Distribution of chlorine and fluorine in benthic foraminifera

Abstract

Over the last few decades, a suite of inorganic proxies based on foraminiferal calcite have been developed, some of which are now widely used for palaeoenvironmental reconstructions. Studies of foraminiferal shell chemistry have largely focused on cations and oxyanions, while much less is known about the incorporation of anions. The halogens fluoride and chloride are conservative in the ocean, which makes them candidates for reconstructing palaeoceanographic parameters. However, their potential as a palaeoproxy has hardly been explored, and fundamental insight into their incorporation is required. Here we used nanoscale secondary ion mass spectrometry (NanoSIMS) to investigate, for the first time, the distribution of Cl and F within shell walls of four benthic species of foraminifera. In the rotaliid species Ammonia tepida and Amphistegina lessonii, Cl and F were distributed highly heterogeneously within the shell walls, forming bands that were co-located with the bands observed in the distribution of phosphorus (significant positive correlation of both Cl and F with P;