Reconstruction of marine environments in the south Pacific during the last deglaciation (15 - 9 ka) using fossil corals collected from Tahiti

Climate responses and variation of marine environments during the deglaciation have been controversial and paleoceanographic data in the south tropical to sub-tropical Pacific is limited in spite of that this region is crucial to investigate ocean-atmosphere interaction. Fossil coral records contain evidence of a dramatic sea level rise in excess 20 m around 14.6 ka, termed meltwater pulse 1A (mwp-1A). Although this event seems to have a significant effect on global climate, the relationship between mwp-1A and the climate system remains a subject of debate. Integrated Ocean Drilling Program (IODP) Expedition 310 has been conducted to establish the course of postglacial sea-level rise and to define variation of marine environments for the last degraciation around Tahiti in the South Pacific. As fossil Porites coral is ideal to assess past marine environments, we selected only Porites specimens and conducted age determinations by 14C method. In addition, XRD and SEM examinations were conducted to check the condition of fossil corals. Consequently, 15 pristine Porites specimens, yielding 15 to 9 ka, composed of only aragonite were obtained. Then bulk samples were taken from all coral specimens by a milling machine and trace elements and Pb isotopic compositions in bulk samples were analyzed by inductively coupled plasma mass spectrometer (ICP-MS) and multiple-collector ICP-MS, respectively. Data of Pb isotope ratios in fossil corals were comparable with those from crust in the Central Andes and revealed its potential for a proxy as wind source and direction. The Pb isotope ratios were variable just before mwp-1A (around 15 ka) and then shifted to relatively stable, suggesting the trade winds, which is related to ENSO condition, were unstable before the mwp-1A. We will also discuss the relationship between upwelling and ENSO condition around the mwp-1A based on trace elements in fossil corals.