Boron incorporation in the foraminifer Amphistegina lessonii under a decoupled carbonate chemistry


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karina.kaczmarek [ at ] awi.de

Abstract

A number of studies have shown that the boron isotopic composition (δ11B) and the B / Ca ratio of biogenic carbonates (mostly foraminifers) can serve as proxies for two parameters of the ocean's carbonate chemistry, rendering it possible to calculate the entire carbonate system. However, the B incorporation mechanism into marine carbonates is still not fully understood and analyses of field samples show species-specific and hydrographic effects on the B proxies complicating their application. Identifying the carbonate system parameter influencing boron incorporation is difficult due to the co-variation of pH, CO32- and B(OH)4-. To shed light on the question which parameter of the carbonate system is related to the boron incorporation, we performed culture experiments with the benthic symbiont-bearing foraminifer Amphistegina lessonii using a decoupled pH–CO32- chemistry. The determination of the δ11B and B / Ca ratios was performed simultaneously by means of a new in situ technique combining optical emission spectroscopy and laser ablation MC-ICP-MS. The boron isotopic composition in the tests gets heavier with increasing pH and B / Ca increases with increasing B(OH)4- / HCO3- of the culture media. The latter indicates that boron uptake of A. lessonii features a competition between B(OH)4- and HCO3-. Furthermore, the simultaneous determination of B / Ca and δ11B on single specimens allows for assessing the relative variability of these parameters. Among different treatments the B / Ca shows an increasing variability with increasing boron concentration in the test whereas the variability in the isotope distribution is constant.



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ISI/Scopus peer-reviewed
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Published
Eprint ID
37612
DOI 10.5194/bg-12-1753-2015

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Kaczmarek, K. , Langer, G. , Nehrke, G. , Horn, I. , Misra, S. , Janse, M. and Bijma, J. (2015): Boron incorporation in the foraminifer Amphistegina lessonii under a decoupled carbonate chemistry , Biogeosciences, 12 (6), pp. 1753-1763 . doi: 10.5194/bg-12-1753-2015


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