Macromorphology

The morphologies of both the surface and subsurface of Arctic soils are shaped by cryogenic processes (Figs. 1.1 and 1.2). The soil surface is associated with various types of patterned ground caused by frost heave and sorting, while the subsurface is dominated by cryoturbation that results in irregular or broken soil horizons, involutions, organic intrusions, and organic matter accumulation, usually along the top of the permafrost table. Oriented rock fragments (Fig. 1.1), silt-enriched layers and silt caps are also common (Bockheim and Tarnocai 1998). The freeze-thaw process produces granular, platy and blocky structures (Table 1.3). The subsurface soil horizons often have massive structures and are associated with higher bulk densities, especially in fine-textured soils. This massive structure results from cryostatic desiccation (cryodesiccation), which develops when the two freezing fronts (one from the surface, the other from the permafrost) merge during freeze-back. Although these macromorphological properties occur primarily in the active layer, they also can be found in the near-surface permafrost because of the dynamic nature of the permafrost (Bockheim and Tarnocai 1998).

Arctic soils generally have high moisture content, especially near the permafrost table, which acts as a moisture barrier. As a result, gleying associated with grayish colours and redoximorphic features is a common occurrence, especially in loamy and fine-textured soils.

Permafrost Diagram
Fig. 1.1 Schematic diagram showing a nonsorted circle type of patterned ground with discontinuous and broken cryoturbated soil horizons (y) and oriented stones in the active layer, and ice lenses in the permafrost layer
Objetos Cueva Lovelock
Fig. 1.2 Strongly cryoturbated soil with contorted and broken soil horizons
Table 1.3 Morphological characteristics of selected pedons

Pedon

Depth

Ice

Special

no.

Horizon

(cm)

Colour

Texture8

Structure6

content

features

1

Ck

0-15

10YR 4/1.5m

fSL

sbk

10% gravel

Cky

15-60

10YR 3/2m

SiL

sbk

-

-

Ckyz

60-100

10YR 3/2.5f

SiL

sbk

medium

ice crystals

2

Ajjl

0-10

10YR 3/2m

C

fgr

_

-

Ajj2

10-18

10YR 4/3m

C

fgr

-

-

Bw

18-34

10YR 4/3m

C

lenticular

_

-

Wf/Bgf

34-40

10YR 4/2f

C

lenticular

high

-

Wf

40-42

-

-

-

ice

pure ice

Wf/Cf

42-57

10YR 4/2f

C

lenticular

high

-

Wf

57-110

-

-

-

ice

pure ice

3

Ah

0-8c

10YR 2/1m

-

gr

_

-

Bmyl

0-14

10YR 4/3m

SL

gr

_

-

Bmy2

14-55

10YR 4/2m

SL

gr

_

-

Cy

55-100

10YR 4/2m

SL

sg

_

oid

Ahyz

40-45c

10YR 2/1f

-

sl

high

-

Cyz

45-80c

10YR 4/2f

SL

sl

high

oid

4

Bmky

2-44c

10YR 3.5/2m

SL

gr

_

vesicular

BCky

10-32c

10YR 3/3m

SL

gr

_

vesicular

Ahky

1-15c

10YR 2/1m

SL

sg

_

vein ice

Ckz

46-100

10YR 4/1m

SL

sl

_

ice crystals

5

A1

0-5c

10YR 3/2m

fSL

platy

_

-

A2

5-40c

10YR 3/2m

fSL

platy

_

-

Ajj

62-70c

7.5YR 3/2m

fSL

fgr

_

oid

C1

0-5c

2.2Y 4/2m

fSL

reticular

_

-

C2

5-25c

10YR 3/2m

fSL

reticular

_

-

Bwjj1

20-60c

10YR 4/2m

fSL

lenticular

_

-

Bwjj2

20-65c

10YR 4/2m

fSL

reticular

_

-

Bwjj3

55-68c

2.5Y 5/1f

fSL

massive

_

-

Wfm/Cf

68-110c

7.5YR 4/1f

fSL

ataxitic

high

70% ice

Cf

80-110c

2.5Y 4/1f

fSL

platy

_

-

6

Oi

0-11c

5YR 3/2m

Peat

-

_

-

A

0-8c

2.5Y 3/2m

SiL

gr

_

-

Bw

0-42c

2.5Y 3/2m

SiL

sbk

_

-

Bwj

0-62c

2.5Y 5/3m

SiL

sbk

_

-

Bgfm

12-15c

2.5Y 3/2f

SiL

sbk

_

-

Ajfm

0-10c

10YR 2/1f

SiL

platy

_

-

Oajfm

0-9c

10YR 2/2f

Organic

massive

_

-

BCgfm

0-10c

2.5Y 3/2f

SiL

massive

_

-

7

Oh

0-30

2.5YR2.5/2m

Peat

-

_

-

Ohz

30-40

5YR 2.5/2m

Peat

-

_

-

Omz1

40-150

7.5YR 3/2f

Peat

-

medium

-

Omz2

150-215

7.5YR 3/2f

Peat

-

medium

-

Wz

215-268

-

-

-

ice

pure ice

Cz

268-288

-

Si

-

high

(continued)

1 Arctic Permafrost Soils Table 1.3 (continued)

Pedon

Depth

Ice

Special

no.

Horizon

(cm)

Colour

Texturea

Structure6

content

features

8

L,H

0-6c

10YR 3/2m

-

litter

-

Bmgyl

0-12

10YR 5/3m

SiL

gr

-

oid

BCgyl

12-24

10YR 4/4m

SiL

sbk

-

oid

BCgyzl

24-47

10YR 4/4m

SiL

sbk

-

oid

Cz1

47-60

5Y 3/1m

SiL

massive

-

-

Cz2

60-100

5Y 3/1m

SiL

massive

-

-

Bmgy2

0-24

10YR 4/2m

SiL

gr

-

oid

BCgy2

24-34

5Y 3/1m

SiL

sbk

-

oid

BCgyz2

34-56

5Y 3/1m

SiL

sbk

-

oid

aTexture: SiL silt loam; SL sandy loam; fSL fine sandy loam; Si silt; C clay

•"Structure: gr granular; fgr fine granular; sg single grain; sl structureless; sbk subangular blocky cRange of thicknesses-given for discontinuous, cryoturbated horizons d oi organic intrusions aTexture: SiL silt loam; SL sandy loam; fSL fine sandy loam; Si silt; C clay

•"Structure: gr granular; fgr fine granular; sg single grain; sl structureless; sbk subangular blocky cRange of thicknesses-given for discontinuous, cryoturbated horizons d oi organic intrusions

Thin eluvial or leached layers resulting from the brunification process occur primarily in sandy soils in the southern part of the Arctic. Salt crusts on the soil surface are also characteristic. These salt crusts develop during dry periods in the summer because of higher evapotranspiration from the soil surface.

Thixotropy, which results in an unstable soil surface, is frequently present in the thawed portion of permafrost-affected soils, and is often associated with soils having high silt content. When a thixotropic soil dries out, a characteristic vesicular structure develops.

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