Physical and biological characteristics of lacustrine sediment from Emerald Lake were used to reconstruct the Holocene glacier history of Grewingk Glacier, southern Alaska. Emerald Lake is an ice-marginal threshold lake, receiving glaciofluvial sediment when Grewingk Glacier overtops the topographic divide that separates it from the lake. Sub-bottom acoustical profiles were used to locate core sites to maximize both the length and resolution of the sedimentary sequence recovered in the 4-m-long cores. The age model for the composite sequence is based on 13 14C ages and a 210Pb profile. A sharp transition from the basal inorganic mud to organic-rich mud at 11.4 ± 0.2 ka marks the initial retreat of Grewingk Glacier below the divide of Emerald Lake. The overlaying organic-rich mud is interrupted by stony mud that records a re-advance between 10.7 ± 0.2 and 9.8 ± 0.2 ka. The glacier did not spill meltwater into the lake again until the Little Ice Age, consistent with previously documented Little Ice Ages advances on the Kenai Peninsula. The retreat of Grewingk Glacier at 11.4 ka took place as temperature increased following the Younger Dryas, and the subsequent re-advance corresponds with a climate reversal beginning around 11 ka across southern Alaska.
Bibliographical noteFunding Information:
We thank B. Boldt and J. Griffith for the assistance in the field and K. Whitacre for help in the laboratory; M. Retelle for use of the acoustic profiler; E. Berg for encouraging the study; R.S. Anderson, J. Briner, P.T. Davis, T. Lowell, L. Owen, A. Nesje and N. Riggs for their comments on an earlier draft; R.S. Anderson for identifying the macrofossils for 14 C dating; B. Jensen, S. Kuehn and P. Zander for analyzing the tephra; the laboratories for various analyses mentioned in the text (LacCore at University Minnesota, Flett Research, Keck Carbon Cycle AMS Facility); and the National Science Foundation ( EAR-0823522 ) and Geological Society of America for funding.
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- Glacier fluctuations
- Grewingk Glacier
- Lake sediments