Radiocarbon-based age models from two lakes on Adak Island, Alaska, were compared using correlated tephra to check the accuracy of the radiocarbon ages and to develop a regional tephrochronology. Andrew and Heart Lakes are located adjacent to and 5km south of Mt. Moffett on the northern part of Adak Island in the central Aleutian Arc. The downcore trends in radiocarbon ages of macrofossils, the 1963 spike in plutonium (239+240Pu) activity, and a lead (210Pb) profile from Andrew Lake were modeled with smooth spline fits. Tephras were correlated based on magnetic susceptibility, particle morphology, and internal stratigraphy including color and particle size. Of the 19 pure tephras in Heart Lake and 21 in Andrew Lake, ten could be confidently correlated between the two lakes. The composite tephrostratigraphy from the two lakes includes at least 30 unique tephras deposited over 9600 years. Radiocarbon ages obtained from mixed aquatic and terrestrial macrofossils with ages hundreds of years too old were inferred for Heart Lake by correlated tephra ties to the Andrew Lake age model. The eroding tephra-soil deposits that crop out along the banks of Heart Lake, and its large shallow platform, may facilitate remobilization of previously stored sediments. Previous studies on Adak Island of archeological sites and tephra-soil outcrops described five tephras that are correlated with a subset of tephras from the lakes based on stratigraphic succession, inferred age, and physical description. Age-depth models for Heart and Andrew Lakes as well as tephrochronology for Adak Island provide geochronological context for future studies.
Bibliographical noteFunding Information:
The US Fish and Wildlife Service, Alaska Maritime Natural Wildlife Refuge and CPS Polar services provided logistical support for fieldwork on Adak Island. Caleb Schiff and Yarrow Axford participated in core collection on Adak Island. Laboratory collaborators integral to this project include J. Southon at the University of California, Irvine, Keck Carbon Cycle AMS Laboratory, M. Ketterer at the Northern Arizona University ICP-MS facility, Katherine Cooper at the NAU Sedimentary Records of Environmental Change Laboratory, and the staff at the University of Minnesota Limnological Research Center. Caleb Schiff conducted the initial analysis of the 2009 surface cores. R.S. Anderson and M. Ort provided input to Krawiec's MS thesis, and C. Murray-Wallace and an anonymous reviewer helped to improve the manuscript. The National Science Foundation Award EAR-0823522 funded this study.
Copyright 2013 Elsevier B.V., All rights reserved.
- Adak Island
- Lake sediments
- Radiocarbon age modeling