6 The Gulf of Finland
183
The entire idea of the smart use of intrinsic dynamics of marine currents for environmental management of semi-enclosed seas, which is the major focus of this
book, first came up in the context of the Gulf of Finland (Soomere and Quak 2007).
Its starting point was not only the necessity of more detailed control of the possible pollution. Another even more important reason was a peculiar combination of
the complexity (seeming randomness) of the dynamics of this basin and frequently
occurring highly ordered transport patterns, at least in numerical simulations (Andrejev et al. 2004a). The situation in this gulf thus is very much different from that
in the south-western Baltic Sea (where the inflow and outflow conditions occasionally replace each other and in this way create a specific pattern of alternating flow
regimes) (Lu et al. 2012) or in the Gulf of Riga (that is much less affected by the
circulation in the other parts of the Baltic Sea and is separated from the saline bottom waters by a sill) (Omstedt and Axell 2003). There is a wide range of impacts
stemming from the Northern Gotland Basin, from the general circulation, buoyancybased and mesoscale features, or internal and surface wave activity, down to a wedge
of saline water that extends deep into the gulf. The dynamics of the Gulf of Finland
represents a delicate balance between these impacts, the voluminous fresh water
river discharge into the eastern end of the gulf, the local bathymetry and specific
forcing.
A thorough description of the physics, circulation, topographic and hydrographic
features, the main dynamical scales and forcing functions affecting the observed
circulation patterns in the gulf is presented in Alenius et al. (1998), Soomere et al.
(2008), Leppäranta and Myrberg (2009). One of the aims of this chapter is to present
an insight about how the entire pool of different forcing and steering factors are interrelated in a subtle way, giving rise to a certain order in the seemingly almost random system of motions. We make an attempt to present a selection of results, based
both on classical measurements and numerical modelling, which at least to some
extent explain the complicated interactions behind the existing and numerically revealed circulation patterns. This information is a critical constituent of the modern field experiments and an essential background for all advanced high-resolution
numerical modelling exercises. Its quality implicitly delineates whether or not the
efforts towards numerical replication of the local circulation, carried out nowadays
for a number of applications, incl. environmental management of the basin, lead to
reliable results or could be interpreted simply as an advanced computer game.
An overview of existing physical knowledge is thus presented from the viewpoint
of high-resolution numerical modelling of its dynamics. Several models used in this
basin are described in detail in Chaps. 4 and 9. We start with the description of the
bathymetry and overall stratification conditions, and then take a short glance at mixing, meteorological forcing and ice conditions that are the main driving factors for
water movements in the Gulf of Finland. The focus is on the circulation dynamics
from mesoscale features up to basin-scale patterns. A common way of its approximate quantification is to introduce the basic scales of the motions of interest. This
material characterizes the basics of the physics of the gulf based on both the past
investigations and in terms of classical oceanographic analyses of current fields and
largely follows the three above-mentioned sources (Alenius et al. 1998; Soomere
et al. 2008; Leppäranta and Myrberg 2009).
183
The entire idea of the smart use of intrinsic dynamics of marine currents for environmental management of semi-enclosed seas, which is the major focus of this
book, first came up in the context of the Gulf of Finland (Soomere and Quak 2007).
Its starting point was not only the necessity of more detailed control of the possible pollution. Another even more important reason was a peculiar combination of
the complexity (seeming randomness) of the dynamics of this basin and frequently
occurring highly ordered transport patterns, at least in numerical simulations (Andrejev et al. 2004a). The situation in this gulf thus is very much different from that
in the south-western Baltic Sea (where the inflow and outflow conditions occasionally replace each other and in this way create a specific pattern of alternating flow
regimes) (Lu et al. 2012) or in the Gulf of Riga (that is much less affected by the
circulation in the other parts of the Baltic Sea and is separated from the saline bottom waters by a sill) (Omstedt and Axell 2003). There is a wide range of impacts
stemming from the Northern Gotland Basin, from the general circulation, buoyancybased and mesoscale features, or internal and surface wave activity, down to a wedge
of saline water that extends deep into the gulf. The dynamics of the Gulf of Finland
represents a delicate balance between these impacts, the voluminous fresh water
river discharge into the eastern end of the gulf, the local bathymetry and specific
forcing.
A thorough description of the physics, circulation, topographic and hydrographic
features, the main dynamical scales and forcing functions affecting the observed
circulation patterns in the gulf is presented in Alenius et al. (1998), Soomere et al.
(2008), Leppäranta and Myrberg (2009). One of the aims of this chapter is to present
an insight about how the entire pool of different forcing and steering factors are interrelated in a subtle way, giving rise to a certain order in the seemingly almost random system of motions. We make an attempt to present a selection of results, based
both on classical measurements and numerical modelling, which at least to some
extent explain the complicated interactions behind the existing and numerically revealed circulation patterns. This information is a critical constituent of the modern field experiments and an essential background for all advanced high-resolution
numerical modelling exercises. Its quality implicitly delineates whether or not the
efforts towards numerical replication of the local circulation, carried out nowadays
for a number of applications, incl. environmental management of the basin, lead to
reliable results or could be interpreted simply as an advanced computer game.
An overview of existing physical knowledge is thus presented from the viewpoint
of high-resolution numerical modelling of its dynamics. Several models used in this
basin are described in detail in Chaps. 4 and 9. We start with the description of the
bathymetry and overall stratification conditions, and then take a short glance at mixing, meteorological forcing and ice conditions that are the main driving factors for
water movements in the Gulf of Finland. The focus is on the circulation dynamics
from mesoscale features up to basin-scale patterns. A common way of its approximate quantification is to introduce the basic scales of the motions of interest. This
material characterizes the basics of the physics of the gulf based on both the past
investigations and in terms of classical oceanographic analyses of current fields and
largely follows the three above-mentioned sources (Alenius et al. 1998; Soomere
et al. 2008; Leppäranta and Myrberg 2009).