Oxygen Isotope and Ba/Ca Ratio Records in Coral Skeletons and their Environmental Explanations from Southern Taiwan
Date Issued
2011
Date
2011
Author(s)
Chiang, Hong-Wei
Abstract
Coral has been one of the best marine archives to study climate change from weekly to decadal timescales. The abundant trace elements and stable oxygen isotopes in massive coral skeletons are affected by the environment condition prevailing at the time of skeleton deposition. In this study two coral heads were collected from the Nanwan Bay, southern Taiwan to test the capabilities of traditional d18O values and recent-developed Ba/Ca ratios, with seasonal to sub-decadal timescales. Firstly, during El Niño episodes the skeletal d18O–SST correlation showed a gentler slope of -0.12 ± 0.04‰ °C-1 rather than the value of -0.21 ± 0.04‰ °C-1 during normal year. The difference was likely caused by enhanced penetration of Kuroshio Current waters into the South China Sea during El Niño summers. Secondly, an annually distinct double-peak feature of Ba/Ca ratios in coral was identified. The earlier peak is not concordant with the time of major precipitation but regularly occurred before the Sr/Ca value reached the minimum. It was resulted from a biotic source and possibly related to Cyanophyta bloom in the early-spring. The later peak happened at the time of raining seasons. Two different linear correlations are presented between skeletal Ba/Ca and accumulated precipitation in July-October. Before 1999, the relationship was given by Ba/Ca=3.02+0.0024*P; while after 1999, the relationship is given by Ba/Ca=2.26+0.0011*P. The decreased Ba/Ca baseline from the end of 1999 to 2001 is believed to relate to the operating of two sewage treatment plants since 1999 and 2000. It also can explain the gentler slope value of Ba/Ca-precipitation regression and the decreased amplitude of Ba/Ca maxima after 1999. Thus, the skeletal Ba/Ca ratios can be applied as a quantitative proxy of the paleo-precipitation in southern Taiwan.
Subjects
Porites corals
stable Oxygen isotopes
Ba/Ca ratios
precipitation
Nanwan Bay
Type
thesis
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