Journal of Nuclear and Radiochemical Sciences, Vol. 10, No.1, pp. 13-17, 200957

Fe Mössbauer Study of Specific Iron Species in the Antarctic Ocean Sediments
Katsumi Shozugawa,*,a Akihito Kuno,a Hideki Miura,b and Motoyuki MatsuoaaGraduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902,
Japanb
Research Organization of Information and Systems, National Institute of Polar Research, Geosciences Group,
Geology and Geomorphology, 1-9-10, Kaga, Itabashi-ku, Tokyo 173-8515, Japan†
Received: October 29, 2008; In Final Form: April 17, 2009
To elucidate the environment of sedimentation in the Scotia and Ross Seas in the Antarctic Ocean during theperiod from upper Pleistocene to the present, sediments from the seas were investigated by 57Fe Mössbauer spectroscopy, instrumental neutron activation analysis, and X-ray absorption near-edge structure. In Mössbauer spectraof Scotia Sea sediment, a specific doublet peak (isomer shifts of 0.57–0.59 mm s-1, quadrupole splitting of 1.70–
1.83 mm s-1) was observed, suggesting the generation of primary glauconite by detailed speciation. In contrast,
sediment cores from the Ross Sea and another sea area around Antarctica had no specific peak in Mössbauer
spectra. Concentrations of iron and other elements in both sediments hardly fluctuated, that is, sedimentation
matter in the Scotia Sea sediments containing iron species was not affected by the origin of specific iron species
but by factors such as early-stage diagenesis.

1. Introduction

2. Experimental

Sea sediments can be probed as records of the environmentof sedimentation. Much attention has been given to clarifying
the environment of sedimentation from an elemental
composition point of view. Valuable infor mation for
paleoceanography has been obtained by several projects suchas the Deep Sea Drilling Project and Ocean Drilling Program.1
In general, the rate of sedimentation in the sea is lower thanrates in rivers or estuaries,2 except when there is a large scalevariation such as massive climate change or an eruption of anundersea volcano in the sea area. 3 There is less pelagic
sediment deposition from terrigenous materials in the deep sea
than on the coast. Therefore, the long term variation in theenvironment of the sea can be determined with the analysis of
sediment cores of short length.
Sea sediments comprise many kinds of heavy metals.
Almost all iron supplied to the sea is included in the terrigenous
fracture. These materials are carried and finally accumulate in
the sea sequentially from the area along the shore throughcarriers such as the atmosphere and rivers. Since iron is an
essential element for many sea organisms, which take in ironfrom seawater, organic matter as product of the food chain
accumulate in the sediments.
In this paper, we focus on the chemical states of iron in
Antarctic sediments. From the analysis of 57 Fe Mössbauer
spectra, ferrous and ferric iron can be represented by silicate
and clay minerals respectively. Uptake of iron from seawaterby phytoplankton mainly causes a redox reaction in the cycleof photosynthesis and respiration. Consequently, the differencein chemical states such as ligand and valence states depends on
the origin of the iron. In addition, chemical states of heavy
metals such as iron and manganese in the sediments change
upon reduction by organic matter. It is important to trace theprocesses of these reactions in discussing the environments of
sediments.

In this study, Antarctic Ocean sediments not subjected toanthropogenic influences were used. The cores for analysis
were collected by JOGMEC (Japan Oil, Gas and Metals
National Corporation) in the Ross and Scotia Seas from 1996
to 1997. Figure 1 shows the sampling sites of GC1806 andGC1603. The collection site GC1806 was at 60°11'08"S and
55°30'27"W in the Scotia Sea, off Elephant Island. The depth
was 3,531 m, the core length was 474 cm and a gravity-corer
was used for sampling. The GC1806 core had a lithographic
boundary line at 203 cm. The upper part of the core (0–203cm) was siliceous silty clay, presenting dark greenish gray fromdark greenish yellow. The lower part of the core (203–474 cm)
was silt presenting gray from dark greenish gray. Sediment
samples were stored at 4 °C immediately after collection, cut
every 2.7 cm, and kept in N2 to prevent oxidization with air.

*Corresponding author. E-mail: cshozu@mail.ecc.u-tokyo.ac.jp
Fax: +81-3-5454-6998†P resent add ress: 10 -3 Midor i-cho, Tach i kawa-sh i, Tok yo
190-8518, Japan.

Figure 1. Sampling sites of GC1806 (60°11'08"S, 55°30'27"W, water
depth 3531 m, core length 474 cm) and GC1603 (67°49'17"S,
178°17'00"E, water depth 3326 m, core length 430 cm).

© 2009 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 05/27/2009

14

Thereby samples were not altered until measurements of thechemical states were taken. For GC1806 and GC1603 cores,
Beta Analytic Inc. analyzed radiocarbon dating of thesedimentation. A half-life of 14 C of 5,568 years was applied
and the isotopic separation was determined. According to thedating, the sediment age of the surface of the GC1806 core wasestimated to be 5,000 y B.P. (Before Present) and the bottom
was 32,000 y B.P. Sedimentation depth was transformed into
sedimentation age using above values.
T he G C1603 core was collected at 67°49'17"S a nd
178°17'00"E in the north Ross Sea for reference. GC1603 wassilty clay and calcareous sandy silt presenting yellowish brown
throughout the core. The sedimentation age of GC1603 wasmuch older than that of GC1806, being 800 ky B.P. at the bottom.
57
Fe Mössbauer spectroscopy and X-ray absorption nearedge structure (XANES) analysis were applied for the speciation of iron in the sediments. Instrumental neutron activation
analysis (INAA) was applied for elemental determination. In
the 57 Fe Mössbauer measurement, 300–500 mg of sediment
was mounted in a sample holder (16 mm in diameter, 1 mm
thick) and packed in an oxygen-impenetrable plastic bag with
N2 . Samples were kept in wetness. The Mössbauer spectra
were measured with an Austin Science S-600 Mössbauer spectrometer using a γ-ray source of 1.11 GBq 57Co/Rh at room
temperature (r.t., ~293 K) and liquid nitrogen temperature (77K). Isomer shifts (IS) were expressed with respect to the centroid of the spectrum of metallic Fe foil, and the Mössbauer
spectra were fitted by a least-squares method with restrictionsof intensity and half width (HW) of peaks. All doublet peaks
were treated as symmetric.
The conditions of INAA for iron determination were as follows. 50 mg quantities of dried (105 °C, 2 hours) sediments

5000

10000
Sedimentation age / y BP

ShozugawaJ. Nucl. Radiochem. Sci., Vol. 10, No. 1, 2009

15000

20000

25000

30000
1.0 1.5 2.0 2.5 3.0 5.0 5.5 6.0 6.5 7.0 10 12 14 16 18 20
Fe / %Al / %

Si / %

were packed in double polyethylene film bags. Samples were
irradiated with neutrons in the T-pipe, JRR-4 at Japan Atomic
Energy Agency, Tokai, Ibaraki, Japan. Irradiation time was 5
minutes, and after 2 weeks cooling, γ-rays of 1099 keV were
measured for 14,400 seconds.
XANES was measured using a synchrotron radiation ring at
the BL-9A and 12C facilities of the Photon Factory, KEK.4 A
Si (111) double-crystal monochromator was used. Each sample
was cut to be 1 cm (ca. 150 mg), immediately sealed withprolene film, and kept at 4 °C until measurement. Being kept
in a N2 atmosphere also prevented oxidization with air. XANES
in iron K-edge spectra was measured in fluorescence modeusing a Lytle-type detector at r.t. under atmospheric pressure.
Reference materials were used as follows: hematite (α-Fe2O3),
magnetite (Fe3O4), pyrite (FeS2), and goethite (α-FeOOH).
3. Results and Discussion
3.1. Concentration. In the measurement of INAA, certified
reference materials, JLk-1 (Lake Sediment, Geological Surveyof Japan, Advanced Industrial Science and Technology) andN I E S No. 2 ( Pond Se d i ment , Nat iona l I nst it ut e forEnvironmental Studies), were irradiated and analyzed for theconfirmation of accuracy. Concentrations obtained for the elements were in good agreement with the certified values.5,6Concentrations of major elements in GC1806 are shown in
Figure 2. The iron distribution showed no significant variation(ca. 1.8 %) from 28,000 y B.P. to 5,000 y B.P. within the relative concentration errors. In the case of sea sediments, it wasquite common for the concentration of iron in the sediments tobe approximately constant.7 Furthermore, changes in the concentrations of major elements were not significant throughout
the core of GC1806, suggesting the sources of sediments did
not change during sedimentation. The source of the supply ofiron to sediments was believed to be mainly terrigenous materials, because the sampling location is adjacent to the Antarctic
Peninsula.
3.2. Chemical states of iron. A Mössbauer spectrum ofGC1806 sediment with a 5,000 y B.P. sedimentation age at 77K
is shown in Figure 3. Three doublet peaks were observed, anda sextet was not detected in the spectra. Among three species,
a doublet peak with small quadrupole splitting (QS) was foundto be Fe3+ from clay minerals, and a doublet peak with large
QS was found to be Fe2+ from silicate minerals, empirically.8
The third doublet was very specific, and the particular value of
QS (1.7–1.8 mm s-1) prevented the determination of the minerals. We have measured many 57Fe Mössbauer spectra for river
sediments,8 lake sediments,9,10 and tideland sediments.11 Basedon the current experience, the specific doublet was attributed toFe3+, considering the value of IS.

5000

Sedimentation age / y BP

10000

15000

20000

25000

30000
1.0

2.0

3.0

Mg / %

4.0 0.2 0.3 0.4 0.5 0.6 2.0 2.5 3.0 3.5 4.0
Ti / %Na / %

Figure 2. Concentrations of Fe (○), Al (●), Si (▲), Mg (◊), Ti (■) andNa (□) in GC1806.

Figure 3. Mössbauer spectrum of GC1806 with 5000 y B.P. at 77K.
Parameters of specific Fe3+ are IS of 0.55±0.01 and QS of 1.79±0.02
mm s-1.

57

Fe Mössbauer Study of Specific Iron Species in the Antarctic Ocean

Mössbauer parameters of GC1806 samples from each sedimentation age are shown in Table 1. Three doublet peaks
including a specific doublet peak in the spectra were observed.

J. Nucl. Radiochem. Sci., Vol. 10, No. 1, 200915

It is noticeable that the relative area of the specific doublet
tended to decrease as sedimentation age increased from 5,500
y B.P. to 11,800 y B.P. This means iron species in sediment

TABLE 1: Mössbauer parameters at 77K of GC1806 for different sedimentation ages
Depth (cm)Conventional sedimentation age(y B.P.)

Species

Relative area (%) IS (mm s-1) QS (mm s-1) HW (mm s-1)

<2

5,000

Fe2+ silicate

55.6(4)1.26(0)2.89(0)0.37(0)3+34.7(4)0.43(1)0.69(1)0.67(3)

3+

Fe p. glauconite

9.7(3)

0.55(1)1.79(2)0.43(4)Fe2+ silicate

59.5(4)1.26(0)2.89(0)0.37(0)Fe clay20.7(4)0.43(1)0.69(1)0.67(3)Fe3+ p. glauconite

19.9(3)0.55(1)1.79(2)0.43(4)Fe2+ silicate

52.0(4)1.27(0)2.89(0)0.36(1)

Fe clay30.5(4)0.43(1)0.69(1)0.68(3)Fe3+ p. glauconite

Fe clay

4.1

5,500

3+

8.2

5,800

3+

16.4

28.7

6,400

7,600

17.5(3)0.56(1)1.83(2)0.38(4)2+

53.4(3)

1.24(0)2.81(0)0.34(0)3+

Fe clay36.8(3)0.41(1)0.51(1)0.69(2)

Fe3+ p. glauconite

9.8(2)

0.55(1)1.78(2)0.29(4)

Fe silicate

57.9(4)1.24(0)2.82(0)0.35(0)Fe3+ clay

Fe silicate

2+34.5(4)0.40(1)0.65(2)0.69(3)3+

7.7(3)

0.57(1)1.74(3)0.38(5)2+

Fe silicate

58.2(4)1.26(0)2.89(0)0.36(0)Fe3+ clay

34.2(4)0.40(1)0.66(2)0.72(4)

Fe p. glauconite

7.6(3)

0.56(1)1.79(3)0.42(6)

Fe2+ silicate

Fe p. glauconite
41.1

8,700

3+

65.7

11,00054.2(3)

1.24(0)2.82(0)0.35(0)3+40.5(4)0.40(1)0.57(1)0.70(3)

3+

Fe p. glauconite

5.4(3)

0.57(1)1.68(3)0.36(6)

Fe2+ silicate

51.3(5)

1.26(0)2.90(0)0.36(0)Fe clay37.8(5)0.39(1)0.54(1)0.70(4)

Fe3+ p. glauconite

Fe clay

69.8

11,400

3+

73.9

102

11,80014,00010.9(5)0.56(3)

1.49(6)0.61(7)2+

57.0(5)

1.24(0)2.82(1)0.35(1)

3+

Fe clay35.1(5)0.40(1)0.63(2)0.66(4)

Fe3+ p. glauconite

8.0(4)

0.64(4)

1.52(7)0.45(8)Fe silicate

54.7(3)

1.24(0)2.82(0)0.33(0)Fe3+ clay

Fe silicate

2+45.3(3)0.37(1)0.64(1)0.74(2)

3+

-

-

-

-

2+

Fe silicate

58.8(6)

1.26(0)2.90(1)0.36(1)

Fe3+ clay

41.2(7)0.43(1)0.45(2)0.58(4)

Fe p. glauconite

-

-

-

-

Fe2+ silicate

54.6(5)

1.26(0)2.89(1)0.37(1)

Fe3+ clay

42.2(6)0.43(0)0.47(2)0.58(3)3.2(6)

0.49(2)

1.21(3)0.44(6)

Fe p. glauconite
184

21,6003+

201

22,8003+

Fe p. glauconite
The errors in the least significant figure are given in parentheses.

16

ShozugawaJ. Nucl. Radiochem. Sci., Vol. 10, No. 1, 2009change with sedimentation age in spite of the constant ironcontents.
A comparison of the XANES spectra for reference materials
and sediment samples showed that all sediment spectra passed
the center of the spectra of both hematite (Fe3+) and olivine(Fe2+) in XANES regions, and hardly varied with sedimentation age. These trends supported the results of Mössbauer
measurements, and suggested the averaged valence of iron in
the GC1806 sediment did not change through the core.
3.3. Verification of specific peak.
Temperature dependency. Mössbauer spectra were measured both at 77 K and r.t. to certify the specific peak is not aghost peak. The possibility of a ghost peak is attributed to thesuperparamagnetic effect. No significant difference between
r.t. and 77 K was observed for all peaks of all sedimentation
ages. Table 2 indicates parameters of surface sediment (5,000
y B.P.) at both 77K and r.t. as an example.
Alteration by oxidation. All samples were packed in oxygen-impenetrable plastic bags with N2 ; however, samples may
have been oxidized by air during a prolonged preservation
time. To check alteration by oxidation, Mössbauer spectra ofsediments were measured again, one year after the first measurements, and the same parameters were obtained for sediment which had 5,000 y B.P. sedimentation age. This suggeststhat one year is too short a period for reactions in sediments,
such as early-diagenesis, and the specific doublet is not attributable to oxidization with air. From the above discussion, it isevident there were iron species that had specific parameters inMössbauer spectra of upper GC1806 sediments.
3.4. Identification of the specific peak. From the 57 Fe
Mössbauer data index,12 a specific peak can correspond to several minerals. Of those minerals, it is reasonable that the specific peak corresponded to glauconite[(K, Na, Ca)(Fe3+, Al,
Mg, Fe) 2 (Si, Al) 4O10 (OH) 2]. The peak has large IS as do clay
minerals; however, its characteristic QS identified the peak as
belonging to glauconite.13
Glauconite generates only at the seabed, and distributes
mainly north and south of 40 degrees latitude. The generationof glauconite is not particularly clear. We tried mineral identification by X-ray diffraction; however, the low concentration
does not allow the confirmation of character peaks of glauconite. Furthermore, a specific doublet peak of glauconite was
not observed in GC1603, which has a different sedimentation
age from GC1806 throughout the core. In addition, a specificdoublet peak in Mössbauer spectra was not found in lake sediments on the Antarctic Continent.14
By contrast, although the sedimentation age was different
from that of GC1806, similar chemical species were slightly
detected in sediments collected from 15 locations in the Gulfof Admiralty at King George Island off the Antarctic
Peninsula.15 The chemical species were also detected in sedimentary rocks from the same location.16
For glauconite in GC1806, local diagenesis was expected in
sediments off the Antarctic Peninsula. Crystalline glauconite
hardly generate, taking the sedimentation age of GC1806 into
consideration. Glauconite is a group of phyllosilicates, forwhich the generation time scale is generally of the Ma order.17,18
Because there are differences in the quantity of glauconite generation with sedimentation depth or age, generation might bedue to local sedimentation environments, such as those withoxidation-reduction potential.19 In the case of clay rich sediment such as GC1806, glauconite was rare (< 1%) in the sediments.20 The conditions for glauconite generation in the sea
sediment were low sedimentation rate, low terrigenous material
supply, low temperature, slightly reducing condition, and suitable substrates.21,22 In spite of a short generation age, the conditions in GC1806 are in good agreement with the above
conditions for glauconite generation. Therefore it is consideredthat mature glauconite did not generate but primary glauconite

TABLE 2: Mössbauer parameters of surface GC1806(5,000 y B.P.) at 77K and r.t.

IS / mm s-1

Species

77K

r.t.

2+

Fe silicate
Fe3+ clay

1.26
0.43

1.12
0.32

Fe3+ p. glauconite

0.55

0.36

Fe silicate
Fe3+ clay

2.89
0.69

2.64
0.84

Fe3+ p. glauconite

1.79

2.07

2+

QS / mm s-1

did in GC1806 sediment.
As a consequence, it is evident that Fe3+ with large QS in the
Mössbauer spectra we obtained can be attributed to primaryglauconite.
4. Conclusion
57
Fe Mössbauer measurements for Antarctic Ocean sediments and a detailed discussion of the spectra showed primaryglauconite in sediments of the surface. Primary glauconite
existed at the sediment generated 5,000 – 18,000 y B.P., andtended to decrease as sedimentation age increased. A timescale of the 10 6 year order is necessary for the generation ofglauconite, however, primary glauconite generated even for asedimentation age of 5,000 y B.P. We were not able to detect
the specific doublet peak corresponding to glauconite in
Mössbauer spectra for the core of Ross Sea sediments. Taking
into account the conditions of glauconite generation, it isbelieved the generation of primary glauconite in GC1806 wasdependent on the specific environment of sedimentation.

Acknowledgements. We wish to thank Dr. Yoshihiro Tsuji(JOGMEC) and Dr. Akira Nishimura (Advanced Industrial
Science and Technology) for helping us to use samples. The
neutron activation analysis has been carried out at the InterUniversity Laboratory for the Joint Use of JAEA Facilities.This
work has been performed with a proposal of the Photon
Factory, KEK, Japan (Proposal No. 2006G106). Drilling surveys were sponsored by the Ministry of International Trade andIndustry (Ministry of Economy, Trade and Industry) and carried out by JOGMEC.
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