The climate of North America and adjacent ocean waters ca. 6 ka

The climate of North America and the adjacent ocean at 6000 BP was estimate d using five independent approaches. Using pollen data, the terrestrial cli mate was estimated by the movement of ecozone boundaries and by the method of modern analogues. Both analyses indicate warmer temperatures in the west ern Great Lakes area and the northern Great Plains. A model of Sphagnum-dom inated peatland initiation, when forced by Canadian Climate Model 6 ka outp ut projected a cooler and (or) wetter climate for continental western North America. Contrary to this, a reconstruction of the distribution of Sphagnu m-dominated peatlands in western Canada indicates that they were located no rth of their modern distribution, suggesting warmer and (or) drier conditio ns at 6000 BP. This interpretation is strengthened by observations of lower lake levels at 6000 BP in western Canada. This drier climate may have been associated with warmer conditions as indicated by the quantitative climate reconstructions. In general, eastern North America was drier, while wester n North America was warmer and drier at 6 ka compared to the present. A mod el of vegetation and carbon storage, when forced using 6 ka Canadian Climat e Model and pollen-based climate reconstructions, showed an increase in are a covered by boreal forest, extending north and south of the present locati on. This was not, however, verified by the fossil data. Additionally, the m odel showed little total change in carbon storage at 6 ka in the terrestria l biosphere. Estimated sea surface temperatures off eastern Canada suggest warmer surface waters at 6 ka, in agreement with reconstructions based on t errestrial records from the eastern seaboard.