Indian Monsoon variability in the Andaman Sea (IODP Site 1448) during the latest Miocene (5-6 Ma)

The Bay of Bengal, in the core area of the Indian Monsoon, provides the opportunity to investigate the monsoon's response to changes in insolation forcing, global ice volume and atmospheric pCO₂. Extended sediment successions, spanning the latest Miocene to earliest Pliocene interval (6 to 5 Ma), were recovered during IODP Expedition 353 at Site U1448 (10°38.03'N/93°00'E, 1098 m water depth) in the Andaman Sea. This interval was characterized by intense, transient Northern Hemisphere cooling events (TG Events), allowing investigation of monsoon variability during rapid cooling/warming episodes with background climate conditions comparable to the present day. We present an orbitally tuned benthic oxygen isotope record combined with paired mixed layer oxygen isotope and Mg/Ca temperature/salinity reconstructions, as well as XRF-scanner derived high-resolution terrigenous runoff records from the Irrawaddy River. Mixed layer temperatures indicate a warming trend of 3°C starting at 5.5 Ma. Cold stages T4 to TG34 (associated with Northern Hemisphere insolation minima at obliquity minima and/or precession maxima), identified in the benthic isotope record, exhibit pronounced sea surface cooling by up to 4°C. Changes in the chemical composition of the sediment discharge (decreasing Log(K/Ti) during TG Events) indicate profound modifications of erosion, weathering and transport-patterns in the Irrawaddy River catchment. These variations mark an important step in the reorganization of the Indian Monsoon system, which was likely driven by a change in the interhemispheric temperature gradient towards a cooler Northern Hemisphere.