AN EXPANDED SURFACE-WATER PALEOTEMPERATURE INFERENCE MODEL FOR USE WITH FOSSIL MIDGES FROM EASTERN CANADA

Using an expanded surface sample data set, representing lakes distribu ted across a transect from southernmost Canada to the Canadian High Ar ctic, a revised midge-palaeotemperature inference model was developed for eastern Canada. Modelling trials with weighted averaging (with cla ssical and inverse deshrinking; with and without tolerance downweighti ng) and weighted averaging partial least squares (WA-PLS) regression, with and without square-root transformation of the species data, were used to identify the best model. Comparison of measured and predicted temperatures revealed that a 2 component WA-PLS model for square-root transformed percentage species data provided the model with the highes t explained variance (r(jack)(2)=0.88) and the lowest error estimate ( RMSEPjack=2.26 degrees C). Comparison of temperature inferences based on the new and old models indicates that the original model may have s eriously under-estimated the magnitude of late-glacial temperature osc illations in Atlantic Canada. The new inferences suggest that summer s urface water temperatures in Splan Pond, New Brunswick were approximat ely 10 to 12 degrees C immediately following deglaciation and during t he Younger Dryas. During the Allerod and early Holocene, surface water temperatures of 20 to 24 degrees C were attained. The new model thus provides the basis for more accurate palaeotemperature reconstructions throughout easternmost Canada.