海相碳酸盐硼同位素反演古海水pH值模型及其应用

Proxy of paleo-seawater pH reconstruction based on boron isotopes of marine carbonates and its applications

王瑞 刘春彤 吴松烨 花绘

Rui WANG Chuntong LIU Songye WU Hui HUA

硼元素（B）在自然界中广泛分布，其稳定同位素（B和B）的分馏特性使其成为古海洋和古气候重建的重要参数。依据硼同位素值（δB）与海水pH值之间的敏感关系，科学家们建立了δB-古海水pH值模型，利用海相碳酸盐矿物中的硼同位素值来反演古海水的pH值，进而分析大气中CO浓度的变化，但模型的准确性仍面临挑战。基于海洋中硼循环和硼同位素测定方法分析，研究了δB-古海水pH值模型的构建机理及应用潜力。研究结果表明：影响该模型准确性的主要因素是生命效应产生硼偏差，硼同位素间分馏系数不准确，海水中硼同位素在B（OH）和两种存在形式之间的交换过程不清楚，不能完全模拟自然环境中碳酸盐沉淀过程中硼同位素的分馏系数。为提高模型的准确性，应与B/Ca元素含量比值等其他指标结合使用，寻找受生命效应影响较小的碳酸盐样品；同时，要努力提高硼同位素分馏系数的计算精度，建立更科学的生命效应校正经验方法，使硼同位素在古海洋气候重建中的应用更加科学、发挥更大的作用。

Boron （B） is widely distributed in nature. The fractionation of its stable isotopes B and B establishes boron as a significant tool for reconstructing paleoceanographic and paleoclimate conditions. The sensitivity of the δB values to seawater pH makes it possible to establish a δB-paleo-seawater pH proxy. This proxy enables the inversion of paleo-seawater pH using the boron isotope values of marine carbonate minerals， which in turn facilitates the analysis of the atmospheric CO concentration changes. Although the δ¹¹B-paleo-seawater pH proxy has great theoretical potential， its accuracy remains a challenge. By analyzing the boron cycling in the ocean and methods for boron isotope determination， we investigate the underlying mechanisms and application potential of the δB-paleo-seawater pH proxy. The results indicate that major factors affecting the proxy accuracy include boron deviation caused by biological effects and inaccuracies in the fractionation coefficient between boron isotopes， insufficient understanding of the exchange processes between B（OH） and in the seawater， and the inability of lab simulations to fully replicate the fractionation of boron isotopes during carbonate precipitation in the natural environment. To enhance the accuracy of the proxy， it is recommended to incorporate additional proxies such as the B/Ca ratio and to select carbonate samples less affected by biological effects. Furthermore， it is necessary to enhance the precision of boron isotope fractionation coefficient calculations， establishing a more scientific empirical method for correcting the biological effects. These advancements will contribute to more scientific and broader applications of boron isotopes in reconstructing paleoceanographic and paleoclimate conditions.

10.11743/ogg20250321