Micromorphological aspects of arctic-alpine pedogenesis in the Okstindan Mountains, Norway

CATENA

Vol. 10, 133-148

Braunschweig1983

MICROMORPHOLOGICAL ASPECTS OF ARCTIC-ALPINE PEDOGENESIS IN THE OKSTINDAN MOUNTAINS, NORWAY*

S. Ellis, Hull SUMMARY The micromorphology of five arctic-alpine soil types has been examined in relation to the processes of organic matter decomposition, development of microstructure, translocation and weathering. In surface horizons, the activity of microorganisms and mesofauna is apparent and organic matter is involved in the formation of spongy, granular and crumb structures. The structures in the subsurface horizons are predominantly single grain and lenticular, showing coatings ofilluvial fines on the upper surfaces of individual grains and peds. Illuviation of organo-metallic complexes is also recognized in the form of coatings and'structural development of granular and crumb elements. The only evidence for weathering is the occasional fracture of biotite grains. These features and processes are discussed in the context of arctic-alpine pedogenesis. 1. INTRODUCTION A series of recent investigations in the Okstindan Mountains of north Norway (Fig. 1) has examined pedological processes in arctic-alpine soils and their responses to environmental controls (for example, ELLIS 1979, 1980a, b, c, GRIFFEY & ELLIS 1979, HARRIS & ELLIS 1980). Studies of the soil micromorphology were made largely to examine the redistribution of the soil mineral fraction in soliflucted materials and profile development associated with recent (Neoglacial) glacial activity. No comprehensive account of the micromorphology has been attempted, however, and it is therefore the aim of this paper to present such an account. The micromorphology of soils representative of the Okstindan area as a whole is described in detail and its development is discussed in relation to the general knowledge of pedogenesis both in this region and similar environments elsewhere. The Okstindan Mountains lie at latitude 66"N, close to the Norwegian-Swedish border, and extend in altitude up to 1916 m above sea level (Fig. 1). They are thought to have been completely covered by the Weichselian Fenno-Scandian inland ice sheet, in view of its maximum extent in northern Europe (ANDERSEN 1975), and were vacated by this ice sheet around 9000 years B.P. (WORSLEY 1970, GRIFFEY 1976). They still support a small plateau ice cap with its associated outlet glaciers, and also a number of cirque glaciers. The study area is located on the northeast flank of the massif (Fig. 1). Here bedrock is predominantly siliceous schist, mantled extensively by an acid, sandy till, thought to be derived from metamorphic and igneous rocks to the east (GAVELIN & KULLING 1955, ELLIS 1980a). This till constitutes the parent material of the majority of soils. Vegetation within the study area concists of birch (Betula pubescens subsp, tortuosa) trees, *

Okstindan Research Project Report No. 39.

134

ELLIS

0 I

kr

c~c~

km

O

Regosol

~ ~l

Glacier

[]

B r o w n £Oll

....

Contours (100rn mtervals)

•

Humtc Regosol

•

Podzol

~7

b o g Soil

•

Summit (metres)

Fig. 1: Locationmap.

extending up to an altitude of approximately 670 m a.s.l., above which occur tundra shrub and herb communities comprising the low-, middle- and high-alpine vegetation zones of RUNE (1965). There is no continuously recording meteorological station within the Okstindan Mountains, but extrapolation of temperature and precipitation data from the nearby stations of Hat~elldal (221 m a.s.1.) and Rosvatn (383 m a.s.l.) respectively, suggests that mean annual air temperature ranges from -0.5"C to -9"C, depending upon altitude, while mean annual precipitation is probably slightly greater than 1500 mm. Although no detailed studies of permafrost distribution within this region have been made, these temperatures suggest the existence of discontinuous permafrost throughout much of the area, possibly becoming continuous at higher altitude (BROWN 1967). On the basis of geomorphic, vegetational and climatic criterea, Okstindan may therefore be regarded as typical of Scandinavian arctic-alpine environments. These occur throughout the highest mountain regions, being represented by areas above and immediately below the upper altitudinal tree limit (DAHL 1975). The study area is also environmentally similar to the subarctic regions of

MICROMORPHOLOGICALASPECTSOF ARCTIC-ALPINEPEDOGENESIS,NORWAY

135

northern Europe and North America, although here the tree limit tends to be latitudinally rather than altitudinally controlled (LOVE 1970, BARRY & IVES 1974).

2. MATERIALS Five major soil types have been recognized in the study area, their classification having been discussed previously (ELLIS 1979), along with the influence of environment on their profile differentiation and spatial distribution (ELLIS 1980b). Profiles representative of each soil type were selected for micromorphological examination (Fig. 1). Site and profile field descriptions, including an indication of classification according to the USDA (SOIL SURVEY STAFF 1975) and Canadian (CANADA SOIL SURVEYCOMMITIEE 1978) systems, are given below. Regosol (Lithic Cryorthent, Orthic Regosol) Elevation: 1500 m a.s.l. Drainage: Free Aspect: East Slope: 1° Parent material: Sandy till Vegetation: Ranunculus glacialis, Salix herbacea, Marsupella condensata 0-2 cm Black (10YR 2/1) humose free sandy loam; pH 3.5; massive and weak; few roots; few angular to subrounded schist, quartzite and granite stones; sharp undulating boundary. 2-15 cm YeUowishbrown (10YR 5/4) f'mesandy loam; pH 3.8; single grain and loose; few roots; few angular to subrounded schist, quartzite and granite stones; sharp straight boundary with bedrock. Brown Soil (Lithic Cryochrept, Orthic Dystric Brunisol) Elevation: 1260m a.s.l. Drainage: Free Aspect: South Slope: 1° Parent material: Sandy till Vegetation: Diapensia lapponica, Juncus trifidus, Empetrum nigrum, Carex bigelowii, Lycopodium selago, Marsupella condensata 0-4 cm Dusky red (2.5YR 3/2) humose fine sandy loam; pH 3.8; massive and weak; few roots; few angular to subrounded schist, quartzite and granite stones; narrow undulating boundary. 4-12 cm Dark yellowish brown (10YR 4/4) fine sandy loam; pH 4.0; single grain and loose; few roots; few angular to subrounded schist, quartzite and granite stones; sharp undulating boundary. 12-48 cm Light olive brown (2.5Y 5/4) free sandy loam; pH 5.0; single grain and loose; few roots; few angular to subrounded schist, quartzite and granite stones; sharp straight boundary with bedrock. Humic Regosol (Typic cryorthent, Cumulic Regosol) Elevation: 780 m a.s.1.

136

ELLIS

Drainage: Free Aspect: North Slope: 10° Parent material: Sandy till Vegetation: Salix herbacea, Potvgonum viviparum, Carex bigelowii, Stereocaulon botryosum Black (2.5Y 2/1) humose fine sandy loam; pH 5.2; massive and fn'm; few 0-5 cm roots; no stones; sharp straight boundary. Grayish brown (2.5Y 5/2) fine sandy loam; pH 5.0; single grain and loose; 5-7 cm few roots; few angular to subrounded schist, quartzite and granite stones; sharp straight boundary. 7-10 cm Black (10YR 2/1) humose free sandy loam; pH 5.3; massive and firm; few roots; no stones; sharp straight boundary. 10 cm+ Light olive brown (2.5Y 5/4) fine sandy loam; pH 5.5; single grain and loose; few roots; few angular to subrounded schist, quartzite and granite stones; bedrock not encountered within 100 cm of surface. Podzol (Typic Cryorthod, Orthic Humo-Ferric Podzol)

Elevation: 670 m a.s.1. Drainage: Free Aspect: East Slope: 9° Parent material: Sandy till Vegetation: Empetrum nigrum, Faccinium myrtillus, Betula nana, Poa alpina, Stereocaulon botryosum 0-10 cm Very dusky red (10R 2.5/2) litter, fermented and humified organic matter layers; pH 4.4; moderate roots; no stones; sharp undulating boundary. 10-14 cm Light gray (5Y 7/1) f'me sandy loam; pH 4.7; single grain and loose; few roots; few angular to subrounded schist, quartzite and granite stones; narrow irregular boundary. 14-34 cm Very dusky red (10R 2.5/2) fine sandy loam; pH 5.2; single grain and loose; few roots; few angular to subrounded schist, quartzite and granite stones; narrow undulating boundary. 34 cm+ Olive yellow (2.5Y 6/6) fine sandy loam; pH 5.4; single grain and loose; few roots; few angular to subrounded schist, quartzite and granite stones; bedrock not encountered within 120 cm of surface. Bog Soil (Terric Borofibrist, Terric Fibrisol) Elevation: 640 m a.s.1. Drainage: poor; watertable at ca. 30 cm depth Aspect: East Slope: 4° Parent material: Sandy till Vegetation: Eriophorum angustifolium, Equisetum sp., Carex bigelowii, Salix spp. 0-33 cm Dark reddish brown (5YR 3/2) fresh and humified organic matter; pH 5.4; moderate roots; no stones; sharp straight boundary. 33 cm+ Dark gray (5Y 4/1) free sandy loam; pH 6.0; single grain and loose; few roots; few angular to subrounded schist and quartzite stones; bedrock not encountered within 60 cm of surface.

MICROMORPHOLOGICALASPECTSOF ARCTIC-ALPINEPEDOGENESIS,NORWAY 3.

137

M E T H O D S AND RESULTS

Undisturbed samples of each horizon were taken, in the vertical plane, using Kubiena boxes measuring approximately 7 X 7 X 4 cm. From these, thin sections were prepared on microscope slides of dimensions 5 X 7.5 cm and 2.5 X 7.5 cm, following impregnation with Araldite resin (FITZPATRICK 1970). Although there are several systems for the description of soil micromorphological phenomena (for example, BREWER 1964, BARRATT 1969, STOOPS & JONGER/US 1975), the scheme of FITZPATRICK (1977, 1980) was adopted since it enabled the description of both organic and mineral forms using a simple terminology.

Tab. 1: SOIL MICROMORPHOLOGICAL DATA Soil type Regosol

Depth Structure (cm) 0-2 GC 2-15 SG L

Organic matter Organic decomposition matter (%)

Faecal pellets (%)

Pores (%)

Detrital grains Illuvial and matrix coatings (%) (%)

St A A

56 3

17 2

19 19

25 78

0 5

Brown Soil

0-4 GC 4-12 SG L 12-48 SG L

St A St A A

43 8 2

17 4 1

20 17 21

37 75 77

2 7 12

Humic Regosol

0-5 5-7 7-10 10+

St A A St A A

62 3 74 2

49 1 53 1

30 30 14 18

8 67 12 80

0 2 0 3

Podzol

0-10

S S GC 10-14 SG L 14-34 G C SG 34+ L SB A

F S1 M St St A St A A A

43 44 47 13 10 1

5 6 19 6 10 1

57 56 50 17 35 32

0 0 3 70 55 67

0 0 0 3 4 15

Bog Soil

0-33 33-t-

F SI M

63

5

37

0

0

0

0

18

82

0

GC SG GC SG L

S

SG

Structure: G - granular; C - crumb; SG - single grain; L - lenticular; S - spongy; SB - subrounded blocky; A alveolar Organic matter decomposition: F - fresh; SI - slightly decomposed; M - moderately decomposed; St- strongly decomposed; A - amorphous The structure of each horizon was noted, along with the extent to which its organic matter was decomposed (Table 1). In addition, quantification of certain micromorphological features was attempted; for each horizon the area of occurrence of the various forms was determined on a percentage basis using an automatic point counter, making 250 counts per slide (Table 1). This gave an absolute error of approximately 2-6% at the 95% confidence limit (VAN D E R PLAS & TOBI 1965), a level of reliability which was considered acceptable in view of the nature of the interpretations which were to be made. Organic matter percentages shown in Table 1 include those of faecal pellets, since all pellets were observed to be exclusively organic in content. These values do not, however, include individual colloidal organic

138

ELLIS

particles, as these cannot be distinguished from the mineral colloidal fraction using an optical microscope. Both of these groups are considered as belonging to the soil matrix. The value for detrital grains and matrix also includes illuvial coatings. For any one horizon, therefore, the sum of percentage organic matter, pores and detrital grains and matrix is 100%, values for faecal pellets and illuvial coatings being components of the organic matter and detrital grains and matrix percentages respectively. In the case of the Podzol surface horizon (0-10 cm depth), three sets of data are given, corresponding to the litter, fermented and humified layers recognized within this zone.

4. 4.1.

DISCUSSION SURFACE HORIZONS

In thin section, surface horizons of the Regosol, Brown Soil and Humic Regosol are seen to contain organic matter of a predominantly strongly decomposed and amorphous nature (Table 1). Much of this material occurs in the form ofcomminuted fragments and faecal pellets, indicating participation of soil mesofauna in organic decomposition. The pellets are angular to subrounded in shape, rarely exceed 100/~m in diameter and generally appear not to be welded to the extent that they become unrecognizable as such (Photo 1). This would suggest that the principal mesofauna responsible for their formation are perhaps mites and enchytraeid worms (BULLOCK 1974, BABEL 1975). There are no apparent remains of fauna themselves, however, possibly as a result of both rapid decomposition upon death in the soil and severe shrinkage of live specimens during the period of drying that precedes sample impregnation. Strongly decomposed organic matter is mainly dark brown in colour and possesses no birefringence characteristics. This contrasts with the brownish yellow colour of fresh and slightly decomposed organic materials, as seen in the Podzol and Bog Soil surface horizons, which occasionally exhibit birefringence and in which the internal structure can frequently be recognized (Photo 2). Changes in colour on decomposition are considered to result from the activity of microorganisms (BABEL 1975), although specific organisms responsible for discoloration have not been identified. The advanced state of decomposition in the Regosol, Brown Soil and Humic Regosol suggests that the rate of decomposition at least equals that of litter supply to the soil surface; little fresh organic matter was observed even in the uppermost parts of their surface horizons. The activity of mesofauna in decomposition would appear more extensive in the Humic Regosol than in either the Regosol or Brown Soil, since faecal pellets constitute a far greater proportion of the organic matter in this soil type (Table 1). Smaller proportions of pellets in the others suggest, therefore, that decomposition by microorganisms is a more extensive process. This may be due to the Humic Regosol possessing litter components more palatable to mesofauna, a soil reaction more favourable for mesofaunal habitation, or both. Estimates of the organic matter content in the surface horizons of these three soil types range from 43% to 62% by volume, the remainder being occupied by pores, detrital grains and matrix (Table 1). Incorporation of organic matter into the upper mineral portion of the profiles is therefore apparent. This process is considered unlikely to result from any mesofaunal burrowing activity, since in none of the soils was there evidence for smooth-sided burrows. Furthermore, the absence of mineral inclusions within faecal pellets suggests that soil-ingesting fauna are unlikely to be present. Cryoturbation is a possible incorporating mechanism, although its effect could be only minor since horizon boundaries are always dis-

MICROMORPHOLOGICALASPECTS OF ARCTIC-ALPINEPEDOGENESIS, NORWAY

139

Photo I: Composite granular and crumb structure in the Humic Regosol (depth 0-5 cm, plain polarized light,frame length -- 4 ram). Faecal materialappears both as individualpelletsand loosely bound aggregatesofpelletsinassociationwith detritalgrains.Thelight areasrepresentpore space infflled wdth impregnating resin.

Photo 2: Spongy structure in the Podzol (depth 0-10 cm, plain polarized light, frame length ~ 2 ram). The plant remains are only slightly decomposed with some oftheir internal structure remaining intact. Note the faecal pellets inside the plant fragment (bottom left) indicating attack by mesofauna.

140

ELLIS

tinct and unconvoluted. The most likely mechanism, however, is considered to be translocation by percolating water, as suggested in previous micromorphological investigations (for example, JONGERIUS & SCHELLING 1960, BAL 1970). A large porosity, ranging from 190/0to 30°/o(Table 1), and the presence of large pores would certainly be expected to permit this process and there would be ample water for its operation during the annual thaw. Percentages of detrital grains and matrix suggest that there is more mixing of organic and mineral material in the Regosol and Brown Soil than in the Humic Regosol. This may be a function of a smaller translocation potential in the latter due to its greater duration of seasonally frozen ground conditions, during which time water is unavailable for the redistribution of soil constituents in solution or suspension (ELLIS 1980b). The association of organic and mineral material gives rise to a composite structure comprising both granular and crumb elements, similar to that recognized in certain arctic and alpine soils of Canada (BREWER & PAWLUK 1975, PAWLUK & BREWER 1975a, b). Faecal pellets produce the granular structural form, while the crumb structure consists of loosely bound porous aggregates of both organic and mineral components (Photo 1). In the Podzol surface horizon, organic matter appears fresh to slightly decomposed in the upper part, becoming increasingly decomposed with depth. This corresponds to the LFH layer sequence, a widely recognized characteristic ofpodzol surface horizons. Increasing decomposition is associated with an increased darkening in colour due to the activity of microorganisms and, as in the previous three soil types, much of the material in the lower part of the horizon occurs as comminuted fragments and faecal pellets resulting from mesofaunal activity. This produces a composite granular and crumb structure similar to that of the surface horizons already discussed. Fresh to slightly decomposed organic matter in the upper part of the horizon produces a spongy structure; organic components are brownish yellow in colour and internal structures of plant stems and leaves are still visible (Photo 2). The surface horizon of the Bog Soil is one in which there is very little apparent decomposition. The fresh to moderately decomposed components give rise to a spongy structure, similar to that observed in the upper part of the Podzol surface horizon. A small content of faecal pellets suggests that what little decomposition exists is due largely to the presence of microorganisms; the poor drainage of this profile is likely to inhibit mesofauna (ELLIS 1980b).

4.2.

SUBSURFACE HORIZONS

Organic matter in subsurface horizons can result from a variety of processes. In all except the Bog Soil, there is evidence of decomposition of plant roots in situ. These range from a slightly decomposed state in which internal structures are still visible to strongly decomposed specimens. Discoloration of root material appars to predominate over its comminution, suggesting that subsurface decomposition is largely attributable to the activity of microorganisms rather than mesofauna (BABEL 1975). In the Regosol, Brown Soil and Humic Regosol subsurface organic matter also occurs in minor quantities in the form of faecal pellets (Table 1). As in the case of the surface mineralorganic horizons, however, this is not considered attributable to mesofaunal burrowing because there are no mineral inclusions within the pellets. In addition, the pellets occur randomly throughout the soil, rather than being concentrated around roots as might be expected with the presence of subsurface organic-ingesting mesofauna. It is therefore more likely that the pellets are translocated into subsurface horizons by percolating water, although this

MICROMORPHOLOGICAL ASPECTS OF ARCTIC-ALPINE PEDOGENESIS, NORWAY

141

process is clearly of minor importance on account of the small number of pellets involved. Unlike any of the other profiles examined, the Humic Regosol possesses an organic-rich subsurface horizon (7-10 cm depth). This is thought to represent burial of a previously existing surface horizon by material moved en masse from upslope (ELLIS 1979, 1980b). In thin section, this horizon is clearly different from the predominantly mineral subsurface horizons of the remaining prof'des in that it shows the same composite structure as the present day surface horizon and similar contents of faecal and non-faecal organic matter (Table 1), indicative of its pre-burial status. It differs from the present surface horizon, however, on account of its smaller porosity, presumably the result of compaction on burial. The possibility of this horizon representing an organic-rich illuvial zone is discounted on both macro- and micromorphological grounds. Its boundaries with adjacent horizons are sharp, its content of mineral material is far lower than any other subsurface horizon examined (Table 1) and there is no evidence of coatings of illuvial organic matter surrounding mineral grains as has been reported for such a horizon in southern Okstindan (GR/FFEY & ELLIS 1979). Furthermore, the low translocation potential of this profile, as discussed earlier, would not favour illuviation of this intensity. In contrast to the surface horizons, there is too little organic matter in the majority of subsurface horizons to contribute significantly to the formation of soil structure. In such cases, single grain and lenticular structures predominate (Table 1). Single grain strtacture comprises individual detrital grains (Photo 3), indicating a lack of aggregation on account of small clay and organic matter contents. Lenticular structure (Photo 4) has been reported in subsurface horizons of many cold environment soils, for example, in Norway (GR/FFEY & ELLIS 1979, ELLIS 1980c, HARRIS & ELLIS 1980), Sweden (LYFORD & TROEDSSON 1973), Iceland (ROMANS et al. 1980), Spitzbergen (FITZPATRICK 1956), Scotland (ROMANS et al. 1966, ROMANS & ROBERTSON 1974) and Canada (BUNTING & FEDEROFF 1974, McKEAGUE et al. 1974, PAWLUK & BREWER 1975a, MERMUT & ST. ARNAUD 1981), where it has been attributed to freezing and thawing processes which in some instances have been supported by laboratory simulation experiments. With the exception of the Bog Soil, illuvial coatings of fines are present in subsurface horizons ofaU the soil types where they occur as deposits on the upper surfaces of both lenticular peds (Photo 4) and individual grains (Photo 5). This feature is also characteristic of cold environment soils in both Europe (for example, FITZPATRICK 1956, ROMANS et al. 1966, 1980, LYFORD & TROEDSSON 1973, BJt)RKHEM & JONGERIUS 1974, ELLIS 1980c, HARRIS & ELLIS 1980) and Noah America (for example, KUBIENA 1972, BUNTING & FEDEROFF 1974, McKEAGUE et al. 1974, BREWER& PAWLUK 1975, DE KIMPE et al. 1976, MERMUT& ST. ARNAUD 1981), being thought to result from translocation following the melting of ice in the soil. The illuvial fines appear to be most extensive in the Brown Soil and Podzol, in which they also increase with depth (Table 1). This would suggest free translocation throughout the profiles, probably because the soil is very porous and drainage is rapid. In addition to single grain structure, the illuvial horizon (14-34 cm depth) of the Podzol exhibits granular and crumb structural elements (Photo 6). Although this is a widely recognized characteristic of podzol illuvial horizons, its mode of formation is the subject of some debate. Certain authors (for example, DE CONINCK et al. 1974, DE CONINCK 1980) have argued that it results from comminution of roots by mesofauna within the illuvial horizon. At Okstindan, however, this would appear not to be the case, because there are so few roots at this depth and there is a general lack of comminution of the few decomposing roots that do occur. It seems more likely that the development of a granular structure at this depth

142

ELLIS

.

..--

,.,

~

, "_

''~

~"~.

'

4"

'~'-.

"*

-~'~..4.~.~-: ~

--

-

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t ~ '

"

.,I~-, ,It~i. ~

'~-~.

,,

,

,-..-~,

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';

.-~,~-"~-

~-

,'~

Photo 3: Single grain structure in the Brown Soil characterized by individual, unaggregated detrital grains (depth 4-12 cm, partially crossed polarized light, frame length = 4 mm). Here pore space is represented by the light gray areas.

Photo 4: Lenticular structure in the Podzol with dark coatings ofilluvial fines on the upper surfaces of the horizontally elongated peds (depth 34 cm+, plain polarized light, frame length -- 4 ram).

MICROMORPHOLOGICAL ASPECTS OF ARCTIC-ALPINE PEDOGENESIS, NORWAY

143

Photo 5: A large detrital grain in the Brown Soil with a coating of illuvial fines appearing as a dark deposit on its upper surface (depth 4-12 era, plain polarized light, frame length = 2 ram).

Photo 6: Granular and crumb structural elements in the Podzol showing both individual and aggregated granular units (depth 14-34 cm, plain polarized light, frame length = 4 mm).

144

ELLIS

Photo 7: Iron-rich illuvial coatings appearing as dark films around detrital grains in the Podzol (depth 14-34 cm, plain polarized light, frame length ~ 2 ram).

Photo 8: Subrounded blocky structure in the Podzol (depth 34 c m + , plain polarized light, frame length = 4 mm). The dense aggregates of mineral material have become partially disintegrated and rounded. Note the dark coatings ofilluvial fines on the upper surfaces of many of the peds and also on the large detrital grain on the left.

MICROMORPHOLOGICALASPECTSOF ARCTIC-ALPINEPEDOGENESIS,NORWAY

145

Photo 9: Alveolar structure in the Podzol characterized by smooth-sided ovoid pores (depth 34 cm-I-, crossed polarized light, frame length ~ 4 ram). Unlike the previous photos, here the pores appear black due to the specimen being viewed in crossed polarized light.

Photo 10: A large biotite grain in the Brown Soil with a smaller grain overlying it on the left (depth 4-12 cm, plain polarized light, frame length ~ 2 mm). The grain appears to be undergoing expansion along cleavage planes, areas of fracture within the grain being represented by the light linear zones in its lower half. Note also the dark coating ofilluvial fines on its upper surface.

146

ELLIS

is caused by iUuvial faecal pellets translocated from the surface organic horizon, or wetting and drying ofiUuvial organic matter in colloidal form, or both. Formation of the crumb structure involves aggregation of these granular units and mineral material, possibly as a result of precipitation ofilluvial organo-metallic complexes (ESWARAN et al. 1972, FITZPATRICK 1980). This horizon also shows evidence of iron-rich illuvial coatings which, in contrast to the illuvial fines discussed above, completely surround mineral grains (Photo 7). This probably represents the effect of improved adhesion afforded by greater concentrations ofilluvial sesquioxides and colloidal material. In addition to its lenticular structure, the Podzol parent material (34 cm + depth) contains subrounded blocky and alveolar elements (Photos 8 & 9). The former comprises dense aggregates of mineral material. At this depth aggregation is likely to be the result of clay, rather than illuvial organic matter and sesquioxides, in the matrix. Similar features in mountain soils of Scotland have been interpreted as lenticular peds which have become partially disintegrated and rounded during soil movement by cryoturbation (ROMANS et al. 1966, ROMANS & ROBERTSON 1974). The same is likely to be so at Okstindan, although any cryoturbation must be slight since much of the lenticular structure remains intact along with the coatings of illuvial frees visible on upper surfaces of the peds (Photo 8). The presence of the alveolar structure in this horizon (Photo 9) might be caused by soil freezing, during which gas bubbles are released. This has been suggested previously in micromorphological investigations of soils in Norway, Spitzbergen and Canada (FITZPATRICK 1956, BUNTING 1977, HARRIS & ELLIS 1980). Micromorphological evidence for weathering was observed only in biotite grains, some of which showed partially accordant fracture surfaces, probably resulting from hydration and associated expansion along cleavage planes (Photo 10). The dearth of such weathering features may be due to the accordance of fracture surfaces being destroyed by cryoturbation, although this process appears to be of only minor importance and removal of evidence in this way is therefore likely to be of no great significance. This apparently slight weathering may be the result of an abundance of resistant minerals in these particular soils (ELLIS 1980a) and also the inefficiency of freeze-thaw weathering in arctic-alpine environments (WHITE 1976, THORN 1979).

5. CONCLUSIONS Micromorphological examination suggests that in the four freely draining soil types organic matter is being decomposed by both microorganisms and mesofauna, the latter being considered responsible for the production of faecal pellets and comminuted organic fragments. In the poorly draining Bog Soil there appear to be very few mesofauna and organic decomposition is thought to be caused primarily by microorganisms. Organic matter in surface horizons has resulted in the development of spongy, granular and crumb structures. Subsurface horizon structure is predominantly single grain and lenticular, with associated coatings of illuvial fines on the upper surfaces of peds and individual grains. These characteristics appear common to many soils of cold environments and are thought to be the result of freezing and thawing processes. The Podzol illuvial horizon exhibits granular and crumb structural elements which are considered to arise from the development of granular organic forms and their aggregation with mineral material by the precipitation of illuvial organo-metallic complexes. Evidence for weathering is slight, occurring only in the form of biotite grains fractured by hydration.

MICROMORPHOLOGICALASPECTS OF ARCTIC-ALPINEPEDOGENESIS, NORWAY

147

ACKNOWLEDGEMENTS

Much of the research described in this paper was conducted during tenure ofa NERC Training Award in the Department of Geography, Reading University. Illustrative material was prepared by members of the Geography Department technical staffat the University of Hull. Thanks are expressed to Dr. E.A_ FitzPatrick and Mr. I.M. Fenwick for their helpful criticism of the original manuscript. REFERENCES

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