Northern Cordilleran Ice Sheet Dynamics in Coastal Alaska from MIS 3 to the Present: Initial Results

Tuesday, 16 December 2014
Michelle L Penkrot1, John M Jaeger1, Leah LeVay2, Guillaume St-Onge3,4, Alan C Mix5, Heinrich Bahlburg6, Maureen Davies-Walczak7 and Sean P S Gulick8, (1)Univ Florida, Gainesville, FL, United States, (2)Texas A & M University, College Station, TX, United States, (3)Université du Québec à Rimouski, Rimouski, Canada, (4)Institut des sciences de la mer de Rimouski (ISMER), Rimouski, Canada, (5)CEOAS, Oregon State University, Corvallis, OR, United States, (6)Westfälische Wilhelms-Universität, Münster, Germany, (7)Australian National University, Canberra, Australia, (8)University of Texas at Austin, Austin, TX, United States
Establishing the timing of northwestern Cordilleran ice sheet (NCIS) advance–retreat cycles in southern Alaska allows for investigation of global synchronicity in glacial-age climate forcing. Integrated Ocean Drilling Program Expedition 341 targeted the glacial dynamics of the NCIS in the coastal St. Elias range. Sediment cores from Site U1419 encompass times of global ice advance and retreat from MIS 3 to the present, based on a preliminary age model with 5-kya resolution developed using oxygen isotopes from benthic and planktonic foraminifera and stratigraphic correlation with a previously C-14 dated site survey core (Davies et al., 2011; doi:10.1029/2010PA002051). CT images of cores were used to identify sedimentary facies and relative ice sheet proximity. Six sedimentary facies were identified in the images; massive mud with and without lonestones, laminations with and without lonestones, massive and stratified diamict (>1 clast/cm). Elemental scanning XRF data were used to delineate possible downcore changes in sediment provenance using provenance-sensitive transition metals. Diamict and gravelly mud are the most common facies, indicative of persistent glacial input interpreted as marine-terminating glacial systems. Stratified diamicts are interpreted as periods of maximum ice extent (~18-20 ka), whereas massive mud (~14 ka-present) suggests terminus retreat. Intervals of laminated mud with and without lonestones are interpreted as periods of reduced ice cover, with the most recent (~14.5 kya) coinciding with the Bølling Interstade of northern Europe/Greenland (Davies et al., 2011). Downcore changes in Al-normalized metal XRF counts vary along with sedimentary lithoficies, suggesting changes in sediment provenance that may be related to the quantity of glacigenic sediment delivery to this location.