To date, we have:
1. Developed methods for the extraction of iron oxides from a rock matrix and their oxygen isotopic analysis by laser fluorination gas-source isotope-ratio mass spectrometry. We verified that the extraction and purification protocols do not affect the isotopic composition of the oxides.
2. Experimentally calibrated the temperature-dependent fractionation of oxygen isotopes between the common iron oxide minerals, goethite and hematite, and their parent fluids. We have done this in both freshwater and seawater.
3. Checked this calibration against iron oxides forming in the modern ocean, at a known temperature and seawater isotopic composition.
4. Collected and analyzed the oxygen isotopic composition of iron oxides from more than 80 locations, spanning the last 2000 million years of Earth history.
5. Used the results of items 2 and 4 above to produce a novel record of the oxygen isotopic composition of seawater over Earth history. The new record suggests that the increase in the abundance of 18O in marine sedimentary rocks reflects a parallel increase in the 18O content of seawater, rather than a gradual cooling from very warm early temperatures to cool recent temperatures.
6. Explored mechanistic explanations for the increase in the 18O content of seawater, with implications for climate regulation and ocean chemistry, among other topics.
7. Collected and begun analyzing the oxygen isotopic composition of marine iron-bearing clays spanning the last 2000 million years of Earth history, which will complement the iron oxide record (item 2). Iron-bearing clays provide built-in constraints on the post-depositional alteration history of the samples, which is a strength of this complementary record.
8. Developed cathodoluminescence methods mounted on a scanning electron microscope (SEM-CL) for petrographic characterization iron-bearing minerals, which are difficult to study by other microscopic techniques. Together with other imaging and geochemical analyses, the SEM-CL methods are used to constrain the post-depositional burial and alteration history of our samples, allowing us to avoid altered/compromised samples.
9. Identified a time interval, approximately 750 million years ago, during which the Earth is thought to have experienced a global glaciation (the Sturtian snowball Earth event), and during which our samples suggest that the ocean was more 18O-enriched than before or after. We collected and analyzed additional samples, which we then used to observationally constrain, for the first time, the volume of ice and the hydrological cycle during this extreme climatic event.
10. Measured the triple oxygen isotope fractionation between seawater and ice for the purposes of constructing an isotopic mass balance to constrain the amount and type of ice present during the Sturtian snowball Earth event.
