Climate, Tree-Ring, and Glacial Fluctuations in the Rio Frias Valley, Rio Negro, Argentina

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Abstract
This study documents the use of dendrochronology for dating oscillations of glaciers and climatic changes related to them. The application of dendrochronological and dendroclimatological methods together allow improvement of the dating of Frias Glacier moraines Rio Negro Argentina (41.degree. 10''S, 71.degree. 50''W), with a precision of a decade or even less. A minimum date for lateral and end moraines was obtained by counting the number of annual rings in the oldest trees growing on each moraine. Precise ages for ice positions were determined from trees that had been damaged by the glacier during its latest-Neoglacial advances. Moreover, due to the similarity found between climate models for tree-growth and glacier front fluctuations, a direct relationship was established between variations in tree-ring width indices of Fitzroya cupressoides Mol. Jhonst. and fluctuations of Frias Glacier front. Cool and wet summers result in advances of glacier front and in the formation of wider tree-rings. Taking into account all these facts, Frias Glacier moraines were dated to the following years: 1977, .apprx.1942, .apprx.1914, ca. 1881, .apprx.1839, .apprx.1747, .apprx.1722, and ca. 1638. These dates are consistent with the historical record inferred from old drawings and photographs as well as with the glacial chronologies proposed for Patagonia east of the Andes. The consistency of the glacial history recorded by the different methods suggests that the combined approach is valid.