[[alternative]]Late Pleistocene Environmental ChangeIndicated by Stable Isotope and Element Compositions of Bivalve Shells from Hengchun Area

[[abstract]]We have analyzed the isotope and element compositions of two modern and two Late Pleistocene Anadara granosa shells to quantitatively characterize the paleoenvironmental change in Szekou Formation, Hengchun area. The δ18O values of modern shells are in good agreement with those calculated values based on available seawater δ18O values and temperature ranges, thus reach apparently isotopic equilibrium. Fossil shells, retaining the originally aragonitic mineralogy, indicate that these shells are not altered by diagenesis. Excluding data from the period of sexual maturity, average δ18O value of fossil A. granosa is 1.5? greater than that of modern species. This difference is probably due to global glaciation effect and is consistent with previous studies. Both fossil specimens show positive linear correlation between δ18O and δ13C values whereas this relationship is not seen for modern samples. This is probably because these fossil shells lived in a lagoon environment whereas modern samples lived in an estuary area where is more opened to seawater. Therefore, samples from Szekou Formation show more significant fresh water-seawater mixing signals than modern ones. Excluding the possible annual temperature variation, the excess -1.4? (Lower Szekou Fm.) and -1.1? (Upper Szekou Fm.) indicate that the extent of riverine input at Lower Szekou Formation (FL) was little bit greater than that of Upper Szekou Formation (FU). Episodic minima of Mg/Ca ratios are generally coincide to δ18O maxima. Thus, Mg/Ca ratio may be also varied as a function of temperature in the aragonitic shells. Because the Sr/Ca ratios decrease with tardy metabolism during growth process, metabolic activity of A. granosa should be the major factor controlling Sr/Ca ratio. Ba/Ca ratio is a indicator of nutrition. Sr/Ca and Ba/Ca data show a broadly positively covariant trend demonstrate that metabolism of A. granosa is also related to nutrition. There is no significant difference in δ18O values between FL and FU. Therefore, the regression occurred from FL to FU was most likely caused by land uplift instead of global ice volume change. Average δ13C value of FL is 1? less than that of FU, whereas Ba/Ca ratio of FL is 13μmol/mol greater than that of FU. Land uplift may have changed Szekou depositional environment from lagoon to estuary and caused decrease in nutrient supply. Increase in δ13C of dissolve inorganic carbon of water from FL to FU may be caused by reduced relative biodiversity and need to be further studied. Assuming the δ18O of seawater was 1.5?, the winter seawater temperature of studied area was about 24℃. The calculated Late Pleistocene seawater temperature is comparable to that of modern observations.