The magnetic deposition record in some Scandinavian peat profiles

• Main Author: Jones, M. D. H.
• Published: University of Liverpool 1986
• Subjects: 538.7; Magnetic mineral persistence
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377116

This study uses a range of magnetic parameters, eg. Susceptibility (X), Saturation Isothermal Remanence (SIRM), Anhysteretic Remanence (ARM), interparametric ratios (ARM/X, SIRM/X, SIRM/ARM) and coercivity of remanence data (IRM-n/SIRM, (BO)CR), coupled with various dating methods (eg. moss increment counting and radiometric dating) to estimate the magnetic deposition onto some Scandinavian peat bogs. The sites available included 4 from southern Finland, 5 from northern Finland, 2 from northern Norway and 1 from southern Denmark. In addition to the magnetic techniques, a range of chemical determinations (iron, copper, zinc, lead, nickel and, where available, manganese) have been made, or are utilised, for all the peat cores. The reproducibility of the primary magnetic deposition record at Kaurastensuo, southern Finland has been examined. The rise in magnetic particulate concentrations, termed the magnetic 'take-off', was consistently dated to about 1931 for 7 of the 8 cores used, regardless of hummock-hollow micro topography. The persistence of magnetic minerals over timescales of 101-103 years has been examined by means of long core profiles from 4 southern Finnish bogs. The mineral magnetic and heavy metal profiles (iron, copper, zinc, lead and nickel) were in reasonable accord with the development of the individual bogs above different mineral soils. The development of peat profiles is dated from between 8000-9000 years BP using 14C dates spanning both the ombrotrophic and minerotrophic phases. The availability of moss increment counts for the northern Scandinavian sites and 210Pb determinations for Draved Moss, southern Denmark and Mo-I-Rana, northern Norway, has allowed estimates of variation in the magnetic deposition to be made. The northern Scandinavian sites all show increasing deposition from 1900, although maximum surface deposition varies from site to site, between 1.24-22.6 10-6Am2yr-1. The magnetic deposition at Draved Moss was estimated to be 21.6 10-6Am2yr-1 at a subsurface maximum dated to between 1967-1978. The increase in lead deposition at Draved Moss is in reasonable agreement with that of published lead deposition profiles from the same site, using earlier attempts at 210Pb determinations. At Mo-I-Rana, northern Norway the maximum magnetic deposition value is estimated to be 8.65 10-6Am'yr-1 for the surface slice, spanning the last 21 years. Any spatial variation in deposition within the Scandinavian sites appears to be partly masked by site-specific features, for example the close proximity of industrial sources at 2 of the Finnish sites and the iron and steel works at Mo-I-Rana. Magnetic deposition at the latter site is in good agreement with the history of iron and steel production within the region since the turn of the century.