The Arctic is increasingly vulnerable to global warming, leading to shortening winter seasons, later freezes, and earlier breakups of sea ice. This project quantifies changes in sea ice seasonality from 1979 - 2023 using passive microwave data and sea ice climate indicator variables. Our results are consistent with those previously published by Bliss et al. (2019) finding statistically significant positive trends in the ice-free season length. We find the most rapid changes in the Chukchi Sea off the northwestern coast of Alaska. Based on current trends, we find that this region could become ice-free in the next 80 years. We also quantify the impact of river discharge on nearshore sea ice, finding correlation between the peak discharge and 90% sea ice concentration threshold dates for the region adjacent to the Mackenzie River delta. The same relationship does not exist near the Yukon River delta, with sea ice melting approximately 60 days before river discharge peaks. These findings will support future work analyzing the impact of ice on Arctic coastal biogeochemistry. 

Sea ice ridges are an important morphological feature that stabilize shorefast ice across the Northern Alaskan coastline. This stability is important to local communities and ecosystems that rely on this habitat for food security and safety. Investigating the development of shorefast ice around Utqiagvik, AK, we describe an approach to identify grounded ridges throughout the winter season. To do this, we utilize high resolution altimetry data from NASA’s ICESat-2 satellite which provides unprecedented along-track detail that allows, for the first time, the detection of individual pressure ridges. We apply the University of Maryland Ridge Detection Algorithm (Duncan and Farrell, 2022) using ICESat-2 elevation data to identify and calculate ridge sail heights along each satellite track. From these heights, we estimate the depth of the ridge using sail/keel height ratios described in the literature. The calculated ridge depths are compared with high-resolution bathymetric data (NCEI Digital Elevation Model Mosaic) to classify potentially grounded ridges. This methodology for identifying and quantifying grounded ridges in shorefast ice will improve our understanding of coastal ice processes in a changing environment.