Sources, Distribution and Paleoenvironmental Application of Fatty Acids in Speleothem Deposits From Krem Mawmluh, Northeast India

Abstract

Integrated 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 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 (10.6–124 μg/L) and moonmilk (1.32–16.5 μg/g) compared to the stalagmite (0.67–2.09 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.

Biomarker proxies for reconstructing Quaternary climate and environmental change

“…Li et al ., 2011; Blyth et al ., 2016; Baker et al ., 2019). As speleothems can also yield fatty acid, n ‐alkanol and n ‐alkan‐2‐one distributions, interpreted to reflect changing soil micro‐organism responses to Holocene climate change (Xie et al ., 2003; Kalpana et al ., 2021), there is further potential to consider ecosystem response to temperature change (see also ‘Reconstructing vegetation using biomarker distributions’), especially as analytical developments reduce sample sizes (e.g. Meckler et al ., 2021).…”

Investigating possible links between Holocene environmental changes and cultural transitions across India

“…Mawmluh Cave (Kathayat et al, 2018); 50. Mawmluh Cave (Kalpana et al, 2021); 51. Debaka Swamp (Dixit and Bera, 2012); 52.…”

“…Zone IV comprises parts of eastern as well as northeastern India with ~75% of the annual precipitation contributed by the ISM. Climatic reconstruction from fatty acids indices on speleothem collected from Krem Mawmluh byKalpana et al (2021) indicate a period of intense monsoon activity from early to Mid-Holocene (~10 to 6.5 cal kyrs BP). Previous research from this location by Dutt et al (2015) offered agreeable interpretations.…”

Lipid biomarkers in modern marine sediments and surface snow: Towards a multi-archive reconstruction of phytoplankton conditions in the southwestern Ross Sea region, Antarctica

“…The carbon preference index for fatty acids (CPI) was calculated for each sample, as it indicates the amount of microbial activity or amount of modification (Equation 3.3) (Kalpana et al, 2021). An even over odd preference indicates relatively unmodified material (e.g.…”

“…The presence and concentration of lower molecular weight (LMW) compounds and higher molecular weight (HMW) compounds provides detail about the dominating source of fatty acids, marine or terrestrial (Kalpana et al, 2021). A high LMW/HMW ratio indicates an aquatic/marine source of fatty acids, whereas a low LMW/HMW ratio indicates a terrestrial or higher plant input of fatty acids (Kalpana et al, 2021). The LMW/HMW ratio was compared to determine whether the dominant source of fatty acids was marine-derived (Equation 3.4).…”