TERRESTRIAL AND OCEANIC RECORD OF THE PAST CLIMATES OF THE INDIAN SUB- CONTINENT: A SYNTHESIS

A diverse range of landforms, ranging from the Desert to alluvial plains, the tectonically active Himalaya and its glaciers, to the Arabian Sea and the Bay of Bengal, make the Indian subcontinent an ideal locale to understand Quaternary processes and climates. A large variety of archives have been used to understand the climate and a common link between the proxy records from various archives is the pre-eminent role of the monsoon. However, a large spatial and temporal variability in monsoon performance exists. These include e.g. the upwelling in the western Arabian Sea vs. the impact of fresh water inputs in the eastern Arabian Sea, regions with summer-dominated and winter-dominated monsoons and spatial heterogeneity in the rainfall intensity. The archives used for paleoclimate reconstructions range from tree rings and cave speleothems to alluvial sediments of humid central India, the desert and the semi- arid southern India, the loess and lacustrine deposits of Kashmir, etc. So far, a major lacuna in paleoclimatic reconstruction has been the absence of reliable radiocarbon chronology due to the lack of species-specific accelerator mass spectrometric radiocarbon ages and to the questionable reliability of bulk radiocarbon ages. Within the terrestrial records, this void is now being filled with the extensive use of Optical ages.

In this contribution, an effort will be made to synthesize the available paleoclimatic records in a time slice mode and discuss their relationship/implications on paleo-monsoon reconstruction. Despite the large-scale heterogeneity in the monsoon performance and different response times/climatic thresholds of different geomorphic surfaces, the available records clearly show a more arid climate during isotopic stages 4 and 2 and at 5-4ka, 2ka and at 0.4-0.2ka and more humid climate during isotopic stage 3 and 1, and during the mid Holocene and the medieval warming. A 1500-year periodicity during the Holocene is also seen. The oceanic records show trends similar to the terrestrial records and provide additional inputs on the monsoon reconstruction. However, areas of discordance between the land and oceanic records do exist, the most important being the oceanic record of strengthening of monsoon in the recent century vs. the terrestrial and instrumental records of static monsoon conditions during the same period.