Biomineralization in Agglutinating Foraminifera: An Analytical SEM Investigation of External Wall Composition in Three Small Test Forms

The walls of many deep-sea foraminiferal tests containabiogenic and biogenic, precipitated and agglutinated,components. Both environmental and genetic factorscan contribute to the great diversity in test form andcomposition in benthic foraminifera. Yet, smallspecimen size and the remoteness of the deep-seaenvironment have limited our ability to describe therelative influence of these biological and chemicalfactors. The use of fossilized foraminiferal tests aspaleo-indicators requires that we understand thecontrols on test composition. Test wall morphologyand composition were examined inforaminifera that colonized experimental substratesdeployed on a seamount in the central North Pacific. Three types of agglutinated forms were identified. Atriserial (Eggerella-like) and two-chambered(Hyperammina-like) form contained a Ca-rich(CaCO3) precipitate and the chamber walls of anencrusting two-chambered form was Ba-rich(BaSO4). We discuss the composition of thesebiologically precipitated minerals in the context ofthe environmental conditions during the life of theseforaminifera.[PUBLICATION ABSTRACT]