ELUCIDATING CHANGES IN CARBONATE PRODUCTION AND BURIAL DURING THE PLIO–PLEISTOCENE IN THE WESTERN EQUATORIAL PACIFIC (IODP SITE U1490) USING GEOCHEMISTRY AND SEDIMENTOLOGY

Understanding how the Earth system will respond to rising temperatures in the coming years is critical for mitigating potentially disastrous consequences. To make better predictions, climate modelers require robust paleoclimate records that target past intervals of global warmth to constrain their model simulations. Here we focus on the Pliocene to recent (5–0 Ma) sediment record from International Ocean Discovery Program (IODP) Site U1490 to examine changes in carbonate production and burial in the Western Pacific Warm Pool (WPWP) as a record of variations in the regional/global carbon cycle. This interval is of particular interest because it spans the Middle Pliocene Warm Period and several super-interglacials including Marine Isotopes Stages 31 and 11. Site U1490 is located on the northern edge of Eauripik Rise at 05°58.95’N, 142°39.27’E in the northern part of the WPWP. At 2341 m water depth, today the site is bathed in Upper Circumpolar Deepwater. Pliocene to recent sediment primarily consists of foraminifer-rich nannofossil ooze, with the sedimentation rate varying between ~1.5 and 3 cm/kyr. Initial shipboard measurement of calcium carbonate content showed little variation (90–95 wt%) at low resolution (1 sample every few meters), whereas our higher resolution measurements every ~75 cm show significantly larger variations between ~70 and 95 wt%. We also collected X-ray fluorescence (XRF) data at 2 cm resolution along the composite stratigraphic section to obtain a qualitative measure of the bulk chemistry of the sediment. We use the weight percent calcium carbonate of the discrete samples to calibrate the XRF Ca data to generate a high-resolution carbonate record. In addition to the variations in the carbonate record, we also observe cyclical variations in the Ca/Ba, which reflects changes in productivity and/or dissolution through this interval. Finally, we measured major and trace elemental abundances and bulk mineralogy to identify small compositional changes in the nannofossil ooze over the studied interval. Our research will allow us to compare these records to those obtained in the eastern and central Pacific, which will better elucidate the nature of the global carbon system during the Plio-Pleistocene.