Artificial Radionuclides in the Northern European Marine Environment

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StrålevernRapport 2000:1

Artificial Radionuclides in the Northern European Marine Environment

Distribution of radiocaesium, plutonium and americium in sea water and sediments in 1995

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This report is based on the Cand. Scient. Thesis:

Grøttheim S., 1999. Artificial Radionuclides in the Northern European Marine Environment in 1995. Distribution of plutonium, americium and radiocaesium in seawater and sediments. Cand. Scient. Thesis. Oslo: Department of Biology, Section of Marine Zoology and Marine Chemistry, University of Oslo, 1999.

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3. Results 28 3.1 Radiocaesium in sea water 28 3.1.1 Distribution of ¹³⁷Cs and ¹³⁴Cs in surface sea water 28 3.1.2 Vertical distribution of ¹³⁷Cs in the water column 29 3.2 Transuranics in sea water 35 3.2.1 Distribution of ^239,240Pu, ²³⁸Pu and ²⁴¹Am in surface sea water 35 3.2.2 Vertical distribution of ^239,240Pu, ²³⁸Pu and ²⁴¹Am in the water column 39 3.2.3 Pu-238 to ^239,240Pu ratios in sea water samples 52 3.3 Sedimentological parameters 54 3.3.1 Dating of sediments using radiochronological techniques 54

3.3.2 Grain-size distribution 57

3.4 Radiocaesium in sediments 58 3.4.1 Cs-137 and ¹³⁴Cs in sediment profiles 58 3.4.2 Distribution of ¹³⁷Cs and ¹³⁴Cs in surface sediments 62 3.5 Transuranics in sediments 65 3.5.1 Distribution of ^239,240Pu, ²³⁸Pu and ²⁴¹Am in surface sediments 65 3.5.2 Pu-238 to ^239,240Pu ratios in surface sediments 70

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4. Discussion 71 4.1 Radiocaesium in sea water 71 4.1.1 Distribution of ¹³⁷Cs and ¹³⁴Cs in surface sea water 71 4.1.2 Vertical distribution of ¹³⁷Cs in the water column 77 4.2 Transuranics in sea water 78 4.2.1 Distribution of ^239,240Pu and ²³⁸Pu in surface sea water 79 4.2.2 Vertical distribution of ^239,240Pu and ²³⁸Pu in the water column 84 4.3 Sedimentological parameters 87 4.3.1 Dating of sediments using radiochronological techniques 87 4.3.1.1 Profiles of ²¹⁰Po and sedimentation rates 88

4.3.1.2 Dating and resolution 89

4.3.2 Grain-size distribution 90

4.4 Radiocaesium in sediments 91

4.4.1 Cs-137 in sediment profiles 92

4.4.1.1 Sediment layers with “unexpected” ¹³⁷Cs activity 92

4.4.1.2 Cs-137 activity peaks 93

4.4.2 Distribution of ¹³⁷Cs and ¹³⁴Cs in surface sediments 94 4.5 Transuranics in sediments 95 4.5.1 Distribution of ^239,240Pu and ²³⁸Pu in surface sediments 97 5. Conclusion 100

Acknowledgement 102

References 103

Personal communication 108

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1. Introduction

In addition to naturally-occurring radionuclides in water masses and sediments of the marine environment, a number of artificial radionuclides have been produced and released to sea water. The major contributions of artificial radionuclides to the northern marine environment originate from global fallout from previous atmospheric nuclear weapons tests, discharges from the Sellafield spent nuclear fuel reprocessing plant (UK) and fallout from the accident at the Chernobyl nuclear power plant (Ukraine) in 1986.

In a global perspective, the dominating source to radioactive contamination is global fallout of debris from the atmospheric nuclear bomb tests conducted in different parts of the world between 1945 and 1980. In total, 520 atmospheric nuclear explosions were carried out, with periods of most intensive testing in the years 1952-1954, 1957-1958 and 1961-1962

[UNSCEAR, 1993]. The atmospheric nuclear weapons tests have mainly been conducted by the United States and Soviet Union, but also by the United Kingdom, France and the People’s Republic of China. The three major tests sites for atmospheric testing were Novaya Zemlya (FSU) in the Arctic Ocean, the Bikini and Eniwetok Islands (US) in the Pacific Ocean and the Nevada test site [Strand HWDO., 1997b]. It has been demonstrated that 12% of the fallout activity has been deposited close to the test site, 10% has been deposited in a band around the earth at the latitude of the test site (tropospheric fallout) and 78% of the fallout activity has been spread over larger areas, and mostly in the same hemisphere as the test site, producing global falloutAs most of the weapons tests have been carried out in the northern hemisphere, the largest radioactive contamination is found there [UNSCEAR, 1993]. These weapons tests have contributed to an overall background contamination level of long-lived fission products and transuranics in the northern marine environment.

After the atmospheric nuclear weapons test, the accident at the Chernobyl nuclear power plant in the Ukraine (see Figure 1.1) on April 26, 1986, was the most significant large-scale source of environmental radioactive contamination [Strand HWDO, 1997b]. The accident was a

consequence of uncontrolled fission in the reactor, followed by a powerful explosion and fire.

The radioactive materials released were carried away in the form of gases and dust particles by air currents. They were widely dispersed over the Soviet Union and several European

countries [UNSCEAR, 1988]. Whereas the weapons tests produced almost no ¹³⁴Cs, the ¹³⁴Cs to ¹³⁷Cs ratio in fallout from Chernobyl was approximately 1:2 (in April 1986) [IAEA, 1986].

This ratio can be used to trace Chernobyl-derived radiocaesium¹. According to IAEA (1991), the total release of α-emitting plutonium nuclides from the Chernobyl accident was

approximately 0.12 % of the total ¹³⁷Cs released to the environment. Furthermore, most of the plutonium nuclides released from the accident were deposited in the vicinity of Chernobyl [IAEA, 1991]. This indicates that the accident has contributed with very low levels of plutonium to the marine environment. Currently, regarding the northern Seas, the main contribution to Chernobyl-derived radiocaesium originates from the heavily contaminated Baltic Sea, reaching the northern marine environment by ocean currents: According to Josefsson (1998), more than 90% of the net outflow of ¹³⁷Cs from the Baltic consists of Chernobyl activity.

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Figure 1.1Illustration of the site at Chernobyl in Ukraine, the dumping sites of nuclear waste in the Kara Sea, the sunken submarine Komsomolets in the Norwegian Sea and Russian nuclear installations (Mayak, Tomsk-7 and Krasjonoyarsk-26) releasing radionuclides to the Russian rivers Ob and

Yenisey

A nuclear fuel reprocessing plant is recovering spent nuclear fuel for reuse in fission reactors.

The remaining radionuclides are either sent to final storage or released to the environment [UNSCEAR, 1993]. In Figure 1.2, the locations of the western European reprocessing plants Sellafield (UK), La Hague (France) and Dounreay (Scotland) are presented. Liquid radioactive waste from the operation of these plants are discharged via pipelines directly into the Irish Sea, the English Channel and into Scottish coastal waters, respectively. Soluble radionuclides from these sources are transported further northwards with ocean currents. Sellafield

(formerly Windscale) has been the main contributor to activity releases among the 3 western European reprocessing plants. Maximum discharges from Sellafield occurred during the mid seventies, but have, with the exception of ⁹⁹Tc-discharges, continually been reduced since that time [Gray HWDO., 1995]. In addition to these western European reprocessing plants, the Arctic may also have received an input of different radionuclides from Russian reprocessing plants situated in the tributaries of the Russian rivers Ob and Yenisey (see Figure 1.1).

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Several sources exist which represent a potential risk to future releases of radionuclides.

Among these are radioactive waste dumped in containers in the Barents and Kara Seas by the Former Soviet Union (FSU), and the sunken submarine Komsomolets in the Norwegian Sea.

The dumping areas and the location of the sunken submarine Komsomolets are given in Figure 1.1. Several investigations have been conducted to detect any leakage from these sources. The joint Russian Norwegian expert group have been investigating the condition of the contained dumped objects and analysed sediment and water samples at the dumpsites.

According to Strand HWDO. (1997a), elevated levels of radionuclides in sediments collected in the vicinity of the dumped objects demonstrated that leakage occur. No contribution to the open sea has been detected [Strand HWDO., 1997a]. The Russian nuclear submarine

Komsomolets caught fire and sank 180 km southwest of Bear Island in the Norwegian Sea at a depth of 1700 metres, April 7th, 1989. The submarine contains a nuclear reactor and two torpedoes with nuclear warheads. The reactor was shut down in an orderly manner prior to sinking. A small leakage of ¹³⁷Cs to the surrounding water has been detected, although it has been difficult to detect because of the great dilution that has occurred [Kolstad, 1995].

The continuation of the North Atlantic Current into the English Channel, the Northern Seas (the Irish Sea, the North Sea, the Norwegian Sea, the Barents Sea and the Greenland Sea) and the Polar Basin is shown in Figure 1.2. Atlantic water is defined as water having salinity > 35

‰ [Sakshaug HWDO., 1994]. The North Atlantic Current is a relatively slow moving (< 0.5 knot) surface current and is in principally driven by the north wind [Kiilerich, 1965]. The transport of radiocaesium (in the form Cs⁺) and other soluble radionuclides with the surface circulation pattern from the Irish Sea to the Arctic has been described in many studies, and summarised by Kershaw and Baxter (1995). After releases to the point source in the Irish Sea, radiocaesium is in principal transported with the surface currents northwards, YLD the North Channel and around the coast of Scotland into the western part of the North Sea [Kershaw and Baxter, 1995]. From the point source off the north coast of Scotland, the soluble radionuclides released from Dounreay are transported with the surface currents following the Scottish coast into the western part of the North Sea. According to Guéguéniat HWDO. (1996), soluble

radionuclides discharged into the English Channel from La Hague are transported south and east of the Sellafield activity in the North Sea.

The origin of the water masses in the North Sea are Atlantic water with a high salinity and freshwater from land [Aure, 1998]. The North Sea receives Atlantic water from the

Norwegian Sea in the north, mainly through the Shetlands and the Faroe Islands, and through the English Channel in the south [Kiilerich, 1965]. The circulation pattern of the North Sea is mainly anti-clockwise, in which nearly all water flows YLD Skagerrak. It is important to stress that this is a climatic average situation, and that changes in this pattern occur [Sætre, 1996].

Skagerrak is also receiving Chernobyl-derived radiocaesium with the out-flowing low-salinity surface waters from the Baltic [Strand, 1994].

Soluble radionuclides are transported further northwards with the Norwegian Coastal Current (NCC) [Kershaw and Baxter, 1995]. The NCC, which is generated by the out-flowing surface waters from the Baltic, flows northwards off the Norwegian coast as a wedge within the Atlantic water masses. At the boarder of Russia, the NCC becomes the Murman Coastal Current. At approximately 40° to 45° east, the coastal current is supported with low-salinity water from the White Sea [Sakshaug HWDO., 1994].

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Figure 1.2 The surface circulation pattern of the Northern Seas. Data used with permission from Grid- Arendal. The site at Sellafield on the west coast of UK, Dounreay on the north coast of Scotland and La Hague in France are illustrated

The continuation of the North Atlantic Current (NAC) is flowing northwards along the continental slope, parallel and west for the NCC [Sakshaug HWDO., 1994]. According to

Josefsson (1998), off the southern Norwegian coast and outwards, the NAC and the NCC stay separated. On their way northwards they become partly mixed [Josefsson, 1998]. Off Troms, northern Norway, the Atlantic current splits into 2 branches, one branch passes eastwards into the Barents Sea as the North Cape Current and one passes northwards off the western coast of Svalbard as the West Spitsbergen Current (WSC). The North Cape current splits into a

southern and a northern branch. Whereas the southern branch joins the NCC eastwards, the northern branch bends under the cold and less salty Arctic water masses and becomes a subsurface current. The main part of the WSC continues northwards along the western coast of Spitsbergen, before it continues through the Fram Strait into the Arctic Ocean further eastwards along the Siberian coast. The less significant part of the WSC bends westwards towards Greenland, joining the south-going East Greenland Polar Current (EGC) as a

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the Norwegian Sea, the Barents Sea, the Greenland Sea, the Iceland Sea and in the North Atlantic. The Norwegian Radiation Protection Authority (NRPA) was also present, as a result of an invitation from BSH. This was an opportunity for the NRPA to collect sea water and sediments and to study the dispersion of artificial radionuclides in the northern marine environment.

The objectives of this study have been to:

• Collect samples of sea water and sediments from the northern marine environment during the German cruise

• Measure the activity of relatively long-lived and important artificial radionuclides such as

137Cs, ¹³⁴Cs, ^239,240Pu, ²³⁸Pu and ²⁴¹Am of the samples, to determine sedimentation rates and grain-size distribution of sediments at selected locations of the study area

• Interpret the results by use of (statistic and) graphical presentations

• Understand and explain the horizontal and vertical distribution of the artificially radionuclides² in sea water and sediments of the northern marine environment in the

context of sources, sea currents, sedimentological parameters and behaviour of the radionuclides in the marine environment

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2. Materials and methods

2.1 The cruise “R/V Gauss 261”

During June and July 1995, the BSH conducted an expedition, R/V Gauss 261, to the

Northern Seas. One of the purposes of the cruise was to collect samples of sea water from the northern marine environment for subsequent analysis on artificial radionuclides. The

expedition route was planned by BSH, based on known radioactive contamination sources and oceanographic conditions in the Northern Seas. The cruise was divided into 2 parts. The first part of the cruise included stations in the eastern part of North Sea, Skagerrak, the Norwegian Sea and the Barents Sea and the second part of the cruise included stations in the Greenland Sea, the North Atlantic and the western part of the North Sea.

BSH was present onboard by several scientists and engineers, among these was a group working on artificial radioactive tracers and a group of physical oceanographers. The NRPA had 2 representatives. The author of this report participated in the first part of the cruise (Station 1-54). Another scientist, also from NRPA, took over the sampling in the second part of the cruise (Station 55-92). The determination of sampling locations for NRPA was made by the Norwegian participants after discussions and advice from experienced employees at NRPA prior to the cruise. Other arrangements for the Norwegian part of the cruise, e.g.

preparation of equipment and chemicals required, were made by the author of this report.

2.1.1 The investigation area

In the following, a brief presentation of the hydrography of the Northern Seas is given:

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Atlantic water enters the Irish Sea from the north and from the south, the latter predominating.

The inflow is mainly balanced by an outflow northwards through the North Channel. There is a counter-clockwise gyral circulation pattern within the Irish Sea, with a very small return flow southwards.The Irish Sea can be sub-divided into two regions. The western part consists of a deep channel exceeding a depth of 100 metres. In the eastern part, the depth seldom exceed 50 metres. In the eastern part of the Irish Sea, the salinity is markedly influenced by freshwater input [Kershaw HWDO., 1992].

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The North Sea boundary to the Norwegian Sea can be regarded as a line from Shetland to the Norwegian Coast near Bergen. In the south it is constricted at the Straits of Dover and in the east it borders on Skagerrak. The North Sea is shallow, the south and south-eastern parts are mostly less than 50 metres. In the north, the water depth is 120-145 meters [Kiilerich,1965].

The Norwegian Trench, outside the Norwegian coast, is deeper, exceeding 700 meters in Skagerrak [Sætre, 1997]. The North Sea receives Atlantic water with high salinity from the Norwegian Sea in the north and through the English Channel in the south. In a climatic average situation, the water circulation in the North Sea is mainly anticlockwise and most of

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This brackish water is a surface current and follows the Norwegian Coast northwards as the Norwegian Coastal Current. The out-flowing surface water from the Baltic Sea is balanced by the outflow of an underlying current of salt and denser water from the North Sea. The salinity in the surface water in the North Sea is generally more than 35 in the northern part. In the south-western part the surface salinity is less, 32-34, because of inputs of freshwater from the continent. The circulation pattern varies with in-flowing Atlantic water, meteorological conditions and river run-off [Sætre, 1996].

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The boundary between the North Sea and Skagerrak can be considered as a line between Lindesnes in Norway and Hanstholm in Denmark. In the south, the boarder of Kattegat is regarded as a line from Skagen in Denmark to Marstrand in Sweden. The water in Skagerrak consists mainly of three different masses of water which are Skagerrak Coastal Water, Skagerrak Water and Atlantic Water, in addition to the brackish water from run-off and from the Baltic Sea. Skagerrak Coastal Water is a mixture of water from the Baltic Sea, river water and water from the southern and central North Sea. The salinity and temperature is in the range 25.0 - 32.0 and 0°C - 20°C, respectively. The Skagerrak Water has a greater supply of water masses from the central North Sea resulting in a higher salinity, from 32.0 - 35.0, and temperature between 3°C - 16°C. Supply of Atlantic water from the Norwegian Sea to Skagerrak has a salinity more than 35.0 and temperature between 5.5°C and 7.5°C. This salt Atlantic water bends under the less dense Skagerrak Water [Sætre, 1997].

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Bordering the North Atlantic are the adjacent Norwegian and the Greenland Seas. The North Atlantic Drift Current (NAC) flows northwards between the Shetland and Faroe Islands into the Norwegian and the Greenland Seas [Pickard and Emery, 1982]. According to Kiilerich (1965), at this location the mean salinity and temperature of the Atlantic Water are 35.45 and 10°C, respectively. In the Norwegian Sea, Atlantic Water is flowing northwards along the continental slope, parallel and west for the NCC [Sakshaug HWDO., 1994]. The East-Greenland Current, originating from the out-flowing Arctic water and, to some extent, from the NAC, flows south-westwards off the Greenland coast. Between the north-going North Atlantic Drift Current in the Norwegian Sea and the south-going East-Greenland Current, there are gyral circulations [Pickard and Emery, 1982].

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The north coast of Norway and Russia forms the southern border on the Barents Sea. In the west, the border is normally considered as the continental slope between Norway and Svalbard. The boundary in the north is regarded as a line between Novaya Zemlya, Frans Joseph Land, the Viktoria Islands and the northern point of Spitsbergen. Novaya Zemlya forms a natural border between the Barents and the Kara Seas. The Barents Sea which lies inside the continental shelf, is on average 230 metres deep and contains several banks and basins. There are two main directions in the currents within the Barents Sea: in the south they move eastward and in the north they move westward. Off the north-western coast of Norway, the continuation of the NAC splits into the West-Spitsbergen Current (WSC) and the North Cape Current. The WSC continues northwards and west of Spitsbergen into the Arctic Ocean, with a branch joining the East-Greenland Current southwards. The North Cape Current moves eastwards into the Barents Sea.

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A branch of the North Cape Current bends under the cold Arctic water of the Barents Sea, another branch continues eastwards and parallel with the NCC, a third branch moves northwards by the west-coast of Novaya Zemlya and enters the Kara Sea. In the northern Barents Sea, Arctic water is transported westwards towards Spitsbergen by the Persey Current.

East of Spitsbergen, the Persey Current receives Arctic water from the north, and is from here termed as the Bear Island Current. The Bear Island Current rounds the south point of

Spitsbergen and moves northwards, inside and parallel to the WSC. The Barents Sea consists of three types of water masses; Atlantic Water, Coastal Water and Arctic Water. Atlantic Water in the Barents Sea is regarded with a salinity greater than 34.95 and temperature above 3°C. The Norwegian and Russian Coastal Water has a lower salinity than the Atlantic Water.

Arctic water has a temperature below 0°C and a salinity between 34.4-34.6 [Sakshaug HW DO.,1994].

In Figure 2.1, a map of the cruise is shown. The labelled stations show the sampling locations for NRPA.

The fifteenth of June, the cruise started in the south-eastern part of the North Sea, and

travelled north-wards YLD Skagerrak and the Norwegian Trench to the Norwegian Sea and the Barents Sea, following the main surface circulation pattern in this area. The route involved both locations on and off the Continental Shelf in the Norwegian Sea. Locations in the vicinity of the sunken submarine Komsomolets, 180 km south-west of Bear Island in the Norwegian Sea, included the stations 34C, 34N, 34W, 34S and 34E. Station 34C (i.e. central) was located in the vicinity of the wreck, whereas the other Stations were located approximately 0.5

nautical mile north, west, south and east, respectively, of Komsomolets. The eleventh of July, the cruise continued southwards, following the main surface circulation pattern in the

Greenland Sea. The cruise went further towards the western part of the North Sea, and terminated in the end of July. The presence of drift ice in the Greenland Sea, resulted in the fact that there was no sampling at the Stations 65 and 66. The Stations 65 and 66 have therefore been excluded from the expedition route.

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Figure 2.1 Map of the expedition route, R/V Gauss 261. The sampling locations for NRPA stand out and are labelled. * Station 34includes 5 sampling locations, i.e. 34C, 34N, 34W, 34S and 34E. Note that the Stations 65 and 66 have been excluded from the expedition route

Several stations have been difficult to allocate to one or other of the sea areas³. In these cases, subjective judgement (of the author) has been used in allocating the stations, as presented in Table 2.1.

Table 2.1 Allocation of the stations to the sea areas, for this report.

Sea area Stations

North Sea 1-6, 13-20, 75 - 92 Norwegian Trench 11-16

Skagerrak 7-12

Norwegian Sea 21-38

Barents Sea 39-54

Greenland Sea 55 -63

Iceland Sea 64-71

North Atlantic 72 - 74

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2.1.2 Determination of sampling for NRPA

The determination of sampling locations for NRPA, for collecting sea water and sediments from the Northern Seas for subsequent analysis on ¹³⁷Cs, ¹³⁴Cs, ⁹⁰Sr, ^239,240Pu, ²³⁸Pu and

241Am, were made by the Norwegian participants prior to the cruise. The framework for this was the information available about sources to radioactive contamination and the sea water circulation pattern in the Northern Seas.

As the cruise served 92 stations, a selection of sampling locations representative for each sea area were made by the NRPA as a consequence of capacity and means for this study. The selected sampling stations for the NRPA are shown in Figure 2.1. However, several of the planned stations for collecting sediments for the NRPA were excluded, as a consequence of unsuccessful sampling due to large depths, stony bottoms etc. (e.g. the Stations 60, 71, 72, 73, 74, 76 and 88). Sampling stations of interest for the NRPA were in the vicinity of the main radioactive sources, and in increasing distance away from these sources following the main surface circulation pattern in the Northern Seas. Sampling locations in the vicinity of the main sources included the western part of the North Sea (in the vicinity of Sellafield and Dounreay) and Skagerrak (which receives water from the Baltic, currently acting as the main source for Chernobyl-derived ¹³⁷Cs [Strand HWDO., 1996]). Skagerrak is also an important area for investigation owing to the fact that an important transport route for releases of radioactive discharge from the European reprocessing plants (Sellafield, Dounreay and La Hague) to the Northern Seas by the sea water circulation pattern is YLD Skagerrak. Collecting of surface seawater and sediments were also planned for intercomparison purposes between BSH and NRPA.

In Table 2.2 and 2.3, the sampling stations for seawater and sediments, respectively, for NRPA have been shown, together with the sampling depths and the radionuclides measured.

2.1.3 Collecting and pre-treatment of samples

Sampling was performed during the R/V Gauss 261 expedition in the period 15^th of June to 29^th of July 1995. The vessel contained all necessary sampling equipment ⁴. BSH collected a large amount of sea water samples for analysis on alpha and gamma-emitting radionuclides.

These samples were pre-treated onboard according to their analytical procedures. The water samples were not filtered. The participants from the NRPA collected sea water and sediments for analysis of alpha, beta and gamma-emitters. These samples were pre-treated on board by the Norwegian participants in accordance with own analytical procedures, as described in the following Sections. These water samples were neither filtered.

2.1.3.1 Collecting and pre-treatment of sea water

Sea water was collected by experienced members of the crew, according to the routine on board. Sea water was collected by 500 litres and 270 litres samplers of Gerard-Ewing design.

These samplers were made from glass-fibre-reinforced plastic, as described by Herrmann HW DO. (1998). The sampling depth was measured by a meter wheelconnected to the wire, which was set in the zero position at the sea surface. Maximum depth was measured by echo sounding.

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The sampling equipment for sea water is shown in Figure 2.2.

Figure 2.2 To the left, a sampler rosette, for measurements of salinity, temperature and density in sea water. To the right, a 270 litres Gerard-Ewing sampler

Profiles of salinity, temperature and density in the water column were measured by a group of oceanographers from BSH, using a CTD probe attached to a sampler rosette.Two different sampler rosettes were used for this purpose, depending on the maximum sea water depth at the sampling locations. One sampler rosette consisted of 12 bottles and the other of 24 bottles, the latter was used in the deepest parts of the investigation area. As the sampler rosette was lowered into the sea water, one by one, the bottles were filled with sea water at selected depths in the water column.

Salinity, temperature and density were measured LQVLWX. Salinity was also measured in the sea water samples at BSH’s laboratories in Hamburg: Sea water was transferred from the bottles of the sampler rosette to glass-flasks, which had been rinsed by flushing the bottles with the sea water. The flasks were put in appropriate boxes and stored at room-temperature until subsequent analysis for salinity at BSH.

The precipitation tanks were made of acid, alkali and rust resistant polyethylene. The tanks had earlier been calibrated at the NRPA up to 200 litres ± 1 litre, and were marked for each 10 litres. The investigation vessel had the necessary equipmentfor pumping sea water to the precipitation tanks, and was carried out according to the procedures onboard.

A total of 15 samples of sea water were collected for analysis of alpha-emitters (each 200 litres), 5 sea water samples for analysis of beta-emitters (each 100 litres) and 13 samples of sea water for analysis of gamma-emitters (each 200 litres). Among these was one sample from drift ice in the Greenland Sea collected for analysis of alpha-emitters. BSH and NRPA

collected surface sea water (for subsequent analysis of alpha and gamma-emitters) in the North Sea for intercomparison purposes.

In Table2.2, an overview of the sea water sampling stations for NRPA is shown, together with sampling-depths and the radionuclides that have been measured at NRPA. Sea water

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Table 2.2 Sampling stations for sea water for NRPA, together with depths and the radionuclides measured at NRPA, with the exception of ⁹⁰Sr that was not measured. At the Stations 83 and 84, surface sea water were collected for intercomparison purposes between BSH and NRPA

Station Depth (m)

Radionuclides

11 150 ²³⁸Pu, ^239,240Pu and ²⁴¹Am 11 150 ¹³⁷Cs

16 150 ²³⁸Pu, ^239,240Pu and ²⁴¹Am 16 150 ¹³⁷Cs

16 150 ⁹⁰Sr

20 150 ²³⁸Pu, ^239,240Pu and ²⁴¹Am 20 150 ¹³⁷Cs

26 50 ²³⁸Pu, ^239,240Pu and ²⁴¹Am

26 50 ¹³⁷Cs

26 50 ⁹⁰Sr

31 50 ²³⁸Pu, ^239,240Pu and ²⁴¹Am

31 50 ¹³⁷Cs

34/C 1500 ²³⁸Pu, ^239,240Pu and ²⁴¹Am 34/C 1615 ²³⁸Pu, ^239,240Pu and ²⁴¹Am 39 150 ²³⁸Pu, ^239,240Pu and ²⁴¹Am 39 150 ¹³⁷Cs

46 150 ²³⁸Pu, ^239,240Pu and ²⁴¹Am 46 150 ¹³⁷Cs

46 150 ⁹⁰Sr

48 200 ²³⁸Pu, ^239,240Pu and ²⁴¹Am 48 200 ¹³⁷Cs

55 150 ²³⁸Pu, ^239,240Pu and ²⁴¹Am

55 150 ¹³⁷Cs

55 150 ⁹⁰Sr

58 150 ¹³⁷Cs

60* 0 ²³⁸Pu, ^239,240Pu and ²⁴¹Am 63 150 ²³⁸Pu, ^239,240Pu and ²⁴¹Am 63 150 ¹³⁷Cs

63 150 ⁹⁰Sr

70 150 ²³⁸Pu, ^239,240Pu and ²⁴¹Am

70 150 ¹³⁷Cs

83 0 ²³⁸Pu, ^239,240Pu and ²⁴¹Am

84 0 ¹³⁷Cs

*Sample from drift-ice

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The precipitations were made according to the analytical procedure described in Chen HWDO. (1991). The equipment utilised in this process have normally been used as a routine according to the procedures at NRPA.

The sample from drift-ice was melted in the 200 litres tank (to 160 litres) and a precipitation was made in the same way as for sea water, according to the analytical procedure described in Chen HWDO. (1991).

Figure 2.3The precipitate from 200 litres of sea water 3UHWUHDWPHQWRIVHDZDWHUIRUEHWDHPLWWHUV

Unfiltered sea water samples, of 100 litres each, were transferred to four 25 litres plastic-cans (Jerry-cans) and acidified to pH 1-2, by adding 1 ml concentrated HCl / l sea water directly into the cans, in accordance to the method at NRPA normally used for this purpose. The cans were cautiously shaken before they were stored on board at room-temperature.

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The sea water samples were pre-treated according to the NRPA’s method, and carried out with equipment that have normally been used for this purpose. The basic of the procedure was to make a precipitation of Cs by adding ammonium molybdophosphate (AMP) to the water samples. Caesium is adsorbed to AMP, which is insoluble in sea water and precipitates.

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2.1.3.2 Collecting and splitting of sediments

The vessel was equipped with necessary sampling gears for sediments. The sediments were collected by experienced members of the Crew. The sediment samples were collected by two different types of collectors, a large (50 cm x 50 cm) and a small (about 20 x 15 cm) box corer, and a Finnish-design Gemini. According to Nies HWDO. (1990), the Gemini sampler is especially designed for soft sediments. It is a gravity sampler with an inner perspex tube, which is, after sampling, removed from the outer device [Nies HWDO., 1990]. The large box corer was used down to 2200 metres, and the small box corer and the Gemini corer were used down to more than 3600 metres. The sediment cores were 20 cm in length and with inner diameters of 9.4 cm for the box corer and 7.9 cm for the Gemini.

NRPA collected sediments using both the two different box-corers and the Gemini. A total of 35 sediment cores and 4 surface sediments for analysis on alpha- and gamma-emitters were collected. At station 34S (approximately 0.5 nautical miles south of the sunken submarine Komsomolets), south of Bear Island in the Norwegian Sea, sediments were collected for an intercomparison purpose (for alpha- and gamma-emitters) between BSH and NRPA.

The sampling equipment are shown in the Figure 2.4.

Figure 2.4 To the left, a large box corer. To the right, a Finnish-design Gemini which consists of 2 cores

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To obtain sediment FRUHV of the sediment collected by one or other of the box-corers, tubes were put into the sediment, as shown in Figure 2.5, and these were subsequently disengaged by removing the surrounding sediment.

Figure 2.5 Tubes have been put into the sediment collected by the large box-corer

The sediment cores were extruded from the tubes using a piston made for this purpose, in which the cores were divided into increments of 2 cm by a sliding sheet.This was done according to the procedures on board.

The sediment samples, divided into increments of 2 cm, were put into plastic-containers and stored onboard at room-temperature. When the samples arrived to NRPA they were, after registration, stored in a freezer until later analytical procedures and analysis at the institute’s laboratories.

The sediment collected for the intercomparison purpose consisted of the top 1 cm from several sediment cores at Station 34S, and were later mixed and homogenised at the BSH according to the laboratory procedures.

In Table 2.3, an overview of the sampling stations for NRPA for sediments is shown.

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Table 2.3 Sampling stations for NRPA for sediments. The sediment cores were divided into

increments of 2 cm, with the exception of the intercomparison sample* which consisted of the top 1 cm of the sediment

Station Core/ Surface layer Sample depth (m)

11 1 core 535

12 1 core 470

16 2 cores 283

20 2 cores 336

26 2 cores 268

27 2 cores 1100

34C 1 core 1679

34N 1 core 1680

34W 1 core 1688

34S 1 core + Intercomp* 1673

34E 1 core 1666

36 1 core 230

39 1 core 271

43 1 core 282

44 1 core 350

46 1 core 288

48 1 core 430

56 2 cores 3330

62 2 cores 1150

63 2 cores 420

67 2 cores 1140

68 2 cores 1150

69 2 cores 1150

70 surface sample 720

83 surface sample 125 84 surface sample 87

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2.2 Methods of analysis for radionuclides

The samples of sea water and sediments collected were analysed for alpha- and gamma- emitters. Sediment cores from 7 stations ( i.e. 16-1, 26-1, 34C, 46-1, 56-2, 62-2 and 63-2) were measured for ¹³⁷Cs and ¹³⁴Cs by the Institute of Energy Technology (IFE) at Kjeller, Norway, under commission from the NRPA. The radioanalytical results have been exchanged between BSH and NRPA, and with their permission this report includes all radioanalytical results obtained from the expedition: Most of the water samples have been analysed (Pu, Am and radiocaesium) by BSH, whereas the sediments and some additional water samples have been analysed by the NRPA.

2.2.1 Methods of analysis for alpha-emitters

The alpha-emitters ^239,240Pu, ²³⁸Pu and ²⁴¹Am were measured alpha-spectrometrically by semiconductor silicon detectors. As alpha-spectrometry is not able to distinguish between

239Pu and ²⁴⁰Pu because the energies of their emitted alpha-particles are too close to be resolved, these isotopes are measured and reported as the sum, ^239,240Pu. Relative efficiencies of the detectors were in the range 25 to 30%. The resolution of the detectors, the full width at half maximum (FWHM), was approximately 20 keV. The detectors covered the energy interval of 3-7 MeV. All samples were measured for approximately 6-7 days.

2.2.1.1 Methods of analysis for

^239,240

Pu,

²³⁸

Pu and

²⁴¹

Am in seawater

The analytical procedure was performed according to Chen HWDO (1991). The different steps of the procedure have been comprehensively discussed by Sidhu (1997).

2.2.1.2 Methods of analysis for

^239,240

Pu,

²³⁸

Pu and

²⁴¹

Am in sediments

The sediment samples were freeze-dried and manually homogenised, using a mortar of porcelain, with the exception of the intercomparison sample which was prepared at the BSH.

The analytical procedure was performed according to Chen HWDO. (1991).

2.2.2 Methods of analysis for gamma-emitters

The samples collected by the Norwegian participants were subjected to gamma-spectrometry by using HPGe detectors. The laboratory is custom-built with low-background activity resulting in low detection limits. Relative efficiencies of the detectors were in the range 23 to 40%. The resolution of the detectors, the full width at half maximum (FWHM), was less than 1.9 keV for all detectors. Three of the detectors covered the energy interval of 50-2000 keV, and two covered the interval 20-2000 keV. All samples were measured for one to three days.

At NRPA, the detection limits for ¹³⁷Cs and ¹³⁴Cs in the sediment samples ranged from approximately 0.3 - 2 Bq/kg (dry weight).

2.2.2.1 Methods of analysis for

¹³⁷

Cs in seawater

The precipitate from each water sample was filtered through a folded filter. The filter used was suitable for high grade crystalline precipitations. The precipitate was then ashed at 400 °C for three hours and subjected to gamma-spectrometric measurements.

2.2.2.2 Methods of analysis for gamma-emitters in sediments

The sediment samples were freeze-dried and manually homogenised and subjected to gamma- spectrometric measurements.

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2.3 Methods of analysis for sedimentological parameters

2.3.1 Dating of sediments using radiochronological techniques

Radiochronological dating of 8 sediment cores (divided into increments of 2 cm) have been performed by the IFE under a sub-contract for NRPA, as described in the following Section.

Sediment cores were selected (by the author) from each sea area and included the Stations 11 (Skagerrak), 16 (North Sea), 26 (Norwegian Sea), 34C (central Komsomolets), 46 (Barents Sea), 56 (west of Spitsbergen), and 62, 63 (Greenland Sea).

Dating of sediments using radiochronological techniques have been described in many

studies, e.g. Jensen (1995), Tadjiki and Erten(1994), Christensen (1982),Pheiffer Madsen and Sørensen (1979). In order to correct for sediment compression a method described by Tadjiki and Erten (1994) was followed.

2.3.2 Analysis of grain-size distribution

Eight surface sediment samples (top 2 cm) were analysed for grain-size distribution at the Sedimentological Laboratory at the University of Oslo. The sediment samples were selected from the Stations: 11, 12, 34C, 34E, 62, 63, 83 and 84. These sediments were chosen to examine a possibly relation between activity fluctuations and grain-size.

The sediment samples, which had been stored in a freezer, were freeze-dried and subsequently manually homogenised/lightly disaggregated at NRPA’s laboratories. Portions of these

sediment samples, which can be considered to represent the bulk sediment samples, were taken out and delivered to the Sedimentological Laboratory for analysis of the grain-size distribution. These analysis included wet-sieving and sedigraph-recording.

The sediments analysed for grain-size distribution at the University in Oslo were fractionated into 4 different groups, as shown in Table 2.4.

Table 2.4 Classification for grain-size distribution of sediments in this report Grain-size Classification

< 2 µm clay

< 2 µm, 63 µm> silt

< 63 µm, 2 mm> sand

> 2 mm pebbles

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2.4 Intercomparison exercises

2.4.1 Radiocaesium in sea water

In Table 2.5, the results from the intercomparison exercise of radiocaesium in sea water are shown.

Table 2.5 Results from the intercomparison exercise: surface sea water sample at Station 84 in the North Sea. The term N.A. indicates not analysed

&V

%TP

&V

%TP

153$ 12.60 0.50 N.A.

%6+ 11.20 0.31 < 0.3

At the NRPA, the ¹³⁷Cs activity concentration obtained in surface sea water from Station 84 was 12.60 ± 0.50 Bq/m³. The sea water sample was not analysed for ¹³⁴Cs.

At BSH, the obtained activity concentration of ¹³⁷Cs in the sea water sample from Station 84 was 11.20 ± 0.31 Bq/m³. The activity concentration of ¹³⁴Cs in the sample was below the detection limit, 0.3 Bq/m³.

The analytical results of the intercomparison exercise showed that the ¹³⁷Cs activity concentrations of surface sea water (Station 84) obtained by the NRPA and BSH agreed within an uncertainty of 2 standard deviations.

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2.4.2 Transuranics and radiocaesium in sediment

In the Tables 2.6 and 2.7, the results from the intercomparison exercise of transuranics and radiocaesium in sea water are shown.

Table 2.6 Results from the intercomparison exercise at the NRPA: sediment sample, top 1 cm, at Station 34S (approximately 0.5 nautical mile south of Komsomolets) in the Norwegian Sea. All values are in Bq/kg. The uncertainty given with the mean specific activity is the standard deviation of the data set

3X 3X $P &V &V

6SHFLILFDFWLYLW\ 0.09 1.28 1.35 12.40 0.60

0.02 0.11 0.10 0.5 0.1

'/ 0.02 0.02 0.05

6SHFLILFDFWLYLW\ 0.03 1.08 1.24

0.01 0.07 0.09

'/ 0.03 0.02 0.01

0.02 0.10 0.08

'/ 0.04 0.04 0.03

0.01 0.07 0.08

'/ 0.02 0.01 0.02

0HDQ

At the NRPA, the bulk of the sediment sample from Station 34S (which had been prepared at BSH) was measured for gamma-emitting radionuclides. Both ¹³⁷Cs and ¹³⁴Cs were detected with specific activities of 12,4 ± 0.5 Bq/kg and 0.6 ± 0.1 Bq/kg, respectively.

Four parallel samples were then taken out from the bulk of the sediment from Station 34S, followed by analytical procedures and methods of analysis for the transuranics (²³⁸Pu, ^239,240Pu and ²⁴¹Am). The analytical results showed that for 3 of the parallels the specific activities of

238Pu fell within 2 standard deviations, whereas the specific activities of ^239,240Pu and ²⁴¹Am fell within 2 standard deviations for all 4 parallels. The mean specific activity of ²³⁸Pu,

239,240

Pu and ²⁴¹Am of the parallels were 0.06 ± 0.02 Bq/kg, 1.14 ± 0.11 Bq/kg and 1.19 ± 0.13

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Table 2.7 Results from the intercomparison exercise at BSH: sediment sample, top 1 cm, at Station 34S (approximately 0.5 nautical mile south of Komsomolets) in the Norwegian Sea. All values are in Bq/kg. The uncertainty given with the mean specific activity is the standard deviation of the data set

3X 3X $P &V &V

6SHFLILFDFWLYLW\ 0.07 1.01 1.11 11.10 < 1,0

0.01 0.07 0.03 0.19

6SHFLILFDFWLYLW\ 0.06 0.91 1.02 12.30 < 0,8

0.01 0.06 0.05 0.17

0HDQ

At BSH, 2 parallels of the sediment sample from Station 34S were measured for gamma- emitting radionuclides. The analytical results showed that for these 2 parallels, the specific activities of ¹³⁷Cs obtained fell within 4 standard deviations. The mean ¹³⁷Cs activity of the parallels was 11.70 ± 0.85 Bq/kg. The specific activity of ¹³⁴Cs in the sediment samples was below the detection limit (1.0 and 0.8).

Two parallel samples were taken out from the bulk of the sediment from Station 34S,

followed by analytical procedures and methods of analysis of the transuranics (²³⁸Pu, ^239,240Pu and ²⁴¹Am). The analytical results showed that for both the 2 parallels the specific activities of

238Pu and ^239,240Pu fell within 1 standard deviation, and for ²⁴¹Am the specific activities fell within 2 standard deviations. The mean specific activity of ²³⁸Pu, ^239,240Pu and ²⁴¹Am of the 2 parallel samples were 0.07 ± 0.00 Bq/kg, 0.96 ± 0.07 Bq/kg and 1.07 ± 0.07 Bq/kg,

respectively.

The analytical results of the intercomparison exercise showed that the mean specific activities for the transuranics (²³⁸Pu, ^239,240Pu and ²⁴¹Am) and ¹³⁷Cs of the sediment sample (Station 34S, top 1 cm) obtained by the NRPA and BSH agreed within an uncertainty of 1 standard deviation.

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2.5 Statistical analysis

2.5.1 Analysis of variance

In this study, analysis of variance were used to test the hypothesis that the means (i.e. mean

239,240

Pu, ²³⁸Pu, ²⁴¹Am and ¹³⁷Cs activity, respectively, of surface water and surface sediments) of several different groups (i.e. sea areas) were equal.

The parametric test One-way ANOVA (SPSS 9.0) and the non-parametric Kruskal-Wallis test (described by Conover, 1980) were used for this purpose.

3XLQVXUIDFHZDWHU

The results from the Levene’s homogeneity-of-variance test on ^239,240Pu in surface water of the different sea areas (i.e. the west North Sea, the east North Sea/Skagerrak, considered as one area due to few measurements, the Norwegian Sea, the Barents Sea, the Greenland Sea, the Iceland Sea and the North Atlantic) indicated equal variance within the groups. Therefore, the One-Way ANOVA procedure was used. This procedure indicated significant differences between the means. The Post Hoc test and pair-wise multiple comparisons (Bonferroni) was used to determine which means differed. Nevertheless, because of relatively few

measurements, the non-parametric test, Kruskal Wallis, was also made, to give strength to the analysis, following the pair-wise multiple comparisons test between each pair of means.

$PLQVXUIDFHZDWHU

The same procedure as that for ^239,240Pu was used for ²⁴¹Am in surface sea water.

3XLQVXUIDFHZDWHU

The Levene’s homogeneity-of-variance test indicated that the variance within each group was XQHTXDO. The non-parametric Kruskal-Wallis test (k indipentent samples) was therefore made, following the pair-wise multiple comparisons test between each pair of means.

&VLQVXUIDFHVHGLPHQWV

The Levene’s homogeneity-of-variance test indicated unequal variance within the groups.

Therfore, the non-parametric Kruskal-Wallis (k independent samples) test was made, following the pair-wise multiple comparisons test between each pair of means.

7UDQVXUDQLFVLQVXUIDFHVHGLPHQWV

The Levene’s homogeneity-of-variance test indicated an unequal variance within the groups.

The results from the following Kruskal-Wallis test showed, however, no significant differences between the means.

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3. Results

3.1 Radiocaesium in seawater

3.1.1 Distribution of

¹³⁷

Cs and

¹³⁴

Cs in surface seawater

The distribution of ¹³⁷Cs and ¹³⁴Cs is presented in Figure 3.1.

# #

#

3.3 - 26 Bq/m³

Cs-137 Cs-134

Figure 3.1 Distribution of ¹³⁷Cs and ¹³⁴Cs in surface water of the Northern Seas (the caesium activity is proportional to the area of the pie charts). At Station 84 where two parallel surface samples have been measured, the mean value has been used for this presentation

The ¹³⁷Cs activity concentrations measured in surface water ranged from 3.3 ± 0.2 - 25.5 ± 0.6 Bq/m³. The highest ¹³⁷Cs activity concentration was measured in surface water in Skagerrak, 26 ± 0.6 Bq/m³. At this location, Station 11, ¹³⁴Cs was also detected in surface water at a level of 0.6 ± 0.1 Bq/m³. For all other locations (see Table 3.1)the ¹³⁴Cs activity concentration in seawater was below the detection limit.

At Station 84, in the north-western part of the North Sea, two parallel surface samples have been measured. The mean value, 11.9 ± 0.4 Bq/m³, was the second highest ¹³⁷Cs activity concentration measured in surface water. The ¹³⁷Cs activity concentration in surface water decreased northwards off the Norwegian coast to an almost constant level at Station 26, 4.6 ± 0.2 Bq/m³. The lowest activity concentrations in surface waters were measured in the northern part of the Norwegian Sea, the Barents Sea and the Greenland Sea with levels in the range 3.3

± 0.2 - 4.6 ± 0.2 Bq/m³. The exact values for ¹³⁷Csand ¹³⁴Cs in sea water are given in Table 3.1.

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3.1.2 Vertical distribution of

¹³⁷

Cs in the water column

Results from measurements of radiocaesium in seawater from selected stations in the Northern Seas are presented in Table 3.1. In Figure 3.2, the ¹³⁷Cs results are illustrated by plotting the ¹³⁷Cs activity against depth, together with salinity and temperature for each station. Salinity especially can be used to identify water masses.

The ¹³⁷Cs activity of the water samples from the entire investigation area ranged from 3.3 ± 0.2 - 25.5 ± 0.6 Bq/m³.

At Station 11 in Skagerrak, the ¹³⁷Cs activity concentration in the low-salinity surface water, 25.5 ± 0.6, was higher than in the underlying Atlantic water, 5.7 ± 0.3 (Atlantic water is defined as waters having a salinity greater than 35). In the Norwegian Sea, radiocaesium was measured at different depths at 2 stations, Station 26 and 31. Here, the ¹³⁷Cs activity was in the range 2.6 ± 0.1 - 4.6 ± 0.2 Bq/m³. At Station 26, the activity concentration of ¹³⁷Cs in the low-salinity surface water, 4.6 ± 0.2 Bq/m³, was higher than the underlying Atlantic water (100-250 m), 2.6 ± 0.1 - 3.6 ± 0.2 Bq/m³.

In the Barents Sea, radiocaesium concentrations versus depth have been determined at 3 stations, namely Station 39, 46 and 48. In WKH%DUHQWV6HD, Atlantic water is, according to Sakshaug HWDO. (1994), defined as waters having a salinity higher than 34.95.The water masses at the Stations 46 and 48 were almost entirely Atlantic water and no difference in the

137Cs activity concentration was observed. This was not the case for Station 39, where the upper water column was influenced by water with lower salinity, having a higher ¹³⁷Cs

activity concentration, 4.2 ± 0.1 Bq/m³, than the underlying Atlantic water, 3.8 ± 0.2 or lower.

The activity measured in the Barents Sea was in the range 3.0 ± 0.2 - 4.2 ± 0.1 Bq/m³. In the Greenland Sea, radiocaesium was measured at 2 stations, Station 55 (in the north) and 63 (in the south). The water masses of both stations had a salinity of less than 35 in the entire water column. The ¹³⁷Cs activity measured was in the range 3.0 ± 0.2 - 3.5 ± 0.1 Bq/m³. In general, the ¹³⁷Cs activity concentration in the water column decreased, or showed no differences, with depth.

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5 0 0 4 0 0 3 0 0 2 0 0 1 0 0

0 -1 0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2

S ta tio n 1 1 , S k a g e rra k

Depth (m)

S a lin ity

T e m p e ra tu re

2 6 2 7 2 8 2 9 3 0 3 1 3 2 3 3 3 4 3 5

4 6 8 1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 4 2 6 2 8 3 0

1 3 7

C s

% T P

500 400 300 200 100

0 -1 0 1 2 3 4 5 6 7 8 9 10 11 12

Station 26, Norwegian Sea

Depth (m)

Salinity

Temperature

34.0 34.2 34.4 34.6 34.8 35.0 35.2

2.0 2.5 3.0 3.5 4.0 4.5 5.0

137Cs

Bq/m³

Figure 3.2a Vertical distribution of ¹³⁷Cs, in Bq/m³, in sea water, together with salinity and temperature, at selected locations of the Northern Seas. Note that at Station 11, both the upper and lower x-axis have another scale than at the other stations, due to the high ¹³⁷Cs activity concentration measured in low salinity water at this station. At Station 26, two parallel

samples have been measured at a depth of 50 m, in which the mean value has been used in the presentation. The sea water depths at the Stations 11 and 26 were 535 m and 268 m,

respectively

Artificial Radionuclides in the Northern European Marine Environment

StrålevernRapport 2000:1