Recent advances in understanding Neogene climatic evolution: Indian perspective

Abstract

This article presents an overview of the research work done during 2015-2019 on the South Asian/Indian monsoon climate variability, based on the Neogene terrestrial and marine proxy records. The paleoclimatic and paleoceanographic records provide better insights into our current understanding of timing of initiation/intensification of the Indian monsoon system; its evolution and seasonal variability pattern through time and underlying mechanisms; and impacts on paleobiogeography of terrestrial fauna and flora and physico-chemical and biological processes in the northern Indian Ocean. The Neogene upliftment history of the Himalaya was reconstructed based on detailed analysis of fossil flora from Himalayan sequences and a link between step wise uplift of Himalaya-Tibetan plateau and Indian summer monsoon intensification was established. The rainfall pattern in the northeast India during the Neogene period was quantified; and the new data suggest the presence of rainfall in the region since 11.6 Ma. δ 13 C record of pedogenic nodules in Siwalik succession provides evidence of major shift in vegetation between ~2.8 Ma and 1.1 Ma due to large variation in temperature and precipitation. New results of the multiproxy based paleoceanographic studies carried out on sediment cores collected during recent IODP expeditions in the Arabian Sea and Bay of Bengal, have major implications on the evolution of the Indian monsoon and dynamics of its seasonal variations in the Neogene. The sedimentological and geochemical records from carbonate platform of the Maldives suggest an abrupt onset of modern monsoon circulation at ~ 12.9 Ma, which cannot be entirely explained by the Himalayan tectonics as many believed earlier. It appears that the global climate also controls Indian monsoon circulation, in addition to the tectonics. Record of past changes in the Arabian Sea denitrification driven mainly by monsoon-wind induced productivity and water column ventilation condition, reveals that the Indian monsoon intensified during ~2.8-3.2 Ma. Recently, based on the integrated multiple proxy records it was inferred that seasonal monsoon circulation was weak during 1.85-2.7 Ma, subsequently followed by the intensification of winter monsoon between ~1.65 and 1.85 Ma, attributed to the development of strong zonal and meridional circulations due to enhanced E-W Pacific temperature gradients.