Landfast Ice Breakup Timing and Processes Along the Alaska Beaufort Sea Coast

Thesis (Master's)--University of Washington, 2017-06The record minimum in the extent of drifting sea ice on the Arctic Ocean was set in 2012, and the ten lowest retreats of summer sea ice were observed in the last decade. In this thesis we investigate whether there have been corresponding changes in the breakup of landfast sea ice using records from GPS buoys deployed on landfast sea ice in the Beaufort Sea region of Alaska between 2007 and 2015 to analyze the timing and cause of the breakup of landfast ice. Between two and five buoys were deployed each winter on stable landfast sea ice in two regions, Camden Bay and Harrison Bay, along the Alaskan Beaufort Coast. In addition to determining the start of landfast ice breakup, we used local surface winds, air temperature, water level, and air pressure data to examine the forces affecting breakup timing. Past studies have shown breakup is caused either by mechanical forcing from wind, currents or tides, or by thermal forcing due to above-freezing temperatures that cause ice to melt and drift away from the shore. We found the average regional timing of breakup to start on June 6 for the 2007 through 2015 breakup seasons. This date follows the trend of an earlier breakup of landfast in this region, as it is five days earlier than observations from the 1990s to early 2000s and 24 days earlier than those from the 1970s. Although the earlier breakup trend is not statistically significant it does show continued changing conditions in the Beaufort Sea landfast ice regime. Exploring the processes affecting landfast ice breakup in our two sub-regions reveals landfast ice in Camden Bay beginning to break free on average on May 27 and in Harrison Bay on June 29. The large difference in breakup timing between the eastern and western Beaufort Sea coast can be attributed to different processes affecting the breakup. In Harrison Bay, break up was classified as thermally driven in all years. However, in Camden Bay break up was classified as mechanically forced in five out of the nine years of this study. These results differ from previous studies of the region, which report no link between atmospheric forcing processes and the timing of landfast ice breakup. This change is most likely related to the overall transition of Arctic sea ice to a younger, thinner ice pack, which now provides a weaker buttress for the landfast sea ice