A first-order model for vertical flux of momentum and scalars in a rotational boundary layer is applied to the oceanic boundary layer beneath sea ice. Model eddy viscosity is proportional to the product of the local friction velocity u* and a master length scale for vertical exchange, which is a function of the rotational length scale u*/f and the local Obukhov length L. The ratio of eddy diffusivity to eddy viscosity is 1 when turbulence is energetic but falls to lower values when turbulence levels are low and stratification high, according to an empirical relation. There are three empirical constants in the theory: &xgr;N, the ratio of the master length scale to the rotational length scale; Rc, the critical flux Richardson number; and a shape factor describing the falloff of the eddy diffusivity ratio at high gradient Richardson numbers. For an idealized simulation of melting and freezing conditions representative of the marginal ice zone, the model agrees closely with a similar implementation of the Mellor-Yamada level 2.5 model. The model is demonstrated by performing a simulation of surface drift and mixed-layer properties observed during the 1984 Marginal Ice Zone Experiment field study in the Greenland Sea. ¿ American Geophysical Union 1987