Palaeoclimate reconstructions on various timescales using stalagmites from Meghalaya, NE India, and applying U/Th dating, stable isotopes and element studies
Final Report Abstract
Present-day conditions and calibration. In order to decompose the various factors governing the geochemical proxies in stalagmites we developed specialized instrumentation and established a detailed microclimatemonitoring program. We developed an automated sampling device to facilitate remote microclimate monitoring, which is currently improved for commercialization. Multi-year microclimate monitoring of water chemistry and cave microclimate in Meghalaya revealed that water stable isotopes and speleothems track rainfall source and seasonality. Palaeoclimate reconstruction. Sub-seasonally sampled stalagmite proxy records reveal temporally non-stationary links between the Indian summer monsoon and ENSO during the past 60 years. Additionally, this record proves a link between the ISM and the Pacific Decadal Oscillation. Further work is dedicated to disentangling rainfall amount and moisture source changes. The last 2000 years of ISM rainfall amount and seasonality changes were reconstructed using replicating stalagmites from Uttaranchal and Meghalaya. We also aimed at a detailed sub-centennially resolved reconstruction of moisture source and rainfall-amount variability, covering the last ca. 45,000 years. As most sensitive with respect to monsoonal precipitation changes we identified two main sampling sites; one in Uttaranchal state (N India) and a second one in Meghalaya (NE India). While logistic complications restricted work at the former location, work in Meghalaya proved highly successful. Multi-year climate monitoring proved essential to resolve forcing factors at Mawmluh Cave, which has become a key site for ongoing climate reconstructions. While the Holocene is well represented in a stalagmite from Krem Umsynrang Cave near the border to Bangladesh, most sites show a peculiar interruption of growth during the mid-Holocene (ca. 5 ka BP), which might be related to changes in monsoonal circulation with the beginning decline of summer insolation. ISM moisture variations on glacial-interglacial time scales are reflected in pronounced Dansgaard-Oeschger (D-O) cycles and Heinrich events during the last glacial found in stalagmites from NE India. Dansgaard-Oeschger cycles and Heinrich events are very pronounced, reflecting significant hydrological changes associated with the ISM during the last 43,000 years.
