Climatic and environmentally driven variability in lacustrine brGDGT distributions at local to regional scales in Alaska and northwestern Canada

Abstract

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) have attracted considerable interest from paleoclimate researchers due to their temperature sensitivity in modern environments, ubiquity, and preservation in the geologic record. BrGDGTs are especially attractive in high-latitude regions where the number of applicable proxies is limited. However, the climatic sensitivity of brGDGT assemblages varies between depositional environments and is uncharacterized for lacustrine systems in Alaska, Yukon, and Northwest Territories. This study addresses this knowledge gap by assessing the climate response of lacustrine brGDGTs from a network of lakes (n = 67) in Alaska and NW Canada (59.5 to 69.4° N). The mean temperatures of months of above freezing (MAF) are highly correlated with the fractional abundance of the IIIa brGDGT (Pearson’s coefficient = -0.79, p < 0.001) as well as the methylation of branched tetraethers (MBT′5ME) index (Pearson’s coefficient = 0.75, p < 0.001) from Alaska, Yukon, and Northwest Territories. The fractional abundance of the IIIa brGDGT and the MBT′5ME index are subsequently calibrated to climate using traditional ordinary least squares analysis and a user-friendly and open-source Bayesian regression analysis that yield comparable results. The climatic sensitivity of lacustrine brGDGTs in Alaska, Yukon, and Northwest Territories is unique in comparison to previously reported global assemblages and further varies between a subset of interior and coastal sites. The driver of this variability cannot yet be constrained, but future applications of brGDGTs as a paleoenvironmental proxy should select calibrations that closely resemble the past environment of interest. Wherever possible, paleoenvironments should be corroborated using independent proxies.