Water exchange in the Pomeranian Bight investigated by satellite data and shipborne measurements

Abstract

The Pomeranian Bight is characterized by the main freshwater input into the western Baltic Sea coming from the Oder and Peene rivers. The rate of river discharge is driven by varying sea level in the southern Baltic, and the distribution patterns of the river plume are dominated by the local wind. This study uses daily available sea surface temperature (SST) maps (4–6 times a day), derived from Advanced Very High Resolution Radiometer (AVHRR) data of the NOAA satellites, to investigate these patterns in relation to the meteorological conditions. Comparisons of SST maps with shipborne measurements for different wind situations confirm the usability of satellite data for investigation of the river discharge. On the basis of about 125 available NOAA scenes scattered over all seasons in the period of 1991–1994, typical horizontal distribution patterns were derived for wind directions of the eight octants. Chlorophyll concentration maps derived from Coastal Zone Colour Scanner (CZCS) data of the NIMBUS-7 satellite are, in special cases, more detailed than corresponding SST patterns (channel 6). They confirm the patterns and the transport of suspended material. Long-term wind records from the Arkona weather station indicate the dominant wind directions and the seasonal variations in wind forcing leading to seasonal preferred patterns and transport directions of the river plume into and out of the bight. Dominant westerly winds in summer, autumn and winter produce an eastward transport along the Polish coast into the Bornholm Sea and further into the Gdansk Bay over more than 300 km. In the period of the main freshwater inflow in spring, easterly winds are dominant and transport the river water along the German coast into the Arkona Sea. This is confirmed by high accumulation rates at the bottom of the Arkona Basin. The results of these investigations allow a prediction of distribution patterns and main transport directions in relation to the prevailing wind situation.