Holocene Sedimentary Record of Unusual Primary Productivity, Dalton Polynya, Sabrina Coast, East Antarctica

Tuesday, 16 December 2014
Amy Leventer1, Leanne Armand2, Mikhaila Redovian1, Eugene W Domack3, Amelia Shevenell3,4, Catherine Smith3, Caroline Lavoie5, Alejandro Hector Orsi6, Bruce A Huber7, Sean P S Gulick8 and Rodrigo A Fernandez-Vasquez9, (1)Colgate University, Geology, Hamilton, NY, United States, (2)Macquarie University, Biological Sciences, Sydney, Australia, (3)University of South Florida St. Petersburg, St Petersburg, FL, United States, (4)University College London, London, United Kingdom, (5)University of Aveiro, Aveiro, Portugal, (6)Texas A & M University, College Station, TX, United States, (7)Lamont-Doherty Earth Obs, Palisades, NY, United States, (8)University of Texas at Austin, Institute for Geophysics, Austin, TX, United States, (9)University of Texas at Austin, Austin, TX, United States
Cruise NBP14-02 surveyed the previously unstudied Moscow University Ice Shelf region, East Antarctica, an area of concern due to recent changes in the glacial system. Using 3.5 kHz sub-bottom geophysical data, we targeted a mid-shelf site with an expanded Holocene sedimentary section, recovering ~ 10 meters of Holocene diatom-rich sediments characterized by an unusual floral assemblage that records the strong and consistent presence of open ocean diatoms. The sedimentary assemblage is dominated by ~50% Fragilariopsis kerguelensis, with a diagnostic contribution of Thalassiosira lentiginosa and Thalassiosira oliverana, species typical of the open Southern Ocean, suggesting southward inflow onto the shelf. A lesser contribution of Fragilariopsis curta indicates the influence of sea ice associated productivity within the polynya. Strong easterly winds and the blocking of sea ice transport into the region by the Dalton Iceberg Tongue to the east appear to be important factors in polynya development and maintenance; sea ice melt within the polynya likely contributes a diatom seed population. Chaetoceros is notably absent, likely due to the polynya opening later in the season (January) and the absence of a typical spring bloom. Unusual Thalassiothrix antarctica layers, up to 15 centimeters thick and comprised of tightly matted valves with a newspaper-like texture, are evident down core. This shade-adapted species can live at depth, maximizing access to nutrients, and is thought to be an under-recognized contributor to oceanic primary productivity due to the patchy subsurface nature of blooms. Thalassiothrix, and other species with a similar thread-like morphology, are often associated with oceanic frontal zones and may be responsible for episodic but significant carbon and silica flux to the sea floor. Temporal variability in the occurrence of Thalassiothrix layers in this Holocene sediment sequence may reflect past changes in the relative proximity and/or strength of Polar and Slope Fronts and/or changes in onshore current flow and strength, transporting large, cohesive diatom mats onto the shelf. Future down core diatom assemblage studies will improve understanding of regional ocean-cryosphere interactions in an environmentally sensitive region.