An expanded surface-water palaeotemperature inference model for use with fossil midges from eastern Canada

Abstract

Using an expanded surface sample data set, representing lakes distributed across a transect from southernmost Canada to the Canadian High Arctic, a revised midge-palaeotemperature inference model was developed for eastern Canada.Modelling trials with weighted averaging (with classical and inverse deshrinking; with and without tolerance downweighting) 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 highest explained variance (r2 jack= 0.88) and the lowest error estimate (RMSEPjack =2.26 0C). Comparison of temperature inferences based on the new and old models indicates that the original model may have seriously under-estimated the magnitude of late-glacial temperature oscillations in Atlantic Canada. The new inferences suggest that summer surface water temperatures in Splan Pond, New Brunswick were approximately 10 to 12 0C immediately following deglaciation and during theYoungerDryas. During the Allerød and early Holocene, surface water temperatures of 20 to 24 C were attained. The new model thus provides the basis for more accurate palaeotemperature reconstructions throughout easternmost Canada.