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ACCUMULATION OF MANGANESE AND LEAD-210 IN DATED SEDIMENTS OF EASTERN LAKE ERIE: INFLUENCE OF RECURRENT EPISODES OF OXYGEN DEPLETION ABOVE THE CENTRAL DEPOSITIONAL BASIN
Citation:
Robbins, J. A., R. W. Rood, N. R. Moorhead, R. Rossmann, AND D. N. Edgington. ACCUMULATION OF MANGANESE AND LEAD-210 IN DATED SEDIMENTS OF EASTERN LAKE ERIE: INFLUENCE OF RECURRENT EPISODES OF OXYGEN DEPLETION ABOVE THE CENTRAL DEPOSITIONAL BASIN. Presented at 43rd Conference on Great Lakes Research, International Association for Great Lakes Research, Cornwall, Ontario, Canada, May 23-26, 2000.
Description:
Burns and Nriagu (1976) showed that, during episodes of oxygen depletion (<50%), waters above the central depositional basin of Lake Erie can become enriched with manganese extracted from near-surface sediments. The authors conjectured that regenerated Mn might precipitate during fall overturn and be transported preferentially by prevailing currents to the eastern basin where it would finally settle. This study confirms their conjecture and suggests that sediment Mn records reflect the historical extent and duration of recurrent episodes near-bottom hypoxia. In lead-210 dated cores collected between 1978 and 1991 in rapidly accumulating sediments from the eastern basin, concentrations of manganese rose exponentially above a 900 ppm baseline from about 1,840 to about 1,100 ppm in the mid-1950s. Between 1955 and about 1975, during the period of intense P-driven hypoxic episodes, sedimentary Mn fluctuated markedly, between 1,100 and 1,800 ppm, in concert with reported variations in extent of oxygen depletion. Between the mid-1970s and 1991 Mn concentrations declined with little variability to about 1,000 ppm. The rate of delivery of excess lead-210 is also correlated with such variations in Mn fluxes to sediments. As a result a quantitative model, that couples Mn and lead-210 delivery rates, improves the accuracy of sediment chronologies.