Dr. Cara K. Thompson has been granted an NSF Earth Sciences Postdoctoral Fellowship to carry out a research and education plan at the State University of New York, Stony Brook. In this study, high-resolution chemostratigraphy of Ordovician marine carbonate platform rocks will be used to understand the ties between climate, perturbations in the marine carbon isotope record and ocean/atmosphere pCO2. The timing and mechanisms behind of the onset of Late Ordovician glaciation are poorly understood, but generally tied to the appearance of large excursions in the marine carbon isotope record. The C-isotope record of the transition between greenhouse climate in the Early to Middle Ordovician to glaciation in the Late Ordovician indicates changes in CO2 drawdown that conflict with sea surface temperature records. These discrepancies highlight the need for a robust proxy for pCO2. The results of this study will represent the earliest record of boron-isotope composition and act as a test for the utility of boron isotope as a proxy for ocean pCO2 in the Paleozoic.
Global climate change is a topic high interest in recent decades. Looking to the past record of pCO2 and global climate is essential to predicting the impact of modern changes in atmospheric carbon dioxide concentration on the biosphere. In this study, the boron isotope record, a proxy for marine pCO2, will be extended to early in Earth's history. The Ordovician represents a time of extreme climate change and an interval in which evidence in the fossil record suggests the most rapid biodiversification followed by one of the largest extinction events in Earth's history. This study will provide ample opportunity to engage high school and undergraduate students in active research. Along with students in the Masters of Arts and Teaching program, the PI will incorporate high school students into field exercises, sample processing, and data interpretation. The PI will teach undergraduate and graduate level courses in geochemical records with emphasis on marine carbon, sulfur and oxygen in Earth's history.
The primary result of this research project is the construction of the earliest known (Late Ordovician; 458-444 million years ago) boron isotope record indicating changes in seawater pH concurrent with rapid changes in global climate. The utility of the boron isotope record as a proxy for ancient seawater pH has been called into question since ambient seawater boron isotope composition is largely unknown. Although absolute values for ambient seawater pH cannot be determined, this study demonstrates that relative changes in pH can be recorded on short (less than a few million years) time scales in the ancient marine record and that those relative changes are meaningful when compared to other climate proxies. This study focused on global climate change in the Late Ordovician Period. Much of the Ordovician time period was characterized by global greenhouse climate with widespread warm, tropical coastal oceans, high sea level, and atmospheric carbon dioxide concentration that are thought to be 14 to 16 times present atmospheric levels. Global glaciation in the latest Ordovician was sudden and drove the second largest extinction event in Earth's history. For this reason it is important to understand the driving mechanisms and to recognize signals indicating onset of such rapid changes in global climate. Data from this study show an increase in seawater pH during a transition from global greenhouse conditions to glaciation in the latest Ordovician. This apparent reduction in seawater acidity is consistent with decreased atmospheric carbon dioxide concentration. Data from this study agree with other climate records, like the marine carbon isotope record, that indicate sudden drawdown of carbon dioxide, which may have been the driver of end Ordovician glaciation. Results from this study have implications for the relationship between climate and atmospheric carbon dioxide concentration throughout Earth's history. With robust marine boron isotope records, relative changes in seawater pH can help constrain the timing and mechanisms behind global climate change in ancient oceans. To further investigate this relationship, I am currently seeking funding with my postdoctoral mentor, Troy Rasbury, SUNY Stony Brook, for study of the lithium isotope record, which can help constrain sources of boron in the Ordovician ocean. The current results have been written up in a manuscript, which is currently being finalized for submission to Geochimica et Cosmochimica Acta. Funding of this project has not only supported scientific research, it has supported high school and undergraduate research. A number of underrepresented minority high school students were involved in research during the 2011-2013 summer break. Many of these students conducted their own research projects using the samples acquired for this study. One high school student among this group, Stephanie Fischer, continued to work with me through the entirety of my postdoctoral research. Stephanie constructed a record of magnesium-calcium ratios to help constrain Ordovician seawater chemistry as it relates to sea surface temperature. Among her many impressive achievements that have stemmed from her involvement in this research, she has been named as a Young Naturalist Finalist by the American Museum of Natural History. Stephanie will be attending Stanford University starting in Fall 2014. Another student, Cory Walker, assisted with field work and sample processing. He has graduated from SUNY Stony Brook in Spring 2014 with a BA/MAT degree in Earth and Space Science Education and is currently seeking a teaching position in Earth Science.
