鹿角珊瑚硼同位素组成与海水表面p H值的相关性研究

Correlation between Boron Isotope of Coral Acropora and p H Value of Seawater Surface

采用串联式水循环系统和插孔式新生长珊瑚培植方法,在保证珊瑚正常生长水化学条件基本一致的条件下,进行了不同海水p H值环境下的鹿角珊瑚养殖实验。采用热电离同位素质谱仪测定了珊瑚的硼同位素组成,以探讨珊瑚硼同位素组成与海水p H值的经验关系。珊瑚和海水B(OH)_3间的硼同位素分馏系数(_(carb-3)与养殖海水p H值的关系研究结果表明,(_(carb-3)不是常数,而是与p H值有关,表明B(OH)_3同时掺入进珊瑚生物碳酸盐。通过实验数据获得的δ^(11)B_(carb)-p H经验方程可用于海水p H值的计算与分析,从而可替代存在争议的采用理论公式由测定的珊瑚生物碳酸盐的δ^(11)B_(carb)值进行海水p H值计算的方法。另外,在珊瑚养殖过程中,高p H值养殖水箱中有Ca CO_3和Mg(OH)_2混合沉淀析出,其δ^(11)B值明显高于养殖海水,表明Mg(OH)_2的存在对硼同位素分馏有显著影响,这是否会对珊瑚的硼同位素组成产生影响值得关注。

Water circulation system with the almost same element composition and socket type were adopted in coral Acropora culture under different seawater pH conditions and the experimental data of the relationship between boron isotopic compositions of coral and seawater pH were obtained by thermoelectric ionization mass spectrometer.From the correlations between αcarb-3 of coral and pH of cultured seawater,α carb-3 was not a constant but related to pH,indicating that B(OH)3 also incorporated carbonate.Therefore,the theoretical formula could not be used to calculate the seawater pH value from theδ11 B carb value of the measured marine biological carbonate.The method using the empirical equations obtained experimentally to calculate the seawater pH value would be an alternative.In addition,a mixed precipitation of inorganic CaCO 3 and Mg(OH)2 was found in aquaculture tanks with high pH value and theδ11 B of the solid was significantly higher than that of cultured seawater.The result indicated that the presence of Mg(OH)2 had a significant effect on the boron isotope fractionation,which deserved our attention.