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Brooks Range Alaska

Paleohydrology Across Central Alaska: A Multiproxy Approach to Lake-Level Records

The primary objective of this project is to produce new multi-proxy paleoclimate records from Central Alaska to test hypotheses concerning the cause of shifts in the precipitation-evaporation balance from 18 ka to present. Previous work suggests (i) a prolonged period of aridity from the Last Glacial Maximum to the glacial to interglacial transition, (ii) a two-stage increase in the moisture balance roughly correlative with the two-step rise in sea level, and (iii) a complicated history of water balance shifts during the Holocene, indicated by multiple transgression-regression sequences in Dune Lake. The proposed research has two key goals (i) expand the network of sites with decadal to century-scale lake-level data to identify the spatial and temporal pattern of changes in the precipitation-evaporation balance from ~18 ka to present and (ii) identify fluctuations in the moisture balance for the past 2000 year at annual to decadal-scale from closed-basin Dune Lake. These records are needed to understand the long-term atmospheric dynamics of the Arctic and to assess the significance of shifts in the precipitation-evaporation balance. We propose to reconstruct the Holocene climate history of the region with a series of studies analyzing the sedimentology, geochemistry, magnetic properties, pollen content, stable isotopic composition, and for the first time in the Arctic, biomarker compounds. The lake cores will be dated at high-resolution by 137Cs, 210Pb and AMS 14C measurements on macrofossils and pollen.

This research will expand the scope of our previous work in central Alaska by combining core transects and seismic surveys to identify water level changes associated with shifts in the P-E balance of the region. Depth transects of contemporary sediment facies will be characterized with sediment, pollen, stable isotope, and biomarker studies, and these results applied to down-core studies to aid in identifying water-level changes. The resulting time-series of climatic shifts from a network new study areas will yield the necessary spatial coverage to identify patterns of regional climate change. We also hypothesize that (i) the cause of the two-stage increase in the moisture balance during the glacial to interglacial transition is related to a global-scale phenomenon and will be present and synchronous across central Alaska, (ii) the millennial to century-scale wet-dry cycles during the Holocene are driven in part by insolation changes that cause long-term shifts in the seasonal location of the Arctic front, thereby regulating the amount of moisture drawn into the region, and (iii) high frequency hydrologic events during the last ~2000 years are caused by long-tern variations in the frequency of El Niño Southern Oscillation (ENSO) events, and changes in the position and intensity of the North Pacific High and Aleutian Low. We can gain insight into the cause of shifts in the precipitation-evaporation balance of the Arctic by examining a network of sites along both west-east and north-south transects to determine if the timing of the major shifts in the moisture balance are synchronous within the region. Such a record of changing effective moisture will provide insight into the long-term climate variability of the western Arctic. Changes in water resources may have also significantly affected people and fauna in this archeologically important region. Knowledge of the frequency and magnitude of these shifts in the moisture balance are critical environmental factors necessary for resource planning, and both present and future human activity in the region.

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