C11C-0771
Whillans Ice Stream from UpB to WGZ: Siliceous Microfossils, Palynomorphs, and Biomarker Evidence of Sub-glacial Processes and Ice Stream History

Monday, 14 December 2015
Poster Hall (Moscone South)
Jason James Coenen1, Reed P Scherer1, Sophie Warny2, Isla S. Castañeda3, Ross D Powell4, Slawek M Tulaczyk5, Rebecca Puttkammer1, Timothy O Hodson1, Jeremy Hu-Chin Wei6 and the WISSARD science team, (1)Northern Illinois University, DeKalb, IL, United States, (2)LSU, Baton Rouge, LA, United States, (3)University of Massachusetts Amherst, Amherst, MA, United States, (4)Northern Illinois Univ., De Kalb, IL, United States, (5)University of California Santa Cruz, Earth and Planetary Sciences, Santa Cruz, CA, United States, (6)Stanford University, Stanford, CA, United States
Abstract:
We report micropaleontological results from sediment cores from Subglacial Lake Whillans (SLW) and the Whillans Grounding Zone (WGZ), in West Antarctica, collected as part of the WISSARD project. Diatoms and other microfossils provide biostratigraphic and paleoenvironmental constraints, inferences regarding ice stream erosion, particulate provenance and glacial mixing.

Most subglacial samples contain a mixture of eroded diatoms which reflect initial deposition throughout the Cenozoic. Pleistocene diatoms reflect erosion of marine sediments deposited in the West Antarctic during ice sheet retreat events. Miocene diatoms reflect extensive Miocene deposition before entering a dominantly glacial phase. Additionally, Paleogene fossils, both marine and non-marine occur widely, reflecting deeper erosion and provide insights into basin history.

SLW contains Upper Miocene fossils with a mix of younger and older marine taxa and Paleogene pollen and spores. These ages and taxa are consistent with samples from 200 km upstream at the Whillans Ice Stream (UpB), suggesting a connection between the sites with little evidence of new erosion of material between these sites. Diatom fragment abundance is on average lower than UpB suggesting sediments have experienced additional cumulative shearing and transport. Biomarker data is used to understand changes in inputs from terrestrial and marine components. UpB has a stronger terrestrial signal, compared with SLW further illustrating mixing and transport of sediments.

WGZ cores exhibit stratigraphic variation in microfossil abundance as well as a transition in age dominance of taxa. The upper 25cm of the sediment core is characterized by an assemblage of Upper Miocene dominating taxa which largely represent rain-out from melting debris-laden ice, but also includes consistent occurrences of Late Pleistocene diatoms. A radiolarian encasing a modern pelagic diatom assemblage was noted at 26cm. An interval, from 45 cm down core contains significantly more abundant diatoms than the upper layers, and below that is a Paleogene-dominated assemblage. The stratigraphic variability at the grounding zone indicates changes in sediment provenance, indicating a variable glaciological regime including a dynamic grounding line and potential input from the Mercer Ice Stream.

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