Recent warming in a 500-year palaeotemperature record from varved sediments, Upper Soper Lake, Baffin Island, Canada

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Abstract
Laminated sediments from Upper Soper Lake on southern Baffin Island provide a new 500-year record of temperature change in the Arctic. Radiometric dating, using 210Pb and Pu, shows that the light-and dark-coloured laminae couplets are annually deposited varves. Dark laminae thickness is strongly correlated to average June temperature from Kimmirut (r = 0.82), reflecting the influence of temperature on snowmelt and fluxes of runoff and suspended sediment. This relationship allowed the construction of a palaeotemperature record that documents large-amplitude interannual to decadal variability superimposed on distinct century-scale trends, including 2°C average warming and maximum temperatures during the 1900s. Similar patterns of change are seen in individual and regionally averaged palaeotemperature records from around the circum-Arctic. Upper Soper Lake records temperatures, rates of change and variance during the twentieth century that are all anomalously high within the context of the last 500 years, and outside the observed range of natural variability. Comparisons of Upper Soper Lake and Arctic average palaeotemperature to proxy-records of hypothesized forcing mechanisms suggest that the recent warming trend is mostly due to anthropogenic emissions of atmospheric greenhouse gases. The magnitude of the warming and decade-scale variability throughout the records, however, indicate that natural forcing mechanisms such as changing solar irradiance and volcanic activity, as well as positive feedbacks within the Arctic environment, also play an important role.