LITTLE ICE AGE GLACIER EQUILIBRIUM-LINE ALTITUDES AND CLIMATE NEAR GOAT LAKE, KENAI MOUNTAINS, ALASKA

Lake sediments, glacier extents, and tree rings were used to reconstruct late Holocene climate changes from Goat Lake at 550 m asl in the Kenai Mountains, south-central Alaska (60° 14' N, 149° 54' W). Goat Lake is situated ~450 m north of a drainage divide that currently separates the lake basin from an unnamed northern outlet of the Harding Icefield (HIF) we refer to as the North Goat Glacier. Radiocarbon dated sediment analyses focused on the last 1000 yr, where a sharp transition from gyttja to overlying inorganic mud around 1660 AD marks the first time since the Pleistocene deglaciation that the North Goat Glacier overtopped the drainage divide to spill meltwater into Goat Lake. The North Goat Glacier continuously discharged meltwater into Goat Lake until around 1890 AD, and has since thinned 150 m and retreated 1.4 km to its 2005 AD location. Ice-marginal features of 12 cirque glaciers around Goat Lake reached their maximum LIA extent in the late 19th century based on lichenometry. Equilibrium-line altitudes (ELA) of the 12 cirque glaciers were reconstructed for the maximum LIA extent based on the accumulation-area ratio (AAR) method and yield an average lowering of 34 ± 18 m below mid 20th century levels. A new 207 yr tree-ring chronology from 25 hemlock trees in the Goat Lake watershed correlates with other regional tree-ring series that indicate an average summer temperature reduction of about 1°C during the 19th century compared with the early-middle 20th century. Assuming that glacier equilibrium-line altitudes (ELA) are controlled solely by summer temperature, then the cooling of 1°C combined with the local environmental lapse rate would indicate an ELA lowering of 170 m. This did not occur, suggesting a reduction in accumulation-season precipitation and implying a weakening of the Aleutian Low pressure system during the late LIA.

Our finding that glaciers in the northern Kenai Mountains reached their maximum Holocene extent late during the LIA is consistent with of the results of the pioneering work by Calkin and his students. However, we find that ELA lowering during the maximum LIA glacier extent on the Kenai Peninsula was somewhat less than previously estimated.