[BPT04-P09] Evaluation of geochemistry in hypercalcified demosponges as a paleoceanographic proxy
Keywords:sclerosponge, oxygen isotope, carbon isotope, trace element, paleoceanogrpahy, Okinawa
Here we present stable oxygen and carbon isotope ratios and trace elements (Mg, Ca, Sr, Ba, Pb and U) from sclerosponges (Astrosclera willeyana and Acanthochaetetes wellsi) collected from Kume-jima, Okinawa-jima and Miyako-jima, Ryukyu Islands in the North Pacific. In order to evaluate the utility of sclerosponge as an environmental proxy, within-skeleton and intraspecific variations in stable isotopic and trace elemental records of 37 samples were investigated. Soft X-ray images of large-size sclerosponges showed highly developed skeletal growth bands with >100 high/low density layers. The secular changes in radiocarbon-dated time series of the sclerosponge carbon records were consistent with previously reported data from Atlantic and Pacific corals and sclerosponges. The long-term oxygen isotopic trends of the samples are characterized by slight depletions throughout their living periods, indicative of an overall trend toward warmer ocean environment around the Ryukyu Islands. Our sclerosponge-based estimates of sea surface temperature and salinity may document thermal and hydrologic variations in the Ryukyu Islands, furthering a better understanding of northwestern tropical-subtropical Pacific climate change for the last several centuries in conjunction with coral-based long proxy records.