Improving the accuracy and reliability of Earth system reconstructions by quantifying mechanisms that modulate sub-micron heterogeneity in marine calcifiers
EMSL Project ID
49766
Abstract
Reconstructions of Earth's biogeochemical history, the interactions between the ocean, atmosphere, and global environmental conditions, are commonly based on reconstructions generated using fossil foraminifera. Foraminifera are marine protists that secrete a calcite test (commonly referred to as a 'shell') composed of the biomineral calcite. Trace elements incorporated into the shell calcite vary with growth conditions such as the temperature, salinity, pH, or nutrient content of the ocean. Fossil specimens are used to reconstruct these environmental parameters through time. The accuracy of these reconstructions relies on both basic calibration relationships and on a solid mechanistic understanding of the organism's biological control on the composition of the shell. Careful examination of the shell composition has uncovered significant gaps in our understanding of the controls over trace element incorporation into foraminiferal calcite, and suggests that unidentified physical or biological controls have a significant influence on the incorporation of trace elements into the shell.Over the past 5 years our research group has cultured living specimens of planktic foraminifera under highly controlled conditions to explore the mechanisms governing the uptake of metals into their calcite shells. Specimens are cultured in isotopically or chemically modified seawater, which allows us to identify the calcite precipitated during growth and link growth conditions to the chemical composition of the shell. We have analyzed the shells of several cultured specimens at EMSL using NanoSIMS and ToF-SIMS analysis and atom probe tomography. The results have dramatically improved our understanding of what controls the variability of magnesium within the shell wall. Our collaborators and we have identified the cations present at the organic/mineral interface where initial calcification takes place, revealing for the first time that spectator ions (Na+) may play a role in biomineral templating.
After completion of our previous research at EMSL, we obtained SEM images suggesting the heterogeneity within the shells may be correlated to compositionally distinct layers, possibly composed of organic materials. We propose to complement our previous analyses to investigate the composition of these layers by identifying elements commonly associated with organic materials. We will also analyze specimens from additional experiments that have not yet been analyzed. The results will further advance our mechanistic understanding of the processes controlling trace element geochemical variability of these organisms, ultimately expanding the utility of foraminiferal climate proxies and the accuracy and fidelity of reconstructions of the Earth's geochemical history. This project is especially well matched with the unique capabilities of EMSL, which has the expertise and key instrumentation (e.g. NanoSIMS, ToF-SIMS, HIM, FTICR, APT) necessary for measuring and quantifying submicron-scale heterogeneity.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2017-10-01
End Date
2019-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Team Members