A long-term proxy for sea ice thickness in the Canadian Arctic: 1996–2020

Abstract. This study presents a long-term winter sea ice thickness proxy-product for the Canadian Arctic based on a Random Forest Regression model trained on CryoSat-2 observations that provides 25 years of sea ice thickness in the Beaufort Sea, Baffin Bay, and, for the first time, the Canadian Arctic Archipelago. An evaluation of the product with in-situ sea ice thickness measurements shows that the presented sea ice thickness proxy product correctly estimates the magnitudes of the ice thickness and accurately captures spatial and temporal variability. The product estimates sea ice thickness within 30 to 50 cm uncertainty. The sea ice thickness proxy-product shows that sea ice is thinning over most of the Canadian Arctic, with a mean trend of −1.4 cm/year in April (corresponding to 35 cm thinning over the 25-year record), but that trends vary locally. The Beaufort Sea and Baffin Bay show significant negative trends during all months, though with peaks in November (−3 cm/yr) and March (−1.8 cm/yr), respectively. The Arctic Ocean Periphery shows thinning above 2 cm/yr during all months but April, with a peak of −3.3 cm/yr in December. The Parry Channel, which is part of the Northwest Passage and relevant for shipping, shows weaker thinning trends, but with high yearly variability. The sea ice thickness proxy product gives, for the first time, the opportunity to study long-term trends and variability in sea ice thickness in the Canadian Arctic, including the narrow channels in the Canadian Arctic Archipelago.