Downcore records of benthic foraminiferal shell composition can provide valuable records of deep water temperature and chemistry in the past. While field based calibration studies have defined the relationships between shell chemistry and bottom water conditions, our ability to interpret benthic foraminiferal proxy records continues to be challenged by the fact that multiple factors-- environmental and biological-- can influence most aspects of shell chemistry. Culture-based studies offer a promising complement to core-top calibrations, because in the laboratory it is possible to vary a single environmental variable while holding others constant. This research builds on previously funded culture work, here focusing on demonstrating calcification in culture, and reproduction and subsequent growth in culture, by Uvigerina and Cibicidoides species, two benthic foraminifera widely used in paleoceanography. Samples collected from the mid-Atlantic margin will be cultured under controlled and monitored physical and chemical conditions in order to assess the consistency of foraminiferal oxygen isotope values from the newly-formed shell material. The main focus is on foraminiferal growth and reproduction, which will lay important groundwork for future efforts toward proxy calibrations under variable environmental conditions. A female postdoctoral researcher will have a central role in the project. Other broader impacts include providing sea-going experience for undergraduate volunteers from non-oceanographic institutions.
800x600 The project goal was to develop and demonstrate the ability to culture benthic foraminiferal species commonly used to provide proxy records of bottom-water temperature and chemistry; we view such culture-based investigations of the controls on foraminiferal shell chemistry as an essential component of the validation and use of paleoenvironmental proxy records based on foraminiferal shell chemistry. The cruise was successful, and provided seagoing research experience to seven volunteer undergraduate students. All seven took part in all aspects of the shipboard work, including coring with the Soutar box corer and on-deck processing (sieving) of the surface sediments. Our main experiment was run at 7C and atmospheric pressure, and included 8 sets of calcein-labeled cultures. Assessment of the samples with epifluorescence microscopy found that growth by one or more species occurred in all samples; we did not observe significant differences in foraminiferal growth as a function of feeding rate. We then conducted a second, preliminary experiment to see if maintenance of foraminiferal populations at pressures more similar to their in situ conditions resulted in more test (shell) growth and/or reproduction. The presence of Rose Bengal-stained juveniles (53-125 µm specimens) in the high pressure experiment indicates that reproduction took place by as many as six species. However, foraminiferal abundances were not high enough to assess the impact of elevated hydrostatic pressure on foraminiferal growth in culture.
