Advanced imaging techniques combined with in situ analyses used to assess diagenesis in benthic foraminifera

Much of our knowledge of the Earth's climate of the past ~100 million years is deduced from shells of marine microorganisms called foraminifera. These single-celled organisms are ubiquitous in the world's oceans and live either in the upper water column (planktic) or on the sea floor (benthic). After their life-cycle is completed, the sand-grain-sized calcite shells are fossilized and contribute substantially to marine sediments. This rich fossil record, combined with the well-studied relationship between environmental parameters and shell-chemistry, make foraminifera a primary climate archive. While chemical and isotopic data collected from benthic and planktic foraminifer shells provide a largely consistent record of the Earth's past climate variability, these paleorecords may be slightly biased, as the chemical composition of fossil shells may be modified after being deposited for millions of years in the sediment column. A precise assessment of this bias could significantly improve critical applications of societal importance such as model simulation of past sea level or ice sheets, as these models strongly rely on the quality of paleoclimate data. This project will apply advanced technological analytical tools to document the magnitude of this bias in chemical composition resulting from alteration of fossil shells. The project will support and train a female graduate student in the research. Project outreach activities include museum quality displays for the Lamont Core Repository and Open House.

Previous studies suggest that certain domains within foraminifera shells are better preserved than the remaining material, and thus provide a robust record of past environmental parameters. However, these well-preserved domains are inaccessible by conventional analytical approaches that require analysis of whole shells. Thus, conventional 'whole-shell' data represent the averaged chemical composition of different generations of shell calcite from a potentially large preservational range. Recent innovations in the combined use of high-magnification imaging by scanning electron microscope (SEM), cathodoluminescence (CL)-spectrometry, secondary ion mass spectrometry (SIMS), and electron probe microanalyzer (EPMA) now allows the identification and chemical analyses of both well-preserved and altered domains in single foraminifera shells. This project will apply this state-of-the-art approach on benthic foraminiferal shells from climate events relevant for climate model simulations, such as the last glacial-interglacial intervals and the Mid Pliocene Warm Period (MPWP), a potential climate analogue ~3.2 - 2.9 m.y. ago. This study will provide model simulations with more robust paleoclimate data, further, a comparison with conventional measurements will permit quantification of the potential bias in published records and thus establish corrections. This is the first study investigating potential alteration in benthic foraminifera with an unprecedented level of detail, and the anticipated outcome will be the compilation of more accurate paleoclimate records, which have a direct impact on the performance of model simulations for long-term forecasts.