Pollen-based summer temperature reconstructions for the eastern Canadian boreal forest, subarctic, and Arctic

Pollen-based paleoclimate reconstructions using response surface and modern analog methods reveal an 8000-year record of July temperature fluctuations for 25 eastern Canadian lake sites located from the forest tundra to the high Canadian Arctic. Postglacial conditions, characterized by warmer than present summer temperatures, prevailed in Baffin Island and NE Labrador beginning about 7500 and 7000 C-14 yr BP, respectively, resulting in warmer than present conditions throughout the region by 6000 C-14 yr BP (+0.5degreesC to 1degreesC). Further south, in Quebec and W Labrador, July temperatures were 1-2degreesC colder than present until after 6000 C-14 yr BP, and only reached modern values after all residual Laurentide ice had melted. Increased summertime insolation and the final disappearance of Laurentide Ice during the middle Holocene probably caused July temperatures throughout eastern Canada to peak between approximately 5000 and 3500 C-14 yr BP. Mid-Holocene warming relative to today was more pronounced in Baffin Island and NE Labrador (+ 1degreesC to 2degreesC) compared to the boreal and subarctic regions of Quebec and W Labrador (< + 1degreesC). Over the past 4000 years, decreasing summertime insolation and colder sea surface temperatures in the Davis Strait and Labrador Sea contributed to a decline in July temperatures of 1-2degreesC throughout Baffin Island, and the tundra regions of N Quebec and Labrador. The absence of similar cooling in the records from the boreal forest may support the notion that the mean position of the summertime polar front blocked the colder Arctic air during the late Holocene. (C) 2004 Elsevier Ltd. All rights reserved.