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.

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

The halophyte Mesembryanthemum crystallinum L. accumulates high concentrations of NaCl (up to 1 M) in its leaf cells as a response to soil salinity. While there is evidence that vacuolar sodium transport is mediated by a tonoplast Na⁺/H⁺ antiporter (Barkla ^{et al.}, 1995), little is known about the transport of Cl^- transport into the vacuole. So far, it has been uncertain whether secondary active transport (e.g. H⁺/C1^- antiporter) is involved or whether a passive mechanism (Cl^- channel) is sufficient to mediate Cl^- accumulation in the vacuole of M.crystallinum. This thesis describes the use of tonoplast vesicles from leaf mesophyll cells of M. crystallinum to study vacuolar Cl^- transport. Cl^- uptake into the vesicles was measured using the Cl^--sensitive fluorescent dye lucigenin (N/N'-dimethyl-9,9'-bisacridinium dinitrate). This work was complemented by a patch-clamp study of ionic currents of leaf-mesophyll vacuoles from M.crystallinum. Cl^- transport into tonoplast vesicles showed saturation-type kinetics with an apparent Km between 10 and 36 mM and a maximum initial change of the intravesicular Cl^- concentration of 4.8 mM min^-, corresponding to an estimated Cl^- flux of 31 nmol m² s^-¹. Vacuolar chloride transport was not affected by sulphate, malate, or nitrate, indicating a high specificity of this transport process for chloride over other anions. By imposing insidepositive membrane potentials using a K⁺/valinomycin clamp revealed a sigmoidal voltagedependent relationship with the steepest increase in vacuolar Cl^- uptake around +30 mV. Only under severe salt treatment with 500 mM NaCl for 3 weeks did 9-week-old M. crystallinum plants show a significant increase (63%) of vacuolar C^- uptake, along with an increased V-type H⁺-ATPase hydrolytic activity (up to 65%). The apparent K_m of vacuolar Cl^- uptake was also increased from 27 mM to 44 mM under these conditions. An inside-acid pH gradient, generated by a K⁺/nigericin clamp, reduced the initial rate of chloride transport into tonoplast vesicles of M.crystallinum. External Cl^-, in contrast to external Na⁺ , did not dissipate an inside-acidic ΔpH generated by various techniques. This is strong evidence against a proton-driven antiport mechanism. The patch-clamp study of ionic currents of whole vacuoles and excised vacuolar membrane patches from M.crystallinum. leaf-mesophyll cells revealed a number of cation channels. At cytosolic free Ca ²⁺ concentrations of 1μM and above, ubiquitous slow-vacuolar type cation currents could be observed. In excised patches, eleven different single channel types, with conductances ranging from 2 up to 200 pS, could be described. However, no clear Cl^-conductance could be identified. The lack of observed vacuolar Cl^- channel activities is discussed in the light of possible lack of Cl^--channel activation due to the loss of a cytosolic factor. The results obtained from the biochemical work on tonoplast vesicles support the hypothesis that a passive transport mechanism (i.e. channel) is sufficient to mediate vacuolar chloride transport in M.crystallinum. The observed upregulation of vacuolar Cl^- transport under severe salt stress shows that it plays an important role in the salt adaptation of this halophytic plant.

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.

Lakes comprise a large portion of the surface cover in northern North America, forming an important part of the cryosphere. Further alterations to the present day ice regime could result in major ecosystem changes, such as species shifts and the disappearance of perennial ice cover. Lake ice has been shown to both respond to, and play a role in the local/regional climate. The timing of lake ice phenological events (e.g. break-up/freeze-up) is a useful indicator of climate variability and change. Trends in ice phenology have typically been associated with variations in air temperatures while trends found in ice thickness tend to be associated more with changes in snow cover. The inclusion of lakes and lake ice in climate modelling is an area of increased attention in recent studies and the ability to accurately represent ice cover on lakes will be an important step in the improvement of global circulation models, regional climate models and numerical weather forecasting. This thesis aimed to further our understanding of lake ice and climate interactions, with an emphasis on ice cover modelling. The Canadian Lake Ice Model (CLIMo) was used throughout for lake ice simulations. To validate and improve the model results, in situ measurements of the ice cover for two seasons in Churchill, MB were obtained using an upward-looking sonar device Shallow Water Ice Profiler (SWIP) installed on the bottom of the lake. The SWIP identified the ice-on/off dates as well as collected ice thickness measurements. In addition, a digital camera was installed on shore to capture images of the ice cover through the seasons and field measurements were obtained of snow depth on the ice, and both the thickness of snow ice (if present) and total ice cover. Altering the amounts of snow cover on the ice surface to represent potential snow redistribution affected simulated freeze-up dates by a maximum of 22 days and break-up dates by a maximum of 12 days, highlighting the importance of accurately representing the snowpack for lake ice modelling. The late season ice thickness tended to be under estimated by the simulations with break-up occurring too early, however, the evolution of the ice cover was simulated to fall between the range of the full snow and no snow scenario, with the thickness being dependent on the amount of snow cover on the ice surface. CLIMo was then used to simulate lake ice phenology across the North American Arctic from 1961–2100 using two climate scenarios produced by the Canadian Regional Climate Model (CRCM). Results from the 1961–1990 time period were validated using 15 locations across the Canadian Arctic, with both in situ ice cover observations from the Canadian Ice Database as well as additional ice cover simulations using nearby weather station data. Projected changes to the ice cover using the 30-year mean data between 1961–1990 and 2041–2070 suggest a shift in break-up and freeze-up dates for most areas ranging from 10–25 days earlier (break-up) and 0–15 days later (freeze-up). The resulting ice cover durations show mainly a 10–25 day reduction for the shallower lakes (3 and 10 m) and 10–30 day reduction for the deeper lakes (30 m). More extreme reductions of up to 60 days (excluding the loss of perennial ice cover) were shown in the coastal regions compared to the interior continental areas. The mean maximum ice thickness was shown to decrease by 10–60 cm with no snow cover and 5–50 cm with snow cover on the ice. Snow ice was also shown to increase through most of the study area with the exception of the Alaskan coastal areas. While the most suitable way to undertake wide scale lake ice modeling is to force the models with climate model output or reanalysis data, a variety of different lake morphometric conditions could exist within a given grid cell leading to different durations of ice cover within the grid cell. Both the daily IMS product (4 km) and the MODIS snow product (500 m) were assessed for their utility at determining lake ice phenology at the sub-grid cell level throughout the province of Quebec. Both products were useful for detecting ice-off, however, the MODIS product was advantageous for detecting ice-on, mainly due to the finer resolution and resulting spatial detail of the lake ice. The sub-grid cell variability was typically less than 2%, although it ranged as high as 10% for some grid cells. An indication of whether or not the simulated ice-on/off dates were within the sub-grid cell variability was determined and on average across the entire province, were found to be within the variability 62% of the time for ice-off and 80% of the time for ice-on. Forcing the model with the future climate scenarios from CRCM predicts ice cover durations throughout the region will decrease by up to 50 days from the current 1981-2010 means to the 2041-2070 means, and decrease from 15 to nearly 100 days shorter between the contemporary and 2071-2100 means. Overall, this work examined the climate-lake-ice interactions under both contemporary and future climate conditions, as well as provided new insight into sub-grid cell variability of lake ice.

The thesis describes the properties of surface wind and air temperature time series recorded at three locations on the pack ice of the Beaufort Sea. Time series consisting of sequential one-half hourly means were constructed for a period of approximately a year. A diurnal fluctuation in air temperature is found for the late summer, early fall and spring seasons only. Wind speed does not show a significant diurnal fluctuation for any season. There is very little seasonal variability in the wind speed while significant variation is present in the air temperature. The integrated wind speed spectrum (i. e. variance) is 80% less than the integrated sum of the wind component spectra indicating that for periods longer than a day, directional fluctuations contribute much more to the variance of the wind record than do speed fluctuations. Although the measurements only approach the microscale region, there seems to be no consistent indication of a microscale peak in the variance preserving representation of the wind speed spectrum. Time series of daily mean horizontal divergence and vertical component of vorticity for both the wind field and ice motion are examined. For a period of 355 days there is significant negative correlation (-0.65) between the wind divergence and wind vorticity series and significant positive correlation (0.65) between the wind vorticity and ice vorticity series. / Graduation date: 1979

Navigating in the arctic has become more common, but it is dicult and dangerousdue to the presence of ice. Any training under safer circumstances is therefore veryvaluable, enter the need for ship simulators. Ship simulators today incorporate manyfeatures, such as cranes, anchors, wires, and state of the art physics. However, theinclusion of ice is very rare due to the complexity of simulating the feedback from theice breaking progress.The purpose of this project is to build a model and numerical methods to simulate icefracture in real-time, which is to be used in ship simulators. The model presented inthis project is implemented with the use of the physics engine AgX Multiphysics madeby Algoryx Simulation ABThe method represents the ice sheet as a non-homogeneous mesh. A collision with thehull of the ship injects deformation energy into the ice. The energy from the inelasticimpact is distributed on the ice sheet according to a quasi-static crack propagationmodel that is dened on a static mesh. The cracks are guided using stress elds thatapproximate the strain in each vertex. The distribution of the strain is done by a simplemodel which allows for breaking ice in non-uniform fragments. This is more realisticthan fracture in predened shapes which is the main contribution of this project. Thefragments become unbreakable rigid body ice oes that interact with the ship's hull bycollision and friction.The implementation of the ice model is tested by using a trimesh model of the TorViking II icebreaker using approximated buoyancy calculations, damping equations,and engine forces.Real-time performance is not achieved yet in the general case, but this is due to thechoice of collision geometry and the oe creation. Unstable force spikes from thecontacts between the ship and the ice is detected, but the overall global ice resistanceshows few abnormalities. Replacing the collision geometry and the rigid body oes isnecessary for the implementation to be able to run in real-time. Further experimentsto compare with real model data is needed to be able to validate the model.