Coupled Mg/Ca and Clumped Isotope Measurements Indicate Lack of Substantial Mixed Layer Cooling in the Western Pacific Warm Pool During the Last ?5 Million Years

The Indo-Pacific Warm Pool (IPWP) plays a crucial role in influencing climate dynamics both the tropics and globally. Yet, there is an ongoing controversy concerning evolution of surface temperatures IPWP since Pliocene, which fueled by contradictory proxy evidence. Temperature reconstructions using TEX86 indicate gradual cooling ?2°C from Pliocene to today while Mg/Ca-based studies planktonic foraminifera do not report any long-term trends. A bias Mg/Ca records due seawater chemistry changes has been suggested as explanation for this mismatch. Here, we present data two independent foraminifera-based temperature proxies, clumped isotopes (?47), measured on same samples IODP Site U1488 IPWP. We reconstructed mixed layer subsurface find very good agreement among ?47 when applying minor correction changing ratios seawater. Diagenetic effects could influence but evaluation preservation at suggests that effect unlikely have masked trend data. While remaining uncertainties prevent us fully ruling out particular hypotheses, our study adds evidence likely did cool substantially, cooled more strongly Pliocene. substantial Pleistocene previously observed consistent with finding interpreting it combined signal.