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...
The macrofossil and pollen records from two cores in the Detour Lake and Kinosheo Lake peatlands in northeastern Ontario cover more than 7000 years and 4000 years of vegetation history, respectively, and record a succession of peatland environments. The Detour Lake pollen record includes the vegetation successions associated with two major climatic shifts, the Mid-Holocene warm period and Late Holocene cooling trend. From 4000 BP, the vegetation successions derived from pollen analysis correlate well with respect to the evolution of the peatland and surrounding upland vegetation. Similar patterns of change were also noted in the pollen and macrofossil stratigraphies from other parts of northern Ontario. Patterns of trace element distribution reflect major changes in the peatlands. The most notable is the decrease in most trace elements as the peatland evolved from minerotrophic to ombrotrophic conditions. Levels of many elements are enriched in the near-surface peat horizons. Based on the data from this study, it is not possible to identify which part of the surface enrichment reflects airborne anthropogenic pollutants, inputs from naturally occurring atmospheric sources, or the relocation of inorganic constituents by physical, chemical, or biological processes.
Quatre sites de la Gaspésie méridionale sont présentés dans le but de reconstituer l'histoire de la colonisation et de l'évolution végétale postglaciaire au nord de la baie des Chaleurs. La région a connu une période non-arboréenne suivie de l'afforestation par le peuplier et l'épinette aux environs de 10 000 ans BP. Par la suite, une formation forestière à grande composante d'aulne crispé, formation semblable à celle de la sapinière à épinette noire observée de nos jours à l'étage subalpin de la Gaspésie, s'établit jusqu'à environ 7000 ans BP. Le maintien de cette formation végétale pendant environ 3000 ans semble traduire un délai dans la migration végétale, délai qui pourrait être relié à un climat régional relativement froid et humide attribuable à la présence de l'Inlandsis laurentidien au nord du Saint-Laurent. La végétation évolue ensuite vers la sapinière ou l'érablière. Entre 7000 ans et 4000 ans BP, les représentations maximales des courbes polliniques de certaines espèces thermophiles décidues et du pin blanc traduisent la réponse de la végétation à un maximum climatique. On note ensuite le déclin graduel de ces espèces, ce qui, depuis 4000 ans, traduirait un refroidissement graduel du climat. L'examen des sédiments supérieurs de certains sites permet de reconnaître la période de colonisation européenne : mise en culture des terres et coupe sélective.Four sites from the southern Gaspé Peninsula are presented with the intention of reconstructing the history of postglacial vegetation colonization and evolution north of Baie des Chaleurs. The study area experienced an unforested period followed by forest development by poplar and spruce about 10 000 years ago. Following this development, a forest with a high representation of green alder, similar to that of the fir/black spruce forest observed in the present sub-alpine region of the Gaspé Peninsula characterized the area until 7000 years BP. The presence of this forest, in place for about 3000 years, seems to indicate that vegetal migration was delayed due possibly to a relatively cool and humid climate, attributed to the presence of the Laurentide Ice Sheet north of the St. Lawrence River. The vegetation subsequently evolved towards fir and/or maple associations. Between 7000 years and 4000 years BP, the maximum value on the pollen curve for deciduous thermophilous species and white pine is interpreted as a response of the vegetation to a warm climate. The gradual decline of these species during the last 4000 years appears to be responding to a gradual cooling in climate. Examination of uppermost sediments at certain sites reveals the period of European colonization, land cultivation and selective forestry.Vier Plâtze der sûdlichen Gaspésie werden mit dem Ziel pràsentiert, die Geschichte der postglazialen Pflanzenansiedlung und -entwicklung nôrdlich der Baie des Chaleurs zu rekonstruieren. In der Gegend gab es zuerst eine baumlose Période, worauf eine Bewaldung durch Pappel und Rottanne um etwa 10 000 v.u.Z. folgte. Danach siedelte sich bis ungefàhr 7000...
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