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TitleEarly Holocene paleoclimate and low water levels in the Laurentian Great Lakes, an opportunity to enhance knowledge of climate-lake level sensitivity
AuthorLewis, C F M; King, J W; Croley, T E, II; Anderson, T W; Blasco, S M; Brooks, G R; McCarthy, F M
SourceEos, Transactions of the American Geophysical Union vol. 90, no. 22, 2009, 1 pages
Alt SeriesEarth Sciences Sector, Contribution Series 20080745
MeetingAmerican Geophysical Union, Geological Association of Canada, Joint Assembly; Toronto; CA; May 25-29, 2009
Mediapaper; on-line; digital
AreaGreat Lakes
Subjectshydrogeology; environmental geology; paleoclimatology; paleoclimates; Holocene; climate effects; climatic fluctuations; climate; limnology; lake water depths; lake sediment thickness; lake water; Cenozoic; Quaternary
AbstractReview of radiocarbon-dated, upwarped shorelines led to an analytical description of glacial rebound throughout the Great Lakes basin, and the reconstruction and comparison of original elevations of former lakes and outlets through time. The comparison revealed that lake levels fell below basin outlets in the relatively dry, early Holocene climate, contrary to the assumption of previous syntheses that lakes were always overflowing water bodies. For example, water levels in the Huron basin declined into hydrologic closure (>20 m below the basin overflow outlet) between about 7900 and 7500 14C (?8770 and 8290 cal) years BP. This phase of closed lowstands has been validated by newly-acquired and re-interpreted older evidence of low water levels in sedimentary records. In the Huron and Georgian Bay basins these data, which also apply to the Michigan basin, include seismo- and litho-stratigraphic evidence of a widespread erosion surface attributed to wave erosion during a period of low lake level, microfossil indications of brackish conditions likely related to enhanced evaporation, and in situ tree stumps up to 43 m below present lake level. Seismostratigraphic evidence of mud-buried beaches implying former water levels 40 to 105 m below present in western Lake Superior has been reported. A submerged beach represents the early Holocene lowstand in the Erie basin, and new and published paleo-environmental findings show that shallow-water conditions occurred in Lake Ontario at the same time. Hydrologic closure occurred in the upper Great Lakes basins when the supply of glacial meltwater was diverted permanently from the basins after 8000 14C (8890 cal) BP. The closed lowstands occurred generally when lake water balances became negative as evaporative losses exceeded precipitation in the drier-than-present early Holocene climate. This unique hydrological event provides an opportunity to evaluate the sensitivity of the Great Lakes system under climatic conditions different than present, thereby increasing confidence in its value. The sensitivity is a key parameter for modeling and projecting future lake levels under global warming.