Recovery of strength in locally versus globally thermally cracked freshwater ice produced in the laboratory and sea ice collected in the Beaufort Sea, 2022-2024

The vulnerability of ocean and lake ice covers to climate change-induced threats, such as decreased extent and increased thermal cracking, necessitates comprehensive investigation. Conducted at Dartmouth College's Ice Research Laboratory from 2022 to 2024, experiments introduced thermal shock to laboratory-grown freshwater ice and natural first-year sea ice using liquid nitrogen to either a narrow band or the entire surface of ice samples. This study explores the impact of thermal cracking on the flexural strength. Results indicate that while both types of ice initially experience strength reduction after thermal shock, full recovery occurs when a narrow region is shocked, whereas only partial recovery is observed when the entire surface is shocked in freshwater ice, contrasting with full recovery in sea ice. Repeated cycles of cracking and healing do not affect flexural strength recovery. Moreover, experiments involving creep reveal the influence of compressive stress on healing, highlighting its role in ice sintering and strength restoration. Application of a compressive stress of 1 MPa for 1 hour enhances strength recovery, with flexural strength almost completely restored. The disparity in behavior between cracking a narrow region versus the entire surface is attributed to residual compressive stresses during healing when a narrow region is shocked. Rapid healing in sea ice is observed, likely due to its porous structure and the presence of brine.

海洋与湖泊冰盖对气候变化引发的威胁（包括冰盖范围缩减、热裂隙发育加剧）具有显著脆弱性，该问题亟需开展系统性研究。本实验于2022至2024年间在达特茅斯学院（Dartmouth College）冰研究实验室开展，以液氮对实验室培育的淡水冰与天然一年海冰样品施加热冲击，冲击方式分为窄带冲击与全表面冲击两类。本研究旨在探讨热裂隙对冰抗弯强度的影响。实验结果表明，两类冰在热冲击后初始阶段均出现强度下降；其中淡水冰在窄区域受冲击后可实现强度完全恢复，但全表面受冲击时仅能获得部分强度恢复；而海冰无论采用何种冲击方式，均可实现强度完全恢复。裂隙与愈合的重复循环并不会对冰的抗弯强度恢复产生显著影响。此外，通过蠕变实验，本研究揭示了压应力对冰体愈合过程的调控作用，阐明了其在冰烧结与强度恢复中的核心机制。施加1兆帕（MPa）的压应力并持续1小时，可有效强化强度恢复过程，使冰的抗弯强度几乎完全复原。窄区域冲击与全表面冲击的行为差异，可归因于窄区域受冲击后愈合阶段留存的残余压应力。海冰展现出更快的愈合速率，该现象大概率与其多孔结构及卤水组分的存在有关。