A model for a turbulent bottom boundary "slab" layer is described. The mode
l is designed to fit under a standard, depth coordinate ocean general circu
lation model, with a view to improving its response both for local and clim
ate problems. The depth of the layer varies temporally and spatially. Both
analytical and numerical versions of the model conserve energy. The model i
s tested using a source of dense water on a slope, and performs satisfactor
ily, with the plume spreading far more than the equivalent case without a b
ottom layer.