| Summary: | Abstract Exploring the Biogeochemical Impacts of Size Variation in Reticulofenestra during the Late Miocene Paul Utuedor Coccolithophores belong to the group of calcifying plankton. They are characterised by the production of calcite platelets called coccoliths. The efficiency of the coccoliths in transporting calcium carbonate into the ocean interior is a factor of their size and abundance. Previous investigations into the evolution of a certain taxonomic group, the reticulofenestrids, have revealed patterns of size variations throughout the Cenozoic. The coccoliths produced by the Reticulofenestra genus typically exhibit a progressive increase in size and a rapid fall in maximum size in Miocene and Pliocene nannofossil assemblages. This project quantified the abundance of Reticulofenestra coccoliths and compared it to the impact of their individual carbonate mass (which is dependent on size and shape) at a North Atlantic deep-sea site during the late Miocene (~5.8 to 10.3 Ma). This research was carried out to determine the efficiency of carbonate export by the Reticulofenestra species during this time. The species of Reticulofenestra are generally classified based on the size of their coccoliths as small (<3 µm), medium (3-5 µm), large (>5- 7 µm), and very large (>7 µm). The most abundant Reticulofenestra group is medium-sized (3-5 μm) and has a low carbonate mass. As a result, they have less significant carbonate flux than expected intuitively from their high abundance, compared to the >7 μm group with a high carbonate mass but low abundance. With an average mass of 69.12 pg, the large-sized group hold eight-fold higher mass per coccolith than the medium-sized coccoliths (average 8.64 pg). Therefore, the coccolith's size impacts carbon export to the ocean floor, affects carbon cycling and, by extension, biogeochemical processes.
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