Reconstruction of climate variability in Indian Summer Monsoon Rainfall (ISMR) using high-resolution long-term multi-proxy records from speleothems of Meghalaya, north-east India


The Indian Summer Monsoon Rainfall (ISMR) has significant contribution in Asian Summer Monsoon Rainfall (ASMR) and its variability has been widely investigated during last decades. A small discrepancy or delay in the ISMR has impact on the environment (frequent floods and droughts), agriculture, socioeconomic and cultural advancement across South Asia. For example, extreme events in various regions in India, such as the Kedarnath flood in 2013, the Kerala flood in 2019, and frequent floods in Assam, Maharashtra, and Gujarat as well as glacier burst in Uttarakhand in 2021. The ISMR exhibits strong variability from seasonal to intra-annual, decadal to multi-decadal and orbital time scales. However, cause or this trend is unclear, either it could be due to natural variability or the increased anthropogenic-induced warming.

In the present study five stalagmite samples from Krem Mawmluh and have been sampled under active drip sites. Their architectural structure is well preserved with alternating laminae/bands mixed calcite and/or aragonite. This has several advantages, such as the affinity to contain high uranium concentrations and high growth rates enabling precise age control. However, at present, less is known about conditions governing δ18O in aragonite compared to calcitic stalagmites. Three of the stalagmites have been micro-drilled from the top and the base using a hand-held dental drill for precise 230Th/U-dating. These ages show that the aragonitic sections are much younger (i.e., almost recent) than the calcitic sections suggesting that the speleothem cover a wide age range between recent growth and much older than the Holocene. This is ideal for the present study to understand the climate variability in ISMR on various time-scales (interannual to millennial and even orbital). In addition, all stalagmites show this transition from calcite to aragonite, which is clear evidence for a big change in the cave system, which could even be induced anthropologically. Additional stalagmite samples from Krem Lymput will be analysed accordingly for 230Th/U-dating.

Three main objectives of the present study are: i) To generate high-resolution paleoclimate data and ISMR variability from Krem Mawmluh and Krem Lymput of Meghalaya, northeast India. ii) Understanding the controlling mechanisms influencing the ISMR variability and its association to the EASM. iii) Understanding the implications of various proxy data and their effect on fabrics preserved in the stalagmite. The proposed research project is planned to achieve the above objectives through an interdisciplinary approach including the state-of-the-art 230Th/U-dating and analysis of several established and novel climate proxies, such as stable isotopes (δ18O and δ13C) and fluid inclusion-hosted H2O, trace-elements (Mg, Sr, etc.), non-traditional isotopes (δ44Ca) on the stalagmite samples from Krem Mawmluh and Krem Lymput in Meghalaya from north-east India.