The mechanical properties of gas-enriched sea ice

To investigate the mechanical properties of sea ice in the Arctic, ice blocks were collected using a ship crane and stored in a cold onboard storage unit during an Arctic expedition. During the transfer of ice blocks from the ship to the transport vehicle after docking, significant brine drainage occurred, artificially increasing the gas volume fraction within the ice. This unexpected shift allowed us to explore the mechanical properties of gas-enriched sea ice and the different impacts of gas and brine on sea ice strength. Examination of the ice crystal structure showed a granular ice layer at the top, underlain by a columnar ice layer. Sea ice samples were machined from the ice blocks for mechanical experiments performed in the laboratory. Three-point bending tests were conducted at ice temperatures of −12 to −3 °C, and uniaxial compressive strength tests were conducted at ice temperatures of −8 to −3 °C with a strain rate range of 10⁻⁶–10⁻² s⁻¹. Ice temperature, density, and salinity of each sample were measured to determine porosity. Results showed that both flexural strength and strain modulus of columnar sea ice exhibited statistically significant decreasing trends with increasing porosity. Flexural strength showed a significant correlation with gas volume fraction (R² = 0.25, p > 0.1) but not with brine volume fraction (R² = 0.37, p < 0.1). Conversely, strain modulus correlated significantly with brine volume fraction (R² = 0.58, p < 0.1) but not with gas volume fraction (R² = 0.06, p < 0.1). Uniaxial compressive strength decreased with increasing porosity and displayed a ductile-to-brittle transition, with strength initially increasing and then decreasing with rising strain rate. The transition strain rate ranged between 1.5 × 10⁻⁴ and 4.0 × 10⁻³ s⁻¹ depending on ice crystal structure. Experimental results from gas-enriched sea ice were compared with previously reported data from natural sea ice (brine-dominated). At equivalent porosity levels, gas-enriched ice exhibited higher flexural strength and strain modulus than natural sea ice, indicating that brine has a stronger influence on bending mechanics than gas. However, the uniaxial compressive strength of gas-enriched ice remained comparable to that of natural sea ice.