Dendrochronology and late Holocene history of Bering Piedmont Glacier, Alaska

Fluctuations of the piedmont lobe of Bering Glacier and its sublobe Steller Glacier over the past two millennia are reconstructed using 34 radiocarbon dates and tree-ring data from 16 sites across the glaciers' forelands. The general sequence of glacial activity is consistent with well-dated fluctua tions of tidewater and land-terminating glaciers elsewhere along the Gulf o f Alaska. Extensive forested areas along 25 km of the Bering ice margin wer e inundated by glacio-lacustrine and glacio-fluvial sediments during a prob able ice advance shortly before 500 cal yr A.D, Regrowth of forests followe d the retreating ice as early as the 7th century A.D., with frequent interr uptions of tree growth due to outwash aggradation. Forests overrun by ice a nd buried in outwash indicate readvance about 1080 cal yr A.D. Retreat foll owed, with ice-free conditions maintained along the distal portions of the forefield until the early 17th century after which the ice advanced to with in a few kilometers of its outer Neoglacial moraine, Ice reached this posit ion after the mid-17th century and prior to 200 yr ago. Since the early 20t h century, glacial retreat has been punctuated by periodic surges. The reco rd from forests overrun by the nonsurging Steller Lobe shows that this west ern ice margin was advancing by 1250 A.D., reaching near its outer moraine after 1420 cal yr A.D. Since the late 19th century, the lobe has dominantly retreated. (C) 1999 University of Washington.