Graduate Thesis Or Dissertation
 

The Occurrence of Coastal Sea Ice Leads and their Impact on the Beaufort Gyre

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/fj2367468

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  • Leads are long fractures wide enough for a ship to travel through the ice pack. Sea ice acts as a barrier between the ocean and the atmosphere, whereas leads allow the transfer of heat and moisture between the two. Leads play a role for marine mammals and are hunting grounds for the First Nations tribes. Winds act as the primary drivers of sea ice motion. In the Beaufort Sea region, a predominance of anticyclones, that forms the Beaufort High in the climatological mean, leads to prevailing clockwise motion of the winds. As a result, the sea ice in the region rotates clockwise on average in the Beaufort Gyre. In this thesis, we discuss large-scale lead patterns in the Beaufort Sea and their effect on the drift of sea ice in the Beaufort Gyre. Leads with widths greater than 250m are visible in Advanced Very High Resolution Radiometry (AVHRR) thermal imagery (channel 4 with wavelengths of 10.3 to 11.3µm). We document repeated patterns of fractures that originate at specific promontories along the coast. These leads often form sequentially, most frequently from west to east, following the movement of high-pressure systems. Most leads in the cloud free satellite imagery form under anticyclonic conditions and the study is biased towards the clear sky conditions associated with high-pressure. We do find examples of leads that form in the coastal region during cyclonic conditions. The patterns are categorized, building on previous work by Eicken et al (2005). ERA-Interim reanalysis data provide an estimate of the mean sea level pressure (MSLP) and 10m-wind field near the time of formation that the leads observed. Lead patterns are associated with the location of anticyclones. However, there is too much overlap between the pressure centers among different lead patterns to accurately predict which individual pattern may form based on pressure alone. Each lead pattern displays a different seasonality from the others. There are some decadal shifts in seasonality of the individual lead patterns as well as trends in the frequency of a few patterns. Despite the well documented thinning of the ice pack and increased rate of deformation of the ice pack in the Beaufort Sea, the number of leads observed in winter does not change. Using daily drift data from the National Snow and Ice Data Center’s Polar Pathfinder Daily 25 km EASE-Grid Sea Ice Motion Vectors, the movement of the sea ice when the leads are active shows enhanced motion of the ice pack, constrained geometrically to the leeward side of the fracture. Flux gates were created to quantify the impact on drift motion resulting from these leads. We find ice speeds ranging from 1.5 to over 4 times the mean ice drift on the leeward side of the leads with less than average speeds on the windward side. This increase in speeds is not fully explained by a linear response to a change in the winds speed. The fractures likely induce a non-linear response in the sea ice drift to the winds. Lastly, as the formation of the leads are directly linked to the movement of anticyclones (with a few cyclonic exceptions), it is hypothesized that these leads provide a mechanism linking variability of the Beaufort High to variability in the Beaufort Gyre.
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  • Existing Confidentiality Agreement
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  • 2018-01-23 to 2018-11-27

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