Lichenometry as Applied to Moraines in Alaska, U.S.A., and Kamchatka, Russia

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Abstract
A selective review of lichenometry as used to date Holocene moraines in five diverse regions of Alaska and in southeastern Kamchatka suggests that growth curves for this North Pacific area may be improved by attention to several factors. These included lichen identification, control point number and distribution, radiocarbon calibration, alternative curve models, and compatibility of lichen growth rate with climate. Support for control points presented for Kamchatka and published for Alaska areas will benefit from supplementary control at and beyond the break from the great growth curve segments of the last centuries. With regard to alternative—linear, logarithmic, and composite curve—models drawn for the published lichenometric data, the composite (logarithmic and linear composite models) appear the best fit for the Brooks Range and Wrangell–St. Elias areas of slow growth and continental interior climates. Calibration of 14C ages make minor changes in well-controlled curves, but differences may be marked where a single age supports the long-term portion of growth curves. Lichen subgenus Rhizocarpon section Geographicum and section Alpicola should, and usually can be, differentiated in North Pacific areas. Nevertheless, growth curves that may represent both yellow-green Rhizocarpons (e.g., central Brooks Range and southeastern Kamchatka) appear to allow derivation of reasonable surface dating where the taxa distribution is similar to that of the curves. Chronologies of glaciation based on lichenometry of moraines over the last millennium in these two areas across the Bering Sea are strikingly similar to each other and to more precisely dated tree-ring-based glacial chronologies in southern Alaska.
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