The development of mixed layer models in so-called density coordinates is d
iscussed. Density coordinates, or isopycnal coordinates as they are sometim
es called, are becoming increasingly popular For use in ocean models due to
their highly desirable adiabatic properties. In contrast, almost all exist
ing mixed layer models assume a continuous density variable and are therefo
re somewhat inconsistent with the density coordinate philosophy. Many exist
ing isopycnal models attempt to join standard surface mixed layer models to
density coordinate interior models. and it is known that problems can aris
e in the physical behavior of the resulting system. The problem of mixed la
yer model development is approached here by adopting a density coordinate f
ramework at the outset, thereby generating a surface layer model whose cons
truction is entirely consistent with that of existing interior density coor
dinate models. Examples of quantitative and qualitative behavior are presen
ted and argued to be encouraging.