Properties and soil development of late-Pleistocene paleosols from Seward Peninsula, northwest Alaska

GEODER.MJ Geoderma 71 (1996) 219-243

Properties and soil development of late-Pleistocene paleosols from Seward Peninsula, northwest Alaska Claudia Hijfle a3*, Chien-Lu Ping b aAlaska Quatenav Center, University of Alaska Fairbanks. Fairbanks, AK 99775, USA h Agriculture and Forestry Experiment Station, Palmer Research Center, lJniL,ersi@ of Alaska Fairbanks, Palmer, AK 99645, USA Received 24 October

1995; accepted

18January 1996

Abstract Soils on Seward Peninsula, northwest Alaska, that were buried about 17,500 years ago and froze after burial present a unique opportunity to study soil development under the conditions of the last glacial maximum. Stratigraphic sections were excavated during the summers of 1993 and 1994. Study sites were located on steep banks of thaw lakes. We described soil morphology (including cryogenic features) and sampled for chemical and physical analyses. All paleosols are permafrost soils that developed in calcareous loess and have roots present throughout. Colors are predominantly grayish and either reflect original loess color or periodic saturation of the soils (possibly caused by the permafrost environment). Active layer thicknesses before burial ranged from 32 to 64 cm. Organic carbon contents average 3.0%, carbon/nitrogen ratios average 9, cation exchange capacities average 19.1 cmol/kg, and base saturations generally exceed 100%. There is no evidence of leaching in the profile. Soil formation occurred simultaneously to the deposition of the parent material loess. Morphological and chemical data suggest that soil development was weak and confined to organic matter accumulation, and hydrolysis of iron. All studied soils show similar morphological, chemical, and physical properties, which suggests a relatively uniform mode of soil formation in the study area. Soil-forming conditions on northern Seward Peninsula during the last glacial maximum were severe, and combined with fairly continuous loess deposition they resulted in weakly developed, nutrient-rich soils.

* Corresponding Center, University

author. Present address: Agriculture and Forestry Experiment Station, Palmer of Alaska Fairbanks, Palmer, AK 99645, USA. Fax: + 1 (907) 746-2677.

0016-7061/96/$15.00 0 1996 Elsevier Science B.V. All rights reserved PII SOO16-7061(96)00007-9

Research

220

C. Hi$e, C-L. Ping / Geoderma 71 (19961219-243

1. Introduction Paleosols have been commonly used as tools for the reconstruction of paleoclimatic conditions (e.g., Catt, 1989; Liu et al., 1985; Bronger and Bruhn, 1989; Messerli and Frei, 1985; Reider, 1990). However, very few permafrost paleosols have been studied and described (Brown, 1969; Smith et al., 1986; Gubin, 1990). Most of the arctic and subarctic soils of Pleistocene age developed during interglacial times in material deposited during the previous glacial period (e.g., Tarnocai, 1990). Few soils that formed during full-glacial times and might help to define the environment during those cold periods which comprised the largest part of the Pleistocene epoch are preserved. Approximately 17,500 years ago the Devil Mountain Lakes maar eruption occurred on northern Seward Peninsula, northwest Alaska (Fig. 1). The resultant basaltic tephra fell cold (J. Beget, pers. commun., 1993) and covered an area of at least 750 km’. The tephra fell on a landscape that was subject to the severe environmental conditions of the last glacial maximum (ca. 18,000 years B.P.). With the newly deposited tephra on top of the former surface, permafrost must have moved upwards rapidly, probably during the winter that followed the eruption. The buried soils and vegetation froze and have been frozen ever since, preserving the paleo-features well and creating a unique “snapshot” of the time of burial. Freezing of the soils minimizes problems that pedologists generally encounter when studying paleosols such as diagenetic changes of pH, organic carbon, carbonate, and iron content after soils were buried (Valentine et al., 1987). The sharp

Fig. 1. Beringia during the last glacial maximum (outlined hy 100 m isobath) and land-based ice limits. Location of the Bering Land Bridge National Preserve, and the study area. (Extent of glacial ice limits in East Beringia and Chukotka after Hamilton and Mann, 1996, and in West Beringia after Bespalyy, 1984.)

C. Hiife, C.-L. Ping / Geodem

71(1996) 219-243

221

boundary between tephra and fine-grained soils removes another obstacle soil scientists face when studying paleosols: the difficulty of recognizing them (Fenwick, 1985). During the cold periods of the Quatemary, the development of land-based ice sheets lowered sea levels worldwide. The broad, shallow Bering and Chukchi Shelves were exposed, creating a land connection between Asia and North America; the Bering Land Bridge. The land bridge was at its maximum extent during the last glacial maximum, stretching over 1600 km from north to south between the frozen Arctic Ocean and the remaining Bering Sea (Fig. 1). The location of the tephra-buried soils, close to the present Chukchi Sea, places them near the center of the former Bering Land Bridge (Fig. 11. The Bering Land Bridge allowed fauna and flora to commute between the two continents throughout the Quatemary. At the end of the Pleistocene, it is of particular interest because the bridge was probably the migration route of humans from the Old into the New World (Miller-Beck, 1982). The paleoenvironment of the late-Pleistocene Bering Land Bridge and of Beringia, the predominantly ice-free region between the Kolyma River of northeast Russia and the Mackenzie River of northwest Canada (Fig. 1) has been discussed for decades (e.g., Hopkins, 1967; Hopkins et al., 1982; Cwynar and Ritchie, 1980; Guthrie, 1990) and many different approaches to its paleoenvironmental reconstruction have been taken, including the studies of pollen, plant macro-fossils, megafaunal remains, and beetles. The Shared Beringian Heritage Program, developed by the US National Park Service, is a long-term study of traditional lifeways, biogeography, paleoecology, and landscape development in the Bering Land Bridge National Preserve. This project is part of the paleoecology and landscape development component and includes the study of the soils and vegetation buried by the Devil Mountain Lakes tephra. The purpose of this paper is to provide a comprehensive description of the morphological, chemical, and physical properties of the buried soils, and a discussion of their soil development.

2. Methods The study area is located around the Devil Mountain Lakes of northern Seward Peninsula, northwest Alaska (Fig. 21, within the boundaries of the Bering Land Bridge National Preserve (Fig. I). Paleosols are exposed on steep banks of thaw lakes (basins created by melting permafrost). We assume that the studied soils were undisturbed because the banks of these lakes are actively eroding. During summers the frozen banks of the lakes continuously thaw and slump into the lake. Any given segment of the lake edge will disappear in a matter of a few years. At several sites the paleosurfaces are tilted (up to about 45”). The strata show a dip towards a gully on the right (facing the section) at one location, and dips towards the lake at other sites. Tephra layers, as well as the surfaces of massive ground ice (if present) dip at the same angles. In no case does the tephra seem disturbed, and layers are still clearly visible. One explanation for these tilts is that the tephra fell on slopes. Considering the unlikeliness of ice wedges growing at such steep angles and that the tephra probably would have been reworked and moved down-slope after its deposition

222

C. H$e,

Chukchi Se0

C.-L. Ping / Geodenna 71 f 1996) 219-243

Cope Espenkrg

Kotzebue Sound

Fig. 2. Study sites on northern Seward Peninsula,

Alaska.

on a fairly steep slope, it is more likely that the tilts occurred after the burial and are linked to the thaw lake formation. During the expansion of thaw lakes in the summer large blocks of material at the lake edge disconnect from their surroundings (caused by thawing ice wedges behind those blocks) and slowly slump into the lake as single masses. Their stratigraphy stays intact until they break up into smaller pieces. Another possible explanation for the tilt is a plastic deformation of frozen material in one piece after the removal of the neighboring supporting area due to thaw lake formation. This process has been described in Russian literature (Gasanov, 1981). Neither of these hypotheses have been tested but it seems reasonable to assume that the studied soils have an unaltered stratigraphy. The paleosols are overlain by tephra of various thickness. In order to ensure that the soils have stayed frozen since their burial, we examined only those soils that had been covered with at least one meter of tephra. In cases with less tephra coverage, we required “intact” paleovegetation, suggesting that the active layer (the part of the soil that thaws out annually) after burial never reached the paleosol. The tephra is generally overlain by fine-grained material, presumably loess, and then an organic layer, in which the present vegetation is rooted. Present active layers range from ca. 25 to 55 cm. Field work was conducted during the summers of 1993 and 1994. The banks were excavated using shovels and a gasoline-powered permafrost drill to dig back into the lake wall to a point where the stratigraphy was undisturbed and the paleosols could be studied and sampled in a frozen, and presumably unaltered, state. We excavated 18 stratigraphic sections. All buried soils in these sections have similar morphological, physical, and chemical properties (Hiifle, 1995). Ten selected profiles

C. H$i’e, C.-L. Ping/Geodem

71 (1996) 219-243

223

will be described here. Documented morphological properties include field texture, structure, color, redoximorphic features, and root distribution according to the Soil Survey Manual (Soil Survey Division Staff, 1993). Redoximorphic features were described according to Vepraskas (1992). All soil depths were measured from the paleosurface downwards. The analytical methods followed procedures defined in the Soil Survey Investigation Report No. 42 (Soil Survey Laboratory Staff, 1992) unless otherwise specified. All values were determined with air-dried soil samples and corrected to oven-dried weights. Particle size distribution was determined by the Bouyoucos-hydrometer method after carbonate removal, pH (H,O) was measured in saturated paste, electrical conductivity from a saturation extract, and carbonate equivalents were determined by the gravimetric method for loss of carbon dioxide. Cation exchange capacity and exchangeable cations were extracted by 1 N NH,OAc and determined by steam distillation and atomic adsorption, respectively. Fe and Al were extracted by dithionite-citrate-, sodium pyrophosphate-, and ammonium oxalate-solutions; the latter was also used for Si extraction. Total C, N, and S were determined by a Leco CNS-2000 analyzer, and organic carbon contents were calculated by subtracting carbonate-carbon values from total carbon values. The presence of iron sulfides was verified qualitatively in the field by applying 1 N HCI; the smell of H,S was used as positive identification. Description of cryogenic features, including ice lenses, ice wedges, and massive ground ice followed standard literature in periglacial geomorphology (e.g., Washburn, 1973; Williams and Smith, 1989; French, 1976). Ice lenses are horizontal features formed by water moving towards freezing fronts during freeze-back. Ice wedges are massive ice features, often wedge-shaped, formed by cracking of the ground in the winter and water accumulating and freezing in the cracks. Large ice masses that could not be positively identified as ice wedges were termed “massive ground ice”. ice nets were first recognized in Russia and are well documented in the Russian literature (Zhestkova, 1982; Shur, 1988). To date, they have not been described in the English literature. Ice nets are characterized by horizontal and vertical ice accumulations and form by a combination of two processes. Horizontal ice accumulations are ice lenses formed due to water migration towards freezing fronts. Vertical ice accumulations are a result of desiccation; the soil cracks when water is drawn away to the freezing front. Subsequently, the cracks fill up with sublimation ice. Ice lenses and ice nets result in platy and blocky soil structures, respectively, upon thawing. The cryogenic features and structures described above were used to estimate paleoactive layer depths (the active layer is the upper part of the soil that thaws annually). For this measurement it is important to note that a “transient layer” commonly forms between the active layer and the permafrost table and represents the depth of thaw during exceptionally warm summers (Shur and Ping, 1994). This transient layer is considered to be part of the permafrost as well as the active layer, since it is usually frozen for two consecutive years or more but does thaw out occasionally. We refer to active layer values as being “true” values for the average depth of seasonal thaw when indicated by the top of ice-rich layers, ice nets, and blocky structures which form in the transient layer. “Maximum” active layer values refer to the maximum depth of thaw as indicated by the tops of massive ground ice bodies, predominantly in form of ice

8-l

4-12 2-10 s-15 2-5

5-10 ’

O-12 12-18 18-25 25-32

O-10 20-40 40-60 60-80 80-100 100-125 125-145

Bw Bgl’ Bg2 ” Mg3 ’

BW

Whitefjsh Thawpond

Lake Rhonda 3

‘ ’

c ’

L

’

O-IO b

o-4 IO-55 55-65 65-75

A Cl c2 Abl

I

3/4

3/2 4/1,3/1,5YR 5/8-4,‘6 4/l, 3/ I, 5YR 5/8-4/6 3/2

IOYR 3/2 5Y 3/2 5Y 3/l 5Y 3/l-2.5/1 5Y 2.5/I 5Y 3/l 5Y 3/i

7.5YR 3/2,3/4, IOYR 5/2 5YR 2/I 80%, N2/0 20% 5Y3/ I-N3/0 5Y4/ 1-N4/0

2.5Y 2.5Y 2.5Y 2.5Y

IOYR 3/3-3/2 2.5Y 3/2 2.5Y, 1OYR 3/2 5Y 4/1-3/l

O-IO IO-20 20-40 6-8

Eh’cho Lake

2.5Y 4/2,3/l-3/2,5YR 5Y 3/2 5Y 4/2 5Y 2.5/I

o-4 O-20 20-44 44-52

BCg Cgl Cg2 Cg3 Cg4 Cg5

Alaska

Moist color

3-6 7-15 20-30

(cm)

Thickness (min-max)

on Seward Peninsula,

Al A2 A3 Bg ”

Mottles

’

O-5 5-20 20-50

A

Bg’ &2

Depth (cm)

of paleosols

Pedon & horizon

and physical properties

Ulu Lake

Lake Rhonda 1

Table I Morphological

15% 15%

3vf,3f 3vf.3f 2vf, I m 2vf 2vf,2f, I c 2vf,2f 2vf,2f

3 vf,lf 3vf,2f,2m 3vf, I f 2vf

3vf,2f,2m 3vf,2f 2vf,2f 3vf,2f

SiL SiL SiL SiL SiL SiL SiL

SiL SiL SiL SiL

SiL SiL SiL SiL

SiL SiL SiL SiL

3vf,3f, I m 3vf, 2f 3vf,lf 3vf

Field texture

SiL SiL SiL SiL

h

2vf. I m 3vf,lf,lm 3vf,lf,lm n.d.

Roots

16 16 22 20 20 22 20

16 18 16 18

18 18 18 20

n.d. n.d. 20 n.d.

10 11 14 n.d.

% Sand

66 72 68 66 70 66 70

69 67 71 63

75 68 71 75

n.d n.d 69 n.d

83 80 79 n.d

Silt

18 12 10 14 8 11 IO

14 16 13 20

7 14 11 4

n.d. n.d. 10 n.d.

6 9 7 n.d.

Clay

Bw Bgl Bg2 Bg3 BCg Ca

A Bwl Bw2 Ab

Tempest Lake B

Fritz Lake

’ Contains

Bw Bgl a Bg2 a BCg a tephra

Tempest Lake A

O-3 3-24 24-39 o-41 o-4 1 o-3 20-25 12-15 O-25 9-10

o-5 5-15 IO-20 20-25 IO-15 5Y 3/l

3-13 O-12 15-35 7-12

8-15 28-32 5-10 4-8

3-15 lo-27 1-5 4-15 5-47 ’ c c c

visible.

IOYR 3/l 2.5Y 4/2, 2.5Y 4/I 2.5Y 4/2 IOYR 3/2 5Y 2/l nd.

1OYR 3/3 N3/0 5Y 3/l 5Y 3/l 5Y 3/2, N3/0 n.d.

1OYR 3/2 N2.5/0 5Y 3/l, N3/0 5Y 3/l n.d.

1OYR 3/2,4/6 1OYR 3/2 60%,2.5YR 2.5Y 2.5/I 5Y 2.5/l n.d.

2.5Y 3/l 2.5Y 4/I, 3/2 5Y 2.5/l 2.5Y 4/2 2.5Y 3/l 2.5Y 4/ 1 2.5Y 4/2 2.5Y 4/2 5Y 3/2

roots. ’ No boundary

o-2 2-13 13-30 30-5 1 51-61 61+

o-3 3-17 17-30 30-40

O-JO IO-40 1O-40 40-45

o-5 5-30 30-32 32-43 43-67 67-90 90-110 110-130 130+

iron sulfides. b Based on preserved

Bg ’ tephra

Bw BC Bgl = Bg2 a tephra

Swan Lake

a a a a

A Bw Abl Bwbl Ab2 Bwb2 BCI BC2 BC3

Egg Lake

3/2

40%

3vf.3f 3vf,3f 3vf,3f, 3vf 2vf,2f _

n.d. nd. n.d. nd. n.d. SiL

lvf _

Im

3vf,3f,2m 3vf,3f 2vf

3vf,2f 2vf I -2vf I-2VF -

n.d. 3vf,3f, I m 3vf 3vf,3f, 1m 3vf,3f 2vf Ivf,lf,lm lvf lvf

SiL SiL SiL SiL SiL SL

SiL SiL SiL SiL SiL 20

SiL SiL SiL SiL SL

SiL SiL SiL SIl LS

SiL SiL SiL SiL SiL SiL SiL SiL SiL

18 15 20 15 20 63

21 nd 35 18 18 72

22 20 20 14 56

14 20 n.d. 14 76

16 18 20 18 28 19 16 15 10

74 73 70 79 72 31

75 n.d. 57 74 76 8

74 74 71 75 36

70 65 n.d. 73 22

76 62 72 76 66 65 73 72 68

8 12 10 6 8

8 8 6

4 6

8 20 8 6 6 16 10 13 23

2

226

C. Hiijle,

C.-L. Ping/

Geoderma

71 (1996) 219-243

wedges. In our study we estimated paleo active layers mostly by determining the true paleo permafrost table (excluding the transient layer), therefore they represent maximum thaw depths. Knob-like paleo-microtopography was classified as earth hummocks (Washburn, 1973). Measurements were taken as diameter and height (in case of round features) or width, length, and height (in case of elongate features) after carefully removing the tephra. In order to ensure that all investigated paleosols were buried at the same time, radiocarbon dates were determined for each site. Samples were submitted to Beta Analytic Inc. in form of herbaceous plant material and shrub wood from the surface or, if those were absent, as bulk material from the uppermost soil horizon.

3. Results The paleosols on Seward Peninsula exhibit the distorted, ruptured and discontinuous horizons common to many cryogenic soils (Rieger, 1983; Ping and Shur, 1994). Horizon thickness values are often difficult to determine and of limited use. Minimum and maximum thickness of each horizon provide more valuable information, and sketches of the soils profiles best describe the spatial complexities involved (Fig. 3). Morphological, physical, and chemical properties of the paleosols are presented in Tables I and 2. The basaltic tephra covering the 10 paleosols ranges in thickness from 0.65 m to 5.2 m. All paleosols are developed in a silt loam parent material. Roots are abundant throughout the profiles at all sites. The determination of the density of roots was based on well preserved roots that presumably have been frozen since permafrost encased the paleosols after their burial. Most iron sulfide mottles have very distinct boundaries, some are more diffuse. They vary in size and shape from small, round concentrations of few millimeters in diameter (some surrounding roots or rodent dung), to irregular three-dimensional shapes in the order of few decimeters to whole horizons. A horizons were identified by coloration and/or organic carbon contents. Bw horizons were distinguished mainly by coloration; generally, they have a slightly more brownish color than BC and C horizons. Bg horizons are horizons with colors of 5Y hue with values of 4 or less and chromas of 2 or less, and horizons colored by iron sulfides (with distinct blackish colors). 3. I.

Soil

age

The radiocarbon ages for paleo-surface material from each site are listed in Table 3. There is a large variation in ages for a surface presumed to be of uniform age (16,880 + 120 years B.P. to 19,990 f 160 years B.P.). This range is possibly caused by the difference in dated material; soil bulk samples are expected to be older than surface plant material since they represent an accumulation of datable material. Another source of error could be contamination which, in most cases, leads to a younger date. The tephra covering the paleosols has been positively identified as of the same origin at

8.2 8.0 7.9 7.9

8.2 8.1 7.9 7.9

Eh’cho Lake A O-10 Cl 10-55 c2 55-65 Abl 65-75

Whitefish Thawpond Bw o-12 Bgf 12-18 Bg2 18-25 Bg3 25-32

Bg

8.0 8.2 8.1 8.0

O-4 O-20 20-44 44-52

Ulu Lake Al A2 A3

8.4 8.2 8.0 N.D.

0.69 0.89 1 0.57

0.07 0.07 0.08 0.07

n.d. n.d. 0.27 n.d.

0.45 0.54 0.79 N.D.

(S/m)

(paste)

(cm)

2.8 2.9 3.0 3.9

3.0 2.0 2.3 3.9

7.1 3.4 2.9 2.6

2.4 2.0 2.6 2.2

(%)

OC

0.30 0.34 0.36 0.42

0.31 0.24 0.25 0.36

0.55 0.33 0.28 0.26

0.25 0.24 0.29 0.27

N

Total (%o)

on Seward Peninsula,

EC

paleosols

pH

Depth

propertiesof

Lake Rhonda I A O-5 5-20 Bgl 20-50 Bg2 Mottles

Pedon & horizon

Table 2 Chemical

0.14 0.23 0.10 0.11

0.06 0.04 0.04 0.08

0.09 0.06 0.06 0.06

0.06 0.07 0.08 0.70

S

9 8 8 9

10 8 9 11

13 10 10 10

10 8 9 8

C/N

Alaska CEC

3.0 2.3 1.5 1.3

2.4 0.5 0.8 2.0

1.3 1.3 0.9 0.9

3.7 3.0 2.5 3.4

19.4 21.3 22.8 25.2

17.1 19.2 19.8 19.8

32.0 21.2 18.8 20.0

14.6 IS.1 18.0 14.8

(700) (cmol/kg)

CO,

33.5 33.8 27.3 25.5

33.2 16.7 22.7 34.1

52.1 32.8 29.1 32.0

27.8 27.4 37.2 40.9

Ca

10.4 11.6 10.9 11.8

5.6 5.3 5.0 5.4

9.9 7.3 5.8 5.7

7.5 7.7 8.7 8.1

Mg

Exchangeable (cmol/kg)

0.3 0.3 0.3 0.3

0.1 0.1 0.1 0.1

0.2 0.2 0.2 0.2

0.2 0.4 0.4 0.4

K

cations

5.8 7.9 8.2 8.3

0.3 0.3 0.4 0.3

1.6 1.9 2.4 2.4

3.7 4.3 5.5 5.0

Na

2.96 2.62 2.79 2.22

2.57 2.80 2.57 2.63

2.54 2.16 1.95 1.91

3.54 3.21 3.16 4.74

Fe

(%)

0.57 0.67 0.69 0.63

0.41 0.49 0.43 0.45

0.70 0.51 0.45 0.45

0.92 1.02 1.06 0.94

Al

Amm. oxalate

0.41 0.37 0.37 0.29

0.22 0.24 0.20 0.27

0.35 0.10 0.04 0.00

0.77 0.75 0.81 0.69

Si

1.06 0.77 0.78 0.57

1.30 1.06 1.06 0.98

0.58 0.49 0.37 0.37

0.73 0.77 0.53 0.89

Fe

(%)

0.08 0.12 0.12 0.12

0.12 0.12 0.12 0.08

0.25 0.24 0.12 0.08

0.20 0.20 0.16 0.16

Al

Pyrophosph.

2.63 2.07 2.31 2.22

1.95 2.07 2.24 1.96

2.08 2.18 2.24 2.16

2.42 1.95 2.12 4.33

Fe

(%)

0.16 0.14 0.16 0.22

0.10 0.18 0.16 0.14

0.23 0.24 0.22 0.22

0.10 0.14 0.18 0.16

Al

Dith.-citr.

I

2.0

4.0

n.d.

0.59

0.24

8.2

8.0

8.7

10-40

40-45

Bg’

Bg2 tephra

0.35

0.4

0.4

8.3

7.9

7.8

17-30

30-40

Bg2

BCg tephra

0.4

2.5

2.1

3.1

2.5

0.79

8.0

3-17

J%’

0.87

7.7

o-3

Bw

Tempest Lake A

2.3

0.96

IO-40

0.2

2.7

0.53

8.0

O-IO

BC

8.4

8.5

7.6

Bw

Swan Lake

1.8

0.15

130+

BC3

1.7

0.17

8.4

I IO- 130

2.0

0.23

BC2

2.6

0.42

8.1

90-110

BCI

7.1

67-90

Bwb2

4.0

0.52

7.6

43-67

3.5

0.56

Ab2

0.37

5.6

0.41

32-43

0.53

2.3

0.42

Bwbl

0.36

3.5

0.13

0.22

0.28

0.26

0.30

0.33

0.01

0.44

0.24

0.26

0.30

0.19

0.19

0.20

0.24

0.42

0.29

0.36

3.5

0.06

8.6 7.9 8.1

0.43

0.38

0.35

3.8

aB1

3.3

0.07

0.38

4.7

5-30 30-32

3.6

I

0.33

0.34

0.06

O-5

3.0

0.16

0.

2.8

0.13

0.07

BW

8.2 8.2 7.9 7.8 7.8 7.7 8.0

A

O-IO

20-40 40-60 60-80 SO-100 loo-125 125- 145

BQ w Q2 cg3 Q4 cg5 Egg Lake

BW

Lake Rlwnda 3

0.08

0.08

0.09

0.19

0.19

0.04

0.19

0.18

0.09

0.10

0.05

0.04

0.04

0.04

0.06

0.05

0.08

0.04

0.07

0.06

0.06

0.06

0.05

0.06

0.04

0.04

8

23

9

8

8

9

13

9

8

9

9

9

9

IO

1I

10

9

I I

8

IO

IO

II

10

9

10

9

0.7

2.0

2.5

3.4

2.7

0.3

2.1

3.2

I .6

2.3

2.7

2.7

2.9

3.0

I.6

1.8

2.0

3.0

2.6

1.6

28.6 4.5

3.2

26.7

38.9

35.2

2.7

27.4

34.7

25.6

29.7

24.4

33.9

24.

29.0

26.6

29.4

36.5

30.8

37.3

23.3

26.9

28.2

30.1

25.4

17.9

16.0

15.4

14.7

1.7

18.9

15.9

19.1

IS.9

15.2

15.4

14.3

15.3

20.1

18.5

26.3

15.9

17.7

21.7

23.3

20.3

1.4 1.2

19.3

21.0

29.2 27.

18.5 19.2

1.5

2.2

1.1

1.6

I

I

1.8

7.9

8.2

8.5

9.2

I.1

8.3

9.9

10.4

12.6

15.9

15.6

14.3

7.5

5.4

5.5

7.8

5.8

6.2

4.8

4.8

4.4

4.4

4.7

4.9

4.6

0.2

0.2

0.4

0.5

0.5

0.4

0.1

0.4

0.4

0.4

0.3

0.1

0.2

0.2

0.2

0.2

0.2

0.2

0.3

0.3

0.2

0.2

0.2

0.2

0.2

0.2

1.5

4.5

4.4

4.9

3.9

1.1

5.3

4.9

7.3

6.0

I.0

0.9

0.7

1.2

2.7

3.3

5.0

3.1

3.5

0.2

0.2

0.2

0.2

0.4

0.5

0.5

1.77

1.24

1.04

0.95

0.87

4.95

2.12

2.21

1.93

2.04

1.77

1.91

2.03

1.97

1.73

1.69

1.78

1.97

1.77

2.08

2.30

2.26

2.18

1.93

1.99

1.81

0.95

0.28

0.24

0.19

0.16

1.36

0.43

0.45

0.43

0.37

0.35

0.43

0.45

0.43

0.29

0.30

0.31

0.41

0.31

0.59

0.61

0.59

0.57

0.35

0.37

0.35

0.04

1.40

0.23

0.19

0.17

0.16

2.97

0.16

0.12

0.12

0.16

0.06

0.08

0.12

0.14

0.14

0.02

0.04

0.08

0.04

0.29

0.31

0.33

0.24

0.08

0.08

0.10

0.31

0.37

0.35

0.30

0.28

0.77

0.97

0.69

0.33

0.33

0.28

0.28

0.24

0.37

0.37

0.53

0.41

0.53

0.37

0.45

0.45

0.41

0.41

0.37

0.45

0.02

0.04

0.04

0.04

0.04

0.04

0.04

0.20

0.08

2.16

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.20

0.00

0.16

0.20

0.16

0.16

0.20

0.16

0.24

0.24

0.73

0.92

0.85

0.62

0.80

2.10

2.01

2.20

0.29

1.97

2.05

2.05

2.1

2.00

1.91

1.88

2.09

I.61

2.08

2.10

2.01

2.05

2.12

2.38

2.42

1

0.03

0.10

0.12

0.1 1

0.08

0.08

0.31

0.28

0.35

0.30

0.33

0.22

0.24

0.18

0.16

0.12

0.18

0.24

0.18

0.16

0.14

0.16

0.16

0.20

0.20

(paste)

(cm)

Fritz Lake A Bwl Bw2 Ab Bg tephra

o-3 3-24 24-39 o-41 41-50

7.8 7.9 7.8 7.7 7.1

7.7

7.4 7.9 8.1 8.2 7.8 7.7

pH

Depth

Tempest Luke B Bw o-2 Bgl 2-13 9g2 13-30 Bg3 30-5 I BQ 51-61 C 61 +

Pedon & horizon

Table 2 (continued)

0.13 0.25 0.21 0.24 0.11 0.35

0.62 0.79 0.4 0.49 0.4 0.3

(S/m)

EC

3.8 2.2 2.6 3.5 3.5 0.3

3.8 2.7 1.7 2.5 2.6 2.4

(%)

OC

0.38 0.26 0.32 0.42 0.41 0.01

0.36 0.30 0.21 0.27 0.30 0.27

N

Total (W)

0.09 0.08 0.07 0.08 0.07 0.07

0.22 0.14 0.08 0.08 0.1 1 0.08

S

10 9 8 8 9 51

10 9 8 9 9 9

C/N

2.3 1.7 2.2 2.1 0.7 0.4

2.1 4.3 3.7 2.7 2.9 2.5

(%o)

CO,

22.0 22.7 25.1 21.3 26.4 2.8

18.3 16.7 16.1 16.8 16.6 16.3

(cmol/kg)

CEC

Exchangeable

37.5 34.6 29.5 31.8 18.8 5.0

31.9 45.4 35.1 31.5 34.4 27.3

Ca

6.5 8.0 10.2 9.7 7.6 1.5

8.0 9.5 7.6 7.4 6.7 5.8

Mg

(cmol/kg)

0.3 0.4 0.3 0.2 0.3 0.2

0.3 0.5 0.5 0.4 0.3 0.2

K

0.3 0.8 0.9 I.2 0.6 0.6

3.3 5.3 4.4 4.5 3.3 2.7

Na

cations

1.07 1.16 0.95 0.92 1.03 1.85

0.91 1.21 1.20 1.23 1.19 1.15

Fe

0.31 0.30 0.29 0.22 0.32 0.91

0.17 0.23 0.28 0.26 0.26 0.26

Al

Amm. oxalate (%)

0.30 0.22 0.21 0.17 0.22 1.50

0.18 0.21 0.25 0.24 0.22 0.20

Si

0.26 0.26 0.29 0.34 0.27 0.08

0.32 0.43 0.27 0.32 0.29 0.24

Fe

(%)

0.04 0.04 0.04 0.06 0.04 0.02

0.04 0.04 0.03 0.05 0.04 0.05

Al

Pyrophosph.

0.77 0.98 0.87 0.72 0.86 0.24

0.68 0.92 0.89 0.87 0.83 0.87

Fe

0.11 0.14 0.13 0.10 0.13 0.02

0.09 0.14 0.13 0.13 0.12 0.12

Al

Dith.-citr. (o/o)

2 3 4 5 6 7 8+9 10

1

Pedon #

Table 3 Radiocarbon

17,420 f 260 yrs 17,850+ 100 yrs 17,980 + 110 yrs 18,!40&2OOyrs 19,630+ 110 yrs 16,880+ 120 yrs 19,990+ 160 yrs 17,740 + 220 yrs 17.360 i 130 yrs

B.P. B.P. B.P. B.P. B.P. B.P. B.P. B.P. B.P.

C 14 age

C 13-adjusted

Lake Rhonda I Ulu Lake Eh’cho Lake Whitefish Thawpond Lake Rhonda 3 Egg Lake Swan Lake Tempest Lake A + B Fritz Lake

Alaska

Name of site

dates of paleosols on Seward Peninsula,

Beta-607 18 Beta-79839 Beta-79837 Beta-79840 Beta-79835 Beta-607 16 Beta-79836 Beta-75529 Beta-79838

Lab#

plant plant plant bulk, wood bulk. wood plant

remains from paleosurface remains from paleosurface remains from paleosurface uppermost 10 cm of soil from paleosurface uppermost 10 cm of soil from paleosurfxe remains from paleosurface

wood from paleosurface

Material dated

C. Hijle,

a

C.-L. Ping/Geodem

Pedon 1, Lake Rhonda 1

231

71 (19961219-243

&pm

Pedon2, Ulu Lake

(cm1 0

80

Pedon4, WhitefishThawpond am7

Fig. 3. Schematic

cross-sections

of paleosols on Seward Peninsula,

Alaska.

several sites, ruling out the possibility of differences in radiocarbon dates due to different eruptions (J. Beget, personal commun., 1995). 3.2. Morphological properties 3.2.1. Pedon I, Lake Rhonda 1 ’

The paleosol at Lake FUtonda 1 (Fig. 3) is developed in and under earth hummocks that measure 30-35 cm in diameter and lo-15 cm in height. An ice wedge is present at about 50 cm depth (measured from the top of the hummocks). The profile is tilted towards a gully to the right (facing the section). The solum is composed of a A-Bgl -Bg2 sequence. The mottles in Bgl, characterized by blackish coloration due to iron sulfides, are particularly concentrated between 15 and 20 cm depth. They were sampled separately for chemical analysis. Redoxmorphic features occur as long, thin

’Lake names are unofficial.

C. Htijle. C.-L. Ping/Geodema

232

b

71 (19961219-243

Pedon 6, Egg Lake

Pedon5, Lake Rhonda 3

0

20

40

60

Pedon 7, Swan Lake

de0m

Pedon 8, Tempest LakeA

60

Pedon9, Tempest Lake B

Fig. 3 (continued).

Pedon 10, Fritz Lake

C. Hiife, C.-L. Ping/Geodem

71 (19961219-243

233

oxidized streaks in the upper horizon, most markedly immediately underneath the surface. 3.2.2. Pedon 2, Ulu Luke The Ulu Lake paleosol (Fig. 3) has a surface that is tilted towards the adjacent thaw lake. The hummock on the right side of the profile exhibits cracks on the surface and the front part is slumped off towards the lake. In addition, the profile had numerous vertical cracks that were filled loosely with soft ice (sublimation ice). These ice-filled cracks were interpreted to be more recent features (developed possibly within the last 10 years) in contrast to horizontal and vertical accumulations of hard, dense ice that are believed to be contemporaneous to the paleosols and present in all soils. The soil is divided into Al, A2, A3, and Bg horizons with a diffuse boundary between A2 and A3. Small, black rocks were found in the A3, possibly tephra. The Bg has many small, black iron sulfide mottles (l-2 mm in diameter). The top of an ice wedge was encountered at about 52 cm depth below the paleosurface. 3.2.3. Pedon 3, Eh’cho Lake The paleosol at Eh’cho Lake (Fig. 3) was excavated to 110 cm depth and has a A-Cl-C2-Abl-C3-Ab2 sequence. The paleosurface of this profile has a single hummock with a diameter of ca. 40 cm. All horizons (except the A) have about 15% oxidized concentrations in vertical and horizontal streaks and soft masses. Organic-rich material occurs as small streaks and continuous horizons (Ab and Ab2). The soil darkened visibly after being excavated and exposed to the air for several minutes implying the reduced condition of the soil material. 3.2.4. Pedon 4, Whitefish Thawpond In Pedon 4 (Fig. 3) the paleosurface as well as the top of the ice wedge (which was encountered at 30-40 cm depth) are strongly tilted toward the lake ( u 45”). This profile is dominated by the presence of iron sulfide-containing, blackish material. The solum consists of Bw-Bgl-Bg2-Bg3 horizons, of which only the Bw horizon is free of iron sulfides. This profile was excavated with the help of a gasoline-powered drill. The paleosurface at Whitefish Thawpond is slightly wavy. 3.2.5. Pedon 5, Lake Rhonda 3 The site at Lake Rhonda 3 (Fig. 3) exhibits a ca. 15 cm thick layer of clear ice between tephra and paleosurface (possibly tephra-buried snow or frozen puddle, or segregation ice). Vegetation is frozen into the ice. The paleosol includes vertical ice-veins (2-5 cm thick) that are connected to the overlying ice and descend to 32-39 cm depth, a 5-10 mm thick horizontal ice accumulation occurs at 39 cm depth. Hummocks on the surface are 33 and 38 cm in diameter. A weakly developed ice net occurs 50 cm below the surface. The ice-rich soil has a massive structure and it liquefies after melting. There are a few small areas of organic-rich material at 35-40 cm depth. The soil has a Bw-BCg-Cgl to Cg5 sequence. Due to the absence of genetic features (besides a different coloration of Bw), it was not possible do determine genetic horizons in the field, therefore, samples were taken by depth increments. Cgl and Cg2 horizons have few iron sulfide-mottles (2-3 mm in diameter), in Cg3 these mottles are common.

234

C. Hiijle, C.-L. Ping/Geodenna

71 (19961 219-243

3.2.6. Pedon 6, Egg Lake

Pedon 6 (Fig. 3) consists of three A and three Bw horizons which are underlain by a BCl-BC2-BC3 sequence. The A and Bw horizons are warped but continuous (except for some separated Ab2 material). There are few iron sulfide mottles present in the Bw (few mm to 1 cm in diameter). The top of a 6 cm thick ice net occurs at 64 cm. Another ice net occurs around 130 cm. Although not shown in the sketch, hummocks are present at this site. Measurements of 8 hummocks yielded widths (short side) of lo-27 cm, lengths (long side) of 19-30 cm, diameters of 26 and 32 cm (round hummocks), and heights of 9-13 cm. 3.2.7. Pedon 7, Swan Lake The Swan Lake paleosol (Fig. 3) measures in some places 30 cm in others 45 cm to the top of the ice wedge. The section is slightly tilted towards the lake and the paleo-surface is relatively flat. Bw, BC, and Bg2 horizons are continuous, and the Bgl is discontinuous. The Bgl and Bg2 contain iron sulfides and are characterized by blackish colors. The area of black color increased with depth in the section. Black parts turned brown (darker than the main matrix) within 24 hours of exposure of the section. The Bgl around 10 cm is ice rich (ice lenses 1-2 mm thick). In the Bw, there are many bigger oxidized streaks of up to 1 cm thick, as well as smaller streaks around roots. In the BC horizon, many oxidation zones occur along root channels and a few as soft masses (N 1 cm in diameter). This horizon also exhibits “recent” cracks with soft ice filling (see Pedon 2). At this site, in contrast to all other sites, no paleovegetation is preserved. The upper 5 mm of Bw are dried out and of a lighter gray color. 3.2.8. Pedons 8 and 9, Tempest Luke A and B The Tempest Lake paleosols (Fig. 3) are located within 5 m of each other. The paleosurface is slightly wavy. Pedon 8 is underlain by an ice wedge at about 40 cm depth. Pedon 9 is located next to Pedon 8 which has no ice wedge. Both profiles are dominated by iron sulfide-containing horizons. The Bw horizons are thin and discontinuous. A 5-10 cm-thick ice accumulation was found in a micro-topographical low on the paleo-surface of Pedon 9. The ice is clear and the lowest tephra layer shows cryogenic structures. Small ice cracks run from this ice into the tephra. 3.2.9. Pedon 10, Fritz L.uke Pedon 10 (Fig. 3) has a relatively flat surface. The A horizon is found only in part of the profile; brown-colored Ab material is dispersed throughout the profile. The few charcoal-black iron sulfide mottles in the Bw 1 are l-2 mm in diameter. The Bg horizon contains many ice lenses a few mm thick. There are oxidation concentrations along root channels with colors of 7.5YR 4/6 in the Bwl and 2.5Y 4/4 in the Bw2. Zones of oxidized masses occur in the Bw2 and Bg (10YR 5/6 and 1OYR 5/8, respectively). The Bwl-Bw2-Bg sequence is underlain by massive ground ice starting at 50 cm. 3.3. Paleo-active

layer depths

Paleo-active-layer depths range from 32 cm up to 64 cm (Table 4) with most depths between 39 and 50 cm. Maximum active-layer depths were determined by measuring the

C. H@le, C.-L. Ping/Geodem

71 (1996) 219-243

235

Table 4 Active layer depths of paleosols

on Seward Peninsula,

Pedon #

Name of site

Pafeo-active depth (cm)

1 2 3 4 5 6 7 8 9 IO

Lake Rhonda 1 Ulu Lake Eh’cho Lake Whitefish Thawpond Lake Rhonda 3 Egg Lake Swan Lake Tempest Lake A Tempest Lake B Fritz Lake

50 52 n.d. 32 39 64 4.5 30 61 40

Alaska layer

Estimated by

Active layer max. or true value

ice wedge ice wedge n.d. ice wedge thick ice lens ice net ice wedge ice net ice-rich layer thick ice lens

max. max. n.d. max. true true max. true true true

distance to the top of ice wedges for Lake Rhonda 1, Ulu Lake, Whitefish Thawpond, and Swan Lake and were 50, 52, 32, and 45 cm, respectively. Ice nets, ice lenses, and ice-rich horizons led to the identification of active layer depths at Lake Rhonda 3, Fritz Lake, Egg Lake, Tempest Lake A, and Tempest Lake B, which were determined to be 39, 40, 64, 30, and 61 cm, respectively. The profile at Tempest Lake A has an ice net at 30 cm indicating a regular active layer to this depth, and an ice wedge at 40 cm marking the permafrost table. Similarly, the Fritz Lake profile has a thick ice lens at 40 cm and massive ground ice at 50 cm depth. These profiles provide evidence for transient layers between 30 and 40 cm depth at Tempest Lake A and 40 and 50 cm at Fritz Lake, where the soils only thaw at rare occasions. Active-layer depth at Eh’cho Lake was not determined. The method of estimation of active layer depth was improved in 1994 and sites excavated in 1993 were re-visited. This resulted in shallower active layers than previously described by Hoefle et al. (1994). 3.4. Physical properties Paleosol textures determined both in the field as well as in the laboratory are uniformly silt loams (Table 1). Percentages vary in the sand fraction from 10 to 35% (average IS%), in the silt fraction from 57 to 83% (average 71%), and in the clay fraction from 4 to 23% (average 11%). Tephra textures range from sandy loam to gravel (pumice). Textures from the lowest 10 cm of tephra are loamy sand to sandy loam. 3.5. Chemical properties 3.5.1. Paleosols Chemical properties of the paleosols are summarized in Table 2. Values were determined with air-dried samples and corrected for oven-dried samples. All paleosols show slightly to strongly alkaline soil reactions (pH 7.4 to 8.6, average pH 8.0). Electrical conductivity (EC) varies from 0.06 to 1.O S/m (average 0.38 S/m), carbonate contents range from 0.5 to 4.3% (average 2.2%). Organic carbon contents range from

236

C. Hi$e, C-L. Ping / Geodermu 71 f 19961219-243

I .7 to 7.1% (average 3.0%), total nitrogen from 0.19 to 0.55% (average 0.32%), and total sulfur from 0.04 to 0.70% (average 0.10%). Carbon/nitrogen ratios lie between 8 and 13 (average 9). Cation exchange capacities (CEC) show an amplitude of 14.3-32.0 cmol/kg (average 19.1 cmol/kg), Exchangeable Ca 16.7-52.1 cmol/kg (average 31 .O), Mg 4.4-15.9 cmol/kg (average 7.9), K 0.1-0.5 cmol/kg (average 0.3), and Na 0.2-8.3 cmol/kg (average 2.9). Ammonium oxalate-extractable Fe ranges from 0.87 to 4.74% (average 1.96%), Al from 0.16 to 1.06% (average 0.44%), and Si from 0.00 to 0.81% (average 0.23%). Sodium pyrophosphate-extractable Fe shows values between 0.24 and 1.30% (average 0.52%), Al between 0.00 and 0.33% (average 0.10%). Dithionite-citrate-extractable Fe values occur between 0.62 and 4.33% (average 1.78%), Al between 0.08 and 0.35% (average 0.17%). The presence of iron sulfides in blackish colored mottles was qualitatively shown by applying HCl and smelling the subsequently developing H, S. 3.5.2. Tephra The range of chemical properties of tephra (Table 2) for the following analyses are: pH = 7.7-8.7; EC = 0.24-0.40 S/m; organic C = 0.2-0.4%; total N = O.Ol-0.02%; total S = 0.04-0.08%; carbonates = 0.3-0.7%; extractable P = 14.1-23.0 ppm; CEC = 1.7-3.2 cmol/kg; exchangeable Ca, Mg, K, Na= 2.7-5.0, 1.1-1.8, 0.1-0.2, 0.6-1.5 cmol/kg, respectively; ammonium oxalate extractable Fe, Al, Si = 1.77-4.95, 0.911.36, 1.40-2.97%, respectively; sodium pyrophosphate extractable Fe and Al = 0.080.28 and 0.02-0.04%, respectively; dithionite-citrate extractable Fe and Al = 0.24-0.80 and 0.02-0.08%, respectively.

4. Discussion 4. I. Lute-Pleistocene

soil formation

on northern Seward Peninsula

The uniform silt loam textures and homogenous appearance of the paleosol profiles suggest the parent material is airborne loess. Alkaline soil reactions and carbonate contents reflect its calcareous nature. Silt derived from glacier-fed streams are the most common source for loess deposits (PCwC, 1975). However, during the last glacial maximum, glaciation in central Beringia was of limited extent due to the strongly continental climate (Hopkins, 1982). The southern portion of Seward Peninsula supported only local, small glaciers (Kaufman and Hopkins, 1986), which probably did not provide much erodible material, and predominantly drained away from the northern peninsula. Rivers draining glaciers in the Brooks Range, located to the northeast of the study area also have to be considered as a potential loess-source. Furthermore, it is possible that the loess originated from exposed marine sediments of the Bering Land Bridge rather than from glacial deposits. Carbonates in the soil are probably primary minerals that have not been altered through pedogenesis; pH and carbonate contents show no trends with depth and no pedogenic carbonates are visible. Evidently, there was not enough moisture to decalcify the loess but it was also not arid enough for upward movement of soluble salts, which is common in polar desert soils (Tedrow and Douglas, 1964). Due to the presence of

C. Htijle. C.-L. Ping/Geodemm

71 (19961219-243

237

carbonates in the soils, base saturations (exchangeable bases/CEC) exceed 100%; in fact, exchangeable Ca values generally exceed CEC values. The sums of exchangeable cation values also surpass CEC values and manifest themselves in high pH and EC values. The low cation exchange capacity values (average 19.1 cmol/kg) are common for silt loams because of low clay contents. These paleosol values are comparable to values from contemporary soils formed in loess in Interior Alaska (DeMent, 1962). Based on CEC, exchangeable Na, and EC values, 48% of all horizons can be classified as saline, 53% as sodic, and 40% as saline-sodic (United States Salinity Laboratory Staff, 1954). The presence of carbonates, a saturated exchange complex, and high exchangeable Na values indicate that no significant leaching has taken place in the soils. Sulfur values do not correlate closely with organic carbon values. Therefore, sulfur probably did not accumulate through biological process. The sulfur present in the soil most likely is derived from the parent material, possibly blown off the exposed continental shelves and has undergone minimal modification through soil development. Organic carbon contents (1.7-7.1%) are high compared with frigid Mollisols and Aridisols in the U.S., whose values are 1.4% and lS%, respectively in the upper 18 cm. 0.9% and 0.7%, respectively at IS-36 cm depth (Kimble, 1991). Serozems (Aridisols in Russia) average 0.8% C (Kononova, 1961) and late-Pleistocene loess paleosols in the Kolyma Lowland of NE Russia; 0.5-1.5% (Gubin, 1990). Organic carbon contents in the paleosols are comparable with amounts in Chemozems (Mollisols) from the Kamennaya Steppe in Russia; 4.1-5.2% C in the upper profile, 0.7-2.0% C in the lower part (Kononova, 1961). Since dark brown or reddish-brown colors, which indicate humified organic matter in mineral soils, are generally missing from the paleosols, the organic carbon contents are possibly elevated by the high density of preserved roots in all horizons, Another explanation for the lack of characteristic soil coloration related to organic carbon is that the humus may be dominated by light-colored fractions, mainly low-molecular-weight acids, rather than humic acids (Ping et al., 1995). Pettapiece (1975) describes horizons with as much as 3% organic carbon where coloration is not visible. He attributes the phenomenon to the presence of free calcium, which fixes organic carbon by complexation. Since there is free calcium in the paleosols, this is also possible. The presence of well-preserved root remains in the paleo-permafrost layer can be explained by the syngenetic nature of the permafrost where development took place simultaneously to the deposition of loess. The active layers froze in the fall and thawed out less in the following summer due to the addition of loess on the paleo-surface. Therefore, the lowest part of the active layer was continuously encased by permafrost. The preservation of roots in this manner requires that roots were distributed throughout the available unfrozen soil in the summer, even close to the permafrost table. High density of roots in the paleo-active layers of the paleosols indicates herbaceous plants in large numbers and/or the presence of species that produce many roots. C/N ratios are narrow and similar to those of most other mineral soils (Stevenson, 1994), but they are in sharp contrast to tundra soils, which have organic horizons with C/N ratios of 20-30 (e.g., Tamocai et al., 1993). (Anomalous organic C and total N values for the Al horizon at Ulu Lake suggest contamination of soil material with plant

238

C. H@le, C.-L. Ping/Geodema

71 (1996) 219-243

material from the paleosurface.) High CEC, high organic C content, and narrow C/N ratios indicate a high nutrient availability in the paleosols. This is probably caused by the constant deposition of loess and the resulting input of new nutrients. Additionally, abundant very fine roots indicate herbaceous vegetation on the paleosurface. Soils with herbaceous vegetation usually have a rapid turnover rate, which probably also enhanced soil fertility. The predominantly grayish colors of the paleosols indicate a saturated soil environment, but continuous root distribution and chemical properties (in particular the presence of carbonates and exchangeable Na) argue against this. These indicators are not necessarily contradictory. Some soils with gray colors have been shown to be saturated for only short periods (Vepraskas and Wilding, 1983). Metal-extractions reveal that iron predominantly occurs in amorphous form (oxalate- minus pyrophosphate-extractable Fe; Parfitt, 19831, probably as ferrihydrite, which suggests alternating reducing and oxidizing conditions. Temporarily reduced conditions probably did occur; during spring thaw, water in the active layer becomes perched above the receding frozen front and, eventually, above the permafrost table. Therefore, the soils may have been temporarily saturated during spring thaw, but were unlikely to have experienced a continuous reducing environment. Crystalline iron (dithionite- minus oxalate-extractable Fe; Pa&t, 1983) only occurs in about 30% of all horizons and has low values, suggesting that most weathered iron has been transformed into ferrihydrite (and probably reduced iron). An average 30% of all iron is organically bound (pyrophosphate-extractable Fe; McKeague et al., 1971). Values for surface horizons are often higher than for subsurface horizons, indicating slightly increased biochemical weathering in the upper part of the soils. We have shown that blackish colored mottles and horizons are due to the presence of iron sulfides. Sulfur is reduced at lower redox potentials than iron. In marsh and bog environments with flooded and saturated soils, the presence of sulfide indicates strong reducing conditions (e.g., Jakobsen, 1988). As mentioned above, there are no clear indications of continuous waterlogging in the paleosols. Additionally, the black colorations occur not only immediately above paleo-permafrost tables (the most likely area for reduction to occur) but also randomly throughout the soils. We suggest that this strong reduction occurred after burial of the soils. After the tephra layer cut off the oxygen supply, soil temperatures probably permitted anaerobic bacteria to be active for some time before permafrost temperatures dropped to values detrimental to microbial activity. Recent studies indicate that microbial activity occurs in permafrost soils at temperatures as low as -5°C (Clein and Schimel, 1995). The areas subject to strong reducing activity could have been confined by the distribution of frozen and unfrozen water, differences in water saturation of the pores, heterogeneity of microbial population, and organic carbon distribution. These mottles may also reflect parts of the profile that experienced reduced conditions before burial. It is also possible that much larger areas in the profiles were colored by sulfides, but that exposure to modem oxygen resulted in a re-oxidation, as the section was exposed along the thaw pond margin. Iron sulfide-containing mottles and horizons are largely limited to the paleo-active layers; table (only exception: C horizon at they do not occur below the paleo-permafrost Tempest

Lake B). This also argues in support of reduction

after burial, since microbial

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71 (19%) 219-243

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activity was probably limited to the active layer. Since there are arguments for a change of color after burial, paleosol colors should be used cautiously in environmental interpretation. Soil development in all paleosols appears to be incipient and confined to organicmatter accumulation and weathering and subsequent transformation of iron. The soils display no distinct genetic horizons, either morphologically or chemically. There is no evidence of carbonate translocation or removal of exchangeable Na, and very little evidence of chemical weathering. Weak soil development was probably due to the severe climate during the last glacial maximum and the lack of time for soil formation because of a constant input of loess and fast-rising permafrost tables. An important question is whether or not the overlying tephra has had any influence on the chemical properties of the soils. As tephra is mostly composed of volcanic glass, silica is a major component (Devil Mountain Lake tephra contains ca. 50% SiOZ; J. Beget, unpublished data). Ammonium oxalate extraction, which detects Si and Al released by weathering of tephra (Pa&t, 19831, shows oxalate-extractable Si values (indicating amorphous Si) are high in the tephras (average 1.96%), but very low in the paleosols (average 0.23%) and with no clear pattern within the profile. Thus, Si in the soils is probably derived from the parent material rather than translocated from the overlying tephra and chemical values of paleosols can be regarded as the original values. 4.2. Syngenetic and epigenetic soil formation The terms “epigenesis” and “syngenesis” are commonly used in describing permafrost environments. Epigenetic soil formation refers to a process where the parent material is deposited first and then soil development takes place (e.g., soil development in a newly deposited glacial moraine). Syngenetic soil formation occurs when the deposition of the parent material and soil development take place at the same time (Shur and Ping, 1994). The latter process was widespread in periglacial landscapes of the Pleistocene. Soils formed simultaneously with fairly continuous loess deposition, and the permafrost table rose as loess accumulated. During the last glacial maximum, loess-deposition was occurring on northern Seward Peninsula and soil formation was predominantly syngenetic. Only the paleosol at Egg Lake has syngenetic as well as epigenetic characteristics. The Bw and Bwb horizons formed under a continuous input of loess, which did not allow time for much soil formation or stronger organic matter accumulation. The A and Ab horizons probably formed under more stable conditions when more organic material was able to accumulate and decompose for varying lengths of time (possibly reflected in different thicknesses of three A horizons). At the other extreme, the Lake Rhonda 3 paleosol shows almost no horizon differentiation at all. This site appears to be under the influence of syngenetic processes only. Epigenetic horizons may reflect episodes of climate with warmer and/or moister conditions increasing plant production and litter accumulation. On the other hand, the effect may have been merely local, for example changes in wind patterns or silt availability. It seems, though, that climatic changes should be reflected in all profiles; therefore changes in local conditions appear the more likely explanation. Paleosols underlain by ice wedges (Lake Rhonda 1, Ulu Lake, Whitefish Thawpond,

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and Swan Lake) are probably of syngenetic character. None of them exhibit clear morphological horizons, organic matter colorations, or accumulations on the surface. The ice wedge at Tempest Lake A was identified as of syngenetic origin because of a narrow protrusion on its top (Y. Shur, pers. commun., 1994). In an environment with more or less continuous loess deposition and syngenetic soil formation, soil development can be expected to be weak because of the high degree of disturbance by loess deposition and the relatively short time before the soil was incorporated into permafrost. The cold climate probably also hindered soil development. The paleosols on Seward Peninsula show only weak soil development, which probably reflects both a severe climate and syngenetic soil formation. 4.3. Paleo-active

layer depth and permafrost

environment

Variations in active layer depth (30-64 cm) might be due to differences in soil moisture, slope, aspect, or snow cover. These are relatively shallow active layers for mineral soils which decreased the time for soil formation: under continuous loess accumulation, every surface turned into permafrost within a few thousand years. Furthermore, the permafrost table perched water and caused temporarily reduced conditions in the soil. A permafrost environment is clearly indicated by the presence of ice wedges and massive ground ice. Further indications are warped, broken, and discontinuous horizons due to cryoturbation (e.g., Egg Lake), platy and blocky structures due to ice lens and ice net formation, and weak soil development mostly due to syngenetic soil formation with simultaneous loess deposition. The presence of preserved roots in the lower parts of the profiles (below the paleo-permafrost table) is another indicator of the presence of permafrost before burial. Only in a frozen state could these roots have escaped decomposition. It is possible that the permafrost environment of the paleosols is responsible for reduced conditions in the soils before burial, even under relatively dry conditions. (A reduced soil environment and redoximorphic features are common in tundra soils with a mean annual precipitation of _< 350 mm; Ping et al., 1993.) On the other hand, properties suggesting post-burial reduction make it impossible to determine if or which redoximorphic features existed before burial. Since the original redox state of the paleosols is not known, we cannot interpret redoximorphic features. A study of paleosols in a permafrost environment in the Old Crow area in northwest Canada (Tarnocai, 1989) reported soils developed in a permafrost environment with gleyed horizons, cryoturbated features, patterned ground, and ice wedges. (A radiocarbon age of 42,000 years BP. + 1,200 years was determined for a bone imbedded in this soil; Tarnocai, 1989.) These general indicators of a permafrost environment match the morphological properties of the paleosols on Seward Peninsula.

5. Conclusions Paleosols on northern years B.P. give valuable

Seward Peninsula that were buried by tephra about information about soil development under full-glacial

17,500 condi-

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tions. All 10 profiles share common morphologicalt physical, and chemical properties. Horizonation is weak, there is no evidence of leaching in the soil profile, and all horizons contain carbonates and are rich in bases. We conclude that more or less continuous loess deposition and resulting syngenetic soil formation, as well as the severe climate of the last glacial maximum, are responsible for these properties. Little variability in soil properties indicates a fairly uniform mode of soil formation in the study area, probably due to severe climatic conditions and a topography with fairly little relief. Reconstruction of late-Quaternary environments is carried out with the help of studies in modern environments. Environmental indicators, such as plants, insects, and soils are used as “modem analogues”, based on the assumption that their requirements for survival or formation are the same today as they were in the past. Modem analogs of the buried soils would be a most valuable tool for paleoenvironmental reconstruction. However, the Seward Peninsula paleosols have very distinct features which do not resemble any soils known to the authors. This lack might be explained by the assumption that the paleosols formed under a climatic and sedimentation regime that currently does not exist. Possibly, comparable places do exist but have not been found yet.

Acknowledgements We wish to express our gratitude to David M. Hopkins, Daniel H. Mann, Gary J. Michaelson, Yuri L. Shur, David K. Swanson, and particularly Mary E. Edwards for valuable discussions and reviews of the manuscript. We also thank the US National Park Service for financial and logistical support.

References Bespalyy, V.G.. 1984. Late Pleistocene mountain glaciation in northeastern USSR. In: A.A. Velichko (Editor), Late Quatemary environments of the Soviet Union. University of Minnesota Press, Minneapolis, MN, pp. 31-33. Bronger, A. and Bruhn, N., 1989. Relict and recent features in tropical Alfisols from south India. In: A. Bronger and J.A. Catt (Editors), Paleopedology. Catena Suppl., 16: 107-128. Brown, J., 1969. Buried soils associated with permafrost. In: S. Pawluk (Editor), Pedology and Quaternary Research, Symposium Held at Edmonton, Alberta. The National Research Council of Canada and The University of Alberta, pp. 115-127. Catt, J.A., 1989. Relict properties in soils of the central and north-west European temperate region. In. A. Bronger and J.A. Catt (Editors), Paleopedology. Catena Suppl., 16: 41-X Clein, J.S. and Schimel, J.P., 1995. Microbial activity of tundra and taiga soils at sub-zero temperatures. Soil Biol. Biochem., 27: 1231-1234. Cwynar, L.C. and Ritchie, J.C., 1980. Arctic steppe-tundra: A Yukon perspective. Science, 208: 1375-1378. DeMent, J.A., 1962. The morphology and genesis of the subarctic brown forest soils of central Alaska. Ph.D. Thesis, Cornell University, Ithaca, NY. Fenwick, I.M., 1985. Paleosols: Problems of recognition and interpretation. In: J. Boardman (Editor), Soils and Quatemary Landscapes Evolution. Wiley, Chichester. French, H.M., 1976. The Periglacial Environment. Longman Scientific and Technical, Essex. Gasanov, S., 198 1. Criolitologicheskij Analisis (Cryolithological Analysis). Nauka, Moscow (in Russian).

242

C. HSjle, C-L. Ping/Geoderma

71 (1996) 219-243

Gubin, S.V., 1990. The late Pleistocene soil formation at the coastal lowlands of northern Yakutiya. In: V.M. Kotlyakov and V.E. Sokolov (Editors), Arctic Research: Advances and Projects. Proceedings of the Conference of Arctic and Nordic Countries on Coordination of Research in the Arctic, Leningrad, 1988, Part 2. Nauka, Moscow, pp. 290-291. Guthrie, R.D., 1990. Frozen Fauna of the Mammoth Steppe. University of Chicago Press, Chicago, IL. Hamilton, T.D. and Mann, D.H., 1996. Late-Pleistocene and Holocene paleoenvironments of the North Pacific coast. Quat. Sci. Rev., in press. Hiifle, C., 1995. Buried soils on Seward Peninsula, northwest Alaska: A window into the late-Pleistocene environment of the Bering Land Bridge. M.Sc. Diss., University of Alaska Fairbanks, Fairbanks, AK. Hoefle, C., Ping. C.L., Edwards, M.E., and Mann, D.H., 1994. Buried soils on Seward Peninsula: A window into the paleoenvironment of the Bering Land Bridge. Curr. Res. Pleistocene, 11: 134- 136. Hopkins, D.M. (Editor), 1967. The Bering Land Bridge. Stanford University Press. Stanford, CA. Hopkins, D.M., 1982. Aspects of paleogeography in Beringia during the late Pleistocene. In: D.M. Hopkins, J.V. Matthews, C.E. Schweger and S.B. Young (Editors), Paleoecology of Beringia. Academic Press, New York, NY, pp. 3-28. Hopkins, D.M., Matthews, J.V., Schweger, C.E. and Young, S.B. (Editors). 1982. Paleoccology of Beringia. Academic Press, New York, NY. Jakobsen, B.H., 1988. Accumulation of pyrite and Fe-rich carbonate and phosphate minerals in a lowland moor area. .I. Soil Sci., 39: 447-455. Kaufman, D.S. and Hopkins, D.M., 1986. Glacial history of the Seward Peninsula. In: T.D. Hamilton, K.M. Reed, and R.M. Thorson (Editors), Glaciation in Alaska. The Geologic Record. Alaska Geological Society. Anchorage, AK. Kimble, J.M., 1991. Proceedings of the Sixth International Soil Correlation Meeting (VI ISCOM). Characterization, Classification, and Utilization of Cold Aridisols and Vertisols. USDA, Soil Conservation Service, National Soil Survey Center, Lincoln, NE. Kononova, M.M., 1961. Soil Organic Matter. Its Nature, its Role in Soil Formation and in Soil Fertility. Academy of Science of the USSR and Pergamon Press, New York. Liu, T.S., An, Z.S., Yuan, B.Y. and Han, J.M., 1985. The loess-paleosol sequence in China and climatic history. Episodes, 8: 21-28. McKeague, J.A., Brydon, J.E. and Miles, N.M., 1971. Differentiation of forms of extractable iron and aluminum in soils. Soil Sci. Sot. Am. Proc., 35: 33-38. Messerli, B. and Frei, E., 1985. Klimageschichte und Paraoobijden in den Gebirgen Afrikas zwischen Equator und ntirdlichem Wendekreis. Geomethodica, 10: 3 I-70 (in German). Miiller-Beck, H., 1982. Late Pleistocene man in northern Alaska and the mammoth-steppe biome. In: D.M. Hopkins, J.V. Matthews, C.E. Schweger and S.B. Young (Editors), Paleoecology of Beringia. Academic Press, New York, NY, pp. 329-352. Parfitt, R.L., 1983. Identification of ahophane in Inceptisols and Spodosols. Soil Taxon. News, 5: 11 and 18. Pettapiece, W.W., 1975. Soils of the Subarctic in the lower Mackenzie basin. Arctic, 28: 35-53. Pew&, T.L., 1975. Quatemary geology of Alaska. Geological Survey Paper 835. Washington, DC. Ping, C.L. and Shur Y.L., 1994. Morphological characteristics of selected cryogenic soils. Agronomy Abstracts, ASA, CSSA, SSSA Annual Meeting, Seattle, WA, p. 334. Ping, C.L., Lynn, W. and Smith, C.A.S., 1993. Redoximorphic features in permafrost soils. In: Joint Russian-American Seminar on Cryopedology and Global Change, Post-Seminar Proceedings, Pushchino, 1992, pp. 233-244. Ping, C.L., Michaelson, G.J. and Malcolm, R.L., 1995. Fractionation and carbon balance of soil organic matter in selected Cryosols. In: B.A. Stewart (Editor), Advances in Soil Science, Lewis Publishers, Chelsea, MI, Chapter 25, pp. 307-314. Reider, R.G., 1990. Late Pleistocene and Holocene pedogenic and environmental trends at archaeological sites in plains and mountain areas of Colorado and Wyoming. In: N. Lasca and J. Donahue (Editors), Archaeological Geology of North America. Geological Society of America Centennial Volume 4, pp. 335ff. Rieger, S., 1983. The Genesis and Classification of Cold Soils. Academic Press, New York. Shur, Y.L., 1988. Verkhniy gorizont tolshchi merzlykh porod i termokarst (Thermokarst and the Upper Horizon of Permafrost). Nauka, Moscow (in Russian).

C. HZjle, C.-L Ping/ Geodenna 71 (19%) 219-243 Shur, Y.L. and Ping, CL.,

1994. Permafrost

dynamics

and soil formation.

243

In: J.M. Kimble and R.J. Ahrens

(Editors), Proceedings of the Meeting of the Classification, Correlation, and Management of PermafrostAffected Soils. USDA, Soil Conservation Service, National Soil Survey Center, Lincoln, NE, pp. 112-l 17. Smith, C.A.S., Tamocai, C. and Hughes, O.L., 1986. Pedological investigations of Pleistocene glacial drift surfaces in the central Yukon. Geogr. Phys. Quat., 40(l): 29-37. Soil Survey Division Staff, 1993. Soil Survey Manual. USDA Handbook No. 18. U.S. Dept. of Agriculture. U.S. Government Printing Office, Washington, DC. Soil Survey Laboratory Staff, 1992. Soil Survey Laboratory Methods Manual. Soil Survey Investigation Report No. 42. USDA-SCS National Soil Survey Center. Lincoln, NE. Stevenson, F.J., 1994. Cycles of Soil. Carbon, Nitrogen, Phosphorus, Sulfur, Micronutrients. Second Edition. Wiley-Interscience, New York. Tarnocai, C., 1989. Paleosols of northwestern Canada. In: L.D. Carter, T.D. Hamilton, and J.P. Galloway (Editors), Late Cenozoic History of the Interior Basins of Alaska and the Yukon. U.S. Geological Survey Circular, pp. 33-44. Tamocai, C., 1990. Paleosols of the interglacial climates in Canada. Geogr. Phys. Quat., 44(3): 363-374. Tarnocai, C., Smith, C.A.S., Fox, C.A., 1993. International tour of permafrost affected soils. The Yukon and Northwest Territories of Canada. Agriculture Canada, Ottawa. Tedrow, J.F.C. and Douglas, L.A., 1964. Soil investigations on Banks Island. Soil Sci., 98: 53-6.5. United States Salinity Laboratory Staff, 1954. Diagnosis and Improvement of Saline and Alkali Soils. USDA Handbook, Washington, DC. Valentine, K.W.G., King, R.H., Dormaar, J.F., Vreeken, W.J., Tarnocai, C., De Kimpe, C.R. and Harris, S.A., 1987. Some aspects of Quatemary soils in Canada. Can. J. Soil Sci., 67: 221-247. Vepraskas, M.J., 1992. Redoximorphic features for identifying aquic conditions. Technical Bulletin 301. North Carolina Agricultural Research Service. North Carolina State University, Raleigh, NC. Vepraskas, M.J. and Wilding, L.P., 1983. Aquic moisture regimes in soils with and without low chroma colors. Soil Sci. Sot. Am. J., 47: 280-285. Washburn, A.L., 1973. Periglacial Processes and Environments. St. Martin’s Press, New York. Williams, P.J. and Smith, M.W., 1989. The Frozen Earth. The Fundamentals of Geocryology. Cambridge University Press, Oxford. Zhestkova, T.N., 1982. Fonnirovaniye kriogennogo stroeniya gmntov (The Formation of Cryogenic Soil Structure). Siberian Branch of Academy of Science, USSR, Permafrost Institute and Nauka, Moscow, USSR (in Russian).