Biomineralization in perforate foraminifera

In this paper, we review the current understanding of biomineralization in perforate foraminifera. Ideas on the mechanisms responsible for the flux of Ca²⁺ and inorganic carbon from seawater into the test were originally based on light and electron microscopic observations of calcifying foraminifera. From the 1980s onward, tracer experiments, fluorescent microscopy and high-resolution test geochemical analysis have added to existing calcification models. Despite recent insights, no general consensus on the physiological basis of foraminiferal biomineralization exists. Current models include seawater vacuolization, transmembrane ion transport, involvement of organic matrices and/or pH regulation, although the magnitude of these controls remain to be quantified. Disagreement between currently available models may be caused by the use of different foraminiferal species as subject for biomineralization experiments and/or lack of a more systematic approach to study (dis)similarities between taxa. In order to understand foraminiferal controls on element incorporation and isotope fractionation, and thereby improve the value of foraminifera as paleoceanographic proxies, it is necessary to identify key processes in foraminiferal biomineralization and formulate hypotheses regarding the involved physiological pathways to provide directions for future research.