Sea ice is a crucial component of Earth’s climate system, having important effects on ocean circulation, sea temperature, surface albedo, etc. As sea ice ages, its porosity and salt content decrease, which directly influences its thermal and mechanical properties and thereby influences its interactions with the surrounding environment. It is of practical significance to understand the physical mechanism controlling the aging dynamics of sea ice.
Recently, a joint research team led by Prof. Chao Sun from Tsinghua University studied the long-term evolution dynamics of sea ice and revealed that sea-ice aging is dominated by diffusive desalination by combining experiments, theoretical modelling and direct numerical simulations.
Fig 1: Newly-formed porous ice in salty water gradually ages into dense ice.
With a well-controlled ice-water phase change experimental system, the research team studied the complete process of salty water freezing till the final state over a period of 20 days. After a relatively rapid icing process, the ice layer continues to age slowly, characterized by a gradual decrease in its porosity (Fig. 1).
Fig 2: In a thermally-equilibrium ice layer, system temperature difference induces salinity gradient, leading to the desalination of ice and the decrease of ice porosity.
Theoretical modelling revealed the aging dynamics of ice. During the aging process, the ice layer is in the thermal equilibrium. The temperature difference in the system leads to a salinity gradient within the ice, which causes the mass transfer of salt out of the ice. As desalination proceeds, the pore structures within the ice continue to freeze (Fig. 2). Further, direct numerical simulation confirmed that the final state of the system is the same as the freezing of a pure liquid. The ice layer becomes dense, pure ice and all the salt expelled into the unfrozen bulk liquid (Fig. 3).
Fig 3: The final state of the system is consistent with the freezing of pure liquid under the same conditions.
This study advances our understanding of the coupled physics of complex fluid flow, heat and mass transfer, and solid–liquid phase change in solution systems, and offers an example for exploring other complicated processes involved in the aging of sea ice via laboratory studies. Combining laboratory studies and field measurement can provide new reference for improving the modelling of sea ice and enhancing the predictability of climate models.
The research paper, titled “Sea ice aging by diffusion-driven desalination”, was published in Physical Review Letters. The paper was also selected as an Editors’ Suggestion, and received coverage in American Physical Society’s Physics Magazine.
Ph.D. student Yihong Du from the Department of Energy and Power Engineering at Tsinghua University is the first author. Shuimu Tsinghua Scholar and postdoc Feng Wang is the corresponding author. The co-authors include Assistant Professor Enrico Calzavarini from the Université de Lille in France, as well as Professor and New Cornerstone Investigator Chao Sun from the Department of Energy and Power Engineering at Tsinghua University.
This work was supported by National Natural Science Foundation of China Excellence Research Group Program for “Multiscale Problems in Nonlinear Mechanics” and the Young Scientist Fund, the New Cornerstone Science Foundation through the New Cornerstone Investigator Program and the XPLORER PRIZE.
Full article: https://journals.aps.org/prl/abstract/10.1103/mct1-6hbw
Editor: Li Han
