Physical Oceanography of the Baltic Sea

verfasst von: Professor Matti Leppäranta, Adjunct professor Kai Myrberg

Verlag: Springer Berlin Heidelberg

Buchreihe : Springer Praxis Books

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik"

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Über dieses Buch

The Baltic Sea oceanographic research community is wide and the research history is over 100 years old. Nevertheless, there is still no single, coherent book on the physical oceanography of the Baltic Sea as a whole. There is a strong need for such a book, coming from working oceanographers as well as the university teaching programmes in advanced undergraduate to graduate levels.

In the regional conference series in physical oceanography (Baltic Sea Science Conference, Baltic Sea Oceanographers' conference, Baltex-conferences) about 500 scientists take part regularly. Even more scientists work in the fields of marine biology, chemistry and the environment, and they need information on the physics of the Baltic Sea as well. There are nine countries bordering on the Baltic Sea and five more in the runoff area. The Baltic Sea as a source of fish, means of transportation and leisure activities is highly important to the regional society. In the runoff area there are a total of 85 million people. Research and protection strategies need to be developed, as the Baltic Sea is probably the most polluted sea in the world.

Since the Baltic Sea has become an inner sea of the EU (apart from small shore parts of Russia in Petersburg and Kaliningrad), it is anticipated that the importance of the region will consequently rise. The book will arouse interest among students, scientists and decision makers involved with the Baltic problems. It will also give important background information for those working with biogeochemical processes in the Baltic Sea, because the physical forcing for those processes is of vital importance.

Inhaltsverzeichnis

Frontmatter

1. Introduction

Abstract

The Baltic Sea¹ is a unique basin of the World Ocean. It is small and shallow, rather a series of basins, and connected to the main Atlantic Ocean only via the Danish Straits (Figure 1.1). The exchange of water through these straits is quite limited, and as a consequence of the positive freshwater balance the Baltic Sea water mass is brackish, with the mean salinity about 7‰—one-fifth of the salinity of normal ocean waters. This elongated sea lies between maritime temperate and continental sub-Arctic climate zones. In winter it is partly ice-covered and during the most severe winters it is completely frozen over. The variable coastal geomorphology and the wide archipelago areas give the Baltic Sea its individual appearance.

2. The Baltic Sea: History and geography

Abstract

This chapter introduces the reader to the Baltic Sea starting with a short life history in Section 2.1. In 13,500 years the basin has undergone several different phases. The treatment in this book, however, focuses on the present brackish water Baltic Sea introduced in Section 2.2. Section 2.3 gives a brief history of Baltic Sea research, which first commenced in the late 1800s making it one of the oldest research basins in oceanography. The last section (Section 2.4) describes the climate and weather conditions in the Baltic Sea region, where influences are felt from the North Atlantic via westerly winds, from continental conditions on its eastern side, and from polar airmasses in the north.

3. Topography and hydrography of the Baltic Sea

Abstract

This section starts with a detailed description of the topographic features of the Baltic Sea. The dimensions of the main basins are listed and a detailed description of each basin is given. In Section 3.2 the basic physical characteristics of brackish water are given. A discussion follows on how brackish waters differ from oceanic waters. In Section 3.3, watermasses and their specific stratification conditions are described in detail and the interaction of the Baltic Sea with the North Sea is discussed. Section 3.4 gives a summary of long-term changes in the hydrographic conditions of the Baltic Sea during the last 100 years, a period in which systematic measurements have been carried out.

4. Water, salt, and heat budgets

Abstract

The temperature and salinity fields of the Baltic Sea were presented in Chapter 3, and in this chapter we shall examine the water, salt, and heat budgets. These budgets guide the evolution of the physical conditions in the Baltic Sea. The water budget determines the flushing of Baltic Sea watermasses, the salinity level is externally forced by the exchange of water between the North Sea and the Baltic Sea, and the heat budget is coupled with atmospheric conditions. Budget questions are among the key objectives of the BALTEX research program (Omstedt et al., 2004). Sections 4.1–4.3 discuss the budget based on observational material, and Sections 4.4–4.5 deal with modeling approaches using one-dimensional models and box models.

5. Circulation

Abstract

In this chapter a detailed description of circulation in the Baltic Sea is given. In Section 5.1 the general theory of ocean dynamics in the Baltic Sea is discussed along with some important special cases. The conservation laws for heat and salt were treated in Chapter 4, and here the focus is on purely dynamic questions. In Section 5.2, general circulation is introduced using different examples based on observations. Section 5.3, “Deepwater circulation and ventilation”, gives an overview of the internal water cycle and internal mesoscale dynamics and mixing. Section 5.4 gives a detailed view of the Major Baltic Inflow—one of the key features in Baltic Sea physics. Section 5.5 gives a brief summary on how three-dimensional numerical models can be used as tools to investigate circulation physics. The tidal phenomenon is not discussed here but will follow in Chapter 6.

6. Waves

Abstract

This chapter is a treatise on wave dynamics with special emphasis on the Baltic Sea. First, a general theoretical framework is given based mainly on linear theory. Waves are periodic solutions of Navier-Stokes equations examined with special techniques, as will be illustrated. The main division of waves in oceanography is into shallow-water waves and deepwater waves; the former lead to basin eigenoscillations, astronomical tides, and internal waves, while the latter lead to wind-generated surface waves. All these types of waves are described and their role in the Baltic Sea is discussed (Figure 6.1).

7. The ice of the Baltic Sea

Abstract

Sea ice forms in the Baltic Sea annually, can be found there for seven months of the year, and has a very important role in the annual course of physical and ecological conditions in the basin. Therefore, a treatise on the Baltic Sea needs a chapter on ice, a topic that is usually less familiar to physical oceanographers. Section 7.1 introduces the ice season, and the following sections then progress from small to large scales. Section 7.2, for example, contains fine-scale questions and shows that brackish ice is structurally like normal sea ice; it also presents ice crystal structure, phase diagram, and sediments. Section 73 focuses on the small scale considering the growth and melting of sea ice, using analytical and numerical models. Section 74 looks at meso-scale and large-scale physics and introduces drift ice, its material structure, kinematics, and dynamics. Sea ice is a peculiar, granular, compressible, non-linear medium. Section 7.5 presents full sea ice models (i.e., basin-scale systems for the growth, drift, and decay of ice with vertical thermodynamics and horizontal dynamics).

8. Coastal and local processes

Abstract

The physical oceanography of the Baltic Sea, including the physics of sea ice, has been presented in the previous chapters. This chapter has a specific regional focus in considering the coastal zone, the area influenced directly by the presence of both land and open sea nearby. Due to the small size of the Baltic Sea, a significant part of it belongs to the coastal zone. In Section 8.1 the basic properties of the coastal zone are discussed. Sections 8.2 and 8.3 present the most important coastal oceanography field in the Baltic Sea: sea-level elevation with its variations and upwelling. Section 8.4 is about coastal ice—from landfast ice to the boundary of drift ice and landfast ice. Section 8.5 is about coastal weather.

9. Environmental questions

Abstract

Physical oceanography and sea ice science are closely connected to ecology and human life in the Baltic Sea area, and these connections need to be understood by physicists themselves. Principally, this relates to the physics of the Baltic Sea which provides the background conditions for ecology in terms of light conditions, temperature, salinity and stratification, current dynamics including transport and diffusion, and the ice season. The life of Baltic Sea peoples has always been influenced by shipping conditions and fishery, and presently eutrophication, pollution, and the construction of infrastructure is an additional severe load to “our sea” (so-called by local people) by humankind. Section 9.1 treats light conditions, and Section 9.2 is about oxygen conditions in deep basins. Human impact is discussed in Section 9.3, and extreme situations for key physical quantities are presented in Section 9.4. Section 9.5 introduces operational oceanography, which has come to the fore in recent years and will have a key role in the future protection of the Baltic Sea.

10. Future of the Baltic Sea

Abstract

The Baltic Sea is a small and shallow brackish water basin, or rather a series of basins connected to the main Atlantic Ocean via the Danish Straits. The variable coastal geomorphology and the wide archipelago areas give the Baltic Sea its characteristic appearance (Figure 10.1). Mean salinity is about 7‰—one-fifth of the salinity of normal ocean water—and haline stratification is strong. This elongated sea lies between maritime temperate and continental sub-Arctic climate zones. In winter it is partly ice-covered and during the most severe winters it is completely frozen over. The Baltic Sea is young, has undergone several brackish and freshwater phases since the Weichselian glaciation, and from about 2,000 years ago salinity has been close to the present level. Land uplift is slowly changing the Baltic Sea landscape. Here it is possible to observe how land rises from the sea and how life on land gradually takes over.

Backmatter

Titel: Physical Oceanography of the Baltic Sea
verfasst von: Professor Matti Leppäranta
Adjunct professor Kai Myrberg
Verlag: Springer Berlin Heidelberg
Electronic ISBN: 978-3-540-79703-6
Print ISBN: 978-3-540-79702-9
DOI: https://doi.org/10.1007/978-3-540-79703-6