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The Baltic Sea todayBernt I. Dybern aa Institute of Marine Research , Lysekil, SwedenPublished online: 22 Dec 2010.

To cite this article: Bernt I. Dybern (1971) The Baltic Sea today, International Journal ofEnvironmental Studies, 2:1-4, 59-69, DOI: 10.1080/00207237108709445

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Intern. J. Environmental Studies, 1971, Vol. 2, pp. 59-69 © Gordon and Breach Science Publishers Ltd.Printed in Exeter, England

THE BALTIC SEA TODAY

BERNT I. DYBERN

Institute of Marine Research, Lysekil, Sweden

(Received October 8, 1970)

The Baltic Sea receives many different pollutants and the quantities are continually increasing. Special topographicaland hydrographical features due to the fiord-nature of the sea, a marked halocline, especially in the Baltic proper,and temporary thermoclines, restrict the water exchange with the sea outside as well as between the upper andlower water layers. This makes the Baltic very sensitive to pollution and many coastal areas are seriously affected.Toxic substances have been shown to accumulate also in animals from the open sea and the oxygen deficiency condi-tions which occur in the deeper water layers may partly be due to the discharge of nutrients from land. Thesenutrients stimulate the productivity of the upper water layers; this is followed by an oxygen uptake from the deeperlayers when sinking organic matter undergoes degradation.

INTRODUCTION

The Baltic Sea is a large fiord with a very restrictedwater exchange with the sea outside it. An excessivefresh-water supply makes the whole water volumebrackish but there is, especially in the southern andcentral parts, a considerable difference in salinitybetween the surface and deep layers. A permanenthalocline is formed between these, so that the waterexchange between them is restricted. During Sum-mer a temporary thermocline may also act as abarrier against the vertical exchange in the upperwater layers.

Due to the slightly increased salinity of thedeeper water layers during the present century theinfluence of the halocline has been strengthened.There has also been a small increase of the meantemperature during recent decades.

The restricted vertical exchange makes the waterof the deeper parts poor in oxygen, especially inthe central Baltic. The oxygen content has decreasedsuccessively during the present century, particu-larly after World War II. This is due to the streng-thening of the halocline, but another reason maybe increased breakdown of organic matter sinkingdown from the surface layers owing to the rise intemperature. There is, however, strong evidencethat the increased quantities of organic wastesdischarged from land greatly account for the pro-nounced oxygen deficiency, and even H2S-produc-tion, which characterizes the development duringrecent years.

The increased discharge of sewage and industrialwastes has negatively influenced many coastal

areas, and damage to recreation areas, marine lifeand fisheries has occurred in many places.

Toxic substances, such as DDT and PCB, havebeen shown to accumulate in the Baltic due to thesluggish movement of water out of the sea, andthe concentrations in certain fish-species and othermarine animals are much higher than in correspond-ing animals in the Skagerrak area. Mercury pollu-tion has affected some coastal areas.

Oil pollution is now a big problem. Radioactivepollution is under control.

The increased pollution by oxygen-demandingsubstances and, especially, by toxic compoundsand oil is alarming and will continue to increase dueto the sensitive hydrographical conditions, unlessextensive precautions are taken. To make effectivepollution abatement possible international co-operation in the form of joint research work andbilateral negotiations will have to be developed.

TOPOGRAPHY

The Baltic Sea covers an area of about 370,000 km2.It is thus smaller than the North Sea (about575,000 km2). The main difference between thetwo seas, however, is that the Baltic, in fact, is alarge fiord with very narrow and shallow entrancesthrough the Danish sounds and the Oresundbetween Denmark and Sweden (Figure 1). Thegreatest sill depth is only 17-18 m (above the sill ofDarss between Denmark and the German Demo-cratic Republic). This, of course, renders the waterexchange between the Baltic Sea and the North

59

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60 B. I. DYBERN

FIGURE 1 The Baltic Sea.

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THE BALTIC SEA TODAY 61

BALTIC PROPERALAND BOTHNIAN

SEA SEA

Land sortDeep

400

FIGURE 2 Longitudinal section.

Sea rather difficult, which is of extreme importancefor the understanding of the special features of theBaltic.

Inside the sounds there is a series of deeperbasins, as shown in Figure 2, the deepest being theLandsort Deep (459 m). Between the Aland Seaand the Bothnian Sea there is evidence of a narrowchannel about 70 m deep (not shown in Figure 2).The greatest depth of the Gulf of Finland is almostexactly 100 m.

The coastal areas are generally relatively shallow.Especially the coasts of Sweden and Finland aresplit up into thousands of small embayments andislands. The Russian, Polish and German coastsare, on the other hand, more open. This renderswater exchange between the coasts and the open seasomewhat different in different parts of the sea.

Figure 1 shows the main subareas and basins inthe Baltic. The names of these will be used frequent-ly below. When the terms "Baltic" and "BalticSea" are used, they mean the whole sea area betweenthe 54th and 66th parallels.

SALINITY

Many rivers discharge fresh water into the Balticand there is also a rather large supply in the form ofprecipitation. The fresh water mixes with the seawater to form a thick surface layer of water of lowsalinity. Part of this flows out as a surface currentthrough the entrance sounds, causing, below it, aweaker deep current of more saline water in theopposite direction. The total water balance is notknown in detail but has been roughly estimatedas follows:1

Runoff + Precipitation -f- Inflow = Evaporation500 km3 200 km3 500 km3 200 km3

+ Outflow1000 km3

The outflow of low salinity water is thus abouttwice as great as the inflow of more saline water.

The inflowing water is successively mixed withthe more brackish water. Therefore, salinitydecreases inwards into the Baltic. At the same timeit also decreases from the bottom to the surface.Table I gives some mean values for differentsubareas and the Kattegat.

TABLE I

Mean salinity values in %„ for the surface and bot-tom waters in different parts of the Baltic and in the

Kattegat

Subarea

Bothnian BayBothnian SeaGulf of FinlandGotland DeepBornholm DeepBight of Kiel (Belt Sea)Central Kattegat

Surface

1-43-43-56-87-8

16-1721-22

Bottom

3-44-58-9

11-1315-1721-2233-34

Between the low salinity surface water and thedeeper more saline layers there is a permanenthalocline which is most marked in the southernand central basins. Figure 3 shows typical hydro-graphical conditions in the Gotland Deep duringsummer. The halocline in this area lies at about50-70 m depth. In the more shallow southern Baltic

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62 B. I. DYBERN

and the Gulf of Finland it rises to depths between15 and 30 m.

The halocline is of great importance, since ithinders to a considerable extent the exchangebetween the upper and deeper water layers. In theBothnian Sea and the Bothnian Bay, where thesalinity differences are small, the influence isconsiderably less than in the Baltic proper.

1 2 3 I* 5 6 7 8 9 10 11 12 13 14 15 16 17 %., °C.m[/l

100

200-

p^ml/l; t°C

GOTLAND DEEP

JULY 22.1961

,7.. S

FIGURE 3 Salinity, temperature and oxygen conditions inthe.Gotland Deep, July 22, 1961 (from Fonselius14).

During recent decades there has been a certainincrease of the salinity, especially in the bottomlayers. For example, in the Gotland Deep thisincrease is about l-2%0, which is rather large whenit is borne in mind that the salinity is, on the whole,rather low. The increase has strengthened thehalocline and has certainly sharpened its effect, too.

Salinity conditions, especially in the Baltic proper,are not quite stable. The flow of more saline wateroccurs at irregular intervals through the entrancesounds. Due to this, deep water salinity maytemporarily increase, but there is, as a rule, a moreor less rapid return to the "normal" conditionsthrough mixing of the new water with the morebrackish water.

TEMPERATURE

During Summer surface water layers down toabout 20 m depth warm up (cf. the temperaturecurve in Figure 3). A temporary thermocline isformed and below it the temperature is low and, onthe whole, remains rather stable for the wholeyear (about 3-6°C). The thermocline disappearsduring the winter when the surface temperaturessuccessively become lower than the deep watertemperature; ice covers big areas during winter.

The thermocline is of great importance since itprevents much of the exchange between the waterlayers at various depths. During autumn and springhomothermic conditions prevail, and the hindranceis thus only a temporary phenomenon, but mayplay an important role, e.g. in the coastal areas.

Also, the mean temperatures of the Baltic haveincreased slightly during the present century. Theincrease is of the order 1-2°C in the Baltic properand seems to be connected with a similar increasein the North Sea area.

MAIN CURRENT SYSTEM

The currents of the Baltic are known only imper-fectly. The general circulation is counterclock-wise,and the subareas belong partly to this system, andpartly they have local current systems.

Since there are almost no tides in the Baltic, tidalcurrents do not play any role. Winds and differencesin the air pressure may, on the other hand, stronglyinfluence the direction and velocity of currents. Incoastal areas, especially in archipelagos, the currentsmay be very complicated.2

OXYGEN

Dead organic matter sinking from the layers nearthe surface, where it is produced, is successivelybroken down on the way to the bottom. This takesoxygen from the water. Even if the breakdown isslow in the cold deep water layers, these will bedepleted in their oxygen content, unless new oxygenis provided. As mentioned above, the halocline isan obstacle against water exchange. This stronglyinfluences the oxygen conditions in the deep basinsof the southern and central Baltic, the oxygencontent below the halocline being considerablylower than above it (cf. the oxygen curve in Figure3). Since the halocline is less pronounced in theBothnian Sea and the Bothnian Bay, conditions aresomewhat better there. In several coastal areasmuch of the oxygen is used up during Summerbelow the temporary thermocline, but generallythe oxygen deficit is more or less eliminated duringAutumn due to the vertical water circulation whichis then possible.

In the open sea, below the halocline, even smallchanges in the conditions may worsen the oxygensituation. In fact, the oxygen content of the deepbasins has successively decreased during the present

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THE BALTIC SEA TODAY 63

century. The magnitude of this decrease has beendemonstrated by Fonselius3 and Figure 4 shows,for example, the decline in the Landsort Deep. Itwill be seen that oxygen values have increased tozero, especially during the last 20 years. Similarconditions have been shown to exist in other deepbasins in the Baltic proper; in the Gulf of Finlandand the Bothnian Sea there has been a certainoxygen decrease in the deep waters during thesame time.

The decline has not been quite regular. Fonseliusand Rattanasen4 have shown that since the 1950s,periods when the deeper layers of the GotlandDeep have contained at least some oxygen havealternated with others when the bottom water hasbeen entirely devoid of oxygen with an accom-panying production of H2S.

The last oxygen-free period started about 1965,being the worst one hitherto, and all oxygen wasused up over large parts of the sea-bed not only in

3.0

2.0

1.0

0

•

*

-

I

• \

i

»

Vi '

1900 10

FIGURE 4halocline inFonselius3).

Mean values of dissolved oxygen below thethe Landsort Deep from 1900 to 1967 (from

10°

60'

F.R.G. \ G.D.R._T

Riga

U.S.S.R.

55'

10° 20* 25'

FIGURE 5 Bottom areas covered by H2S-containing sea water. Shaded areas show the situation in January 1969,fine-shaded areas the situation in December 1969 (from Francke and Nehring15).

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64 B. I. DYBERN

the Gotland Deep but also in other deep basinsof the Baltic proper, causing production of H2S, asshown in Figure 5. The figure also indicates, how-ever, that conditions improved during 1969. This isdue to a heavy influx of new saline and oxygen-containing water through the entrance sounds. Thenew water pushed, so to speak, the old H2S-waterin front of it, and at present (Summer, 1970) onlyvery small sea-bed areas are still covered withoxygen-free water. A research ship from the GermanDemocratic Republic was able to observe the turn-over in the Gotland and Faro Depths, and Figure 6gives a "snapshot" of the complicated conditionswhich then arose.

POLLUTION BY OXYGEN-DEMANDINGSUBSTANCES

Sewage from towns and villages and industrial andagricultural waste waters contain organic and othermaterials in suspension or solution which whencarried out and broken down in the sea take upoxygen from the water. Many of these substancesalso increase the production of marine organisms,thus causing an eutrophication of the environmentwhich may have a negative effect on the oxygenbalance, too.

The oxygen-demanding substances derive in thefirst place directly from areas at the coasts but also

BY10B BY11B Anchor station BV15A BY19B BY20A BY21B

15.10 11.101969 '250

FIGURE 6 Variations of oxygen and hydrogen sulflde during the turnover in the Gotland Deep in October1969 (from Nehring, Francke and Brosin16).

The oxygen values of the deep basins are, how-ever, still very low and there are already signs of anew decrease. Most scientists expect that in a rathershort time new H2S-water will again be formed overlarge bottom areas of the Baltic proper.

The reasons for the successive decline of theoxygen content in the deep basins have beendiscussed at length. The primary reason is certainlythe halocline, which has been strengthened due tothe increase of the average salinity of the deepwater. It makes the latter more or less stagnantand hinders oxygen from the surface waters frompenetrating downwards. Another reason may beincreased production and breakdown of organicmatter due to the slight temperature increase of theBaltic waters mentioned above. But especially afterWorld War II the discharge of nutrients from landvia sewage and industrial waste waters from allBaltic countries has also increased. This may havehad some influence, and I will return to it later.

to some extent indirectly from inland areas. Further-more, the quantities depend on the degree of treat-ment of the sewage and waste waters. It is a com-mon phenomenon in all Baltic countries thatsewage treatment is better inland than in coastalareas. From the latter most wastes are removedwithout any or with only primary treatment be-cause it is thought that dispersal and dilution ofpollutants occur much better in the sea than ine.g. inland lakes. Such ideas may prove dangerousbecause, as mentioned, the water exchange betweenthe Baltic and the sea outside is very restricted.

Table II shows the pollution caused by sewageand industrial wastes estimated in terms of BOD5.For several reasons such an estimation must bevery rough but it gives a hint of the magnitude fordifferent parts of the Baltic. It must, however, beremembered that neither secondary pollution causedby eutrophication nor the real influence of substan-ces only very slowly broken down are included in

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THE BALTIC SEA TODAY 65

TABLE IIApproximative estimation of oxygen-demanding pollution in terms of BOD5 from sewage and industrial waste water. Directpollution comes from population and industries at the coast: indirect pollution from just inside the coast. (Based on

calculations in ICES Report5).

Area

Bothnian BayBothnian SeaGulf of FinlandBaltic proper

Sum

Belt SeaOresundKattegat

Total

Millioninhabitants

Direct

0-2300-5654-8683-335

8-998

1-1951-7700-625

12-588

Indirect

0-1670-4950-7972-065

3-524

2-6000-3100-360

6-794

SewageBOD5 tons/year

Direct

560013,600

121,40060,900

201,500

40,10040,60016,000

298,200

Indirect

450012,20019,20030,000

65,900

21,00026005000

94,500

Industrial waste watersBOD 5 tons/year

Direct + Indirect

159,000384,000115,000

~ 110,000

-760,000

< 10,000< 10,000-25,000

-800,000

BOD5 tons/year

Total

169,000410,000256,000

-200,000

-1,025,000

70,00053,00046,000

-1,200,000

calculations with the BOD5 method. The totalpolluting effect of oxygen-demanding substances istherefore considerably greater than the figures inTable II show.

The BOD5 figures are nevertheless rather high,that is much oxygen is required for the breakdownof the substances being carried away from land.In the Bothnian Bay and the Bothnian Sea industrialpollution outweighs sewage pollution to a greatextent, depending on the sparse population andheavy cellulose industry on both the Finnish andSwedish side. In the Gulf of Finland and the Balticproper the ratio is about fifty-fifty, due to denselypopulated regions around the cities of Leningrad,Helsinki, Tallinn, Riga, Gdansk, Stockholm, etc.,and at the same time to a rather heavy industriali-zation of many coastal areas. In the Belt Sea andthe Oresund with a high population density andnot so much industrialization at the coasts, sewagepollution outweighs industrial pollution.

Among the substances carried out into the Balticthose containing phosphorus play a great role.Phosphorus compounds can influence oxygenconditions by stimulating the production of livingorganisms in the surface layers, which gives riseto an increased amount of sinking organic matterthat is continuously broken down. The phosphorusconcentration in the open sea of the Baltic, as awhole, is rather low compared with, e.g., the con-centration in the North Sea. Taking into considera-tion the special hydrographical situation, especiallythe oxygen conditions and the poor water exchangewith the sea outside, the effects of an increased

phosphorus supply, even if rather small, ought tobecome evident in a short time.

Table III shows the estimated quantities of phos-phorus carried into different parts of the Baltic,and Table IV shows the net supply according todifferent methods of analysis. Without going intodetails it can be said that the determinations arevery difficult to make, since almost nothing isknown about phosphorus transport by air and very

TABLE III

Estimation of the discharge of phosphorus. In tons per year(Based on calculations in ICES Report5)

Area

Bothnian BayBothnian SeaGulf of FinlandBaltic proper

Sum

Belt SeaOresundKattegat

Total

Direct

290780

50503880

10,000

12401960890

14,090

Indirect

220600870

2370

4060

2800350400

7610

Total

510138059206250

14,060

404023101290

21,700

little about the supply of natural phosphorus. How-ever, the net supply seems to lie somewhere between8000 and 20,000 tons per year. Most of it comesfrom sewage water (industries only provide about10-30% as compared with the human population).Therefore, the Gulf of Finland, parts of the Baltic

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TABLE IV

Net supply of phosphorus to the Baltic accord-ing to different calculations. In tons per year.

(Based on ICES Report5)

P tons/year

Supply: Highest values Lowest values

Sewage 15,000Air 3000Natural 3000The Sounds 6000Total 27,000

Outflow 4- I i' IThe Sounds 7000 10,000 7000 10,000

Net to supply 20,000 17,000 10,000 7000

proper, the Belt Sea and the Oresund are the mainrecipients.

Most oxygen-demanding substances, includingthe phosphorus compounds, certainly stay in thecoastal areas, especially along the coasts of Finlandand Sweden, where a great number of inlets andarchipelagos act as a kind of filter preventing muchof them from reaching the open sea. Also in theinnermost part of the Gulf of Finland and in theBay of Riga much of these compounds seems to beretained. But part of them may, directly by watermovements or indirectly via the food productionchains, reach the surface layers above the deepbasins, thus influencing the organic production ofthe former and the oxygen consumption of thelatter.

The quantity of substances carried out has in-creased, especially since World War II, due toincreased human population and urbanisation inthe coastal areas, increased industrialization, in-creased use of fertilizers in agriculture and ofsynthetic washing powders containing phosphoruscompounds; at the same time the construction oftreatment plants has proceeded very slowly. Cal-culations have shown that the average quantity ofphosphorus in Swedish sewage water has more thandoubled during the last 15-20 years (from about1-5 g P/person/day to about 4 g P/person/day), anda similar increase is more or less true also for otherBaltic countries. Fonselius3 has shown that duringthe same period the phosphate concentrations inthe deep basins of the Baltic proper have increasedconsiderably (an example is given in Figure 7),which indicates an increased productivity in the

surface layers of the open sea; this is certainly dueto some extent to the increased supply of organicwastes from land. The period is also the same underwhich the oxygen curves for the deep basins havegone steepest towards zero and there must be somecorrelation, even if, as mentioned before, the hydro-graphical conditions play the most important role.The organic wastes, indeed, tipped the scale.

jug at/1

t% >-

3.0 -

2 0 -

1.0 -

1938 • 1954 55 56 57 58 59 60 61 62 63 64 65 66 67 68

FIGURE 7 Mean values of phosphate concentrations inthe deep water of the Landsort Deep (from Fonselius3).

Many coastal areas in all countries are at presentmore or less affected, sometimes destroyed, byorganic pollution. This means that if we want torestore the coastal areas and save the deep basinsfrom being depleted of their oxygen, and conse-quently of their life, all countries around the Balticmust reduce their discharge of directly or indirectlyoxygen-demanding substances.

ORGANIC POLLUTION AND MARINELIFE

As already intimated, many coastal areas are moreor less affected by pollution of oxygen-demandingsubstances. A great number of investigations havebeen carried out on these problems in all Balticcountries. It is impossible to mention them here,and the reader is referred to the extensive literaturelists in the Report on Baltic pollution recentlypublished by ICES.5

Among the main areas of investigation concern-ing the influence of sewage water are the fiords ofSchleswig-Holstein, the Bay of Lubeck, the

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THE BALTIC SEA TODAY 67

Gdynia-Gdansk region, the Bay of Riga, the Gulfof Finland and the archipelago off Stockholm. Theinfluence of industrial pollution has especially beeninvestigated outside the paper and pulp plants alongthe coasts of Finland and Sweden.

The results of most investigations show damageto marine flora and fauna. Furthermore, manyareas have become less valuable as recreation areas,e.g. by increased quantities of coliforme and otherbacteria. Economic setbacks have hit some areaswhere fishery has become more or less impossible.

As to the open sea, there are considerably fewerbiological investigations. According to the opinionof some scientists primary production has increasedin the surface layers, at least in some parts of thesouthern and central area. This may have a bene-ficial influence, e.g. for the fishery of pelagic fishes.Since large water volumes above the deeper partsof the sea now contain very little or no oxygen,fishes in the deeper layers have moved from theseareas. This may have given rise to a higher popula-tion density in the adjacent oxygen-containingareas, and if this is the case the economic damagefor the fishery is very restricted. There is, however,reason to believe that if the oxygen-deficient watervolumes become too large this must decrease thetotal fish population to such a degree that fisherieswill suffer.

As will be seen in the next section, marine life ofboth coastal and open sea areas is threatened alsoby other things.

POLLUTION BY TOXIC SUBSTANCES

Hundreds of substances known to be toxic formarine life are discharged into the Baltic. Theyderive from sewage water and industrial and agri-cultural waste waters and may even be carried outby the air, falling down with the rain and snow.Many of them are easily taken up by organismswhich tend to accumulate them, and when certainthreshold values are reached they become danger-ous. Predators eating contaminated food may inthis way ingest very high concentrations and viafish, for example, toxic substances may reach man.

As is well known, DDT is found in organismsover the whole world, even where it is not used.This dispersal has, on the whole, occurred sinceWorld War II, that is during about 25 years. This is,among other things, due to the fact that it is veryslowly broken down (also its breakdown productshave in many cases proved to be toxic). Swedish

investigations have shown that the complex ofpolychlorinated biphenyls (PCB) deriving fromcertain industries and from many ship-paints havesimilar toxic effects and that they are still moreresistent than DDT.6

The DDT and PCB concentrations in marineanimals in the Baltic and on the Swedish west coasthave been investigated for a few years. The resultshitherto obtained show that certain fishes and fish-eating seals and sea-birds from the Baltic open seamay have concentrations 10 times or more of thesesubstances than corresponding animals from theSwedish west coast.7 This indicates that there is ahigher accumulation of DDT and PCB in the Balticwaters than in the waters of the Skagerrak. Theincreased accumulation must be due to the poorwater exchange between the Baltic and the sea areaoutside, causing a long residence time of the Balticwater (the average residence time is calculated tobe about 20 years5 but differs, of course, in differ-ent parts).

There is reason to believe that also other toxicsubstances accumulate in the Baltic waters, andthe situation is alarming. Many scientists considerthis problem to be greater than the problem ofoxygen-demanding substances. It has, for instance,been shown in investigations outside the Balticarea that the presence of DDT in the water even insuch low concentrations as a few ppb stronglyinfluences the uptake of carbon by marine algae8

thus reducing the rate of primary productions. Itwas also shown that a DDT concentration of 20 ppbnegatively influences the learning ability of trout.9

If the DDT content of the Baltic waters becomestoo high we may expect disturbances in the migra-tion of salmon from the sea to their home rivers,which they find by using their organs of smell andmemory.

Mercury compounds have been used as pesticidesin several countries. Especially in Finland andSweden they have been used as fungicides andslimecides in the paper- and pulp industries. Theyare also derived from other sources.

High mercury contents have been found in fishfrom inland lakes and coastal waters in Denmark,10

Finland11 and Sweden.12 In Sweden, waters witha higher content than 1 mg Hg/kg wet weight fishhave been declared prohibited fishing areas, whichmeans that fish from them can neither be sold norgiven away as gifts. About ten such areas arespread along the Baltic coast, but hitherto there isno evidence of a high mercury content in fish fromthe open sea.

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Other heavy metals are known to occur in thewater and sediments in many places along thecoasts. In Sweden, and probably also in otherBaltic countries, investigations have recently beenstarted to elucidate how marine life is influenced.

One source of toxic substances are materialsdumped from ships into the open sea. After WorldWar II British and probably other ships dumpedGerman war material into the Bornholm Deep.Mustard gas from these dumpings causes consider-able trouble for fishing in this area and manyfishermen have been injured during recent years.The gas containers are often found far outside thedumping area marked on the charts.

OIL POLLUTION

Oil pollution increases rapidly in the Baltic andnew oil slicks are reported almost every day.Damage has occurred in the Swedish and Finnisharchipelagos, influencing recreation areas, fishinggear and sea-bird and other marine life. Also in theopen sea and in harbour areas of other countriesoil pollution is a problem, not the least because ofthe effects of some of the means of combating theoil. It is also known that some air-borne pollutants,like DDT, easily dissolve in oil, and via bacteriadigesting oil they can reach the food productionchains in the water.

Underwater prospecting for oil will be started inthe southern Baltic proper in the near future. Ifoil is found, it is important that every kind of pre-caution is taken to prevent accidents like that whichoccurred at Santa Barbara outside California. Suchan accident would be a catastrophe for an enclosedsea area like the Baltic.

OTHER KINDS OF POLLUTION

Radioactive pollution is strictly controlled in allBaltic countries and presents for the moment noimmediate problems. Several planned nuclear powerplants, a few of which are now under construction;may give rise to an increased radioactivity whenthey are completed, unless very careful precautionsare taken. From these plants, and other kinds ofelectricity power stations, heated cooling water maygive rise to local problems. Other pollution sourcesare the heavy ship traffic, sand-sucking operationsand deposition of mud and sludge. They are, how-ever, as yet of only minor and very local importance.

INTERNATIONAL CO-OPERATION

As it has been made clear from the above discussionthe Baltic Sea is polluted in different ways and thereare signs of a continuous deterioration of thesituation. Even if most pollutants stay in the coastalareas, some of them may reach international waters,and substances like pesticides and oil may passfrom one country to another. The Baltic pollutionproblem is thus to a great extent an internationalone, and different kinds of co-operation betweenthe countries have been evolved during recent yearsin order to try to get the situation under control.On the whole we are, however, only at the begin-ning of this. One great difficulty is that the GermanDemocratic Republic is not recognized by some ofthe other countries. This seems to make officialagreements for the whole area rather impossible.Much of the developing co-operation, therefore,rests on a bilateral basis.

Since 1955 Denmark and Sweden have co-operat-ed as regards the conditions of the Oresund andthey are also carrying out some common investi-gations in the Belt Sea. The German DemocraticRepublic and Poland co-operate on commonproblems in the Baltic border area between thecountries. Finland and the U.S.S.R. started in 1968a rather extensive collaboration on conditions inthe Gulf of Finland. Finland and Sweden worktogether to improve, among other things, theabatement of wastes from the cellulose industry.Negotiations concerning collaboration betweenSweden and the U.S.S.R. have just been started.

Within the International Council for the Explora-tion of the Sea (ICES) joint works on hydrographi-cal and fishery problems have been going on for along time. The German Democratic Republic is theonly Baltic state which is not a member of ICES,but it takes part in the joint hydrographical workof the unofficial organisation of "The Baltic Oceano-graphers". In 1969-1970 this body carried out along expedition called the "Baltic Year" in whichresearch ships from all Baltic countries succeededeach other in an almost continuous hydrographical(and partly biological) survey over a period of about15 months at a fixed net of stations, mainly in theBaltic proper. The "Baltic Year" happened tobegin just after the above-mentioned influx of newoxygen-containing water into the deep basins, andinteresting results have come to light13 (see alsothe proceedings of the 7th Conference of "TheBaltic Oceanographers" in Helsinki, May 1970).

In 1968 the organization, the Baltic Marine

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Biologists, was founded to facilitate co-operationbetween people concerned with biological prob-lems. It arranges Baltic marine biological symposiaevery second year (the next will be in Stockholm inJune, 1971).

REFERENCES

1. A. Voipio, "Hydrographie aspects on the pollution ofthe Baltic Sea" Lecture at the 7th Conference of theBaltic Oceanographers, Helsinki (11-15 May 1970)(Mimeogr.).

2. G. Otterlind, "Östersjöns hydrografi och fisket". 1. Salt-halt, temperatur och strömmar. Ostkusten 40, 4-6 (1968).

3. S. H. Fonselius, "Hydrography of the Baltic deep basins—III" Fishery Board of Sweden, Series Hydrography,Rep. No. 23. 97 pp. (1969).

4. S. H. Fonselius and Ch. Rattanasen, "On the waterrenewals in the Eastern Gotland Basin after WorldWar II" Meddel, fr. Havsfiskelabomtoriet, Lysekil,No. 90. 6 pp. (Mimeogr.) (1970).

5. ICES Report of the Working Group on Pollution ofthe Baltic Sea. International Council for the Explorationof the Sea. Cooperative Research Report No. 15. 86 pp.

6. S. Jensen, Miljögiftproblematik. Flora och Fauna 5,190-195 (1968).

7. S. Jensen, A. Johnels, M. Olsson and G. Otterlind,

"DDT and PCB in marine animals from Swedish waters"Nature 224, 247-250 (1969).

8. C. F. Wurster, "DDT reduces photosynthesis by marinephytoplankton" Science 159, 1474-1475 (1968).

9. J. M. Anderson and H. B. Prins, "Effects of sublethalDDT on a simple reflex in Brook Trout" Journal Fish.Res. Board Canada 27, 331-334 (1970).

10. S. Dalgaard-Mikkelsen, "Kvicksølvforekomsten i miljøeti Danmark" Nordisk Hygienisk Tidskrift 50, 34-36(1969).

11. E. Häsänen and V. Sjöblom, "Kalojen elohopeapitoisuuSuomessa vuonna 1967" Suomen Kalatalous, No. 36.24 pp. (1968).

12. G. Westöö and K. Norén, "Kvicksilver och metylkvick-silver i fisk" Vår Föda 10,135-178 (1967).

13. S. Carlberg (ed.), "Compiled cruise-reports from theBaltic Year 1969-70" Meddel, fr. Havsfiskelaboratoriet,Lysekil No. 87 (Mimeogr.) (1970).

14. S. H. Fonselius, "Hydrography of the Baltic deep basins—II" Fishery Board of Sweden, Series Hydrography,Rep. No. 20, 31 pp. (1967).

15. E. Francke and D. Nehring, "First results on a new in-flow of high saline water into the Baltic during February1969" 7th Conference of the Baltic Oceanographers,Helsinki (11-15 May 1970) Abstracts.

16. D. Nehring, E. Francke and H. J. Brosin, "Observationson the Oceanological variations in the Gotland Deepduring the turnover in October 1969" 7th Conference ofthe Baltic Oceanographers, Helsinki (11-15 May 1970)Abstracts.

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