Recovery of Strength in Thermally Cracked Freshwater and Salt-Water Ice

Abstract. The integrity of ocean and lake ice covers is increasingly threatened by climate change, which reduces ice extent and promotes breakup. In addition to thinner ice and larger waves, thermal cracking may also contribute to ice cover failure. This study investigates the impact of thermal cracking on the flexural strength of freshwater and sea ice. Laboratory experiments show that when a narrow region of ice is thermally shocked, the flexural strength of both freshwater and sea ice initially decreases but subsequently recovers completely. In contrast, when the entire surface is thermally shocked, strength recovery is only partial in freshwater ice, while sea ice again fully recovers its strength. Repeated cycles of cracking followed by healing do not affect the recovered flexural strength. Additional experiments involving creep demonstrate that compressive stress enhances healing, highlighting the role of ice sintering in strength recovery. The differing behavior between localized and full-surface cracking is attributed to residual compressive stresses that develop during healing when only a narrow region is shocked. Rapid healing observed in sea ice is likely facilitated by its porous structure and the presence of brine, suggesting that natural sea ice may retain significant mechanical integrity even after thermal cracking.