IIntegrated multiproxy geochemical studies are essential to reconstruct the paleoenvironment through different time scales. Pristine terrestrial archives such as speleothems provide an excellent opportunity to study these changes by measuring the stable isotope and biomarker trends preserved in these records. Here, we investigated fatty acids in drip water, moonmilk, and a stalagmite (KM-1) retrieved from Krem Mawmluh in northeast India to constrain the sources and distribution of these compounds. Besides, we tested their compatibility with established glycerol dialkyl glycerol tetraethers (GDGT) and stable isotope proxies in KM-1 to probe the use of fatty acid-derived proxies for paleoclimate reconstruction. We observe a similar composition of fatty acids in drip water as well as the cave deposits with significantly higher concentrations of fatty acids in drip water (10.6 to 124 µg/L) and moonmilk (1.32 to 16.5 µg/g) compared to the stalagmite (0.67 to 2.09 µg/g). In KM-1 stalagmite, fatty acids and the presence of azelaic acid transported from surface soils indicate that these compounds are derived from bacterial activity both within the cave and the overlying soil cover. The branched C15 fatty acid index (iso+anteiso C15/nC15) increases during the Holocene, suggesting enhanced microbial production under warm/wet conditions. Fluctuations in the fatty acid indices coincide with abrupt shifts in the TEX86 and BIT proxies reflecting the warm/wet Holocene and cold/dry Late Pleistocene. These trends imply the potential use of fatty acids for reconstructing past climate changes in speleothems but need more analytical reference points to provide statistical data.

中文翻译：

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印度东北部 Krem Mawmluh Speleothem 矿床中脂肪酸的来源、分布及古环境应用

综合多代理地球化学研究对于通过不同时间尺度重建古环境至关重要。通过测量这些记录中保存的稳定同位素和生物标志物趋势，原始陆地档案（如洞穴探险）提供了研究这些变化的绝佳机会。在这里，我们研究了滴水、月奶和从印度东北部克雷姆莫姆鲁赫回收的石笋 (KM-1) 中的脂肪酸，以限制这些化合物的来源和分布。此外，我们测试了它们与已建立的甘油二烷基甘油四醚 (GDGT) 和 KM-1 中稳定同位素代理的兼容性，以探讨脂肪酸衍生代理用于古气候重建的用途。与石笋相比，我们观察到滴水和洞穴沉积物中的脂肪酸组成相似，滴水（10.6 至 124 µg/L）和月奶（1.32 至 16.5 µg/g）中的脂肪酸浓度明显更高（ 0.67 至 2.09 微克/克）。在 KM-1 石笋中，脂肪酸和从表层土壤传输的壬二酸的存在表明这些化合物来自洞穴内和上覆土壤覆盖层的细菌活动。支链 C15 脂肪酸指数 (iso+anteiso C15/nC15) 在全新世期间增加，表明在温暖/潮湿条件下微生物产量增加。脂肪酸指数的波动与反映暖/湿全新世和冷/干晚更新世的 TEX86 和 BIT 代理的突然变化相吻合。