The energy balance of the Earth is regulated in part by ice clouds, which both reflect shortwave solar radiation and absorb infrared radiation from the Earth. These clouds appear frequently worldwide, with up to 70% coverage in tropical regions. The microphysics of ice clouds determines their radiative properties, and is important for accurately predicting the role of ice clouds in Earth’s energy balance. However, describing the microphysics of ice clouds remains a challenging problem, especially with regard to the shape of ice particles and the degree of ice particle surface roughening. In-situ studies have found evidence for ice surface roughness and have found many complex ice geometries; however, these studies are limited spatially and temporally. An approach which allows large-scale analysis is to retrieve these properties via theoretical modeling using satellite observations of polarized reflectance from ice clouds, since polarized reflectance is sensitive to the shape and roughness of ice particles. The theoretical model requires the scattering properties of simulated ice particles. These properties are obtained for 10 different ice shapes and 17 different levels of surface roughness. Simulations are performed for 3 different effective ice particle diameters: 30, 60 and 90 μm. Overall, the retrieved shape is dominated by the compact aggregate of columns. Although the exact composition of shapes varies from month to month, the compact aggregate of columns remains the most commonly retrieved shape. The retrieved roughness varies from moderately rough at σ = 0.1 to severely rough at σ = 0.5. Retrieved roughness varies more than shape, and smooth surfaced ice is most prominent in January. Tropical regions tend to have ice particles that are more roughened, while the midlatitudes and polar regions tend to have more smooth ice. In almost all cases, roughened ice represents > 60% of the total retrievals. The asymmetry parameter inferred from the retrieval of ice particle shape and roughness has a mean value near 0.77, with only small differences based on assumed ice effective diameter. The median value of the asymmetry parameter has a nearly constant value of approximately 0.75.

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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.

The importance of the cryosphere, and of sea ice in particular, for contaminant transport and redistribution in the Arctic was pointed out in the literature. However, studies on contaminants in sea ice are scarce, and entirely neglect the sea ice geophysical and thermodynamic characteristics as well as interactions between various cryospheric compartments. This thesis addresses those gaps. Ice formation was shown to have a significant concentrating impact on the levels of HCHs in the water just beneath the ice. Both geophysical and thermodynamic conditions in sea ice were shown to be crucial in understanding pathways of accumulation or rejection of HCHs. Although HCH burden in the majority of the ice column remains locked throughout most of the season until the early spring, upward migration of brine from the ice to the snow in the winter has an effect on levels of HCHs in the snow by up to 50 %. In the spring, when snow melt water percolates into the ice delivering HCHs to the upper ocean via desalination by flushing, levels of HCHs in the ice can increase by up to 2 %-18 % and 4 %-32 % for α- and γ-HCH, respectively. Brine contained within sea ice currently exhibits the highest HCH concentrations in any abiotic Arctic environment, exceeding under-ice water concentrations by a factor of 3 in the spring. This circumstance suggests that the brine ecosystem has been, and continues to be, the most exposed to HCHs. α-HCH levels were shown to decrease rapidly in the last two decades in the Polar Mixed Layer (PML) and the Pacific Mode Layer (PL) of the Beaufort Sea due to degradation. If the rate of degradation does not change in the near future, the majority of α-HCH could be eliminated from the Beaufort Sea by 2020, with concentrations in 2040 dropping to < 0.006 ng/L and < 0.004 ng/L in the PML and the PL, respectively. Elimination of α-HCH from sea water takes significantly longer than from the atmosphere, with a lag of approximately two decades.

Manitoba Hydro's diversion of the Churchill River at Southern Indian Lake, part of a multi-million dollar hydro-electric development in northern Manitoba, will have extensive economic, social and environmental implications. The impact that the project may have on slush-ice formation in the estuary at the Port of Churchill is one such implication. Previous studies have suggested that reduced flows on the lower Churchill River may alleviate the problem of slush-ice formation which physically terminates the navigation season at Churchill. A reduction in the formation of slush ice would make feasible an average tow week extension of the navigation season. The primary objective of this study was to assess the effect of the Churchill River diversion on the length of the navigation season at the Port of Churchill. A secondary objective was to determine the relationship between the physical variables (slush ice and sedimentation) and the economic variable (insurance coverage) that influence the length of the navigation season. A field trip to Churchill was made in late July, 1973 to collect data. Interviews with hydrologists, ice observers, and National Harbours Board personnel were conducted at this time. In the data analysis, October Churchill River discharges and meteorological data on climatic factors were correlated with dates of Churchill harbour closure due to slush ice for the period 1928-1972......

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.