Mathematics – Logic
Scientific paper
May 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990gecoa..54.1443h&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 54, Issue 5, pp.1443-1451
Mathematics
Logic
4
Scientific paper
Arctic environmental conditions present special difficulties with the use of nuclides 210 Pb and 137 Cs for measuring lake sediment chronology. Fluxes of these nuclides are lower in the Arctic than in mid-latitudes, shortening the history that can be resolved. Ice prevents atmospheric input of nuclides to sediment during much of the year and can cause redistribution of sediment in shallow lakes. Results from analyses of seven sediment cores from two lakes on the Belcher Islands in southeastern Hudson Bay show that sediment redistribution by ice is a major process in one of the lakes. In order to measure an undisturbed sedimentation rate, it is necessary that a total input or flux of 137 Cs and 210 Pb be measured or estimated. Total unsupported 210 Pb in the area, 14.8 dpm/cm 2 , is the average of measurements in three cores from two lakes that have consistent total 137 Cs inventories closest to the estimated 137 Cs flux. Cores from undisturbed sites have slower sedimentation rates, and 137 Cs appears in layers dated before the early 1950s when it would have first appeared in sediment. 137 Cs cannot be used for chronological evaluation of these cores. Mixing of surface sediment layers and lower dating resolution than in other cores are responsible for the apparent downward movement of this nuclide. 210 Pb measurements of undisturbed sedimentation rates in the lakes range from 0.0044 to 0.0180 g/cm 2 /a. The sedimentation rate in a lake used for raw sewage oxidation doubled after the beginning of sewage input. Rates at sites where sediment is redistributed range from 0.0259 to 0.0309 g/cm 2 /a with similarly higher total 137 Cs and unsupported 210 Pb values. Dates of sediment layers measured using the constant rate of supply model are verified by 210 Pb profile discontinuities corresponding to major storms in 1958 and in 1940.
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