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QUANTITATIVE PALEOCLIMATE RECONSTRUCTION FROM POLLEN ASSEMBLAGES PRESERVED IN ARCTIC LAKE SEDIMENTS

FRéCHETTE, BIANCA  GEOTOP UQAM-McGill.
de Vernal, Anne  GEOTOP UQAM-McGill.
Wolfe, Alexander P.  University of Alberta.
Fredskild, Bent  Greenland Botanical Survey.
Kerwin, Micheal W.  University of Denver.
Miller, Gifford H.  INSTAAR University of Colorado.
Richard, Pierre J.H.  Université de Montréal.

Surface sediment pollen assemblages from 390 lakes in northwestern Canada, northern Québec, the Canadian Arctic Archipelago and Greenland have been analyzed in order to provide modern analogs for quantitative paleoclimatic reconstruction. This represents a modern environmental gradient spanning 2400mm of mean annual precipitation, 14.7°C of July temperature, and 32.7°C of January temperature. The modern pollen data includes relative frequencies of the 35 most common taxa.

Correspondance analysis (CA) was used to explore spatial distribution of pollen assemblages and relationships with climatic parameters. The CA demonstrates a clear latitudinal pattern, with Axis 1 (27.1% of variance) positively and disgnificantly correlated (r=0.85) with July air temperature. The use of closest modern analogues for quantitative paleoclimatic reconstruction was evaluated by estimating modern climate from surface pollen spectra. The best results were obtained using a chord distance dissimilarity metric and the 5 closest analogues. Observed versus estimated modern variables produced root-mean-squared errors of prediction (RMSEP) of ±1.98°C and ±0.71°C for the January and July temperatures, respectively, and ±175.32mm for annual precipitation.

Detailed pollen analyses and paleoclimate reconstructions have been undertaken on Holocene sediments from two well dated lake cores on Cumberland Peninsula, Baffin Island. Squared chord distances between successive pollen spectra were first used to identify periods of vegetation change. Notable transitions occurred at 8000, 3000 and 500 cal BP. Although climate reconstructions from both sites indicate some local differences, there are generally consistent features on a regional scale, including a progressive 1.5°C decrease in July temperature since 8000 cal BP, a progressive 5°C increase in January temperature since 7000 cal BP and an increase in annual precipitation. These reconstructions are therefore consistent with a progressive reduction in the seasonal amplitude of Holocene paleotemperatures, which is tentatively attributed to enhanced oceanic influences at the regional scale.



Figure 1. From left to right are illustrated: (1) Squared chord distance (SCD) between successive pollen spectra. (2) Relative frequency of selected taxa expressed as z-score. (3) Climate reconstruction. The vertical line marks the mean for the post-8300 cal BP period.


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