The Stommel model of shallow coastal lagoons

The Stommel equations describing the behaviour of a coastal lagoon, in the absence of freshwater input, are generalized to include ocean exchange proc esses that are independent of the density difference between the waters of the lagoon and ocean. The resultant model clearly demonstrates the tendency of the system to adopt a state in which the lagoonal waters have a density that is only slightly greater than that of the ocean. In this quasi-neutra l inverse (QNI) state, there is only very slow exchange between the ocean a nd lagoonal waters so that the lagoon is environmentally fragile. The model indicates that the lagoon can readily jump to this QNI state following onl y minor changes to its physical parameters.