Hydro-climatic variability during last five thousand years and its impact on human colonization and cultural transition in Ladakh sector, India

摘要

The Ladakh Range in the Trans Himalaya houses sub-routes of the Silk route through its passes (La in local language) which may have been the main commercial and cultural passage to connect the central Asia and Tibetan region with the rest of India. A ca 6400-220 cal yr B.P. hydroclimatic record of two lakes viz Tsoltak lake and Yaya Tso near the Chang La and Hor La passes of Ladakh Range is presented here. The overall record (mineral magnetic analysis and microbiota) from the Ladakh range shows wetter conditions ca 6400 cal yr BP consistently declining till similar to 5000 cal yr BP and moderately wet and stable till similar to 4300 cal yr BP, followed by an arid cold phase (similar to 4300-4000 cal yr BP). This precedes two moderately wet phases (ca 4300-3500 cal yr BP and ca 1260-220 cal yr BP) and the peak arid conditions between 3500 and 2860 cal yr B P and 2230-855 cal yr BP, which may have affected the trade activities and had an adverse affect of cultural transitions during these periods across the Ladakh Range on the to and fro movements from this northern sub-route branch. The biotic assemblage is rich in Non Pollen Palynomorphs (76%) with minor amounts of pollens (24%). An improvement in the conditions since 855 cal yr BP and thereafter from 340 to 220 cal yr BP records the onset of the cold arid conditions again in the Ladakh Range. Presently due to contemporary deglaciation the Ladakh Range is becoming ice free and a number of lakes surrounded by herbaceous meadows are seen in the area due to glacial melt, likely to encourage the human settlements to soon occupy the higher reaches that will negatively affect the natural lake productivity.