西沙群岛砗磲壳体碳、锶同位素研究及其对比

Study and Correlation of C and Sr Isotope in the Shell of Tridacna Squamosa from Xisha Islands

本文系统地测定了西沙群岛中双壳类鳞砗磲壳体碳、锶同位素,结果发现鳞砗磲壳体的碳、锶同位素的生长变化曲线表现出明显的周期性。碳同位素受到鳞砗磲新陈代谢作用的影响,幼年时期壳体的δ^(13)C变化幅度小于发育期,这主要是由于鳞砗磲体内在幼年期能量的消耗大于发育期。通过与其壳体上的生长纹的对比,碳同位素的周期就是生物年生长周期。锶同位素的周期性主要是由于附近大陆年周期性降雨量的变化所引起的,它不受生物生长作用的影响。

The authors systematically collect sampled from the growth layers in Tridacna squosama from the Xisha Islands, and determined the C, O and Sr isotopic compositions, obtained their growth curves of the mollusk. On the basis of the isotope data and the published information the following conclusion can be drawn.The C and Sr isotopic growth curves appears periodicity and twelve and ten cycles can be found respectively. Affected by the metabolism of the Tridacna squamosa, the variation range of δ13C in the shell during its developing stage is higher than that in the lava stage. The reason lies in the difference of energy consumption in the different stages. By Comparing with the growth layers in the shell the cycles of δ13C are considered to be annual. The value of δ13C is controlled by the ratio of photosynthesis to respiration(P/R) , the higher ratio of P/ R, the higher value of δ13C in the shell. But the Oxygen isotope does not show similar periodicity as the carbon isotope.The Sr isotopic growth periodicity is relates to the annual variation of Sr isotope in the surface layer of sea-water. In the rainy season (from May to October) more continent runoff with high 87Sr/86Sr value flowing into ocean causes the increase of 87Sr/86Sr in the shell of Tridacna squamosa; with during the dry season (from November to April) less runoff results in decrease of the 87Sr/86Sr value in the shell. Therefore,the growth curve of Sr can reflect the mollusk's growth, the peaks and valleys in the curves correspond to the rain season and dry seasons respectively, and the curve can give clues of the growth years of the Tridacna squamosa.