Development And Evolution Of The South Asian Monsoonal Rainfall During The Miocene Climatic Optimum And Middle Miocene Climate Transition(～16-14 Ma)

The Miocene Climatic Optimum(MCO,～16.9-14.7 Ma)indicated an abnormally warm period in the world which reveal the long-term Cenozoic cooling trend for more than 2 million years.However,only a few proxy records for changes in South Asian Monsoon(SAM)rainfall during the MCO exists for the peninsular India and the eastern Arabian Sea region.For that reason,planktic foraminiferal trace element(Mg/Ca and Ba/Ca)and stable oxygen isotope analyses were performed in order to reconstruct the regional surface hydrography and thus the hydroclimate in the Eastern Arabian Sea region related to the South Asian monsoon(SAM)during the MCO and Middle Miocene Climate Transition(MMCT).Periods of increased monsoonal rainfall are associated with a decrease in SSTs in the EAS but also with a decrease in SST records from the tropical Easter Indian Ocean and the subantarctic Southwest Pacific.Periods of increased rainfall in the SAM between～16-14 Ma are most likely attributed to high-latitude cooling in the southern hemisphere and Antarctic cryosphere expansion which might have caused a stronger Mascarene High that increased the cross-equatorial circulation and thus the SAM rainfall.A dominant～29 kyr cyclicity(>95%Confidence Interval)in the planktic foraminiferal stable oxygen isotope data which is not that pronounced(>80%Confidence Interval)in the seawaterδ18O data suggests that changes in SAM rainfall in peninsular India are driven by the nonlinear interaction between eccentricity and obliquity between～16 Ma and 14 Ma.