USING SHELL MORPHOMETRICS TO UNDERSTAND OCEAN ACIDIFICATION IMPACTS ON THE CALCIFICATION OF FORAMINIFERA

Anthropogenic fossil fuel emissions since the Industrial Revolution have led to increased concentrations of carbon dioxide (CO₂) in the atmosphere, with approximately 30% of emitted CO₂ being absorbed by the ocean. Ocean acidification refers to the absorption of CO₂ in seawater resulting in chemical reactions that lower pH and carbonate ion concentration [CO₃^2-], which is important to many marine calcifiers. Sediment trap samples collected biannually (fall and spring) from 2008-2018 in the Gulf of Mexico (GOM) are used here to investigate long term changes in calcification of planktonic foraminifera, which are ubiquitous throughout the global ocean and contribute to carbon cycling. Using these samples, morphometric data including shell weight, 2-D surface area, and thickness (estimated by individual weight/area; area density) were determined for two species: Orbulina universa and Neogloboquadrina dutertrei. Preliminary results suggest significant reduction in calcification by both species, and potential presence of an O. universa cryptic species in our study region. A 0.5 m sediment core collected adjacent to the sediment trap mooring will be used to determine morphometric changes in O. universa and N. dutertrei over the Industrial Period. The combination of sediment trap and core analyses will provide insight on the impacts of anthropogenic OA on marine calcifiers in the GOM. An extension of this work includes a time series analysis of Amphistegina gibbosa (reef-dweller) where preliminary morphometric data indicates an increase in calcification.