of methyl group of brGDGTs may be another mechanism for some soil bacteria to adapt to the ambient pH change in addition to the well-known cyclization. National Basic Research Program of China [2014CB954001]; National Science Foundation of China [41176164, 41476062] SCI(E) ARTICLE yunpingxu@pku.edu.cn 11 3141-3151 12

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