Multiple T-S states for estuaries, shelves, and marginal seas

Simple theoretical box-models and laboratory experiments demonstrate that an estuary subjected to freshwater flux and heating or cooling can possess more than one stable, stationary state if a well-defined set of forcing conditions are present. Two types of estuaries can develop such multiple temperature-salinity states. The same may be true of continental shelves and marginal seas. One type receives freshwater runoff from land but is cooled in the winter. The second has net freshwater loss from evaporation but also receives strong solar heating. Criteria are found which define the conditions needed for multiple states. It is shown that under most conditions, the density difference vetween estuary and ocean would be dominated by salinity if the inlet is sufficiently small (such as inland seas). In contrast, if the inlet is sufficiently wide and atmospheric cooling and heating is sufficiently great, the density difference would be dominated by temperature. Multiple states lie between these extremes. One of the multiple states is dominated by the salinity difference between estuary and ocean, the other by temperature difference. Each state is stable.