Ice rind

From Glossary of Meteorology

ice rind

(Also called ice crust.) A thin but hard layer of sea ice, river ice, or lake ice.

Apparently this term is used in at least two ways: 1) for a new encrustation upon old ice; and 2) for a single layer of ice usually found in bays and fjords where freshwater freezes on top of slightly colder seawater.
See ice crust.