Impact of Western Pacific Warm Pool variability on regional and global climate evolution during the late Miocene and early Pliocene

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As the warmest water body on the planet, the Western Pacific Warm Pool (WPWP) strongly influences the dynamics of the El Niño Southern Oscillation and the Asian-Australian monsoon system, affecting planetary-scale atmospheric circulation, atmospheric heating, and tropical hydrology. To date, there is considerable uncertainty regarding the response of the tropical Pacific climate to rising greenhouse gas concentrations and sea level due to our limited understanding of the WPWP past variability and conflicting results from data and model simulations.During IODP Expedition 363, an extended (sedimentation rate: ~6 cm/kyr), undisturbed upper Miocene to lower Pliocene hemipelagic succession was retrieved for the first time at the southwestern edge of the present day WPWP (Site U1482, 15°3.32 S, 120°26.10 E, water depth: 1466 m). This carbonate- and clay-rich sequence provides an ideal archive to document temperature and precipitation variations in the WPWP under different climate background states and to better constrain climate sensitivity in relation to changes in radiative forcing (CO2 and insolation). Using a combination of high-resolution ocean temperatures and salinity reconstructions (based on oxygen isotope and Mg/Ca analyses of mainly unaltered, glassy planktonic and intermediate water benthic foraminifers) and XRF-scanner derived monsoonal runoff records, we propose: 1) to monitor variations in the spatial extent of the WPWP in relation to high-latitude climate change on orbital timescales; 2) to investigate the relationships between changes in the Equator-to-pole temperature gradient and the long-term evolution of the Australian monsoon; 3) to assess changes in the zonal SST gradient of the tropical Pacific Ocean during intense, global cooling and warming episodes and 4) to evaluate the role of intermediate waters as a buffer of high-latitude climate variations during late Miocene and early Pliocene climate reversals.Our project will focus on the late Miocene to early Pliocene period, which represents a geologically recent, relatively warm climate phase that is considered a potential analog of future conditions on Earth. This interval was marked by several episodes of fundamental climate re-organization, offering a challenging opportunity to explore climate-carbon cycle dynamics on a warmer-than-today Earth as well as to investigate the impact of WPWP variations on the evolution of the Asian-Australian monsoon system and on zonal equatorial Pacific processes (e.g. past El Niño state) and, thus, to help guide models and constrain predictions of climate change and sensitivity.