No description available.

An understanding of the adaptability of belugas (Delphinapterus leucas) to changing ice-conditions is required to interpret and predict possible changes in habitat selection in response to projected loss of sea ice throughout the circumpolar Arctic. Beluga spring distribution in the eastern Beaufort Sea was described by analyzing observations from aerial surveys conducted from 1975 to 1979. Repeated surveys along the Franklin Bay fast-ice edge in June 2008 were used to study the distribution and behaviour of belugas and bowheads. Despite inter-annual variability in ice extent, belugas consistently selected areas with water depths of 200-500 m, heavy ice concentrations (8/10 to 10/10) and seafloor slope ≥0.5 degrees in spring 1975 to 1979. While predator avoidance may partially explain the observed distribution, foraging success likely has more influence on beluga habitat selection in the spring. In ice-covered offshore regions, belugas may be engaged in under-ice and deep water foraging on Arctic cod (Boreogadus saida). In lighter ice years, belugas may expand their distribution and shift shoreward to take advantage of high prey densities along fast-ice edges. Both belugas and bowheads appeared to be feeding along the Franklin Bay ice edge in June 2008. More research is required to examine and compare possible changes in distribution since the late 1970s and to investigate the factors driving the patterns described.

The veracity of a Radiometric Microwave Profiling Radiometer (MWRP) while mounted onboard a ship in the Arctic marine environment was assessed. The MWRP was validated against radiosonde data by calculating the RMS and bias for simultaneous measurements taken for temperature and absolute humidity profiles. The vertical resolution of the MWRP was calculated using the inter-level covariance method. Based on the comparisons, the MWRP provided reliable measurements of both temperature and absolute humidity while mounted on the CCGS Amundsen. Satellites CloudSat and Calipso were assessed over the Arctic marine cryosphere. Temperature and absolute humidity from the ECMWF-aux data product was compared with profiles from the ship based MWRP. The cloud base heights measured by the ceilometer and MWRP were compared to CloudSat and Calipso's GeoProf-lidar. Due to a large number of possible false detections, the constraints used by the GeoProf-lidar data product for cloud detection may need to be further refined.

This dissertation presents new research into the study of simulation and measurement techniques for microwave remote sensing of sea ice. We have embarked on a major study of the microwave propagation and scattering properties of sea ice in an attempt to link the physics of the sea ice medium to experimentally obtained concomitant scatterometer measurements. During our fieldwork, we studied the polarimetric backscattering response of sea ice, focusing on newly-formed sea ice under a large assortment of surface coverage. Polarimetric backscattering results and physical data for 40 stations during the fall freeze-up of 2003, 2006, and 2007 are presented. Analysis of the co-polarization correlation coefficient showed its sensitivity to sea ice thickness and surface coverage and resulted in a statistically significant separation of ice thickness into two regimes: ice less than 6 cm thick and ice greater than 8 cm thick. A case study quantified the backscatter of snow-infiltrated frost fl owers on new sea ice, showing that the presence of the frost flowers enhanced the backscatter by more than 6 dB. In our simulation work, an efficient method for simulating scattering from objects in multi-layered media was incorporated into a scattered-field formulation of the FVTD method. A total-field 1D-FDTD solution to the plane-wave propagation through multi-layered meda was used as a source. The method was validated for a TE-polarized incident-field through comparisons with other numerical techniques involving examples of scattering from canonically-shaped objects. Methods for homogenization of inhomogeneous media were developed and validated using well-known dielectric mixture models. A Monte Carlo Method for simulating scattering from statistically rough surfaces was developed and was validated through favorable comparison with the SPM method for rough surface scattering. Finally, we presented a new Monte Carlo Method for simulating sea ice remote sensing that utilized the framework of the FVTD method for scattering simulations. The modeling process was driven by actual physical measurements of sea ice, wherein dielectric and physics-based modeling techniques were employed. The method was demonstrated through a series of case studies where the scattering from newly-formed sea ice was simulated using a TE-polarized incident- eld. Good agreement between experimental scatterometer measurements and simulated results was obtained for co-polarized returns, whereas cross-polarized results indicated that more depolarizing features must be taken into account.

Melt ponds greatly increase the transmission of solar radiation through sea ice relative to snow covered or bare ice. This rise in transmittance has the potential to enhance water column heating and primary production. I examine how spatially variable sea ice surfaces control the under-ice salinity, temperature and photosynthetically active radiation (PAR) and provide estimates of solar heating and primary production during melt. Conductivity, temperature and PAR profiles were measured in the Canadian Arctic under snow covered ice, leads, bare ice and melt ponds. The under-ice light field to a depth of 10 to 13 m was highly variable, controlled by increased transmission under melt ponds and shading by bare ice. Below, the light field became relatively homogeneous showing the depth the surface heterogeneity had an effect on transmitted PAR. Furthermore, one water column profile is not representative of the PAR, salinity or temperature under a spatially heterogeneous surface.

During the fourth International Polar Year, an interdisciplinary study was conducted to examine the couplings between sea ice, ocean, atmosphere, and ecosystem in the southeastern Beaufort Sea. This thesis examines components of the system that control the air–sea exchange of carbon dioxide. Using eddy covariance measurements, we found enhanced CO2 exchange associated with new ice formation in winter flaw leads. This exchange was typically directed towards the surface, although we also measured one instance of outgassing. Sea surface dissolved CO2 measurements (pCO2sw) in Amundsen Gulf showed significant undersaturation with respect to the atmosphere at freeze–up, followed by a slow increase over the winter until spring phytoplankton blooms caused strong undersaturation at break–up. Over the summer, pCO2sw increased until becoming slightly supersaturated due to surface warming. Along the southern margins of Amundsen Gulf and on the Mackenzie Shelf we found pCO2sw supersaturations in the fall due to wind–driven coastal upwelling. In the spring, this upwelling occurred along the landfast ice edges of Amundsen Gulf. By combining observations of enhanced winter gas exchange with observations of pCO2sw in Amundsen Gulf, we derived an annual budget of air–sea CO2 exchange for the region. This exercise showed that uptake through the winter season was as important as the open water season, making the overall annual uptake of CO2 about double what had previously been calculated. Prior to this work, the prevailing paradigm of air–sea CO2 cycling in Arctic polynya regions posited that strong CO2 absorption occurs in the open water seasons, and that a potential outgassing during the winter is inhibited by the sea ice cover. As a new paradigm, we propose that the spatial and temporal variability of many processes – including phytoplankton blooms, sea surface temperature and salinity changes, upwelling, river input, continental shelf processes, and the potential for high rates of winter gas exchange – need to be considered in order to understand the carbon source/sink status of a given Arctic polynya region. A paradigm that considers such varied processes is useful in understanding how climate change in the Arctic can impact air–sea CO2 exchange.

The ocean is the largest sink of anthropogenic carbon from the atmosphere and therefore the magnitude of ocean carbon uptake largely determines the airborne fraction of emissions and the ultimate severity of surface climate change. However, climate-feedbacks on ocean carbon uptake over the historical period and in the future are uncertain. In particular, much uncertainty in the ocean carbon response hinges on the influence of wind-driven changes in the Southern Ocean, which is the most significant region of anthropogenic carbon uptake. Here I show that the Southern Hemisphere westerly winds simulated by the Coupled Model Intercomparison Project Phase 3 (CMIP3) and CMIP5 climate models have significant biases in their pre-industrial and satellite era-climatologies, relative to observationally based estimates. I also show that the models project the westerlies to intensify and shift poleward under anthropogenic forcing over the 20th and 21st centuries, but that they significantly underestimate the trends over the satellite era. I then use a novel experimental design, wherein I isolate the influence of the models pre-industrial wind bias on simulations of ocean carbon uptake and climate. I do this by using the UVic Earth System Climate Model (ESCM) with an ensemble of members, each forced by the winds from an individual CMIP model. I show here that the climate model pre-industrial wind bias can significantly increase ocean carbon uptake in transient climate change simulations, reducing the airborne fraction and projected climate change. By contrast, the simulated wind-changes over the 20th and 21st centuries reduce ocean carbon uptake, largely through an increase in outgassing from the Southern Ocean. However, I show that this transient- wind effect is i) smaller than the pre-industrial bias effect and ii) does not occur when using a variable formulation for the Gent-McWilliams coefficient of eddy diffusivity in the coarse resolution model, under simulated or observed wind-changes. I then go on to demonstrate that the simulated transient wind-changes significantly reduce the Antarctic sea-ice area simulated by the UVic ESCM. I also test the influence of fresh water input to the Southern Ocean from dynamic Antarctic Ice Sheet mass loss, which is a forcing absent from the CMIP5 models. The magnitude of the fresh water effect is small and has little influence on the sea-ice area trends simulated by the CMIP5 models over the historical era. These results have significant implications for previous model-based studies of the ocean carbon cycle, as well as for the quantification of the wind-induced uncertainty in future climate projections by current Earth System Models. / Graduate / 0725 / 0425 / 0415

An understanding of the adaptability of belugas (Delphinapterus leucas) to changing ice-conditions is required to interpret and predict possible changes in habitat selection in response to projected loss of sea ice throughout the circumpolar Arctic. Beluga spring distribution in the eastern Beaufort Sea was described by analyzing observations from aerial surveys conducted from 1975 to 1979. Repeated surveys along the Franklin Bay fast-ice edge in June 2008 were used to study the distribution and behaviour of belugas and bowheads. Despite inter-annual variability in ice extent, belugas consistently selected areas with water depths of 200-500 m, heavy ice concentrations (8/10 to 10/10) and seafloor slope ≥0.5 degrees in spring 1975 to 1979. While predator avoidance may partially explain the observed distribution, foraging success likely has more influence on beluga habitat selection in the spring. In ice-covered offshore regions, belugas may be engaged in under-ice and deep water foraging on Arctic cod (Boreogadus saida). In lighter ice years, belugas may expand their distribution and shift shoreward to take advantage of high prey densities along fast-ice edges. Both belugas and bowheads appeared to be feeding along the Franklin Bay ice edge in June 2008. More research is required to examine and compare possible changes in distribution since the late 1970s and to investigate the factors driving the patterns described.

The veracity of a Radiometric Microwave Profiling Radiometer (MWRP) while mounted onboard a ship in the Arctic marine environment was assessed. The MWRP was validated against radiosonde data by calculating the RMS and bias for simultaneous measurements taken for temperature and absolute humidity profiles. The vertical resolution of the MWRP was calculated using the inter-level covariance method. Based on the comparisons, the MWRP provided reliable measurements of both temperature and absolute humidity while mounted on the CCGS Amundsen. Satellites CloudSat and Calipso were assessed over the Arctic marine cryosphere. Temperature and absolute humidity from the ECMWF-aux data product was compared with profiles from the ship based MWRP. The cloud base heights measured by the ceilometer and MWRP were compared to CloudSat and Calipso's GeoProf-lidar. Due to a large number of possible false detections, the constraints used by the GeoProf-lidar data product for cloud detection may need to be further refined.

This dissertation presents new research into the study of simulation and measurement techniques for microwave remote sensing of sea ice. We have embarked on a major study of the microwave propagation and scattering properties of sea ice in an attempt to link the physics of the sea ice medium to experimentally obtained concomitant scatterometer measurements. During our fieldwork, we studied the polarimetric backscattering response of sea ice, focusing on newly-formed sea ice under a large assortment of surface coverage. Polarimetric backscattering results and physical data for 40 stations during the fall freeze-up of 2003, 2006, and 2007 are presented. Analysis of the co-polarization correlation coefficient showed its sensitivity to sea ice thickness and surface coverage and resulted in a statistically significant separation of ice thickness into two regimes: ice less than 6 cm thick and ice greater than 8 cm thick. A case study quantified the backscatter of snow-infiltrated frost fl owers on new sea ice, showing that the presence of the frost flowers enhanced the backscatter by more than 6 dB. In our simulation work, an efficient method for simulating scattering from objects in multi-layered media was incorporated into a scattered-field formulation of the FVTD method. A total-field 1D-FDTD solution to the plane-wave propagation through multi-layered meda was used as a source. The method was validated for a TE-polarized incident-field through comparisons with other numerical techniques involving examples of scattering from canonically-shaped objects. Methods for homogenization of inhomogeneous media were developed and validated using well-known dielectric mixture models. A Monte Carlo Method for simulating scattering from statistically rough surfaces was developed and was validated through favorable comparison with the SPM method for rough surface scattering. Finally, we presented a new Monte Carlo Method for simulating sea ice remote sensing that utilized the framework of the FVTD method for scattering simulations. The modeling process was driven by actual physical measurements of sea ice, wherein dielectric and physics-based modeling techniques were employed. The method was demonstrated through a series of case studies where the scattering from newly-formed sea ice was simulated using a TE-polarized incident- eld. Good agreement between experimental scatterometer measurements and simulated results was obtained for co-polarized returns, whereas cross-polarized results indicated that more depolarizing features must be taken into account.