Impacts of snow data and processing methods on the interpretation of long-term changes in Baffin Bay early spring sea ice thickness

Abstract

In the Arctic, multi-year sea ice is being rapidly replaced by seasonal sea ice. Baffin Bay, situated between Greenland and Canada, is part of the seasonal ice zone. In this study, we present a long-term multi-mission assessment (2003–2020) of spring sea ice thickness in Baffin Bay from satellite altimetry and sea ice charts. Sea ice thickness within Baffin Bay is calculated from Envisat, ICESat, CryoSat-2, and ICESat-2 freeboard estimates, alongside a proxy from the ice chart stage of development that closely matches the altimetry data. We study the sensitivity of sea ice thickness results estimated from an array of different snow depth and snow density products and methods for redistributing low- resolution snow data onto along-track altimetry freeboards. The snow depth products that are applied include a refer- ence estimated from the Warren climatology, a passive mi- crowave snow depth product, and the dynamic snow scheme SnowModel-LG. We find that applying snow depth redistri- bution to represent small-scale snow variability has a consid- erable impact on ice thickness calculations from laser free- boards but was unnecessary for radar freeboards. Decisions on which snow loading product to use and whether to ap- ply snow redistribution can lead to different conclusions on trends and physical mechanisms. For instance, we find an uncertainty envelope around the March mean sea ice thick- ness of 13 % for different snow depth/density products and redistribution methods. Consequently, trends in March sea ice thickness from 2003–2020 range from −23 to 17 cm per decade, depending on which snow depth/density product and redistribution method is applied. Over a longer timescale, since 1996, the proxy ice chart thickness product has demon- strated statistically significant thinning within Baffin Bay of 7 cm per decade. Our study provides further evidence for long-term asymmetrical trends in Baffin Bay sea ice thick- ness (with −17.6 cm per decade thinning in the west and 10.8 cm per decade thickening in the east of the bay) since 2003. This asymmetrical thinning is consistent for all com- binations of snow product and processing method, but it is unclear what may have driven these changes.