MILLENNIAL-SCALE VARIABILITY IN HOLOCENE PALEOCEANOGRAPHIC RECORDS FROM THE EASTERN CANADIAN MARGIN

The view that the Holocene was characterized by low amplitude paleoceanographic changes (or by the absence of change) stemmed from the use of low resolution marine records and is increasingly challenged. Evidence for millennial-scale variability during the Holocene, both in paleoceanographic (Bond et al. 1999; Bischof 2000; Knudsen and Eiriksson 2002) and paleoclimatic records is accumulating (Viau et al. 2002).

The cause of this variability is still unknown. Dyke et al. (1996, 1997) suggested that shifts in the position of the Transpolar Drift and changes in sea-ice extent in Arctic channels could have affected the properties of the Labrador Current during the Holocene (Dyke et al. 1996, 1997). Petrie and Drinkwater (1993) who showed the role of the Labrador Current in the Great Salinity Anomaly of the 1960s further support this idea. Recent advances in ocean and climate modelling also show an important connection between the Arctic and the mid-latitudes. Following these suggestions, we examined the evolution of sea surface conditions along a Nova Scotia-Baffin Bay transect in relation with known changes in the Arctic.

Paleoceanographic reconstructions from 5 high-resolution records (sedimentation rates 100 cm/1000 yr) are presented. They are from the North Water Polynya (Baffin Bay), Cartwright Saddle, La Have and St. Anne's Basins (Scotian Shelf) and Bay of Islands (Newfoundland). The cores provide a resolution of 50-100 years and have multiple radiocarbon ages. Reconstructions of sea surface temperature (SST), salinity (SSS) and sea ice cover duration were based on proxydata from dinoflagellate cysts and on paleobioclimatic transfer functions.

Recurrent drops in SST and SSS are reconstructed throughout the Holocene, even after the end of the deglaciation. Over the last 7000 years SST oscillated by ± 3-5 ºC and SST by ± 2-5 psu. There are indications that change in SST and SSS in paleoceanographic records from Atlantic Canada could be linked with changes in Arctic surface circulation or ice extent in Arctic channels. Evidence is not unequivocal as the direction of paleoceanographic changes is not always consistent along the transect. Spectral analysis confirms a 1500 year cyclicity for these low SST and SSS intervals and their timing generally correspond with similar events elsewhere in the North Atlantic.