Paleoclimatic implications of Late Holocene lake-level fluctuations in Lower Herring Lake, Michigan.

Paleolimnological techniques were used to reconstruct past lake-level fluctuations in the Lake Michigan basin. A sediment core (3.9 m) was obtained from Lower Herring Lake, a marginal lake once occupied by pre-Lake Michigan waters. Sediments were analyzed for biogenic silica, organic carbon and carbonate content, grain size, and microfossils. These analyses revealed signals of previous lake-level fluctuations in the Lake Michigan basin and provided an independent verification of changes proposed by Curt Larsen. Additionally, this investigation found evidence for short-term declines in lake level during the two most recent high-lake stands, and diatom microfossil data provided independent evidence for changing climatic conditions. Sediment and microfossil changes also recorded development of Lower Herring Lake from an embayment to an enclosed lake system, and the effect of human activities. Recent diatom microfossil data (since 1944) indicated a shift to assemblages with no previous analogue in the lake's history. Prior to lake isolation, sediments revealed evidence of two former low-lake stages (ca. 3900-3600 B.P. and 3200-2900 B.P.). Gradual isolation from the Lake Michigan basin lasted approximately 500 years, with final isolation occurring just prior to a low-lake period ca. 2000 B.P. Following isolation, two additional low-lake stages were identified (ca. 1530-1180 B.P. and 730-500 B.P.) and three high-lake stages (ca. 1800-1530 B.P., 1180-730 B.P., and 500-280 B.P.). Comparison with previous regional paleoclimatic and lake-level investigations indicates close correlations between lake-level and climate changes. A final signal of lower lake levels begins ca. 280 B.P. (ca. AD 1700) but is interrupted by deforestation of the basin ca. AD 1845. Signals of known lake-level changes (since recorded data, 1863) are present but weak as a result of the overpowering signal of anthropogenic effects in Lower Herring Lake, with low-lake levels of the 1930's most clearly identified. Results from Lower Herring Lake sediments indicate occurrence of lake-level fluctuations approximately every 250-300 years in the Lake Michigan basin, fluctuations that are primarily driven by climatic change. Evidence from Lower Herring Lake suggest a return to high-water levels, however, natural increases in lake level may be counteracted by the effects of anthropogenically induced global warming.PhDNatural ResourcesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/103158/1/9303839.pdfDescription of 9303839.pdf : Restricted to UM users only