THE PHASE EVOLUTION OF YOUNG SEA-ICE

Sea ice forms as a porous matrix consisting of pure ice crystals in eq uilibrium with brine. We present an experimental and theoretical study that reveals that the brine expelled by growing sea ice initially rem ains trapped within the crystalline interstices but that drainage into the underlying water is ultimately triggered abruptly due to the onse t of buoyancy-driven convection. The onset is quantified by a critical porous-medium Rayleigh number, and we present an empirical marginal s tability diagram that defines the transition.