Soil Morphological Properties

Antarctic soils are coarse-textured, with coarse particles >2 mm typically exceeding 50% (Table 2.1). Horizon development is weak, and mostly restricted to colour changes that diminish in intensity with increasing depth, to lithologi-cally related textural changes, or to the presence of salt accumulations (Fig. 2.4). The soil surface is usually a stone pavement including loose material derived from fragmentation of surface clasts. On younger surfaces, clasts are mainly angular, coarse and unweathered, while on older surfaces, clast rounding, rock pitting, ventifaction, oxidation and disaggregation may be prominent. Weakly developed vesicular structure may be present in the surface horizon as a result of freezing when the soil is moist. Where there is an increased proportion of fine material, a thin surface crust may be present. Below the surface, the soil is usually structureless and pulverulent, except where salt concentrations occur, when the soil material may be firmly cohesive. In older soils, the disaggregation of coarsegrained clasts by salt weathering results in rock ghosts that indicate a highly stable soil environment.

Table 2.1 Coarse fraction (weight %) for a typical soil from Marble Point, McMurdo Dry Valleys area

Soil depth (cm)

Weight (%) of coarse fractions

2-5 mm

5-20 mm

20-75 mm

0.1-75 mm

>2 mm (whole soil)

0-3

7

55

4

90

66

3-15

6

11

41

88

58

15-32

7

11

39

87

57

32-45

8

12

53

92

73

45-69

11

22

41

91

74

69-100

10

20

79

79

49

Fig. 2.4 Profile of weathering stage 3 soils from dolerite and sandstone till from the Asgard Range in Wright Valley. The surface pavement is well-developed, with moderate reduction, rounding and staining of surface boulders. A weakly developed salt horizon is present, with a concentration of salts to the right of the tape beneath a boulder that was removed. Ice-cemented permafrost is at 35 cm

Fig. 2.4 Profile of weathering stage 3 soils from dolerite and sandstone till from the Asgard Range in Wright Valley. The surface pavement is well-developed, with moderate reduction, rounding and staining of surface boulders. A weakly developed salt horizon is present, with a concentration of salts to the right of the tape beneath a boulder that was removed. Ice-cemented permafrost is at 35 cm

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