Collaborative Research into Indo-Asian Monsoon Variability: Data and Model Assessment of Northern- and Southern-Hemisphere Mechanisms

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Under this award the PIs will generate and analyze proxy records of the Asian monsoon system over the interval from 5 to 2 million years before present and to run a core set of eight GCM experiments which will test three hypotheses regarding key climate processes that lead to intensification and evolution of the Indian and Asian monsoons:1) The timing of strong Northern Hemisphere summer-monsoons is more sensitive to the export of latent heat from the Southern Hemisphere than to direct sensible heating over Asia.2) The initiation and development of large-scale ice volume in the Northern Hemisphere strengthens the winter monsoon, weakens the summer monsoon and is the root cause of the observed non-stationary phase response relative to orbital forcing (i.e. the timing of the strongest summer-monsoon drifts relative to insolation forcing).3) The intensity of winter- and summer-monsoon circulation is dynamically coupled and linked to glacial evolution in the Northern Hemisphere. Testing these hypotheses using the geological record will be accomplished by analyzing and comparing the monsoon response during the rapidly evolving, high ice-volume interval from 3.2 Ma to present and the warm, relatively stable, minimal ice interval 5 to 3.2 Ma. The combined data/model strategy of analyzing monsoon variability during two intervals of Earth history with very different large-scale boundary conditions will enable differentiation of internal (climate feedback) and external (insolation) mechanisms responsible for seasonal monsoon variability at orbital time scales.