Landfast sea ice in Hudson Bay and James Bay

Through analysis of Canadian Ice Service ice charts, we have characterized the temporal and spatial variability of landfast sea ice (or fast ice) surrounding Hudson Bay and James Bay from 2000 to 2019. Over this 19-year period, we observed contrasting changes in fast-ice persistence between the western and eastern sides of Hudson Bay and James Bay. Fast ice in western Hudson Bay and James Bay trended towards later freeze-up and earlier break-up that resulted in a shortening of the fast-ice season at a rate of 6 days/decade. Contrastingly, eastern Hudson Bay and James Bay showcased relatively earlier freeze-up and delayed break-up, and an overall trend towards a longer fast-ice season at a rate of 8 days/decade. The general trend in air temperature followed a similar spatial pattern to the changing fast-ice persistence; however, the timing of fast-ice break-up did not have a strong relationship with the thawing-degree days during spring. Variations in fast-ice area showed latitudinal and meridional gradients, with greater fast-ice area in eastern Hudson Bay and James Bay compared to the west. Given the overall warming trend in the Arctic, observing areas of decreasing fast-ice persistence is unexpected; however, this study highlights the role of regional factors, such as coastal orientation and bathymetry, in controlling the stability, growth and decay of fast ice.