Organic geochemistry of the McMurdo Dry Valleys soil, Antarctica

Advances In Organic Geochemistry 1989

0146-6380/90 $3.00 + 0.00 Copyright © 1990Pergamon Press plc

Org. Geochem. Vol. 16, Nos 4-6, pp. 781-791, 1990 Printed in Great Britain.All rights reserved

Organic geochemistry of the McMurdo Dry Valleys soil, Antarctica GENKI I. MATSUMOTO,l AKIO HIRAI,2 KOITSU HIROTA3 and KUNIHIKOWATANUKI1 1Department of Chemistry, College of Arts and Sciences, University of Tokyo, Komaba, Meguro-ku, Tokyo 153, Japan 2Technical Research Center, Teikoku Oil Company, Kitakarasuyama 9-23-30, Setagaya-ku, Tokyo 157, Japan 3Shonan Institute of Technology, Nishikaigan, Tsujido, Fujisawa, Kanagawa-ken 251, Japan (Received 19 September 1989; accepted 27 December 1989) Abstract--Organic geochemical studies of 12 soil samples from Wright and Taylor Valleys of the McMurdo Dry Valleys (Ross Desert) in southern Victoria Land, Antarctica, were carried out. Long-chain n-alkanoic acids (C20-Cr,), with a predominance of even-carbon numbers, were abundant in all the samples. 3-Hydroxy acids (C8-C30) with a predominance of even-carbon numbers were found in the samples, together with 2-, o~- and (m-1)-hydroxy acids. ~t,~o-Dicarboxylicacids (Cs-C3~) were detected having near*unity values of carbon preference indices; mainly the C~3 dicarboxylic acid predominated. Visual kerogen revealed that amorphous materials are major components (68-98%) with small amounts of very fine coals (2-32%), but no woody and herbaceous materials. The occurrence of mature isomers of steranes and triterpanes, the paucity of n-alkenoic acids and data from the microscopic study suggest that organic components in the soil samples are derived from erosion of Beacon Supergroup sedimentary rocks and past biological debris containing vascular plant waxes as well as wind-transported cyanobacterial mats, including cyanobacteria, microalgae, bacteria and fungi, rather than from living organisms. Key words--hydrocarbon, Antarctic soil

sterane, triterpane, fatty acid, hydroxy acid, x,~o-dicarboxylic acid,

INTRODUCTION Although Antarctica is mostly covered by an ice sheet with an average thickness of 2450 m, there are a number of ice-free areas--mainly in the coastal regions of Antarctica. Antarctica is an extremely harsh environment for living organisms, and can be characterized by the absence of vascular plants, except in the northern part of the Antarctic Peninsula (Greene et al., 1967). Thus, organic components in the continent are supplied mainly from microorganisms, such as microalgae, cyanobacteria, fungi and bacteria. Also, Antarctica is far removed from the industrialized northern hemisphere, and thus is the least-polluted continent on earth. Hence, Antarctic ice-free areas provide suitable fields for the study of microbial biomarkers. Matsumoto and his co-workers have studied various organic compounds in Antarctic lake waters and sediments, soils and/or Beacon Supergroup sedimentary rocks in the McMurdo Dry Valleys (Ross Desert) of southern Victoria Land, the Lfitzow-Holm Bay region and the Vestfold Hills of Princess Elizabeth Land (e.g. Matsumoto et al., 1979, 1981a, 1982, 1986, 1987a, 1989). Also, organic components in suspended solids in waters and sediments from Ace Lake of the Vestfold Hills have been reported by Volkman (1986; Volkman et al., 1986, 1988). Recently, Matsumoto 0989) summarized the features of organic components in Antarctic lake waters and 781

sediments. Long-chain n-alkanoic acids (C20-C34)are often predominant fatty acids in Antarctic lake and pond sediments (Matsumoto et al., 1981b; Volkman et al., 1988; Matsumoto, 1989). Also, 24-ethylcholest5-en-3fl-ol is frequently the predominant sterol in Antarctic lacustrine environments (Matsumoto et al., 1982; Volkman, 1986; Matsumoto, 1989), in spite of the absence of vascular plants in the studied areas. Another unusual observation is that long-chain n-alkanes and n-alkenes with a predominance of odd-carbon numbers, and long-chain n-alkanoic acids with a predominance of even-carbon numbers are the major components in soil samples from the McMurdo Dry Valleys (Matsumoto et al., 1981a, 1990a). Here we report features of the distributions of organic components--hydrocarbons, including triterpanes and steranes, n-alkanoic acids, hydroxy acids and ct,co-dicarboxylic acids--in soil samples from the McMurdo Dry Valleys of southern Victoria Land, Antarctica, in relation to their sources materials. Also, a microscopic study for visual kerogen was carried out. MATERIALS AND METHODS

Sampling sites and samples The features of the sampling sites and samples have been reported elsewhere by M atsumoto et al. (1990a). The McMurdo Dry Valleys mainly consist of the Taylor, Wright and Victoria Valleys (Fig. 1). They

782

G E N K I I. M A T S U M O T O

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Fig. 1. Sampling locations in the McMurdo Dry Valleys, Antarctica: I~, ice-free areas• ~, Beacon Supergroup outcrop [modified from Barrett and Kyle (1975)]. Sampling site: 1-6, DJ1-DJ6; 7, BWl; 8, BC1; 9, BE2; 10, BE8; I1, BE9; 12, BE12. are the largest ice-free areas in Antarctica and extend over 4000 km 2. The valley depressions are covered with moraine and fluvioglacial deposits of Quarternary to Recent age (McKelvey and Webb, 1962). Only soil-like materials (silt and fine sand) are distributed in some valley depressions. In December 1981 and 1983, surface soil samples (0-10 cm) were collected from the east side of Don Juan Pond in Wright Valley and the surroundings of Lake Bonney in Taylor Valley of the McMurdo Dry Valleys in southern Victoria Land, Antarctica, and kept frozen at -20°C until analyzed in 1987-1988.

Analyses of organic compounds The analytical methods for identification and quantitation of organic compounds are given elsewhere (Matsumoto et al., 1979, 1984, 1987a; Matsumoto and Nagashima, 1984), Soil samples (40-80 g) were refluxed with 0.5 N potassium hydroxide in methanol (80°C, 2 h) and extracted with ethyl acetate after acidification with concentrated hydrochloric acid. The ethyl acetate extracts were chromatographed through a silica gel column (160 × 5 mm i.d., 100 mesh, 5% water). Hydrocarbons, fatty acids, and hydroxy and dicarboxylic acids were eluted with 2 column volumes of hexane, 3 column volumes of benzene/ethyl acetate (95:5) and 3 column volumes of benzene/ethyl acetate (1:1), respectively. Fatty, hydroxy and dicarboxylic acids were methylated with 14% borontrifluoride in methanol. The hydroxy acid methyl esters were further treated with 25% bis(trimethylsilyl)acetamide in acetonitrile to obtain their trimethylsilyloxy ether methyl ester derivatives. These organic compounds were analyzed using a Shimadzu QP1000 gas chromatograph-mass spectrometer (GC-MS). The GC-MS was operated using a fused silica capillary column (DB-5, 30 m x 0.32 mm i.d., film thickness 0.25/~m) connected to

an on-column injector. The column temperature was programmed from 70 to 120°C at 25°C/min, then from 120 to 310°C at 6°C/min except for the analysis of triterpanes and steranes. The temperatures of the molecular separator and the ion source were maintained at 320 and 250°C, respectively. The flow rate of the helium carrier gas was 4.3 ml/min. Mass spectra (m/z 50-600) were obtained continuously with a scan speed of 1.3 s at 70eV. Mass fragmentography was run for the analysis of triterpanes (m/z 191 and M +) and steranes (m/z 217 and M +) with the column temperatures programmed from 70 to 210°C at 15°C/min and from 230 to 310°C at 2°C/min. These organic compounds were identified by comparison of retention sequences and mass spectra with those of authentic compounds and/or those in the published literature (Wardroper et al., 1977; Matsumoto et al., 1979, 1987a; Seifert and Moldowan, 1979; Phiip, 1986; Volkman et al., 1986; Venkatesan, 1988a). Saturated fatty, 3-hydroxy and ~,co-dicarboxylic acids were quantified by the comparison of peak heights with those of authentic compounds, methyl hexadecanoate and tetracosadecanoate, 1-methyl,3-trimethylsilyloxyhexadecanoate and 1,14-dimethyl tetradecanedioate, on the m/z 74, 175 and 98 mass chromatograms, respectively, or TIC gas chromatogram (unsaturated fatty acids: methyl cis-9-octadecenoate). Triterpane and sterane compositions were determined by the peak heights on the m/z 191 and 217 mass fragrnentograms, respectively. The analytical uncertainty throughout the procedures was within + 12%.

Visual kerogen The analytical method used for visual kerogen has been described elsewhere (Matsumoto et al., 1987a). After removal of the carbonate-carbon, soil samples

Organic geochemistry of Antarctic soil

783

Table 1. Triterpanes, triterpenes and rnoretanes found In soil samples from the MoMurdo Dry Valleys, Antarctica* DJ1 Composition (%)# 1 180~H),22,29,30-Tr isnorneohopane 0.3 2 22,29,30-Tr isnorhop- 17(21)-erie 9.3 2.3 3 17~H )-22,29,30-Tr isnorhoDane 16.4 4 17~H)-22,29,30-Tr isnorhopane 5 Eplmers 17~H),2113(H)-blsnorhopane ÷ 17B(H),2l~(H)-28,30-bisnor hopene 0.0 2.5 6 17c{(H),2lt}(H)-30-Nor hopane 0.2 7 C30=1Hopene 8 Hop-17(21)-ene 27.8 9 17~H),21a(H)-30-Nor moretane 2.6 10 18a(H)-Oleanane 0.0 11 17a(H),21B(H)-Hopane 3.6 12 Neohop-13(18)-ene 8.5 4.2 13 C30=1 Hopene 14 17B(H),2lC{(H)-Moretane 1.8 15 (22S)-17a(H),2l(}(H)-30-Homohopene 0.2 16 (22 R)- 17ct(H),218(H)-30-Homohopene 1.2 17 176(H),21~H)-Hopene 8.6 18 Unknown 0.0 19 Hop-22(29)-ene 2.1 20 (22$)- 17<~(H),2113(H)-30,31-Bishomohopene 0.3 0.4 21 (22R)- 17a(H),2113(H)-30,31-Bishomohopene 1.2 22 1713(H),2 le(H)r 30,31-Bishomomor etane 23 Unknown 0.0 24 17B(H),21B(H)-30-Homohopane 6.8 25 (20S)-17~H),21B(H)-30,31,32-Trishomohopane 0.0 26 (20R)-17a(H),21B(H)-30,31,32-Trishomohopane 0.0 17a(H),21B(H)I17B(H),21B(H)-Hopene 0.42 (22S/22R)-lTa(H),21t~(H)-30-Homohopane 0.18

DJ2 0.0 7.2 1.9 18.9

DJ3

DJ4

DJ6

BWl

0.2 0.0 0.0 0.4 9.2 9.5 9.7 1.9 0.0 0.0 0.0 3.8 16.5 13.4 21.6 29.0

0.6 5.1 0.0 7.2

0.1 0.0 0.0 1.4 1.0 1.6 0.0 0.2 0.3 9.9 15.1 20.8 3.3 1.8 2.0 0.0 0.0 0.2 2.4 1.1 2.9 14.8 15.1 1 4 . 0 1.6 1.4 7.0 2.0 2.3 2.0 0.4 0.6 0.2 1.2 2.1 1.6 14.4 10.7 9.6 0.0 0.0 0.0 7.1 12.6 5.1 0.0 0.2 0.0 0.1 0.2 0.3 2.4 2.2 1.7 0.0 0.0 0.3 11.2 7.4 7.7 0.0 0.0 O.0 0.0 0.0 0.0 0.16 0.10 0.30 0.30 0.29 0.10

*Sample abbreviations: OJ1-DJ6 • Don Juan-1 - Don Juan-6. -E8,-E9 and -E12, respectively. #Arabic figures correspond to the peak numbers in Fig. 2.

were treated with a mixture of 55% hydrofluoric acid and 35% hydrochloric acid to remove minerals, and then centrifuged. The kerogen composition was determined using a microscope equipped with an automatic point counter. RESULTS

Triterpanes and triterpenes The analytical results for triterpanes and triterpenes are summarized in Table 1. The major com-

DJ5

BC1 2.9 2.2 4.0 20.0

BE2

BE8 BE9 BE12

1.7 8.3 2.9 9.5

3.7 1.0 4.7 8.1

0.0 0.0 0.0 0.4 0.3 2.1 3.3 3.2 10.8 8.2 0.5 0.3 0.5 0.7 1.1 12.6 3.4 9.4 0.9 3.9 3.0 5.6 3.2 4.7 4.8 0.3 0.2 0.4 0.9 0.9 3.1 5.2 4.2 1 2 . 3 1 1 . 5 12.3 13.5 8.0 6.1 6.8 1.9 0.0 1.0 0.0 0.6 3.5 3.7 0.4 1.8 0.7 Trace 0.6 1.1 3.9 3.3 2.1 2.8 1.9 3.9 4.6 10.9 13.0 13.3 6.3 8.6 0.0 0.0 0.0 1.5 0.0 3.0 0.9 23.1 4.4 2.5 0.0 0.3 0.6 2.4 2.2 0.5 0.6 0.6 2.0 1.9 1.6 0.4 1.8 0.5 1.8 0.5 0.7 3.9 0.3 0.8 1 0 . 8 10.2 10.4 5.1 11.0 0.0 0.0 0.0 1.2 1.3 0.0 0.0 0.0 1.1 0.9 0.28 0.40 0.31 2.0 1.3 0.01 0.22 0.55 1.0 0.71

2.6 0.9 1.6 4.8 3.6 2.0 9.1 13.7

0.6 0.7 0.4 1 4 . 8 11.4 6.6 1.1 0.9 0.6 1.5 1.0 1.6 5.5 4.3 4.6 2.1 1.6 0.5 1 8 . 0 15.7 8.9 4.8 5.5 9.1 0.0 0.0 0.4 0.7 1.1 0.8 6.0 5.1 3.0 5.6 4.8 4.8 2.7 7.3 8.9 2.0 1.9 2.3 2.1 5.0 5.9 3.4 3.0 2.4 3.5 2.3 1.4 0.0 0.7 2.5 1.5 1.1 0.6 2.8 6.8 11.9 2.3 1.6 0.8 1.6 1.3 0.8 6.7 2.2 1.0 1.1 1.1 0.62

BW1, BC1, BE2, BE8, BE9 and BE12 = Bonney-Wl, -C1, -E2,

pounds in the Don Juan samples are triterpenes, such as hop-17(21)-ene, neohop-13(18)-ene and hop22(29)-ene, as well as triterpanes, i.e. 17fl(H)-22,29,30trisnorhopane, 17fl(H),21fl(H)-hopane and/or 17fl(H),21fl(H)-homohopane; whereas those in the Bonney samples are mainly 17fl(H)-22,29,30trisnorhopane, 17~t(H),21fl(H)-30-norhopane and 17~(H),21fl(H)-hopane. An example of a mass fragmentogram of triterpanes and triterpenes (m/z 191) is shown in Fig. 2.

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Fig. 2. Mass fragrnentogram of triterpanes and triterpenes (m/z 1 9 ] )

Dry V a l l e y s ,

Antarctica

(D J2). Peak

identifications

o f a soil sample from a r e listed in T a b l e I.

the McMurdo

GENKII. MATSUMOTO

784 Table 2.

et al.

Steranes and diasteranes founcl in soil samples from the MCMurdo Dry Valleys, Antarctica* DJI

Composition (%)# 1 (20S)- 138(H). 17a(H)-D iachotestane 2 (20R)-13~H),t7¢l(H)-Diacholestane 3 (208)- 13~(H), 17B(H)-DiacholeStane 4 (20R)-13~H),17~H)-Diacholestane 5 (20S)-24-Methyl- 138(H), 17ct(H)-cliacholestane 6 (20R)-24-Methyl- 138(H),lTa(H )-cliacholestane 7 (20S)-5c¢(H),14~(H),17ct(H)-Cl~olestane 8 (20S)-24-Met hyl- 13B(H ), 17c¢(H)-cliacholestane * (20R)-5~(H), 148(H}, 1713(H)-cholestane 9 (20S)-Sct(H),1413(H),178(H)-Ct~olest ane + (20R)-24- met hyt- 13a(H ), 17B(H)-cliacholestane 10 (20R)-5r,(H),14ct(H),17e(H)-Ci~olestane 11 (20R)-24-Ethyl-13B(H),17ct(H)-diacholestane 12 (20S)-24-Et hy{- 13a(H), 1713(H)-cliacholestane 13 (20S)-24-Methyl-5a(H),14a(H),17a(H)-cholestane 14 (20R)-24- Methyl-5et(H).14 ~H), 178(H)-cholestane * (20R)-24-methyl-5B(H),14~(H),17ct(H)-cholestane 15 (20S)-24-Methyl-5~(H). 148(H), 178(H )-cholest ane 16 (20R)-24-Met hyl-5ct(H), 14a(H), 17c¢(H)-cholestane 17 (20S)-24-Ethyl-Sa(H), 14c¢(H), 17ct(H)-cholestane 18 (20R)-24-Ethyl-Sct(H), 14B(H),17B(H)-cholest ane * (20R)-24-ethyl-58(H),14ct(H),17ct(H)-cllolestane 19 (20S)-24-Ethyl-5o(H), 1413(H),17B(H)-cholestane 20 (20R)-24-Ethyl-5a(H),14a(H),17a(H)-cholestane (20S/20R}-24-Ethyl-5ct(H),14o(H),17a(H)-choiestane (20R+20S)-5(~(H).148(H),178(H)/5a(H),14a(H),17ct(H)-cholestane Relative abunclances of (20R)-5a(H),14a(H),17a(H)-sterane (%) Cz~ Cme C2s (20R)-5a(H),14a(H),17a(H)-C=t/C=v Sterane

D J2

D J3

D J4

DJ5

DJ6

BWl

BC1

BE2

BE8

BEg

BE12

2.3 0.5 0.0 1.6 0.3 0.0 0.7 5.4 3.7 1.4 0.0 0.0 1.6 0.6 1.1 2.2 1.4 1.6 28.0 29.0 17.6

0.0 0.0 2.1 0.0 0.5 3.9 6.9

0.6 3.5 0.5 1.7 2.9 0.0 0.0 2.2 0.5 2.2 2.8 2.9 8.3 21.0

4.8 3.0 1.6 2.9 3.9 2.9 4.9

7.3 4.3 1.9 2.4 3.5 3.4 7.4

5.8 3.6 3.6 3.1 3.4 3.1 5.7

5.9 3.8 1.8 3.7 4.5 3.2 6.8

5.8 3.5 2.4 3.7 3.9 3.4 6.4

4.5 3.4 1.6 3.3 3.3 2.9 0.0

0.0

0.0

4.8

8.1

7.5

7.7

8.6

9.0

1.0 0.0 0.0 0.0 0.0 2.1 2.3 12.8 18.1 22.1 12.0 10.2 12.0 24.0 1.9 0.0 0.0 0.0 0.0 4.0 2.5 1.0 0.0 0.0 0.0 0.0 0.9 1;0 6.9 4.5 11.9 7.1 6.1 2.6 3.8

4.6 6.5 4.3 1.3 3.0

4.6 9.0 4.3 1.8 4.0

5.2 S.0 4.8 1.5 2.8

5.2 7.5 4.3 1.3 3.0

8.7 10.7 4.4 2.1 3.2

8.5 4.7 3.7 5.1

5.3 5.8 4.2 5.1

7.1 4.1 4.7 4.9

5.9 4.1 4.6 5.2

8.5 2.5 5.0 5.8

6.3 4.9 9.1 0.56 0.79

6.8 6.7 6.8 5.5 5.5 4.2 7.4 9.1 12.3 0.66 0.57 0.47 1.0 0.85 0.61

2.6

0.0

0.0

5.0 1.0 1.6 2.6

7.3 2.4 2.4 2.9

7.9 3.3 1.9 2.1

1.7 0.0 2.1 1.2

9.8 0.0 16.2 0.16 0.52

9.1 0.0 16.2 0.18 0.48

7.2 0.0 19.6 0.10 0.33

21.2 0.0 41.4 0.03 0.50

0.0

2.5 11.1 0.0 1.5 2.7 2.3 1.4 3.1 25.7 0.0 36.1 0.04 0.68

11.2 0.0 16.0 0.20 0.59

2.2 2.4 3.8 5.4

8.3 7.2 4.4 5.2 11.1 7.8 0.49 0.65 0.78 0.96

41.9 49.3 50.6 21.7 20.8 39.7 61.6 5,1 6.5 4.4 3.7 5.4 7.5 9.9 53.0 44.1 45.0 74.6 73.8 52.9 28.5 1.3 0°89 0.89 3.5 3.6 1.3 0.48

36.2 20.8 43.0 1.2

40.5 39.8 35.3 38.4 18.7 23.3 21.7 17.8 40.8 36.9 43.1 43.9 1.0 0.93 1.2 1.1

*Sample abbreviations are the same as Table 1. #Arabic figures correspond to the peak numbers in Fig. 3.

Steranes and diasteranes

5~t(H), 14ct(H),17~ (H)-cholestane. Generally, the sterane composition of the Bonney samples is more complex than those of the Don Juan samples, and comprises many isomerized forms.

The steranes and diasteranes found in the soil samples are listed in Table 2. In the Don Juan samples, the sterane composition is rather simple but a number of unidentified peaks are detected in the m/z 217 mass fragmentogram (e.g. Fig. 3). The major steranes and diasteranes were (20S)5~t(H), 14ct(H), 17ct (H)-cholestane, (20R)-5~t (H), 14ct(H), 17~ (H)-cholestane, (20R)-24-methyl-5~ (H), 14fl (H), 17fl (H)- cholestane / (20R)- 24 - methyl- 5fl (H), 14ct (H), 17~ (H)-cholestane, (20R)-24-ethyl-5~t(H), 15fl(H), 17fl(H)-cholestane/(20R )-24-ethyl- 5fl(H), 14~t(H),17~t(H)-cholestane, and/or (20R)-24-ethyl-

Fatty acids Normal alkanoic acids ranging from n-Cs to n-C~ were found with a predominance of even-carbon numbers in the soil samples, together with small amounts of n-alkenoic, and iso- and anteiso-alkanoic acids (Fig. 4). The relative abundances of n-alkanoic acids showed bimodal distributions maximizing at n-C,6, n-C,8 or n-C20, and n-C24, n-C26 or n-C2s.

10

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18

13 6 I

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30

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Fig. 3. Mass fragmentogram of steranes and diasteranes (m/z 217) of a soil sample from the McMurdo Dry Valleys, Antarctica (DJ2). Peak identifications are list~ in Table 2.

Organic geochemistry of Antarctic soil

Table 4. Concentrations of hydrocarbons, fatty acids, 3hydroxy acids and ~00J-dicarboxylic acids in soil samples from the McMurdo Dry Valleys, Antarctica (ng/g of dry soil)

15~

10. Sample Wright Valley Don Juan-1 Don Juan-2 Don Juan-3 Don Juan-4 Don Juan-5 Don Juan-6 Taylor Valley Bonney-W1 Benney-C 1 Bonney-E2 Bonney-E8 Bonney-E9 Bonney-E12

5-

ODon Juan-6

#

i

5

Hydrocarbons*

Fatty acids

56 880 7200 70 66 14

4100 8000 48000 7500 4800 2700

42 26 31 26 17 180

ND 810 510 630 330 5500

*Normal alkanes and n-alkenes. (1990a). LD: Less than detection limits. ND: No data.

o

.~

785

3-Hydroxy acids

a.w-Dicarboxylic acids

LD 47 18 45 24 18

LD 54 45 68 56 62

49 48 9,2 LD 3,8 31

31 190 1,4 100 9.7 99

Data from Matsumoto et a/.

~nr~y-C1

"~ 10-

0-

17.2 Bonney-E2

5

0 10

15

20

25

30

Carbon chain length

Fig. 4. Fatty acid distributions in selected soil samples from the McMurdo Dry Valleys, Antarctica (total = 100%): - - , n-alkanoic adds; . . . . . n-alkenoic acids; . . . . . iso-alkanoic acids; - - , anteiso-alkanoic acids.

indices for short-chain (CPIs, C~2-C~8) and longchain (CPIL, C20-C32) n-alkanoic acids are generally low, ranging from 1.2 to 4.8 and from 1.7 to 3.3, respectively (Table 3), compared, for example, with soil samples from Tokyo, Japan (Matsumoto and Hanya, 1980). Of special interest is the paucity of n-alkenoic acids in all the samples. These fatty acid distributions are very different from those in common lacustrine and marine sediments, but are generally similar to those in previous results (Matsumoto et al., 1981a). The concentrations of fatty acids ranged from 330 to 48,000 ng/g of dry soil (Table 4), which are generally much lower than those in lake and pond sediments in the same area (Matsumoto et al., 1979; , Matsumoto, 1989).

Hydroxy acids 2-, 3-, o)-, (o9-1)-Hydroxy acids were found in most soil samples. Here, 3-hydroxy acids will be discussed in detail because quantitative results were obtained for these acids. A suite of normal 3-hydroxy acids ranging from /~-Cs to t-C30 were found with a predominance of even-carbon numbers, together with iso- and anteiso-3-hydroxy acids (Fig. 5). The major

Unusually, the major fatty acids comprised longchain components, such as n-C24, n-C26 and n-C28, in addition to n-C~6. Thus, the long(n-C2o-n-C34)/ short(n-Cl2-n-Clg)-chain n-alkanoic acid ratios are very high (0.80-3.0, Table 3). The carbon preference

Table 3. Long (C=0-C=,)/short (Cl=-C=s)-chaln ratios and carbon preference indices of short-chain (CPIs. C=2-C~e) and long-chain (CPIL, Ca0 -C==) components for straight-chaincombounds found in soil samples from the McMurbo Dry Valleys, Antarctica* n-Alkene@ Sample Wright Valley Don Juan-1 Don Juan-2 Don Juan-3 Don Juan-4 Don Juan-5 Don Juan-6 Taylor Valley Bonn,y-W1 Bonney-C I Bonn*y-E2 Bonn*y-E8 Bonn*y-E9 Bonn*y-E12

n-Alkene@

n-Alkanoic acid

3-Hydroxy acid

CPI

Long/ short CPIS CPI L

Long/ short CPIS CPIL

Long/ short

CPIS

CPIL

6.5 5.2 4.1 3.4 4.9 3.0

0.85 3.0 0.91 2.7 1.7 2.0

1.2 1.5 1.2 1.9 1.5 2.0

1.9 2.0 2.7 3.3 2.5 2.1

ND 1.3 0.61 0.63 0.53 0.88

ND 4.8 3.4 7.0 3.5 3.7

ND 2.2 2.0 4.7 2.0 3.1

ND 0.66 0.23 0.66 0.55 0.85

ND 1.1 1.0 1.1 0.97 0.90

ND 0.84 0.88 0.95 0.83 0.84

17 17 Large # 7.8 Large # 3.5 Large#= 1.6 Large • 3.2 Large # 3.2

ND 0.95 1.0 1.2 1.4 0.80

ND 1.9 4.8 2.2 3.6 3.6

ND 2.2 2.2 1.7 1.9 2.4

0.03 0.35 0.27 ND 0.07 0.23

21 1.3 4.5 ND 5.8 6.7

ND 1.8 ND ND ND 2.3

0.46 0.05 0.42 0.20 0.03 0.14

0.81 0.86 0.80 0.86 0.93 0.82

0.80 0.70 0.82 0.69 ND 0.93

Long/ short CPI

Long/ short

3.4 5.5 2.0 9.1 6.5 13

2.3 2.3 2.7 2.8 2.3 1.9

49 330 99 16 16 Large #

6.1 6.9 16 8.9 15 11

2.0 1.5 1.9 1.4 1.8 2.0

=,=-Dicarboxylio

*CPI values, showing odd/even-carbon ratios for n-alkanes and n-alkenes, and even/odd-carbon ratios @aDlkanoic, 3-hydroxy and a~o-dlcarboxyllc aclds, were calculated according to Kvenvolden (Ig66). ate from Matsumoto e¢ e l . (1990a). ND: No data.

acid

for n-

786

GENK!I. MATSUMOTOet al. 15

15,

Don Juan-2

Don Juan-2 10-

5-

0

Don Juan-3

10"

,l II,

LII]11111 Ii ,,!! ill!

5

Don Juan-3 10-

5-

llll

0

~

10.

I!Ijl

.~ s tl::

0-

10

II,

Don Juan-4

~

i

I ]iii,l,i,],1 los ]

15

20

25

30

Don Juan-6

II

10-

"~ IOn,'

0-

],!, I,

0

r

10

,

i

~

15

i

i

i

] i

r

i

i

i

20

i

15

20

25

30

Carbon chain length I

Don Juan-5

0

10

J

25

,!,i

i

i

30

Fig. 6. ct,co-Dicarboxylicacid distributions in selected soil samples from the McMurdo Dry Valleys, Antarctica (total = 100%). predominances were not observed in any sample, as evidenced by the near-unity values of carbon preference indices for short-chain (CPIs, 0.80-1.1) and long-chain (CPIL, 0.69--0.95) dicarboxylic acids (Table 3).

Carbon chain length

Fig. 5.3-hydroxy acid distributions in selected soil samples from the McMurdo Dry Valleys, Antarctica (total = 100%): normal 3-hydroxy acids; ..... iso-3-hydroxy acids; - - , anteiso-3-hydroxy acids. 3-hydroxy acids are chiefly short-chains fl-Cx4, fl-C~6 and fl-Cjs. Thus, the long/short-chain n-3-hydroxy acid ratios are much lower than unity (0.03-0.88) except for the Don Juan-2 sample (Table 3). The carbon preference indices for short-chain (CPIs, 1.3-7.0) and long-chain (CPIL, 1.8--4.7) n-3-hydroxy acids showed a predominance of even-carbon numbers (Table 3). These CPI values are generally considerably lower than those in lake and pond sediments in the same area. The concentrations of 3-hydroxy acids (3.8-49 ng/g) in the soil samples are much lower than those of the fatty acids (Table 4), and those in the lake and pond sediments (Matsumoto et al., 1988).

Visual kerogen Amorphous kerogen (68-98%) due to microbial debris was found as the major component, with small amounts of very fine coals (2-32%), but no woody and herbaceous kerogens were detected in the soil samples (Table 5). DISCUSSION

Thermal maturity The isomer distributions of triterpanes and steranes are widely used to estimate the sources, maturation, migration and thermal effects of organic matter in petroleums and sedimentary environments (Seifert and Moldowan, 1979, 1981; Mackenzie et al., 1982; Mackenzie, 1984; Philp, 1985, 1986; Matsumoto et al., 1987a). Triterpanes having biologically synthesized configurations, such as 17fl(H),21fl(H)hopane and (22R)-C3r to (22R)-C32-hopane, are

ct,co-Dicarboxylic acids Table 5,

ct,co-Dicarboxylic acids ranging from d-Cs to d-C31 were detected (Fig. 6). Most soils contained bimodal distributions maximizing at d - C , , d-Cn or d-C~3, and d-C:~ or d-C2~. This is the first report of the occurrence of ~t,co-dicarboxylic acids in Antarctic samples. The major ct,w-dicarboxylic acids are all short-chain components d-Cl~-d-Cj4, and thus the long/short-chain dicarboxylic acid ratios are much lower than unity (0.03-0.85, Table 3). Even-carbon

Visual kerogen results for soil samples from the McMurdo Dry Valleys, Antarctica (%)

Sample Wright Valley Don Juan-2 Don Juan-3 Don Juan-4 Taylor Valley Bonney-Wl Bonney-C1 Bonney-E8 Bonney-E 12

Amorphous

Coaly

94 68 98

6 32 2

97 92 93 83

3 8 7 17

Organic geochemistry of Antarctic soil chiefly found in the Don Juan samples, whereas significant amounts of thermally altered forms of 17ct(H),21fl(H)-hopane and (22S)-C31- to (22S)-C33hopane are distributed in the Bonney samples (Table 1). Also, steranes having biologically synthesized configurations, e.g. (20R)-5ct(H),14ct(H), 17~t(H)-steranes are predominant in the Don Juan samples, while thermally altered configurations (20R)- and (20S)-5~(H),14fl(H),17fl(H)-steranes, and diasteranes are found in considerable quantity in the Bonney samples (Table 2). A fairly good correlation (r=0.91, n = 1 2 ) between (22S/22R)-C3]-hopane ratios and 17~(H), 21 fl (H)/17fl (H),2 lfl (H)-hopane ratios, a good correlation between (20S/20R)-5~t(H),14~(H)17ct(H)-CEqsterane ratios and (22S/22R)-C3,-hopane ratios (r = 0.96) as well as a relatively good correlation between ( 20S / 20R )- 5ct(H),14ct (H ),17~t(H)-CE9-sterane ratios and (20R +20S)-5~(H),I4fl(H),17fl(H)/ 5~t(H),14~t(H),17ct(H)-C29-sterane ratios (r=0.85) were obtained for these soil samples (Fig. 7). These hopane and sterane ratios show that the Don Juan samples (Don Juan-1 to Don Juan-6: DJ1-DJ6) are less mature than those in the Bonney samples (Bonney-W1, -C1, -E2, -E8, -E9 and -El2: BWI, BC1, BE2, BE8, BE9 and BE12, respectively), and can be clearly classified from the Bonney samples. No soil samples, however, reached the thermal equilibrium values of (22S/22R)-C3~-hopane ratios (1.5) and of (20S/20R)-5ct(H),14ct(H),17ct(H)-C29-sterane ratios (1.2) (Seifert and Moldowan, 1981; Mackenzie et al., 1982; Suzuki, 1984; Philp, 1985; Matsumoto et al., 1987a). The Beacon Supergroup in the McMurdo Dry Valleys were baked by basaltic dykes in the Jurassic period (Funaki, 1983), and thus contains triterpanes and steranes having a wide variety of maturation from near zero to equilibrium ratios, although triterpenes are not common (Matsumoto et al., 1987a). It is much likely, therefore, that moraines in the Bonney samples are composed of the Beacon Supergroup containing more thermally influenced organic matter than those in the Don Juan samples. Also, volcanic activity evidenced by a number of cinder cones and volcanic vents in the surroundings of Lake Bonney during 2.5-4.5m.a. BP (Kurasawa, 1986) might be influenced on the maturation of organic matter. Our soil samples, however, contain considerable amounts of triterpenes and less matured triterpanes and steranes, indicating the presence of young organic matter due to biological activity other than the Beacon Supergroup. However, significant changes in organic compounds except for the triterpanes, steranes and CPI values of n-alkanes were not observed between two sampling sites (e.g. Table 3). These results may be explained by the relative thermal stability of organic compound classes as well as the contribution of young organic matter, none of which experienced thermal stresses as discussed below. OCi 16/4/6~J

6.6-

787 (l) BE8

r = 0.91 (except for BE8)

• BE9 BC1

~ 2.0~ 1.5• BE2

~ 1.o0.s0.0

•BE12 DJ1 D J5 IIDj 6 • aDd2 DJ4 • D J3

I 0.4 0~6 0.8 (22S/22R)-C3z Hopane

012

0,0

•BWI

11o BE9 •

1.0-

• BE8

r = 0.96

BC1

0.8

o

0.6

BWl• IBE12

IDJ1

0.4

•BE2

• D J2

~-~

• D J3 0.2

•DJ6

IDJ5 • D J4

0.0 0,0

ol

o12

o18

o4'

(20S/20R)-~a-C29

os

016

Sterane

1.0-

B C l l B~8

r = 0,85

• BE9 • BE2

0.8BWI

i

•DJ5

• DJ6

• D J4

IDJ1

•BE12

0.6DJ2

0.4-

• DJ3 0,2-

0.0 0.0

I

o,

o12

03

o4

os

o16

(20S/20R)-etc~-C ~9 Sterane

Fig. 7. Correlation between maturation parameters of triterpanes and steranes for soil samples; r = correlation coetficient. Sample abbreviations are the same as in Table 1.

Sources of organic components The features of organic compounds in the soil samples suggest that organic matter is derived from various organisms ranging from bacteria to vascular plants, with various ages from Devonian (Beacon Supergroup) to Recent. No vascular plants occur in the McMurdo Dry Valleys. Thus, direct contribution of vascular plants is unlikely. Also, no aeolian transport of the waxes of vascular plants from the mid and lower latitudes are important sources, because the compositions of the soil hydrocarbons and fatty acids are very different from those in the waxes of vascular plants, as discussed elsewhere (Matsumoto et al., 1981a, 1990a). Visual kerogen suggests that the main sources of organic matter are microorganisms and ancient vascular plants (Table 5). Generally, n-alkenoic acids are major fatty acids in living organisms, but were not abundant in all the

788

GENKI I.

MATSUMOTOet al.

soil samples. Detailed microscopic studies reveal that no living cyanobacteria and microalgae occur, but small amounts of their debris are found in some soil samples (Matsumoto et al., 1990a). Also, Friedmann and Kibler (1980) reported that living cells of cyanobacteria and microalgae in soils of the McMurdo Dry Valleys are generally not abundant. Thus, living organisms are not important sources of soil organic matter, and organic matter can be attributed to the following three major sources: (1) Erosion o f the Beacon Supergroup. The Beacon Supergroup of Gondwanaland sediments containing various plant fossils are widely distributed in the McMurdo Dry Valleys and adjacent regions (Fig. 1) (e.g. Barrett and Kyle, 1975). These sedimentary rocks contain hydrocarbons, involving triterpanes and steranes, and n-alkanoic acids (Matsumoto et al., 1986, 1987a). (2) Past biological activity. Before and inter-glaciation of Antarctica (Eocene-Oligocene), warm climatic conditions provided a favorable habitat for various organisms, involving vascular plants in the McMurdo Sound region (e.g. Harwood et al., 1989). Thus, organic matter produced by this biological activity may be buried under the ice-sheet, and glacially eroded and transported to the valley depressions as moraine. Thus, our soil samples may contain such organic matter. Also, organic matter may have been produced by in situ biological activity, and accumulated for a geological time. (3) Wind-transported cyanobacterial mats. Cyanobacterial mats containing various organisms are commonly distributed in and around the streams, lakes and ponds of the McMurdo Dry Valleys (e.g. Vincent, 1988; Matsumoto G. I., personal observations). Katabatic wind in the valleys is strong and, thus the wind-transportation of these organisms and their detritus may be responsible for the sources of soil organic matter. For instance, cyanobacterial debris found in the soil samples may be due to wind-transported materials. Complex organic matter in the soil samples may be, therefore, result via a mixture of these three sources. Triterpanes found in the soil samples are widely distributed in sedimentary rocks, including Beacon Supergroup samples and petroleums (Seifert and Moldowan, 1979; Mackenzie et al., 1982; Philp, 1985; Matsumoto et al., 1987a), although 17fl(H)-22,29, 30-trisnorhopane is abundant in the soil samples (Table 1). This is consistent with the low maturity of the samples. Triterpanes are not common in living organisms. Thus, our triterpanes are mainly attributed to the Beacon Supergroup and/or past biological activity. Triterpenes are not common in the Beacon Supergroup samples, but are predominant components in

Recent lacustrine (Volkman et al., 1986; Matsumoto et al., 1987b, 1989) and marine (Venkatesan and Kaplan, 1987; Venkatesan, 1988a, b; Matsumoto et al., 1990b) sediments, Antarctica. These triterpenes are widely distributed in various organisms, involving bacteria, cyanobacteria, lichens, mosses and vascular plants (Rohmer et al., 1984; Matsumoto and Kanda, 1985; Philp, 1985; Venkatesan, 1988a, b). Thus, biological activity in the past and/or wind-transported cyanobacterial mats are believed to be sources of triterpenes in the soil samples, although specific organisms are not yet clear. Steranes found in the soil samples are ubiquitous in petroleums and sedimentary rocks. Steranes and diasteranes are generally accepted to be derived from sterols, and thus reflect the sterol composition of organic matter in sedimentary environments (Seifert and Moldowan, 1981; Mackenzie et al., 1982; Philp, 1985). The relative abundances of C27-C29 steranes do not change significantly with increasing thermal stress (Lewan et al., 1986), but are suggested to change, in certain cases, due to oil generation (Mackenzie, 1984). It is unlikely that the Beacon Supergroup generates oils. Thus, in our case, the relative abundances of C27-C29steranes are a good tool to estimate the sources of organic matter. The predominance of 24-ethylcholest-5-en-3fl-ol (C29 sterol) or C29 sterane over C27 and CEs sterols or steranes is usually indicative of a vascular plant origin in environmental samples in the mid and lower latitudes (Nishimura, 1977; Huang and Meinschein, 1979; Volkman, 1986). 24-Ethylcholest-5-en-3fl-ol is, however, frequently the major sterol in Antarctic lake waters and sediments, derived mainly from cyanobacteria and green algae (Matsumoto et al., 1982; Volkman, 1986; Matsumoto, 1989). 24-Methylcholest-5-en-3fl-ol is the predominant sterol in Antarctic mosses (Matsumoto and Kanda, 1985) and certain diatoms (Volkman, 1986; Nichols et al., 1989), although recently Nichols et al. (1989) found a predominance of 24-ethylcholest-5-en-3fl-ol in a diatom community from McMurdo Sound. In the triangular diagram, (20R)-5~t(H),14ct(H), 17~(H)-C29-sterane is predominant in the DJ4, DJ5, D J1 and D J6 samples, whereas (20R)-5~t(H),14ct(H), 17ct(H)-C27-sterane predominates in the BW1 sample (Fig. 8). Generally, (20R)-Sct(H),14g(H),17g(H)-C2ssterane is not abundant in these samples. Also, (20R)-5~t (H), 14g (H), 17ct(H)-C29/C27-sterane ratios in 7 of the 12 soil samples are greater than unity (Table 2). These sterane results suggest that organic matter in the soil samples originates from both vascular plants and/or Antarctic cyanobacteria/green algae as well as common cyanobacteria/algae, as reported for the mid and lower latitudes, while the contribution of mosses and/or diatoms should be small. Generally, long-chain n-alkanes and n-alkanoic acids with marked predominances of odd- and evencarbon numbers, respectively, in environmental samples from the mid and lower latitudes are believed

Organic geochemistry of Antarctic soil Cza

50

Cz-~

50

5O

Cz9

Fig. 8. Relative abundances of (20R)-5~ (H), 14e (H), 17e (H)C27-C29-steranes for soil samples. Sample abbreviations are the same as in Table I. to originate from the waxes of vascular plants even in the open ocean sediments (Matsuda and Koyama, 1978; Simoneit, 1978; Gagosian and Peltzer, 1986). Unexpectedly, long-chain n-alkanes and n-alkenes with a predominance of odd-carbon numbers are found in all the soil samples (Table 3; Matsumoto et al., 1990a). Also, long-chain n-alkanoic acids showing a predominance of even-carbon numbers are abundant in all the soil samples (Fig. 4, Table 3). These results suggest a large contribution from the waxes of vascular plants to the soil organic matter other than from the Beacon Supergroup, because this contains near-unity ratios of n-alkanes (Matsumoto et al., 1986). It is probable that past biological activity, including vascular plants, contribute to the soil organic matter. The occurrence of iso- and anteiso-alkanoic acids indicates a contribution of bacteria (Kaneda, 1967; O'Leary, 1982). 3-Hydroxy acids are widely distributed in bacteria, yeasts and vascular plants (Eglinton et al., 1968; Boon et al., 1977; Kawamura and Ishiwatari, 1982; Goossens et al., 1986), cyanobacteria (Drews and Weckesser, 1982; Matsumoto and Nagashima, 1984) and microalgae (Matsumoto and Nagashima, 1984). 3-Hydroxy acids are not common in sedimentary rocks, and may be degraded over a geological time. Thus, 3-hydroxy acids found in our soil samples may be due to past biological activity and/or wind-transported cyanobacterial mats, rather than from the Beacon Supergroup. The occurrence of iso- and anteiso-3-hydroxy acids can be again explained by the contribution of bacteria (Matsumoto et al., 1988, 1989). There is a paucity of ct,~o-dicarboxylic acids in cyanobacteria or algae, although esterified dicarboxylic acids are present in many plants, and it is known that certain bacteria produce and accumulate these dicarboxylic acids (Johns and Onder, 1975). Ishiwatari et al. (1980) suggested that dicarboxylic acids are formed from corresponding n-alkanoic acids in the early stage of diagenesis. ~t,o)-Dicarboxylic acid distributions in the soil samples are very

789

different from those in n-alkanoic acids (Figs 4 and 6, Table 3) and from recent sediments, where evencarbon numbered dicarboxylic acids usually predominate (Johns and Onder, 1975; Ishiwatari et al., 1980), but similar to those in ancient sediments, e.g. Scottish Torbanite (Carboniferous), in which no even-carbon dicarboxylic acids predominate (Douglas et al., 1970). Hence, direct o-oxidation of corresponding n-alkanoic acids is unlikely. It is probable, therefore, that these dicarboxylic acids are derived from the Beacon Supergroup. Interestingly, the most dominant dicarboxylic acids in the soil samples are mainly d-Cl3, which is similar to those in ancient sediments (Haug et al., 1967; Douglas et al., 1970), probably occurring via similar diagenetic/ catagenetic processes in geological environments. Consequently, complex organic composition in soil samples from the McMurdo Dry Valleys may be attributed to the mixing of different ages from Devonian to Recent as well as various source organisms from bacteria to vascular plants, i.e. glacially eroded Beacon Supergroup sedimentary rocks and past biological debris containing vascular plant waxes, and wind-transported cyanobacterial mats, rather than from living organisms. S U M M A R Y AND C O N C L U S I O N S

The geochemical features and sources of organic components found in soil samples from the McMurdo Dry Valleys of southern Victoria, Land, Antarctica, are summarized as follows: (i) Long-chain n-alkanoic acids having a predominance of even-carbon numbers are the major fatty acids; n-alkenoic acids are rare. (2) Triterpanes and steranes having biologically synthesized configurations--I 7fl(H),21 fl(H)hopane, (22R)-triterpanes, (20R)-5ct(H), 14~(H),17,t(H)-steranes--are predominant components in the Don Juan samples, while thermally altered forms of triterpanes and steranes are found in considerable quantity in the Bonney samples, probably reflecting the different thermal stresses of source organic matter between the two sampling sites. (3) 3-Hydroxy acids having a predominance of even-carbon numbers are found in most soil samples, together with 2-, (o-, (co-l)-hydroxy acids, whereas ~t,og-dicarboxylic acids show near-unity CPI values. (4) Amorphous materials due to microbial debris are the major visual kerogen, with small amounts of very fine coals; woody and herbaceous kerogens do not occur. (5) The organic compounds in soil samples are probably derived from the erosion of the Beacon Supergroup and biological debris in the past containing vascular plant waxes as well as wind-transported cyanobacterial mats, rather than from living organisms.

790

GENKI I. MArSUMOrOet al.

Acknowledgements--We are greatly indebted to the Antarctic Division, DSIR, New Zealand, the U.S. National Science Foundation, the U.S. Navy, the Japan Polar Research Association and the National Institute of Polar Research (Japan) for their support in Antarctic researches. Also, we thank K211 members led by Professor T. Torii for their help in collecting samples, and Professor Y. Yoshida of the National Institute of Polar Research, Japan, for his useful suggestion.

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