Grounded Ridge Detection and Characterization along the Alaskan Arctic Coastline using ICESat-2 Surface Height Retrievals

Abstract. Grounded sea ice ridges are an important morphological feature that stabilize shorefast ice along Arctic coastlines. Investigating the development of shorefast ice around Utqiaġvik, AK, we employ high-resolution altimetry data from NASA’s ICESat-2 satellite to describe an approach to identify grounded ridges and to track the development of shorefast ice over the winter season. We apply the University of Maryland Ridge Detection Algorithm (Duncan and Farrell, 2022) using ICESat-2 ATL03 elevation data to identify and calculate ridge sail heights and estimate ridge depths using empirical relationships based on first-year ice ridge geometries surveyed in the Beaufort, Chukchi, and Bering Seas. The estimated ridge depths are then compared with 15 arc-second resolution bathymetric data from the General Bathymetric Chart of the Oceans (GEBCO) to detect likely grounded ridges. This approach for identifying and characterizing grounded ridges in shorefast ice is then applied across the entire Alaskan Arctic coastline in the 2021–2022 winter to characterize grounded ridge depth, height, width, number of ridges per track, and distance from shore. We find that distributions in ridge grounding depth skew towards shallower water and ridges are narrower and closer to shore on the Chukchi side of the Alaskan Arctic.  Mean grounding depths of 5.4 m in the Chukchi and 9.1m in the Beaufort are notably shallower than the traditional "stamuki" zone (≥10 m). With further application of the methods demonstrated here, we can begin to map patterns in shorefast ice stability, seasonality, and improve our understanding of near-shore ice dynamics across Arctic coastal regions in a changing climate.