Organic carbon abundance and isotopic composition of sediments in a coastal plain are potentially used to indicate depositional environments and hinterland organic sources. Since Taiwan is located on the eastern margin of the Eurasian continent facing eastward to the Pacific, its geographical position is sensitive to interactions between the sea and land. Changes in the climate have a direct bearing on the costal environment and types of terrestrial plant species that inhabit it. In this study, we sampled two cores drilled from the coastal plain of southwestern Taiwan, and conducted concentration and isotopic analyses of organic carbon.

Compared with the generally accepted environmental evolution of Taiwan, our study shows the dominant marine organic source have brought on relatively stable carbon abundance and low level isotopic values for total organic carbon (TOC), whilst input from terrestrial sources attributed to arid-climate-induced C₄ plant blooms make TOC content and δ¹³C value vary more widely. The lower parts of the cores indicate the entire study area was inundated by seawater as a result of the high sea-stand of MIS (marine isotope stage) 5. At Machouhou (MCH), the sedimentary environment became terrestrial in MIS 4, but returned to a shallow marine environment in MIS 3. The environment probably remained terrestrial at Tsungyeh (TY) during MIS 2 & 3; a period characterized in the cores as having high fluctuations in TOC with strong C₄ plant signals. Subsequently both of these areas evolved into shallow marine environments after the beginning of the Holocene due to the world-wide postglacial transgression. Although the coastal environment and climate of southwestern Taiwan display characteristics consistent with the major trends in global change occurring during the late Pleistocene, they also exhibit subtler features influenced by local geography and neotectonics.