Quantitative reconstruction of sea-surface conditions over the last150 yr in the Beaufort Sea based on dinoflagellate cyst assemblages: the role of large-scale atmospheric circulation patterns

[摘要] Dinoflagellate cyst (dinocyst) assemblages have been widely used over theArctic Ocean to reconstruct sea-surface parameters on a quantitative basis.Such reconstructions provide insights into the role of anthropogenic vsnatural forcings in the actual climatic trend. Here, we present thepalynological analysis of a dated 36 cm-long core collected from theMackenzie Trough in the Canadian Beaufort Sea. Dinocyst assemblages were usedto quantitatively reconstruct the evolution of sea-surface conditions(temperature, salinity, sea ice) and freshwater palynomorphs fluxes were usedas local paleo-river discharge indicators over the last ~ 150 yr.Dinocyst assemblages are dominated by autotrophic taxa (68 to 96%). Cystof Pentapharsodinium dalei is the dominant species throughout mostof the core, except at the top where the assemblages are dominated byOperculodinium centrocarpum. Quantitative reconstructions ofsea-surface parameters display a series of relatively warm, lower sea ice andsaline episodes in surface waters, alternately with relatively cool and lowsalinity episodes. Variations of dinocyst fluxes and reconstructedsea-surface conditions may be closely linked to large scale atmosphericcirculation patterns such as the Pacific Decadal Oscillation (PDO) and to alesser degree, the Arctic Oscillation (AO). Positive phases of the PDOcorrespond to increases of dinocyst fluxes, warmer and saltier surfacewaters, which we associate with upwelling events of warm and relativelysaline water from Pacific origin. Freshwater palynomorph fluxes increased inthree phases from AD 1857 until reaching maximum values in AD 1991,suggesting that the Mackenzie River discharge followed the same trend whenits discharge peaked between AD 1989 and AD 1992. The PDO mode seems todominate the climatic variations at multi-annual to decadal timescales in thewestern Canadian Arctic and Beaufort Sea areas.

[学科分类] 地球化学与岩石