CSI Microscale: Calcification Scene Investigation of calcareous microbenthos -- Method development and test case

Joan M. Bernhard, Geology and Geophysics


Project summary

Because of their small size and inhabitation of deep-sea sediments, understanding when and
where calcareous microbenthos form their skeletons is not easily pinpointed. Thus, we liken this task to the popular CSI television franchise, where Crime Scene Investigators use a barrage of high-tech methods to solve their assigned cases. Wearing research-detective hats, we propose to unravel this mystery by developing a new method that will unequivocally identify where and when important calcareous microfauna such as benthic foraminifera calcify in situ. Chemical signatures in the carbonate shells of benthic foraminifera are arguably the most commonly used tool in paleoceanography; not knowing where and when such microfauna calcify introduces significant uncertainty in paleoceanographic and paleoclimate data. Uncertainty in science can quickly be viewed as fraud by a large sector of the public, as evidenced by the recent allegations of misconduct by scientists interpreting climate change data. Regardless of the details and outcome of the subsequent investigations into “Climategate”, clearly climate scientists should devote effort into decreasing uncertainty in their interpretations.

This proposed project will develop a tool to help minimize uncertainty in paleoceanographic proxy data. Specifically, we propose to develop a method to fluorescently label calcite as it is precipitated in benthic foraminiferal shells while they are living in situ using osmotic pumps to slowly dispense calcein, a fluorescent compound incorporated into carbonates precipitated during such incubation. More specifically, we propose to: (1) Use spectrometry and whole core incubations to determine the duration osmopumps dispense in sediment cores at bathyal seafloor temperatures. (2) Use whole-core incubations, culture approaches, and epifluorescence microscopy to determine the lateral and vertical extent that calcein is dispensed from osmopumps to tag calcifying foraminifera in situ. (3) Use analysis of δ13C of pore-water and foraminiferal tests, and distributions of Rose Bengal-stained and calcein-labeled populations from whole-core osmopump incubations to test the hypothesis that benthic foraminifera calcify in one sediment horizon and then migrate vertically. Due to the relevance of this project to OCCI (relevance to paleoceanography / paleoclimatology), OLI (relevance to ecology), and DOEI (deep-sea method development), we seek joint funding for these activities.