VARIATIONS IN CARBONATE PRODUCTION, DISSOLUTION, AND BURIAL IN THE MIOCENE OF THE WESTERN EQUATORIAL PACIFIC (IODP SITE U1489): AN INTEGRATED GEOCHEMICAL AND SEDIMENTOLOGICAL APPROACH

Paleoclimate records of past variation in the global carbon cycle are critical to understanding how the Earth might respond to rising pCO₂ concentration. The Western Pacific Warm Pool (WPWP) is of particular interest as this region exerts a major influence on global atmospheric circulation, heat storage in the ocean, and ultimately global temperatures and pCO₂. International Ocean Discovery Program (IODP) Expedition 363 sought to determine the nature of and driving forces behind climate variability in the WPWP region throughout the Neogene. Here we focus on the Miocene (19–9 Ma) record from IODP Site U1489 to examine changes in carbonate production, dissolution, and burial as a record of variations in the regional/global carbon cycle. This interval is of particular interest because it spans the Miocene Climatic Optimum, the Middle Miocene Climate Transition, and the late Miocene carbonate crash. Site U1489 is located on the western slope of the southern Eauripik Rise at 02°07.19’N, 141°01.67’E in the northern part of the WPWP. At 3421 m water depth, today the site is bathed in Lower Circumpolar Deepwater and is located near the carbonate compensation depth (CCD), thus situated to examine past changes in the CCD. Miocene sediment at Site U1489 primarily consists of foraminifer-bearing/rich clay-rich chalk, although a thin interval with abundant biogenic silica is present in the lower Miocene. The sedimentation rate in the early to middle Miocene was very low (<1 cm/kyr), increasing to ~2 cm/kyr in the late Miocene. Our results show calcium carbonate content in the Miocene varied from ~68 wt% to 94 wt%. We collected X-ray fluorescence (XRF) data at 2 cm resolution along the composite stratigraphic section over the 19–9 Ma interval to obtain a qualitative measure of bulk sediment chemistry. We use the carbonate content of discrete samples to generate a high-resolution carbonate record from the XRF data. We also measured major and trace element abundances and bulk mineralogy to further understand sedimentological changes. Ultimately our research will allow for comparison among records from these cores located in the western equatorial Pacific to those obtained in the eastern and central Pacific to better elucidate the nature of the carbon system during the Miocene.