Abstract
Northern Midwest climate changes leading up to the Wisconsinan glacial maximum
Abstracts with programs - Geological Society of America, Vol.45(7), p.778
Geological Society of America, 2013 annual meeting & exposition
2013
Abstract
A speleothem from Spring Valley Caverns (SVC) in Fillmore County, MN gives a record of Northern Midwest climate changes during the late Pleistocene. The ages of growth phases were obtained using the U/Th disequilibrium method. Consistent growth is observed from 105-88 ka, followed by short periods (on the order of several decades to several centuries) of growth at 60 ka, 53 ka, 41.5 ka, 40 ka, and 29 ka. Fluorescent banding was identified in portions of the speleothem using a Nikon A1R MP multiphoton confocal microscope. Where banding is well-developed, band counts are consistent with U-series dates and are likely annual. Analyses of stable oxygen and carbon isotopes were obtained at 5 mm intervals along the main growth phase and at 1 mm intervals across the small growth phases. The total range of delta (super 18) O values is 5 ppm, with a general trend from depleted values to enriched values with time. The delta (super 18) O record is interpreted as a function of temperature-dependent fractionation during calcite precipitation and fraction of convective rainfall at the cave site. This interpretation suggests a change from warmer climate with significant convective rainfall to colder climate with less convective rainfall from 105 ka to 29 ka. The delta (super 13) C record is consistent with this general idea with a trend from enriched delta (super 13) C values, consistent with C4-type prairie grasses at 105 ka, to depleted delta (super 13) C values, consistent with a C3-type forest closer to glacial maximum. The trends in our delta (super 13) C values are similar to those from Crevice Cave, MO, suggesting some regional coherence in vegetation patterns. The smaller, more recent growth phases after 60 ka are likely linked to global events. The 60 ka growth phase correlates with the last centuries of Heinrich Stadial 6, immediately prior to Greenland Interstadial 17. The other short growth phases correlate with Greenland Interstadial Events.
Details
- Title: Subtitle
- Northern Midwest climate changes leading up to the Wisconsinan glacial maximum
- Creators
- Joel S MacKinney - Wheaton College, Department of Chemistry Wheaton, IL USA United StatesJulie B RetrumI. J OrlandSushmita DasguptaE. Calvin AlexanderJeffrey A DoraleR. Lawrence Edwards
- Resource Type
- Abstract
- Publication Details
- Abstracts with programs - Geological Society of America, Vol.45(7), p.778
- Conference
- Geological Society of America, 2013 annual meeting & exposition
- Publisher
- Geological Society of America (GSA)
- ISSN
- 0016-7592
- Alternative title
- Geological Society of America, 2013 annual meeting & exposition
- Language
- English
- Date published
- 2013
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984240791202771
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