TOWARDS RESOLVING IN SITU, CENTIMETER-SCALE LOCATION OF BIOMINERALIZATION IN CALCAREOUS MICROBENTHOS

Geochemical proxies recorded in biomineralized carbonate have provided a sound foundation for paleoceanography and paleoclimate studies, yet significant uncertainties exist about where and when certain key taxa calcify. Insights into environmental conditions such as sea surface temperatures, deep-water temperatures, salinity, ice volumes, oceanic circulation patterns, paleoproductivity, and nutrient cycling have all been obtained from geochemical analyses of biomineralized carbonate of marine organisms. However, we cannot fully understand geochemical proxy incorporation and the fidelity of such in species until we better understand fundamental aspects of their ecology at scales relevant to these (micro)organisms. In an effort to better understand benthic foraminiferal ecology and their geochemical proxy fidelity, we are developing a method to assess in situ calcification by fluorescently labeling calcite as it is precipitated by organisms living in marine sediments. The fluorescent marker is calcein, which is commonly used in laboratory or short-term incubations to mark carbonate skeletal materials in a wide variety of organisms. Once calcein is incorporated into the carbonate, it can be detected with an epifluorescence microscope. While an experiment with benthic foraminifera is ongoing, promising results have been obtained from a separate experiment with juvenile quahogs (Mercenaria mercenaria). The in situ fluorescent-tagging method will be described and initial results will be presented from an experiment that lasted ~4.5 months. Ultimately, this method will allow determinations of in situ growth rate in deep-sea organisms and provide insights about microhabitats where paleoceanographically relevant benthic foraminifera actually calcify. Funded by WHOI’s Ocean Life Institute (to JMB), Ocean and Climate Change Institute (to JMB), Gori Fellowship (to FM), and Robert W. Morse Chair for Excellence in Oceanography (to JMB).