Holocene climate inferred from glacier extent, lake sediment and tree rings at Goat Lake, Kenai Mountains, Alaska, USA

Daigle, Thomas; Kaufman, Darrell

Lake sediment, glacier extent and tree rings were used to reconstruct Holocene climate changes from Goat Lake at 550masl in the Kenai Mountains, south-central Alaska. Radiocarbon-dated sediment cores taken at 55m water depth show glacial-lacustrine conditions until about 9500 cal. yr BP, followed by organic-rich sedimentation with an overall increasing trend in organic matter and biogenic silica content leading up to the Little Ice Age (LIA). Through most of the Holocene, the northern outlet of the Harding Icefield remained below the drainage divide that currently separates it from Goat Lake. A sharp transition from gyttja to inorganic mud about AD 1660 signifies the reappearance of glacier meltwater into Goat Lake during the LIA, marking the maximum Holocene (postglacial) extent. Meltwater continued to discharge into the lake until about AD 1900. A 207 yr tree-ring series from 25 mountain hemlocks growing in the Goat Lake watershed correlates with other regional tree-ring series that indicate an average summer temperature eduction of about 18C during the 19th century compared with the early–mid 20th century. Cirque glaciers around Goat Lake reached their maximum LIA extent in the late 19th century. Assuming that glacier quilibrium-line altitudes (ELA) are controlled solely by summer emperature, then the cooling of 18C combined with the local environmental lapse rate would indicate an ELA lowering of 170 m. In contrast, reconstructed ELAs of 12 cirque glaciers near Goat Lake average only 34 18m lower during the LIA. The restricted ELA lowering can be explained by a reduction in accumulation-season precipitation caused by a weakening of the Aleutian low-pressure system during the late LIA.

Holocene climate inferred from glacier extent, lake sediment and tree rings at Goat Lake, Kenai Mountains, Alaska, USA

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