[1] The Canadian Ice Service Digital Archive (CISDA) is a compilation of weekly ice charts covering Canadian waters from the early 1960s to present. The main sources of uncertainty in the database are reviewed and the data are validated for use in climate studies before trends and variability in summer averaged sea ice cover are investigated. These data revealed that between 1968 and 2008, summer sea ice cover has decreased by 11.3% ± 2.6% decade −1 in Hudson Bay, 2.9% ± 1.2% decade −1 in the Canadian Arctic Archipelago (CAA), 8.9% ± 3.1% decade −1 in Baffin Bay, and 5.2% ± 2.4% decade −1 in the Beaufort Sea with no significant reductions in multiyear ice. Reductions in sea ice cover are linked to increases in early summer surface air temperature (SAT); significant increases in SAT were observed in every season and they are consistently greater than the pan-Arctic change by up to ∼0.2°C decade −1 . Within the CAA and Baffin Bay, the El Niño-Southern Oscillation index correlates well with multiyear ice coverage (positive) and first-year ice coverage (negative) suggesting that El Niño episodes precede summers with more multiyear ice and less first-year ice. Extending the trend calculations back to 1960 along the major shipping routes revealed significant decreases in summer sea ice coverage ranging between 11% and 15% decade −1 along the route through Hudson Bay and 6% and 10% decade −1 along the southern route of the Northwest Passage, the latter is linked to increases in SAT. Between 1960 and2008, no significant trends were found along the northern western Parry Channel route of the Northwest Passage.

ABSTRACT. An eXlstmg thermodynamic ice-growth model (Semtner, 1976) has been tested for its ability to predict the growth of fast ice in McMurdo Sound, Antarctica. Significant discrepancies between observed and predicted ice thicknesses were found to occur, primarily due to the presence of sub-ice platelets and the formation of a snow-ice layer. Although these ice-growth processes are not well enough understood to permit rigorous physical modelling, it is shown that fairly simple modifications to the model greatly improve the accuracy of the thickness predictions, ano serve to highlight the importance of these processes in the Antarctic fast-ice environment.Surface flooding and snow-ice formation are assumed to occur immediately upon the establishment of a positive hydrostatic water level, and a surface temperature in excess of a critical value, above which interconnecting channels in the ice matrix permit the flow of water to the surface. The presence of the sub-ice platelet layer is assumed to increase columnar ice growth at a rate proportional to the volume fraction of ice in the platelet layer, a simple technique but one that permits estimates of platelet-enhanced growth without detailed knowledge of oceanographic conditions. The resulting model predictions are in close agreement with measurements of fast-ice growth and decay in McMurdo Sound; however, data suitable for testing the model over a complete range of conditions and over multi-year cycles are not available at the present time.

* This only constitutes a subset of the images that were investigated; many images were scrutinized without any ice islands being identified. † These values represent the contents of the database based on digitization that was completed through December 2012. ‡ Ice islands originating from these glaciers were not always monitored from the time of initial calving.

ABSTRACT. Observations of the physical properties of the snow cover and underlying young fast ice in Resolute Passage, N.W .T., Canada, were made during the winter of 1982. Detailed measurements of snow density, and ice and snow temperatures, salinities, and brine volumes were made over a period of 46 d, beginning when the ice was 0.4 m thick and about 8 d old. The recorded values are used in a theoretical mixture model to predict the dielectric properties of the snow cover over the microwave frequency range. The results of this analysis are then used to investigate the effects of the snow properties on the radar back-scatter signatures of young sea ice. The results show that back-scatter is a function of the incidence angle and can change significantly over short periods of time during the early evolutionary phase of ice and snow-cover development. This has important consequences for the identification of young ice forms from Synthetic Aperture or Side Looking Airborne Radar images.