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TitreNew dinoflagellate and isotopic data from the northeast Newfoundland Shelf
AuteurLevac, E; Lewis, M C; Miller, A A; Keigwin, L
SourceEos, Transactions of the American Geophysical Union vol. 90, no. 22, 2009, 1 pages
Séries alt.Secteur des sciences de la Terre, Contribution externe 20100029
RéunionAmerican Geophysical Union, Geological Association of Canada, Joint Assembly; Toronto; CA; mai 25-29, 2009
Documentpublication en série
Mediapapier; en ligne; numérique
ProvinceRégion extracotière de l'est
Sujetspaléoclimatologie; océanographie; palynologie; temperature; température de l'eau; changement climatique; paléontologie; géologie des dépôts meubles/géomorphologie; Nature et environnement
ProgrammeLes géosciences à l'appui de la gestion des océans, Aléas géologiques et contraintes à la mise en valeur des ressources extracôtières
Résumé(disponible en anglais seulement)
The drainage of glacial Lake Agassiz could be responsible for the 8.2 ka cold event recorded in the Greenland Ice Sheet and tentative links with the Preboreal Oscillation have been made. Recent studies show clear evidence for drainage of large volumes of meltwater through Hudson Strait and Coriolis deflection predicts a southward flow over the Labrador shelf. Indeed, detrital carbonate (DC) beds in cores from the Labrador and Newfoundland shelves suggest that plumes of suspended DC sediment were carried through Hudson Strait into the Labrador Current, and as far south as Grand Bank at least. DC beds in cores from Notre Dame Channel have been dated and correspond with known periods of meltwater flow out of Hudson Strait. We re-evaluated the correction for early radiocarbon dates from the Labrador Shelf to range up to -730 years. The correction varies as pre-bomb reservoir ages and/or ice cover durations change. Onshore-offshore correlations of dated palynological records from Newfoundland and the Newfoundland shelf are used to verify our dating scheme and to lend support to the corrections we propose. The timing of meltwater drainage is critical when attempting to link freshwater drainages with cooling events and/or slowing of thermohaline circulation in the North Atlantic. Dinocyst assemblages support our hypothesis that the Labrador Current was significantly enhanced by the ouflow from Lake Agassiz. Detrital carbonate layers show increased proportions of Impagidinium pallidum indicating cooler sea surface conditions and the overall dinocyst assemblages suggest stronger vertical stratification, and hence reduced surface salinity. In the previous DC bed, which is correlated with the Noble Inlet ice advance, the appearance of Spiniferites elongatus suggests more northern influence. Transfer functions based on dinoflagellate cysts also show a reduction in sea surface salinity, before and during the DC bed. Oxygen isotope analyses performed on calcareous dinoflagellate Thoracosphaera heimii from Notre Dame Channel will be presented.