58th Annual Report on Research 2013 Under Sponsorship of the ACS Petroleum Research Fund

Boron isotope paleo-ocean pH proxy is based upon four working hypotheses that basically support the idea that the pH of seawater dictates the boron isotope composition of marine calcium carbonates. Therefore, a variety of marine carbonates have been examined for their boron isotope compositions to reconstruct ancient ocean pH variations and thus to better understand Earth’s environmental changes. However, one of its founding working hypotheses, predicting that borate is preferentially incorporated into the crystal structure of carbonate minerals without a significant kinetic effect, has never been thoroughly examined. 

The main research objective of my ACS-PRF proposal is to address this issue by undertaking laboratory synthesis experiments which enable us to systematically evaluate not only the speciation of boron-bearing aqueous species, but their incorporation into the two most common polymorphs of CaCO₃. Over the last two and a half years, my research group has successfully developed experimental techniques for the preparation of kinetic and vital effects-free inorganic calcium carbonates (aragonite and calcite) from various pH values.  It should be noted that synthesizing kinetic and vital effects-free inorganic aragonite or calcite from a different, but stable pH value is essential for the successful achievement of my research objectives. Aragonite samples synthesized from various conditions using our new experimental techniques have been analyzed to determine their boron isotope compositions by our collaborators at the University of Southampton in the U.K. and calcite samples will be sent out soon for further testing. Our boron isotope analysis of kinetic and vital effects-free aragonites indicates that borate ions are preferentially incorporated into the aragonite crystal, supporting the proposed working hypothesis.

The ACS-PRF New Directions (ND) grant has enabled me to pursue new research with my undergraduate and graduate students. Over the last 2.5 years, four graduate students have been involved in my ACS-PRF research project and I have been fortunate to be able to hire a number of young and promising undergraduate students who were interested in pursuing a career in areas within ACS-PRF’s scope of funding. Most undergraduate students were assigned to various tasks that were directly related to my proposed research project, but a few of them were also involved in some exploratory tasks that could help us to achieve our main research goal. Students who were involved in my ACS-PRF research project have learned various laboratory techniques that are essential in the field of geochemistry and Earth sciences. I strongly believe that this hands-on laboratory experience is an invaluable asset for their future careers as geoscientists. The preliminary experimental results of my ACS-PRF research look promising and are expected to provide an important basis for the development/calibration of reliable paleo-ocean pH proxies for biogenic carbonates.