Reports: ND252457-ND2: Examining Evidence for a Dynamic Sulfur Cycle During the Early Triassic with Isotopic Measurements of Carbonate Associated Sulfate
printer friendlyThe post-doctoral fellow funded through this project, Dr. Katja Meyer, traveled to Northwestern University in September of 2012 to learn the methods for extracting carbonate associated sulfate (CAS) from limestones in the lab of our collaborator, Professor Matthew Hurtgen.
Soon after this visit, the post-doctoral fellow took a seven month leave following the birth of her child. This situation has necessarily slowed progress on the project as there was not sufficient time to identify another qualified individual to conduct the project and the duration of the post-doctoral fellow’s leave was uncertain. Dr. Meyer returned to the lab in July 2013 but took additional time away from the project in August 2013 after her father’s death.
We were able to make some progress during Dr. Meyer’s absences. A graduate student from Stanford traveled to the lab of Professor Alex Sessions at Caltech in Dr. Meyer’s place during October 2012 to learn an alternative technique for analyzing CAS sulfur isotopes via inductively coupled plasma mass spectrometry (ICP-MS) and to obtain pilot data via this technique. The advantage of this technique over more traditional methods of gas phase isotope ratio mass spectrometry is that it requires substantially less sample material – 1 mg vs 100 g of rock – and therefore allows for more targeted sampling of the carbonate phases within a given sample that are most likely to record primary seawater sulfur isotope values. Our goal is to analyze a suite of samples to compare the results of the traditional, bulk rock method with results of the newly developed ICP-MS approach.
Over the past six months, Dr. Meyer prepared ~50 samples for CAS analysis via the traditional (100 g) method. We have an agreement in place with Professor Hurtgen to measure the sulfur isotope composition of samples prepared by the traditional method, and these samples will be analyzed in the coming months at Northwestern University. We are in the process of setting up logistics that may allow us to analyze a subset of samples via ICP-MS at Caltech.
To aid in the interpretation of our sulfur isotope data, the Dr. Meyer and a graduate student have developed a quantitative model of the global carbon and sulfur cycles as well as a one-dimensional model of sulfur cycling within the marine water column. These models will allow us to quantitatively interpret secular variation in the CAS sulfur isotope record within the context of known variation in the global carbon and calcium cycles as well as within the context of the investigated depth gradient. Because these cycles are tightly linked via their effects on seawater alkalinity and the coupling of the carbon cycle to the alkalinity flux via silicate weathering, it is essential that any interpretation of sulfur isotope variation be carried out in light of constraints from these other isotope systems.
During 2014, Dr. Meyer was offered and accepted a faculty position at Willamette University starting in September 2014. Her work on this project was a critical component of her success on the job market and she will continue to collaborate on this project over the coming year. Dr. Meyer has a newly renovated lab at Willamette and will be able to train undergraduates in both methods of CAS sample preparation.
During the 2014-2105 academic year, we will have our new CAS results from Northwestern and will use the developed model framework to interpret these analyses in addition to recently published CAS data from the field site. Meyer will involve undergraduates in the model-data comparison as well as CAS sample preparation using the new, low-volume sample technique. With this plan in place, we anticipate submitting our results for publication during summer 2015.
Overall, this project has already yielded benefits for both me and Dr. Meyer. I have had the opportunity to learn new methods of sample preparation and new modeling techniques for data interpretation. These data will ultimately provide an ideal complement to the carbon, calcium, and uranium isotope data that we are collecting from the same stratigraphic sections in order to provide an integrated view of Permian-Triassic global change. For Dr. Meyer, this project has provided an opportunity to learn a new isotope system, new sample preparation techniques, new analytical techniques, and opportunities to manage grant funds and undergraduate assistants under the supervision of the PI. It will also provide an ideal project to continue collaborating on with her own undergraduate students as she begins her new faculty position at Willamette.
