A single-channel magnetic induction system operating at 10 MHz has been constructed. The system consists of an excitation coil and a sensing coil, between which different objects can be scanned. The eddy currents induced in the object cause perturbations in the sensed magnetic field, which are measured with a phase-sensitive detector with backing off of the signal to improve sensitivity. Scans were obtained for saline solutions with conductivities ranging from 0.001 to 6 Sm-1, encompassing the range for biological tissues. The imaginary part of the perturbation in the sensed magnetic field was found to be proportional to saline conductivity, consistent with theoretical prediction, and had a constant of proportionality of -1.2% per Sm-1. A filtered back-projection algorithm was used to generate tomographic images from the scans.

ABSTRACT. Hudson Bay experiences a complete cryogenic cycle each year. Sea ice begins to form in late October, and the Bay is usually ice-free in early August. This seasonally varying ice cover plays an important role in the regional climate. To identify secular trends in the cryogenic cycle, we examined variability in the timing of sea-ice formation and retreat during the period 1971-2003. The dates of ice freeze-up and breakup at 36 locations across Hudson Bay were catalogued for each year from weekly ice charts provided by the Canadian Ice Service. We used the nonparametric Mann-Kendall test to determine the statistical significance of the trends and the Theil-Sen approach to estimate their magnitude. Our results indicate statistically significant trends toward earlier breakup in James Bay, along the southern shore of Hudson Bay, and in the western half of Hudson Bay, and toward later freeze-up in the northern and northeastern regions of Hudson Bay. These trends in the annual ice cycle of Hudson Bay coincide with both the regional temperature record and the projections from general circulation models. If this trend toward a longer ice-free season continues, Hudson Bay will soon face important environmental challenges. Le test non paramétrique Mann Kendall a été utilisé pour déterminer la signification statistique des tendances alors que la méthode de Theil Sen nous a fourni un estimé de l'ampleur de ces mêmes tendances. Notre analyse statistique nous indique qu'il existe des tendances significatives vers une date de déglacement plus avancée dans la Baie James, le long de la côte sud de la Baie d'Hudson, et dans la partie ouest de la Baie d'Hudson. De plus, des tendances significatives vers un gel plus tardif ont été observées dans les régions du nord et du nord-est de la Baie d'Hudson. Ces tendances dans le cycle annuel de glace de la Baie d'Hudson coïncident avec les tendances des températures de la région de même qu'avec les projections des modèles de circulation générale. Si cette tendance vers une durée plus courte du couvert de glace continue, la région de la Baie d'Hudson relèvera des défis environnementaux importants dans un proche avenir.

The observations of community members and instrumental records indicate changes in sea ice around the Inuit community of Igloolik, in the Canadian territory of Nunavut. This paper characterizes local vulnerability to these changes, identifying who is vulnerable, to what stresses, and why, focusing on local and regional use of sea ice for the harvesting of renewable resources and travel. This analysis is coupled with instrumental and sea ice data to evaluate changing temperature/wind/sea ice trends over time, to complement local observations. We demonstrate the relationships between changing sea ice conditions/dynamics and harvesting activities (i.e. dangers and accessibility), with specific emphasis on ringed 364 Climatic Change (2009) 94:363-397 seal and walrus seasonal hunting, to illustrate current sea ice exposures that hunters are facing. Community members are adapting to such changes, as they have done for generations. However, current adaptive capacity is both enabled, and constrained, by social, cultural, and economic factors that manifest within the modern northern Hamlet. Enabling factors include the ability of hunters to manage or share the risks associated with sea ice travel, as well as through their flexibility in resource use, as facilitated by sophisticated local knowledge and land/navigational skills. Constraining factors include the erosion of land-based knowledge and skills, altered sharing networks, as well as financial and temporal limitations on travel/harvesting. The differential ability of community members to balance enabling and constraining factors, in relation to current exposures, comprises their level of vulnerability to sea ice change.

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A 16-channel magnetic induction tomography (MIT) system has been constructed for imaging samples with low conductivities (<10 S m−1) such as biological tissues or ionized water in pipelines. The system has a fixed operating frequency of 10 MHz and employs heterodyne downconversion of the received signals, to 10 kHz, to reduce phase instabilities during signal distribution and processing. The real and imaginary components of the received signal, relative to a synchronous reference, are measured using a digital lock-in amplifier. Images are reconstructed using a linearized reconstruction method based on inversion of a sensitivity matrix with Tikhonov regularization. System performance measurements and images of a pipeline phantom and a human leg in vivo are presented. The average phase precision of the MIT system is 17 millidegrees.

General circulation models (GCMs) are unanimous in projecting warmer temperatures in an enhanced CO 2 atmosphere, with amplification of this warming in higher latitudes. The Hudson Bay region, which is located in the Arctic and subarctic regions of Canada, should therefore be strongly influenced by global warming. In this study, we compare the response of Hudson Bay to a transient warming scenario provided by six-coupled atmosphere-ocean models. Our analysis focuses on surface temperature, precipitation, sea-ice coverage, and permafrost distribution. The results show that warming is expected to peak in winter over the ocean, because of a northward retreat of the sea-ice cover. Also, a secondary warming peak is observed in summer over land in the Canadian and Australian-coupled GCMs, which is associated with both a reduction in soil moisture conditions and changes in permafrost distribution. In addition, a relationship is identified between the retreat of the sea-ice cover and an enhancement of precipitation over both land and oceanic surfaces. The response of the sea-ice cover and permafrost layer to global warming varies considerably among models and thus large differences are observed in the projected regional increase in temperature and precipitation. In view of the important feedbacks that a retreat of the sea-ice cover and the distribution of permafrost are likely to play in the doubled and tripled CO 2 climates of Hudson Bay, a good representation of these two parameters is necessary to provide realistic climate change scenarios. The use of higher resolution regional climate model is recommended to develop scenarios of climate change for the Hudson Bay region.

The southwestern region of Hudson Bay is one of the last areas in the Hudson and James Bay lowlands region to become free of sea ice in the spring. This late breakup is due to the effects of winds and currents. By analyzing time series with three different statistical techniques, we found a statistically significant increase in the length of the ice-free season in this region from 1971 to 2003. Much of this increase was attributed to earlier breakup of the ice, which is consistent with increased spring temperatures in this region. The onset of breakup advanced by at least three days per decade over the study period.

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