Geochemistry and extractable Fe and Al in cold-temperature soils of northwestern Siberia
Post on 15-Jun-2016
ctf northwestern SiberiaNCO
elemenwestern Siberia were analysed to determine profiles of geochemical uniformity, element mobility andthe release and build-up of extractable Fe and Al. The scope of this study involves weathering processes
ents that yield importantinformation on profile chemical uniformity and the movement
The field area is drained by the Ob Estuary and borders the KaraSea along the Siberian Arctic coast (Fig. 1) (Mahaney et al.,1995). The flat to gently undulating land surface has a
JOURNAL OF QUATERNARY SCIENCE (2010) 25(2) 178189Copyright 2009 John Wiley & Sons, Ltd.Published online 21 July 2009 in Wiley InterScience(www.interscience.wiley.com) DOI: 10.1002/jqs.1290* Correspondence to: W. C. Mahaney, Quaternary Surveys, 26 Thornhill Ave.,Thornhill, Ontario, Canada, L4J 1J4.Low-temperature soils and palaeosols (Cryosols) are subject tocryoturbation (Fedorova and Yarilova, 1972; Ellis, 1980;Mahaney and Fahey, 1988; Mahaney et al., 1995; Jakobsenet al., 1996; Earl-Goulet et al., 1998), and to accumulations ofextractable Fe and Al linked to present and past soil-formingenvironments (Mahaney and Fahey, 1988; Mahaney, 1990;Mahaney and Hancock, 1996; Earl-Goulet et al., 1998;Mahaney et al., 1999). They are among the least understoodsoils in terms of the degree to which palaeoclimate affectedchemical weathering processes. Extractable Fe and Al havebeen used to classify soils (Blume and Schwertmann, 1969;Lutwick and Dormaar, 1983; Mahaney and Fahey, 1988); todate deposits (Mahaney and Sanmugadas, 1985; Birkelandet al., 1989; Mahaney, 1990; Mahaney et al., 1991, 1999); toanalyse pedogenesis in tundra podzols (Pereverzev, 2007); andto determine perched water tables (Mahaney and Fahey, 1988).The neutron activation analysis of soils not only provides totalconcentrations of Fe and Al, but also the concentrations of other
of soluble chemical elements. Only rarely have low-temperaturesoils been analysed for geochemical trends using instrumentalneutron activation analysis (INAA) (Earl-Goulet et al., 1997).
This study expands on previous stratigraphic and pedologicalresearch of Mahaney et al. (1995) in the YamalGydan area,and seeks to analyse distributions of total elements andextractable Fe and Al, to determine parent material uniformity,as well as leaching and weathering histories. In particular, thisinvolves the interpretation of oxihydrite levels, and behaviourof Fe and Al. As the distribution and concentration of rare earthelements (REEs) in Arctic soils are in general poorly understood(McLennan, 1989), the geochemical profiles of light and heavyREEs are used to assess parent material uniformity.
Field areathe age of a profile by its physical characteristics. However, it appears possible to determine broad ageranges from the isotopic composition of water in soils. Copyright # 2009 John Wiley & Sons, Ltd.
KEYWORDS: Arctic climatic optimum (Hypsithermal) palaeosol; FeAl extractions; chemical/geochemical indices of Cryosol pedogenesis.relative to total Fe increases in the AhBw horizons compared with the lower horizons, whereoxidation is weaker. Low total Fe reflects reworked felsic deltaic and shallow marine deposits fromthe Permian to the early Tertiary, thereafter emplaced by episodic flooding of glacial meltwater fromthe Arctic Urals and/or the Kara Sea Ice Sheet. Organically complexed Al (Alp), uniformly low in allsoils, nevertheless shows trends indicating some downward movement, a rather unique occurrence inArctic tundra soils. As indicated by the slow increase of oxihydrites, it may not be realistic to estimate
Introduction major, minor and trace elemextracts are investigated to elicit information regarding profile ag
over all or part of the Lateglacial to the Holocene Epoch (
In areas of ice-rich permafrost and massive ground ice(Astakhov, 2006), thermokarst modification is extensive to
ice wedges, in places, extend to within 12 m of the surface (forpermafrost extent see http//www.iiasa.ac.at/Research/FOR/
SIBERIAN CRYOSOLS 179incised the coastal plain to depths of 15 m a.s.l. Massive groundice bodies, which are believed to have an origin either assegregated ice or glacier ice (Trofimov et al., 1975; Astakhov,2006), have been significantly affected by thermokarstprocesses due to human impact and global warming (Popovaand Shmakin, 2009). The mean annual air temperature (MAAT)over Russia has risen by18C in the last 20 years (Shmakin andPopova, 2006). Pleistocene ice sheet limits reported by Formanet al. (2002), Ehlers and Gibbard (2004) and Svendsen et al.(2004) shown in Fig. 1 indicate the area has been ice-free sinceearly Weichselian time, and under periodic lacustrine andalluvial flooding (Forman et al., 2002) since at least the lastinterstade (ca. 45 ka). This interpretation is compatible with theage and origin of sediments reported in this study. Vasilievskayaet al. (1986) stress that the vegetation cover is highly dependenton the radiation/energy balance, which is
University for oxygen isotope analysis by mass spectrometry atn
180 JOURNAL OF QUATERNARY SCIENCErefers to C (subsoil) horizons with a brown colour that is at least10YR 5/4 or darker (see Mahaney, 1990, for an outline ofhorizon designations). The Cu designation refers to unweath-ered, unconsolidated and undifferentiated parent material(Hodgson, 1976). The soils all formed in fluvial deposits ofpresumed Holocene age, with minor airfall influx deposits ofsilt, and all are situated in topographic high positions with grass/herb tundra vegetation representative of the region. Parentmaterials are a mix of quartz and feldspar-rich sedimentsderived from crystalline basement rock; airfall sediments have asimilar source lithology. The three profiles are representative ofCryosols selected from among a suite of profiles studied acrossGydan and Yamal.
Organic samples collected for radiocarbon dating werehandled with metal implements and stored in aluminium foil,kept cool, and dated within two weeks of collection. Sampleswere dated at the University of Waterloo RadiocarbonLaboratory. Despite the presence of suitable minerals foroptically stimulated luminescence dating (OSL) quartz, albiteand orthoclase replicate dating of these beds for comparisonwith radiocarbon was not possible given funding constraints.Other sections in the general area were dated by OSL (seeMahaney et al., 1995).
The soil samples were air-dried and analysed for hygroscopicmoisture. The air-dried equivalent of 50 g oven-dried soil waslater subsampled for particle size analysis following proceduresoutlined by Day (1965). The coarse material (2 mm to 63mm)was separated by wet sieving. The fine material (
Taxonomically, the soil is a Regosolic Static Cryosol as definedin the Canadian Soil System.
The YAM9 profile (Fig. 3) contains a highly deformed surfacesoil over a buried peat showing only minor deformation,indicating a pedostratigraphic complex with frost heavingconfined to percolating meteoric water rather than from melt inthe active layer. The degree of deformation of horizons in thesurface pedon is consistent with classification as a BrunisolicDystric Turbic Cryosol. The surface peat contains anabundance of silt and fibrous brownish-black (10YR 2/3)organic material. Minor variations in colour occur with depth inthe surface epipedon, texture coarsens slightly down-profilewhile structure remains a fine grade of granular; both the Ah1and Ah2 horizons have friable consistence and lack plasticityand stickiness. Despite similar particle size characteristics inthe epipedon and subsurface B horizon, the structure becomesweak angular blocky and the material is slightly sticky andplastic.
Below the Bw horizon, clay increases in the Cox horizon,though with insufficient concentration to warrant a tdesignation. The matrix material is massive, with a firmconsistence, non-sticky and non-plastic. Below the ground soil/buried soil contact, the Lb horizon has a black (10YR 1/1)colour and is of loam texture with finely disseminated organicmaterial (unfortunately we lacked sufficient sample to analysethe organic carbon content; see under Soil chemistry). Theburied peat (Lb horizon) rests on frozen silty sand beds ofalluvial origin, weathered to a dull yellowish-brown (10YR 5/4)colour, with a silt loam texture, massive, friable consistenceand non-sticky and non-plastic. The lowermost Coxb horizonmakes a sharp contact with an ice wedge below.
The surface soil consists of wavy horizons and disjunct Ah/
Figure 2 GYDAN4 profile. This is a Fluvisol formed in stream sedi-ment overlying massive ground ice
Figure 3 YAM9 profile over an ice wedge. A surface Inceptisol with A/B/C hoburied L horizon, (b) the whole profile
Copyright 2009 John Wiley & Sons, Ltd.
SIBERIAN CRYOSOLS 181Bw/Cox horizons that are highly deformed and indicative offrost heaving. Whereas similar massive frost heave has beenreported elsewhere (Mahaney and Fahey, 1988), the soil
rizons formed over a buried peat (L horizon). Part (a) shows details of theJ. Quaternary Sci., Vol. 25(2) 178189 (2010)DOI: 10.1002/jqs
stratigraphic relationships suggest that the horizons that spilledon the surface were removed by wind and water erosion prior tothe build-up of the surface peat. Thus the peat may reflect acooling (Neoglaciation?) that occurred in the latter part of theHolocene, resulting in lower microbial activity. Frost heavingof subsurface horizons onto the surface is far more commonthan the infilling of surface material into melted frost/icewedges, as reported previously in Yamal by Vasilievskaya et al.(1986).
Certainly the development of a Bw horizon representssignificant weathering and pedogeneisis relative to GYDAN4,sufficient in effect to produce an Ah/Bw/Cox profile prior tofrost heaving and the later emplacement of the surface peat. Thecharacter of the deformed beds indicates that the soil formed inplace prior to a deformation in the sub-boreal climatic coolingfollowing the Climatic Optimum, which correlates well withwork carried out by Koshkarova and Koshkarov (2004) inCentral Siberia. While no 14C dates are available, the lessnegative 18O composition of the clays and bulk soils suggeststhat the surface soil represents weathering during the HoloceneClimatic Optimum.
Ice wedges, common on Yamal and Gydan, are alsocommon further southwest in taiga and forest communitieswhere ice wedge casts contain surface soil materials (ABhorizons) that have spilled downward (see Vasilievskaya et al.,1986), the opposite of the process described above. In southernexposures newly formed organic-rich horizons in topographicdepressions have started to reform in upper pseudo-ice wedge
the taiga and mixed taigaforest communities to the southwest,soil depth reaches to1.0 m and more (see Vasilievskaya et al.,1986).
increase in clay that is marginally below that required for a Bt,although the extractable Fe reported below and the field colourmight equivocally support a B horizon designation.
182 JOURNAL OF QUATERNARY SCIENCEcasts, presumably in response to cooling during the latter part ofthe Holocene (see Fig. 9 in Forman et al., 2002, for ananalogous situation). Mineral soils in the south contain organic-rich horizons approximately one-third to one-fifth the depth,and correspondingly of much younger age, than soils in Yamaland Gydan (see p. 56 in Vasilievskaya et al., 1986).
The YAM10 profile (Fig. 4) at Khalev Lake, a Gleysolic StaticCryosol with a thin Bw horizon, overlies C horizons withvariable weathering effects including significant gleyingcommon in Siberian soils (Federova and Yarilova, 1972).The original alluvial stratification, still pronounced as in the
Figure 4 YAM10 profile at Khalev Lake. Peaty Inceptisol with a thincolour B horizon (Bw) in a lacustrine terraceCopyright 2009 John Wiley & Sons, Ltd.Oxygen isotopes
The isotopic composition of pore waters and ground ice reflectsthe composition of the source water and provides informationon the freezing history of the ice (Michel and Fritz, 1978, 1982;Vasilchuk and Trofimov, 1988; Michel et al., 1989). Isotopicanalysis of ice wedges is particularly useful for determiningtemperature conditions during the period of their growth(Vasilchuk, 1987, 1992; Konjachin, 1988; Michel, 1990;Vasilchuk and Vasilchuk, 1996, 1997); thus wedges of varyingages can be of aid in assembling a climatic record oftemperature variations through time. Within the seasonallyfrozen active layer overlying permafrost, the isotopic compo-sition of pore ice can help to identify freezing processes relatedto the upward and downward migration of water due to strongtemperature gradients (Michel, 1982).
Samples collected at the three sites reported here andadditional sites in the area included pore ice, large and smallsegregated ice lenses, ice wedge ice, massive banded andParticle size
The analysis of sand, silt and clay, shown as depth distributionsin Fig. 5, are intended to illustrate the degree of modification ofthe original parent materials. All three profiles show an upwardincrease in silt, with an increase of silt between 15% and 60%compared with lower horizons suggesting airfall influx (similarto data interpretations of Forman et al., 2002). In one case(YAM10), this trend is mirrored by an upward increase in clay.The textures of these soils range from silty clay loam, silt loamand sandy clay loam in the Ah horizons, to silty clay loam andsandy loam in the Cox/Cg horizons. The Lb horizon in YAM9has a loam texture overlying a Cub horizon with a silt loamtexture. The texture of the Cox horizon in YAM9 shows anGYDAN4 profile, indicates only slight turbation duringpedogenesis (despite the presence of a Bw horizon). Hencethe texture (Fig. 5) reflects mainly the original depositionalvariation commonly associated with detrital effects. The Cghorizon, intensively gleyed, indicates periodic water saturationthat is supported by the ferrihydrite distributions reported laterin the paper. The profile, possibly of a similar age comparedwith the ground soil in YAM9, lacks an Ah horizon and containsa Bw horizon that is massive with a very friable to looseconsistence, non-sticky and non-plastic material. Rootspenetrate into the C horizon, which is a medium sandy loam,massive material with loose consistence, non-sticky and non-plastic.
Perched water above the massive ground ice has led togleying represented by the greyish olive colour, similar to whathas been previously recorded by Fedorova and Yarilova (1972)in soils of western Siberia. Periodic gleying in soils of Yamaland Gydan contrasts with extensive gleying in soils further tothe southwest, where soils are under strong reducing conditionsclose to the surface, often in the B horizons. Along transects intoJ. Quaternary Sci., Vol. 25(2) 178189 (2010)DOI: 10.1002/jqs
modern summer precipitation, and heavier than local surface
SIBERIAN CRYOSOLS 183massive segregated ice and ice-rich clay sediments. Oxygenisotope data for the three sites are compiled in Table 1. Modernsmall ice wedges in this part of northwest Siberia have d18Ovalues between 17% and 19% (Vasilchuk and Trofimov,1988), while surface waters (rivers and lakes) in the area rangefrom12% to16%. Annual precipitation averages18.0%.
The isotopic composition of the massive banded ground iceand deformed ice-rich clay at YAM10 and GYDAN4 indicatesthat this ice formed under climatic conditions somewhat coolerthan found at present, as did the large-scale reticulated icelenses at YAM10. By comparison, the small ice lenses foundwithin the oxidised sediments of YAM10, and the uppermostice-rich sediments at GYDAN4, are isotopically similar toaverage modern precipitation and most likely represent theinfiltration of recent precipitation into the active layer.
At YAM9, the isotopic composition of the large ice wedge ismore negative than modern ice wedges and therefore indicatesgrowth during a cooler climatic period than currently exists. Incontrast, the segregated ice of the grey clays enclosing the ice
Figure 5 Depth distributions of silt and clay for the three profileswedge formed from water that was isotopically heavier thanaverage present-day precipitation, and thus reflects either amassive influx of isotopically heavy summer precipitation(considered very unlikely), recharge during warmer climaticconditions prior to the formation of the ice wedge, orpreservation of a mixed marine/freshwater body (estuary?) intowhich the clays were deposited originally.
Water from pore ice and small ice lenses within thesediments overlying the ice wedge and clays at YAM9consistently yielded oxygen isotope compositions similar to
Table 1 Oxygen isotope data for ground ice sampled at the three study sit
Site Sample description
YAM9 Ice wedgeIce-rich clay adjacent to wedgeSediments above wedge
YAM10 Massive banded iceLarge ice lenses in claySmall ice lenses in oxidised sediments
GYDAN4 Ice-rich clay (deformed)Upper ice-rich sediments
Copyright 2009 John Wiley & Sons, Ltd.waters or average annual precipitation. The isotopic compo-sition is probably indicative of precipitation infiltrating duringwarmer climatic conditions when thaw conditions extendeddeeper than at present. This indicates that the soil developedduring the Hypsithermal, while soils at the other two sitesdeveloped subsequently.
The top of the massive ground ice bodies represents themaximum depth of thaw that could have occurred during theHypsithermal. The overlying seasonally thawed soil wouldhave been subjected to strong vertical thermal gradients andrelatively wet conditions due to the melting of the underlyingmassive ice and the impediment of drainage by existing ice.Thus the Hypsithermal period provided an optimum time formaximum soil development. Since the Hypsithermal, perma-frost has generally aggraded above the top of the massiveground ice and resulted in a thinner active layer and limitedwater infiltration.Geochemistry
Since we are dealing with complex mineral systems in thesesoils, it is not unexpected that the major, minor and traceelements, representatives of which are shown in Table 2,display concentration variations by factors of two to threewithin the three profiles. These concentration differences are
# of samples Range in 18O (%)
21 18.8 to 22.43 10.3 to 12.55 13.3 to 16.45 21.7 to 22.1
10 20.2 to 23.82 17.5 to 18.01 23.13 15.0 to 20.2
J. Quaternary Sci., Vol. 25(2) 178189 (2010)DOI: 10.1002/jqs
presumably caused by a combination of mineral and organic correlate negatively with their cation exchange capacities,
Table 2 Selected elemental data for soils in northwestern Siberia
Site Horizon (cm) Depth (%) Na (%) Ca (%) Al (ppm) Ti (%) Fe (ppm) Sc (ppm) Hf (ppm)
GYDAN4 Ah 08 0.87 0.7 5.74 3520 3.91 13.5 4.67Cox 834 1.06 0.5 6.55 4010 3.53 12.9 5.64
YAM9 Ah1 012 0.65 0.5 3.44 2320 2.25 7.84 5.07Ah2 1225 0.85 0.4 4.64 2900 1.73 7.09 7.80Bw 020a 0.90 0.5 4.15 2920 1.97 6.61 8.65Cox 0.65a 1.02 0.5 5.44 3860 2.49 9.96 8.18Lb 6575 0.67 0.6 4.35 3110 2.45 10.2 5.97Coxbf 75 1.52 1.1 6.08 4680 3.11 12.5 8.37
YAM10 L 40 0.62 0.3 4.54 2710 2.26 9.46 6.77Bw 08 0.85 0.6 5.10 3570 1.72 5.52 8.81Cox 828 0.95 0.6 4.57 3120 1.15 4.81 10.2Cg 28 0.81 0.6 8.60 4820 5.14 17.7 4.43
a See Fig. 4.
184 JOURNAL OF QUATERNARY SCIENCEdilution effects on the parent material, which is probablyrepresented here by the materials in the lower C horizons ofeach section.
Taking the ratios of selected potentially mobile (Na and Ca)and immobile (Sc, Ti, Al and Hf) elements (Table 3) to test fordownward or upward movement of soil water and parentmaterial uniformity, it is clear that although some ratiovariations indicate minor translocations throughout the pro-files, parent material is uniform down each profile. The totalvariability in inter-element ratios is less than a factor of three forall but Hf-including ratios, for which the factor escalates to nine(Table 3), confirming the more complex nature of the sources ofHf in the samples.
The data in Table 6 show that significant organic dilutions areto be expected in a number of horizons, but that these wouldexplain only differences in inorganic constituents of up to 1020%. Mineral dilutions must therefore account for the largervariations observed in these sections. The clue to a main sourceof these mineral dilutions comes from the observation that mostelements with high concentration measurements for all samplescorrelated positively with one another. The sole clear exceptionwas Hf (see Table 2 and Fig. 6). If Hf derives from zircon-richsilica sands (Hancock, 1984), then a primary mineral diluentaffecting these profiles could well be zircon-rich silica. Thisappears likely, since the Hf concentrations of different horizonsTable 3 Elemental ratios (Na, Camobile; Ti, Al,a Hf and Sc immobile)
Site Horizon Na/Ti Na/Al
GYDAN4 Ah 0.25 0.15Cox 0.26 0.16
YAM9 Ah1 0.28 0.19Ah2 0.29 0.18Bw 0.31 0.22Cox 0.26 0.19Lb 0.22 0.15Coxbf 0.32 0.25
YAM10 Ah 0.23 0.14Bw 0.24 0.17Cox 0.30 0.21Cg 0.17 0.09
Range 0.170.31 0.090.25Range ratio (max./min.) 1.8 2.8
a Minor amount of Al (Alp) is organically complexed and capable of translo
Copyright 2009 John Wiley & Sons, Ltd.which mainly reflect clay content (Fig. 5).As representatives of elements associated with the parent
materials in these profiles, Fe and Sc concentrations are highesteither in the surface Ah horizons or in the horizons closest topermafrost, massive ground ice or ice wedges (see Table 2).
The ratios of mobile to immobile elements (Na/Ti and Ca/Tiin Table 3) indicate negligible additional mobile element-induced ratio variations through the three profiles. The Bwhorizons, which are the chemically excited zones in the soils,show only slight increases of mobile elements such as Na andCa (e.g. in YAM9), presumably from downward translocation.
Chondrite-normalised rare earth element plots (Fig. 7) wereanalysed to determine the degree of chemical, and hencemineral, homogeneity of the parent materials. The REE plots forall samples fall within the envelope shown in Fig. 7. The REEprofiles are of similar shape for all horizons in each soil profileand display dilution effect variations similar to the otherelements. This, despite the particle size evidence for aeolianinflux, indicates the profiles are geochemically quite uniform.Hence the geochemistry indicates that the increase in siltupward in the soils is probably locally derived. These findingscontrast sharply with REE distributions for Spodosols innorthern Sweden (Earl-Goulet et al., 1997) and in the ZillertalAlps of Austria (Mahaney and Hancock, 1996), which show theaddition of aeolian-influxed sediment from distant sources.in soils of northwestern Siberia
Ca/Ti Ca/Al Hf/Sc Ti/Al
0.20 0.12 0.35 6100.12 0.08 0.44 6100.21 0.15 0.65 6700.14 0.09 1.10 6300.17 0.12 1.31 7000.13 0.09 0.82 7100.19 0.14 0.59 7100.23 0.18 0.67 7710.11 0.07 0.72 6000.17 0.12 1.60 7000.19 0.13 2.12 6800.12 0.07 0.25 560
0.110.23 0.070.18 0.252.12 5607702.1 2.6 8.8 1.4
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Extractable Fe and Al
The extractable and total Fe and Al values are given in Table 4.The pyrophosphate extractions were considered to representorganically complexed Fe and Al (Alexander, 1974;Mahaney and Sanmugadas, 1985). Following the work of
Figure 6 Scatterplot of ppm Hf versus ppm Sc (*) and cmol kg1 CEC(). The data indicate that Hf and Sc correlate positively with percen-tage of clay
SIBERIAN CRYOSOLS 185Parfitt and Childs (1988) and Earl-Goulet et al. (1998), theFigure 7 Chondrite-normalised REE plots for representative soilhorizons show a rather narrowly constrained distribution of heavyand light rare earths from La to Lu. All other horizons fall within theenvelope
Copyright 2009 John Wiley & Sons, Ltd.pyrophosphate-Al (Alp) alone is considered to representaccurately the Al that may be translocated. The Alp distributionsindicate that only the YAM9 profile shows any movement oforganically complexed Al into the Bw horizon from the surfacehorizon.
Oxalate-extractable Fe and Al, formerly thought to representthe concentration of organically bound and amorphous Fe andAl (Alexander, 1974; Mahaney and Sanmugadas, 1985), is nowconsidered to represent, in the case of Fe, only the amount offerrihydrite in the sample (Feo 1.7; Parfitt and Childs, 1988).As reported in Table 4, Alo values are often spurious with higherAlo than Ald, a trend reported elsewhere by Birkeland et al.(1989) and Mahaney (1990). Taking the raw data into account,the Feo is highest either in the Ah horizons or in the C horizonsclose to the massive ice bodies, where water was plentiful andin a liquid state during the Hypsithermal summers, as discussedabove. The Feo data also indicate either a slight increase(YAM9) or no increase (YAM10) in the Bw horizons relative tothe surface horizons.
Dithionite-extractable Fe and Al, formerly considered torepresent the sum total of organically bound, amorphous andcrystalline Fe and Al (Coffin, 1963; McKeague and Day, 1966),is now thought by Parfitt and Childs (1988) only to accuratelyreflect the amount of oxihydrites of Fe and Al in soils. Using theraw data to approximate goethite plus haematite plusferrihydrite, it is possible to arrive at an approximation of totalfree iron less ferrihydrite from FedFeo. As shown in Table 4,Fed ranges as high as 2.21% and some concentrations arehighest close to available water supplies sourced from icebodies during time of thaw. As shown in Table 4, Ald is oftenlower than Alo concentrations, which supports the conclusionsof Parfitt and Childs (1988) and must mean that sodiumdithionite does not extract all the oxihydrites of Al (seeBirkeland et al., 1989; Mahaney, 1990; Mahaney et al., 1995;Earl-Goulet et al., 1998). The total Fe and Al is given as Fet andAlt in Table 4.
Taking the various Fe and Al concentrations as ratios andarithmetic functions it is possible to test for the amounts offerrihydrite and lattice Fe, build-up of free Fe over total Fe andconcentration of ferrihydrite over the sum of ferrihydrite plusgoethite and haematite. The quantification of lattice (FetFed)and various forms of pedogenic Fe and Al are given in Table 5.The amount of lattice Fe is expected to increase in youngerprofiles and down-profile towards the parent material whereless weathering has occurred. Higher concentrations are foundin the GYDAN4 profile and in the lower horizons of YAM9 andYAM10 profiles (Table 5), which supports the field obser-vations. The Bw horizons, which would be expected to showlower lattice Fe relative to the underlying horizons, do notalways do so (e.g. YAM9 Bw), probably as a result of youngerage or frequency of fluctuation of a water table as in YAM10.
The concentrations of ferrihydrite (Feo 1.7) are expected toincrease with time, provided soil water does not remove it(Parfitt and Childs, 1988). It may increase in profiles wheresustained perched water saturates the soil but does not drain toa particular level. The GYDAN4 profile shows a decrease of Feodown-profile that may reflect removal into water-saturatedsediments at the top of the massive ice column where soil watermoves laterally on top of the ice to remove Feo. The YAM9profile shows slight increases in the Bw and in the Coxb (frozensilt) horizons, suggesting only minor movement and lowerconcentrations than in the GYDAN4 profile. In the YAM10profile the data illustrate a build-up of ferrihydrite in the lowerCg horizon, a pattern compatible with a perched water table.
The activity ratio (Feo/Fed) of Lutwick and Dormaar (1983),formerly a measure of the conversion of amorphous Fe tocrystalline Fe (Alexander, 1974), is now considered to representJ. Quaternary Sci., Vol. 25(2) 178189 (2010)DOI: 10.1002/jqs
Table 4 Concentrations of pyrophosphate (p), oxalate (o), dithionite (d) and totala (t) iron and aluminium in soils from northwestern Siberia
Site Horizon Extractable Fe Fe total Extractable Al Al total
Fep % Feo % Fed % Fet % Alp % Alo % Ald % Alt %
GYDAN4 Ah 0.51 1.05 1.22 3.91 0.10 0.29 0.22 5.74Cox 0.13 0.83 1.03 3.53 0.05 0.23 0.18 6.55
YAM9 Ah1 0.25 0.41 0.47 1.73 0.08 0.16 0.14 4.64Ah2b Bw 0.33 0.53 0.66 1.97 0.19 0.19 0.16 4.15Cox 0.10 0.47 0.68 2.49 0.04 0.13 0.12 5.44Lb Coxbf 0.17 0.53 0.58 3.11 0.04 0.14 0.08 6.08
YAM10 Ah 0.37 0.61 0.83 9.46 0.20 0.30 0.33 4.54Bw 0.30 0.56 0.67 5.52 0.11 0.13 0.14 5.10Cox 0.04 0.16 2.21 4.81 0.03 0.07 0.28 4.57Cg 0.10 1.03 1.47 4.78 0.05 0.28 0.30 8.60
a Totals of Fe and Al determined by instrumental neutron activation analysis. The Fe and Al in extracts were measured by atomic absorptionspectrophotometry.b , insufficient sample.
186 JOURNAL OF QUATERNARY SCIENCEthe ratio of ferrihydrite to total free iron (ferrihydri-te goethite haematite). In this profile sequence the ratiosare similar to GYDAN4, with higher values in the surfacehorizons and buried parent material in YAM9, and highconcentrations in the surface horizons and gleyed horizon ofYAM10. Essentially, the data indicate the possibility of perchedwater in all three profiles, with considerable fluctuations inYAM9.
The ratio Fed/Fet is used to measure the oxihydrites of Ferelative to the total Fe in a horizon. The values shown for allthree profiles are low, as expected for cold-temperature soils,and with slightly higher values in the soil sola. The Cu andlower C horizons are lower in Fed/Fet compared with theoverlying A/B horizon complexes. The Bw and Cox horizonsare highest in the YAM9 and 10 profiles, supporting the soilcolours that indicate release of oxihydrites. The lowermosthorizon in YAM9 (Coxbf) gives the lowest value, which likelyreflects the reworking of old secondary oxides. These results arecompatible with other studies that point to use of Fed as ageochronometer in warmer environments (McFadden andHendricks, 1985; Kendrick and McFadden, 1996).
Total Fe reported here, in the range of 1.15.1% (see Table 2),is considerably lower than samples analysed 400 km to theTable 5 Quantification of ferrihydrite (Feo), goethite haematite (Fed Feoand organically complexed Al (Alp/Alt) in soils from northwestern Siberia
Site Horizon Feo1.7a % Fed Feo %
GYDAN4 Ah 1.79 0.17Cox 1.41 0.20
YAM9 Ah1b 0.70 0.06Ah2 i.s. i.s.Bw 0.90 0.13Cox 0.80 0.21Lbb i.s i.s.Coxbf 0.90 0.05
YAM10 Ah 1.04 0.22Bw 0.95 0.11Cox 0.27 2.05Cg 1.75 0.44
a based on Parfitt and Childs (1988) calculation of ferrihydrite.b i.s., insufficient sample.c The Fed/Fet ratio is used to measure the release of free Fe relative to total Fdiscussion of the interpretation of this ratio). The arithmetic function Fed
Copyright 2009 John Wiley & Sons, Ltd.south in the taiga and mixed taigaforest, where reportedconcentrations reach 20% (Vasilievskaya et al., 1986) andsomewhat similar to within 10% of reported values in tundrapodzols of the Kola Peninsula (Pereverzev, 2007).
The Alp/Alt ratio approximates the release and movement oforganically bound Al relative to the total concentration. Thedata show no movement in GYDAN4 and YAM10 profiles.However, in YAM9 the increase of Alp/Alt in the Bw horizonindicates minor translocation. While movement of organicallycomplexed Al is slight, the trend is similar to that observedin Spodosols at more southerly locations in Scandinavia(Earl-Goulet et al., 1998).
Iron data for zones II, III and IV, discussed by Vasilievskayaet al. (1986), include total Fe, silicate Fe (equivalent to latticeFe) and non-silicate Fe, which approximates sodiumdithionite-extractable Fe discussed above (see Zonn, 1982).The silicate Fe is determined by taking the total Fe lessthe non-silicate percentages. However, iron concentrationsfor the taiga and taigaforest profiles are considerably higherthan percentages calculated for sites discussed here, withvalues for total Fe in the 20% range. This may result fromlithological and climatic/biotic changes or from instrumenterror.), lattice Fe (Fet Fed), pedogenic Fe (Fed/Fet), Fe activity ratio (Feo/Fed)
Fed/Fetc % Fet Fed % Feo/Fed % Alp/Alt %
0.31 2.69 0.86 0.020.29 2.50 0.81
Soil chemistry: pH, conductivity, carbon/ the soil microtopography into account where all profiles
Table 6 Selected soil chemical parameters for northwestern Siberian soilsa
Site Horizon pH (in H2O)(1:5)
nitrogen (%)Cation exchange capacity
(CEC) (cmol kg1)
GYDAN4 Ah 5.6 0.06 9.87 0.72 46.2Cox 6.4 0.04 1.82 0.19 24.0
YAM9 Ah1 5.0 0.04 7.24 0.30 16.6Ah2a Bw 5.1 0.03 1.99 0.09 13.0Cox 6.4 0.03 0.93 0.07 13.5Lb Coxbf 7.2 0.12 0.73 0.02 14.4
YAM10 Ah 4.8 0.08 Bw 5.2 0.03 2.94 0.19 12.4Cox 5.5 0.02 0.24 0.03 4.5Cg 6.8 0.04 0.82 0.10 30.6
a , insufficient sample.b EC, electrical conductivity.
SIBERIAN CRYOSOLS 187nitrogen and cation exchange capacity
The pH distributions in these profiles range from acidic toneutral (Table 6). In general, the A and B horizons aremoderately acidic, becoming neutral at depth, possibly as aresult of increasing distance from overlying sources of organicmatter. Overall, the data show little downward movementof H ions below the surface epipedons. The total saltsdetermined by electrical conductivity give low values,indicating that there is sufficient soil water movement presentto effect removal.
The organic carbon and total nitrogen analyses were studiedto determine the build-up of organic matter and theirdownward or upward movement in the profiles. The organicmatter (organic carbon 62% of organic matter) is mostabundant in the surface Ah horizons and shows somemovement into the lower Bw and Cox horizons. Even thefrozen sediment at YAM9 has 0.73% organic carbon. Totalnitrogen follows the organic matter distributions, ranging frommost abundant in the surface horizons to least in the lowersubsurface horizons. In YAM10 total nitrogen increases again inthe Cg horizon, suggesting downward movement and accumu-lation probably as a result of a frozen subsurface layer. TakingFigure 8 Clay mineralogy determined by plotting percentage C against thremoved suggest the presence of smectite which follows from limited leach
Copyright 2009 John Wiley & Sons, Ltd.were sampled on high turf hummocks, the N concentrations areprobably a minimum. Other workers (Biasi et al., 2005) havefound higher N in topographic depressions where slope washprocesses tend to lead to downslope movement of humus andincreased biotic components in low-lying areas of the TamyrPeninsula, further to the west.
Calculations of organic carbon in permafrost across much ofSiberia and Alaska give values of2.6% on average, with wideranges, considered by Zimov et al. (2006) to be nearly 1030times the average carbon found in deep, non-permafrost, low-organic-matter, mineral soils. Yet the data provided hereinshow values of 7 to10% organic carbon in surface epipedonswith transport into subsurface horizons in all analysed profiles.The B horizons have concentrations of 2 to 3% and themineral soils
water tables at various times in the past.
SYamal Expedition (1990) and the former Soviet Pipeline ConstructionMinistry for logistical and financial support to W. C. Mahaney and F. A.
Jakobsen BH, Siegert C, Ostroumov V. 1996. The effect of permafroster0.
Kendrick KJ, McFadden LD. 1996. Comparison and contrast of pro-cesses of soil formation in the San Timoteo Badlands with chron-osequences in California. Quaternary Research 46: 149160.
188 JOURNAL OF QUATERNARY SCIENCEMichel. This research was supported by an Infrastructure Grant from theNatural Sciences and Engineering Research Council of Canada to theSLOWPOKE Reactor Facility of the University of Toronto. Financialsupport by the Estonian Research Council (project no. 0180048s08)to V. Kalm is gratefully acknowledged. Dr Pavel A. Barsukov, Instituteof Soil Science and Agrochemistry, Russian Academy of Sciences,Novosibirsk, provided invaluable source material on publishedAcknowledgements We thank the Joint Soviet, Canadian and Ucertain limits (see Birkeland, 1999), it is important to removethe organic matter to determine the CEC 100 g1 clay. Ingeneral, the CEC without the organic influence is between 50and 90 CEC l00 g1, supporting the presence of smectite, whichis the most abundant clay mineral in all the profiles, previouslyreported by Mahaney et al. (1995).
The morphogenetic aspects of the soils are similar to thatreported by other workers; namely, an expected andcomparatively small degree of mineral weathering, limitedbut important diversity of Fe and Al extracts, low decompo-sition and humification of plant remains, limited chemicalmovement in shallow profiles, and significant hydromorphismwith peaty surface layers often accompanied by gleyed zones atdepth, water-logged horizons perched over impermeable icelenses or massive segregated ice layers. Soil horizon defor-mation and gleying are the two chief characteristics of theCryosols investigated, with relict forms of frost heavingcommon in some instances. Rather than finding mineralmaterial spilling into melted ice wedge casts as reportedelsewhere, frost heaving of C horizon material onto the surfaceis far more prevalent. The organic carbon content in the threeprofiles indicates significant stores of organic carbon, not onlyin the surface horizons but also in the subsurface immediatelyadjacent to ice wedges and massive ground ice bodies.
Elemental concentration variations up to a factor of 2 to 3may be attributed to organic and mineral (mainly zircon-richsilica) dilutions of a single, relatively uniform, parent material.While most elements correlate positively with one another,they all correlate negatively with Hf. The increase in Hf is takento indicate an increase in free zircon-rich silica. A geochemicaltest for parent material uniformity showed the presence of oneparent material in each profile with local source aeoliancontributions. The ratios of mobile to immobile elementsshowed slight increases in the B horizons and in the fresh parentmaterial (Cu) but, overall, the downward translocation is slightand presumably occurs as moisture is lost by drying out orleaching of the active layer in summer.
The extractable Fe and Al data yield information on relativemovement and weathering within the profiles. While therelative downward movement in the soils is negligible,movement below GYDAN4 and YAM9 is restricted by animpermeable substratum (massive ground ice, ice wedge orpermafrost). Given the Fe-depleted nature of the acidiclithology, the degree of weathering is high considering thehigh latitude and probably reflects the extent to which water isavailable in the soils from summer thaw. The quantification ofextractable Fe and Al shows slight increases in ferrihydrite,variable increases in free iron relative to total Fe, and slightmovement of Alp downward in the profiles. As usual,ferrihydrite provides a reliable record of fluctuating perchedCopyright 2009 John Wiley & Sons, Ltd.Khain VE, Nikishin A. 1997. Russia. In Encyclopedia of European andAsian Regional Geology, Moores EM, Fairbridge RW (eds). Chap-man & Hall: London; 631652.and palaeo-environmental history on soil formation in the lowKolyma Lowland, Siberia. Danish Journal of Geography 96: 405research on the Yamal and Gydan peninsulas as well as informationon laboratory methods. We gratefully acknowledge helpful criticismfrom an anonymous reviewer and Professor Chris Caseldine.
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