As sea ice cools, the small-scale (mm to sub-mm size) brine inclusions decrease in size due to brine freezing out of solution. At a liquid volume fraction of around 50 to 70 ppt, brine layers are generally assumed to segregate into isolated pores. This process is believed to be critical for sea-ice permeability, with much lower permeabilities at lower ice temperatures corresponding to isolated pores.

It has been hypothesized that upon warming of the ice the isolated brine pockets do not assume the original planar shape but grow as spherical or slightly oblong inclusions, thereby maintaining a state of separate pores to higher temperatures and brine volume fractions than observed during the original cooling.

Such segregation at the pore scale is extremely important for organisms residing within the ice matrix, as they would be effectively cut off from the supply of nutrients or other dissolved/particulate matter as well as prevented from interacting with each other in the "segregated-pore" regime. The transition between a connected pore system and a segregated, isolated pore system hence represents an important transition. This becomes even more important for would-be habitats such as the briny ice on the Jovian moon Europa, where the issues of temporal and spatial scales in the potential evolution and survival of life are critical.

In-situ measurements of sea-ice permeability indicate that the intrinsic permeability does drop to values below about 10^-12 m² at lower (effective) porosities, but from what limited data is available, even at very small porosities, sea ice exhibits a finite permeability.

In the context of sea ice as a habitat for bacteria and other microorganisms, the question is whether this small but finite permeability can offset or compensate for the problems outlined above.

This image shows two actual examples of the transition between a "closed", low-temperature system at temperatures of -30 C (horizontal thin sections of sea ice, pores shown black) and the linking of pores observed in samples from the same ice cover at temperatures around -2.5 and -1.5 C (these images were obtained from an experiment studying the thermal evolution of pore space in artificial sea ice).