Calcium (Ca) is a key component of the long term carbon cycle, and the weathering of Ca-bearing silicate minerals regulates global climate over geologic time. Tracing Ca cycling is therefore of paramount importance to understanding the role of weathering on the carbon cycle. My PhD research involved using Ca isotopes as a means of tracing Ca cycling during basalt weathering. By characterizing the Ca isotope geochemistry of different materials in Iceland, I can identify what types of minerals (silicate or carbonate) are weathering and I can trace processes that affect Ca cycling in rivers.
Here is a video summary of what happens once I return from the field with samples from Iceland.
Rock processing in this video consists of:
- Cut rocks with saw to remove “weathering rind” and to create manageable sized portions
- Smash rocks into smaller chunks
- Smash into even smaller chunks, then
- load into “Shatterbox” to powder the rocks.
- Set up weigh station in clean lab then
- weigh subsamples of rock powder into Teflon beakers.
- Fill beakers containing rock powder with HF-HNO3 mixture to dissolve them.
- Wait 3-5 days while they “digest” on the hot plate at 130 C
- Transfer the “rock solution” into bottles.
- Dilute “rock solution” to measure on the ICP-OES for cation analysis.
- Prepare for Ca isotope processing, then purify sample aliquots with cation-exchange column chemistry.
At Northwestern University, I used a Thermal Ionization Mass Spectrometer (TIMS) to analyze samples for Ca isotopes. For a more technical tour of the Radiogenic Isotope Lab, check out this video made by our lab manager, Meagan Ankney, for the Earth and Planetary Sciences Department virtual graduate student recruitment in February of 2021.
Claire Nelson 