Synchronous reduction in Indian summer and winter monsoon intensity during the northern hemisphere cold episodes: possible implications on climate modelling

摘要

The economy of most Asian countries including India by and large depends on the monsoon conditions. There has been a growing interest in recent years to understand better the dynamics of the monsoon climate and factors driving changes in the monsoon circulation and to evolve predictive models. Enhanced understanding of variability pattern of the seasonal monsoon wind systems (southwesterly in summer and northeasterly in winter) and its relationship with other climate components of the Earth is critical to our ability to predict monsoon in the context of current climate change scenario. A wide range of palaeontological, mineralogical, geochemical and isotopic signatures recorded from the marine archives are used to document past changes in the monsoonal climate. The tests of the microscopic fauna and flora preserved in the ocean sediments provide reliable indicators of past climatic conditions, as they are remarkably sensitive to minor changes in oceanic environment induced by monsoon circulation pattern. The sedimentary records of the Arabian Sea are the best archives of Indian monsoon history, as the physico-chemical condition and biology of this basin is primarily influenced by the seasonal changes in monsoon circulation. In the recent past, there have been a number of studies from the Arabian Sea on reconstruction of palaeo-monsoon history using micropalaeontological, isotopic and geochemical tracers. Palaeoclimatic reconstructions and climate modelling studies have demonstrated that the Indian monsoon system is highly variable over the longer to shorter timescales. Most of these studies were focused on the summer monsoon variability and as a result substantial understanding of its driving mechanism has been gained by now. Summer monsoon variation on longer timescales (glacial/ interglacial) is generally explained by the orbital precession that affects the insolation reaching the Earth 1,2 . Earlier studies have demonstrated that summer monsoon on millennial scales is linked with shortterm high-latitude northern hemisphere climatic events 3,4 .