Observations of preferential summer melt of Arctic sea-ice ridge keels from repeated multibeam sonar surveys

• Published in: The Cryosphere
• Main Authors: Salganik, Evgenii, Lange, Benjamin A., Katlein, Christian, Matero, Ilkka, Anhaus, Philipp, Muilwijk, Morven, Høyland, Knut V., Granskog, Mats A.
• Format: Text
• Language: English
• Published: 2023
• Subjects: Arctic; ice pack; Sea ice
• Online Access: https://doi.org/10.5194/tc-17-4873-2023; https://tc.copernicus.org/articles/17/4873/2023/

Sea-ice ridges constitute a large fraction of the total Arctic sea-ice area (up to 40 %–50 %); nevertheless, they are the least studied part of the ice pack. Here we investigate sea-ice melt rates using rare, repeated underwater multibeam sonar surveys that cover a period of 1 month during the advanced stage of sea-ice melt. Bottom melt increases with ice draft for first- and second-year level ice and a first-year ice ridge, with an average of 0.46, 0.55, and 0.95 m of total snow and ice melt in the observation period, respectively. On average, the studied ridge had a 4.6 m keel bottom draft, was 42 m wide, and had 4 % macroporosity. While bottom melt rates of ridge keel were 3.8 times higher than first-year level ice, surface melt rates were almost identical but responsible for 40 % of ridge draft decrease. Average cross-sectional keel melt ranged from 0.2 to 2.6 m, with a maximum point ice loss of 6 m, showcasing its large spatial variability. We attribute 57 % of the ridge total (surface and bottom) melt variability to keel draft (36 %), slope (32 %), and width (27 %), with higher melt for ridges with a larger draft, a steeper slope, and a smaller width. The melt rate of the ridge keel flanks was proportional to the draft, with increased keel melt within 10 m of its bottom corners and the melt rates between these corners comparable to the melt rates of level ice.