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    Mapping bottomfast sea ice in Arctic lagoons using Sentinel-1 interferometery

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    Author
    Pratt, Jacob W.
    Chair
    Mahoney, Andy
    Committee
    Iken, Katrin
    Kasper, Jeremy
    Romanovsky, Vladimir
    Keyword
    Sea ice
    Arctic Coast
    Climatic changes
    Lagoons
    Synthetic aperture radar
    Arctic regions
    Ice cores
    Metadata
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    URI
    http://hdl.handle.net/11122/13090
    Abstract
    Sea ice is an important component of Arctic coastal ecosystems. Where the water is shallow enough, it can extend all the way to the seafloor and become bottomfast sea ice (BSI), the lateral extent of which depends upon ice thickness and the regional nearshore slope. Sea ice thickness is a well-known indicator of climate change in the Arctic and in areas with gently sloping seafloors, we expect the extent of BSI to be a sensitive indicator of changes in ice thickness. Contact with the seafloor can help cool and aggregate subsea permafrost and restrict under-ice habitats. It also prevents or reduces motion experienced by floating landfast ice in response to wind, ocean, and ice forcing. Bottomfast ice is in turn more stable than floating ice with implications for human activities on ice. BSI cannot easily be distinguished from floating landfast ice using optical imagery and synthetic aperture radar (SAR) is not typically able to penetrate to the bottom of saline ice. As a result, large-scale mapping of BSI has previously been limited to brackish waters near Arctic deltas, where (SAR) can detect the ice-water interface. However, recent work has demonstrated that SAR interferometry (InSAR) can be used to delineate BSI based on an absence of small-scale surface motion over time. Here, we utilize the Alaska Satellite Facility's Hybrid Pluggable Processing Pipeline (HyP3): A cloud-based infrastructure to process interferograms from the entire Sentinel-1 record over three lagoon systems across the Beaufort Sea coast of Alaska near Utqiagvik, Prudhoe Bay, and Kaktovik. We develop and test a mapping approach that discriminates bottomfast ice based on a near-zero gradient in interferometric phase change, which on floating lagoon ice is primarily caused by surface motion from tides and thermal stress. This enables the comparison of the date of onset, maximum extent, and seasonal evolution of BSI between the lagoons from 2016-2020. We also evaluate the use of electromagnetic sounding in tandem with in-situ drilling to verify BSI extent with greater detail. Based on this work, we argue that mapping BSI could significantly improve our understanding of Arctic lagoons in terms of detailed bathymetry, winter habitats, and saline stress on benthic communities, and the thermal regime of the underlying permafrost.
    Description
    Thesis (M.S.) University of Alaska Fairbanks, 2022
    Table of Contents
    1. Introduction -- 2. Methods and data -- 2.1. Study regions -- 2.2. Detecting BSI using SAR interferometry -- 2.3. Detecting BSI using electromagnetic (EM) sounding -- 2.4. Drill hole observations -- 2.5. Ice and sediment coring -- 2.6. Freezing degree days. 3. Results -- 3.1. Transect data -- 3.1.1. Overview of transects in Elson Lagoon -- 3.1.2. Drill-hole data -- 3.1.3. EM conductivity data along transects -- 3.1.4. InSAR data along transects -- 3.2. Seasonal progression and interannual variability of BSI extent -- 3.2.1. Overview of InSAR-derived BSI extent -- 3.2.2. Elson Lagoon -- 3.2.3. Simpson Lagoon and Stefansson Sound -- 3.2.4. Kaktovik, Jago, and Avery lagoons -- 3.3. Bottom fast ice core observations. 4. Discussion -- 4.1. Validation of InSAR-derived BSI extent -- 4.1.1. Detection of BSI vs floating ice -- 4.1.2. Distinction between bonded and unbonded BSI -- 4.2. Assessment of EM conductivity profiling for detecting BSI -- 4.3. Quality of detection for each observation method -- 4.3.1. Interferometric phase values -- 4.3.2. Coherence values -- 4.3.3. Conductivity values -- 4.4. Spatial and temporal variation -- 4.5. Submarine permafrost impacts -- 4.6. Ecological impacts. Conclusion -- References.
    Date
    2022-08
    Type
    Thesis
    Collections
    Geosciences

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