Keul, Nina, Langer, Gerald, de Nooijer, Lennart Jan, Nehrke, Gernot, Reichart, Gert-Jan and Bijma, Jelle (2013) Incorporation of uranium in benthic foraminiferal calcite reflects seawater carbonate ion concentration. Geochemistry, Geophysics, Geosystems, 14 (1). pp. 102-111. DOI 10.1029/2012GC004330.

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Abstract

The chemical and isotopic composition of foraminiferal shells (so-called proxies) reflects the physico-chemical properties of the seawater. In current day paleoclimate research, the reconstruction of past seawater carbonate system to infer atmospheric CO2 concentrations is one of the most pressing challenges and a variety of proxies have been investigated, such as foraminiferal U/Ca. Since in natural seawater and traditional CO2 perturbation experiments, the carbonate system parameters co-vary, it is not possible to determine the parameter of the carbonate system causing e.g. changes in U/Ca, complicating the use of the latter as a carbonate system proxy. We overcome this problem, by culturing the benthic foraminifer Ammonia sp. at a range of carbonate chemistry manipulation treatments. Shell U/Ca values were determined to test sensitivity of U incorporation to various parameters of the carbonate system. We argue that [CO32-] is the parameter affecting the U/Ca ratio and consequently, the partitioning coefficient for U in Ammonia sp DU. We can confirm the strong potential of foraminiferal U/Ca as a [CO32-] proxy.

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