A physicochemically constrained seawater culturing system for production of benthic foraminifera

Abstract

We present an apparatus and procedure for culturing deep-sea (i.e., bathyal) benthic foraminifera under physicochemically constrained conditions. A 1600-L recirculating culture system was constructed to contribute negligible trace metal contamination; the system was housed in an environmental room maintained near in situ temperatures but at atmospheric pressure. Peristaltic pumps continuously circulated 3 mL seawater min-1 from the reservoir to 9 to 12 culture chambers. A 2-mm-thick layer of high-purity clay-sized silica substrate was used to minimize the impact of sedimentary microhabitats. Physicochemical parameters (salinity, alkalinity, pH, temperature) varied <2% throughout two culture experiments. Trace metal concentrations were initially set near open-ocean values and remained constant (i.e., within our analytical precision) during the experiments. Culture seawater was equilibrated with atmospheric CO2, thus dissolved inorganic carbon δ13C varied ~1‰ over the course of each experiment, reflecting the seasonal atmospheric CO2 isotopic variation. Culture seawater δ18O varied ~0.2‰. Each culture chamber was inoculated with as many as 100 foraminifers of single or multiple species. Pre-existing foraminiferal calcite was identified by fluorescent labeling prior to specimen introduction into culture. The cultures remained viable for >200 d in each experiment and produced up to 2,800 individuals per culture. The growth and reproduction of benthic foraminifera in a physicochemically constrained culture provide a new method for the experimentation and validation of geochemical proxies.