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Boron isotopic fractionation in laboratory inorganic carbonate precipitation:Evidence for the incorpora-tion of B(OH)_3 into carbonate

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Science china Earth sciences 2008年第12期51卷 1776-1785页

作者： xiao yingkai1,2, li hualing1,3, liu weiguo4. wang xiufang1 & jiang shaoyong5 1 qinghai institute of salt lakes, chinese academy of sciences, xining 810008, china 2 State Key Laboratory of Environmental Geochemistry, institute of Geochemistry, chinese academy of sciences, Guiyang 550002, china 3 Nanjing institute of Geology and Mineral Resources, Nanjing 210016, china 4 State Key Laboratory of Loess and Quaternary Geology, institute of Earth Environment, chinese academy of sciences, Xi’an 710075, china 5 State Key Laboratory for Mineral Deposits Research, Department of Earth sciences, Nanjing University, Nanjing 210093, china 1. qinghai institute of salt lakes Chinese Academy of Sciences Xining 810008 China 2. State Key Laboratory of Environmental Geochemistry Institute of Geochemistry Chinese Academy of Sciences Guiyang 550002 China 3. Nanjing institute of Geology and Mineral Resources 210016 Nanjing China 4. State Key Laboratory of Loess and Quaternary Geology Institute of Earth Environment Chinese Academy of Sciences Xi’an 710075 China 5. State Key Laboratory for Mineral Deposits Research Department of Earth Sciences Nanjing University Nanjing 210093 China

A laboratory inorganic carbonate precipitation experiment at high pH of 8.96 to 9.34 was conducted, and the boron isotopic fractionations of the precipitated carbonate were measured. The data show that boron isotopic fractionation factors (αcarb-3) between carbonate and B(OH)3 in seawater range 0.937 and 0.965, with an average value of 0.953. Our results together with those reported by Sanyal and collabo-rators show that the αcarb-3 values between carbonate and B(OH)3 in solution are not constant but are negatively correlated with the pH of seawater. The measured boron isotopic compositions of carbonate precipitation (δ11Bcarb) do not exactly lie on the best-fit theoretical δ 11B4-pH curves and neither do they exactly parallel any theoretical δ 11B4-pH curves. Therefore, it is reasonable to argue that a changeable proportion of B(OH)3 with pH of seawater should also be incorporated into carbonate except for the dominant incorporation of B(OH)4- in carbonate . Hence, in the reconstruction of the paleo-pH of sea-water from boron isotopes in marine biogenic carbonates, the use of theoretical boron isotopic frac-tionation factor (α4-3) between B(OH)4- and B(OH)3 is not suitable. Instead, an empirical equation should be established.

关键词： boron isotopic fractionation biogenic carbonate B(OH)3 incorporation

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Boron Isotopic Fractionation and Trace Element Incorporation in Various Species of Modern Corals in Sanya Bay, South china Sea

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Journal of Earth Science 2014年第3期25卷 431-444页

作者： Haizhen Wei shaoyong jiang yingkai xiao N Gary Hemming State Key Laboratory for Mineral Deposits Research Department of Earth Sciences Nanjing University State Key Laboratory of Geological Processes and Mineral Resources Faculty of Earth ResourcesChina University of Geosciences Wuhan qinghai institute of salt lakes Chinese Academy of Sciences Lamont-Doherty Earth Observatory of Columbia University Queens College School of Earth and Environmental sciences

The boron isotope paleo-pH proxy has been extensively studied due to its potential for understanding past climate change, and further calibrations were considered for accurate applications of the proxy because of significant variability related to biocarbonate microstructure. In this work, we studied the boron isotopic fractionation between modern marine corals and their coexisting seawater collected along shallow area in Sanya Bay, South china Sea. The apparent partition coefficient of boron（KD） ranged from 0.83×10-3 to 1.69×10-3, which are in good agreement with previous studies. As the analyzed coral skeleton（~5 g） spanned the growth time period of 1–2 years, we discussed the boron isotopic fractionation between pristine corals and modern seawater using the annual mean seawater pH of 8.12 in this sea area. Without taking the vital effect into account,（11B/10B）coral values of all living corals spread over the curves of（11B/10B）borate vs.（11B/10B）sw with the α4-3 values ranging from 0.974 to 0.982. After calibrating the biological effect on the calcifying fluid pH, the field-based calcification on calcifying fluid pH（i.e., Δ（pHbiol-pHsw）） for coral species of Acropora, Pavona, Pocillopora, Faviidae, and others including Proites are 0.42, 0.33, 0.36, 0.19, respectively, and it is necessary to be validated by coral culturing experiment in the future. Correlations in B/Ca vs. Sr/Ca and B/Ca vs. pHbiol approve temperature and calcifying fluid pH influence on skeletal B/Ca. Fundamental understanding of the thermodynamic basis of the boron isotopes in marine carbonates and seawater will strengthen the confidence in the use of paleo-pH proxy as a powerful tool to monitor atmospheric CO2 variations in the past.

关键词： boron isotope paleo-pH proxy boron isotopic fractionation trace element modern coral.

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