Ocean Science www.ocean-sci.net 1812-0784 1812-0792 2 1 2006 10.5194/os-2-71-2006 http://www.ocean-sci.net/2/71/2006/ http://www.ocean-sci.net/2/71/2006/os-2-71-2006.html http://www.ocean-sci.net/2/71/2006/os-2-71-2006.pdf 71 86 2006-07-20 On the representation of regional characteristics by hydrographic measurements at central stations in four deep basins of the Baltic Sea J. H. Reissmann Institut für Ostseeforschung Warnemünde, Rostock, Germany In this work the eddy resolving data sets of salinity, temperature, and oxygen content aquired in the framework of the German-Russian project MESODYN (MESOscale DYNamics) in the Arkona Basin, the Bornholm Basin, the Stolpe Furrow, and the Eastern Gotland Basin during summer and winter stratification situations are utilized to examine to which extent the observations at the central monitoring stations within these basins are representative for the spatial mean state of the corresponding region with respect to comparative monitoring purposes of the whole Baltic Sea. The investigation covers profiles of salinity, potential temperature, oxygen content, potential density, and squared buoyancy or Brunt-Väisälä frequency. Moreover, some parameters of the halocline, namely its depth, thickness, and upper and lower boundaries, and the first baroclinic Rossby radii are subject to the investigation. The profiles match best for the squared buoyancy or Brunt-Väisälä frequency. The profiles of salinity match best in the Eastern Gotland Basin and worst in the Arkona Basin both for summer and winter stratification situations. The overall agreement for the halocline parameters is good. The baroclinic Rossby radii match their spatial mean values well, if the depth range considered for their calculation is restricted to the mean depth in each region at the bottom side. In doing so they also match the spatial mean values of the first baroclinic Rossby radii calculated considering the whole depth range at each station. Overall, the regional characteristics of the investigated quantities and parameters are represented well by the hydrographic measurements at the central stations in the four regions in spite of some significant differences between the spatial mean states and the observations at the central stations. In particular, the observations at the central stations seem to be usefull for comparisons between these regions. However, the observed differences may affect regional investigations covering just a single region. Bergström, S. and Carlsson, B.: River Runoff to the Baltic Sea: 1950–1990, AMBIO, 23, 280–287, 1994. Feistel, R.: A new extended Gibbs thermodynamic potential of seawater, Progress in Oceanography, 58, 43–115, 2003, Corrigendum, 61, 99, 2004. Feistel, R.: Numerical implementation and oceanographic application of the Gibbs thermodynamic potential of seawater, Ocean Sci., 1, 9–16, 2005. Fennel, W., Seifert, T., and Kayser, B.: Rossby radii and phase speeds in the Baltic Sea, Continental Shelf Res., 11, 23–36, 1991. Hagen, E. and Feistel, R.: Observations of low-frequency current fluctuations in deep water of the Eastern Gotland Basin/Baltic Sea, J. Geophys. Res., 109, C03044, doi:10.1029/2003JC002017, 2004. HELCOM: Water balance of the Baltic Sea, Baltic Sea Environment Proceedings No. 16, Baltic Marine Environment Protection Commission, Helsinki, Finland, 1986. Hennemuth, B., Rutgersson, A., Bumke, K., Clemens, M., Omstedt, A., Jacob, D., and Smedman, A.-S.: Net precipitation over the Baltic Sea for one year using models and data-based methods, Tellus, 55A, 352–367, 2003. Kõuts, T. and Omstedt, A.: Deep water exchange in the Baltic Proper, Tellus, 45A, 311–324, 1993. Lindau, R.: Energy and water balance of the Baltic Sea derived from merchant ship observations, Boreal Environ. Res., 7, 417–424, 2002. Matthäus, W.: Charakteristische Eigenschaften von Stagnationsperioden im Tiefenwasser der Ostsee, Beiträge zur Meereskunde, 55, 39–53, 1986. Omstedt, A. and Axell, L B.: Modeling the seasonal, interannual, and long-term variations of salinity and temperature in the Baltic proper, Tellus, 50A, 637–652, 1998. Omstedt, A. and Nohr, C.: Calculating the water and heat balances of the Baltic Sea using ocean modelling and available meteorological, hydrological and ocean data, Tellus, 56A, 400–414, 2004. Omstedt, A., Elken, J., Lehmann, A., and Piechura, J.: Knowledge of the Baltic Sea physics gained during the BALTEX and related programmes, Progress in Oceanography, 63, 1–28, 2004. Rodhe, J.: The Baltic and North Seas: A Process-orientated Review of the Physical Oceanography, in: The Sea, edited by: A R. Robinson and K H. Brink, 11, 24, 699–732, John Wiley & Sons, Inc., New York, 1998.