BG Biogeosciences BG Biogeosciences 1726-4189 Copernicus Publications Göttingen, Germany 10.5194/bg-9-5391-2012 Quantitative reconstruction of sea-surface conditions over the last 150 yr in the Beaufort Sea based on dinoflagellate cyst assemblages: the role of large-scale atmospheric circulation patterns Durantou L. 1 Rochon A. 1 Ledu D. 2 Massé G. 2 Schmidt S. 3 Babin M. 4 Institut des sciences de la mer (ISMER), Université du Québec à Rimouski, 310 allée des Ursulines, Rimouski, QC, Canada LOCEAN Institut Pierre-Simon Laplace, UMR7159, 4 Place Jussieu, BP100 75252 Paris Cedex, France Université de Bordeaux, EPOC, UMR5805, 33400 Talence, France Takuvik Joint Laboratory, Université Laval, Pavillon Alexandre-Vachon, 1045, avenue de la Médecine, local 2064, Quebec city, Canada 21 12 2012 9 12 5391 5406 Copyright: © 2012 L. Durantou et al. 2012 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://bg.copernicus.org/articles/9/5391/2012/bg-9-5391-2012.html The full text article is available as a PDF file from https://bg.copernicus.org/articles/9/5391/2012/bg-9-5391-2012.pdf

Dinoflagellate cyst (dinocyst) assemblages have been widely used over the Arctic Ocean to reconstruct sea-surface parameters on a quantitative basis. Such reconstructions provide insights into the role of anthropogenic vs natural forcings in the actual climatic trend. Here, we present the palynological analysis of a dated 36 cm-long core collected from the Mackenzie Trough in the Canadian Beaufort Sea. Dinocyst assemblages were used to quantitatively reconstruct the evolution of sea-surface conditions (temperature, salinity, sea ice) and freshwater palynomorphs fluxes were used as local paleo-river discharge indicators over the last ~ 150 yr. Dinocyst assemblages are dominated by autotrophic taxa (68 to 96%). Cyst of <i>Pentapharsodinium dalei</i> is the dominant species throughout most of the core, except at the top where the assemblages are dominated by <i>Operculodinium centrocarpum</i>. Quantitative reconstructions of sea-surface parameters display a series of relatively warm, lower sea ice and saline episodes in surface waters, alternately with relatively cool and low salinity episodes. Variations of dinocyst fluxes and reconstructed sea-surface conditions may be closely linked to large scale atmospheric circulation patterns such as the Pacific Decadal Oscillation (PDO) and to a lesser degree, the Arctic Oscillation (AO). Positive phases of the PDO correspond to increases of dinocyst fluxes, warmer and saltier surface waters, which we associate with upwelling events of warm and relatively saline water from Pacific origin. Freshwater palynomorph fluxes increased in three phases from AD 1857 until reaching maximum values in AD 1991, suggesting that the Mackenzie River discharge followed the same trend when its discharge peaked between AD 1989 and AD 1992. The PDO mode seems to dominate the climatic variations at multi-annual to decadal timescales in the western Canadian Arctic and Beaufort Sea areas.

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