LAKE SEDIMENT RECORDS OF LATE QUATERNARY PALEOCLIMATE CHANGE FROM ALASKA AND NEWFOUNDLAND DEVELOPED USING SEDIMENTOLOGY AND GEOCHEMICAL PROXIES

High-latitude regions are particularly sensitive to climate change through positive feedbacks linked with cryospheric processes and further exert a significant influence on the global climate system. Long term records of natural climate variability are essential to give context to potential future climatic scenarios and to put them into perspective. Sediments from Harding Lake in the interior and Burial Lake in northwest Alaska were used to reconstruct lake-levels and paleoenvironmental conditions spanning the Last Glacial Maximum using a detailed analysis of core sedimentology and a multiproxy geochemical approach. Relatively high lake-levels during late Marine Isotope Stage 3 are followed by extremely arid and windy conditions evinced from very low lake-levels during the Last Glacial Maximum (LGM). Ameliorating climate conditions and rising lake-levels commence by 19,600 cal yr BP at Burial Lake and by 15,700 cal yr BP at Harding Lake. Holocene hydroclimate conditions are broadly characterized by high and stable lake-levels along with variable levels of terrestrial and aquatic productivity. Major climatic transitions in Alaska coincide with changes in summer insolation, Laurentide Ice Sheet extent, eustatic sea level, and related changes in paleogeography. Millennial variations in aquatic productivity at Burial Lake occur over the last 10,000 cal yr BP, which are related to changes in the duration of the ice-free season and the availability of limiting nutrients. Productivity variations coincide with changes in the mean-state Arctic Oscillation on millennial time scales, suggesting the millennial variations are driven by an internal forcing mechanism related to an ocean-atmosphere interaction. Sediments from Cheeseman Lake in Newfoundland were used to reconstruct hydroclimate variability using the oxygen isotopic composition of authigenic carbonates (δ18O). Increasing δ18O values from 10,200 to 7,950 cal yr BP reflect warming temperatures that are superimposed by abrupt negative δ18O shifts at 9,700 and 8,500 cal yr BP from short lived cooling events. Decreasing δ18O values after 7,950 to 1,200 cal yr BP indicate a cooling trend consistent with declining insolation, cooling surface temperatures, and a cooling trend inferred from Greenland ice cores. The results highlight the sensitivity of Newfoundland climate to ocean-atmosphere interactions on century to orbital time scales