USING FORAMINIFERA TO RECONSTRUCT PAST OCEAN OXYGEN CONCENTRATIONS

Foraminifera, single-celled organisms with a hard outer shell called a test, have been the focus of much research to reconstruct past ocean oxygen concentrations. This is because their test, made up of calcium carbonate, contains pores which seem to vary in size and abundance with oxygen concentrations (e.g., Rathburn et al., 2018). It is thought these pores become more prevalent in low oxygen conditions to facilitate gas exchange and the preservation of these features can help reconstruct environmental conditions in which foraminifera lived. The surface area of the pores in the test of Cibicidoides wuellerstorfi, an epibenthic foraminifera common in the deep ocean, logarithmically decreases with increasing dissolved oxygen concentration (Rathburn et al., 2018). However, under anoxic conditions foraminiferal ecologies change and C. wuellerstorfi abundances decrease and species such as Bolivina spissa become dominant. As such, to apply oxygen reconstructions based on foraminifera pores it is necessary to apply the proxy on multiple species. This study seeks to extrapolate the work of Rathburn et al. (2018) to B. spissa to facilitate the application of this proxy downcore in records where oxygen is likely to significantly alter foraminiferal ecologies and abundances. It is not likely that C. wuellerstorfi and B. spissa would have the same response to changes in oxygen levels in the ocean because C. wuellerstorfi lives in bottom waters, which have more stable oxygen levels reflecting ocean bottom water conditions, while B. spissa lives within the sediment thereby influenced by pore waters which can be highly variable. The ultimate goal of this research is to determine if there is a consistent offset between the two species' responses to changes in oxygen levels, and to see if it is possible to combine their records into one complete oxygen proxy that would allow scientists to better understand how oxygen levels in the ocean have changed over time, and to track changes in marine ecosystems.