Paleoclimatic and instrumental records of environmental variability in northeastern North America

Abstract

Clastic varves and tree-rings offer unique opportunities to decipher various changing paleoclimatic and environmental conditions through the past. The environmental signals they contain can differ greatly from one proxy to the other, but given their common annual resolution, these signals can be isolated, compared and eventually brought together to obtain a clearer picture of local, regional or global environmental changes. This thesis examines three different approaches by which climatic, paleoclimatic and sedimentary time series from northeastern North America can be used as proxies of changing environmental conditions. Using existing and new paleoclimatic records from the eastern Canadian Boreal biome and the Arctic, we show that common variance shared by different independent proxies appears to correspond to an oscillation in North Atlantic sea surface temperatures commonly referred as the Atlantic Multidecadal Oscillation (AMO) and demonstrate that the AMO can be traced back to 1550 in the Canadian Arctic. By comparing historical climate records with an integrated record of North Atlantic sea surface temperature anomalies, we show, seasonally, the extent of the North Atlantic influence on the eastern and Arctic climate. Our analysis demonstrate the relative importance of the AMO on summer and spring climate in northern Canada as well as its imprint along the St. Lawrence during the winter months. Finally at the local level, using an array of techniques, we investigate the sedimentary history of Temiskaming Lake (Québec/Canada). The recent clastic varve sediments found this lake appear to be the product of three main controls: (1) a significant increase in fluvial input to the lake and accessibility to large supply of fine grained sediments due to historical land use changes; (2) an open, unstable landscape that promotes fluvial erosion and rapid streamflow during snowmelt period; and, (3) highly seasonal river discharge and presence of winter ice cover conditions that ensure the formation of annual structures within the sediments. These conditions have previously not been investigated or reported in the boreal region of North America and these results point to the potential for other recent varve records in areas with suitable lakes and postglacial sediment supplies.