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SERIAL STUDY OF LAKE MICHIGAN SEDIMENTS BY 57Fe MÖSSBAUER SPECTROSCOPY
G. Perlow, W. Potzel, D. Edgington
To cite this version:
G. Perlow, W. Potzel, D. Edgington. SERIAL STUDY OF LAKE MICHIGAN SEDIMENTS BY 57Fe MÖSSBAUER SPECTROSCOPY. Journal de Physique Colloques, 1974, 35 (C6), pp.C6-547-C6-548.
�10.1051/jphyscol:19746116�. �jpa-00215728�
JOURNAL DE PHYSIQUE Colloque C6, suppliment au no 12, Tome 35, Dicembre 1974, page C6-547
SERIAL STUDY OF LAKE MICHIGAN SEDIMENTS BY 7Fe MOSSBAUER SPECTROSCOPY
(*)G. J. PERLOW, W. POTZEL (**) and D. EDGINGTON Argonne National Laboratory, Argonne, Illinois 60439, USA
Rhum6. - Nous avons Btudik par spectroscopie Mossbauer le fer contenu dans des sections horizontales d'une carotte extraite des sediments du lac Michigan. Une composante due B des oxydes ferriques antiferromagnetiques diminue rapidement avec la profondeur, ce que l'on attribue A la pollution atmosphkrique des aciBries situkes au sud du lac.
Abstract. - Mossbauer effect studies have been made of the 57Fe content of serial sections taken from a core of State Michigan bottom sediments. A component attributable to antiferromagnetic ferrioxides shows a rapid decrease with depth and is considered to a result of air pollution from the steel mills at the southern shores of the lake.
We have examined the dependence with depth of the spectra of iron compounds in a sediment core from the southern end of Lake Michigan. The sample was taken in 1972 in a region of high sedimentation 19 km northwest of Benton Harbor (400 17' N ; 860 38' W) at which point the lake has a depth of 64 m. The pro- perties of the sediment in this area are well characte- rized. The mean sedimentation rate as determined by 'lOPb dating [I] is about 0.17 cm/year, below the first few cm. The core was sectioned on shipboard in 1 cm intervals down to 6 cm, and thereafter in 2 cm intervals to 12 cm. An adjacent core furnished samples to 24 cm ( w 140 years). The fractions were air-dried, ground to a powder, and absorbers prepared containing 59 mg/cm2 of sediment dispersed in a iucite disk.
The source was 57Co in Cu. Runs were made at temperatures of 296 K, 77 K and 4.2 K, and the data were fitted for the purpose of this study with a sum of two quadrupole-split spectra and one magnetic spectrum.
Figure 1 is a composite of spectra at three depths, with samples from the sections 0-1 cm, 6-8 cm and 10-12 cm respectively. The temperature was 77 K.
Three major components are readily identified. There
(*) Work performed under the auspices of the U. S. Atomic
Energy Commission.
(**) Permanent address : Physik-Department E 15, Tech- nische Universitat Miinchen, D-8046 Garching bei Miinchen, Germany.
is first a magnetic spectrum (M 3) whose hyperfine field is typically about 525 kOe, and hence attributable to high spin Fe3'. The line widths indicate an admix- ture of compounds. They are presumably ferric oxides variously hydrated and by no means simply charac- terizable. A second major component of all of the spectra is a prominent incompletely resolved dou- blet (P 3), essentially unshifted with respect to the Cu source, hence consisting mainly of paramagnetic Fe3
'.
Some small fraction of P 3 could be superparamagne- tic M 3. The third component is the higher energy member of a typical Fez+ doublet (P 2), whose other member is concealed, along with the two inner lines of the magnetic spectrum, within the central structure.
The intensities of the three components can be obtained with some assurance, as the resolved part of the spec- trum furnishes adequate information. Other details are not of immediate interest.
The behavior with increasing depth is striking and is seen in figure 2. The intensities of the M 3 and P 3 components display a similar initial rise. The para- magnetic ferrous (P 2) is nearly constant but rises slightly with increasing depth. Below 4 cm, the beha- vior of the three species is remarkably divergent.
M 3 drops exponentially, decreasing at the rate of a factor of two in 3 cm (18 years). Below 11 cm (about the year 1915) the intensity levels off down to the deepest sample taken (about 1840). The variation of P 2 and P 3 is consistent with measurements by
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19746116
C6-548 G. P. PERLOW, W. POTZEL AND D. EDGINGTON
l ~ l ' l m ~ l ~ ' ~ s \ YEAR (opprox.)
evidence for a prominent M 3 component in the
FIG. 1. - Mossbauer spectra at three depths below the water-
sediment interface. Canadian and English lake studies, it is somewhat more probable that we are observing the effect of
1972 1955 1935 1915 1895 1875 1855
I I I I I I
-
ur 0.1 -\ -
E
E - a TOTAL Fe -
air from the extensive steel mill complex Coey [2] for an English oligotropic lake. The ratio along the southern shores of Lake Michigan, and that P 2/P 3 shows a steady increase with depth, and the growth of the industry is displayed historically reflects increasing reducing conditions in the deeper in the sediment.
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W I-
Z 0.01
References
6n\,
(M3+P3+P2)- -
Z0/0< -
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~ :
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o p3 -
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I I I I t I I l t l l
[I] ROBBINS, J. A. and EDGINGTON, D. N., Geochim. Cosmochim.
Acta (in press).
[2] COEY, J. M. D., Geochim. Cosmochim. Acta (in press).
[3] COEY, J. M. D., SCHINDLER, D . W. and WEBER, F., Can. J.
Earth Sci. (in press).
0 4 8 12 16 20
DEPTH ( c m )
FIG. 2. -Depth dependence of the intensities of magnetic Fe3+, (M 3) ; paramagnetic Fe3+, (P3) ; and paramagnetic
Fez+ (P 2).
sections. M 3, however, is substantially absent from Coey's spectra and also from the spectrum of surface sediments in various Canadian lakes [3].
The total iron (M 3
+
P 2+
P 3) displays the maximum near 4 cm and a drop by a factor of two thereafter. A similar shape has been obtained by chemical analysis [l]. It is mainly M 3 that is respon- sible for the decrease. If therefore the decrease in M 3 is attributed to selective diagenesis, not applicable-12 -8 -4 0 4 8 12 to P 3, the transformation must be chiefly into soluble
VELOCITY ( m m / s ) iron. This is possible. However, because there is no
