Frazil deposition under growing sea ice

Abstract

Platelet ice may be an important component of Antarctic landfast sea ice. Typically, it is found at depth in first-year landfast sea ice cover, near ice shelves. To explain why platelet ice is not commonly observed at shallower depths, we consider a new mechanism. Our hypothesis is that platelet ice eventually appears due to the sudden deposition of frazil ice against the fast ice-ocean interface, providing randomly oriented nucleation sites for crystal growth. Brine rejected in plumes from landfast ice generates stirring sufficient to prevent frazil ice from attaching to the interface, forcing some of it to remain in suspension until ice growth rate and brine rejection slow to the point that frazil can stick. We calculate a brine plume velocity and match this to frazil rise velocity. We consider both laminar and turbulent environments. We find that brine plume velocities are generally powerful enough to prevent a significant range of frazil sizes from sticking in the case of laminar flow and that, in the turbulent case, there may be a critical ice thickness at which most remaining circulating frazil suddenly settles.