Chironomid assemblages in surface sediments from 182 lakes across New England and Eastern Canada: Development and validation of a new summer temperature transfer function

This study investigates the distribution of subfossil chironomid assemblages in surface sediments from 182 lakes in New England and Eastern Canada, aiming to develop a new summer paleotemperature transfer function across an extended latitudinal gradient. Canonical analyses reveal a strong empirical relationship between chironomid taxa and summer temperatures, highlighting both direct physiological constraints and indirect environmental interactions. These results emphasize the importance of ecological assessments in interpreting subfossil records to verify the prominent role of summer temperature in driving assemblage changes. Two inference models for mean summer air temperature are developed: one using the commonly employed weighted averaging partial least squares (WAPLS) and another with the newly introduced frequency-corrected tolerance-weighted WAPLS (fxTWAPLS). Both cross-validation and independent assessments using downcore data against meteorological measurements confirm that subfossil chironomids are overall reliable proxies for summer temperatures. The fxTWAPLS model demonstrates superior reconstruction performance by effectively addressing the compression bias inherent in classical WAPLS. New inference models are applied on an existing postglacial record from the eastern Canadian boreal forest. The reconstruction is improved by the greater availability of warm modern analogues, allowing for the clear identification of the warm Mid-Holocene and the subsequent Neoglacial cooling, as well as a warming episode possibly related to the Roman Warm Period. The fxTWAPLS model further improves the reconstruction by inferring a wider range of temperatures, with both colder and warmer periods than modern conditions. This transfer function constitutes a new valuable operational tool for producing high-quality paleoclimatic reconstructions of Late-Quaternary summers in the Nearctic region. • New Nearctic chironomid training-set covering a broad temperature gradient. • Modern chironomid distribution is strongly linked to mean summer air temperature. • Limnological features can influence taxon responses to summer air temperature. • The fxTWAPLS method yields more accurate inferences than WAPLS. • The new transfer function enhances a postglacial temperature reconstruction.