Long-term ocean environmental variability recorded in geochemistry of sclerosponges from Akuseki-jima, Tokara Islands.

Abstract

Long-term understanding of Kuroshio changes is important for understanding climate change. However, continuous observation records such as water temperature of the Kuroshio are limited to the past few decades, and data expansion using geological samples is required. In this study, we analyzed the carbon and oxygen isotopic compositions and trace element concentrations of present-day sclerosponges collected from Akuseki-jima in the Tokara Islands, located in the Kuroshio current, with the aim of long-term reconstruction of physical and chemical characteristics (water temperature, salinity, isotopic composition of dissolved inorganic carbon, etc.) of the ocean in the northern Ryukyu Islands. Radiocarbon isotope concentrations were measured with high precision and resolution, and time series data from 1840 to 2012 were constructed. Oxygen and carbon isotopic compositions and Sr/Ca ratios show a long-term decrease, which may reflect the warming and Suess effect since the mid-20th century.