Abstract The widely distributed paleoclimate archives in Tajikistan, such as loess-paleosol sequences and the fluvial and lacustrine sedimentary rocks, are excellent materials for studying the aridification histories and mechanisms of the westerlies and the uplift of the Pamirs. The branched glycerol dialkyl glycerol tetraethers (brGDGTs)-based proxies have been increasingly used to reconstruct the paleoenvironmental parameters, e.g., paleo-pH, paleotemperature and paleoaltitude, from sedimentary records and represent potential tools to address the above issues. However, a knowledge of the applicability and factors affecting brGDGT-based proxies remains incomplete, especially in westerlies-dominating areas. Here, we present results from a study with 53 surface soils that are collected along altitudinal transects in the windward slope of the western Pamirs, Tajikistan with large environmental parameter gradients (mean annual air temperature (MAT) varying from −5.1 to 12.6 °C; mean annual precipitation (MAP) spanning a range from 135 to 882 mm; pH ranging from 5.9 to 8.9; soil water content (SWC) changing from 0.102 to 0.183 m3/m3). The proxies (CBT5ME, IR6ME, CBT′ and IBT) show significant correlations with measured pH values (r2 = 0.51, 0.52, 0.51 and 0.53, respectively), implying the great potential of these proxies for pH reconstructions in Tajikistan. For the alkaline soils, the reconstructed temperature lapse rates (TLR) are constrained to be −1.0 °C/km (actual values ranging from −4.9 to −5.4 °C /km) using the MATmr, a brGDGT-based paleothermometer which is thought to be independent of pH. Similar to the traditional brGDGT-based paleothermometer MBT′/CBT, the anomalies in alkaline soils are related to the fact that pH-dependent 6-methyl brGDGTs are not completely excluded from the calculations in MATmr. The paleothermometer which excludes 6-methyl brGDGTs (MBT′5ME) is no longer influenced by pH, and records MAT variations along the altitudinal transects for soils lower than ~3.3 km. For soils higher than ~3.4 km, the correlations between the brGDGT-derived MAT and altitude are statistically significant only in samples with high SWC. However, the calculated MAT and TLR are both overestimated in high SWC samples. Our results suggest that brGDGT-based proxies have the potential to reconstruct palaeoenvironmental parameters in arid and semi-arid Tajikistan with the discretion of the appropriate proxies and calibrations.

中文翻译：

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评估西风带中土壤细菌四醚代理的潜力，塔吉克斯坦西帕米尔高原及其对古环境重建的影响

摘要 塔吉克斯坦境内分布广泛的黄土-古土壤层序、河湖相沉积岩等古气候档案是研究西风带干旱化历史和机制以及帕米尔高原隆升的极好资料。基于支链甘油二烷基甘油四醚 (brGDGT) 的代理越来越多地用于从沉积记录重建古环境参数，例如古 pH、古温度和古海拔，并代表解决上述问题的潜在工具。然而，关于影响基于 brGDGT 的代理的适用性和因素的知识仍然不完整，尤其是在以西风为主的地区。这里，我们展示了一项研究的结果，这些土壤沿塔吉克斯坦西帕米尔高原迎风坡的海拔断面收集，环境参数梯度较大（年平均气温 (MAT) 从 -5.1 到 12.6 °C；年平均气温变化）降水 (MAP) 范围从 135 到 882 毫米；pH 值范围从 5.9 到 8.9；土壤含水量 (SWC) 从 0.102 到 0.183 立方米/立方米）。代理（CBT5ME、IR6ME、CBT' 和 IBT）与测量的 pH 值显着相关（分别为 r2 = 0.51、0.52、0.51 和 0.53），这意味着这些代理在塔吉克斯坦的 pH 重建方面具有巨大潜力。对于碱性土壤，使用 MATmr 将重建的温度递减率 (TLR) 限制为 -1.0 °C/km（实际值范围为 -4.9 至 -5.4 °C /km），一种基于 brGDGT 的古温度计，被认为与 pH 值无关。与传统的基于 brGDGT 的古温度计 MBT'/CBT 类似，碱性土壤中的异常与 pH 依赖性 6-甲基 brGDGT 并未完全排除在 MATmr 计算之外的事实有关。排除 6-甲基 brGDGTs (MBT'5ME) 的古温度计不再受 pH 值的影响，并记录了海拔低于 ~3.3 km 土壤的 MAT 变化。对于高于~3.4 km 的土壤，brGDGT 衍生的 MAT 与海拔之间的相关性仅在具有高 SWC 的样本中具有统计显着性。然而，计算的 MAT 和 TLR 在高 SWC 样本中都被高估了。