No abstract

Geomorphology of a beach-ridge complex and adjacent lake basins along the northern shore of Lake Michigan records fluctuations in the level of Lake Michigan for the last 8000 to 10 000 14C yr B.R (radiocarbon years Before Present). A storm berm at 204.7-206 m (671.6-675.9 ft) exposed in a sandpit provides evidence of a pre-Chippewa Low lake level that is correlated with dropping water levels of Glacial Lake Algonquin (c. 10 300-10 100 14C yr B.R). Radiocarbon dates from organic material exposed in a river cutbank and basal sediments from Elbow Lake, Mackinac Co., Michigan, indicate a maximum age of a highstand of Lake Michigan at 6900 14C yr B.E, which reached as high as 196.7 m (645 ft), during the early-Nipissing transgression of Lake Michigan. Basal radiocarbon dates from beach swales and a second lake site (Beaverhouse Lake, Mackinac Co.) provide geomorphic evidence for a subsequent highstand which reached 192.6 m (632 ft) at 5390 4-70 14C yr B.R Basal radiocarbon dates from a transect of sediment cores, along with tree-ring data, and General Land Office Surveyor notes of a shipwreck, c. A.D. 1846, reveal a late-Holocene rate for isostatic rebound of 22.6 cm/100 radiocarbon years (0.74 ft/100 radiocarbon years) for the northern shore of Lake Michigan, relative to the Lake Michigan-Lake Huron outlet at Port Huron, Michigan. Changes in sediment stratigraphy, inter-ridge distance, and sediment accumulation rates document a mid-to late-Holocene retreat of the shoreline due to isostatic rebound. This regression sequence was punctuated by brief, periodic highstands, resulting in progressive development over the past 5400 14C yr of 75 pairs of dune ridges and swales each formed over an interval of approximately 72 years. Times of lake-level fluctuation were identified at 3900, 3200, and 1000 14C yr B.R based on changes in inter-ridge spacing, shifts in the course of Millecoquins River, and reorientation of beach-ridge lineation. Soil type, dune development, and selected pollen data provide supporting evidence for this chronology. Late-Holocene beach-ridge development and lake-level fluctuations are related to a retreat of the dominant Pacific airmass and the convergence of the Arctic and Tropical airmasses resulting in predominantly meridional rather than zonal air flow across the Great Lakes region.

No abstract

During July 1986, atmospheric concentrations and deposition rates of Pb, Cd, Zn, and Mn were measured at a spruce forest in the Great Smoky Mountains National Park, and meteorological data were recorded. Precipitation, cloud water impaction, and dry deposition were quantified. Average total fluxes of 12, 1.0, 53, and 40 tsg m -2 d -l for Pb, Cd, Zn, and Mn, respectively, were measured; dry deposition constituted 46, 32, 62 and 66% of each of the totals. Cloud impaction (unusually low for this particular month) was measurable but not quantitatively important. Dry deposited Pb and Zn were washed from the canopy by subsequent rainfall -revealing greater throughfall fluxes associated with increasing antecedent dry period durations. Cadmium and Mn did not, however, show this relationship. Measurements revealed little interaction of Cd with the forest canopy, while considerable net leaching of Mn was evident (as had been expected). The canopy behaviors of both Pb (i.e., leaching) and Zn (i.e., uptake) were contrary to expectations.

A radiocarbon-dated series of 75 beach ridges, formed at regular intervals averaging 72 yr over the past 5400 yr, provides further support for the existence of a 70-yr oscillation in Northern Hemisphere climate, postulated recently from instrument data representing less than two cycles of this climate oscillation. Results from this study lend support to the interpretation that internal variations in the ocean–atmosphere system are an important factor in climate fluctuations on a decadal–centennial time scale. A temperature oscillation with a period of about 70 yr has been a previously unrecognized but fundamental part of the global climate system since at least the middle Holocene.