This paper focuses on recent changes in interannual sea ice extent (SIE) and ice freeze-up/ice breakup dates within the subarctic region of eastern Canada, including Hudson Bay, Foxe Basin, and Hudson Strait, from 1980 to 2010. Changes in sea ice are examined as a function of dynamic and thermodynamic forcing. Strong negative trends in SIE are a relatively recent phenomenon within the satellite record. Prior to the mid-1990s, much of eastern Canada, including Baffin Bay/Davis Strait and the Labrador Sea, showed a slight positive trend in SIE (2.0 × 10 4 km 2 year-1), and the Hudson Bay region showed similar positive trends in SIE (Parkinson and Cavalieri, 1989; Deser and Teng, 2008). Positive trends in ice breakup date (later breakup) based on Canadian Ice Service (CIS) data (1971-1989) were also noted by Galbraith and Larouche (2011): +2.3 days decade-1 for Hudson Strait, 2.0 days decade-1 for Hudson Bay, and a weak negative trend (-0.9 days decade-1) for Foxe Basin.

Abstract. Sea ice melt pond fraction (f p ), linked with lower sea ice surface albedo and increased light transmittance to the ocean, is inadequately parameterised in sea ice models due to a lack of observations. In this paper, results from a multiscale remote-sensing program dedicated to the retrieval of level first-year sea ice (FYI) f p from dual co-and crosspolarisation C-band synthetic aperture radar (SAR) backscatter are detailed. Models which utilise the dominant effect of free-water melt ponds on the VV/HH (vertical transmit and vertical receive/horizontal transmit and horizontal receive) polarisation ratio at high incidence angles are tested for their ability to provide estimates of the subscale f p . Retrieved f p from noise-corrected Radarsat-2 quad-polarisation scenes are in good agreement with observations from coincident aerial survey data, with root mean square errors (RMSEs) of 0.05-0.07 obtained during intermediate and late stages of ponding. Weak model performance is attributed to the presence of wet snow and slush during initial ponding, and a synoptically driven freezing event causing ice lids to form on ponds. The HV/HH (horizontal transmit and vertical receive/horizontal transmit and horizontal receive) ratio explains a greater portion of variability in f p , compared to VV/HH, when ice lids are present. Generally low HV channel intensity suggests limited applications using dual crosspolarisation data, except with systems that have exceptionally low noise floors. Results demonstrate the overall potential of dual-polarisation SAR for standalone or complementary observations of f p for process-scale studies and improvements to model parameterisations.

[1] The principal objective of this study is to describe the autumn sea ice regime of Hudson Bay in the context of atmospheric forcing from 1980 to 2005. Both gridded Canadian Ice Service (CIS) data and Passive Microwave (PMW) data are used to examine the freezeup period for weeks of year (WOY) 43-52. Sea ice concentration (SIC) anomalies reveal statistically significant trends, ranging from −23.3% to −26.9% per decade, during WOY 43-48 using the CIS data and trends ranging from −12.7% to −16.8% per decade during WOY 45-50 using the PMW data. Surface air temperature (SAT) anomalies are highly correlated with SIC anomalies (r 2 = 0.52-0.72) and with sea ice extents (r 2 = 0.53-0.72). CIS data show that mean sea ice extents based on SICs ≥80% (consolidated ice) have decreased by 1.05 × 10 5 to 1.17 × 10 5 km 2 for every 1°C increase in temperature in late November; PMW data show similar results. Regression analysis between SAT and standardized climate indices over the 1951-2005 period show that the East Pacific/North Pacific index is highly predictive of interannual SATs followed by the North Atlantic Oscillation and Arctic Oscillation indices. The data show that the Hudson Bay area has recently undergone a climate regime shift, in the mid 1990s, which has resulted in a significant reduction in sea ice during the freezeup period and that these changes appear to be related to atmospheric indices.

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