When seawater freezes, most salt remains in liquid, increasing salinity and density and potentially driving convection.
A temperature gradient can move a brine inclusion by melting its warmer wall and freezing its colder wall. This slow process can redistribute salt, but is generally much less effective at net desalination than gravity drainage of sea-ice brine or meltwater flushing of sea ice.
// Target: geophysics.bigb
Freezing within a brine inclusion expands the solid fraction and can force concentrated liquid into neighboring pores or channels. Expulsion redistributes salt internally; net desalination requires a path crossing the ice boundary.
// Target: geophysics.bigb
Surface meltwater with a positive hydraulic head can percolate through permeable sea ice, displacing brine into the ocean. Flushing can efficiently desalinate warm summer ice, but requires meltwater and connected flow paths.
// Target: geophysics.bigb
Dense saline liquid in connected pore space can drain from sea ice while fresher seawater enters. The process is controlled by buoyancy, permeability of a porous medium and network connectivity, and is a major means of growing-ice desalination.
// Target: geophysics.bigb
If a fraction of initial liquid mass freezes into salt-free ice, all original salt remains in a liquid mass fraction . Writing salinity as salt concentration per mass gives , hence . For equal initial cooling and subsequent freezing heat extraction, . The liquid specific heat capacity, rather than the ice value, determines the initial heat removal. If ice retains salt, the mass balance instead reads .
Let liquid mass freeze incrementally, and let each new ice increment retain salinity with constant , where is the instantaneous well-mixed liquid salinity. Conservation gives , hence . Integrating yields . For frozen mass fraction , . Specifying a fixed bulk ice salinity instead produces a different, though first-order compatible, finite-mass balance.
For equal heat extraction, the density increase caused by brine rejection can exceed that caused by cooling near the freezing point because the thermal density response is weak. Using conservation of salt during freezing, the ratio is , with . This is a parcel comparison, not a guarantee that freezing overcomes any ambient density stratification.
Articles by others on the same topic
Brine rejection refers to the process by which concentrated saltwater (brine) is expelled from certain environments, particularly in relation to the formation of sea ice or during the desalination process in natural bodies of water. This phenomenon has significant ecological and climate implications. 1. **Sea Ice Formation**: When seawater freezes to form sea ice, the salt does not become incorporated into the ice structure.