Scherer, Reed P.
M.S. (Master of Science)
Department of Earth, Atmosphere and Environment
Anthropogenically induced climate change in the polar regions has rapidly become an emergent global issue, especially for low-lying coastal communities, which are most affected by sea-level rise. The future of the West Antarctic Ice Sheet (WAIS) is of significant concern due to its history of instability and retreat, especially in light of the observed ongoing changes. Establishing rates of retreat is critical to forecasting future behavior of the WAIS, and previous studies have been unable to establish rates of ice sheet collapse in part because Antarctic continental shelf records are impacted by erosional hiatuses. In 2019, International Ocean Discovery Program Expedition 379 obtained records from the Amundsen Sea continental rise, to document WAIS history in an area currently experiencing the largest ice loss in Antarctica. The recovered sections of Site U1532 contain no apparent unconformities and include intervals characterized by diatomite and diatomaceous ooze, coincident with deposition of pulses of ice rafted debris (IRD). Low vacuum scanning electron microscope (SEM) imagery was used to document microstratigraphic records of environmental change through a Mid-Pliocene interval of diatomite, tentatively interpreted as representing deposition during the MIS Gi-17 interglacial near the end of the Gilbert subchron (~3.9 Ma). SEM imagery was also used to capture several instances of soft-sediment micro-deformation associated with IRD falling into concurrently accumulating diatomite. Intervals with little or no evidence of IRD are bioturbated and have lower diatom abundance, suggesting lower accumulation rates. Occurrences of layers containing high abundance of IRD along with nearly monospecific assemblages of the pelagic diatom Thalassiothrix antarctica and plankton fecal pellets with concentrated clusters of barite grains are interpreted as representing high primary productivity resulting from direct nutrient input from iceberg melt. This observation confirms inference and observations of modern phytoplankton response to iceberg melt, and may offers insight into past WAIS collapse. High absolute diatom abundance (ADA) values correlate with an IRD cluster near the top of the interval. This IRD-diatomite cluster differs from most of the studied interval in that it that have a gradual increase in IRD to the peaks at the top of the interglacial and then an abrupt drop. ADA values were compared to shipboard magnetic susceptibility data, and based on shipboard diatom biostratigraphy and magnetostratigraphy, the interval under study likely represents an interglacial sequence (MIS Gi-17) during the end of the Gilbert Subchron (~3.9 Ma). The data provides evidence to support the hypothesis that continually sourced nutrient seeding of the Southern Ocean by ice sheet retreat seeded diatom productivity in the Amundsen Sea. Apparent pulses of IRD likely coincide with marine ice sheet retreat and collapse with melting icebergs primarily from the Thwaites and Pine Island Glaciers. The subglacially weathered material likely resulted in increased transport of bioavailable iron and other micronutrients that triggered intense diatom productivity. These results may contribute to interpreting past WAIS history by providing another proxy from Southern Ocean sediments and contribute to ice sheet models of potential future collapse.
Furlong, Heather Leanne, "Microfabric Analysis of Mid-Pliocene Amundsen Sea interglacial Sediments Demonstrates A Link Between Iceberg Melt and Diatom Productivity (iodp Exp. 379)" (2022). Graduate Research Theses & Dissertations. 7051.
Northern Illinois University
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