Brassicasterol as a Biomarker in the Ross Sea

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During the austral spring, diatom species and the colonial prymnesiophyte Phaeocystis antarctica form large blooms in the Ross Sea. The diatom blooms are typically localized in the western Ross Sea while the P. antarctica blooms typically develop in the southeastern and south central regions of the Ross Sea. Recent data suggest that the dominance of non-siliceous phytoplankton organisms, such as P. antarctica may be responsible for the drawdown in atmospheric CO2 that occurred during the last glacial maximum. The proposed project would focus on developing a new method to test whether the algal sterol, brassicasterol, could be a useful sediment biomarker for delineating the relative abundance of P. antarctica in over-lying waters. Sediment samples from each of these regions will be analyzed to test whether a compound-specific d13C method could be used to determine the relative abundance of Phaeocystis antarctica from over-lying waters. Specifically, laboratory cultures and core materials would be used to look for a depleted d13C sediment brassicasterol signal. If the method proves valid in the Ross Sea, then it could provide some definitive answers regarding the potential role of P. antarctica during the glacial/interglacial boundary. Positive results would be potentially important to a diverse array of scientists including: biogeochemists, biological oceanographers, paleoceanographers, and global climate modelers.