Ocean acidification is widely referred to as "the other CO2 problem." Marine invasion of anthropogenic carbon dioxide (CO2) causes reduced pH and lowers the calcium carbonate (CaCO3) saturation of seawater. Coral calcification rates decrease as the CaCO3 saturation state of their ambient waters decreases. Marine plankton such as pteropods (also known as sea butterflies) show evidence of shell dissolution when subjected to seawater under-saturated with respect to CaCO3. Similar to corals, if pteropods prove unable to adapt to living in continuously under-saturated waters, their geographic distribution may be limited in the future. While some of the effects of ocean acidification on biota in the modern ocean can be directly observed, forecasting how fast changes will occur as anthropogenic CO2 continues to increase in the atmosphere and how organisms will respond to these changes presents challenges. Reconstructing the marine saturation state of CaCO3 in the past, using the geological record, is important for understanding the potential future outcomes of modern ocean acidification because it provides a record of natural variability and sensitivity of the carbonate system, and a baseline from which to understand perturbations.
The goal of this project, led by a professor at Grand Valley State University in Michigan, is to develop a new proxy for quantifying the degree and effect of ocean acidification events in Earth's past by studying the preservation of fossilized pteropod shells in marine sediments. A reliable and quantitative indicator of CaCO3 preservation in deep sea sediments will help discern geographic and hydrographic shifts in benthic (e.g. corals, calcifying algae) and planktonic ocean communities (e. g. pteropods, coccolithophores, foraminifers) driven by ocean acidification or alkalization events. Such a proxy will also aid in understanding ocean circulation changes, water mass boundary changes, changes in ocean carbonate chemistry on millennial timescales, and other factors that may cause dissolution of CaCO3 such as changes in fluxes of CaCO3 and organic carbon to the deep sea. Funding supports four undergraduates in data generation, data analysis, and dissemination of results to the scientific community. The results of this study are disseminated to the public in outreach events and postings on science blogs.
