SE9800216

Anthropogenic Radionuclides in the Arctic Ocean Distribution and Pathways

Dan Josefsson

LUND UNIVERSITY 1998 Organization Document name LUND UNIVERSITY DOCTORAL DISSERTATION Department of Radiation Physics Dateofi ue The Jubileum Institute * May 12, 1998 Lund University Hospital CODEN:LUNFD6/(NFRA-1036)/1 -159/1998 S-221 85 Lund, Sweden LUMEDW/fMERI-1036)/1-159/199fi Authors) Sponsoring organization Dan Josefsson Title and subtitle Anthropogenic Radionuclides in the Arctic Ocean: Distribution and Pathways

Abstract Anthropogenic radionuclide concentrations have been determined in seawater and sediment samples collected in 1991,1994 and 1996 in the Eurasian Arctic shelf and interior. Global fallout, releases from European reprocessing plants and the Chernobyl accident are identified as the three main sources. From measurements in the Eurasian shelf seas it is concluded that the total input of l34Cs, 137Cs and '°Sr from these sources has been decreasing during the 1990's, while 129I has increased. The main fraction of the reprocessing and Chernobyl activity found in Arctic Ocean surface layer is transported form the Barents Sea east along the Eurasian Arctic shelf seas to the Laptev Sea before entering the Nansen Basin. This inflow results in highest I37Cs, 129I and '"Sr concentrations in the Arctic Ocean surface layers, and continuously decreasing concentrations with depth. Chernobyl- derived 137Cs appeared in the central parts of the Arctic Ocean around 1991, and in the mid 1990's the fraction to total 137Cs was approximately 30 % in the entire Eurasian Arctic region. The transfer times for releases from Sellafield are estimated to be 5-7 years to the SE Barents Sea, 7-9 years to the Kara Sea, 10-11 years to the Laptev Sea and 12-14 years to the central Arctic Ocean. Global fallout is the primary source of plutonium with highest concentrations found in the Atlantic layer of the Arctic Ocean. When transported over the shallow shelf seas, particle reactive transuranic elements experience an intense scavenging. A rough estimate shows that approximately 75 % of the plutonium entering the Kara and Laptev Seas are removed to the sediment. High seasonal riverine i input of 239'240Pu is observed near the mouths of the large Russian rivers. Sediment inventories show much higher concentrations on the shelf compared to the deep Arctic Ocean. This is primarily due to the low particle flux in the open ocean.

Keywords radioactivity, Arctic, ocean, currents, shelf, sediment, nuclear, fallout Sellafield, Chernobyl, cesium, strontium, iodine, plutonium, americium Classification system and/or index terms (if any)

Supplementary bibliographical information Language . English

ISSN and key title ISBN 91-628-2967-X Recipient's notes Number of pages ^g Price

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I, the undersigned, being the copyright owner of the abstract of the above-mentioned dissertation, hereby grant to all reference sources permission to publish and disseminafe'the abstnct of the above-mentioned dissertation.

Signature . rw. April 29, 1998 Anthropogenic Radionuclides in the Arctic Ocean

Distribution and Pathways

Dan Josefsson Fil. kand.

Akademisk avhandling som, for avlaggande av filosofie doktorsexamen i radiofysik vid matematisk-naturvetenskapliga fakulteten vid Lunds Universitet, kommer att offentligen forsvaras

Fredagen den 5 juni 1998, klockan 10.15 i onkologiska klinikens forelasningssal, Lunds Universitetssjukhus, Lund

Fakultetsopponent: Dr Hugh Livingston, IAEA-MEL, Monaco. Anthropogenic Radionuclides in the Arctic Ocean

Distribution and Pathways

Dan Josefsson

Department of Radiation Physics The Jubileum Institute Lund University S-221 85 LUND Sweden Doctoral dissertation Department of Radiation Physics The Jubileum Institute Lund University

ISBN91-628-2967-X Printed in Lund, Sweden by Bloms i Lund Tryckeri AB, 1998

Copyright © 1998 Dan Josefsson (Pages 1-55) All rights reserved Utan tvivel ar man inte klok (Tage Danielsson) This thesis is based on the following papers, which are referred to in the text by their Roman numerals.

I Josefsson, D., E. Holm, P. Roos, B. Persson and J.N. Smith (1998), Radiocaesium, 90Sr and 129I in the Eastern Arctic Shelf Seas. Submitted to Continental Shelf Research.

II Roos, P., D. Josefsson, E. Holm. Distribution of plutonium and radiocaesium isotopes in the Arctic Ocean, 1991. Manuscript.

III Josefsson, D., E. Holm, P. Roos, M. Eriksson, B. Persson and J.N. Smith (1998), Distribution and circulation of Chernobyl and reprocessing radioactivity in the central Arctic Ocean. Submitted to Deep Sea Research.

IV Josefsson, D., E. Holm, P. Roos, M. Eriksson and A. Aarkrog (1998), Transuranic elements in the waters of the Arctic Ocean shelf and interior. Submitted to Journal of Environmental Radioactivity.

V Josefsson, D., E. Holm, and P. Roos (1998), Plutonium and 137Cs in the bottom sediments of the Arctic Ocean shelf and interior. Manuscript.

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INTRODUCTION 9

SAMPLING AND MEASUREMENT 11

THE ARCTIC OCEAN 15 Water exchange between the Arctic Ocean and adjacent seas The shelf seas The Arctic interior MAJOR SOURCES OF ANTHROPOGENIC RADIOACTIVITY 25 Fallout from nuclear weapons testing Civil nuclear power The Chernobyl accident Other significant sources

ANTHROPOGENIC RADIOACTIVITY IN THE ARCTIC 35 Input to the Arctic Ocean The shelf seas The Arctic interior Arctic Ocean outflow and the East Greenland Current

MAIN CONCLUSIONS 46

ACKNOWLEDGEMENTS 47

REFERENCES 48

PAPER I-V 57

NEXT PAGEfS) left BLANK INTRODUCTION

The release of anthropogenic (man-made) radionuclides into the marine environment started with the nuclear era. The, so far, greatest global input originated in the atmospheric testing of thermonuclear bombs, which culminated in the late 1950's and early 1960's. Being injected to the stratosphere, the debris was distributed worldwide, with the largest fallout in the northern hemisphere. This global fallout results in an estimated total collective effective dose of 3xlO7 man Sv, of which the major part will be delivered by the long-lived radioactive isotope 14C over several millenniums to come (UNSCEAR, 1993). Atmospheric nuclear weapons tests account for 15 % of the collective effective dose from all anthropogenic sources, and less than 5 % of that from the natural sources. Global fallout at high latitudes was low, but currents from the North Atlantic have since deposition constituted a continuous transfer of activity to the Nordic and Arctic Seas. Other significant sources of marine radioactivity are the plants for reprocessing nuclear waste situated in northern Europe, whose marine discharges are transported with sea currents towards the Arctic regions. A possible threat also comes from potential sources such as radioactive waste dumped in the world oceans and other high activity disposals. Although the current collective dose from environmental anthropogenic sources is low, it constitutes an unwanted additional source, especially to possible critical groups, and it is of great importance to estimate the pathways and fate of the known releases, as well as to estimate the potential releases from other sources. The unique properties of the radionuclides present in different sources often enable precise spatial resolution of the transport pathways while the corresponding variations in time of their characteristics yield their temporal resolution. Thus, investigations of marine releases from European reprocessing plants have provided information on pathways, transfer times and transfer factors of both soluble and particle reactive elements in the Nordic Seas. This is of importance not only in determining the fate of radioactive as well as other contaminants, but also to evaluate the role of the northern North Atlantic in controlling themohaline circulation, and subsequently a link in the estimation of the effects of global warming. Due to its harsh climate and logistic difficulties, less emphasis have been put on exploring the central Arctic Ocean. Its permanent ice-cover and the large riverine input of fresh water gives it very special features. A strong horizontal stratification prevents vertical exchange and creates layers with different movements and residence times of the water masses. Early investigations of the anthropogenic radioactivity in the Arctic Ocean were performed from ice-camps, which limited the horizontal resolution. Later, the use of ice-breaking vessels as research platforms has enabled the simultaneous determination of radionuclide concentrations in larger areas of the Arctic Ocean. This thesis is based on the results from three such ship-based expeditions, two to the Arctic Ocean interior and the third along the Eurasian Arctic shelf. From water column profiles and sediment samples, the distributions and concentrations of several anthropogenic radionuclides have been determined, and from these results are drawn conclusions regarding pathways, transfer times and source terms.

10 SAMPLING AND MEASUREMENT

The field samples which are the basis of this thesis were obtained during three Arctic Ocean expeditions (Figure 1), all arranged by the Swedish Polar Secretariat. The International Arctic Ocean Expedition 1991 was a joint operation between the Swedish Icebreaker Oden, the German R/V Polarstern and the American R/V Polar Star. On board Oden, work was devoted mainly to oceanography and marine chemistry. The expedition crossed the Barents Sea, entered the central Arctic Ocean by the Fram Strait and traversed the Nansen and Amundsen Basins to the northern Makarov Basin. The return route covered the western Nansen and Amundsen Basins, followed the continental shelf slope north of Spitsbergen and passed through the Fram Strait. On September 8, Oden became, together with Polarstern, the first non-nuclear surface vessel to reach the North Pole. (Due to technical problems, Polar Star abandoned the expedition at an early stage.) During the whole cruise, surface water was sampled to determine the concentrations of 137Cs, 134Cs, 90Sr, 239-240Pu and 241Am. At three stations additional depth profiles were obtained by Polarstern. Sediment samples were also recovered by sampling from Polarstern, but only in the area around Svalbard, and were subject to natural (210Pb, 228Th and 232Th) and 137 238 239 240 anthropogenic ( Cs, Pu and - pu) radionuclide analysis, as well as nutrient studies in corporation with the Department of Analytical and Marine Chemistry, Goteborg University. During the Swedish-Russian Tundra Ecology -94 expedition, we got the opportunity of carrying out research in the Eurasian Arctic shelf seas, which were both earlier and are now again essentially closed to Western scientists. During June to September, the coastal areas of the Barents, Kara, Laptev and East Siberian Seas were traversed. Primarily a terrestrial expedition, the Russian research vessel Academic Fedorov was used as a logistic platform from which researchers were put ashore using large helicopters. Simultaneously marine research work was carried out on board. The ship followed a route in the shallow waters close to land, the sampling depths generally not exceeding 50 metres. For determinations of 134Cs, 137Cs,

9oSr i29I? 238Pu? 239,24oPu ^ 241^^ surface water was sampled at a total number of 28 stations, with additional near-bottom samples at most stations. Sediment samples from some of the stations were analysed for 137Cs, 239'240Puand241Am.

11 "Arctic Ocean -91 Tundra -94 'Arctic Ocean-*96

Figure 1. Expedition routes.

The third expedition, Arctic Ocean -96, was also conducted on I/B Oden, slightly to the east of the area examined in the Oden 1991 expedition. From northern Norway and the Barents Sea, the route passed through the St. Anna Trough in the northern Kara Sea. After crossing the Nansen and Amundsen Basins, the major part of the expedition was spent on the Lomonosov Ridge. The return route went through the northern Makarov Basin to the North Pole, and then along approximately 15 °E towards Spitsbergen. The sampling program was similar to that of the Tundra -94 expedition, sediment and water profiles being taken at approximately 17 stations and additional surface water samples in between. Water was generally sampled at three or four depths down to 850 or 1000 metres and analysed for 137Cs, 90Sr 1291,238Pu and 239240Pu. In surface water ,l34Cs activities were also determined.

12 In all three expeditions, surface water was collected using a shipboard pumping system. The subsurface samples taken by Oden and Polar stern were collected in large (100 or 270 litres) Go-Flow bottles. Near- bottom water samples from the Tundra -94 expedition were either collected through a tube lowered from the ship, or in a 30 litre Go-Flow bottle. To enable determination of the low 134Cs/137Cs activity ratio, large volumes of water passed through large cotton-wound filters impregnated with copper ferrocyanide (Cu2Fe(CN)6), an efficient caesium adsorber. The work on board was conducted in well-equipped laboratories in 20 foot long containers. The analytical procedures on all three expeditions were similar. To reduce the volumes, water samples were preconcentrated on board the ship. Only the subsurface samples from Polar stern in 1991 were transported intact to the laboratory. After acidification by HC1 (pH<2) the chemical yield determinants 134Cs, 85Sr, 242Pu and 243Am were added and the samples mixed for about 30 minutes to obtain isotopic equilibrium. Caesium was adsorbed onto a copper ferrocyanide precipitation at pH<8. At pH«4 strontium was precipitated as the oxalate, using sea water strontium and calcium as carrier. Plutonium and americium were coprecipitated as iron and magnesium hydroxides at pH^ 10, obtained by adding sufficient amount of NaOH to the sample. Precipitations were often performed sequentially so as to recover all the relevant radionuclides from the same sample. Back at the laboratory the copper ferrocyanide precipitations were further concentrated and dried and the copper ferrocyanide filters ashed at 420 °C. Radiocaesium activity was then measured using high purity (HPGe) or lithium-drifted germanium detectors. The oxalate precipitations were converted to carbonates at 550 °C overnight and dissolved in concentrated HNO3. Separation of strontium was performed using a method developed by Bojanowski and Knapinska-Skiba (1990). The activity was determined by measuring the equilibrium activity of the daughter nuclide ^Y on a anticoincidence shielded gas-flow GM counter. The hydroxide precipitates were dissolved in HC1 and Pu and Am coprecipitated on iron hydroxide at pH^ 10 by the addition of ammonia. Plutonium and americium were then separated following the methods described in IAEA Technical Report 295 (1989) and electroplated on stainless steel discs. The alpha activity was measured on either surface- barrier detectors or passivated ion-implanted silicon detectors (PIPS). The 1991 sediment samples from Polar stern and the 1996 Oden

13 sediment samples were obtained with a multiple corer and sliced on the ship. On Academic Fedorov, either a HAPS or a box corer was used, the core being obtained by subsampling into a plastic tube. The samples were later sliced in the laboratory. Cs-137 activity were measured using HPGe- detectors. For alpha activity analysis, sediments were ashed at 550 °C overnight, and then oxidised in aqua regia for approximately 12 hours. After filtering to remove the remaining sediments, the continued procedure continued as described for the water samples.

14 THE ARCTIC OCEAN

The Arctic Ocean is circumscribed by the Canadian and Eurasian continents (Figure 2), with the border to the Atlantic Ocean generally drawn from northern Norway to Svalbard and across the Fram Strait to northern Greenland. It has a mean depth of 1330 metres and a surface area of 9.5><106 km2. When discussing the Arctic Mediterranean, as part of the Atlantic Ocean, the Greenland-Scotland ridge is regarded as the border and the area becomes 17><106 km2. Links to the Atlantic Ocean are found through the Barents Sea, the Fram Strait, and the Canadian archipelago, while the Bering Strait constitutes the only passage to the Pacific Ocean. The Arctic sea ice covers 7xlO6 km2 in summer and double that in winter (Carmack, 1990). 180E

Figure 2. The Arctic Ocean.

15 Water exchange between the Arctic Ocean and adjacent seas

With a sill depth of 2600 metres and a width of 600 km, the Fram Strait constitutes the only deeper connection to the surrounding oceans. The Greenland Sea is situated south of the Fram Strait, and the Norwegian Sea further to the east. The Pacific Ocean connection goes through the Bering Strait between Asia and North America. The width is 85 km and the sill depth 50 metres.

180E

Figure 3 a. Surface water circulation in the Arctic Mediterranean.

16 Currents of the Arctic Mediterranean surface and subsurface layers are shown in Figure 3a and 3b respectively. The inflow through the Bering Strait is primarily driven by the difference in sea level between the Pacific and Arctic Oceans, which creates a total mean net inflow of 0.8 Sv/year. The relatively fresh water, 31-33 %> with a long-term mean of 32.5 %o (Aagaard and Carmack, 1989), is mainly assumed to spread out in the PML and the upper halocline of the Canadian Basin (McLaughlin et ah, 1996).

180E

Figure 3b. Atlantic water circulation in the Arctic Mediterranean.

17 The largest input of sea water to the Arctic Ocean conies from the Atlantic inflow. As the Norwegian Atlantic Current (NAC), a northerly extension of the Gulf stream, the Atlantic water enters the Nordic Seas through the Faeroe-Shetland channel and follows the Norwegian coast north along the shelf break. A smaller fraction of the Atlantic water is transported through the English Channel, to the North Sea, where river water and output of low salinity Baltic Sea water reduces the salinity. The outflow from the North Sea follows the Norwegian coast northward as the Norwegian Coastal Current (NCC). From salinity sections from the southern Norwegian coast outwards, it is clear that the NAC and NCC water masses stay separated, with the less saline NCC as a wedge above and to the east of the NAC. On the route north, they become partly mixed and at the Barents Sea the current splits, one branch continuing north as the West Spitsbergen Current (WSC) and the other entering the Barents Sea. From the entrance at the Faeroe- Shetland channel to Spitsbergen, the Atlantic water temperature drops about 5 degrees to 3-6 °C, and salinity 0.3 units to 35 %o (Johannessen, 1986).

The shelf seas

Vast continental shelves, on the Eurasian side up to 80 km wide, surround the central Arctic Ocean and occupy a significant part of the total surface area. The shelves receive a high input of river water, about 3 500 km3 per year (Carmack, 1990), from a catchment area as large as the Arctic Ocean itself. In summer, river water is transferred from the shelf to the surface layer of the central Arctic Ocean, while, in winter, brine from ice-formation produces high density water, which may penetrate below the Arctic Ocean surface layer. Along the Eurasian shelf we find, from west to east, the Barents Sea, the Kara Sea, the Laptev Sea, the East Siberian Sea and the Chukchi Sea (Figure 2). The Barents Sea is the largest of the shelf seas, with a depth generally in the range 100-350 metres (Weber, 1989). To the east, it is bounded by Novaya Zemlya and the St. Anna Trough (in the north-west Kara Sea) and to the west by the Norwegian Sea. The inflow of relatively warm Atlantic water keeps the south-western part of the Barents Sea ice-free even in winter. The fresh water component is melt water, and only low amounts of river water reach the Barents Sea (Ostlund, 1994).

18 The Kara Sea is bordered to the east by the Taimyr peninsula on the Asian continent and the Severnaya Zemlya archipelago to the north-east. To the north, the St. Anna and Voronin Troughs cut deep into the continental shelf, acting as deeper connections to the central Arctic. The mean depth of the Kara Sea is 111 metres. Greater depths are found in the north and it is often shallower than 50 metres in the south (Pavlov and Pfirman, 1995). Among the shelf seas, the Kara Sea receives the highest input of river water, about 55 % of the total input to the Arctic Ocean. The largest contributors are the Ob and Yenisey rivers which discharge 400 and 630 km3 y1 respectively (Pavlov and Pfirman, 1995). The river water content is about 1 % in the western and 5-9 % in the eastern part, with an average residence time of 5 years (Ostlund, 1994). The Laptev Sea, east of the Taimyr peninsula, is separated from the East Siberian Sea by the New Siberian Islands. It contains about 11 % river water, mainly originating from the Lena river which yearly releases 520 km3. The residence time of the fresh water is 3 years (Ostlund, 1994). The East Siberian Sea receives river water primarily from the Indigirka and Kolyma, 57 and 102 km3 y'1 respectively. The Chukchi Sea is situated north of the Bering Strait and receives the Bering Strait inflow of Pacific water. The general direction of the current on the shelf is eastward, transferring both river water and Atlantic water between the shelf seas (Schlosser et at, 1995) (Figure 3a). A smaller fraction of the inflow from the Barents Sea to the Kara Sea passes through the Straits between Novaya Zemlya and the Russian mainland, although the main flow is north of Novaya Zemlya, en route to the Arctic Ocean. The net flow through the Vilkitsky Strait is eastward, transferring about 0.35 Sv/year from the Kara to the Laptev Sea (Pavlov and Pfirman, 1995). In Paper I and III we show that the anthropogenic radionuclides carried north by the NCC tend to follow the western Taimyr current into the Laptev Sea rather than enter the surface layer in the Nansen Basin. Water from the Laptev Sea is similarly assumed to be transferred either into the central Arctic Ocean or in to the East Siberian Sea (Schlosser et al, 1995). Our measurements show that the latter transport path is less likely, since the concentrations of 129I and 137Cs are much lower east of 150 °E (Paper I). The water in the East Siberian Sea is instead assumed to originate in the Pacific and carry mainly global fallout radioactivity. River outflow brings large quantities of sedimentary material to the

19 Arctic shelf seas. The larger particles will settle in the sediments in the estuaries while the smaller ones are transported further away before settling. Also, the high productivity in summer results in high transport of biogenic particles to the bottoms of the shelves. Outflow towards the deep basins carries sediment that is mainly deposited on the continental slope (Honjo, 1990).

The Arctic interior

The Arctic Ocean interior is divided into the Eurasian and Canadian Basins by the Lomonosov Ridge which stretches north from the Laptev Sea past the North Pole to northern Greenland (Figure 2). The Lomonosov Ridge was once part of the Eurasian Shelf, but some 60 million years ago, was pushed by continental drift to its present position. The mean depth of the ridge is approximately 1000 metres and the sill depth about 1400 metres (Carmack, 1990). The seismologically-active Nansen-Gakkel ridge marks the border between the separating continental plates, and also divides the Eurasian Basin into the Nansen Basin to the south and the Amundsen Basin to the north. In a similar way, the Canadian Basin is divided by the Alfa and Mendeleev Ridges into two basins with the Makarov Basin closest to the Lomonosov Ridge and the Canada Basin to the south. The maximum depths in the abyssal plains are around 4000 metres. One of the most important features of the Arctic Ocean is its strong horizontal stratification, which divides it into layers with limited vertical exchange. The layers are characterized by specific properties resulting from their different origin, and hence the formation of the water masses is strongly linked to water-exchange with the Atlantic and Pacific Oceans as well as the river input of fresh water. Typical depth-distributions of salinity and temperature obtained from Station 15 during the Arctic Ocean -96 expedition are shown in Figure 4. The upper 50 metres contains the relatively fresh Polar Mixed Layer (PML), with temperatures close to freezing point. In the Eurasian Basin, the fresh water component is either melt or river water, while inflow of Pacific water gives an additional fresh water input mainly to the Canadian Basin. Salinity, temperature and chemical properties in the Eurasian Basin reveal in the Nansen Basin south of 83-85 °N that melt water is the main fresh water

20 component, while the fresh water north of this approximate boundary is riverine and hence must originate in or east of the Kara Sea (Anderson and Jones, 1992; Anderson et al., 1994; Schlosser et al., 1994). Ice-formation during winter results in uniform salinities and temperatures, while summer melting creates salt stratification. Immediately below the PML, the halocline is characterized by increasing salinities with depth. Temperatures often shows a minima at 75 metres and then increases in a thermocline. The halocline may be subdivided in an upper and lower part, the former characterized by a nutrient maximum and salinities around 33.1 %o, and the latter by a nutrient minimum and salinities of around 34.2 %o. Between approximately 200-800 metres, the Atlantic layer is characterized by high temperatures (> 0 °C) and salinities (>34.90 %o), while the deep water has lower temperatures but approximately the same salinity as the Atlantic layer.

33 33.5 34 34.5

Halocline

Depth

Deep water 1000 4

Figure 4. Temperature and salinity depth distributions in the Arctic Ocean (Station 15 from the Arctic Ocean -96 expedition)

21 In a review by Schlosser et. al. (1995) the approximate residence times for the PML, halocline and Atlantic layer respectively, were reported to be 5, 10 and tens of years. Deeper layers have residence times exceeding 100 years. The surface current of the Canadian Basin is dominated by the large Beaufort Gyre, driven by the prevailing anti-cyclonic winds. The Transpolar Drift transfers surface water from the northern Beaufort Gyre and from the Laptev Sea area across the Amundsen and Nansen Basins to the Fram Strait (Figure 3a). Its average speed is 2-3 cm/s, corresponding to transport times from the Laptev Sea to the Fram Strait of approximately 2-3 years (Schlosser et al, 1995). When entering the Arctic Ocean, the inflowing saline and warm WSC encounters the cold and fresh PML. The main part sinks to depths below 200 metres, while the upper fraction mixes with the PML, which in this area reaches down to approximately 100 metres (Rudels et al., 1996). Together with the deeper lying Atlantic water, the lower part of the PML is supposed to flow east along the continental slope, while the upper PML probably moves in the opposite direction. On reaching the areas north of the Kara and Laptev Seas, the surface water receives an input of low-salinity shelf water. The reduced salinity results in a shallower intrusion of brine- enriched water during winter, and an intermediate halocline is created (Rudels et al., 1996). In the Canadian Basin, the upper halocline is formed, mainly from Pacific water, with a density that places it between the lower halocline and the PML. Additional input to the halocline may come from shelf input of water with equal density (Anderson et al., 1994; Steele et al., 1995), and the relative importance of these two mechanisms for the formation of the lower halocline is not fully understood. It is estimated that about two-thirds, equal to 2 Sv, of the Atlantic inflow to the Arctic Ocean enters across the Barents Sea (Loeng et al., 1997). Of the WSC, two-thirds are recirculated in a western loop in the Fram Strait, back into the Greenland Sea, leaving approximately 1 Sv or less to enter the Arctic Ocean (Figure 3b). The path crosses the Yermak plateau north of Spitsbergen and follows the continental slope eastward as the Svalbard branch (Manley, 1995). In the cold and fresh Barents Sea, the properties of the Atlantic water change and water masses of different densities are created. Those in turn enter the Nansen Basin at depths with equivalent densities. The main inflow is assumed to occur through the St Anna Trough, forming a wedge between

22 the continental slope and the Svalbard branch. In the eastern Nansen Basin, this wedge, identified by lower salinity and temperature, is observed to extend from 200 to 1300 metres depth and stretch 200 km out from the slope (Schauer et al., 1997). Observations on the shelf slope further to the west have produced evidence of an inflow between Spitsbergen and Franz Josef Land down to about 500 metres depth (Schauer et al., 1997). On its movement eastward, parts of the Atlantic core branch off to the north at the Nansen-Gakkel and the Lomonosov Ridges. The remaining fraction, mainly consisting of the Barents Sea branch crosses the Lomonosov Ridge into the Canadian Basin. The different branches later reunite north-east of Greenland and leave the Arctic Ocean through the western Fram Strait as part of the East Greenland Current (Anderson et al., 1994). The 1996 results for the Arctic Ocean Atlantic layer, presented in Paper III, reflect this transport pathway. As an effect of the decreasing inputs of 137Cs and 90Sr and the increasing 129I input, the concentrations of the former two increase along the route and that of the latter decreases. The deep water of the Arctic Ocean was previously assumed to originate in the deep waters of the Norwegian and Greenland Seas flowing in through the Fram Strait (e.g. Aagaard et al., 1985). Recent studies, however, suggests that two other sources are more important. High density water produced by brine release by ice formation on the shelves, is assumed to follow the continental slope downward, on the way entrapping intermediate water which constitutes the larger part of the sinking water. Also, Atlantic water inflowing across the Barents Sea is assumed to gain enough density by cooling to let it follow the St Anna Trough down to the deep water layers (Jones et al., 1995). On the average, the circulation is assumed to follow that of the Atlantic layer (Jones et al., 1995). As in most deep sea regions, the particle flux in the central Arctic Ocean is assumed to be low. Finer particles do not settle by themselves, but are incorporated into larger aggregates and delivered to the seafloor at a relatively high speed. Scavenging of particle-reactive radionuclides in the Nansen Basin is about equal to that in the open North Atlantic Ocean, but higher than in the Canadian Basin (Cochran et al., 1995). The residence- time for particulate thorium in the Nansen Basin is estimated to be 1 -3 months in the PML, and 2-9 years below 1500 metres (Cochran et al., 1995). No direct measurements of sediment fluxes have been conducted in

23 the central Arctic Ocean, but sediment trap data from the Nordic Seas provide information on central Arctic Ocean sedimentation. From sediment traps deployed for three years at 400 metres above the seafloor in the NCC and the EGC, the annual flux rates were determined to 16.6-28.4 and 7.2- 10.2 g/m2 respectively (Honjo, 1990). As an effect of higher productivity, the sedimentation-rate was highest in summer, also in the EGC, with relatively large particle sizes. The low productivity in the central Arctic limits the in situ production of larger settling particles, but particles incorporated in sea-ice may be released by melting and transferred to the seafloor. Sediment cores from the Nansen Basin indicate annual flux rates of 5-20 g/m2 and below 5 g/m2 on the Gakkel Ridge (Bohrmann, 1991). The annual flux rate under a permanent ice-cover in the Canadian archipelago, as determined from sediment traps, is only 1.1 g/m2 (Hargrave et ah, 1994). From the 230Th distributions in sediment the long-term sedimentation rates have been determined to be approximately 1 mm/1000 y on the western Lomonosov Ridge, 3 mm/1000 y on the eastern Lomonosov Ridge (Somayajulu et al. 1989) and 3-6 mm/1000 y on the Gakkel Ridge (Bohrmann, 1991).

24 MAJOR SOURCES OF ANTHROPOGENIC RADIOACTIVITY

Releases of anthropogenic radionuclides to the environment started with the advent of the nuclear era in the 20'th century. A large number of (radioactive) anthropogenic isotopes, ranging over the whole isotopic mass spectra, have been released to the environment. In the global perspective, the dominating source is the worldwide fallout of debris from the thermonuclear bomb tests performed in the late 1950's and early 1960's, which are still, through ocean currents, supplying the Arctic Ocean with more long-lived radionuclides. Another very important source of radioisotopes for the Arctic Ocean has been releases from the nuclear waste reprocessing plant Sellafield (former Windscale) in the UK on the Irish Sea. Soluble discharges to the Irish Sea are transferred to the Arctic, and although the total releases are lower than the global fallout, they give a higher input of radioactivity to the Arctic Ocean. The accident at the Chernobyl nuclear power plant in Ukraine in April 1986 also caused extensive fallout of radioactive substances. High fallout levels were recorded locally and in parts of Scandinavia and central Europe. Since the accident, run off and sea currents from the north European seas have continuously transferred activity to the Arctic Ocean. Other sources are the accidental releases of unfissioned plutonium at Thule, NW Greenland, releases from the Mayak nuclear facility to the Ob river and dumping of solid and liquid radioactive wastes in the Barents and Kara Sea. Since the experimental work in this thesis has mainly dealt with radiocaesium, 90Sr, 129I, plutonium and americium, this overview of sources will focus on these radionuclides.

Fallout from nuclear weapons testing

The explosive power of an atomic bomb is obtained either from the fission of heavy nuclei like 239Pu and 235U, or by fusion of mainly hydrogen isotopes. Radioecologically, the most important debris is fission products such as 90Sr and I37Cs, but also longlived transuranic elements like 239>240Pu. The atomic weapons tests performed in New Mexico, USA, in July 1945 resulted in the first significant releases of anthropogenic radionuclides to the environment (Perkins and Thomas, 1980). Due to the low yields

25 involved and hence atmospheric spreading only in the troposphere, the first years of testing resulted mostly in local environmental contamination. Higher explosive power were reached in the thermonuclear bombs (H- bombs) and resulted in global fallout of radioactive materials. Over 90 % of the total atmospheric release occurred in a first period from 1952 until 1958 and a second one from 1961 to 1962 (UNSCEAR, 1993). In 1963 a treaty banning all atmospheric test explosions, was signed by most nations with nuclear weapons, thereby resulting in a large decrease in total global fallout release. In all, 520 atmospheric nuclear test detonations have taken place, the major part by the US and the former USSR (UNSCEAR, 1993) The resulting total releases of some selected radionuclides are presented in Table 1. The241 Am, not included in Table 1, is mainly produced from the decaying 241Pu, and a total decay will result in a 241Am activity of 12.4 PBq.

Table 1. Production (released activity) of selected radioactive isotopes by past atmospheric nuclear tests (UNSCEAR, 1993) *(Raisbeckera/., 1995) ** (UNSCEAR, 1982).

Isotope Half-life [years] Production [PBq] 28.2 604 )37Cs 30.0 912 6 >29j 16xlO 0.0003 (2 xio26 atoms)* 238Pu 87.7 0.33** 239Pu 24 100 6.5 240Pu 6570 4.3 24)pu 14.4 142

The nuclear explosion debris reaching the stratosphere spreads latitudinally around the globe and only partially crosses the equator. Hence, since most bomb tests have occurred in the northern hemisphere, it also has received the major part of the global fallout, with most of the deposition occurring between latitudes 40-50 °N (UNSCEAR, 1982). The lowest amount of direct deposition occurred in the polar regions. The latitudinal

26 deposition pattern was observed in the Atlantic distribution of 137Cs in 1972- 73, which shows the highest activity concentrations at these latitudes (Holm etal, 1996). Surface activity concentrations of 137Cs in the north Atlantic at about 45 °N were approximately 6 Bq/m3 in 1967 (Bowen and Roether, 1973), 5 Bq/m3 in 1972 (GEOSECS, 1987), 4 Bq/m3 in 1982-84 (Nies, 1988) and 2.5 Bq/m3 in 1992 (Dahlgaard et al., 1995). The corresponding 90Sr activities were 4, 3, 2.5 and 1.6 Bq/m3. This results in effective half-lives of about 20 years for both radionuclides and a stable element residence time of 80-100 years (Dahlgaard et al., 1995). The long half-life is explained by the large circulation gyres in the north Atlantic (Nyffeler et al., 1996). The release '"Cs/^Sr fallout activity ratio in the beginning of the 1960's was 1.45, almost identical to the measured ratios in Atlantic Ocean surface and subsurface water in 1966-1967,1.43 and 1.44 respectively (Bowen et al., 1974). The release ratio given by Unscear (1993) for the total atmospheric releases was 1.51 and the 1992 ratio in the same waters gave a mean surface ratio of 1.55, indicating that fallout was still the dominating source (Dahlgaard et al., 1995). Due to the lower particle affinity of ^Sr, river runoff and coastal ratios are significantly lower. Bowen et. al. (1974) reported a mean 137Cs/90Sr ratio of 1.07 for different North American coastal waters in 1970. The fallout 129I/137Cs atom ratio has been determined from archived sea water samples to 2.0 (Edmonds et al., 1997). In surface water, 239-240Pu-concentrations show a more rapid decrease. In the period 1972-89, the decline from 60 to 10 mBq/m3 in the north east Atlantic corresponded to an effective half-life of 7-8 years (Holm et al., 1991). The 1995 fallout activity concentration of 239>240Pu in surface water in the northern North Atlantic was 8.3 mBq/m3 (Herrmann et al., 1998). The ^pu/239'24^ activity ratio in fallout has been estimated to be 0.03 (UNSCEAR, 1993), but the debris from the burn-up of the SNAP-9A satellite over the Indian Ocean in 1964 raised this ratio, especially in the southern hemisphere. Measured ratios in the North Atlantic were 0.04 in the beginning of the 1980's (Nies, 1988). The ^Am/239'24^ activity ratio in integrated global fallout was estimated to be 0.22 in 1974 (Perkins and Thomas, 1980). Concentrations of fallout radionuclides in subsurface layers have increased with time. Comparisons between measurements in 1967 (Bowen and Roether, 1973), 1972 (GEOSECS, 1987) and 1983-85 (Nies, 1988) in

27 the north-east Atlantic show increasing 137Cs and 239240Pu concentrations with depth. At two stations in the north-west Atlantic at the beginning of the 1980's, Cochran et. al. (Cochran et al., 1987) investigated the depth- distributions of natural and anthropogenic radionuclides. In the top 1000 metres, the higher particle reactivities of plutonium and americium were evident in their concentration maxima found several hundred metres below the 137Cs maxima. Assuming that caesium is not significantly removed by particle scavenging, they concluded that advection may supply between 35- 80 % of the inventories of 239'240Pu and 241Am at greater depths.

Civil nuclear power

Marine discharges from the civil use of nuclear power originate mainly from nuclear power plants and reprocessing plants. In 1997, a total number of 440 nuclear power reactors were in operation all over the world. Of these 188 were in Europe (SVA 1997). Nuclear energy is obtained from neutron-induced fission of heavy nuclei, usually 235U or 239Pu, the resulting fission products being concentrated to two mass-ranges, from 80-110 and 125-155 u respectively. Other elements, such as actinides and corrosion products, are created by neutron capture in the reactor fuel or construction materials. Releases of radioactivity to the marine environment are result from the diffusion of fission and activation products into the reactor coolant, often river- or sea- water. Liquid discharges of beta emitters (other than tritium) from European reactors peaked in the beginning of the 1980's with a total yearly release of 80-90 TBq (McColl et al., 1989). About 5 % of the spent fuel totally generated is brought to nuclear reprocessing plants for recovery (UNSCEAR, 1993). After interim storage leaving short-lived products to decay, the unfissioned part of the spent fuel is separated by liquid extraction for reuse in fission reactors. The remaining radionuclides are either sent to final storage or released. From the approximately 10 reprocessing plants operating over the world, the most important releases to the Arctic originate from Sellafield in UK and Cap de La Hague in France (UNSCEAR, 1993). The Arctic may also have received substantial input from reprocessing plants situated in the tributaries of the Ob and Yenisey Rivers in Russia. Regarding both alpha- and beta-emitters,

28 the reprocessing plants are the major sources of civil nuclear discharge, being responsible for more than 97 % of the total European releases until 1984(McCollefa/., 1989). A review of discharge data for the Sellafield reprocessing plant for the period 1951-1992 have been published by Gray et. al. (1995). Discharges from the solvent extractors and pond water from the fuel storage are transferred through pipelines to the Irish Sea. During the first 10 years, the releases were relatively low (Figure 5a). A period with high discharges began in 1967 and ended in 1985 when new techniques and procedures brought the discharge down to lower levels. For the period 1951-92, the total releases decay corrected to 1996 are presented in Table 2. In addition to the directly released241 Am, a major source is also build-up from its mother nuclide 241Pu, which, with a half-life of only 14.4 years produced a decay- corrected 241Am activity of 0.44 PBq by 1996.

Table 2. Sellafield releases for the period 1951-92 [PBq] (Gray et al., 1995).

137Cs I34Cs 90Sr 238Pu 239,240pu 24lpu 241Am

Total releases 41 5.8 6.2 0.12 0.61 21 0.54

Releses decay 26 0.012 3.8 0.11 0.61 7.9 0.52 corrected to 1996

Releases from La Hague are not so well documented. Compared to Sellafield, La Hague releases are relatively low and amount to 2.3, 12.2 and 0.4 % of the Sellafield releases of 137Cs, 90Sr and 239Pu respectively (Kershaw and Baxter, 1995). Of the radionuclides of discussed in this thesis, only the releases of 129I are larger than Sellafield releases. The I29I releases from Sellafield and La Hague and its use as an oceanographic tracer have been examined by Raisbeck et. al. (1995). Sellafield releases have remained rather constant since 1968, in the range 10-30 kg/year, while La Hague releases have increased from 30 kg/year in the late 1980's to 240 kg/year in 1995 (Raisbeck et al., 1997). To distinguish between reprocessing and fallout radioactivity,

29 6000 60 Cs-137 Sr-90 /; 5000 A -- 50 *

S 4000 -- 40 t ! : o mI fc. <» 3000 /' - 30 o •D CM C of re * CO

" 2000 20 Q. w O 1000 - 10

0 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 Release year

0.40 12 -Cs-134/Cs-137

0.35 T Pu-238/Pu-239,240 -Cs-137/Sr-90

0 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 Release year

Figure 5a and 5b. Sellafield releases and release activity ratios.

30 different activity ratios may be utilized (Figure 5b). The use of the 137Cs/90Sr activity ratio as a Sellafield tracer have been evaluated by, e.g., Livingston (1982,1982A) and shown to be very useful. For the whole period 1951- 1992, although varying between 2 and 11, release ratio has remained higher than the fallout ratio. The low releases of 137Cs and 90Sr after 1985 have limited its use further away frow the Irish Sea. Due to the increasing releases of 134Cs combined with the decay of fallout-derived I34Cs, the 134Cs/137Cs ratio was from 1974 to 1986 also an excellent Sellafield tracer (Aarkrog et al, 1987). The decreasing 137Cs releases from Sellafield together with the increasing 129I releases from mainly La Hague led to a increasing I29I/137Cs atom ratio for the combined release beginning in the mid 1980's, with ratios greatly exceeding the fallout ratio. Apart from the source-term function, the increasing ratio is useful also as a time marker for transit time estimations. Compared to the fallout ratio of approximately 0.04, the 238puy239,240pu ratj0 j^a iso been larger in Sellafield releases, with a cumulative ratio since 1980 of about 0.20-0.23 (Kershaw and Baxter, 1995). Due to the low La Hague releases, the above ratios also hold for the combined Sellafield and La Hague signal. The 241Arn/239i240Pu activity ratio (241Pu build up and direct release), decay corrected to the mid 1990's, has been rather constant at unity since the 1976 releases. It is not necessary for the release ratios to remain constant after introduction into sea water. Particle affinity, described by the distribution coefficient, Kd, determines the fraction bound to particles relative to the dissolved fraction. For caesium, strontium and iodine, Kd is estimated to 2- 3xl03, 0.2-1 xlO3 and 0.02-0.2xl03 kg/kg respectively (IAEA, 1985), which means that strontium and especially iodine may be regarded conservative, while caesium has a slightly higher particle affinity. It is estimated that 2.5 % (i.e. 850 TBq) of the total environmental inventory of Sellafield 137Cs is present in the sediment of the north-eastern Irish Sea (Woodhead, 1997). The decreasing releases in later years has led to much lower water concentrations, putting a larger emphasis on the Irish Sea sediment as a potential source of 137Cs via remobilisation. Due to its different oxidation states, plutonium has a little more complicated behaviour. In oxidised form, i.e., oxidation states V and VI, 3 plutonium has higher solubility with Kd~ 10 , while the reduced forms in 6 oxidation states III and IV are more particle reactive with Kd~ 10 . It is estimated that 80 % of the plutonium in seawater is in oxidation state V

31 (Woodhead, 1997). Kj for americium is about 2><106, the highest value among the radionuclides discussed here.

The Chernobyl accident

The most serious nuclear power plant accident hitherto occurred in Chernobyl in the Ukraine on April 26,1986. During a test of the capability of the reactor, several safety procedures were ignored. This resulted in uncontrolled nuclear fission in the reactor, followed by a powerful explosion and fire. Large amounts of radioactivity were released. It is estimated that approximately 100, 50 and 8 PBq of 137Cs, 134Cs and 90Sr were released, about 70 % of the radiocaesium and 10 % of the 90Sr being deposited outside the European part of the USSR. Releases of transuranics were much lower, 55, 25 and 6 TBq of 239-240Pu, 238Pu and 241Am respectively, of which less than 20 % is expected to have been deposited outside the (former) USSR (WHO, 1989). For 10 days after the explosion, fire in the graphite moderators of the reactor continued to release radioactivity and the weather conditions prevailing determined the dispersion and deposition pattern. Fallout of Chernobyl radioactivity, mainly radiocaesium, was reported from all Europe, with the highest depositions in Austria, Switzerland, southern Germany and Scandinavia (NEA, 1996). Fallout was also detected globally in the northern hemisphere, mainly north of 30 °N (Cambray et al, 1987; Aoyama, 1988; Aoyama and Hirose, 1995). The low 90Sr releases from the Chernobyl accident were reflected in the 137Cs/90Sr activity ratio of 30, as measured in dust over the Baltic Sea (Aarkrog, 1988). The best tracer of Chernobyl activity was 134Cs activity, which with high activities and a ratio of approximately 0.5 to 137Cs exceeded I34Cs activity in the marine environment originating from Sellafield releases. Due to different times of release from the reactor the 134Cs/!37Cs ratio in debris from the Chernobyl accident varied between different sampling areas. In northern Europe the ratio was above 0.5, measurements in the Baltic Sea and eastern Denmark registering ratios of 0.59 and 0.56 respectively. Air samples from central Sweden had a ratio of 0.53 (Devell, 1991) while Mitchell (1988) reports 0.56 from Lowestoft in Great Britain. Deposition in the sea was more difficult to map. The deposition of

32 I37Cs in the Baltic Sea is estimated to be 5200 TBq. Of this, 360 TBq were found in the sediment in 1986 and 900 TBq in 1987 (Holm, 1996). The fallout of plutonium from Chernobyl into the Baltic Sea is estimated to be 1.5 and 0.72 TBq of 239-240Pu and 238Pu respectively, approximately 99 % of which is assumed to have been rapidly transferred to the sediment. Deposition in the Baltic Sea of 239>240Pu and 238Pu amounts to about 10 % and 100 % of the global fallout content respectively. Measurements in the North and Norwegian Seas in the summer after the accident, revealed a rapid appearance of Chernobyl activity, indicating direct fallout (Mitchell and Steele, 1988). The North Sea measurements showed higher 134Cs/137Cs activity ratios in the northern part. Elevated ratios were also recorded in the Norwegian Sea south of 70 °N. Although Chernobyl fallout was recorded worldwide, it is difficult to determine whether any significant deposition occurred over the Arctic Ocean. Fallout from Chernobyl over the Kola peninsula constituted 30 % of the total 137Cs inventory (Semenov, 1993). The same Chernobyl fraction was recorded in northern and north-eastern Norway while in north-western Norway Chernobyl 137Cs constituted above 90 % of the total 137Cs inventory (Bergan 1998). In the summer of 1987, Chernobyl caesium also amounted to 30 % of the total caesium activity at the continental shelf slope north-east of Spitsbergen (Cochran et al, 1995). Since transport time across the Barents Sea is estimated to be about 1 year, it is possible that significant deposition occurred also in the Barents Sea or neighbouring areas. Today, outflow from the Baltic Sea is assumed to be the main source of activity from Chernobyl to the Nordic Seas. Holm (1996) estimates the net outflow of 137Cs from the Baltic Sea to some 50 TBq/y in 1996, of which more than 90 % consists of Chernobyl activity (unpublished data).

Other significant and potential sources

In the Ural mountains, the Russian nuclear facility Cheliabinsk-40 (Mayak) has released radioactive waste to the Techa river, a tributary of the Ob river. During 1949-1956, about 100 PBq, of this about 13 and 12 PBq were 137Cs and 90Sr respectively, and 2 TBq alpha emitters were discharged. It is not known how much of this activity has reached the Arctic Ocean, but most of it is assumed to remain in different reservoirs at the upper Techa river

33 (Aarkrog, 1994). From the early 1960's to 1991, the former USSR dumped approximately 5.3 PBq solid radioactive waste into the Barents and Kara Seas (Nyffeler et al., 1996). Measurements in the vicinities of the dumped objects reveals that leakage occurs, but only in relatively small amounts (Strand and Nikitin, 1997). In the period 1949-1982, several West-European countries dumped approximately 27 PBq packaged radioactive waste into the north-east Atlantic Ocean, 3H, 241Pu, 90Sr, 137Cs and 60Co comprise the major part of the activity (Nyffeler et al, 1996). Although not yet known to release any substantial amounts, the dumped activity constitutes a large potential source of radioactivity for the Arctic region. The reservoirs at Mayak also contains large amounts of activity, in 1993 about 45 PBq, which, in the event of an accident, could partially be released to the Arctic seas. On an aeroplane crash in 1968 at the US airbase at Thule, NV Greenland, unfissioned material from four nuclear weapons was spread on the sea ice (Aarkrog et al, 1987). Much of the debris was recovered, but approximately 1 TBq 239-240Pu still remains on the seafloor. Resuspension from sediment to seawater is low, and, compared to other locations in the north Atlantic, no enhanced plutonium concentrations have been observed.

34 ANTHROPOGENIC RADIOACTIVITY IN THE ARCTIC

Input to the Arctic Ocean

Marine transport of radionuclides to the Arctic follows the sea currents. Global fallout of nuclear weapon debris was only to a small degree deposited directly in the Arctic, the main fraction of fallout radioactivity has been transported from the North Atlantic. Hence, it will follow the NAC and enter the Arctic Ocean either across the Barents Sea or through the Fram Strait. Together with activity output from the Baltic Sea, releases from the European reprocessing plants follow the Norwegian coastal current northward. An extensive review of current knowledge of transfer from the European reprocessing plants to the Arctic Ocean has been given by Kershaw and Baxter (1995). Releases from Sellafield to the Irish Sea are forced by the Atlantic currents to follow the coast of Scotland closely and emerge into the North Sea. Their main route leads in a loop through the southern North Sea before proceeding north into the NCC, with a second fraction taking a shortcut across the northern North Sea (Guegueniat et al., 1996; Livingston et al., 1982A). Releases from La Hague into the English Channel are transported south and east of the Sellafield activity in the North Sea, and to the NCC (Guegueniat et al., 1996). Water profile sections from the Norwegian coast outwards at 65 °N show higher I37Cs concentrations in surface water and in the east (Kershaw and Baxter, 1995), reflecting the boundary between NCC and the NAC, as described above. For the same reason, it is reasonable to assume that activity fro the Baltic Sea, carried by water with lower salinity than the North Sea water, will be found above and to the east of the reprocessing activity, at least at the entrance to the NCC. The successive mixing of the NCC and the NAC results in slight decreases in activity concentrations as one goes north (e.g. Holm et al., 1983; Kershaw and Baxter, 1995). Temporal variations at 59-61 °N in the NCC showed the highest concentration of 137Cs, 120 Bq/m3, in 1979 (Kershaw and Baxter, 1995), reflecting the maximum Sellafield releases in 1975. Assuming the same transport time from Sellafield, 90Sr and 239240Pu reached maximum concentrations approximately in the same year, the concentrations in 1980 in the south NCC being 23 and 0.020 Bq/m3 for 90Sr and 239-240Pu respectively (Kautsky, 1986). Cs-137/90Sr and

35 activity ratios of 4-5 and 0.11-0.14 respectively reveal the influence of high releases from Sellafield on the total concentrations at that time (Kershaw and Baxter, 1995). Present (1996) NCC concentrations at the same latitude 3 137 239240 are about 8.0 and 0.008 Bq/m for Cs (>50 % Chernobyl) and pu respectively (unpublished data). The activity carried by the NCC surface water to a high degree follows the coast into the Barents Sea, as revealed by 137Cs contours from different investigations in the Barents and Norwegian Seas (Casso and Livingston, 1984; Wedekind et al., 1997). It is estimated that 30 % of the Sellafield 137Cs discharges flows into the Barents Sea (Wedekind et al., 1997) and 22 % continues to the central Arctic Ocean (Kershaw and Baxter, 1995). A signal with lower concentration, probably as a result of dilution by Atlantic water, has been traced in the WSC. The westerly extent of surface water activity in the WSC is revealed by a strong 137Cs gradient 200 km west of Svalbard observed in 1981-82 (Casso and Livingston, 1984), and also in 1983 for both the 134Cs and 137Cs concentrations (Aarkrog et al., 1985). Inflow via the Fram Strait is estimated to amount to 13 % of the total Sellafield releases (Kershaw and Baxter, 1995), and the remaining fraction of the NCC activity being recirculated from the WSC into the Greenland Sea. During transit to the Arctic, it is estimated that 40 % of the Sellafield 137Cs is removed by sedimentation (Wedekind et al., 1997). It is likely that this relationship between the two input paths hold also for the Chernobyl activity transported by the NCC, although with a higher tendency towards the former, if the Baltic Sea outflow to a higher degree follows the Norwegian coast. Several estimates of transit times from the north European seas to the Arctic region have been conducted and are summarized in Table 3. Many of the investigations utilize the Sellafield peak releases of 137Cs in 1975 or changes in the 134Cs/137Cs ratio. The increasing 129I/137Cs ratio from the combined source Sellafield and La Hague was first used by Smith et. al. (1997) and is also applied in Paper I and III.

The shelf seas

The shelf seas receive radioactivity input both from sea and river water. Aarkrog (1994) estimates that the Arctic rivers have contributed with global

36 fallout runoffs of 0.5 and 1.5 PBq of 137Cs and 90Sr respectively to the Arctic Ocean (decay corrected to 1993). Additional 1-5 PBq of each radionuclide are attributed to other riverine sources, such as discharges from Russian nuclear facilities into the Ob and Yenisey river systems. Sediment samples from the Ob river reveal that at least 75 % of the riverine input of 137Cs and plutonium to the shelf seas have been of global fallout origin (Sayles et al., 1997). It is reasonable to assume that also 90Sr and 129I inputs have been mainly of global fallout origin. Russian restrictions on research in the eastern Barents Sea and the other shelf seas have limited the number of non-Russian investigations. Russian data on 90Sr in the shelf seas are available for the period 1963-1996. High Barents Sea concentrations, up to 24 Bq/m3, were registered in 1963 and 1964, as an effect of global fallout. High fallout concentrations were also registered in the Kara, Laptev, East Siberian and Chukchi Seas, with mean surface activities in 1964 of 39, 28, 21 and 18 Bq/m3 respectively (Chumichev, 1997). At the beginning of the 1980's, Sellafield releases caused a second maximum which reached around 16 Bq/m3 in the south-east Barents Sea (Chumichev, 1997). No similar 137Cs results from the 1960's are known to have been published for the seas east of Barents Sea, but regarding the 137Cs/90Sr ratio of 1.5 in direct fallout and equal or lower in the river runoff, the 137Cs concentrations in the same period are assumed not be more than 1.5 times higher than 90Sr concentrations. Cs-137 concentrations in the south-west Barents Sea were in the range 15-25 Bq/m3 in 1965, and rose to over 45 Bq/m3 in 1980 (Kershaw and Baxter, 1995). Other references report similar concentrations in the beginning of the 1980's with 15-20 Bq/m3 in the WSC (Aarkrog et al., 1985; Dahlgaard et al., 1986), 16-20 Bq/m3 in the central Barents Sea (Casso and Livingston, 1984; Holm et al., 1983) and SO- SO Bq/m3 in the southern Barents Sea (Casso and Livingston, 1984; Dahlgaard et al., 1986). Since then, activity levels have decreased substantially, to the current (1996) concentration of 2.5-3.4 Bq/m3 (Paper III). Reports of nuclear reactors from Russian submarines dumped in the fjords of Novaya Zemlya in the Kara Sea led to a Russian-Norwegian collaboration in 1992-1994. To investigate possible environmental contamination, sampling was conducted in the near vicinity of the dumping sites, but also further out in the Kara Sea. Enhanced contamination close to the dumped object reveals that leakage occurs, but is not traced further away

37 (Strand and Nikitin, 1997). In the south-western Kara Sea, an extensive set of data on both the surface and subsurface concentrations of 137Cs, 90Sr, 238Pu, 239240Pu and 241Am was obtained in 1992. The 137Cs activities were in the range 3.3-20.4 Bq/m3, with the higher values observed in high salinity Atlantic and NCC water. The reverse relationship vis-a-vis salinity was observed in the 90Sr concentrations, being in the range 3.1-11.4 Bq/m3, with the higher activities being associated with low salinity river runoff (Strand et al., 1994). Cs-134 activities were primarily attributed to the Chernobyl accident, which contributed approximately 30 % of the observed 137Cs activity. The Swedish-Russian Tundra Ecology Expedition in 1994 constituted one of the first possibilities for western researchers to get access to the Eurasian shelf seas further to the east. In Paper I, the influence of Sellafield, Chernobyl and fallout activity to the Barents, Kara, Laptev and East Siberian Sea is investigated. The Chernobyl contribution to the I37Cs concentrations is estimated from the 134Cs/137Cs activity ratio and amounts to approximately 30 % in the Barents, Kara and Laptev Sea. No 134Cs was detected in the East Siberian Sea and, together with low concentrations of 129I and 137Cs, it is concluded that these waters are mainly influenced by Pacific Sea inflow carrying primarily global fallout activity. As an effect of the decreasing input of reprocessing and Chernobyl activity as well as runoff contributions of fallout 90Sr from the Russian rivers, the 137Cs and 90Sr activities generally increased from Barents Sea to the Kara and Laptev Seas. Cs-137 activity ranged from 5.3-8.1, 5.0-12.8 and 7.9-15.1 Bq/m3, in the three seas respectively, but with lower values in the low salinity waters near the river mouths. The corresponding figures for 90Sr were 1.6-3.4, 2.0-4.0 and 3.5-4.7 Bq/m3. As a consequence of the increasing European reprocessing releases, the 129I concentration decreased towards the east, and was in the range of 21.9-0.76 xlO8 atoms/litre. Other investigations in the shelf seas from the beginning of the 1990's show similar I37Cs, 90Sr and 129I activity concentrations (Nikitin et al., 1997; Chumichev, 1997; Beasley et al., 1995; Raisbeck etal, 1993). In comparison with the Tundra -94 expedition results for the Kara Sea, the Oden 1996 expedition (Paper III) data showed much lower concentrations of 129I as well as a lower 134Cs/137Cs ratio in the Nansen Basin just north of the St. Anna Trough. This led to the conclusion that no significant surface water input of shelf activity from the Kara Sea occurs to

38 the central Arctic Ocean. The major surface inflow is instead supposed to originate in the Laptev Sea, since equally high levels of 1291,137Cs and the 134Cs/137Cs ratio were found in the eastern Kara Sea and western Laptev Sea in 1994 and two years later above the Lomonosov Ridge at 85-88 °N. Apart from the Ob and Yenisey river sediment, few data on transuranic concentrations have been reported for the shelf seas. The Russian-Norwegian expedition reported south-west Kara Sea water 239-240Pu concentrations in the wide range of 2-16 mBq/m3 and 241Am from below detection limit and up to 2.6 mBq/m3 (Strand et al., 1994). Results from the St Anna and Voronin Troughs in the northern Kara Sea in 1996 (Mitchell et al., 1998), show 239240Pu concentrations in the range 2-8 mBq/m3, with a 238pu/239,24opu ratio iess than Q Qj^ indicating mainly global fallout origin. 239 240 241 The Tundra -94 expedition results on the > pu and Am sea water concentrations are reported in Paper IV, the levels generally being between 2 and 10 mBq/m3 (with some exceptions) and decreasing slightly towards east. In the areas around the mouths of the Ob, Yenisey and Lena rivers, 3 238 239 24O however, the concentrations rose to 25-90 mBq/m . The pu/ ' pu activity ratio was below 0.06 and indicate only fallout origin, also in the high activity river runoff. Sediment samples from the Petchora Sea in 1992 contain integrated 137 23924O 2 Cs and pu activities in the range 251-1065 and 13-938 Bq/m respectively (Smith et al., 1995; Strand et al., 1994). The upper range was affected by local releases from underwater nuclear tests in the Chernaya Bay, south Novaya Zemlya. Corresponding levels in the south-western Kara Sea were 120-500 and 2.5-18 Bq/m2 respectively (Strand et al., 1994), and north of the mouths of the Ob and Yenisey rivers 157-397 and 2,6-10,8 Bq/m2 respectively (Baskaran et al., 1996). During the Tundra -94 expedition, several sediment cores were obtained from the shelf seas. Probably due to the shallow waters in which they were obtained, most of the cores showed considerable mixing. Moreover, the mixing often went deeper than the sample depth which prevented the estimation of a precise activity inventory. However, five cores from the Kara, Laptev and East Siberian Seas with sufficient length to include the total anthropogenic radioactivity were analysed for 137Cs, and showed integrated activity in the range 120-840 Bq/m2 with the highest activity in the eastern Laptev Sea and the lowest in the East Siberian Sea. At three of the stations, integrated 239240Pu activities were determined to be in

39 the range 4.9-34.3 Bq/m2, with a ratio to I37Cs of approximately 0.05 (Paper V). The difference to the global fallout ratio, which in 1994 was about 0.024, is primarily due to the additional I37Cs input from Sellafield and the Chernobyl accident

The Arctic interior

Harsh climate and relative inaccessibility have limited the number of investigations of radioactivity in the central Arctic Ocean. Earlier expeditions were performed from drifting ice camps and sampling was thus limited to a small area. The first reports of anthropogenic radionuclides were for 90Sr concentrations under the ice cover in the Canadian Basin and the Chukchi Sea between 1957 and 1962 (Bowen and Sugihara, 1964). At that time, it was concluded that their origin was global fallout transported from the Pacific Ocean. The first radionuclide profile in a water column from the central Arctic was obtained from the LOREX ice station in 1979 (Livingston et al, 1984). While drifting approximately 200 km from the Makarov Basin to the Fram Basin across the Lomonosov Ridge at about 89 137 90 239240 241 °N, samples for Cs, Sr, pu and Am determinations were obtained at 8 depths from the surface down to 3000 metres. The highest concentrations of 137Cs and 90Sr (6.5 and 5.5 Bq/m3) were found in the surface and upper halocline layers respectively, while the 239240Pu concentration showed a slight maximum of 18 mBq/m3 in the Atlantic water sample at 500 metres. Except for the 1500 metre sample, all samples contained only global fallout-derived activity. From the 137Cs/90Sr ratio of 1.24 in the PML, about 50 % of the activity origin was assumed to be runoff water, which has a ratio of 1 or less. The 134Cs surface activity was below the limit of detection, and thus yet not influenced by the increasing releases from Sellafield. The 137Cs/90Sr ratio in the upper halocline, identified by high silica concentrations, was about 1.0 and assumed to be an effect of higher scavenging of 137Cs compared to ^Sr on the Bering Sea shelf. This 239 240 scavenging did not, however, seem to affect the > pu concentration in the + same layer, probably due to the plutonium existing as PuO2 , which is less particle reactive. Am-241 concentrations were in the range 5-7 mBq/m3 in the PML, while no 24! Am activity could be detected in the upper halocline sample. Since most americium was supposed to have been removed by

40 sedimentation over the Bering and Chukchi Seas and no buildup from 24lPu could be detected, the transport time from these seas to the LOREX station was supposed to be less than approximately 6 years. It was also concluded that very low scavenging took place between the depths of 75 and 110 metres. Sampling for 137Cs and some natural radionuclides was also made at the CESAR ice station in 1983, positioned above the alpha ridge in the Canadian Basin. The 137Cs results were reported by Smith and Ellis (1995) together with data for 137Cs and other radionuclides from an ice station on the Canadian continental shelf in 1985,1986 and 1989. Surface water 137Cs activities at both stations were similar (5.5 Bq/m3 at CESAR) and slightly lower than LOREX surface water. Higher 137Cs concentrations were observed in the lower halocline samples at CESAR relative to the corresponding shelf samples, indicating later arrival of the fallout pulse to the latter. The 137Cs/90Sr ratios observed at the CESAR station are low and indicate only fallout origin (Livingston, 1988). In the 1500 metres sample at LOREX, the high 137Cs and 90Sr concentrations together with an I37Cs/90Sr activity ratio of 2.16 led to the conclusion that Sellafield-derived activity had reached this depth, possibly following the inflow over the Bering Sea and there gaining enough density to reach larger depths in the Arctic Ocean. From release ratios and concentrations, the transit time from Sellafield was estimated to be about eight years. The signal was rather local, since the 500, 1000, 2500 and 3000 metre samples had ratios equal to or slightly greater than the fallout ratio. A high influence of Sellafield activity was also observed at the AIWEX station in the southern Canadian Basin in 1985. Accompanied by increased 137Cs concentrations, the Sellafield signal increased from the surface layer down to 1500 metres. Due to its sill depth of 1400 metres, the Lomonosov Ridge is assumed to prevent the inflow into the Canadian Basin of deeper lying reprocessing activity (Livingston, 1988). Similar maxima, both in 137Cs and in the 137Cs/90Sr ratio, were also observed at about 1000 to 1500 metres depth at Polarstern station 331 in the northern EGC in 1984 and was attributed to the same source (Livingston, 1988). Despite high I37Cs activities, the surface water at the AIWEX and PS-331 stations has a 137Cs/90Sr ratio at fallout level, which shows the longer transit times for surface waters, compared to upper deep water, to these stations. In later years, surface and submarine cruises have enabled

41 simultaneous sampling across the Arctic Basins. During the 1987 ARK IV/3 cruise of the R/V Polar stern, water profiles from the Nansen Basin for radionuclide analysis were obtained (Cochran et al., 1995). On the shelf slope north east of Spitsbergen, the highest total I37Cs activity concentrations of approximately 10 Bq/m3 were observed in surface water and in the Atlantic layer. Somewhat lower levels, decreasing with depth from 9.3 Bq/m3 at the surface to 3.4 at 550 metres and 1.9 at 1500 metres, were found at the station above the Gakkel Ridge. Samples from the shelf slope north east of Spitsbergen contained 30 % Chernobyl 137Cs down to 500 metres and 20 % at the slope direct north of Spitsbergen. Further into the interior of the Nansen Basin, a weaker Chernobyl signal was traced in the upper 300 metres, while no Chernobyl traces were observed above the Gakkel Ridge. The Chernobyl activity may have entered with the inflowing WSC, possibly originating in the Norwegian Sea, which, as mentioned above, contained high Chernobyl activity already shortly after the accident (Mitchell and Steele, 1988). An alternative, perhaps more likely inflow pathway, leads across the Bering Sea east of Svalbard, and then down along the shelf slope. Such inflows of high density water have been observed by Schauer et al (1997), penetrating down to about 500 metres. High I34Cs/137Cs ratios were also observed in surface water in the central Arctic Basin in 1991 (Paper II). In the Nansen Basin south of 85 °N, Chernobyl-derived 137Cs amounted to 20-50 % of the total activity. In the area around the North Pole, the ratio was only 0.004-0.008 and most of the I37Cs was attributed to Sellafield. The highest Chernobyl fractions did not coincide with the highest 137Cs concentrations, which were observed in the area closest to the North Pole (87-89 °N and 50-180 °E), and were instead assumed to originate in the large Sellafield releases during 1974-79. The depth distribution at the station above the Gakkel Ridge was about the same as the 1987 results (Cochran et al., 1995). In 1996, the Chernobyl-derived surface water activity was redistributed, and the highest 134Cs/137Cs ratios coincided with the highest I37Cs concentrations. These were found, together with highest surface water concentrations of 129I and 90Sr, in a band stretching from the northern Lomonosov Ridge past the North Pole and then south along 10-15 °E to the Gakkel Ridge. All of the 1996 137Cs, 90Sr and 129I depth distributions, in total about 15 profiles down to 850 and 1000 metres depth, showed activities

42 decreasing with depth. The only exceptions were the lower halocline 137Cs samples above the Lomonosov Ridge and in the northern Makarov Basin which contained higher activity concentrations than both surface and Atlantic layer samples. Since 134Cs was only measured in surface water samples, and elevated 137Cs/90Sr ratios may be an effect of both Sellafield and Chernobyl activity, the origin of these samples was not easily determined. Residence times in surface and halocline layers are estimated to be 2-6 and up to 15 years respectively (Schlosser et al., 1995), which means that a temporary input of activity to both layers would, after sufficient time, appear as a halocline maxima. Since no corresponding maxima was seen for i29j or 90gr^ jt js assumecj that the source is Chernobyl caesium, introduced into the surface layers around 1990. The extent of reprocessing activity into the Canadian Basin has been traced using the 129I distribution (Smith et al., 1997A). In surface water, the front is placed approximately along the Mendeleev Ridge, with concentrations in the Atlantic-derived water above 8 x 108 atoms/litre and below 1*1O8 atoms/litre in water with Pacific origin. In the halocline, this front is displaced somewhat towards North America and in the Atlantic layer samples even further in the same direction. Indications of this boundary are also observed in our I29I data from the area of the Lomonosov Ridge with slightly decreasing concentrations in the Makarov Basin, in both the PML and Atlantic layer samples (Paper III). The Atlantic layer decrease is, however, a reflection of the Atlantic water which follows the Lomonosov Ridge towards the Fram Strait, and not significantly cross the ridge. The concentration of plutonium activity north of Svalbard was in 1987 17-18 mBq/m3 (Cochran etal, 1995), comparable to the 15-17 mBq/m3 measured in 1980 (Holm et al., 1986). In 1991, the concentration had decreased to 7-8 mBq/m3 and were approximately equal in 1996 (Paper II and IV). The 1980 results showed some influence of Sellafield-derived 238 239 240 activity, as concluded from the pu/ . pu ratio, but could not in 1996 be distinguished from the fallout ratio. Further to the north, in the Amundsen 239 240 and northern Makarov Basins, - pu concentrations were almost constant in the 1991 and 1996 results (Paper II and IV). Plutonium depth distributions show maxima at 200-400 metres in the Atlantic layer in 1996 (Paper IV) and somewhat deeper in the Nansen Basin in 1987 (Cochran etal, 1995). Am-241 results from 1987 (Cochran etal, 1995) and 1996 suggests a higher removal of americium on the shelves as

43 compared to plutonium, resulting in 241Arn/239i240Pu ratios of 0.6-0.2. Water column inventory estimates have been reported from 1979 (Livingston et al., 1984), 1987 (Cochran et al., 1995) and 1996 (Paper III and IV). Comparing the 1979 data from the Canadian and Eurasian side of the northern Lomonosov Ridge (Livingston et al., 1984) with 1987 data from Nansen Basin interior (Cochran et al., 1995), shows an increase in the 137 239240 241 total integrated activity of Cs, pu and Am in the water column. The 1996 inventories were determined only in the upper 900 metres. Compared to LOREX data in the corresponding depth range, they show the same integrated 239-240Pu activity and double the 137Cs and 90Sr activities. The mean integrated activity of I29I down to 900 metres in 1996 was 350x1012 atoms/m2. Compared to the Arctic shelf, sediments in the central Arctic Ocean show much lower activity levels. The mean integrated I37Cs and 239>240Pu activities are 43 and 0.60 Bq/m2 respectively, with a 239>240Pu/137Cs ratio of 0.013. Coarse calculations show that approximately 75 % of the plutonium activity and 10 % of the I37Cs activity, which have passed the shelf seas were deposited in the shelf sediment. Corresponding figures for the central Arctic Ocean are 0.9 % and 0.3 % respectively (Paper V).

Arctic Ocean outflow and the East Greenland Current

The East Greenland Current carries the major outflow of radioactivity from the Arctic Ocean. Since the outflow is limited laterally, the radionuclide composition reflects the contents of the Arctic Ocean and WSC. Throughout the 1970's and 1980's, EGC surface water contained higher fallout-derived radionuclide concentrations than the north Atlantic Ocean, despite the higher direct fallout to the latter (Dahlgaard, 1994). This is primarily supposed to have been the effect of runoff activity from the large catchment areas of the Arctic rivers, contributing with substantial fallout activity, but also to the dumping of liquid nuclear wastes in the Arctic Ocean shelf seas and close fallout from the Novaya Zemlya nuclear test sites (Dahlgaard, 1994). In 1982, the first Sellafield-derived activity in the surface water of the EGC was detected. The measured 134Cs/137Cs activity ratio with higher fractions in the eastern part of the EGC, were in agreement with Sellafield release ratios in 1975 (Aarkrog et al., 1983), and the Sellafield-derived

44 activity were supposed to have been transferred directly from the WSC, and not have entered the Arctic Ocean. In 1988 and 1990, the water masses in two profile sections between Greenland and Jan Mayen Island and in the Denmark Strait between Greenland and Iceland were studied (Dahlgaard, 1994). The surface layer originating in the Arctic Ocean PML showed higher concentrations of 137Cs, 90Sr and "Tc, compared to the deeper layers. This reflects the depth distribution in the Arctic Ocean, but is also an affect of the return WSC which, due to decreasing Sellafield releases, will dilute primarily the subsurface EGC layer. At the same time, the return WSC permitted the 134Cs signal from the Chernobyl accident, deposited in the Norwegian sea but not in the Arctic Ocean, to appear in the subsurface layer in the EGC (Dahlgaard, 1994).

45 MAIN CONCLUSIONS

Global fallout, releases from the European reprocessing plants Cap de La Hague and Sellafield and from the Chernobyl accident are identified as the three main sources of anthropogenic radionuclides in the Arctic Ocean. From measurements in the Norwegian Sea and the Eurasian shelf seas it is concluded that the total input of 134Cs, 137Cs and 90Sr from these sources has been decreasing during the 1990's. The main fraction of the reprocessing and Chernobyl activity found in Arctic Ocean surface water is being transported from the Norwegian coastal current to the Barents and Kara Seas and then east along the Eurasian Arctic shelf. From the Laptev Sea it enters the central Arctic Ocean and follows the transpolar drift to the East Greenland current. In the central Arctic Ocean, the highest 137Cs, 129I and 90Sr concentrations are found in the surface layers, which reflects the reprocessing and Chernobyl origin as being the major source terms. Chernobyl-derived 137Cs appeared in the central parts of the Arctic Ocean in 1991, and in the mid 1990's the fraction to total 137Cs was approximately 1/3 in the Eurasian Arctic region. The transfer time for Sellafield releases are estimated to be 5-7 years to the SE Barents Sea, 7-9 years to the Kara Sea, 10-11 years to the Laptev Sea and 12-14 years to the central Arctic Ocean. Global fallout is the primary source of plutonium both in the shelf seas and in the Arctic Ocean interior. This controls the depth distribution, with highest concentration found in the Atlantic layer of the Arctic Ocean. On transport over the shallow shelf seas, particle reactive transuranic elements experience an intense scavenging. A rough estimate shows that approximately 3/4 of the plutonium entering the Kara and Laptev Seas are removed to the sediment. High seasonal riverine input of 239240Pu is observed near the mouths of the large Russian rivers, and the isotopic signature suggests that the source is not exclusively of fallout origin. Sediment inventories show much higher concentrations on the shelf compared to the deep Arctic Ocean. This is primarily due to the low particle flux in the open ocean. Continued research is required to comprehensively understand the pathways and fate of the anthropogenic radionuclides in the Arctic Ocean. The particle reactive transuranic elements which have shown complicated behaviour in the shallow shelf seas requires particular attention, not least in the light of potential releases from dumped nuclear waste in the Kara Sea.

46 ACKNOWLEDGEMENTS

I wish to express my sincere gratitude to all colleagues at the Radiation Physics Department and all the friends I have made during the Arctic expeditions. Special thanks are due to:

Associate professor Elis Holm, my supervisor, for introducing me to the field of marine radioecology, for giving me the opportunity to do exciting research in the fascinating Arctic environment and for his scientific guidance.

Dr Per Roos, for friendship, fruitful discussions, invaluable advise and support, and patience with all my questions.

My fellow PhD-students and friends, especially Lena Johansson, Katarina Sjogreen, Aaro Ravila, Mats Eriksson and Birgitta Roos, for sharing lots of thoughts, laughs and lunches.

The laboratory personnel, Gertie Johansson, Birgit Amilon and Carin Lingardh, for kind assistance with all my samples.

Professor Bertil Persson for good advise and collaboration during two Arctic expeditions.

Kjell-Ake Carlsson for sampling assistance during the Tundra expedition.

Olle Olsson for keeping the electronic equipment in good shape.

Jannika Gustafsson, my girlfriend and best friend, for love and mental and logistic support during the writing of this thesis.

Financial support was given by: The Swedish Radiation Protection Institute The Swedish Polar Research Secretariat The European Community (Contract no. F14P-CT95-0035) The Nordic Nuclear Safety Research The Swedish Natural Science Research Council

47 REFERENCES

Aagaard, K. and E.C. Carmack (1989) The Role of Sea Ice and Other Fresh Water in the Arctic Circulation. Journal of Geophysical Research, 94 (CIO), 14485-14498.

Aagaard, K., J.H. Swift, and E.C. Carmack (1985) Thermohaline circulation in the Arctic Mediterranean seas. Journal of Geophysical Research, 90 (C3), 4833-4846.

Aarkrog, A. (1988) The Radiological Impact of the Chernobyl Debris Compared to that from Nuclear Weapons Fallout. Journal of Environmental Radioactivity, 6 (2), 151-162.

Aarkrog, A. (1994) Radioactivity in Polar Regions-Main Sources. Journal of Environmental Radioactivity, 25 (1-2), 21-35.

Aarkrog, A., S. Boelskifte, H. Dahlgaard et al. (1987) Technetium-99 and caesium-134 as long distance tracers in Arctic waters. Estuarine, Coastal Shelf Sci.,, 24, 637-647.

Aarkrog, A., S. Boelskifte, H. Dahlgaard et al. (1987) Studies of transuranics in an Arctic marine environment. Journal ofRadioanalytical and Nuclear Chemistry,, 115 (1), 39-50.

Aarkrog, A., H. Dahlgaard, L. Hallstadius, H. Hansen, and E. Holm (1983) Radiocaesium from Sellafield effluents in Greenland water. Nature, 304,49-51.

Aarkrog, A., H. Dahlgaard, H. Hansen et al. (1985) Radioactive tracer studies in the surface waters of the northern North Atlantic including the Greenland, Norwegian and Barents Seas. Rit Fiskideildar,, 9, 37-42.

Anderson, L.G., G. Bjork, O. Holby et al. (1994) Water masses and circulation in the Eurasian Basin: Results from the Oden 91 expedition. Journal of Geophysical Research,, 99 (C2), 3273-3283.

Anderson, L.G. and E.P. Jones (1992) Tracing Upper Waters of the Nansen Basin in the Arctic Ocean. Deep-Sea Research part A-Oceanographic Research Papers, 39 (2A), 425-433.

Aoyama, M. (1988) Evidence of stratospheric fallout of caesium from the Chernobyl accident. Geophysical Research Letters, 15 (4), 327-330.

Aoyama, M. and K. Hirose (1995) The temporal and spatial variation of 137Cs concentration in the western North Pacific and its Marginal seas during the period from 1979 to 1988. Journal of Environmental Radioactivity, 29 (1), 57-74.

Baskaran, M., S. Asbill, P. Santschi et al. (1996) Pu, 137Cs and excess 210Pb in Russian Arctic sediments.. Earth and Planetary Science Letters,, 140 (1-4), 243-257.

48 Beasley, T.M., L.W. Cooper, J.M. Grebmeier and L.R. Kilius (1995) Iodine-129 in Western Arctic Waters, p. 108 In: Environmental Radioactivity in the Arctic, Strand P and Cooke A, editors, NRPA. Osteras.

Bergan, T.D. (1998), Institute for Energy Technology, Oslo, Norway. Personal Comm.

Bohrmann H, Radioisotopenstratigraphie, Sedimentologie und Geochemie jungquartärer Sedimente des östlichen Arktishen Ozeans. Berichte zur Polarforschung. ISSN 0176-5027. Alfred Wegener Institute. Bremerhaven. 1991

Bojanowski, R. and D. Knapinska-Skiba (1990) Determination of low-level ^Sr in environmental materials. A novel approach to the classical method. Journal of Radioanalytical and Nuclear Chemistry, 138 (2), 207-218.

Bowen, V.T., V.E. Noshkin, H.L. Volchok, H.D. Livingston, and K.M. Wong (1974) 137Cs to ^Sr ratios in the Atlantic Ocean 1966 through 1972. Limnology and Oceanography, 19, 670-681.

Bowen, V.T. and W. Roether (1973) Vertical distribution of Strontium 90, Cesium 137 and Tritium near 45° North in the Atlantic. Journal of Geophysical Research, 78 (27), 6277-6285.

Bowen, V.T. and T.T. Sugihara (1964) Fission product concentration in the Chukchi Sea. Arctic, 64, 198-203.

Cambray, R.S., P.A. Cawse, J.A. Garland et al. (1987) Observations on the radioactivity from the Chernobyl accident. Nuclear Energy,, 26 (2), 77-101.

Carmack, E.C., Large-Scale Physical Oceanography of Polar Ocean, pp. 171-222. In: Polar Oceanography, Part A, Physical Science, Smith WO, editor. Academic Press, Inc. San Diego, 1990.

Casso, S.A. and Livingston HD, Radiocesium and Other Nuclides in the Norwegian-Greenland Seas 1981-1982. WHOI-84-40. Woods Hole Océanographie Institution. Woods Hole. 1984

Chumichev, V.B. (1997) Long-term investigations of 90Sr content in the waters of the Arctic Ocean seas (White, Barents, Laptev, East-Siberian and Chukchi seas), pp. 189-191. In: Environmental Radioactivity in the Arctic, Strand P, editor, NRPA. Osterâs, Norway.

Cochran, J.K., D.J. Hirschberg, H.D. Livingston, K.O. Buesseler, and R.M. Key (1995) Natural and anthropogenic radionuclide ditributions in the Nansen Basin, Arctic Ocean: Scavenging rates and circulation timescales. Deep-Sea Research II, 42 (6), 1495-1517.

Cochran, J.K., H.D. Livingston, DJ. Hirschberg, and L.D. Surprenant (1987) Natural and

4 49 anthropogenic radionuclide distributions in the north west Atlantic Ocean. Earth and Planetary Science Letters, 84, 135-152.

Dahlgaard, H. (1994) Sources of 137Cs, ^Sr and ^Tc in the East Greenland Current. Journal of Environmental Radioactivity, 25 (1-2), 37-55.

Dahlgaard, H., A. Aarkrog, L. Hallstadius, E. Holm, and J. Rioseco (1986) Radiocaesium transport from the Irish Sea via the North Sea and the Norwegian Coastal Current to East Greenland. Rapport et Proces - Verbaux Reunion Conseil Internationale Exploration de Mer, 186,70-79.

Dahlgaard, H., Q.J. Chen, J. Herrmann et al. (1995) On the background level of "Tc, 90Sr, and 137Cs in the North Atlantic. Journal of Marine Systems,, 6 (5-6), 571-578.

Devell, L. Composition and properties of plume and fallout materials from the Chernobyl accident, pp. 29-46. In: The Chernobyl fallout in Sweden. Results from a research program on environmental radiology, Moberg L, editors. Swedish Radiation Protection Institute, Stockholm: 1991.

Edmonds, H.N, J.N. Smith, L.R. Kilius et al. (1997) Anthropogenic 129I in Archived Seawater Samples: Source Functions and Tracer Comparisons.. Radioprotection,, 32 (C2), p. 117

GEOSECS, Atlantic, Pacific, and Indian Ocean Expeditions. Shorebased Data and Graphics. National Science Foundation. Washington, D.C., USA. 1987

Gray, J., S.R. Jones, and A.D. Smith (1995) Discharges to the environment from the Sellafield site, 1951 -1992. Journal of Radiological Protection, 15, 99-131.

Guegue"niat, P., J. Hermann, P. Kershaw, P. Bailly du Bois and Y. Baron (1996) Artificial Radioactivity in the English Channel and the North Sea, pp.121-154. In: Radionuclides in the Oceans: Inputs and Inventories, Guegueniat P, Germain P, and Metivier H, editors, Les editions de physique. France.

Hargrave, B.T., B. Vonbodungen, P. Stoffynegli, and P.J. Mudie (1994) Seasonal variability in particle sedimentation under permanent ice cover in the Arctic Ocean. Continental Shelf Research, 14 (2/3), 279-293.

Herrmann, J., H. Nies, and I. Goroncy (1998) Plutonium in the deep layers of the Norwegian and Greenland Seas. Radiation Protection Dosimetry, 75 (1-4), 237-245.

Holm, E. (1996) Radioactivity in the Baltic Sea. Chemistry and Ecology, 12, 265-277.

Holm, E., R.B.R. Persson, L. Hallstadius, A. Aarkrog, and H. Dahlgaard (1983) Radio-cesium and transuranium elements in the Greeland and Barents Seas. Oceanologica

50 Ada, 6 (4), 457-462.

Holm, E., A. Aarkrog, S. Ballestra, and H. Dahlgaard (1986) Origin and isotopic ratios of plutonium in the Barents and Greenland Seas. Earth and Planetary Science Letters, 79, 27-32.

Holm, E., P. Roos, D. Josefsson and B. Persson (1996) Radioactivity from the North Pole to the Antarctic, pp.59-74. In: Radionuclides in the Oceans. Inputs and Inventories, Guegueniat P, Germain P, and Metivier H, editors, Les editions de physique. France.

Holm, E., P. Roos, R.B.R. Persson et al. (1991) Radio-caesium and plutonium in Atlantic surface waters from 73 °N to 72 °S, pp.3-11. In: Radionuclides in the study of marine processes, Kershaw PJ and Woodhead DS, editors, Elsevier Science Publishers Ltd. Barking, England.

Honjo, S., Particle Fluxes and Modern Sedimentation in the Polar Oceans, pp. 688-739. In: Polar Oceanography, Part B: Chemistry, Biology, and Geology. Smith WO, editor. Academic Press, Inc. San Diego, 1990.

IAEA, Sediment Kds and Concentration factors for Radionuclides in the Marine Environment. Technical Reports Series. 247. International Atomic Energy Agency (IAEA). Vienna. 1985

IAEA, Measurement of Radionuclides in Food and the Environment. Technical Report Series. 295. International Atomic Energy Agency (IAEA). Vienna. 1989

Johannessen, O.M. Brief overview of the physical oceanography, pp. 103-27. In: The Nordic Seas, Hurdle BG, editors. Springer-Verlag, New York: 1986.

Jones, E.P., B. Rudels, and L.G. Andersson (1995) Deep waters of the Arctic-Ocean: origins and circulation. Deep-Sea Research I, 42 (5), 737-760.

Kautsky, H., Artificial radioactivity in the North Sea and the northern North Atlanticduring the years 1977 to 1986. Hamburg, Germany. 1986

Kershaw, P.J. and M.S. Baxter (1995) The transfer of reprocessing wastes from north-west Europe to the Arctic. Deep-Sea Research II, 42 (6), 1413-1448.

Livingston, H.D. (1988) The use of Cs and Sr isotopes as tracers in the Arctic Mediterranean Seas. Seas. Philos Trans. R. Soc. London. Ser. A, 325, 161-176.

Livingston, H.D. and V.T. Bowen (1979) Pu and 137Cs in coastal sediments. Earth and Planetary Science Letters, 43, 29-45.

Livingston, H.D., V.T. Bowen, and S.L. Kupferman (1982) Radionuclides from Windscale

51 discharges I: nonequilibrium tracer experiments in high latitude oceanography. Journal of Marine Research, 40 (1), 253-272.

Livingston, H.D., V.T. Bowen, and S.L. Kupferman (1982A) Radionuclides from Windscale discharges II: Their dispersion in Scottish and Norwegian coastal circulation. Journal of Marine Research, 40(4), 1227-1258.

Livingston, H.D., S.L. Kupferman, T.B. Vaughan, and R.M. Moore (1984) Vertical profile of artificial radionuclide concentrations in the Central Arctic Ocean. Geochimica et. Cosmochimica Acta, 48,2195-2203.

Loeng, H., V. Ozhigin, and B. Adlandsvik (1997) Water fluxes through the Barents Sea. ICES Journal of Marine Science, 54, 310-317.

Manley, T.O. (1995) Branching of Atlantic Water within the Greenland-Spitsbergen Passage: An estimate of recirculation. Journal of Geophysical Research, 100 (C10), 20627-20634.

McColl, N.P., van Weers, A.W. and Cooper, J.R., Civil Nuclear Discharges into North European Waters. Report of Working Group I of CEC Project MARINA. National Radioecological Protection Board. Chilton, Oxon, UK. 1989

McLaughlin, F.A., E.C. Carmack, R.W. Macdonald, and J.K. Bishop (1996) Pysical and Geochemical properties across the Atlantic/Pacific water mass boundary in the southern Canadian Basin. Journal of Geophysical Research, 101 (Cl), 1183-1197.

Mitchell, N.T. and A.K. Steele (1988) The Marine Impact of Caesium-134 and -137 from the Chernobyl Reactor Accident. Journal of Environmental Radioactivity, 6 (2), 163-175.

Mitchell, P.I., C.A. McMahon, L. Leon Vintro, and R.W. Ryan (1998) Plutonium in Arctic surface and sub.surface waters at the St Anna and Voronin Troughs. Radiation Protection Dosimetry, 75 (1-4), 247-252.

NEA, Chernobyl, Ten Years On. Radiological and Health Impact. Nuclear Energy Agency, OECD. Paris, France. 1996

Nies, H. (1988) Artificial Radioactivity in the Northeast Atlantic, pp.250-259. In: Radionuclides: A tool for oceanography, Guary JC, Guegueniat P, and Pentreath RJ, editors,

Nikitin, A.I., L.A. Bovkun and m.fl (1997) Field investigations of marine environment radioactive contamination in the seas of the Eastern Russian Arctic during the year 1993, pp.41-42. In: Environmental Radioactivity in the Arctic,

Nyffeler, F., A.A. Cigna, H. Dahlgaard and H.D. Livingston (1996) Radionuclides in the

52 Atlantic Ocean: A Survey, pp. 1-28. In: Radionuclides in the Oceans. Inputs and Inventories, Guegueniat P, Germain P, and Metivier H, editors, Les Editions de Physique. France.

Ostlund, G. (1994) Isotope tracing of Siberian Water in the Arctic Ocean. Journal of Environmental Radioactivity, 25, 57-63.

Pavlov, V.K. and S.L. Pfirman (1995) Hydrographic structure and variability of the Kara Sea: Implications for pollutant distribution. Deep-Sea Research II, 42 (6), 1369-1390.

Perkins, R.W., Thomas, C.W. Worldwide Fallout, pp. 53-82. In: Transuranic Elements in the Environment, Hanson WC, editors. U.S. Department of Energy, 1980.

Raisbeck, G.M., F. Yiou, Z.Q. Zhou, and L.R. Kilius (1995) 129I from nuclear fuel reprocessing facilities at Sellafield (UK) and La Hague (France): Potential as oceanographic tracer. Journal of Marine Systems, 6, 561-570.

Raisbeck, G.M., F. Yiou, Z.Q. Zhou, L.R. Kilius and H. Dahlgaard (1993) Anthropogenic 1-129 in the Kara Sea, pp. 125-128. In: Environmental Radioactivity in the Arctic and Antarctic, Strand P and Holm E, editors, NRPA. Osteras.

Raisbeck, G.M., F. Yiou, Z.Q. Zhou, L.R. Kilius, and P.J. Kershaw (1997) Marine Discharges of 129I by the Nuclear Reprocessing Facilities of La Hague and Sellafield. Radioprotection, 32 (C2), 91-95.

Rudels, B., L.G. Anderson, and E.P. Jones (1996) Formation and evolution of the surface mixed layer and halocline of the Arctic Ocean. Journal of Geophysical Research-Oceans, 101 (C4), 8807-8821.

Sayles, F.L., H.D. Livingston, and G.P. Panteleyev (1997) The history and source of paniculate 137Cs and 239240Pu deposition in sediments of the Ob River Delta, Siberia. The Science of the Total Environment, 202, 25-41.

Schauer, U., R. Muench, B. Rudels, and L. Timokhov (1997) Impact of eastern Arctic shelf waters on the Nansen Basin intermediate layers. Journal of Geophysical Research, 102 (C2), 3371-3382.

Schlosser, P., D. Bauch, R.G. Fairbanks, and G. B6nisch (1994) Arctic river-runoff: mean recidence time on the shelves and in the halocline. Deep-Sea Research I, 41 (7), 1053-1068.

Schlosser, P., J.H. Swift, D. Lewis, and S.L. Pfirman (1995) The role of the large-scale Arctic Ocean circulation in the transport of contaminants. Deep-Sea Research II, 42 (6), 1341-1367.

53 Semenov, A. (1993) Impact of Chemobyll accident on the Kola peninsula radiation conditions, pp.353-356. In: Environmental Radioactivity in the Arctic and Antarctic, Strand P and Holm E, editors, NRPA. Osteras.

Smith, J.N. and K.M. Ellis (1995) Radionuclide tracer profiles at the CESAR Ice station and Canadian Ice Island in the western Arctic Ocean. Deep-Sea Research II, 42 (6), 1449-1470.

Smith, J.N., K.M. Ellis, L.R. Kilius et al. (1997) The Transport of 129I and 137Cs from European Reprocessing Plants through the Kara Sea. Radioprotection,, 32 (C2), 97-103.

Smith, J.N., K.M. Ellis and L.R. Kilius (1997 A) The Transport of Reprocessing Plant Tracers 1291 and 137Cs through the Arctic Ocean: Measurements from US Navy nuclear submarines, pp.38-40. In: Environmental Radioactivity in the Arctic

Smith, J.N., K.M. Ellis, K. Naes, S. Dahle, and D. Matishov (1995) Sedimentation and mixing rates of radionuclides in Barents Sea sediments off Novaya Zemlya. Deep-Sea Research II, 42 (6), 1471-1493.

Smith, J.N., K.M. Ellis, and L.R. Kilius (1998) 1291 and 137Cs tracer measurements in the Arctic Ocean. Deep-Sea Research, In press

Somayajulu, B.L.K., Sharma, P., Herman, Y. Thorium and Uranium Isotopes in Arctic Sediments, pp. 571-80. In: THE ARCTIC SEAS; Climatology, Oceanography, Geology, and Biology, Herman Y, editor. Van Nostrand Reinhold Company, New York: 1989.

Steele, M., J.H. Morison, and T.B. Curtin (1995) Halocline water formation in the Barents Sea. Journal of Geophysical Research, 100 (Cl), 881-894.

Strand, P. and Nikitin AI, Dumping of radioactive waste and investigation of radioactive contamination in the Kara Sea. ISBN 82-993079-5-3. NRPA. Osteras, Norway. 1997

Strand, P., A.L. Nikitin, A.L. Rudjord et al. (1994) Survey of Artificial Radionuclides in the Barents Sea and the Kara Sea. Journal of Environmental Radioactivity,, 25 (1-2), 99-112.

SVA,. Kernkraftwerke der Welt, 1997. (1997), Bern, Switzerland: Schweizerische Vereinigung fur Atomenergie (SVA).

UNSCEAR, Ionizing radiation: sources and biological effects. United Nations. New York. 1982

UNSCEAR, Sources and effects of ionizing radiation. United Nations. New York. 1993

Weber JR. Physiography and Bathymetry of the Arctic Ocean Seafloor. pp. 797-828. In:

54 The Arctic Seas, Herman Y, editors. Van Nostrand Reinhold Company, New York: 1989.

Wedekind, C, I. Gabriel, G. Goroncy, G. FrSmcke, and H. Kautsky (1997) The Distribution of Artificial Radionuclides in the Waters of the Norwegian-Greenland Sea in 1985. Journal ojEnvironmental Radioactivity, 35(2), 173-201.

WHO (1989), Health hazards from Radiocaesium Following the Chernobyl Nuclear Accident: Report on a WHO Working Group. Journal of Environmental Radioactivity, 10 (3), 257-295.

Woodhead, D.S. The behaviour of radionuclides discharged from Sellafield in UK coastal waters, pp. 195-235. In: Strategies and Methodologies for Applied Marine Radioactivity Studies, IAEA, Vienna: 1997.

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