High-resolution paleoclimate reconstructions of the Canadian Arctic

Paleoclimate inferences from the Canadian Arctic have been hindered by a lack of continuous sedimentary sequences, poor chronological control and lack of modern data that are needed for the development of transfer functions or to determine modern analogues. In recent years, a number of lake sediment cores from across the Canadian Arctic have been analyzed, including several sequences from the central and western Arctic. These data are providing, for the first time, high-resolution pollen, diatom, chironomid, loss-on-ignition, biogenic silica, and magnetic susceptibility data dated by 210Pb and 14C based chronologies that document multi-scale climate variability across the Canadian Arctic. Several datasets of modern samples (pollen, diatoms, chironomids) have also recently been made available that permit, for the first time, the quantification of past environmental conditions. The early Holocene was warm across much of the Arctic, up to 1oC warmer than today at some sites in the central Arctic, although the timing of maximum warmth is not yet established and may vary regionally. In high- resolution proxy climate records, major transitions occurred at approximately 8.0, 5.8, 3.7, and 2.5ka, as well as during the Medieval Warm Period and Little Ice Age, with the exact date depending on site. The transitions occur approximately at the same time as transitions identified in ice cores and regional pollen curves from more southern regions, although it is not clear at this time if they are synchronous. These climate variations impacted both terrestrial and aquatic ecosystems. In the former case, the changes to the local vegetation were subtle, but still noticeable. In the latter case, both the diversity and the productivity of the communities were greatly impacted. Periods of dissolution of diatoms or hiatuses in the cores suggest the climate changes were sufficient to have large impacts on Arctic ecosystems. Climate changes of the past 150 years have clearly impacted the lake ecosystems, but the impacts on the vegetation are as yet unclear.