Global Changes

Stable Isotope Research Approach
By means of analyzing organic carbon concentrations and isotopic compositions of sediments, we may obtain the paleoecological, paleoenvironmental and paleoclimatic information since late Pleistocene, and further clarify local variations in terms of global environments. This approach is also advantageous to the stratigraphic correlations and explanations of local structural activities.

Example Case I: Organic Carbon Inferred Environmental Fluctuations during Late Quaternary, Southwestern Taiwan

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 £_ 13C 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.

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Full Text: Hung-Wei Chiang and Yue-Gau Chen (2005) TAO, V. 16, No. 5, 1121-1132

Example Case II: Environmental Change in the Southwestern Coastal Plain of Taiwan Since Late Pleistocene: Using Multiple Proxies of Sedimentary Organic Matter

In an attempt to discriminate between organic matter sources and reconstruct further the paleoenvironment of the southwestern coastal plain of Taiwan, organic carbon and nitrogen content (C/N) ratios and isotope composition ( £_ 13C and £_15N) are measured for sedimentary core samples collected from San-liao-wan, Zai-kang and Yihju in the southwestern coastal plain of Taiwan. Heavy £_ 13C values (up to -14.3000) and high C/N ratios (average 9.3) with good correlation indicate that this area underwent a period of relative aridity from early Marine Isotopic Stage (MIS) 2 to the early MIS 1. In MIS 1, the £_ 13C and C/N ratio both vary initially before later steadying, indicating that the environment became progressively more stable, with C3 plants becoming dominant again. The Zai-kang core appears to have come from a shallow lagoon system that potentially preserved the record of £_15N from autochthonous primary producers. Regional organic source variation is revealed through the high £_15N values and constant C/N ratios in MIS 1 of the Zai-kang core. This may suggest that mangroves and macrophytes were the main aquatic organic matter source in the Zai-kang area during MIS 1.

Full Text: Huei-Wei Ku, Yue-Gau Chen and Tsung-Kwei Liu (2005) TAO, V. 16, No. 5, 1079-1096