Glacier Variations in the Sierra Nevada, California, as Related to a 1200-Year Tree-Ring Chronology

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Abstract
A time-series of tree-ringwidth indices for alpine timberline foxtail pine (Pinus balfouriana) from the Sierra Nevada of California shows a growth response to summer, late fall, and early winter temperatures that is the inverse of that resulting in the expansion of alpine glaciers. These are correlated with lichen-dated moraines and avalanche deposits that accumulated during subsequent decades. Minima in the ringwidth record, reflecting marked temperature declines occurred at 810, 1470, 1610, 1700 and 1810. Cold periods of lesser extent are also indicated between 1190 to 1400 and suggest that the initial pulses of the Sierran Matthes advances may have begun as early as 1190, or 150 yr earlier than previously dated. The Matthes advances were preceded by a period of pronounced warmth from 900 to 1190 during which timberline rose 10 m to its present elevation. A warm period is also indicated between 1500 and 1580. Recent work extending the tree-ring chronology to 3031 yr B.P. and radiocarbon dating of weathered samples to 6300 yr B.P. suggests that the chronology may ultimately be applicable to the dating of earlier Sierran glacier advances.
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