Documenting alteration and preservation of fossil coral skeletons
Fossil coral skeletons are valuable archives of past environmental change as long as their original mineralogical structures and compositions are preserved. Good preservation of fossil coral skeletons is very rare, however, because corals make their 'hard parts' out of a calcium carbonate mineral called aragonite, which is metastable at Earth's surface conditions. My previous work has found that while well-preserved fossil corals are difficult to find, it is possible to identify some well preserved samples going back to 200 million years ago (Gothmann et al. 2015).
The goals of this project are to: (1) continue examining a large suite of fossil coral samples to identify if skeletons are well-preserved or not (2) determine which physical and geochemical features best indicate the presence/absence of alteration and (3) to use well-preserved coral skeletons to reconstruct past environmental properties. We use tools including Scanning Electron Microscopy at St. Olaf College (see an SEM image taking by CURI student, Huy Nguyen, to the right), X-ray Diffractometery and Inductively Coupled Plasma Mass Spectrometry (Carleton College). There may also be opportunity to measure isotope ratios via ongoing collaborations.
Fossil coral skeletons are valuable archives of past environmental change as long as their original mineralogical structures and compositions are preserved. Good preservation of fossil coral skeletons is very rare, however, because corals make their 'hard parts' out of a calcium carbonate mineral called aragonite, which is metastable at Earth's surface conditions. My previous work has found that while well-preserved fossil corals are difficult to find, it is possible to identify some well preserved samples going back to 200 million years ago (Gothmann et al. 2015).
The goals of this project are to: (1) continue examining a large suite of fossil coral samples to identify if skeletons are well-preserved or not (2) determine which physical and geochemical features best indicate the presence/absence of alteration and (3) to use well-preserved coral skeletons to reconstruct past environmental properties. We use tools including Scanning Electron Microscopy at St. Olaf College (see an SEM image taking by CURI student, Huy Nguyen, to the right), X-ray Diffractometery and Inductively Coupled Plasma Mass Spectrometry (Carleton College). There may also be opportunity to measure isotope ratios via ongoing collaborations.
The above image of a coral skeleton was acquired using a Scanning Electron Microscopy by CURI student Huy Nguyen '21. Note the needle-like texture of the crystals present in the skeleton, which are characteristic of good preservation of the mineral aragonite.
The photo above shows Huy Nguyen '21 (Physics major) presenting his research on fossil coral preservation through analysis of Scanning Electron Microscope images at the CURI 2018 final symposium.
Investigating how uranium is incorporated in sediments
Uranium incorporation in sediments has been shown to be influenced both by oxygen and carbon - two environmentally and biologically important elements. Through the help of Charles Umbanhowar (Biology) we have obtained access to a set of sediments from lakes in Mongolia that vary greatly in the concentration of oxygen and carbon species. This project will focus on analyzing the uranium concentrations in sediments by Inductively Coupled Plasma Mass Spectrometry (available through collaboration with Carleton College).
The photo to the right shows Henry Henson '20 (Environmental Studies and Biology major) presenting his research on Uranium concentrations in Mongolian lake sediments at the CURI 2018 final symposium.
Developing a system for culturing live coral for proxy development
One way to develop indicators (or 'proxies') of past environments is to obtain samples from different modern environments and explore how variables change across that set of samples. However, these proxy calibration studies may be made difficult if environmental variables co-vary across modern sites. For example, if you wanted to identify an indicator of temperatures on land, but that variable was correlated with humidity at many of your sites, it might be difficult to tell whether your indicator of interest was responding to temperature or humidity.
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In the case of coral or shell-based proxies, culture experiments offer an elegant way to control environmental variables for proxy development. In the fall of 2018, we are beginning to develop a system for conducting culture experiments with live coral (or potentially other marine organisms). Students will work to establish temperature, pH, and nutrient control for this system. Students can also gain experience with experimental design.
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The figure above shows a micro-CT image of a cultured juvenile cold water coral (Balanophyllia elegans) that I grew as a postdoctoral scholar at the University of Washington in Seattle. B. elegans is native to the Pacific Northwest and lives in waters with naturally high acidity.
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The figure to the right shows the setup for coral culturing at Friday Harbor Labs (Friday Harbor, WA). The corals are incubated in bottles with seawater measured in the bottles before and after incubation to asses coral calcification rates. Photo courtesy of Max Miner (REU Student at Friday Harbor Labs, Summer 2016).
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