Age and renewal time of water masses in a semi-enclosed basin — application to the Gulf of Finland

To estimate the water-renewal time of the Gulf of Finland, a numerical-model simulation comprising the years 1987 — 1992 was carried out for realistic meteorological forcing. The results concerning water age as well as renewal index proved to reflect properties of the mean circulation system. The highest water ages (of around 2 yr) were found in the south-eastern part of the Gulf. The water-age distribution after the 5-yr simulation proved to be almost identical to that obtained after 3 yr, indicating that the circulation in the Gulf may be rather stable. The analysis of the renewal-index results showed that it takes around 5 yr to renew 98% of the water masses of the Gulf. When local maxima of the renewal index are found in conjunction with high water ages, this may indicate that the region is particularly vulnerable to eutrophication.

[1]  Eric Deleersnijder,et al.  The concept of age in marine modelling I. Theory and preliminary model results , 2001 .

[2]  Inter-annual variability in the temperature of the North Sea , 1996 .

[3]  A. Lehmann,et al.  On the thermohaline variability of the Baltic Sea , 2000 .

[4]  Peter Lundberg,et al.  Mean circulation and water exchange in the Gulf of Finland: a study based on three-dimensional modelling , 2003 .

[5]  D. Stauffer,et al.  Optimal determination of nudging coefficients using the adjoint equations , 1993 .

[6]  Matthew H. England,et al.  The Age of Water and Ventilation Timescales in a Global Ocean Model , 1995 .

[7]  L. Hasse,et al.  Evaporation over the Baltic Sea as an example of a semi-enclosed sea , 1998 .

[8]  S. Bergström,et al.  River runoff to the Baltic Sea : 1950-1990 , 1994 .

[9]  Eric Deleersnijder,et al.  Toward a general theory of the age in ocean modelling , 1999 .

[10]  Andrew F. Bunker,et al.  Computations of Surface Energy Flux and Annual Air–Sea Interaction Cycles of the North Atlantic Ocean , 1976 .

[11]  T. Stipa.  Baroclinic adjustment in the Finnish coastal current , 2004 .

[12]  O. Andrejev,et al.  Water exchange of the Stockholm archipelago—a cascade framework modelling approach , 2003 .

[13]  Jorge L. Sarmiento,et al.  Tracer dating and ocean ventilation , 1990 .

[14]  I. Orlanski.  A Simple Boundary Condition for Unbounded Hyperbolic Flows , 1976 .

[15]  K. Myrberg,et al.  The physical oceanography of the Gulf of Finland: a review , 1998 .

[16]  Kai Myrberg,et al.  Main upwelling regions in the Baltic Sea a statistical analysis based on three-dimensional modelling , 2003 .

[17]  A. Engqvist.  Long-term Nutrient Balances in the Eutrophication of the Himmerfjärden Estuary , 1996 .

[18]  A. Stigebrandt,et al.  A model for the dynamics of nutrients and oxygen in the Baltic proper , 1987 .

[19]  A. Omstedt,et al.  Use of Baltic Sea modelling to investigate the water cycle and the heat balance in GCM and regional climate models , 2000 .

[20]  Bert Bolin,et al.  A note on the concepts of age distribution and transit time in natural reservoirs , 1973 .

[21]  A. Omstedt,et al.  Interannual, seasonal and regional variations of precipitation and evaporation over the Baltic Sea , 1997 .

[22]  W. Krauss,et al.  Effects of remote and local atmospheric forcing on circulation and upwelling in the Baltic Sea , 2002 .