Estuarine transport versus vertical movement and mixing of water masses in the Gulf of Finland (Baltic Sea)

Weekly mapping of vertical temperature and salinity fields was carried out across the Gulf of Finland in summer 2006 and spring 2007. Using successive cross-gulf vertical sections of salinity and wind data from the region the variations of estuarine and transverse circulation are described. Changes of deep layer phosphate-phosphorus concentrations are found to be related to the described variations in circulation patterns in a season with strong vertical stratification of the water column. Cumulative volume transport estimates were obtained using the results of a 3D baroclinic circulation model (HIROMB). We suggest that the north-easterly winds, which intensify the estuarine circulation and lead to the upwelling events along the southern coast of the Gulf of Finland, could have a major impact to the Gulfpsilas ecosystem by importing more saline and phosphorus rich waters. These events with many-fold more intense upward movement and mixing of deep waters (upward diapycnal transport) could contribute significantly to the ventilation of deep layers of the northern Baltic proper.