The magnetic deposition record in some Scandinavian peat profiles
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.