ESH: COLLABORATIVE RESEARCH: Climatic Variations During the Last Glaciation in suthwestern Alaska

Darrell S. Kaufman Darrell.Kaufman@nau.edu  (Principal Investigator current)

Abstract

     We propose to study the history of late Quaternary
     environmental change preserved in Arolik Lake, southern Alaska, to obtain a
     paleoclimate record with centennial-scale resolution.  We already have two
     continuous 6-to-8m-long cores from the lake, including one that extends back at
     least 22,000 yr (22 14C ka).  Now we propose to return to the lake armed with
     geophysical equipment for obtaining more detailed bathymetric charts and
     subsurface stratigraphic profiles to place these and new cores into a
     basin-wide stratigraphic context, to identify features indicative of lake-level
     fluctuations, and to locate sites within the basin for additional coring where
     a longer record (>60 ka) might be obtainable.  We will also measure the
     sub-bottom stratigraphy at a second lake (Nimgun Lake), 26 km northwest of
     Arolik Lake, to locate targets for cores extending into the last full-glacial
     period.  All cores will be processed for basic physical parameters and the most
     promising core will be selected for concentrated study of complementary
     physical (grain size, bulk density, magnetic susceptibility), biochemical
     (organic carbon, biogenic silica), and ecological (pollen, diatoms) proxy
     climate indicators, and for geochronology (AMS 14C and tephrochronology).  The
     goal is to obtain centennial-scale resolution for the proxy-climate indicators.
     The analyses will be a collaborative effort by workers with experience in
     obtaining sediment cores and acoustic-stratigraphic data from lakes (Kaufman,
     Werner), and by experts in the analysis of pollen (Hu), diatoms (Smol), and
     tephra (Riehle) from southwestern Alaska.  The results will contribute to
     previous and on-going work by PALE researchers in Beringia whose goal is to
     provide highly resolved records of paleoclimate to compare with climate model
     simulations and with records from glacier ice and marine sediment.

     Arolik
     Lake is in a good position to record paleoenvironmental changes.  Among other
     factors, the sedimentology of the lake should reflect changes in the regional
     glacial activity.  It is situated at the optimal distance from a source of
     eolian sediment derived from a late Wisconsin outwash plain: close enough to
     deliver a signal, but not so close as to overwhelm the lake deposits.  Nimgun
     Lake was fed distally by a small cirque glacier during the late Wisconsin. Both
     lakes are within the area where we have conducted extensive research into the
     extent and timing of late Pleistocene glacier fluctuations, where previous
     studies in the adjacent lowlands provide an independent framework of Quaternary
     paleoenvironmental change, and where we are developing a tephrostratigraphy for
     precise intra-and inter-basinal stratigraphic correlation's.  The lakes are
     dammed by moraines of early Wisconsin age (~110 -60 ka).

     Because lake
     sediments accumulate continuously over tens of thousands of years and are often
     dateable, they afford one of the best natural archives of past climate
     variability on the continents.  A continuous record of climate change extending
     back through the full-glacial period has not yet been obtained from
     southwestern Alaska, but is important for assessing whether the rapid climate
     oscillations known in marine and ice cores from North Atlantic region also
     affected continental regions of northwestern North America.  Assessing whether
     rapid climate changes occurred synchronously between these regions, or whether
     the spatial and temporal patterns are random, or even anti-phase, is
     fundamental to understanding the mechanisms that control climate oscillations.
     Developing this understanding for the full-glacial period is important in
     southwestern Alaska because deglacial records (15-10 ka) are potentially
     influenced by regional-climatic effects resulting from the submergence of
     extensive continental shelf.

     The record of full-glacial climate will also
     be used in a data-model comparison of a fundamental feature of atmospheric
     circulation simulated by global circulation models: The glacial anticyclone. At
     18 ka, the simulated anticyclone generates strong southerly flow that warms
     Alaska, especially during the winter.  A candidate for full-glacial warming in
     eastern Beringia is the so-called "Hanging Lake thermal event" dated in
     paleovegetation records in northern Alaska and western Canada at ~22-20 ka.
     This interval is represented in the core from Arolik Lake by increased plant
     macrofossil abundance.  We will evaluate the hypothesis that this warming is
     attributable to the glacial anticyclone as simulated by global climate models
     by assessing the fossil (pollen, plant macrofossils, and diatoms) evidence for
     higher winter temperatures and increased snowfall (and therefore for reduced
     lake ice), and the physical evidence for glacier fluctuations.