Dinkum Sands — a recently foundered Arctic island

Dinkum Sands was mapped in 1949 as a small island, one link in a 95-km-long chain of barrier islands near Prudhoe Bay, Alaska. Questions about its status as an Arctic island and the submerged land ownership led to a Federal/State joint monitoring program using topographic surveys, tide gauges, and other approaches. On the basis of the results the Supreme Court concluded that Dinkum Sands is a shoal rather than an island. The shoal attracts the yearly formation of pressure ridges at least as high as 15 m and undergoes drastic changes in location, shape, and elevation. Pressure ridges form from 10-cm-thick new ice when shifting and compression result in crumbling and the introduction of ice slabs into the sandy gravel shoal. This leads to a seasonal increase in shoal volume and height. With summer warming and sea-ice melting, part of the ice in the crest of the shoal (∼50%) melts and its height accordingly drops to below sea level. This lowering requires neither wave action nor lateral sediment transport. The original disappearance of the island in the 1950s, however, probably was not caused by diminished sediment supply from rivers or from coastal erosion, but by diminished local sediment supply through ice pile-ups or by increased erosion from wave attack. Similar changes in sediment volume as those observed in Dinkum Sands probably also occur on fully submerged shoals ranging to water depths of 20 or more meters, which are also marked by seasonal pressure ridge formation

Effects of Storm Surges on the Beaufort Sea Coast, Northern Alaska

In 1970, a major storm surge caused by gale-force westerly winds inundated low-lying tundra plains and deltas as far as 5000 m inland and left a driftwood line as much as 3.4 m above normal sea level along the Beaufort Sea coast of Alaska. The height of the surge followed a predictable pattern and was highest along windward-facing shorelines. Coastal retreat and thermoerosion are greatly accelerated on such west-facing shores with eastward sediment transport opposite to normal littoral drift. Evidence suggests an approximate 100-year recurrence interval for similar surges, with potential for damaging the developing oil fields on the North Slope

Distribution and Character of Naleds in Northeastern Alaska

Satellite imagery and high- and low-altitude aerial photography of the North Slope of Alaska indicate that naleds (features formed during river icing) are widespread east of the Colville River but less abundant to its west. Where naleds occur, stream channels are wide and often braided. Their distribution can be related to changes in stream gradient and to the occurrence of springs. Large naleds, such as occur on the Kongakut River, often survive the summer melt season to form the nucleus of icing in the succeeding winter. Major naleds also are likely to significantly influence the nature of permafrost in their immediate vicinity. A map of naleds may serve as a guide to sources of perennially flowing water

An Arctic Kelp Community in the Alaskan Beaufort Sea

The discovery of the "Boulder Patch", an area of cobbles and boulders with attached kelp and invertebrate life, is reported from Stefansson Sound, near Prudhoe Bay, Alaska. Geophysical surveys using side-scan sonar and low-frequency recording fathometers reveal that cobbles and boulders occur in patches of various sizes and densities. Despite a seasonal influx of sediments, the Boulder Patch is a nondepositional environment. Physical disruption of cobbles and boulders by deep draft ice is minimal due to offshore islands and shoals which restrict the passage of large ice floes into Stefansson Sound. The apparent absence of similar concentrations of rocks with attached biota along the Alaskan Beaufort Sea coast is explained by the scarcity of rocks in areas protected from ice abrasion and with no net sediment deposition. In Stefansson Sound, the rocks provide a substratum for a diverse assortment of invertebrates and several species of algae. Recolonization by the biota was minimal on twelve boulders denuded and then left undisturbed for a three-year period. Sedimentation and grazing activity appear to be the major factors inhibiting recolonization. Linear growth in the kelp, Laminaria solidungula, is greatest in winter and early spring when nutrients are available for new tissue growth. The plant draws on stored food reserves to complete over 90% of its annual linear growth during the nine months of darkness under a turbid ice canopy. These reserves are accumulated by photosynthetic activity during the preceding summer. The total carbon contribution made by kelp in Steffansson Sound under these conditions is about 146 million g/yr or 7 g/m²/yr. A small percentage of this carbon is consumed directly by herbivores, but its importance to other organisms in not known and is under investigation.Key words: kelp, Laminaria solidungula, Flaxman boulders, Beaufort Sea, Boulder Patch, productivity, recolonization, geophysical surveys, side-scan sonar, lag depositsMots clés: varech, Laminaria solidungula, grosses pierres Flaxman, mer de Beaufort, Boulder Patch, productivité, recolonisation, levées géophysiques, sonar à balayage latéral, accumulations de pierres par déflatio

Changes in Driftwood Delivery to the Canadian Arctic Archipelago: The Hypothesis of Postglacial Oscillations of the Transpolar Drift

Driftwood appears to be absent in the Beaufort Gyre but abundant in parts of the Transpolar Drift (TPD), which crosses the Arctic Ocean from the Chukchi Sea to the vicinity of northeastern Greenland. Nearly 300 radiocarbon dates on Holocene driftwood from the Canadian Arctic Archipelago reveal two regions with contrasting histories of driftwood incursion: the region accessible to wood brought into Baffin Bay by the West Greenland Current and the rest of the archipelago, which receives wood from the Arctic Ocean. We hypothesize that when the TPD was deflected westward along northern Greenland, wood was delivered widely to the Canadian Arctic Archipelago; when the TPD exited entirely through Fram Strait via the East Greenland Current, little or no wood was delivered to most of the archipelago, but some continued into Baffin Bay via the West Greenland Current. A split TPD delivered wood to both regions. The regional driftwood incursion histories exhibit multiple maxima and minima that can be explained through this hypothesis. The Larix to Picea ratio of wood arriving in the Canadian Arctic Archipelago has also changed through time. This may indicate varying contributions from Russian versus North American sources, which in turn may indicate variable mixing of wood en route. The inferred discharge paths of the TPD were apparently stable for intervals ranging from several millennia to centuries or perhaps only decades. The last major switch broadly correlates with the onset of Neoglaciation. Variations in the path and strength of the TPD may have important oceanographic and climatic consequences downstream in the North Atlantic Ocean.Il semble qu'il n'y ait pas de bois flotté dans la circulation de Beaufort mais qu'on en trouve en abondance dans certaines parties du courant d'impulsion transpolaire, qui traverse l'océan Atlantique depuis la mer des Tchouktches jusqu'au voisinage du nord-est du Groenland. Près de 300 datations au carbone 14 effectuées sur du bois flotté datant de l'holocène et provenant de l'archipel Arctique canadien mettent en évidence deux régions qui possèdent un passé divergent quant à l'incursion de bois flotté: la région que peut atteindre le bois transporté dans la baie de Baffin par le courant groenlandais oriental, et le reste de l'archipel, qui reçoit le bois en provenance de l'océan Arctique. Nous avançons l'hypothèse que, quand le courant transpolaire était défléchi vers l'ouest le long de la partie septentrionale du Groenland, il y avait un fort apport de bois dans l'archipel Arctique canadien; quand le courant transpolaire passait en sa totalité par le détroit de Fram pour rejoindre le courant groenlandais oriental, peu de bois, sinon aucun, atteignait la plupart de l'archipel, un peu étant cependant acheminé dans la baie de Baffin via le courant groenlandais occidental. Un courant transpolaire divisé amenait du bois aux deux régions. L'historique des incursions régionales de bois flotté révèle l'existence de nombreux maxima et minima que peut expliquer cette hypothèse. Le rapport du bois provenant de Larix à celui provenant de Picea transporté dans l'archipel Arctique canadien a aussi évolué au cours du temps. Cela peut indiquer une variation dans la contribution provenant de Russie par rapport à celle provenant d'Amérique du Nord, ce qui, à son tour, peut révéler un mélange variable de bois durant le parcours. Les trajets inférés de la décharge du courant transpolaire ont été apparemment stables durant des périodes allant de plusieurs millénaires à des siècles, voire des décennies. Le dernier grand changement est, dans l'ensemble, corrélé à l'arrivée de la néoglaciation. Les variations dans le trajet et la puissance du courant transpolaire pourraient avoir d'importantes conséquences océanographiques et climatiques en aval dans l'océan Atlantique Nord

East Siberian Arctic Region Expedition '92: The Laptev Sea - Its Significance for Arctic Sea-Ice Formation and Transpolar Sediment Flux

Darin enthalten: Expedition to Novaja Zemlja and Franz Josef Land with RV "Dalnie Zelentsy" / by D. Nürnberg and E. Groth, pp. 45-7

Transport of 137Cs And 239,240Pu with Ice-rafted Debris in the Arctic Ocean

Ice rafting is the dominant mechanism responsible for the transport of fine-grained sediments from coastal zones to the deep Arctic Basin. Therefore, the drift of ice-rafted debris (IRD) could be a significant transport mechanism from the shelf to the deep basin for radionuclides originating from nuclear fuel cycle activities and released to coastal Arctic regions of the former Soviet Union. In this study, 28 samples of IRD collected from the Arctic ice pack during expeditions in 1989-95 were analyzed for 137Cs by gamma spectrometry and for 239Pu and 240Pu by thermal ionization mass spectrometry. 137Cs concentrations in the IRD ranged from less than 0.2 to 78 Bq/kg (dry weight basis). The two samples with the highest 137Cs concentrations were collected in the vicinity of Franz Josef Land, and their backward trajectories suggest origins in the Kara Sea. Among the lowest 137Cs values are seven measured on sediments entrained on the North American shelf in 1989 and 1995, and sampled on the shelf less than six months later. Concentrations of 239Pu + 240Pu ranged from about 0.02 to 1.8 Bq/kg. The two highest values came from samples collected in the central Canada Basin and near Spitsbergen; calculated backward trajectories suggest at least 14 years of circulation in the Canada Basin in the former case, and an origin near Severnaya Zemlya (at the Kara Sea/Laptev Sea boundary) in the latter case. While most of the IRD samples showed 240Pu/239Pu ratios near the mean global fallout value of 0.185, five of the samples had lower ratios, in the 0.119 to 0.166 range, indicative of mixtures of Pu from fallout and from the reprocessing of weapons-grade Pu. The backward trajectories of these five samples suggest origins in the Kara Sea or near Severnaya Zemlya.  Le transport glaciel constitue le principal mécanisme responsable du transport des sédiments à grain fin depuis les zones côtières jusqu'à la fosse du bassin Arctique. La dérive des débris du transport glaciel pourrait constituer un important mécanisme de transport, depuis la plate-forme continentale jusqu'à la fosse marine, pour des radionucléides provenant d'activités connexes au cycle du combustible nucléaire, radionucléides qui sont éliminés vers les zones côtières arctiques de l'ancienne Union Soviétique. Dans cette étude, on a analysé 28 échantillons de débris de transport glaciel recueillis dans la glace arctique au cours d'expéditions effectuées de 1989 à 1995, en vue d'y déceler du 137Cs par spectrométrie gamma ainsi que du 239Pu et du 240Pu par spectrométrie de masse réalisée par thermo-ionisation. Les concentrations de 137Cs dans les débris de transport glaciel allaient de moins de 0,2 à 78 Bq/kg (poids sec). Les deux échantillons ayant les concentrations en 137Cs les plus élevées ont été recueillis à proximité de l'archipel François-Joseph, et leurs trajectoires régressives suggèrent qu'ils proviennent de la mer de Kara. Parmi les plus faibles valeurs de 137Cs, sept ont été mesurées sur des sédiments arrivés sur la plate-forme continentale nord-américaine en 1989 et 1995 et prélevés sur celle-ci moins de six mois plus tard. Les concentrations en 239Pu et 240Pu allaient d'environ 0,02 à 1,8 Bq/kg. Les deux valeurs les plus élevées venaient d'échantillons recueillis au centre du bassin Canada et près du Spitzberg; le calcul des trajectoires régressives suggère que le 239Pu est resté au moins 14 ans en circulation dans le bassin Canada et que le 240Pu tire son origine des environs de Severnaïa Zemlia (à la frontière de la mer de Kara et de la mer des Laptev). Tandis que la plupart des échantillons de débris de transport glaciel révélaient des rapports 240Pu/239Pu proches de la valeur moyenne (0,185) des retombées radioactives mondiales, cinq des échantillons affichaient des rapports inférieurs, allant de 0,119 à 0,166. Cette fourchette est caractéristique de mélanges de Pu provenant de retombées radioactives et du retraitement du Pu pouvant être utilisé à des fins militaires. Les trajectoires régressives de ces cinq échantillons suggèrent qu'ils proviennent de la mer de Kara ou des environs de Severnaïa Zemlia