Yi-Wei Liu Dissertation Defense
Congratulations to Yi-Wei Liu who successfully defended her dissertation on May 7, 2015.
Advisor: Sarah Aciego
Abstract: To better understand how the seawater pH varies spatially and temporally with respect to elevated atmospheric carbon dioxide level, and the impacts of ocean acidification to marine organisms, a high-throughput boron purification method coupled with total evaporation thermal ionization mass spectrometry technique has been developed. By using this method, we are able to measure boron isotopic composition in carbonate with less then 1 ng of boron in the sample and further reconstruct calcification pH for biogenic carbonate archive. In this dissertation thesis, we applied this method to investigate how environmental factors influence the boron incorporation in two unconventional biogenic carbonate archives: aragonite bivalve shells and calcite coccolithophore. In the bivalve shell Arctica islandica study, we found that shells will regulate their calcification pH, but also boron incorporation into the shell has a potential temperature dependence. Therefore, a culture experiment with fixed temperature and salinity, but variable pH is required to evaluate the species-specific boron to ambient seawater pH relationship and the potential use of this proxy in this species. In the coccolithophorid species Pleurochrysis carterae study, we found an ability to adapt to ocean acidification. The boron isotopic composition in the coccoliths suggests it regulates vesicle pH to sustain calcification with decreasing environmental pH. With other geochemical constraints including the particulate inorganic carbon to particulate organic carbon ratio (PIC/POC) and stable isotopic compositions we found this coccolitophorid species is likely to change usage of inorganic carbon species from HCO3- to CO2 as ambient medium pH decreases. This dissertation work provides insights on the diverse response of marine organisms to ocean acidification. Extending work on boron to pH calibration in unconventional species will help reconstruct seawater pH records over a wide geographic range through geologic time. Further applications in different marine calcifiers can help us better understand the mechanisms for diverse biological responses to ocean acidification and to predict the potential bioremediation capacity in the ocean.