Summary: Evidence from lake sediments and glacier forefields from two
hydrologically isolated lake basins is used to reconstruct Holocene
glacier and climate history at Hallet and Greyling Lakes in the
central Chugach Mountains of south-central Alaska. Glacial landform
mapping, lichenometry, and equilibrium-line altitude reconstructions,
along with changes in sedimentary biogenic-silica content, bulk density,
and grain-size distribution indicate a dynamic history of Holocene
climate variability. The evidence suggests a warm early Holocene
from 10 to 6 ka, followed by the onset of Neoglaciation in the two
drainage basins, beginning between 4.5 and 4.0 ka. During the past
2 ka, the glacial landforms and lacustrine sediments from the two
valleys record a remarkably similar history of glaciation, with two
primary advances, one during the first millennium AD, from ~500 to
800 AD, and the second during the Little Ice Age (LIA) from ~1400 to
1900 AD. During the LIA, the reconstructed equilibrium-line altitude
in the region was no more than 83±44m (n = 21) lower than the modern,
which is based on the extent of glaciers during 1978.
Differences between the summer temperature inferred from the
biogenic-silica content and the evidence for glacial advances
and retreats suggest a period of increased winter precipitation
from 1300 to 1500 AD, and reduced winter precipitation from
1800 to 1900 AD, likely associated with variability in the
strength of the Aleutian Low.
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