HR: 1340h
AN: PP13B-1283    [Abstracts]
TI: The Late Quaternary Oxygen Isotope Composition of Lake Michigan
AU: * Macdonald, R A
EM: rmacdo@uwo.ca
AF: The University of Western Ontario, Department of Earth Sciences, 1151 Richmond Street, B&GS Rm. 154, London, ON N6A 5B7, Canada
AU: Longstaffe, F J
EM: flongsta@uwo.ca
AF: The University of Western Ontario, Department of Earth Sciences, 1151 Richmond Street, B&GS Rm. 154, London, ON N6A 5B7, Canada
AU: Crowe, A S
EM: Allan.Crowe@ec.gc.ca
AF: National Water Research Institute, Environment Canada, 867 Lakeshore Road, P.O. Box 5050, Burlington, ON L7R 4A6, Canada
AB: We present stable isotope records for porewater (oxygen, hydrogen) and biogenic carbonates (oxygen, carbon; ostracode and clam shells) in sediment cores from the Chippewa, Milwaukee and South Chippewa Basins of Lake Michigan. The oxygen and hydrogen isotope compositions of porewater from the South Chippewa Basin core showed very little variation with depth. At the maximum depth of 16.6m, δ¹⁸O values were within 2‰ and δD values were within 12‰ of modern Lake Michigan water (average δ¹⁸O = -5.9‰; average δD = -45‰); original porewater compositions have not been preserved. The oxygen isotope results for the biogenic carbonates, by comparison, provide a record of the isotopic composition of Lake Michigan over the last ~11,000 years, including significant incursions of very low-¹⁸O water, as first reported by Colman et al. (1990) and Forester et al. (1994). The low-¹⁸O waters originated from the retreating Laurentide ice sheet and may have been routed through Lakes Agassiz and Superior and discharged as large volumes over very short intervals of time. Periods characterized by much higher oxygen isotope compositions likely record the isotopic composition of regional precipitation over the catchment area. In summary, the large variations in the oxygen isotope composition of early Lake Michigan water arose from regional climate change and changing water sources during the times of ice-sheet retreat.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1807 Climate impacts
DE: 4914 Continental climate records
DE: 4942 Limnology (0458, 1845, 4239)
DE: 4944 Micropaleontology (0459, 3030)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting