Late Holocene paleoenvironmental changes in the southern Okinawa Trough inferred from a diatom record

Abstract

We analyzed sediment diatoms from core MD05-2908 to infer climate and paleoenvironmental changes in the southern Okinawa Trough (SOT) over the past 1000 years. Because the study area is located in the East Asia monsoon area and beneath the main axis of Kuroshio Current, the climatic and hydrographical conditions are strongly influenced by both of these factors. The species used as environmental indicators, including the Kuroshio Current species (KC species) and freshwater species, were investigated in this paper. Changes in the abundance of the two groups of species revealed significant variations in water temperature and hydrography in the SOT during the Medieval Warm Period (MWP) and the Little Ice Age (LIA). From 950–1500 AD, the abundance of the KC species increased fluctuantly, while the freshwater species decreased, showing that the influence of the Kuroshio Current was intensified at that interval and the precipitation of the study area was relatively low. The KC species decreased remarkably and was maintained at a low abundance during the interval of 1500–1900 AD, which suggests that the impact of the Kuroshio Current on the SOT weakened during the period corresponding to the LIA. Moreover, the high abundance of the freshwater species at the same interval indicates a distinct increase in precipitation in northeastern Taiwan, which may be correlated to the south-detention of the rainfall belt in China caused by the southward migration of the western Pacific subtropical high.