Calibration and Reconstruction of Past Temperature Changes from Glacial Varved Sediments

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ABSTRACTHughenOPP-0096751Donard Lake, Baffin Island, contains annually laminated sediments produced by the summer melting of the Caribou Glacier, which currently dominates its catchment. Donard Lake laminated sediments are classic glacio-lacustrine varves and contain a record of summer temperature variations, potentially as far back as 5,000 years before present. Previous efforts to calibrate Donard Lake varve thickness using a single core showed a correlation of varve thickness to temperature (r=0.57), but also a large amount of unexplained variance. The correlation was greatly improved when both temperature and varve thickness data were smoothed into three-year averages (r=0.82), suggesting that the low correlation for annual data was caused by error and random noise contained in the single-core varve chronology. Research on varved sediments in other Arctic lakes has shown that averaging together measurements from multiple cores is necessary for accurate calibration studies, to eliminate errors in the annual chronology and to reduce noise from random variability contained within individual cores. Detailed calibration data sets are critical to improving the utility of laminated sediments records as paleotemperature proxies, both for accurate quantitative reconstructions of the magnitude of temperature change at individual locations, as well as for the development of integrated spatial networks of paleoclimate records throughout the Arctic.The Principal Investigator will use a suite of five new sediment cores, retrieved with the sediment-water interfaces intact, to construct a high-quality, multiple-core varve chronology for Donard Lake. Cross correlation of the multiple cores will provide a precise layer-count chronology for confirmation of annual deposition using a combination of independent dating methods, including 137 Cs and 210Pb. The cross-correlated chronology will also allow averaging of each year's varve thickness measurements between several cores, providing a lake-wide varve thickness record that is much less influenced by random noise from individual cores. This varve thickness record will be calibrated to summer temperature using monthly instrumental meteorological data from nearby Cape Dyer, resulting in precise and accurate temperature calibration relationships for Donard Lake varves. The meteorological data will also be used to investigate the possible influence of precipitation on varve thickness. The multiple-core varve chronology used to calibrate varve thickness to temperature will be extended back in the new cores for approximately 500 years. This new, 500-year record of temperature change in the eastern Canadian Arctic will provide important quantification of the precise magnitude of warming at the end of the Little Ice Age, and will help efforts to discriminate between natural and anthropogenic forcing of global climate change. In addition, the annual nature of the paleotemperature record will also allow precise determination of variance and rates of change during the past five centuries and place recent climatic changes into a longer-term perspective of natural variability.ABSTRACTHughenOPP-0096751Donard Lake, Baffin Island, contains annually laminated sediments produced by the summer melting of the Caribou Glacier, which currently dominates its catchment. Donard Lake laminated sediments are classic glacio-lacustrine varves and contain a record of summer temperature variations, potentially as far back as 5,000 years before present. Previous efforts to calibrate Donard Lake varve thickness using a single core showed a correlation of varve thickness to temperature (r=0.57), but also a large amount of unexplained variance. The correlation was greatly improved when both temperature and varve thickness data were smoothed into three-year averages (r=0.82), suggesting that the low correlation for annual data was caused by error and random noise contained in the single-core varve chronology. Research on varved sediments in other Arctic lakes has shown that averaging together measurements from multiple cores is necessary for accurate calibration studies, to eliminate errors in the annual chronology and to reduce noise from random variability contained within individual cores. Detailed calibration data sets are critical to improving the utility of laminated sediments records as paleotemperature proxies, both for accurate quantitative reconstructions of the magnitude of temperature change at individual locations, as well as for the development of integrated spatial networks of paleoclimate records throughout the Arctic.The Principal Investigator will use a suite of five new sediment cores, retrieved with the sediment-water interfaces intact, to construct a high-quality, multiple-core varve chronology for Donard Lake. Cross correlation of the multiple cores will provide a precise layer-count chronology for confirmation of annual deposition using a combination of independent dating methods, including 137 Cs and 210Pb. The cross-correlated chronology will also allow averaging of each year's varve thickness measurements between several cores, providing a lake-wide varve thickness record that is much less influenced by random noise from individual cores. This varve thickness record will be calibrated to summer temperature using monthly instrumental meteorological data from nearby Cape Dyer, resulting in precise and accurate temperature calibration relationships for Donard Lake varves. The meteorological data will also be used to investigate the possible influence of precipitation on varve thickness. The multiple-core varve chronology used to calibrate varve thickness to temperature will be extended back in the new cores for approximately 500 years. This new, 500-year record of temperature change in the eastern Canadian Arctic will provide important quantification of the precise magnitude of warming at the end of the Little Ice Age, and will help efforts to discriminate between natural and anthropogenic forcing of global climate change. In addition, the annual nature of the paleotemperature record will also allow precise determination of variance and rates of change during the past five centuries and place recent climatic changes into a longer-term perspective of natural variability.