Directional Solidification of Salt Water: Deep and Shallow Cells

The common observation of cellular substructure ((1 ÷ 10 -2 )mm) at the sea-ice-ocean interface is explained by modelling the natural solidification of seawater as that of a dilute H 2 O-NaCl solution. Linear and nonlinear perturbation theories reveal that the one-dimensional planar steady state is morphologically unstable, and a bifurcation to cells occurs in geophysically relevant growth regimes. We compute the range of solidification velocity V c < V < V a in which the system is unstable for fixed far-field solute concentration C ∞ , and bound the geophysical observations. The system exhibits weak wavelength selection near V c and the nonlinear theory shows that the bifurcation to cells is subcritical.