Late Holocene Fluctuations of the Fiord Glacier System in Icy Bay, Alaska, U.S.A.

Porter, Stephen

A 2000-yr chronology of expansion and contraction of the tidewater glacier in Icy Bay, Alaska, is constrained by 30 calibrated radiocarbon ages of wood and peat sampled from stratigraphic sections along the 50-km-long fiord system that has been progressively deglaciated since the end of the last century. The earliest ages indicate ice-free conditions in the upper fiord at the beginning of the Christian era. The outermost moraine complex at the mouth of the bay continues seaward as a submarine shoal and dates from A.D. 400 to 850. Subsequent ice recession led to deglaciation of the fiord system by A.D. 1000. Renewed glacier expansion at the onset of the Little Ice Age (13th century A.D.) led to damming of the lower ice-free reaches of several tributary fiords and to submergence and burial of fiord-margin forests by lake sediments. Continued expansion during the main phase of the Little Ice Age probably culminated in the early 19th century subsequent to Vancouver's initial sighting of the Icy Bay glacier system in 1794. Major episodes of advance in Icy Bay have encompassed about 300 to 500 yr whereas deglaciation of the fiord system takes less than 150 yr. Although the Icy Bay and other Alaskan tidewater glaciers display a lack of synchrony on a decadal time scale, broad similarity in the chronology of first-order advances and retreats suggests they may be triggered by shifts in climate that are responsible for the onset and termination of glaciological events on the scale of the Little Ice Age.

Late Holocene Fluctuations of the Fiord Glacier System in Icy Bay, Alaska, U.S.A.

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