培养条件下埃及真星介碳同位素分馏及对古环境重建的意义

CARBON ISOTOPE FRACTIONATION IN OSTRACOD EUCYPRIS MAREOTICA FROM CULTURE EXPERIMENTS AND ITS IMPLICATION FOR PALAEOENVIRONMENT RECONSTRUCTION

选取青海湖咸水介形虫——埃及真星介为研究对象,通过温度培养实验评价胖真星介壳体的碳氧同位素分馏状况及对古环境重建的意义。实验结果表明,埃及真星介壳体的碳同位素组成来自其生长水体DIC,10℃、15℃和19℃下埃及真星介与其生长水体DIC之间的平均碳同位素差值分别为-0.48‰、-0.59‰和0.7‰。介壳与水体DIC之间存在明显的碳同位素分馏,但是两者之间的碳同位素分馏几乎不受温度的影响。与碳同位素平衡分馏条件下形成的无机方解石相比,随水体pH值的升高,埃及真星介壳体与水体DIC之间的碳同位素分馏越接近平衡分馏。因此,在利用介形虫的碳同位素组成进行古环境重建时,应该考虑不同水体生长环境中介形虫的碳同位素分馏对重建结果产生的可能影响。

Culture experiments under controlled temperatures were conducted to study the carbon and oxygen isotopic fractionation between water and ostracod shells,as well as its significance in paleoclimatic reconstructions.The carbon isotopic composition of ostracod shells is mainly controlled by the carbon-isotope of water DIC in which the shells formed.The average offsets between δ^13C of shells and the co-existing water DIC are-0.48‰,-0.59‰ and 0.7‰ for culture temperature 10 ℃,15 ℃and 19 ℃ respectively.Our experiments show that temperature is probably not a significant factor controlling the carbon isotopic fractionation between ostracod shells and DIC.However,the carbon fractionation factors of E.mareotica are very close to those of the synthetic inorganic calcite formed in isotopic equilibrium with the increase in water pH.So,the carbon isotopic fractionation of different species living in different water environment should be considered,if the measurements of ^13C/^12C ratios of non-marine ostracod valves are used in palaeoenvironmental reconstruction.