In-situ microanalysis of elemental ratios in a single oyster shell from the South Yellow Sea, China and its environmental implications

Biogenic calcium carbonates are widely used natural archives to study environmental history and human activities as they preserve a wealth of information of climatic and environmental changes. With the NIST610 glass as the reference material and ⁴³Ca as the internal element to calibrate, major and trace elements in a modern Pacific Oyster shell (Crassostrea gigas) taken from the offshore area of South Yellow Sea near Haimen were measured with laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS). The primary objecitve is to reveal elemental compositions and environmental implications. Our results show very good correlations between the variations in Mg/Ca, Sr/Ca, Na/Ca ratios and the seasonal growth increments of the shell. This might suggest that variations in elemental ratios of the shell are mainly controlled by physical and chemical properties of the ambient sea water. In most cases, the chalky calcite layers in oyster shells correspond to the period of higher sea water temperature, while the foliated calcite layers are associated with the period of lower temperature. In general, the chalky calcite layers are featured by high Mg/Ca and Sr/Ca and low Na/Ca ratios. By applying Mg/Ca-temperature reconstruction equation published in literature, we obtained reliable sea surface temperature for the study area based on Mg/Ca ratios in the oyster shell, which is supported by the overall consistence between gauged water temperatures and the reconstructed.