Climatic variability in Central Indian Himalaya during the last ～ 1800 years: Evidence from a high resolution speleothem record

摘要

Stable isotopes from a U/Th dated aragonite stalagmite from the Central Kumaun Himalaya provide evidence of variation in climatic conditions in the last ～1800 years. The δ~(18)O and δ~(13)C values vary from -43‰ to -7.6‰ and -3.4‰ to -9.1‰ respectively, although the stalagmite was not grown in isotopic equilibrium with cave drip water, a clear palaeoclimatic signal in stalagmite δ~(18)O values is evident based on the regional climate data. The stalagmite showed a rapid growth rate during 830-910 AD, most likely the lower part of Medieval Warm Period (MWP), and 1600-1640 AD, the middle part of Little Ice Age (LIA). Two distinct phases of reduced precipitation are marked by a 2‰ shift in δ~(18)O values towards the end of MWP (～ 1080-1160 AD) and after its termination from ～ 1210 to 1440 AD. The LIA (～ 1440-1880 AD) is represented by sub-tropical climate similar to modern conditions, whereas the post-LIA was comparatively drier. The Inter Tropical Convergence Zone (ITCZ) was located over the cave location during wetter/warmer conditions. When it shifted southward, precipitation over the study area decreased. A prominent drop in δ~(18)O and δ~(13)C values during the post-LIA period may also have been additionally influenced by anthropogenic activity in the area.