Branched glycerol dialkyl glycerol tetraethers in Arctic lake sediments: Sources and implications for paleothermometry at high latitudes

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are analyzed indifferent lakes of the Mackenzie (Canadian Arctic) and Kolyma (SiberianArctic) River basins to evaluate their sources and the implications forbrGDGT-based paleothermometry in high-latitude lakes. The comparison ofbrGDGT distributions and concentrations in the lakes with those in riversuspended particulate matter, riverbank sediments, and permafrostmaterial indicates that brGDGTs in Arctic lake sediments have mixedsources. In contrast to global observations, distributional offsetsbetween brGDGTs in Arctic lakes and elsewhere in the catchment areminor, likely due to the extreme seasonality and short window ofbiological production at high latitudes. Consequently, both soil- andlake-calibrated brGDGT-based temperature proxies return sensibletemperature estimates, even though the mean air temperature (MAT) in theArctic is below the calibration range. The original soil-calibratedMBT-CBT (methylation of branched tetraethers-cyclisation of branchedtetraethers) proxy generates MATs similar to those in the studied riverbasins, whereas using the recently revised MBT'-CBT calibrationoverestimates MAT. The application of the two global lake calibrations,generating summer air temperatures (SAT) and MAT, respectively,illustrates the influence of seasonality on the production of brGDGTs inlakes, as the latter overestimates actual MAT, whereas the SAT-basedlake calibration accounts for this influence and consequently returnsmore accurate temperatures. Our results in principle support theapplication of brGDGT-based temperature proxies in high-latitude lakesin order to obtain long-term paleotemperature records for the Arctic,although the calibration and associated transfer function have to beselected with care