Physical path POLFOTO hways of contaminant transport STAFFAN WIDSTRAND In the mid-1950s, airplane pilots flying in the North American Arctic saw a strange, discolored haze on the horizon. It was thick enough to obscure visibility and different than any flying conditions they had come across before. In the 1980s, the haze was identified as aerosols of sulfate and soot, along with some soil particles, which were carried by winds from heavily industrialized areas in Europe. This Arctic haze was the first sign that the northern polar environment is closely connected to activities in other parts of the world. Other observations have added to this insight. Around Sval- bard, Norway, and in Canada, measurements of toxic organic compounds in polar bears have shown unexpectedly high levels. Svalbard had been chosen as a background station for environmen- tal monitoring and was thought to be an example of a clean, undisturbed environment. Where did the pollution come from? Local sources could not explain the high levels. A third example made the issue of long-range transport of contaminants into the Arctic even more acute. A study of traditional foods from the sea showed that some people in native communi- ties in Canada ingested high levels of the environmental contaminant PCB in their diet. Could the nourishing food, so essential for health and culture, also be a threat? Again, local sources of PCB could not explain the high levels. It must have been transported from regions outside the Arctic. High levels of contaminants in Arctic environments that had been thought pristine led to intensi- fied research into the pathways by which pollutants reach the Arctic – the air and water that enter the region from industrialized areas of the world. As it turns out, its geographical characteristics and cold climate make the Arctic a sink for many contaminants that are spread around the globe.

This chapter describes the pathways involved in transferring contaminants from one place to another and the physical processes that determine their fate in the Arctic. 22 The atmosphere help break down some contaminants, explains Physical pathways why sulfates and soot from Eurasia can con- The atmosphere contains relatively small tribute to haze throughout the lower layer of amounts of contaminants compared with the the Arctic atmosphere in winter and spring. It total load in polar soil, sediments, and water. takes 13 to 16 days for contaminants in the However, the rapid movement of air makes it lower atmosphere to travel from Europe to an important pathway for delivering contami- Alaska during the winter. nants to the Arctic. Any chemically stable, North America and East Asia only rarely wind-borne material will follow winds and contribute to Arctic haze since air masses from weather patterns into and within the Arctic these areas move over huge ocean distances region. The atmosphere is the fastest and most before reaching the Arctic, where low pressure direct route from the source of pollution: systems give rain and snow a chance to clean transport from the sources to the Arctic occurs the air. They may, however, be important in a matter of days or weeks. source areas for occasional bursts of high lev- els of contaminants that are not efficiently removed by rain and snow. Winter and spring winds carry dirty air In summer, the continental high-pressure Air-transport patterns are highly dependent on systems break up, and the low-pressure sys- season and on the position of major weather tems over the oceans become weaker. There- systems. In winter and spring, an intense high- fore, the transport of air and contaminants pressure system over Siberia pushes the Arctic from mid-latitudes becomes much less impor- front far to the south, so that important pol- tant in summer than in winter. Summer is also luted areas of Eurasia are actually within the warmer, allowing for cloud formation and for Arctic air mass, the lower one-to-two kilome- drizzling rain that can remove contaminants ters of which can move contaminants across from the air before they are carried far. More- the pole. Winds that can carry contaminants to over, sunlight during the summer months al- the Arctic are therefore more frequent in win- lows for photochemical degradation of some ter and spring than in summer and autumn. contaminants. The transport of contaminants during the The position of the Arctic winter is made even more effective by Particles take one hop from source to site Arctic front influences the lack of clouds and precipitation over the contaminant transport areas dominated by high-pressure systems. Contaminants that are in the form of minute in the atmosphere. The figure shows the mean Low wind speeds and temperature inversions, particles, or aerosols, are relatively easy to position of Arctic air caused by the cold winter weather, allow con- track. This is also true for gases that transform mass in January and taminants to accumulate in the atmosphere. into particles, such as sulfur dioxide. These July and the winter and Rather than falling to the ground in the vicin- contaminants start their journey with a ride on summer frequencies of winds driving the major ity of the source, they follow the large-scale northflowing winds from the source. Once south-to-north transport patterns of atmospheric circulation. This, they land, they usually stay on the ground. routes. together with the lack of light, which would They are often labeled one-hop contaminants. Acids carried as sulfates, non-volatile metals, and radionuclides are some examples. Non- Wind frequencies Winter: 25% volatile organic compounds behave the same Summer: 5% way. One-hop contaminants follow the same route as Arctic haze, from mid-latitude sources, mainly in Eurasia, to the Arctic. The distances over which one-hop contami- nants travel is determined by the location of ter win their sources in relation to the Arctic airmass, nt, er fro m tic m precipitation patterns, and how far the airmass rc u A s t, n moves during the atmospheric lifetime of the o fr ic particles. In the Arctic winter, particles can t c r stay in the air as long as 20 to 30 days, creat- A ing conditions for long-range transport and accumulation of contaminants in the polar

Wind frequencies region. In summer, the contaminants usually Winter: 15% stay in the air for only 2 to 5 days. Summer: 5%

Volatile substances gain global distribution Some contaminants are transported as gases. Wind frequencies Winter: 40% This is true for volatile and semi-volatile Summer: 10% organic compounds. Their behavior is differ- ent from particle-bound contaminants and aerosols in that their journey consists of sev- Modeling the fate of contaminants Atmosphere Where do contaminants come from? How do they get from one point to the other? Much of what is known about contaminant transport comes from computer models that mathematically simulate pathways. The input to the models are data on emissions, information Snowpack, river ice, River ice, about meteorological conditions such as winds and pre- Sea ice lake ice, glacial shore ice cipitation, and equations describing processes that change the chemical and physical characteristics of the compounds or that remove them from the air. Single-hop compounds, such as radionuclides and sul- fate aerosols, can be modeled in the same way as weather Terrestrial, freshwater Delta, estuary, fjord Surface ocean parameters in computer-based weather forecasts. Winds, precipitation, temperature, humidity, clouds, and deposi- Shelf Central tion to Earth’s surface are the major factors that deter- mine the pathway from source to deposition site. Such models have been used to describe the fallout from Chernobyl, the fate of pollution from the Kuwaiti oil Sediments Sediments Sediments fires, and the impact of acid rain in Europe, eastern North America, and southeast Asia. Models for multi-hop compounds are much more complex. In addition to the meteorology, a model has to describe how the contaminant moves between different environmental compartments, such as the atmosphere, Deep the land, and the ocean. To get a more accurate picture, ocean the compartments are often subdivided: Will the contam- inant enter the surface of the ocean and remain there or will it also reach the deep layers? Will it adhere to parti- cles and end up in soil or sediments, or will it dissolve in water and follow land runoff to a river? Often, the same contaminant will be present in several compartments, and there is an exchange between them that depends on the A multi-compartment representation of the major pathways Bottom temperature and on the total mass of the compound pre- of contaminants to and within the Arctic environment. water sent in each compartment. The model should, for exam- ple, be able to describe how a decrease in the load of contaminants in the atmosphere can turn a sink, such as the oceans, into a source. Similar models exist for marine Sediments environments. An illustrative example of this phenome- non is how the pesticide hexachlorocyclohexane spreads around the globe by moving in and out of the ocean. eral hops. The compounds are first picked up air, which eventually land on the ground. They by the winds as gases. They can then land on can also condense directly onto the Earth’s sur- the ground, on ice, or in the oceans by adher- face. At the low temperatures typical of the ing to particles or organic films, as well as by Arctic, they are not as likely to revolatilize as dissolving in water. But this is not necessarily in warmer climates. Another explanation is the end of their journey. When summer brings that gases dissolve in water more readily at higher temperatures, the compounds can vol- low Arctic temperatures than in warmer envi- atilize again, re-enter the atmosphere, and con- ronments. tinue their journey as gases. If the contami- nants do not break down, as is the case for The breathing oceans persistent organic pollutants and mercury, and if the temperature conditions are right, the For multi-hop contaminants, it is difficult to process can repeat itself a number of times. pinpoint the sources of the high levels that Eventually, the compounds might break down have been detected in the Arctic. Some of these to less harmful chemicals or be deposited in contaminants have been used for decades, dur- bottom sediment in oceans and lakes. ing which time a portion of the chemicals has Multi-hop compounds can travel great dis- ended up in the world’s oceans or in soils. For tances and become truly global in distribution. some compounds, the concentration in the At some point in their journey, the winds are oceans can be thousands of times higher than likely to carry them into the Arctic, which in the air. This capacity to hold on to contami- explains why chemicals that have never been nants is especially pronounced when the water used in the Arctic can still be found in the tis- is cold, as it is in the Arctic Ocean. When the sues of people and wildlife in the region. temperature increases, the capacity of the For some compounds, the levels are higher water to retain the contaminants decreases, in the Arctic than one would expect, even tak- and the oceans ‘breathe out’. Because the mass ing transport into account. Why? One expla- of contaminants is higher in the water than in nation lies in the cold climate. As the tempera- the air, the ocean can be expected to have ‘bad ture drops, the compounds condense out of the breath’ for a long time, at least ten years for gas phase onto particles or snowflakes in the the Arctic Ocean. For contaminants that 24 adhere to particles, soil can serve as a similar condense on the cold ground where they Physical pathways reservoir. adhere to soil particles or plants. For many To understand the levels of multi-hop conta- contaminants in the Arctic, wet and dry depo- minants in the air, one has to know the condi- sition from the atmosphere is the major pollu- tions under which the oceans and the land tion source. breathe out. First, there is a seasonal pattern. For example, an increase in water temperature may lead to a release of contaminants. The breakup of ice in spring and the fall break- The land and rivers down of water stratification can also turn the The Arctic landmass receives contaminants ocean into an important seasonal source to the from the atmosphere. Contaminants are also air. Contaminants captured in snow or soil transported to the Arctic by large rivers that behave in a similar manner and can also be can move material from polluted areas farther released to the atmosphere when temperatures south along the river. Mines, metal processing rise in summer. facilities, factories, oil and gas drilling, waste Over the long term, the concentration of dumps, and settlements can add to the local contaminants in the air will determine the role load. The diagram opposite gives a conceptual of oceans and soils as sources. If air concentra- picture of some different pathways. tions drop, as they would if we were to place The fate of contaminants in the terrestrial restrictions on use, the oceans and the land environment depends on the landscape as well may release more of their loads. as on the physical and chemical characteristics of each compound. Water-soluble compounds will be carried by snow-melt, surface water, Rain, snow, fog, and rime clean the air groundwater, and rivers. Unless they degrade, Contaminants are cleaned out from the air by they tend eventually to end up in the ocean. several processes. They can be caught when Contaminants with low water solubility nor- raindrops or snow crystals form in a cloud or mally adsorb onto particles in the soil or sedi- when the rain or snow is actually falling. Fog ment. Their fates depend on whether erosion can scavenge contaminants and deposit them will wash the soil into waterways and, if so, on when it condenses onto surfaces. Rime ice, what happens to the particles during a river’s journey to the ocean. Radioactive rain 137Cesium deposition, kBq Precipitation, mm, May-June 1986 28-30 April, Precipitation was important 1986 in washing wind-borne ra- Snowmelt creates a chemical surge dionuclides from the Cher- nobyl accident out of the air Melting snow plays an important role in trans- and onto the ground. 2 porting contaminants in the terrestrial envi- In Scandinavia, the de- ronment. By spring, the snow has had a whole position of radionuclides 2 winter to accumulate contaminants from the was very similar to the pat- 15 0 30 air. A deep snow pack can even retain volatile tern of local rain showers. 5 9 5 2 9 5 contaminants, which shallow snow packs The areas that had rain the 15 10 20 days after the accident were 20 would release back to the air. 30 those with the highest levels 50 When the temperature rises, water-soluble 0 of cesium-137 in the ground. 30 25 chemicals concentrate in the melt-water, and For example, the city of 30 25 the initial 20 to 30 percent of the meltwater Gävle, where it rained the 85 Gävle 20 15 2 can remove 40 to 80 percent of the total mass day after the accident, re- 9 ceived substantial deposi- 5 0 of pre-melt contaminants. Most of the meltwa- tion, as did the reindeer 5 ter flows over frozen ground directly into herding grounds in the mid- streams and lakes. The chapter on acidification 9 dle parts of northern 9 Sweden. The Saami reindeer provides an example of the effect this chemical herders farther north were 9 surge can have on the water quality of small 0 much less affected by the 5 streams. fall-out. 5 Meltwater can also be a powerful erosive 5 force. In areas where the ground cover has been disturbed, the rushing water easily forms which forms when supercooled cloud droplets erosion gullies and washes away soil. Over- freeze on contact with snow crystals or sur- grazing, seen in Scandinavia, Russia, and faces, is also an important scavenger of conta- North America, can thus affect water quality. minants from the air. In Greenland, rime ice Construction work is another potentially dam- has been estimated to contribute about 5 per- aging activity, especially if the permafrost is cent of the annual snow load, while account- disturbed. ing for approximately 30 percent of the annual Erosion also introduces suspended particles, deposition of contaminants. which provide surfaces to which contaminants An additional route from the air is dry can attach. Therefore, erosion can increase deposition. Particles can land by themselves contaminant transport in a river. and semi-volatile, gaseous contaminants can Revolatilization 25 Wet and dry atmospheric deposition Revolatilization Physical pathways

Revolatilization

Wetland (bog/swamp)

Coastal runoff Transformation Lake Watershed Ocean Transformation Groundwater Resuspension drainage Runoff Wetland outflow Sedimentation Water + particulate matter Sedimentation + transformation in transport Resuspension Industrial delta/estuarine zone Municipal Sedimentation

Riverine transport Mining Transformation

Different pathways of contaminant transport in the terrestrial and Agriculture freshwater environ- ments. water from the ground, most of it in late sum- mer. Only during this short period can the chemical and biological composition of the active layer affect the contaminant load Permafrost makes surface water brought by precipitation. In spring and early vulnerable summer, the lake gets its water directly from Even when the ground is not completely surface runoff, and the active layer plays no frozen, the shallow active layer of Arctic soils role. Farther south, groundwater becomes pro- makes patterns of water transport over and gressively more important as the active layer through the ground very different than in becomes thicker. warmer areas. Specifically, there is a greater risk of surface water contamination, whereas Rivers are key pathways the groundwater is relatively more protected. For example, a small lake in a permafrost area Rivers are central to many Arctic settlements, might only receive slightly more than half its providing drinking water and fish for food.

Tundra with River. Drawing: Ruth Qual- luaryuk. 26 They are also important pathways for conta- of the Kola Peninsula was treated according to Physical pathways minants. specified purification standards. In general, Rivers are also key pathways for long-range however, the main watersheds in both Russia transport. They can gather water and particu- and North America are relatively clean, and late matter from huge catchment areas and they have many lakes and reservoirs that act as transport them over long distances. The major traps for contaminated sediment. inflow of freshwater to the Arctic Ocean comes from rivers that originate outside the Arctic. Early summer brings peak input The catchment areas of large rivers often and floods include many diffuse sources of contaminants, such as agricultural runoff loaded with pesti- The flow in Arctic rivers is highly seasonal, cides. Discharges of municipal and industrial especially in those unregulated by dams and sewage from heavily populated and industrial- reservoirs; see the graphs opposite. In winter, ized areas south of the Arctic also contribute water flow is very low, and some rivers even to the contaminant load. Other polluting activ- freeze to the bottom. Peak flow usually comes ities are mining and oil and gas exploitation. in June and July, and this is when one would In Russia, some rivers are used as roads and expect the largest input of contaminants to for dumping dirty snow in winter. Contami- the Arctic Ocean. nants from vehicles and from materials gath- The peak flow in the rivers coincides with ered in the snow will also be carried by the the greatest transport of river ice, and in some water or by the ice during spring melt. rivers the combination of high flow and ice Some of the Arctic rivers have polluting jams leads to flooding. If the landscape is flat, activities in their catchment areas. The major as is the case in many parts of the Russian tun- Russian rivers, in particular the Yenisey and dra, the water can cover vast areas. Floods can the Ob, have their upstream basins in heavily leave contaminant-laden sediments on the developed areas with industries, urban centers, flood plain, temporarily removing them from and intensive agriculture. However, very little the riverine pathway. However, in years where is known about what these rivers actually flooding is extreme, the water may pick up transport. In North America, the Nelson River previously deposited material, and the load of system, which empties into Hudson Bay, flows contaminants will then reflect inputs from sev- through areas with intensive agriculture in eral years. mid-west Canada. The same is true, though to Slower-flowing rivers with well-developed a lesser extent, for the Mackenzie River. flood plains usually do not rise until the rivers The large rivers in the Arctic and in the sub- are clear of ice and might thus be more effici- arctic receive most of their water during spring ent in moving contaminants to the coast. snowmelt, and in most areas the melted snow In summer, heavy rains or periods of dry is also the most important source of contami- weather control river flow. In small waterways, nation. In highly urbanized regions, such as the water level can change dramatically depend- the large industrial cities of the Russian Arctic, ing on the weather. Nonetheless, most sedi- direct discharges of wastewater are equally ment transport occurs during the spring flood. important. In Russia, large volumes of industrial and River ice gathers contaminants municipal waste water are not treated. For Dirty river ice, example, in 1994 less than 5 percent of the River ice has a special role in the transport of Lena delta. waste water produced in the Murmansk region contaminants. The ice gathers material from the atmosphere and from the river itself as the water freezes. The incorporation of particle- borne contaminants from the water can con- tinue throughout the winter as the ice grows. When the water freezes all the way to the bottom of a river, material from the river bot- tom gets caught in the ice. Also, if the entire water column in the river is supercooled, i.e. has a water temperature below freezing, a sud- den change in temperature or turbulence can lead to ice formation around rocks and sedi- ment on the bottom of the river. Known as anchor ice, these formations can lift rocks as heavy as 30 kilograms. Supercooled water is also involved in formation of frazil ice, which collects small particles in the water and incor- porates them into the ice cover. As a result, river ice can contain large amounts of sediments. The sediments and any contaminants in the

HEIDI KASSENS ice itself are released to the river water during the spring melt, when the biological producti- Water discharge, m3/second 27 40 000 vity of the water is at its peak. The seasonal Mackenzie River, 1973-1990 freeze-thaw cycle thus creates conditions in Daily mean discharge 35 000 Average of daily means which the contaminant load built up in winter 30 000 can be effectively incorporated into animals. 25 000 Lakes and dams trap sediment 20 000 The landscape through which a river flows 15 000 plays an active role in the fate of contami- 10 000 nants. Many contaminants are bound to par- 5000 ticles, and sedimentation and resuspension 0 processes will determine whether the contami- Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec nants reach the Arctic Ocean or are deposited along the way. When a river flows slowly, par- Concentration of sediment in water, mg/liter 4000 Mackenzie River, 1972-1991 ticles usually settle, and bottom sediments can Daily mean concentration become enriched in metals, persistent organic 3500 Average of daily means pollutants, and hydrocarbons. However, the river bottom is usually only a temporary trap 3000 since turbulent flow can lead to the resuspen- sion of particles. Large lakes, on the other 2500 hand, can serve as permanent traps for conta- minants. Great Slave Lake on the Mackenzie 2000 River system, for example, blocks much pole- ward transport of contaminants, particularly 1500 those bound to particles. 1000 Man-made lakes are no less important. Dams constructed along the Yenisey River in 500 the 1960s and 1970s illustrate the role of man- made lakes as particle traps. Eight reservoirs, 0 controlling about one-fourth of the river flow, Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec caused a three-fold reduction in the amount of tances even when contaminants are adsorbed Top: Variation in dis- sediment that reached the mouth of the river. to particles. Through resuspension of bottom charge of water in the These sediments were deposited in the reser- sediments, these fine clay particles also gather Mackenzie River over the year. voirs. Dams can also change the seasonal pat- metals and hydrocarbons originating from Bottom: Variation in tern of the flow, distributing it more evenly natural weathering processes. concentration of sedi- throughout the year. Living organisms help the sedimentation ment in the water of the The fate of specific contaminants is deter- process in lakes, just as they do in deltas and Mackenzie River over mined by how well they adhere to particles estuaries. Phytoplankton extract material that the year. and by the type of particles in the water. The is dissolved in the water, and many zooplank- smallest particles often have the highest con- ton and larger filter feeders gather suspended centrations of contaminants due to their matter, effectively packaging small particles larger relative surface area, and these settle into larger ones. The material is deposited on less quickly than coarser material. There is the bottom, which becomes a mixture of inor- thus a potential for transport over long dis- ganic sediment, shells, and excrement.

Flooding of Yenisey River shown in yellow

© NOAA/TSS/AKVAPLAN-NIVA © on satellite image. Rivers carry fresh water and time in the flat landscape. During spring melt, sediment to the Arctic seas they will follow the runoff and end up in rivers. In total, Arctic rivers carry Wetlands are thus important secondary sources about 4200 cubic kilometers Yukon 60 million tonnes of pollution to surface rivers in this region and of water per year into Arctic seas, along with about 221 Kolyma are likely to remain so for a long time. Mackenzie million tonnes of sediment 16.1 million tonnes Another example where wetlands act as sec- 42 million tonnes per year. The landscape de- Lena ondary sources is in areas with intensive metal termines the role of each 17.6 million tonnes industries, such as the Kola Peninsula, where particular river. Those cros- Nelson metals are likely to leach into waterways even sing flat, frozen tundra gen- Yenisey 5.9 million tonnes 0.7 million tonnes after emissions decrease. erally carry relatively small 16.5 million tonnes Ob amounts of sediment. The Mackenzie River, on the 13.5 million tonnes other hand, flows through Pechora a much steeper landscape, 3.8 million tonnes Where the river with less permafrost and Northern Dvina meets the sea with abundant surficial Yearly discharge of material that can be eroded. suspended sediment Rivers enter the ocean through estuaries and Consequently, it carries by major rivers. deltas along the coastal zone. The physical and larger amounts of sediment. biological processes in these environments have a major impact on the fate of contami- Lakes do not control the transport of water- nants carried by river water and river ice. borne contaminants as much as they do for particle-bound substances. Often, snowmelt Deltas and estuaries serve as particle traps flows through small Arctic lakes without mix- ing. Therefore, at least for headwater lakes, In the context of contaminant transport, the most of what comes in also flows out. The major physical role of deltas and estuaries is as load of contaminants in lakewater is therefore particle traps for particulate matter in river more likely to reflect input from rain and water. Rivers flow more slowly and with less ground runoff during summer. turbulence when they reach the coast, allowing particles to settle. The containment of particles is enhanced when sediments that settle farther Wetlands can be contaminant sources out are transported back toward the river Through snow, rain, and dry deposition, the mouth by inflowing seawater. The sediment is vast wetland areas in the Arctic, with numer- thus advected back upstream before it finally ous shallow lakes, swamps, marshes, and bogs, deposits. The settling process is enhanced by gather contaminants from the air. Water in the mixing of fresh water and sea water, which wetlands naturally contains much organic makes fine colloidal particles stick together matter, such as humic substances from peat. and become large enough to settle. Hydrophobic contaminants tend to bind to Some water-soluble substances can also be organic matter, in both soil and water. Some caught in deltas and estuaries. The main mech- of these bound contaminants remain in the anism for this is flocculation, in which dissolv- ground but some will enter waterways. ed organic and mineral substances are gath- Local sources add to the load. For example, ered into suspended particles. The process is oil and gas exploitation in northwest Siberia driven by changes in acidity and salt concen- releases untreated waste water as well as oil to tration. Living organisms also help the sedi- depressions in the landscape. The cold weather mentation process. does not allow for much decay of the organic The efficiency of coastal sediment traps Mackenzie River delta. pollutants, which are likely to stay for a long depends to a large extent on whether a delta is formed, i.e. a depositional plain where the sediments build up new land into the sea; or if tides and waves eventually carry most sedi- ments away from the river mouth. The largest deltas are created by major rivers draining large areas and carrying abundant sediment. If the continental shelf is shallow, the delta plain can continue far out to sea, beneath the ocean surface. Two examples of huge deltas are those of the Lena River in Russia and the Mackenzie River in Canada. The Mackenzie Delta accu- mulates several centimeters of overbank sedi- ment every year. This can be compared with accumulation rates of 10-100 centimeters in 1000 years in estuaries, or 1-3 millimeters per 1000 years for ocean sedimentation. Large amounts of the suspended matter in

STAFFAN WIDSTRAND rivers can thus be deposited and excluded from further transport to the open ocean. Along the during part of the year, which allows for the 29 Russian Arctic coast, only 10 to 20 percent of exchange of contaminants between water and Physical pathways the particulate matter in the Ob and Yenisey air; and they have high biological productivity, Rivers travels farther than the borders of the which provides a route for contaminants into deltas and the Kara Sea shelf. the food web. The diagrams below summarize the major processes for redistribution of conta- minants in the coastal zone. Landfast ice keeps sediments close to shore Sea ice may gather Many Arctic rivers discharge into areas with and transport contaminants extensive ice cover. Maximum river flow occurs at the time that the landfast ice in the In recent years, sea ice has become a focus of shelf seas is about to break up. If the early, research concerning contaminant pathways in sediment-laden river water flows on top of the the Arctic. The picture is just emerging, but ice, the heavy load of dark particles will speed some hypotheses are interesting to consider. up the melt, and the sediments will settle to the There are two major ways in which sea ice bottom along the coast. If the near-shore ice gathers contaminants: from the atmosphere, cover is anchored to shallow off-shore banks, where its large surface area makes it an effi- it can form a barrier to offshore transport of cient trap for air-transported contaminants, any floating material such as dirty river ice. In and from the water during ice formation. Sea both cases, the sedimentary material will most ice can incorporate sediments in much the likely be deposited near the shore. same way as river ice: frazil and anchor ice formation capture material from the sea bot- tom. This incorporation of particles in ice is especially effective for silt-size or smaller parti- The continental shelves cles. Because many contaminants are preferen- The shallow continental shelves surrounding tially associated with these fine-grained parti- the Arctic Ocean are important for the trans- cles, the ice can become more contaminated port of contaminants within the Arctic for with these substances than the water. three reasons: they are the primary areas of ice When ice formed in the shelf seas becomes formation and ice melt; they have open water part of the pack ice, associated contaminants

Atmospheric transport Gas exchange Sediment deposition Turbid plume River inflow Pack ice Ice melt Summer stratified layer Flocculation

Bottom resuspension Biogenic Particles from by waves particles melting ice

Salt wedge

Upwelling

Spring/summer

Gas exchange Sediment incorporated in ice River inflow Landfast ice Shear Strong stratification zone Anchor ice Brine drainage

Suspension freezing Polar mixed layer

Ice scouring

Summary of different processes determining the fate of contaminants along the coast and in Winter the shelf seas in spring/ summer and in winter. contaminant-laden particles often form pools of dirt on the surface, so called cryoconites. Once at the surface, any semi-volatile material can interact with the atmosphere. Other mate- rials will be released when the ice melts. Sediment traps along the Fram Strait show that most of the ice-carried debris will be released in the marginal ice zone. The timing and location of the ice melt coincide with the bloom of biological activity, and thus provides an opportunity for contaminants to enter the food chain. Many small plants and animals live at the ice-water interface (the epontic zone), and can be exposed to much higher lev- els of contaminants than would be expected from the contaminant load of the water. Similar processes also occur under the ice in the central Arctic Ocean, but are less well understood. If the sediments have aggregated into pel- lets, they will sink to the ocean floor much faster than fine particles. If the ocean is deep enough, contaminants in these pellets are less likely to be taken up in the food chain.

Water-soluble contaminants follow the brine

© NOAA/TSS/AKVAPLAN-NIVA © Water-soluble substances behave differently Satellite image of sea ice are carried away by the drifting ice. Much of than those that adhere to sediments, but sea- in the Barents and Kara the ice in the Arctic Ocean circulates for one to ice formation can still provide a route for long Seas. The large white seven years before it leaves the basin and range-transport. The mechanism is quite dif- area is snow-cover on Novaya Zemlya, Russia. melts. The map on page 32 shows the major ferent. When sea water freezes, brine (a con- circulation patterns. centrated salt solution) is expelled into the Ice is not a passive vessel for contaminants. water, and water-soluble compounds follow Melting at the surface, drainage, and refreez- along. If the water is not stratified, the brine ing from the bottom will redistribute the mate- mixes with the surrounding water and can rial carried by the ice. Most of it will appear at penetrate into the deep parts of the ocean. In the surface after a few years. The dispersed, the absence of particles, even contaminants

Ice can scour the sea floor Icebergs are a spectacular feature of Arctic ice. They are pieces of glaciers that have broken off and floated away in the sea. Calving glaciers cover much of Greenland, Svalbard, Franz Josef Land, Severnaya Zemlya, and the northern island of Novaya Zemlya. The photos show ice- bergs near the Jakobshavn Icebrae, Ilulissat. Beneath the surface, icebergs can reach depths of more than 100 meters, and can scour the bottom in shallow areas. Such scouring marks can be several meters deep and tens of meters wide. Icebergs are not important for transporting contaminants but might disrupt waste contain- ers that have been dumped on the sea floor. Sea ice can also disturb the bottom, especially along shallow shores and when it is compressed into thick pressure ridges. The ridges can scour the bottom and stir up contaminant-laden sediment, making it available to biota and to further transport by water currents.

Iceberg sources Arctic Ocean Major Minor

Canada Ilulissat Greenland Common iceberg tracks

Atlantic Ocean

Common iceberg tracks Left: HENNING SLOTH PETERSEN; right: ANNIKA NILSSON that normally adhere to particles, such as radiocesium, follow the brine. 31

Open water allows for atmospheric exchange Pacific water In summer, the shelf seas are relatively free of ice, while in winter, ice covers the areas closest to the coast. Farther out, between the landfast Beaufort Gyre 0.8 Transpolar Drift ice and the permanent pack ice, offshore winds often form areas of open water. These flaw Precipitation leads, also called coastal polynyas, can extend 0.05 over thousands of square kilometers. Flaw leads along the coast are important

areas for the interchange of semi-volatile cont- 1.9 0.04 aminants between water and air. For example, 1.7 2.0 soluble, gaseous pollutants that make their way to the Arctic can dissolve in the cold Arc-

1.2 tic waters. 0.16 3.1 Moreover, the leads typically form the locus 4.9 of ice break-up from late April to mid May Atlantic water and thus are a gathering place for many marine animals. As is the case along the marginal ice 8.0 zone, the high primary productivity and rich Atlantic water + Intermediate layer, 200-1700 m wildlife of these areas provide a route for cont- Pacific water, 50-200 m aminants to enter biological pathways, as is Surface water circulation further discussed in the chapter Arctic Ecology. River inflow Figures are estimated in- or outflows in Sverdrups (million m3 per second) The transport of water with the main ocean cur- other oceans only through restricted passages. rent systems in the Arctic. The Arctic Ocean The Atlantic-layer water The major inflow of ocean water passes from mass originates from the The Arctic Ocean and the surrounding seas the North Atlantic through Fram Strait and surface of the North At- receive contaminants from air, other oceans, the Barents Sea. There is also some inflow lantic Ocean and descends rivers, and from direct discharges. The fate of from the North Pacific through the Bering below less-dense Arctic these substances is determined both by Arctic Strait. The ocean transport of pollutants is Ocean surface water, which is affected by fresh- Ocean circulation patterns and by the stratifi- slow, taking years to decades to transport water from rivers. The cation of the ocean waters. water from industrialized, temperate coastal Pacific water mass is pro- Geographically, the Arctic Ocean is often regions to the Arctic Ocean. duced by modification of described as a ‘mediterranean’ sea because it is The movement of water and pollutants in water entering the Bering surrounded by land, communicating with the Arctic Basin is best understood by viewing Strait on the broad Chuk- chi Shelf and occurs in the Ice Canada Basin. Polar mixed layer Pacific halocline Atlantic halocline

Bering Strait Fram Strait Depth, m 0 ca. 10 years 200 Pacific water ca. 10 years 400 Atlantic water ca. 25 years 600 ca. 30 years Atlantic layer 800 1000 Arctic deep water

Bering Norwegian Sea Strait and Greenland Sea ca. 75 years deep water 2000 Canada Makorov Basin Basin Fram Alpha Strait Ridge

3000 ca. 300 years Amundsen Nansen Basin Basin Vertical section of the Arctic Ocean and the ca. 290 years Lomo- Nansen different water masses nosov Gakkel with their approximate Ridge Ridge 4000 residence times. The ver- tical scale is exaggerated Bold figures denote residence times compared to the hori- zontal scale. 32 breaks up and allows surface waters to sink and deep water to rise to the surface. This hap- pens every fall and winter when the water cools and when ice starts to build, expelling brine. This vertical mixing allows both nutrients and contaminants from deeper layers to reach the surface in the shelf seas and Nordic Seas. 5 4 Two main features characterize the circula-

3 tion of the surface water: the Beaufort Gyre 6 Beaufort and the Transpolar Drift; see map left. The Gyre 2 Beaufort Gyre is a large clockwise gyre extend- ing over the entire Canadian Basin. It circu-

1 lates slowly between the pole and the Cana- Transpolar dian Archipelago. In this way, water is ex- Drift ported both to Baffin Bay through the Cana- dian Archipelago and to the Transpolar Drift. Fram Strait The Transpolar Drift runs east to west across the Eurasian Basin from the Siberian coast out through the western Fram Strait. Tracer studies show that about 10 percent of the water in this current comes from rivers, making it a conveyer belt for any contami- nants that reach the open ocean through estu- aries and deltas. The rest of the water comes from the Bering Strait and from the shelf seas.

Ice cover The transport takes only five years from the September continental shelves to Fram Strait. March the ocean as a layered system; see the diagram Surface water below. circulation Atlantic layer circulation Number of years has been traced with radionuclides x for sea ice to exit Fram Strait Arctic surface water has a mixed layer and a halocline Immediately below the Arctic surface layer is Sea-ice extent in Septem- the Atlantic layer. This water enters the Arctic ber and March and the The Arctic surface water extends to a depth major surface currents Ocean at the surface through Fram Strait and governing the transport of approximately 200 meters. This water can the Barents Sea, submerges, circulates around of sea ice. The numbered be further subdivided into the polar mixed the Arctic Basin, and exits back through the lines show the expected layer (0 to 50 meters depth) and the halocline Fram Strait, still submerged. time in years for the ice (50 to 200 meters depth). The water comes Radionuclides from Sellafield, a nuclear at that location to exit the Arctic Ocean through from rivers, the shelves, and from the Atlantic reprocessing plant on the northwestern coast the Fram Strait. Ocean through the Fram Strait. One of the of England, give a tell-tale sign of water cur- most important routes is via the North Atlan- rents. The North Atlantic Current (an exten- tic Current. The polar mixed layer is formed in winter Arctic Ocean when the ice freezes and excludes brine, and in summer by melting sea ice and river runoff 10 4-6 years along the coast. It is the only water within the 1-2 4000 km 6-8 years Arctic that has direct contact with the atmos- 5000 km phere and consequently the only water that can exchange semi-volatile contaminants with 3000 km Greenland the air. 50 3-4 years The halocline is a structurally complex 6000 km region with water of increasing density. It is Norway 2000 km Time taken for radio- crucial to the transport of contaminants. Over 50 7000 km 4 years cesium released from the shelves, it transports water laterally, away 100 Sellafield to be trans- 3 years from the coast, as heavy, saline water sinks 1000 km ported to the Arctic 1000 along the bottom. 1 year Sellafield Ocean. Bold figures rep- Atlantic Ocean resent relative concen- Away from the shallow coast, the role of the UK trations at different halocline depends on the season. In spring and points. summer, it provides a barrier between the sur- face water and any deeper waters, effectively sion of the Gulf Stream) transports large quan- blocking vertical mixing of contaminants. It tities of warm water from the Gulf of Mexico also limits the exchange of volatile contami- via the European coast to the Arctic. Any con- nants between deeper layers of the ocean and taminants entering the current from rivers, the atmosphere. One important transport ocean dumping, or the atmosphere will be car- process thus takes place when the halocline ried along. Radiocesium from the Sellafield Fridtjof Nansen counted on the Transpolar Drift and the Barents Sea as the Bering Strait is too 33 ‘Everywhere, the ice has stopped people in their quest shallow. The water moves counter-clockwise. Physical pathways to reach the North. Only in two cases have the ships Contaminants enter Arctic deep water drifted northward once they were stuck in the ice . . . By mainly by flow of dense water off the shelves. reading the history of Arctic research, it became clear to Once there, they can be transported long dis- me that it would be difficult to capture the secrets of the unknown widths of ice by the routes that have been tried. tances. One example is the anomalously high But where did the road go?’ ratio of cesium-137 to strontium-90, which in The transpolar drift was documented in the 19th 1979 was observed at the Eurasian Basin flank century by the Norwegian polar explorer Fridtjof Nansen of the Lomonosov Ridge. It represents a signal with his ship Fram. Three observations gave him the idea that water and ice moved according to a particular pat- from the Sellafield nuclear reprocessing plant tern. He had found trees from Siberian forests as drift- on the Irish Sea. The signal was carried either wood on the eastern coast of Greenland. He had also from Spitsbergen or from the continental slope found a throwing tool for bird hunting that was typical off the Barents Sea to the North Pole and then around the perimeter of the Eurasian Basin in about 3 years. The Arctic deep water has an extremely long residence time, and any contaminants The Inuit throwing tool entering this layer might stay in the Arctic for up to 300 years.

Summary of Alaskan Inuit on the Greenland shore. But most im- portant, pieces from the American ship Jeanette had been Air, water, and ice can carry contaminants over found on the drift ice south of Greenland. Jeanette had great distances. been lost in the ice near the New Siberian Islands on her way north from the Bering Strait. Nothing but drifting In winter, industrial areas of Eurasia are ice could have carried this material over such long dis- within the Arctic air mass, which provides for tances. There had to be a current from east to west, and efficient air transport of particle-bound conta- Fridtjof Nansen was determined to take advantage of this minants across the pole. Semi-volatile com- in his quest to cross the unexplored polar sea. He built a pounds are carried to the Arctic by cycles of ship that would survive the crushing forces of the ice and set out on his journey in the summer of 1893. By mid evaporation, transport, and condensation in a fall, the ship was securely lodged in the pack ice north of multi-hop process. The cold climate traps them the New Siberian Islands, just as predicted, and it was more effectively here than anywhere else on only a matter of time and patience to let the currents do the globe. their job. The journey was slow and trusting his theory Snow, rime ice, rain, and dry deposition was not always easy. Every sign of progress was noted in his diary: cleanse the air and contaminate the surfaces on ‘Friday February 16. Hurrah! Our meridian observa- which they land. The contaminants often end tion this morning gave 80°1'N. We have come a few min- up in meltwater that feeds both rivers and the utes northward since last Friday, even though the wind ocean surface layer. has been blowing constantly from the north since Mon- Rivers process contaminants along their day. It is very strange. Could it be, as I have thought myself, observing the skies and the misty air, that it has routes by sedimentation and resuspension of been a southerly wind further south, which stops the drift particles. Lakes, estuaries, and deltas serve as of the ice in that direction? Or have we finally come sediment traps and sinks for contaminants. within an area where a current acts?’ Ice forming in the shelf seas can pick up Time proved that Fridtjof Nansen was right, that there is an east-to-west current. After three years, in contaminants from the coastal shelves, and can August 1896, Fram was released from the ice as the travel far in the Beaufort Gyre and Transpolar Transpolar Drift reached Spitsbergen. Drift. The ice may release its load of contami- nants in the biologically productive shelf seas nuclear reprocessing plant can, for example, be and in the North Atlantic, where they can be detected all along the Norwegian coast as well taken up into the food chain. as in the Arctic Ocean. Some of the north- Another important pathway is via ocean flowing water is returned to the North Atlantic currents. They act slowly compared with the in a subsurface flow along the eastern coast of atmosphere, but take water with water-soluble Greenland, but a substantial part of this his- and particle-adsorbed contaminants from dis- torical discharge now resides in the Arctic tant industrialized coasts into the Arctic within Ocean. a few years, and out again through the East Greenland Current and the Canadian Arctic deep water Archipelago. The sea is the final resting place has extremely long residence time for most contaminants. Modeling is a useful tool for understanding Arctic deep water extends from 800 meters contaminant transport. Its importance will downward and is divided into the Canadian grow as the basic processes become better Basin deep water and the Eurasian Basin deep understood and the models improve. water. The only inflow is through Fram Strait