Environmental Controls on 11B in Unconventional Biogenic Carbonate Archives.

Abstract

A method for high-throughput boron purification coupled with total evaporation thermal ionization mass spectrometry was developed to allow investigation of how the seawater pH varies spatially and temporally with respect to elevated atmospheric carbon dioxide level, and the impacts of ocean acidification on marine organisms. 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 as a biogeochemical archive. In this dissertation, we applied this method to investigate how environmental factors influence the boron incorporation in two unconventional biogenic carbonate archives: aragonite bivalve shells and calcite coccolithophores. In the bivalve shell Arctica islandica study, we found that shells regulate their calcification pH, and that 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 relationship between boron and ambient seawater pH and the potential use of this proxy in this species. In the coccolithophorid species Pleurochrysis carterae study, we observed an ability for this organisms 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(aq) 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 will help us better understand the mechanisms for diverse biological responses to ocean acidification and to predict the potential capacity to sequestrate exceeded atmospheric CO2 in the ocean.