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This article presents a comparison of sediment input by rivers and by coastal erosion into both the Laptev Sea and the Canadian Beaufort Sea (CBS). New data on coastal erosion in the Laptev Sea, which are based on field measurements and remote sensing information, and existing data on coastal erosion in the CBS as well as riverine sediment discharge into both the Laptev Sea and the CBS are included. Strong regional differences in the percentages of coastal erosion and riverine sediment supply are observed. The CBS is dominated by the riverine sediment discharge (64.4510 6 t a ±1 ) mainly of the Mackenzie River, which is the largest single source of sediments in the Arctic. Riverine sediment discharge into the Laptev Sea amounts to 24.1010 6 t a ±1 , more than 70% of which are related to the Lena River. In comparison with the CBS, the Laptev Sea coast on average delivers approximately twice as much sediment mass per kilometer, a result of higher erosion rates due to higher cliffs and seasonal ice melting. In the Laptev Sea sediment input by coastal erosion (58.410 6 t a ±1 ) is therefore more important than in the CBS and the ratio between riverine and coastal sediment input amounts to 0.4. Coastal erosion supplying 5.610 6 t a ±1 is less significant for the sediment budget of the CBS where riverine sediment discharge exceeds coastal sediment input by a factor of ca. 10.

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 Stefansson Sound under these conditions is about 146 x lo6 gyr" or 7 g.m-2.yr". A small percentage of this carbon is consumed directly by herbivores, but its importance to other organisms is not known and is under investigation.

ABSTRACT. 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 by 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.Key words: driftwood, Transpolar Drift, Beaufort Gyre, sea ice, ocean currents RÉSUMÉ. 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...

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