On the creation and maintenance of stratification in the Gulf of Riga

Factors affecting the creation and maintenance of stratification under simp le conditions in a boreal estuary (Gulf of Riga, Baltic Sea) are studied in terms of buoyancy forcing. It is found that the ratio r = beta C(p)s/alpha determines if the stratification is created by freshwater or heat fluxes. H ere beta and alpha are the haline contraction and thermal expansion coeffic ients of sea water, s is salinity and C-p is specific heat. It is discovere d that stratification in this gulf, as well as in the Baltic Sea in general , is created by dilution of salinity due to freshwater fluxes, the thermal contribution being negligible. Data from four cruises in three consecutive years are used to illustrate this effect. An almost ideal river plume bulge and an associated coastal current is found in the gulf, and their spreadin g rate compared with recent eddy parameterizations. A restratification time scale for the gulf is estimated as 5 weeks and found to be in reasonable a greement with available observations. (C) 1999 Elsevier Science B.V. All ri ghts reserved.