Abstract
Abstract. Rather than being solid throughout, sea ice contains liquid brine inclusions, solid salts, microalgae, trace elements, gases, and other impurities which all exist in the interstices of a porous, solid ice matrix. This multiphase structure of sea ice arises from the fact that the salt that exists in seawater cannot be incorporated into lattice sites in the pure ice component of sea ice, but remains in liquid solution. Depending on the ice permeability (determined by temperature, salinity and gas content), this brine can drain from the ice, taking other sea ice constituents with it. Thus, sea ice salinity and microstructure are tightly interconnected and play a significant role in polar ecosystems and climate. As large-scale climate modeling efforts move toward "earth system" simulations that include biological and chemical cycles, renewed interest in the multiphase physics of sea ice has strengthened research initiatives to observe, understand and model this complex system. This review article provides an overview of these efforts, highlighting known difficulties and requisite observations for further progress in the field. We focus on mushy layer theory, which describes general multiphase materials, and on numerical approaches now being explored to model the multiphase evolution of sea ice and its interaction with chemical, biological and climate systems.
Highlights
Biologists in the polar regions face an apparent contradiction: the bulk salinity of sea ice is considerably smaller than that in the underlying polar oceans – salty brine drains from sea ice – and yet chlorophyll concentrations in sea ice can be two orders of magnitude larger than in the surrounding ocean (Arrigo et al, 1997)
Studies using large-scale sea ice models with various representations of multiphase physics point to the importance of (i) storage of latent heat within brine inclusions associated with the penetration of solar radiation into sea ice, (ii) the reduction of the energy required to form or melt ice associated with significant liquid fractions, and (iii) the role of salinity on ice-ocean salt and freshwater exchanges
Research into the multiphase physics of sea ice has been an active field for decades
Summary
Biologists in the polar regions face an apparent contradiction: the bulk salinity of sea ice (around 5 ppt) is considerably smaller than that in the underlying polar oceans (around 32 ppt) – salty brine drains from sea ice – and yet chlorophyll concentrations in sea ice (a measure of microalgal biomass) can be two orders of magnitude larger than in the surrounding. Other constituents in the sea water, such as algae and bacteria, can exist in the interstices of the solid matrix, along with the salt Communities of these organisms form within the ice, their life cycles largely determined by penetrating sunlight and by fluxes of nutrients between the ocean and ice. The nutrient fluxes are, in turn, controlled by the porous ice structure that depends critically on the temperature and salinity of the ice. For example, cold or warm fronts passing vertically through the ice after the onset of storms cause the brine inclusions to contract or expand, altering the permeability.
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