AMP: Overview of the Ahklun Mountains Project

Overview of the Project

The Ahklun Mountains project is an on-going collaborative effort aimed at reconstructing aspects of the Quaternary history of the Ahklun Mountains region in southwestern Alaska. Extensive and repeated advances by valley glaciers and ice-cap outlet glaciers are documented from: 1) well-preseved moraines in alpine valleys and in the lowlands, and 2) extensive river and coastal exposures of glacial, glacial-fluvial, and glacial-marine sediments. Drift-impounded lakes throughout the region contain continuous, high-resolution records of late Quaternary (pre-late Wisconsin through Holocene) environmental changes.
AMP research has incorporated a wide range of techniques working over a broad geographic area. AMP follows a 3-year NSF project with co-PI Peter Lea (Bowdoin College) that focused on the eastern Bristol Bay region. The first two years of AMP research concentrated on the glacial history of the southwestern Ahklun Mountains and adjacent lowlands. The glacial history has been placed in a regional and global context by a suite of geochronologic techniques: Relative-age data, including measurements of loess cover, soil development, and moraine morphology, successfully distinguish pre-Wisconsin, early Wisconsin, and late Wisconsin drift; and 14C, cosmogenic 36Cl, amino acid, fission track, 40Ar/39Ar, tephra geochemistry, and thermoluminescence analyses support and refine this relative chronology. Another ongoing aspect of the project involves using GIS for ELA analyses and related paleoclimatic interpretations. Subsequent work has focused on lake cores: Several long (>6 m) sediment cores obtained from Arolik Lake, beyond the limit of late Wisconsin glaciers, are enabling detailed reconstructions of environmental changes through the last glacial maximum. Glacial mapping combined with lake coring in the northwestern Ahklun Mountains has provided high-resolution records of deglacial and Holocene glacial/environmental changes. In 1999, the project's focus shifted towards the Holocene, and mapping and lake coring near the range's modern glaciers. Further coring is planned for the 2000 field season.
Synthesized, the results of this geographically and chronologically broad-based study thus far define multiple extensive middle Pleistocene advances, one or more extensive early Wisconsin advances, and a restricted late Wisconsin advance occurring late during marine oxygen-isotope stage 2. It appears that the relative extents of glacier advances in the Ahklun Mountains do not coincide with those evidenced by the global marine oxygen-isotope record. Moisture availability modulated by sea-level fluctuations is proposed as the porminent control on ice volume in this region. Future work, inlcuding lake core analyses, cosmogenic dating, ELA analyses, and paleoecological reconstructions, will further refine the chronology and nature of paleoclimatic changes that have occurred in the Ahklun Mountains region.

Note: Text modified from Axford et al., 1998.