Inorganic calcium carbonate precipitation from natural seawater and saline water at various pH values was carried out experimentally. The results show the clear positive relationships between boron concentration and δ 11 B of inorganic calcium carbonate with the pH of natural seawater and saline water. However, the variations of boron isotopic fractionation between inorganic calcite and seawater/saline water with pH are inconsistent with the hypothesis that B(OH) 4 − is the dominant species incorporated into the biogenic calcite structure. The isotopic fractionation factors α between synthetic calcium carbonate precipitate and parent solutions increase systematically as pH increases, from 0.9884 at pH 7.60 to 1.0072 at pH 8.60 for seawater and from 0.9826 at pH 7.60 to 1.0178 at pH 8.75 for saline water. An unusual boron isotopic fractionation factor of larger than 1 in synthetic calcium carbonate precipitated from seawater/saline water at higher pH is observed, which implies that a substantial amount of the isotopically heavier B(OH) 3 species must be incorporated preferentially into synthetic inorganic carbonate. The results propose that the incorporation of B(OH) 3 is attributed to the formation of Mg(OH) 2 at higher pH of calcifying microenvironment during the synthetic calcium carbonate precipitation. The preliminary experiment of Mg(OH) 2 precipitated from artificial seawater shows that heavier 11 B is enriched in Mg(OH) 2 precipitation, which suggests that isotopically heavier B(OH) 3 species incorporated preferentially into Mg(O This result cannot be applied to explain the boron isotopic fractionation of marine bio-carbonate because of the possibility that the unusual environment in this study appears in formation of marine bio-carbonate is infinitesimal. We, however, must pay more attention to this phenomenon observed in this study, which accidentally appears in especially natural environment.Keywords: boron, isotopic fractionation, calcium carbonate precipitate, seawater, saline water.Many investigations focused on boron incorporation into marine organisms by co-precipitation with biogenic carbonate minerals, attempting to reconstruct the past oceanic pH using the isotopic composition of boron in coral and foraminifera [1][2][3][4][5][6][7][8][9][10] . Spivack et al. [3] reported that 21 Ma ago, the surface ocean pH was only 7.4 ± 0.2, which then increased to 8.2 ± 0.2 about 7.5 Ma ago. Sanyal et al. [5] estimated that the deep An unusual isotopic fractionation of boron in synthetic calcium carbonate precipitated from seawater & saline water 455 Atlantic and Pacific oceans had a pH 0.3±0.1 unit higher during the last glaciation. Pearson and Palmer [9] found that the pH was significantly lower during early Palaeogene than in the Neogene period. The application of boron isotope studies in marine biogenic carbonate to the reconstruction of paleo-pH of seawater relies on three hypotheses as follows: (i) A large isotopic fractionation between the two aqueous species, B(OH) 3 and B(OH) 4 − of boron in seawate...

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As a result of the important roles of boron (B) in the growth of plants, the uptake of B by plants is dependent upon the existing form and content of available B in soil, which can bring about the local cycle of B isotope equilibrium. A method using water-heating extraction combined with three-step ion-exchange chromatography was developed for the extraction and isotopic analysis of available B in soil. The extraction efficiency and fractionation of B isotopic composition in the procedure were investigated. The results showed that, in the upper layers of soils, the change of δ11B values was opposite that of the mass concentration and a similar variation between δ11B and content occurred in the lower layers. The isotope of available B in soil can create a featured isotopic signature to further understand the geochemical details related to the soil properties and molecular mechanism of B uptake in plants.