The consolidation of saline ice blocks in water of varying freezing points: Laboratory experiments and computer simulations

- We examine the interaction of saline ice blocks with water at varying freezing points.
- Experiments and numerical modelling show that such interaction leads to thermodynamic consolidation of ice blocks.
- This process could explain summer transformation of first-year ice ridges.

The thermodynamic consolidation of ice rubble in the ridge keel is an important mechanism both in global heat balance and when it comes to offshore structure interaction. Classically, it is considered that consolidation in the keel occurs due to reserved cold at the stage of formation and due to further atmospheric cooling. Such scenario brings consolidation layer thickness to a value of about two times only thicker than the level ice around the ridge, while in-situ observations after summer season show that many ice ridges are almost fully consolidated. The authors propose a thermodynamic process inside ridge keels during the summer season, which may cause the keel to become more consolidated. They assume that fresh water can flow through the keel increasing the freezing point of fluid in the caves, which allows extracting additional cold from the solid ice of the keel and, as a consequence, freezing fluid inside caves. The physical mechanism of possible keel summer transformation in water with varying freezing points was investigated in the laboratory and numerically.Two types of experiments were performed to investigate mass and salinity development of saline ice samples. In the first type of experiment we used samples with an opening of 2 cm, cut off from the sample in the middle part of it. This was made to illustrate visually the process of rubble consolidation and macro-porosity reduction. In the second type of experiment the samples of same dimensions, but without the gap, were used. In both experiments, samples were periodically moved between water reservoirs of different salinities (0 and 35 ppt), held at their freezing points. The mass, salinity and shape of the samples were observed. The experiments demonstrated a gradual increase in the total mass of the samples and significant variations of the salinity of the ice samples during stages at different reservoirs. We demonstrate that such salinity variations are very important for the accumulation of ice mass. Numerical simulations performed using the finite element method in Comsol Multiphysics 4.3a confirm the experimental results.