The declining summer Arctic sea ice is impacting cyclone-forcing of dynamic and thermodynamic processes in Arctic sea at different spatial and temporal scales throughout the annual cycle. A catalogue of daily synoptic weather types is generated for the southern Beaufort Sea, covering the period 1979 to 2011 using NCEP/NCAR reanalysis mean sea level pressure data, principle components and k-means cluster analyses. Synoptic type statistics are used to assess changes in atmospheric circulation characteristics, sea ice vorticity, and lead formation. Significant (p < 0.05) seasonal synoptic type frequency anomalies are revealed between 1979 – 1998 and 1999 – 2011, and indicate a stronger Beaufort high, and increased easterly wind forcing in autumn and winter. High rates of young ice production in November and December 2007 were linked to strong easterly wind forcing. A case study of the atmospheric boundary layer during a lead formation event (03 – 18 February 2008) revealed sensible heat fluxes between 0 – 80.14 W • m2 (13 February 2008). First-ever observations of a physical forcing mechanism between Arctic cyclones, the Arctic Ocean, and Arctic sea ice within the southern Beaufort Sea were observed on 06 September 2009. Large swells intruded into the multi-year pack ice, causing instantaneous widespread fracturing, and reduced the large (>1 km) parent ice floes to small (100 – 150 m diameter) floes. This process increased the ice floe perimeter exposed to the ocean by a factor of 4.5. Analysis of Radarsat-2 imagery showed that open water fractional area in the multi-year ice cover initially decreased from 3.7% to 2.7%, then increased to ~20% due to wind-forced divergence. 11.54 MJ • m-2 of additional energy was estimated for lateral melting as a result of the fracture event using radiation budgets prior to and following the event. Earlier occurrences of flexural fracture could hypothetically provide up to three times more additional energy for lateral melt. Furthermore, this process may increase the likelihood of storm-driven upwelling of ocean heat, thereby enhancing bottom melt in the ice cover. This process is therefore presented as a potentially powerful positive feedback process that may accelerate the loss of Arctic sea ice.

Sea ice drift and associated forcing mechanisms within the Beaufort Sea are examined within the context of a mechanically weakening Arctic ice pack. Extensive in situ observations of ice drift, ice mass balance and surface winds are supplemented by remotely sensed and modeled data to analyse the forcing of sea ice motion. First we analyse the anomalous export of 13.4 x 103 km2 of sea ice through the Bering Strait during winter 2011-2012. The event highlights a tendency towards increased ice transport through the Bering Strait since 2008 as a result of climate induced weakening of the arctic ice pack. Secondly, as part of the Beaufort Regional Environmental Assessment we analyse the seasonal evolution of ice drift in the Beaufort Sea during Spring as the ice pack transitions from mechanically strong conditions in late winter to weak summer conditions that foster free drift and thus increased ice drift speeds.

The declining summer Arctic sea ice is impacting cyclone-forcing of dynamic and thermodynamic processes in Arctic sea at different spatial and temporal scales throughout the annual cycle. A catalogue of daily synoptic weather types is generated for the southern Beaufort Sea, covering the period 1979 to 2011 using NCEP/NCAR reanalysis mean sea level pressure data, principle components and k-means cluster analyses. Synoptic type statistics are used to assess changes in atmospheric circulation characteristics, sea ice vorticity, and lead formation. Significant (p < 0.05) seasonal synoptic type frequency anomalies are revealed between 1979 – 1998 and 1999 – 2011, and indicate a stronger Beaufort high, and increased easterly wind forcing in autumn and winter. High rates of young ice production in November and December 2007 were linked to strong easterly wind forcing. A case study of the atmospheric boundary layer during a lead formation event (03 – 18 February 2008) revealed sensible heat fluxes between 0 – 80.14 W • m2 (13 February 2008). First-ever observations of a physical forcing mechanism between Arctic cyclones, the Arctic Ocean, and Arctic sea ice within the southern Beaufort Sea were observed on 06 September 2009. Large swells intruded into the multi-year pack ice, causing instantaneous widespread fracturing, and reduced the large (>1 km) parent ice floes to small (100 – 150 m diameter) floes. This process increased the ice floe perimeter exposed to the ocean by a factor of 4.5. Analysis of Radarsat-2 imagery showed that open water fractional area in the multi-year ice cover initially decreased from 3.7% to 2.7%, then increased to ~20% due to wind-forced divergence. 11.54 MJ • m-2 of additional energy was estimated for lateral melting as a result of the fracture event using radiation budgets prior to and following the event. Earlier occurrences of flexural fracture could hypothetically provide up to three times more additional energy for lateral melt. Furthermore, this process may increase the likelihood of storm-driven upwelling of ocean heat, thereby enhancing bottom melt in the ice cover. This process is therefore presented as a potentially powerful positive feedback process that may accelerate the loss of Arctic sea ice.

During the summers of 2007 and 2008, we determined net, new and regenerated primary production and phytoplankton biomass in Arctic and Sub-Arctic marine waters around North America. Carbon and nitrogen uptake rates were measured using the 15N and 13C tracer technique in 24-hr on-deck incubations, and phytoplankton biomass was determined by in vitro fluorometry. Average net primary production was highest in the north Bering and south Chukchi Seas (998 mg C m-2 d-1) and defined as primarily new production (f-ratio of 0.57), potentially indicating high particulate export from surface waters. Phytoplankton biomass was also high (39 mg chl a m-2) in this region and comprised mostly (61%) of cells >5 μm, supporting the conclusion of a high export system. Average net primary production was lowest in the Canada Basin (50 mg C m-2 d-1) with an f-ratio of 0.17 and characterized by low phytoplankton biomass (8 mg chl a m-2), comprised of mostly (19%) cells <5 μm. In much of the study area, the presence of ice cover appeared influential in affecting Arctic primary production patterns. Water column stratification in the wake of retreating sea ice produced conditions favorable to initiating seasonal blooms, which most likely terminated due to nutrient exhaustion. Areas characterized by persistent sea ice cover were particularly unproductive, most likely due to light limitation, and nutrient exhaustion due to reduced wind-mixing. These results indicate that primary production in Arctic and Sub-Arctic waters is highly variable, and provide an important baseline for future studies of phytoplankton dynamics in this rapidly changing region. / Graduate

No description available.

Sea ice is essential to the survival of many human settlements in Arctic Canada in that it provides a means for basic sustenance, travel and largely defines the seasons. Northern communities base their livelihoods on these traditionally well established cryogenic cycles. In this work, seasonal sea ice is analyzed off the coast of Cape Dorset, Nunavut. Significant trends are established for earlier sea ice break-up and later freeze up dates for the period 1982 to 2007. The timing of sea ice formation and retreat is significantly changing in the Cape Dorset region, with the ice free season increasing ~40 days since 1982. Relationships are established statistically between the shifting ice free season and temperature, weather types (air masses), precipitation, and wind. The results of this study illustrate the changing nature of sea ice formation and retreat in Cape Dorset and the importance of completing localized studies in the Arctic.

Sea ice is essential to the survival of many human settlements in Arctic Canada in that it provides a means for basic sustenance, travel and largely defines the seasons. Northern communities base their livelihoods on these traditionally well established cryogenic cycles. In this work, seasonal sea ice is analyzed off the coast of Cape Dorset, Nunavut. Significant trends are established for earlier sea ice break-up and later freeze up dates for the period 1982 to 2007. The timing of sea ice formation and retreat is significantly changing in the Cape Dorset region, with the ice free season increasing ~40 days since 1982. Relationships are established statistically between the shifting ice free season and temperature, weather types (air masses), precipitation, and wind. The results of this study illustrate the changing nature of sea ice formation and retreat in Cape Dorset and the importance of completing localized studies in the Arctic.

Thesis (doctoral)--Helsinki University of Technology, 2004. / Includes bibliographical references (p. 136-142). Also available on the World Wide Web.

Thesis (M.S.)--University of Wisconsin--Madison, 1984. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 71-73).

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (p. 91-109).