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210Pb and 137Cs were measured in 25 sediment cores collected during the International Polar Year from a transect spanning the North American Arctic margin, from the North Bering Sea to Baffin Bay/Davis Strait. Profiles and inventories of the radioisotopes were used to determine sediment mixing and accumulation at each site and to assess the intensity of scavenging and burial. Sediment accumulation rates derived from 210Pb and validated using 137Cs are between ≤0.04 and 0.23 g cm−2 yr−1. 210Pb cannot be used to derive sedimentation rates for vigorously biomixed sediments from the North Bering‐Chukchi shelf. Elevated 137Cs activities and inventories in recently deposited sediments imply delayed inputs of particle‐associated 137Cs to the sediments, likely transported from the watershed to the coast and subsequently redistributed to shelf/slope sediments. Inventories of 210Pbex in all cores meet or exceed the estimated supply of 210Pbex from atmospheric deposition and decay of 226Ra in the water column. This implies that in contrast to the deep Arctic Ocean basin, there is a sufficient supply of suspended particulates along the North American Arctic margin to scavenge the supply of 210Pbex. 210Pbex inventories in sediments are up to 21‐fold greater than the in situ supply at some sites. Large inventories of 210Pbex in sediments along the North Bering‐Chukchi shelf result primarily from focusing, while those along the north Chukchi slope (Barrow Canyon) and in Baffin Bay/Davis Strait reflect strong boundary scavenging, likely supported by lateral exchanges with deep/interior Atlantic‐origin waters.
210Pb and 137Cs were measured in 25 sediment cores collected during the International Polar Year from a transect spanning the North American Arctic margin, from the North Bering Sea to Baffin Bay/Davis Strait. Profiles and inventories of the radioisotopes were used to determine sediment mixing and accumulation at each site and to assess the intensity of scavenging and burial. Sediment accumulation rates derived from 210Pb and validated using 137Cs are between ≤0.04 and 0.23 g cm−2 yr−1. 210Pb cannot be used to derive sedimentation rates for vigorously biomixed sediments from the North Bering‐Chukchi shelf. Elevated 137Cs activities and inventories in recently deposited sediments imply delayed inputs of particle‐associated 137Cs to the sediments, likely transported from the watershed to the coast and subsequently redistributed to shelf/slope sediments. Inventories of 210Pbex in all cores meet or exceed the estimated supply of 210Pbex from atmospheric deposition and decay of 226Ra in the water column. This implies that in contrast to the deep Arctic Ocean basin, there is a sufficient supply of suspended particulates along the North American Arctic margin to scavenge the supply of 210Pbex. 210Pbex inventories in sediments are up to 21‐fold greater than the in situ supply at some sites. Large inventories of 210Pbex in sediments along the North Bering‐Chukchi shelf result primarily from focusing, while those along the north Chukchi slope (Barrow Canyon) and in Baffin Bay/Davis Strait reflect strong boundary scavenging, likely supported by lateral exchanges with deep/interior Atlantic‐origin waters.
ABSTRACT. Arctic lakes can provide a long-term perspective on environmental change, including trends in long-range atmospheric transport and deposition of contaminants, inferred from studies of sediment cores. In this study, we conducted the first detailed bathymetric survey of Lake Hazen (Quttinirpaaq National Park, Ellesmere Island, Nunavut), the world's largest lake north of 74˚ latitude. With these data we were able to determine optimal locations for sediment coring and to collect and analyze profundal sediment cores. A bathymetric map of Lake Hazen was developed on the basis of 362 spot soundings obtained with GPS-coupled sounding equipment placed directly on the ice combined with additional soundings from a small boat. The deepest point in the lake (81˚49.5ʹ N; 70˚42.8ʹ W) was found to be 267 m deep. The lake volume was estimated to be 5.14 × 10 10 m 3 , about 10% larger than previous estimates. Using estimates of the discharge of Lake Hazen from the Water Survey of Canada, we estimated the water retention time to be 89 years. Sediment cores were dated using 210 Pb and ) in horizons dated to 1950 -1880. The majority of elements measured in sediment (24 of 29 consistently above detection limits), as well as organic carbon, showed less than 20% variation in concentrations in the top 10 cm (compacted depth), which represent deposition over approximately 140 years. Geochemical characteristics of the sediment suggest that erosional inputs from annual glacial melting are the major source of essentially all elements and that anthropogenic inputs from long-range transport of toxic metals such as mercury and lead are very low.Key words: bathymetry, sediment, metals, depth sounding, lake volume, water residence time, radiometric, dating RÉSUMÉ. Les lacs de l'Arctique peuvent fournir une perspective à long terme en matière de changement environnemental, notamment en ce qui a trait aux tendances relatives au transport atmosphérique et au dépôt de contaminants sur de longues périodes, tendances inférées à partir d'études de carottes de sédiments. Dans le cadre de la présente étude, nous avons effectué le premier levé bathymétrique détaillé du lac Hazen (parc national Quttinirpaaq, île d'Ellesmere, Nunavut), le plus grand lac de la planète situé au nord de 74˚ de latitude. Grâce aux données prélevées, nous avons réussi à déterminer les meilleurs emplacements pour le prélèvement de carottes de sédiments de même que pour la collecte et l'analyse de carottes de sédiments profonds. Une carte bathymétrique du lac Hazen a été dressée en fonction de 362 sondages obtenus au moyen de matériel d'appareils phoniques dotés de GPS placés directement sur la glace et supplémentés par des sondages recueillis à partir d'un petit bateau. Le point le plus profond du lac (81˚49,5ʹ N; 70˚42,8ʹ O) a été trouvé à 267 m de profondeur. Le volume du lac a été évalué à 5,14 × 10 10 m 3 , soit 10 % de plus que les évaluations précédentes. À l'aide d'estimations du déversement du lac Hazen obtenues auprès de la Division des relevés hydrologiques du...
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