On the thermohaline variability of the Baltic Sea

A coupled ice-ocean model is utilized to investigate the transports of heat , salt and water in the Baltic Sea for the years 1986, 1988, 1993 and 1994. The oceanic component of the coupled system is a three-dimensional barocli nic model of the Baltic Sea including the Belt Sea and the Skagerrak/Katteg at area. The model has a horizontal resolution of similar to5 km and 28 ver tical levels specified. The icr: model is based on the Hamburg Sea Ice mode l, with the same horizontal resolution. The coupled system is driven by atm ospheric data provided by the Swedish Meteorological and Hydrological Insti tute (SMHI; Norrkoping, Sweden) and river runoff taken from a monthly mean runoff database. The thermohaline variability of the Baltic Sea strongly de pends on the fluctuations of the atmospheric forcing conditions. Therefore, high demands on the spatial and temporal resolution of the meteorological forcing are required. Besides heat and radiation fluxes, precipitation and evaporation rates have to be taken into account. From the coupled runs, the different components determining the energy and water cycle of the Baltic Sea ale identified and estimates of the water, heat and salt transports are given for the different years. Furthermore, the thermohaline variability i s investigated with respect to the relevant forcing mechanisms including at mospheric, as well as fresh water fluxes. Besides the heat and water fluxes of the Baltic Sea and the water mass exchange with the North Sea, internal flu,:es of heat, salt and volume between the different subbasins of the Ba ltic Sea are presented. Sensitivity studies on the variation of the net fre sh water flux indicate that uncertainties in precipitation and/or river run off can have a strong impact on the inflow of highly saline water from the North Sea, thus, influencing the thermohaline circulation of the Baltic Sea . (C) 2000 Elsevier Science B.V. All rights reserved.