Miocene Indian Ocean circulation and monsoon variability: New sediment archives from IODP Expedition 353

New sediment archives from IODP Expedition 353 (iMonsoon) enable the reconstruction of Indian Monsoon variability and of Indian Ocean surface and deep-water circulation in the Bay of Bengal and Andaman Sea. Here, we present initial results from three outstanding sediment archives recovered from Sites U1443, U1447 and U1448. Site U1443 (2925 m water depth), drilled on the crest of the Ninetyeast Ridge at the southern end of the Bay of Bengal, provided the first complete record of deep water paleoceanography extending back to the early Miocene. High-resolution oxygen and carbon isotope records of benthic foraminifers in combination with X-ray fluorescence (XRF) scanner elemental data track the abrupt onset and development of the Miocene Climatic Optimum (MCO). Our records show that transient carbonate dissolution events during warmer phases of the MCO were not restricted to the Pacific Ocean and extended to the Indian Ocean. An intense carbonate dissolution episode between 13.2 and 8.5 Ma correlates with the "Carbonate Crash", originally identified in the Equatorial Pacific and Caribbean regions, providing new evidence for its global character. The recovery from the "Carbonate Crash" and early onset of a "Biological Bloom" in the tropical eastern Indian Ocean are coupled to a marked increase in biological productivity at 11 Ma, which we relate to a strengthening of monsoonal winds and upper ocean mixing. At Sites U1447 (1392 m water depth) and U1448 (1098 m water depth) in the Andaman Sea, high-resolution monsoonal run-off records derived from XRF-scanning elemental data, combined with temperature/salinity reconstructions from paired stable isotope and Mg/Ca records, reveal pronounced pulsed cooling of surface and intermediate waters between 6 and 5.5 Ma, associated with changes in monsoonal discharge from the Asian continent into the Andaman Sea.