Upper boundary conditions for numerical models of the ocean are conventionally formulatedunder the premise that the boundary is a material surface. In the presence of an ice cover, suchan assumption can lead to nonconservative equations for temperature, salinity, and other tracers.The problem arises because conditions at the ice-ocean interface differ from those in the waterbeneath. Advection of water with interfacial properties into the interior of the ocean thereforeconstitutes a tracer flux, neglect of which induces a drift in concentration that is most rapid forthose tracers having the lowest diffusivities. If tracers are to be correctly conserved, either thekinematic boundary condition must explicitly allow advection across the interface, or the fluxboundary condition must parameterize the effects of both vertical advection and diffusion in theboundary layer. In practice, the latter alternative is often implemented, although this is rarelydone for all tracers.