Abstract
Abstract. 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 Pentapharsodinium dalei is the dominant species throughout most of the core, except at the top where the assemblages are dominated by Operculodinium centrocarpum. 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.
Highlights
Recent observations revealed that the Arctic has experienced a warming at a rate nearly twice the global average during the past decades (e.g. IPCC, 2001, 2007; McBean, 2005; Hassol, 2004) and sea-ice extent recorded still declines, with a new minimum reached in mid-September 2012 (National Snow and Ice Data Center)
The sediment core was collected as part of the Malina Program in an attempt to provide a paleoenvironmental perspective on the recent climatic evolution in the Beaufort Sea coastal region, which has experienced a drastic reduction of both area and thickness of sea ice cover over the last few decades (Barber and Hanesiak, 2004)
The results exposed here show that the evolution of temperature, salinity, sea ice cover and dinoflagellate productivity of the Mackenzie Trough area may be linked with the phases of the Pacific Decadal Oscillation (PDO) at a decadal timescale
Summary
Recent observations revealed that the Arctic has experienced a warming at a rate nearly twice the global average during the past decades (e.g. IPCC, 2001, 2007; McBean, 2005; Hassol, 2004) and sea-ice extent recorded still declines, with a new minimum reached in mid-September 2012 (National Snow and Ice Data Center). The lack of long-term observations in the Arctic makes it impossible to reach any definitive conclusion concerning the environmental changes induced by climatic oscillations in Arctic regions (e.g. Polyakov et al, 2002). In this context, paleoceanographic studies at high temporal. L. Durantou et al.: Paleoceanography on the Beaufort Sea resolution (i.e. multi-annual to decadal scales) were recently solicited in order to acquire a better knowledge about past and actual climate affecting high latitudes. The actual understanding of natural variability versus the anthropogenic warming contribution, mainly based on past observations with both proxy and instrumental records still needs to be better documented at adequate temporal scales. The sediment core was collected as part of the Malina Program (http://www.obs-vlfr.fr/Malina) in an attempt to provide a paleoenvironmental perspective on the recent climatic evolution in the Beaufort Sea coastal region, which has experienced a drastic reduction of both area and thickness of sea ice cover over the last few decades (Barber and Hanesiak, 2004)
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