A 1500-year record of climatic and environmental change in ElkLake, Minnesota I: Varve thickness and gray-scale density |
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| Authors: | Walter Dean Roger Anderson J Platt Bradbury David Anderson |
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| Institution: | (1) US Geological Survey, MS 980, Federal Center, 80225 Denver, USA;(2) Department of Earth and Planetary Sciences, University of New Mexico, 87131 Albuquerque, USA;(3) Paleoclimate Program, National Oceanic and Atmospheric Administration, 325 Broadway, 80303 Boulder, USA |
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| Abstract: | The deepest part (29.5 m) of Elk Lake, ClearwaterCounty, northwestern Minnesota, contains a complete Holocene section that iscontinuously varved. The varve components are predominantly autochthonous(CaCO3, organic matter, biogenic silica, and several iron andmanganese minerals), but the varves do contain a minor detrital-clastic(aluminosilicate) component that is predominantly wind-borne (eolian) andprovides an important record of atmospheric conditions. Singular spectrumanalysis (SSA) and wavelet analysis of varve thickness recognized significantperiodicities in the multicentennial and multidecadal bands that varied inpower (i.e., variable significance) and position (i.e., variable period) withinthe periodic bands. Persistent periodicities of about 10, 22, 40, and 90 years,and, in particular, multicentennial periodicities in varve thickness and otherproxy variables are similar to those in spectra of radiocarbon production, aproxy for past solar activity. This suggests that there may be a solar control,perhaps through geomagnetic effects on atmospheric circulation. Multicentennialand multidecadal periodicities also occur in wavelet spectra of relativegray-scale density. However, gray-scale density does not appear to correlatewith any of the measured proxy variables, and at this point we do not know whatcontrolled gray scale. |
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| Keywords: | Cycles Elk Lake Gray-scale Minnesota Varves |
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