Late glacial and Holocene history of the Greenland Ice Sheet margin, Nunatarssuaq, Northwestern Greenland

Friday, 18 December 2015
Poster Hall (Moscone South)
Lauren Brett Farnsworth1, Meredith A Kelly2, Yarrow Axford3, Gordon R Bromley4, Erich C Osterberg1, Jennifer A Howley1, Susan R H Zimmerman5, Margaret Scott Jackson1, Gregory Everett Lasher3 and Jamie Marie McFarlin3, (1)Dartmouth College, Hanover, NH, United States, (2)Dartmouth College, Department of Earth Sciences, Hanover, NH, United States, (3)Northwestern University, Evanston, IL, United States, (4)Climate Change Institute, University of Maine, Orono, School of Earth and Climate Science, Orono,, ME, United States, (5)Lawrence Livermore National Laboratory, Livermore, CA, United States
Defining the late glacial and Holocene fluctuations of the Greenland Ice Sheet (GrIS) margin, particularly during periods that were as warm or warmer than present, provides a longer-term perspective on present ice margin fluctuations and informs how the GrIS may respond to future climate conditions. We focus on mapping and dating past GrIS extents in the Nunatarssuaq region of northwestern Greenland. During the summer of 2014, we conducted geomorphic mapping and collected rock samples for 10Be surface exposure dating as well as subfossil plant samples for 14C dating. We also obtained sediment cores from an ice-proximal lake. Preliminary 10Be ages of boulders deposited during deglaciation of the GrIS subsequent to the Last Glacial Maximum range from ~30-15 ka. The apparently older ages of some samples indicate the presence of 10Be inherited from prior periods of exposure. These ages suggest deglaciation occurred by ~15 ka however further data are needed to test this hypothesis. Subfossil plants exposed at the GrIS margin on shear planes date to ~ 4.6-4.8 cal. ka BP and indicate less extensive ice during middle Holocene time. Additional radiocarbon ages from in situ subfossil plants on a nunatak date to ~3.1 cal. ka BP. Geomorphic mapping of glacial landforms near Nordsø, a large proglacial lake, including grounding lines, moraines, paleo-shorelines, and deltas, indicate the existence of a higher lake level that resulted from a more extensive GrIS margin likely during Holocene time. A fresh drift limit, characterized by unweathered, lichen-free clasts approximately 30-50 m distal to the modern GrIS margin, is estimated to be late Holocene in age. 10Be dating of samples from these geomorphic features is in progress. Radiocarbon ages of subfossil plants exposed by recent retreat of the GrIS margin suggest that the GrIS was at or behind its present location at AD ~1650-1800 and ~1816-1889. Results thus far indicate that the GrIS margin in northwestern Greenland responded sensitively to Holocene climate changes. Ongoing research will improve the chronological constraints on these fluctuations.