RAISE YOUR GLASS: A CULTURE EVALUATION OF DIATOMS AS ARCHIVES OF PAST NUTRIENT CONSUMPTION

• Main Author: Jones, Colin Anthony
• Format: Text
• Language: unknown
• Published: DigitalCommons@URI 2020
• Subjects: Antarctic; Antarctic Peninsula; Southern Ocean; Antarc*
• Online Access: https://digitalcommons.uri.edu/oa_diss/1187; https://doi.org/10.23860/Jones-Colin-2020; https://digitalcommons.uri.edu/context/oa_diss/article/2201/viewcontent/Jones_uri_0186A_12407.pdf

Nitrate is the most common limiting nutrient in the ocean and plays a critical role in the extent and intensity of marine primary production, and therefore the global ocean’s biological pump. Characterization of the supply and demand of nitrate constrains how ocean biology may regulate climate, so understanding the degree of nitrate consumption in the past is a fundamental step towards understanding controls on past climate. The nitrogen isotopic composition (as δ15N) of phytoplankton biomass can be used to infer the degree of nitrate consumption in nitrate-replete surface waters such as the Southern Ocean. This signal is recorded in the underlying sediment and can be used to construct a history of nitrate utilization. However, δ15N values of phytoplankton biomass are subject to alteration during sinking and sedimentation, leading to uncertainty in estimations. The nitrogen isotopic composition of nitrogen within the shells of diatoms (δ15NDB), a photosynthetic microorganism, is protected from alteration and potentially a more robust tracer of past nitrate dynamics. However, this assumption may be complicated by species-specific isotope effects and the high variation in Southern Ocean diatom assemblages through climate transitions. The goals of this dissertation are twofold: first, to investigate the impact of different Southern Ocean diatom communities (Chapter 1) and individual species (Chapter 2) on the δ15NDB proxy and second, to use δ15NDB to examine paleo-nutrient utilization and oceanographic conditions of the coastal West Antarctic Peninsula (WAP), a region of high seasonal productivity and carbon drawdown (Chapter 3). Two distinct Southern Ocean surface ocean diatom communities were grown in triplicate cultures to determine the impact of diatom community composition on δ15NDB. We found that although the community growouts had distinct diatom assemblages, the εDB (= biomass δ15N - δ15NDB) was indistinguishable between the two growouts at -4.8 ± 0.8‰. This suggests that species composition is not the ...