Paleolimnological reconstruction of Holocene climatic trends from two boreal treeline lakes, Northwest Territories, Canada

Paleolimnological analyses of two lakes located near the northern treeline in the central part of the Canadian Northwest Territories document a histor y of abrupt postglacial climatic and limnological changes. A diatom-based t ransfer function, based on weighted-averaging partial least squares regress ion (WA-PLS) techniques, was used to give quantitative estimates of past tr ends in lakewater dissolved organic carbon (DOC), a Limnological variable s trongly aligned with catchment vegetation and soils. The diatom record from the sediment cores provides evidence for profound limnologic change during the mid-Holocene, corresponding to maximum Forest-tundra development betwe en 5000 and 3000 C-14 yr BP in both Queen's and Toronto lakes, with a diato m-inferred relative change in lakewater DOC of up to 5.8 mg L between the m id-Halocene and the present-day. Comparison of the diatom-inferred environm ental changes with other proxy data (pollen, stable isotopes) from the same lakes provides strong evidence for an episode of climatic amelioration and lake responses to the associated vegetational changes (from tundra to fore st-tundra) at sites near the central Canadian treeline. This study illustra tes the usefulness of diatoms as quantitative indicators of past climate-re lated environmental change in northern treeline regions, and implies that a quatic ecosystems at high latitudes might respond with extreme sensitivity to climate warming.