HR: 0800h
AN: PP51A-0191    [Abstracts]
TI: Holocene Climate Oscillations in the Eastern Part of the Northwest Passage : A Possible Influence of the Lunar Nodal Cycle
AU: * Ledu, D
EM: david.ledu@uqar.qc.ca
AF: ISMER-GEOTOP-UQAM-McGill, 310 Allée des Ursulines, Rimouski, QC G5L 3A1, Canada
AU: Rochon, A
EM: andre_rochon@uqar.qc.ca
AF: ISMER-GEOTOP-UQAM-McGill, 310 Allée des Ursulines, Rimouski, QC G5L 3A1, Canada
AU: de Vernal, A
EM: devarnal.anne@uqam.ca
AF: ISMER-GEOTOP-UQAM-McGill, 310 Allée des Ursulines, Rimouski, QC G5L 3A1, Canada
AU: Labrie, J
EM: jacques.labrie@uqam.qc.ca
AF: ISMER-GEOTOP-UQAM-McGill, 310 Allée des Ursulines, Rimouski, QC G5L 3A1, Canada
AB: The Arctic climate has undergone dramatic changes over the past four decades. The observations reveal a decrease in sea ice extent and thickness, and a modification of the hydrological cycle. These changes have been attributed mostly to the Northern Hemisphere annular mode (e.g. NAO, AO) coupled with anthropogenic impacts. However, the instrumental climate data for the Arctic only cover the last three decades. In order to improve our understanding of the mechanisms and provide new inputs in the climate simulation experiments, we have collected 4 piston cores (~6 m) for palynological analysis along the main axis of the Northwest Passage, respectively in Lancaster Sound, Barrow, Victoria and Dease straits. Here we present the preliminary results of the 2004-804-009 PC located in Lancaster Sound. This core has been sub-sampled every 10 cm for the analysis of dinoflagellate cysts (dinocyst) assemblages, which allow us to develop transfer functions (best analogue method) in order to reconstruct the sea surface hydrological parameters (sea ice cover, salinity, T °C). Radiocarbon ages indicate that the sequence spans the last 10,323 cal B.P., with a calculated sedimentation rate of 0.57 mm/year. Therefore we can achieve a secular resolution for the reconstruction of climate oscillations. Grain size and geochemical analyses show a prevalence of the fine fraction in the major part of the core, indicating a hemipelagic sedimentation. The base of the core records a higher percentage of sand and CaCO3 and high values of the C/N ratio, which suggest an erosive dynamic with a large inflow of freshwater indicating a terrestrial sedimentation that we associate with the retreat of the Laurentide Ice Sheet in this area. Dinocyst analyses show four different zones. The first zone covers the beginning of the Holocene and shows a maximum abundance of pre-Quaternary palynomorphs with an absence of cysts in the lowermost 40 cm of the core consistent with a glacio-marine environment and high meltwater input. The second zone covers the early to middle Holocene and is dominated by the heterotrophic taxa Brigantedinium sp. and Islandinium minutum. The third zone covers the middle Holocene, where the percentage of autotrophic taxa increases with Spiniferites frigidus/élongatus, Operculodinium centrocarpum, Pentapharsodinium dalei between 4000 and 2000 cal B.P. The fourth zone represents the modern conditions with the dominance of heterotrophic taxa. The increase in the relative abundance of autotrophic taxa between 4000 and 2000 cal B.P. suggests that environmental conditions were more suitable to sustain photosynthetic dinoflagellate populations, probably as a result of an increase of nutrients avaibility, a decrease in the sea ice cover or a combination of both. The G/P (Gonyaulacoid/Peridinioid) ratio records a strong increase of autotrophic taxa between 4500 and 2500 cal B.P. accompanied by an increase of the reconstructed August T °C and a decrease of both the ice cover and summer salinity, suggesting the imprint of the Holocene thermal optimum. Wavelet analysis shows a cyclicity near 1800 year in dinoflagellate percentage as well as in the reconstructed summer salinity and T °C. A similar cycle was recorded in the relative abundance of a brackish palynomorph in sediment core from northern Baffin Bay, near our sampling site. The similarity between both signals could be the result of a sub-harmonic cycle of the 18.6 year nodal, which triggers a strong tidal mixing.
DE: 3030 Micropaleontology (0459, 4944)
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4952 Palynology
DE: 9315 Arctic region (0718, 4207)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting