Download - Geochemistry and extractable Fe and Al in cold-temperature soils of northwestern Siberia

JOURNAL OF QUATERNARY SCIENCE (2010) 25(2) 178–189Copyright � 2009 John Wiley & Sons, Ltd.Published online 21 July 2009 in Wiley InterScience
(www.interscience.wiley.com) DOI: 10.1002/jqs.1290
Geochemistry and extractable Fe and Al incold-temperature soils of northwestern SiberiaWILLIAM C. MAHANEY,1* VOLLI KALM,2 RONALD G. V. HANCOCK,3 FRED MICHEL4 and BARBARA KAPRAN1

1 Quaternary Surveys, Thornhill, Ontario, Canada2 Faculty of Science and Technology, Institute of Ecology and Earth Sciences, Tartu University, Tartu, Estonia3 Department of Medical Physics and Applied Radiation Sciences and Department of Anthropology, McMaster University,Hamilton, Ontario, Canada4 Department of Earth Sciences, Carleton University, Ottawa, Ontario, Canada

Mahaney, W. C., Kalm, V., Hancock, R. G. V., Michel, F. and Kapran, B. 2010. Geochemistry and extractable Fe and Al in cold-temperature soils of northwesternSiberia. J. Quaternary Sci., Vol. 25 pp. 178–189. ISSN 0267-8179.

Received 10 August 2008; Revised 29 March 2009; Accepted 6 April 2009

ABSTRACT: The concentrations of major, minor and trace elements in three Cryosols from north-western 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 processesover all or part of the Lateglacial to the Holocene Epoch (<10 ka) in a cold environment. Iron and Alextracts are investigated to elicit information regarding profile age and palaeoclimate. ‘Free’ iron (Fed)relative to total Fe increases in the AhþBw horizons compared with the lower horizons, whereoxidation is weaker. Low total Fe reflects reworked felsic deltaic and shallow marine deposits from
the 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 estimatethe 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; Fe–Al extractions; chemical/geochemical indices of Cryosol pedogenesis.

Introduction

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

* Correspondence to: W. C. Mahaney, Quaternary Surveys, 26 Thornhill Ave.,Thornhill, Ontario, Canada, L4J 1J4.E-mail: [email protected]

major, minor and trace elements that yield importantinformation on profile chemical uniformity and the movementof 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 Yamal–Gydan 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 area

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 amaximum elevation of 40 m a.s.l.; numerous rivers have

Figure 1 Location of sites on the Yamal and Gydan peninsulas, north-western Siberia. Weischelian ice limits indicate the sites have been icefree since the early stage of the last glaciation (see Ehlers and Gibbard,2004; Svendsen et al., 2004)

SIBERIAN CRYOSOLS 179

incised 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 by �18C 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 <10 kcal cm�2,increasing to the south towards the Ural Mountains. Most heatis used in evaporation, leaving the tundra with little energyavailable for soil development.

The basement complex of the West Siberia–Kara Sea Basin isknown only from fragmentary information, its delimited extentstill incompletely understood (Khain and Nikishin, 1997). Theoverall subsidence of the basin followed a period of extensiverifting during the Late Permian–Early Jurassic along ameridional trend to the east as far as the Irtysh River. Extensiverift structures are known in the basement of West Siberia, alongwith accompanying volcanism almost all of which is basaltic.The sedimentary cover of the basin dates from the Middle–Late

Copyright � 2009 John Wiley & Sons, Ltd.

Triassic in the north to the Middle Jurassic in the south andincludes a range of near-shore terrestrial to shallow, largelyunlithified, marine sediments. Deep-water marine sedimentswere emplaced starting in Late Jurassic to Early Cretaceous timeand continuing into the Palaeogene, ultimately being reworkedby continental sedimentation. The entire thickness of soft rockreaches �10 km. The Late Cenozoic witnessed repeatedmeltwater flooding and alluvial sedimentation, the uppermostlayers of which are discussed later.

Reworking of these alkaline basement rocks into the lateQuaternary sediments and soils farther west of Yamal, asdiscussed by Vasilievskaya et al. (1986), may explain the highFe reported there. The lithology of the sediments describedherein from which the soils formed is primarily felsic with highamounts of quartz and feldspar. This contrasts with iron-rich,amphibolitic and olivine-rich parent materials that will tend toweather more quickly given global warming.

In areas of ice-rich permafrost and massive ground ice(Astakhov, 2006), thermokarst modification is extensive todepths of 10 m in high Arctic terrain identified as Zone I (highArctic) by Vasilievskaya et al. (1986). Massive ground ice andice wedges, in places, extend to within 1–2 m of the surface (forpermafrost extent see http//www.iiasa.ac.at/Research/FOR/russia_cd/perm_maps.htm), above which a thin mantle of soilhas formed in sediments that thaw in summer. Cryosols in ZoneI (high permafrost content) adjacent to the Barents Sea, whichwere left undocumented by Vasilievskaya et al. (1986), aredescribed here in considerable detail with respect to theirmorphogenetic and geochemical properties, as well as theirrelationship to massive segregated ice and ice lenses. Permafrost,while more massive in Zone I of Vasilievskaya et al. (1986, p. 8for map) than in Zones II and III, further southwest in theBol’shezemel’skaya and Komi regions, appears to have led to asimilar low redox potential and high intensity of gleying inprofiles within a more dynamic active layer.

The MAAT on Yamal, at Bovanenkovo (Fig. 1, near YAM9), is�228C, with an absolute minimum of �638C (Climatic Office,1977). Only during July and August are mean temperaturesabove 08C and day temperatures can reach þ308C. Daytemperatures during 1990 reached 408C (highest on record)and fires in the tundra were common and widespread. Themean annual precipitation (MAP) is 300 mm, the bulk of whichoccurs from July through September. Minimum precipitation ofapproximately 15 mm occurs in February.

Materials and methods

Three soil profiles were chosen as they represent sites adjacentto massive ground ice and ice wedges (GYDAN4 and YAM9),or stratified alluvial sands (YAM10), which together make upthe dominant pedo-stratigraphic units in the area. Depositswere sectioned off, and samples were collected down throughthe profile and into the parent materials. These soils werepreviously discussed (Mahaney et al., 1995) along with othersections in relation to the Late Pleistocene and Holocenestratigraphy of North Siberia, adjacent the Kara Sea (Fig. 1).Soils were described following the guidelines of the Soil SurveyStaff (1999, 2006), Birkeland (1999) and Soil ClassificationWorking Group (1998). Soil colours were determined using thesoil colour charts of Oyama and Takehara (1970). The L/Ahdesignations follow the Soil Classification Working Group(1998), where L¼O horizon and Ah¼A of the Soil Survey Staff(2006). The Cryosols described are equivalent to Gelisols asdefined by Beyer et al. (1999). The Cox horizon designation

J. Quaternary Sci., Vol. 25(2) 178–189 (2010)DOI: 10.1002/jqs

180 JOURNAL OF QUATERNARY SCIENCE

refers 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 (<63mm) wasanalysed by hydrometer. The coarse particle size fractions(2000–63mm) follow the Wentworth Scale of Folk (1968) withthe clay/silt boundary at 2mm (Soil Survey Staff, 1999).

Extracts of Fed (d¼Na dithionite) and Ald were achievedusing 1 g (<2 mm bulk fraction) of air-dried samples to whichsodium dithionite and sodium citrate buffer were addedfollowing procedures outlined by Coffin (1963). Sodiumdithionite removes ‘free’ oxides and hydroxides (oxihydrites)of Fe (mainly haematite and goethite and, if present,lepidocrocite, maghemite, magnetite and ferrihydrite) (Parfittand Childs, 1988) and Al. However, according to Parfitt andChilds (1988), not all free aluminium is dissolved by sodiumdithionite. Oxalate (Al, Feo) and pyrophosphate (Al, Fep)-extractable Fe and Al were determined using methodsdescribed by McKeague and Day (1966). Iron extracted byacid ammonium oxalate (extracted in the dark), whenmultiplied by the constant 1.7, is a measure of the ferrihydritecontent (Parfitt and Childs, 1988); sodium pyrophosphateextracts mainly the organically complexed form of Al; the Fep isconsidered an unreliable estimate of organically complexed Fe(Parfitt and Childs, 1988), although formerly the pyrophosphateextractions were thought to represent organically complexed Feand Al (Alexander, 1974; Mahaney and Sanmugadas, 1985).All extracts were measured with a Model 373 PerkinElmeratomic absorption spectrophotometer, which provides resultsto a hundredth of a percent. To guard against small amounts ofmagnetite influencing the acid ammonium oxalate extractions,magnetite was removed prior to analysis.

Cation exchange capacity was determined by replacing allexchangeable cations with ammonium ions (modified SoilConservation Service, 1992, method). Ammonium chloridewas added to each sample and washed with ethanol until theleachate, silver nitrate solution, gave a negative test for thechloride ion. The ammonium-saturated soil was leached with10% acidified NaCl solution. The leachate was made to volumeand analysed for NH4-N with a Technicon II Autoanalyzer IIsystem. Organic carbon was determined following a modifiedWalkley and Black (1935) method. Total carbon and nitrogenwas determined with a Leco CHN Autoanalyzer.


Soil samples were also analysed by INAA at the SLOWPOKEReactor Facility of the University of Toronto using 600–850 mgsamples (Hancock, 1984) and appropriate standards. Concen-trations of chemical elements that produce short-livedradioisotopes (Al, Ca, Cl, Dy, Mg, Mn, Na, Ti, U and V) weredetermined by irradiating the samples for 5 min at a neutronflux of 1.0� 1011 n cm�2 s�1. After a delay of about 18–20 minto allow for the decay of 28Al to acceptable levels, thesubsamples were assayed using 5 min counts with on-sitegamma ray spectrometers. A 1-day delay and recountingallowed Eu, Ga, K and Na to be determined. To determine theconcentration of elements that produce long-lived radioiso-topes, the samples were batch irradiated for 16 h at a neutronflux of 2.5� 1011 n cm�2 s�1. Following a 6- to 7-day delay, thesamples were counted for an average of 10 min to determinethe concentrations of As, Br, Fe, La, Na, Sb, Sm, Sc, U and Yb.At 13–14 days after irradiation, the samples were recountedsequentially for 100 min to determine the concentrations of Ba,Ce, Cr, Cs, Eu, Fe, Hf, Lu, Ni, Rb, Sc, Sr, Ta, Tb, Th and Yb. Iron,Sc and Yb were used to cross-check the long-lived radioisotopemeasurements. With the equipment used, Zr could not bemeasured reliably.

Massive ground ice bodies of varying origin (ice wedge, icelens, stratified ice) were studied in detail to determine theiroxygen isotope composition. Representative samples of theoverlying and enclosing frozen soils and surface water bodies ateach site were also collected for isotope analysis. Samples wereallowed to thaw within sealed bags in the field. The meltwaterwas subsequently transferred to bottles and returned to CarletonUniversity for oxygen isotope analysis by mass spectrometry atthe Stable Isotope Laboratory of the Ottawa–CarletonGeoscience Centre.

Results and discussion

The soil profiles

The soils, previously described briefly as part of the overallstratigraphy in the field area (see Mahaney et al., 1995), arediscussed at greater length to correlate with the 18Ointerpretation, while geochemistry and Fe/Al extract data areexamined later in the paper.

The GYDAN4 site (Fig. 2) contains an L/Ah/Cox profileweathered to depth without encountering fresh parent material.The profile, situated above deformed marine clays containingabundant segregated ice, is composed principally of stratifiedalluvial silt with lesser amounts of clay and fine sand. Thehigher silt content in the Ah horizon (discussed later under‘Particle size’) represents a fining upward sequence in theprofile and may represent an admixture of wind-blown silts,although the source would have to be local, as demonstratedlater under ‘Geochemistry’. The presence of stratificationsuggests minimal pedogenic influences, but mottled colours of10YR 4/3 and 5Y 5/1 are sufficient to warrant a designation ofCox in the profile morphology. Structure grades from granularin the Ah horizon to massive at depth; consistence ranges fromfriable in the Ah to firm in the Cox horizon. All horizons areslightly sticky and slightly plastic. The absence of a B horizonand shallow depth of the profile suggest a young age; however,organic material just above the ice-rich clay (WAT-2524)yielded a radiocarbon age of 10 700� 110 14C a BP. Theinconsistent profile versus radiocarbon age suggests the profilemay have been subjected to deflation at some time in the past.


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



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 ‘t’designation. 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/Bw/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 the



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 (AþBhorizons) 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 wedgecasts, 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 terrace


GYDAN4 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 intothe taiga and mixed taiga–forest communities to the southwest,soil depth reaches to �1.0 m and more (see Vasilievskaya et al.,1986).

Particle 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 anincrease 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.

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 and


Figure 5 Depth distributions of silt and clay for the three profiles


massive 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 rangefrom �12% to �16%. Annual precipitation averages �18.0%.

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 icewedge 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


modern summer precipitation, and heavier than local surfacewaters 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

es

# 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


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 0–8 0.87 0.7 5.74 3520 3.91 13.5 4.67Cox 8–34 1.06 0.5 6.55 4010 3.53 12.9 5.64

YAM9 Ah1 0–12 0.65 0.5 3.44 2320 2.25 7.84 5.07Ah2 12–25 0.85 0.4 4.64 2900 1.73 7.09 7.80Bw 0–20a 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 65–75 0.67 0.6 4.35 3110 2.45 10.2 5.97Coxbf 75þ 1.52 1.1 6.08 4680 3.11 12.5 8.37

YAM10 L 4–0 0.62 0.3 4.54 2710 2.26 9.46 6.77Bw 0–8 0.85 0.6 5.10 3570 1.72 5.52 8.81Cox 8–28 0.95 0.6 4.57 3120 1.15 4.81 10.2Cg 28þ 0.81 0.6 8.60 4820 5.14 17.7 4.43

a See Fig. 4.


presumably caused by a combination of mineral and organicdilution 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 10–20%. 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 horizons

Table 3 Elemental ratios (Na, Ca¼mobile; Ti, Al,a Hf and Sc¼ 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 0.17–0.31 0.09–0.25Range ratio (max./min.) 1.8 2.8

a Minor amount of Al (Alp) is organically complexed and capable of translo


correlate negatively with their cation exchange capacities,which mainly reflect clay content (Fig. 5).

As representatives of elements associated with the parentmaterials 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

0.11–0.23 0.07–0.18 0.25–2.12 560–7702.1 2.6 8.8 1.4

cation.


Figure 6 Scatterplot of ppm Hf versus ppm Sc (*) and cmol kg�1 CEC(þ). The data indicate that Hf and Sc correlate positively with percen-tage of clay


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 ofParfitt and Childs (1988) and Earl-Goulet et al. (1998), the

Figure 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


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 total‘free’ iron less ferrihydrite from Fed–Feo. 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 (Fet–Fed)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 Feo

down-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 represent


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.


the ratio of ferrihydrite to total ‘free’ iron (ferrihydri-teþ goethiteþ 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 1.1–5.1% (see Table 2),is considerably lower than samples analysed 400 km to the

Table 5 Quantification of ferrihydrite (Feo), goethite þ haematite (Fed � Feo

and organically complexed Al (Alp/Alt) in soils from northwestern Siberia

Site Horizon Feo�1.7a % 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 �


south in the taiga and mixed taiga–forest, 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 taiga–forest 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 <0.010.27 1.26 0.87 0.02i.s. i.s. i.s. i.s.

0.34 1.31 0.80 0.050.27 1.81 0.69 <0.01i.s. i.s. i.s. i.s.

0.19 2.53 0.91 <0.010.37 8.63 0.73 0.040.39 4.85 0.84 0.020.46 2.60 0.07 <0.010.29 3.31 0.70 <0.01

e (see Mahaney et al., 1999, and McFadden and Hendricks, 1985, for aFeo is used to calculate goethite plus haematite.


Table 6 Selected soil chemical parameters for northwestern Siberian soilsa

Site Horizon pH (in H2O)(1:5)

ECb

(mS cm�1)Organic

carbon (%)Total

nitrogen (%)Cation exchange capacity

(CEC) (cmol kg�1)

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.


Soil chemistry: pH, conductivity, carbon/nitrogen 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 Hþ 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 carbon¼ 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. Taking

Figure 8 Clay mineralogy determined by plotting percentage C against thremoved suggest the presence of smectite which follows from limited leach


the soil microtopography into account where all profileswere 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 of �2.6% on average, with wideranges, considered by Zimov et al. (2006) to be nearly 10–30times the average carbon found in deep, non-permafrost, low-organic-matter, mineral soils. Yet the data provided hereinshow values of 7 to �10% 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 <1% in the three profiles. While the population isa minimum, the data suggest that surface soils of Holocene agemay well contain significantly greater concentrations of carbonthan previously thought, perhaps even greater than what iscontained in permanently frozen ground as indicated by Zimovet al. (2006).

The cation exchange capacity (CEC) was measured to assessits influence on the abundance of clay minerals (Fig. 8). Asdifferent species of clay minerals have CECs that range within

e cation exchange capacity. The calculated CECs with percentage Cing effects and pH in the �5–6 range



certain limits (see Birkeland, 1999), it is important to removethe organic matter to determine the CEC 100 g�1 clay. Ingeneral, the CEC without the organic influence is between 50and 90 CEC l00 g�1, supporting the presence of smectite, whichis the most abundant clay mineral in all the profiles, previouslyreported by Mahaney et al. (1995).

Conclusions

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 perchedwater tables at various times in the past.

Acknowledgements We thank the Joint Soviet, Canadian and USYamal Expedition (1990) and the former Soviet Pipeline ConstructionMinistry for logistical and financial support to W. C. Mahaney and F. A.Michel. 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 published


research 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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