Brine channels form between the ice crystal lattices as the ice freezes. These are extensive, as shown in Figure 6 (Weissenberger et al. 1992). These channels contain the hypersaline fluid remaining, as only pure water forms the ice crystals. The brine water has higher salinity and an increased concentration of ions and minerals, compared to the surrounding sea water.
Meiners et al. (2009) demonstrated that in the Weddell Sea pack ice, the channels in the frazil zone had average temperatures of below -50C and high brine salinities (greater than 60). Diffuse fluxes were slow; these, combined with heterotrophic remineralisation, provided the only sources of nutrients in this semi-enclosed system. Channels in the lower sections of the columnar ice were higher in temperature (approximately -20C) and lower in salinity (below 40) and had a higher productivity due to the exchange of nutrients with the underlying seawater (Meiners et al. 2009). The effect of salinity changes and temperature changes on the photosynthetic capabilities of microalgae is discussed later.
The small area prevents predation by large herbivores but bacteria are present to break down and recycle nutrients that would otherwise be quickly exhausted as there is little to no water ingress into the channels and pores.