- Email: [email protected]
Origins and simulated thermal alteration of sterols and keto-alcohols in deep-sea marine sediments of the Okinawa Trough
Org. Geochem. Vol. 21, No. 3/4, pp. 4t5-422, 1994 Copyright © 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0146-6380/94 $7.00 + 0.00
Pergamon
Origins and simulated thermal alteration of sterols and keto-aleohols in deep-sea marine sediments of the Okinawa Trough JIANG SHANCHUN,I TERESAO'LEARY,2 JOHN K. VOLKMAN,2 ZHANGHUIZHI,l JIA RONGFEN,1 YU SUHUA,l WANGYAN,1 LUAN ZUOFENG,3 SUN ZOOQING3 arid J1ANGRONGHUA3 tGuangzhou Institute of New Technology for Geology, Chinese Academy of Sciences, Guangzhou, P.R. China, 2CSIRO Division of Oceanography, Hobart, Tasmania, Australia and 3Institute of Oceanology, Chinese Academy of Sciences, Qingdao, P.R. China Abstract---Compositional data on the sterol and alcohol fractions isolated from deep-sea marine sediments from the Okinawa Trough were obtained to determine the relative contribution from marine and terrestrial inputs. Following extraction, the total saponifled neutral fraction was derivatized with BSTFA and then analysed by capillary GC and GC-MS. A suite of C2~--C29stenols and stanols and C30-C32keto-alcohols were identified in the sediments. Major sterols included 27-nor-24-methylcholesta-5,22E-dien-3fl-oland cholest-5-en-3fl-ol,which are most likely from marine fauna, and the C2s sterols 24-methylcholesta-5,22Edien-3fl-ol and 24-methylcholesta-5,24(28)-dien-3fl-ol,both of which are common in diatoms. C29 sterols were dominated by sterols with 24-ethyl substitution of higher plant origin, but 23,24-dimethyl sterols which are found in some marine phytoplankton were also quite abundant. The major 4-methyl sterol was 4~,23,24-trimethyl-5~-eholest-22E-en-3~-olwhich is considered a common indicator of dinoflagellates. Each sterol co-occurred with the corresponding 5~-stanol. Other indicators of terrestrial input such as a- and fl-amyrin were also identified. The sediments also contained significant amounts of the C30 keto-alcohol triacontan-15-one-l-ol, as well as smaller amounts of C3~ and C32 keto-alcohols. These unusual lipids are found in many marine sediments, and they may be formed by the oxidation of the corresponding C30-C32 alkyl diols found in some marine microalgae. The thermal stability of the compounds in these sediments was studied by heating portions of the surface sediment in glass tubes for 16 h at temperatures ranging from 100°C to 200°C. The C27 stanol/stenol ratio increased with increasing temperatures up to 140°C, as did the corresponding C28 and C29 stanol/stenol ratios. The keto-alcohols were more stable than sterols under these conditions. Key words----sterols, stanols, keto-alcohols, thermal alteration, Okinawa Trough
INTRODUCTION The Okinawa Trough is a back-arc basin which lies between the East China Sea shelf and the Ryukyu Islands in the marginal island arc of the West Pacific (Fig. 1). The sediments of the Okinawa Trough consist mainly of a calcareous brownish-grey ooze with abundant shell fossils. Sediments were sampled in order to obtain compositional data on the organic material present and to determine possible origins. Sterols occur in high concentrations in most recent sediments. They are comparatively stable and hence have a long geological record. Over the past two decades, extensive research has been carried out on the sterol distributions in sediments and seawater to investigate their potential as ecological markers for the contribution from t/;rrestrial and marine organisms to sediments (Nishimura and Koyama, 1977; Volkman et aL, 1983, 1987; Bang Shanchun et aL, 1992). The sterol distribution can also give an indication of early-stage diagenesis and microbial transformations. However, chemical, physical and microbial transformation of sterols produce complex
mixtures of diagenetic products that can limit their usefulness as source indicators. Sterol diagenesis in deeper sediments is expected to be controlled by physicochemical variables such as redox and temperature. The relative stabilities of various sedimentary sterols towards physical and chemical degradation has been studied. Dreier et al. (1988) concluded that 4-methyl sterols were more stable than 4-desmethyl sterols after heating a series of sterols in lacustrine sediments from 150 to 250°C. It is a common observation that the 5~-stanol/A5stenol ratio increases with depth in marine sediments. For example Jiang Shanchun et al. (1992) in their study of marine sediments from Beibu Gulf in the South China Sea, reported that the C27 5~-stanol/A5stenol ratio increased from 0.57 to 1.74 over the depth range 50-465 cm. The present study presents the first compositional data for sterols, and other neutral constituents, in marine sediments from the Okinawa Trough, off the coast of China. The sterol distribution of sediment sample Z-17-4 was analysed. As an adjunct to this study, simulated thermal alteration experiments were performed on the same sediment sample.
415
J1ANGSHANCHUNet al.
416
(80: 20 v/v) at 80°C for 2 h. The neutral fraction was treated with bis(trimethylsilyl)trifluoroacetamide (BSTFA) immediately before G C analysis to convert compounds containing free hydroxyl groups to their trimethylsilyl-ether derivatives•
E X P E R I M E N T A L
Sample collection Marine sediments were collected during an investigatory cruise of Oceangoing Science Ship No. 1 by researchers from the Institute of Oceanology, Chinese Academy of Science, Qingdao, P.R. China. Sediment grab sample No. Z-17-4 was obtained from 26°35'N, 125<~52'E in the Okinawa Trough at a water depth of 1670m (Fig. 1). The bottom sediments consisted of a brownish-grey ooze, which contained abundant shells and a considerable amount of calcium carbonate.
Simulated thermal maturation experiment The wet sediment was dried in an oven overnight at 50°C. Four 50 g portions of dry sediment were put into glass tubes, which were then sealed under nitrogen. Each tube was then placed in the oven and heated at 100, 140, 175 and 200~C respectively for 16 h. The sterol fraction was isolated using T L C and derivatized using B S T F A prior to analysis by G C and GC-MS.
Lipid extraction and fractionation Wet sediment was weighed and quantitatively extracted by the modified one-phase c h l o r o f o r m methanol Bligh and Dyer method (Bligh and Dyer, 1959). After phase separation, the lipids were recovered in the lower chloroform phase. The solvents were then removed under vacuum. The upper aqueous phase containing salts and water-soluble material was discarded• The total saponified neutral lipid (TSN) fraction was obtained by reducing an aliquot of the total solvent extract to near dryness under N2 followed by saponification in 5% K O H with methanol-water
1180 34° ,
,
,
120° , v
~
~ , l
122° , ,
!,
Analysis by capillary gas chromatography (GC) The TSN fractions were analysed with a Shimadzu 9A gas chromatograph equipped with an F I D and cool OCI-3 on-column injector (SGE, Australia). Samples were dissolved in chloroform to which a known amount of n-docosane (n-Cz2) was added as an internal standard• Samples were injected, at an oven temperature at 4 5 C . onto a fused-silica capillary column (nonpolar methyl silicone: 50 m × 0.32 mm i.d., Hewlett-Packard). After 1 min. the oven temperature was raised to 1 2 0 C at
124* ,! i
i,
126° I
i
128°
130°
132°
i ~ l
Yellow Sea 32* Shangh~
:;
..-'÷Dl/
30* Il/
P.R.C h i n a / L
.~
EastChinaSea
LFujii , 26 ° /
Z-17--4O
f"
II
ij
.
.
•
.
.!
.
~.~
'~
...,>
Taiwan" •
<>£
," ~" "';" ,"
,vincqtif'
d
° .
.
.
.~ ff .
.
.
.
.
.
.
.
.
.
.
24 °
Fig. 1. Map of East China Sea showing sample site 7.-17.4. Note the proximity of the sample to the edge of the continental shelf (marked by 201)m depth contour) even though it was collected at 1670 m water depth.
Sterols and keto-aleohols in deep-sea sediments 30°C/min and then to 320°C at 4°C/min, and then held for 20 min. Hydrogen was used as the carrier gas. The detector temperature was 330°C. Analysis by gas chromatography-mass spectrometry (GC-MS) G C - M S analyses were performed with an HP 5890 GC and 5790 MSD fitted with a direct capillary inlet. The nonpolar column, injector and chromatographic conditions were similar to those described above with the exception that helium was used as the carrier gas. Electron impact mass spectra were acquired and processed with an HP 59970A Computer Workstation. Typical MSD operating conditions were: electron multiplier 2200 V; transfer line 310°C; electron impact energy of 70eV; 0.8 scans/s; mass range 40--600 Da. Quantitation Peak areas were quantified from the GC traces using chromatography software (DAPA Scientific Software); however, due to the complexity of the sterol chromatogram and co-elution of some components, it was necessary to quantify some peaks using ratios obtained from GC-MS data. A5 sterols were identified using the following ions: m/z 129, 255, and 386. The 5~-stanols were identified from m/z 215, 257 and 388 mass fragmentograms. RESULTS AND DISCUSSION The organic carbon content in the surface sediment from sample site Z-17-4 is quite low (0.76%) when compared to highly productive marine areas. For example, in the upwelling region off Peru, organic carbon comprises between 3 and 5% of the sediment (Volkman et al., 1983, 1987). The organic carbon content reflects both the primary productivity in the water column (Henrichs and Farrington, 1984) and degree of preservation (e.g. Emerson and Hedges, 1988). Steroi abundances are low in the Okinawa Trough (2.3 gg/g dry wt) when compared to Peru ( ~ 1 3 0 # g / g dry wt) and more like concentrations found in intertidal sediments (2.0 gg/g dry wt; Volkman et al., 1981) reflecting low productivity in the water column, the effects of diagenetic processes such as dehydration to sterenes, oxidation to steroid ketones and reduction to 5~-stanols (e.g. Volkman et al., 1987). 4-Desmethyl sterols A complex distribution of sterols was found in the sediment (Fig. 2), which is characteristic of many marine sediments containing both marine and terrestrially-derived organic matter (e.g. Volkman et al., 1981, 1987; Jiang Shanchun et al., 1992). The major C27 sterols in the sediment are cholest-5en-3fl-ol and cholesta-5,22E-dien-3fl-ol and their corresponding stanols (Table 1). Cholest-5-en-3p-ol (cholesterol) is the most abundant sterol and corn0(3 21-3/4--N
417
prises 9.3% of the total identified sterols. Cholesterol is common in marine sediments, and is most likely derived from zooplankton (Gagosian et al., 1980) and benthic animals, although microalgal sources are also possible (Volkman, 1986). Sterols with 27-nor side-chains were also identified in the sediments from the Okinawa Trough. These sterols occur widely in the marine food web, and in sediments, but their origins are not well known (de Leeuw et al., 1983). C2s sterols comprised 23% of the identified sterols. These included 24-methylcholesta-5,22E-dien-3fl-ol and 24-methylcbolesta-5,24(28)-dien-3fl-ol and their corresponding stanols. 24-Methylcholest-5-en-3fl-ol is also present in significant amounts (Table 1). The presence of 24methylcholesta-5,22E-dien-3fl-ol, with cholesta5,22E-dien-3fl-ol and 23,24-dimethylcholesta5,22E-dien-3fl-ol suggests that diatoms are likely to be their major source (Volkman, 1986; Volkman et al., 1987). The 24-ethyl substituted sterols dominate the C29 sterol distribution and comprise 24% of the total identified sterols. The most abundant C29 sterols present are 24-ethylcholest-5-en-3fl-oi (8.0%), 24-ethylcholesta-5,22E-dien-3fl-ol (3.7%) and 24ethylcholesta-5,24(28)Z-dien-3fl-ol (3.8%). The corresponding stanols are also present in significant amounts (Table 1). The 23,24-dimethyl substituted sterol distribution is dominated by 5ct-stanols such as 23,24-dimethyl-5ct-cholest-22E-en-3fl-ol (4.9%) and 23,24-dimethylcholestan-3fl-ol (3.4%). The corresponding stenois constituted 2.3 and 0.77% respectively. The abundance of 23,24-dimethyl substituted sterols most likely reflect a dinoflageilate source as the 23,24-dimethyl substitution is a common feature of the 4-methyl sterols of these algae (Alam et al., 1979). For example, de Leeuw et al. (1983) attributed the presence of 23,24-dimethylcholesta5,22E-dien-3fl-ol, 23,24-dimethyl-5~-cholest-22E-en3fl-ol, 23,24-dimethylcholest-5-en-3fl-ol and 23,24dimethyl-5~-cholestan-3fl-ol in Black Sea sediments to dinoflagellates. Minor contributions from diatoms and prymnesiophytes are also possible (Volkman, 1986). The dominance of 24-ethyl substituted C29 sterols is unusual for a surface marine sediment. 24-Ethylcholesterol is commonly thought to derive from vascular plants of terrestrial origin, however several species of phytoplankton are now known to contain large amounts of this sterol (Volkman, 1986; Nichols et al., 1986). The two other common sterols in vascular plants are 24-ethylcholesta-5,22E-dien-3fl-ol and 24-methylcholest-5-en-3fl-ol (Volkman et ai., 1987) both of which occur in significant amounts in the Okinawa Trough sediments. The ratios of these three sterols is 2.9:1.3:1 respectively. This is similar to the ratio of these three sterols in sediments in the upwelling zone off Peru (3.5:1.8:1), where these
418
JL~qGSHANCltUNet al.
21
a) sterols (TMSi-ethers)
16
7
10
/ L7+lg
13
19
VI
tO r~
22
I
I
I
I
t
60
62
64
66
68
23+24
b) diols & keto-ols (TMSi-ethers)
25 26
.J [
I
I
I
t
70
72
74
76
78
Time (minutes) Fig. 2. Partial gas chromatogramsshowingdistributionsof (a) sterolsand (b) long-chaindiols and keto-ols (as TMSi-ethers)from sediment Z-17-4. Peaks are identifiedin Table 2. The peaks in 2(a) are enhanced by halving the attenuation compared with the peaks in 2(b). sterols were thought to be derived mainly from organic matter of terrestrial origin (Volkman et al., 1987).
cannot be excluded (Volkman et al., 1993). Small amounts of 4,24-dimethyl-5~-cholestan-3fl-ol were also observed.
4 - M e t h y l sterols
5~-Stanols / A 5-stenols
Among marine microalgae that have been studied, only the dinoflagellates (Alam et al., 1979) and a few prymnesiophytes (Volkman et al., 1990) produce large amounts of 4-methyl sterois. The major 4methyl sterol identified in the Okinawa Trough sediments is 4~,23,24-trimethyl-5,,-eholest-22E-en-3/1-ol (dinosterol), which comprised 9.1% of the total identified sterols (Table 1). The occurrence of such high concentrations of dinosterol is indicative of a dinoflagellate source (Boon et al., 1979), although the possibility of a minor contribution from diatoms
Previous reports have shown that stanols are more stable to oxidative degradation than stenols (Nishimura, 1977). Nishimura (1977) predicted that stanol/stenol ratios would be higher in more reduced sediment. Gagosian et al. (1980) reported stanol/stenol ratios ranging from 0.48 to 2.7 for anoxic sediments from Black Sea cores, whereas stanol/stenol ratios ranged from 0.21 to 0.50 for the more oxic sediments of the western North Atlantic. The 5~-stanols/AS-stenol ratios from the Okinawa
Sterols and keto-alcohols in deep-sea sediments Trough surface sediments ranged from 0.2 to 4.42 depending on which pair is examined. It is very likely that the high ratios may be attributable to a direct input o f 5~t-stanols such as 23,24-dimethyl-5ctcholestan-3fl-ol rather than from conversion of the corresponding stenol.
Triterpene alcohols Jiang Shanchun and Fu Jiamo (1984) previously noted that higher plant detritus is constantly transported by wind and surface currents from Fujian (Fig. 1) and Zhejiang provinces into the Okinawa Trough region. These authors identified several monoterpenes including cyclohexane, 1-methyl-5(1-methylethenyl)-cyclohexene and l-methyl-4-(1methylethylidene)-cyclohexanes which they attributed to terrestrial plant inputs. Biomarker evidence of this was also obtained in the present work from the identification of ~- and flamyrins. These were identified from their mass spectra (Volkman et al., 1987) and from comparison of retention times on the m / z 218 mass fragmentogram (Fig. 3) with authentic standards which were run separately. The concentrations of 0r- and [3-amyrin were 11 and 15 ng/g dry wt respectively. These concentrations are very low when compared to sediments from the Peru upwelling zone where the concentrations of ct- and
419
fl-amyrin were up to l0 times higher (Volkman et al., 1987).
C m and C~2 alkane diols and keto-alcohols The C30, Cal and C32 keto-alcohols were identified from their characteristic mass spectra and their retention times on the m / z 130 mass fragrnentogram (Fig. 4). The C30 c o m p o u n d is approximately four times more abundant than the C32 c o m p o u n d (Table l). These keto-alcohols have been identified in many aquatic sediments (e.g. de Leeuw et al., 1981; Smith et al., 1983; Nichols and Johns, 1986), but a biological source has still not been identified. The corresponding alkyl-1,15-diols have been identified in a natural bloom of the cyanobacterium Aphanizomenon flos-aquae (Morris and Brassell, 1988), but the same compounds were not found in studies of this species in laboratory culture (de Leeuw et al., 1992). The C30 diol is more abundant than the corresponding C30 keto-alcohol (Table l). Volkman et al. (1992) have identified C30-C32 diols in marine microalgae from the class Eustigmatophyceae, so an algal source for the diols seems likely. The keto-alcohols present in the sample may arise from oxidation of the diols, or perhaps they are synthesized by an algal species which has not yet been studied. Further research on the origins and diagenesis of these compounds is clearly still needed.
Table 1. Concentrations (ng/g dry wt of sediment) of sterols and long-chain diols and keto-ols identifiedin sediment sample from site Z-17-4 in the Okinawa Trough GC peak* Sterol identification ng/g dry wt % Total sterols I 27-nor-24-methylcholesta-5,22E-dien-3fl-ol 21 I. 1 2 cholesta-5,22E-dien-3fl -ol 110 5.7 3 27-nor-24-methyl-5~t-cholest-22E-en-3fl-ol 20 1.0 4 5ct-cholest-22E-en-3fl-ol 76 4.0 5 cholest-5-en-3/~-ol 179 9.2 6 5:t-cholestan-3fl-ol 85 4.4 7 24-methylcholesta-5,22E-dien-3fl-ol 147 7.7 8 24-methyl-5~t-cholest-22E-en-3fl-ol 77 4.0 9 24-methylcholesta-5,24(28)E-dien-3fl-ol 49 2.5 10 24-methyl-5ct-cholest-24(28)E-en-3fl-ol 86 4.5 l0 24-methylcholest-5-en-3fl-ol 54 2.8 I1 24-methyl-Sct-cholestan-3fl-ol 32 1.7 12 23,24-dimethylcholesta-5,22E-dien-3fl-ol 44 2.3 13 23,24-dimethyl-5~t -cholest-22E-en-3fl-ol 96 5.0 13 24-ethylcholesta-5,22E-dien-3fl-ol 71 3.7 14 24-ethyl-Sct-cholest-22E-en-3fl-ol 46 2.4 15 23,24-dimethylcholest-5-en-3fl-ol 15 0.8 16 24-ethylcholest-5-en-3fl -ol 154 8.0 16 24-ethylcholesta-5,24(28)E-dien-3fl -ol 26 1.4 16 23,24-dimethyl-Sct-cholestan-3fl-ol 65 3.4 17 24-ethylcholesta-5,24(28)Z-dien-3fl-ol 73 3.8 17 24-ethyl-5~t-cholest-24(28)E-en-3fl-ol 9 0.5 18 24-ethyl-5ct-cholestan-3fl-ol 67 3.5 19 4,24-dimethyl-5~t-cholestan-3fl-ol 30 1.6 20 24-ethyl-50t-cholest-24(28)Z-en-3fl-ol 16 0.8 21 4~t,23,24-trimethyl-5ct-cholest-22E-en-3fl-ol 175 9.0 22 C30-Sct-stanols 101 5.2 TOTAL 23 24 25 26
l,l 5-dihydroxytriacontane triacontan- 15-one-I-ol I,I 5-dihydroxydotriacontane dotriacontan-15-one-l-ol
TOTAL *Peak numbers refer to Fig. 2.
1923 231 121 63 27 442
100
420
JIANGSHANCHUNet al. Okinawa "/'rough Z-17-4 Tnterpeae alcohols (TMSi-ethers)
~-myrm
m/z218 a-amyrm
8 <
51
53
55
Time (minutes) Fig. 3. Mass fragmentogram fbr m/z 218, the base peak in mass spectra of ~-amyrin (urs-12-en-3fl-ol) and fl-amyrin (olean-12-en-3fl-ol).
S i m u l a t e d thermal alteration
Major changes to the sterol distributions were observed as the sediments were heated up to 175°C (Fig. 5). At 200°C the sterols are almost completely destroyed. The C27 and C 2 9 5~-stanol/Atstenol ratios increase with increasing temperature up to 175°C, as do the C27 and C28 A22 stanol/AS'n-stenol ratios (Table 2). Previous studies of thermal alteration have shown that the distributions of sterols in sediments are affected by temperature (Ikan et al., 1975; Sieskind et al., 1979; Dreier et al., 1988), although different results have been obtained. Ikan et al.
(1975) showed that cholesterol is released by heating sediment. Maximum yields were obtained by heating sediments at 100°C for 30 days, presumably due to the release of sterols from bound forms. Higher temperatures led to significant decreases in sterol concentrations as a result of thermal degradation. Dreier et al. (1988) also noted increasing yields of extractable sterols after heating lacustrine sediments up to a temperature of 20OC. Sieskind et al. (1979) demonstrated the conversion of cholestanol to a mixture of steranes (40%) and sterenes (35%) when heated with kaolinite at 140°C for 16h.
C3o Okmawa Trough Z-17-4 Alkan-15-one-1-ol (TMSi-ethers) m/z 130
C32
<
,
55
,
,
57 Time (minutes)
,
,
,
59
Fig. 4. Mass fragmentogram for m/z 130, showing the distribution of the C30~Cn long-chain alkan-I 5-one-l-ols.
Sterols and keto-alcohols in deep-sea sediments
was unaffected at temperatures up to 175°C, indicating that they are more stable than sterols under these conditions. However, at 200°C the ketoalcohols were also substantially degraded.
Room Temp.
7
24
CONCLUSIONS
Data on the distribution of sterols, and ketoalcohols, in a deep-sea marine sediment from the Okinawa Trough are presented for the first time. The sediments are low in total organic carbon, possibly reflecting either low productivity in the overlying water column or high relative accumulation rates of inorganic detritus. The predominance of C27 and C2s sterols is typical of marine sediments derived from autochthonous sources and such as zooplankton moults, carcasses and faecal pellets, and phytoplankton such as diatoms. The presence of dinosterol, and the high proportion of 23,24-dimethyl-substituted sterols (12%), is consistent with an input from dinoflagellates. The high proportion of 24-ethylcholest-5-en3fl-ol and the presence of g- and fl-amyrin provides clear evidence for terrigenous organic matter in these marine sediments, which is probably derived from aeolian inputs. C30-C32 keto-alcohols were present in comparable abundance to the major sterols, and are presumed to derive from the oxidation of the corresponding diols found in microalgae such as eustigmatophytes. Simulated alteration experiments carried out at 100, 140, 175 and 200°C show that the C27 and C29 5~t-stanol/AS-stenol ratios and C27 and C28 A22 stanol/AS.2:-stenol ratios increase with increasing temperature. The distribution of C30-'C32 keto-alcohols was unaffected by heating to 175°C indicating they are more stable than sterols. Sterols and ketoalcohols were destroyed by heating the sediment at 200°C.
26 __A__
100 *C 7
8
12
13
J
421
24
140"C 24
24
175"c
26
Tkne
Acknowledgements--We thank engineers Liu Zhi Chun and
Fig. 5. Partial chromatograms of sterol fraction after simulated thermal alteration experiments. Peak identification given in Table 2.
The chromatogram for the sample heated at 175°C (Fig. 5) shows a very strong predominance of the keto-ols relative to sterols. It is of interest that the distribution of C30-C32 keto-alcohols
Shao Min for assistance with obtaining mass spectra. These analyses were performed as part of a collaborative study between the National Laboratory of Organic Geochemistry (Guangzhou, China) and CSIRO Division of Oceanography (Hobart, Australia). This work was funded by the Chinese National Science Foundation, the Chinese National Laboratory of Organic Geochemistry and the CSIRO Division of Oceanography, Australia. Jiang Shanchun gratefully acknowledges the support provided by Dr Angus McEwan, Chief of the Division of Oceanography, during his visit to Hobart.
Table 2. 5,,-Stanol/A 5 stenol ratios in sediment from the Okinawa Trough after simulated thermal alteration experiments Temp. (°C)
50 100 140 175 200
5~-C27AX2E/C27A5"22E 0.46 0.55 0.85 0.31 .
.
5a-C27A°/C2~ As
50t-C2sA22E/C2sA5'22E
50t-C29A22E/C29A5'22E
0.35 0.53 0.93 2.11
0.49 0.44 1.06 --
0.41 0.44 0.73 0.27
.
*Ratios determined from GC-traces shown in Fig. 4.
.
422
JIANG SHANCHUN et al, REFERENCES
Atam M., Sansing T. B., Busby E. L., Martinez D. R. and Ray S. M. (1979) Dinoflagellate sterols. I. Sterols of the dinoflagellates of Gonyaulax species. Steroids 33, 197-203. Bligh E. G. and Dyer W. J. (1959) A rapid method of total lipid extraction and purification. Can. J. Bioehem. Physiol. 37, 912~917. Boon J. J., Rijpstra W. 1., de Lange F,, de Leeuw J. W., Yoshioka M. and Shimizu Y. (1979) Black Sea sterol--a molecular fossil for dinoflagellate blooms. Nature 277, 125 127. Dreier F., Buchs A. and Giilaqar F. O. (1988) The degradation rates of some sterols in a heated sediment. Geochim. Cosmochim. Acta 52, 1663 1666. Emerson S, and Hedges J. L. (1988) Processes controlling the organic carbon content of open ocean sediments. Paleoceanography 3, 621-634. Gagosian R. B., Smith S. O., Lee C., Farrington J. W. and Frew N. M. (1980) Steroid transformations in recent marine sediments. In Advances in Organic Geochemistry 1979 (Edited by Douglas A. G. and Maxwell J. R.), pp. 407-419. Pergamon Press, Oxford. Henrichs S. M. and Farrington J. W. (1984) Peru upwelling region sediments near 15S. 1. Remineralization and accumulation of organic matter. Limnol. Oceanogr. 29, 119. lkan R., Baedecker M. J. and Kaplan I. R (1975) Thermal alteration experiments on organic matter in recent marine sediments- -III. Aliphatic and steroidal alcohols. Geochim. Cosmochim. Acta 39, 195 203, Jiang Shanchun and Fu Jiamo (1984) Monoterpenes as terrigenous markers in Okinawa Trough sediments. Geochemistry 3, 342 345. Jiang Shanchun, Jia Rongfen and Luan Zuofeng (1992) The evolution of stenols and stanols in marine sediment core from Beibu Gulf of the South China Sea. Chin. J. Oeeanol. Limnol, 10, 92-96. de Leeuw, J, W., Rijpstra W. I. C. and Mur L. R. (1992) The absence of long-chain alkyl diols and alkyl keto-l-ols in cultures of the cyanobacterium Aphanizomenon flosaquae. Org. Geoehem. 18, 575 578. de Leeuw J. W., Rijpstra W. 1. C. and Schenck, P. A. ( 1981 ) The occurrence and identification of C~0, C~ and C3: alkan-l,15-diols and alkan-15-one-ols in Unit I and Unit II Black sea sediments. Geochim. Cosmochim. Acta 45, 2281 -2285. dc Leeuw J. W.. Rijpstra W. I. ('., Schenck P. A. and Volkman J. K. (1983) Free, esterified and residual bound sterols in Black Sea Unit 1 sediments. Geochbn. Cosmochim. Acta 4% 455-465.
Morris R. J. and Brassell S. C. (1988) Long-chain alkanediols: biological markers for cyanobacterial contributions to sediments, Lipids 23, 256-258. Nichols P. D and Johns R. B. (1986) The lipid chemistry of sediments from the St. Lawrence estuary. Acyclic unsaturated long chain ketones, diols and ketone alcohols. Org. Geochern. 9. 25 30. Nichols P, D., Palmisano A. C., Smith G. A. and White D. C (1986) Lipids of the Antarctic sea-ice diatom Nitzschia cvlindrus. Phytoehemistry 25, 1649-1653. Nishimura M. (1977) Origin of stanols in young lacustrine sediments. Nature, London 270, 711-712. Nishimura M. and Koyama T. (1977) The occurrence of stanols in various living organisms and the behaviour of sterols in contemporary sediments. Geochim. Cosmochim. ,4eta 41, 379 385. Sieskind O., Joly G. and Albrecht P (1979) Simulation oi the geochemical transformations of sterols: superacid effect of clay minerals. Geochim. Cosmoehim. Aeta 43, 1675 1679 Smith D. J , Eglinton G. and Morris R. J. (1983) Occurrence (~f long-chain alkan-diols and alkan-15-one-l-ols in a quaternary sapropel from the Eastern Mediterranean. Lipid~ 18, 902 905. Volkman J, K. (1986)A review ol sterol markers for marine and terrigenous organic matter. Org. Geochem. 9, 83 99. Volkman .I.K., Kearncy P and Jeffrey S. W. (1990) A ne,a source of 4-methyl sterols and 5:((H)-stanols in sediments: prymnesiophyte microalgae of the genus Pavlova. Org Geoclwm. 15, 489 497. Volkman J. K.. Farrington J. W. and Gagosian R. B. (19871 Marine and terrigenous lipids in coastal sediments from the Pcru upwelling region at 15 S: sterols and triterpene alcohols Org. Geochem. ! I, 463-477. Volkman ,1. K., Barrett S. M., Dunstan G. A. and Jeffie} S. W. ( 19921 C~0 C~: alkyl diols and unsaturated alcohols m microalgae of the class Eustigmatophyceae. Org. Geochem. 18, 131 138. Volkman J. K., Barrett S. M.. l)unstan G. A. and Jeff're.,, S. W. {1993) Geochemical significance of the occurrence ~,t" dinosterol and other 4-methyl sterols in a marine diatom Org. Geochem 20. 7 15 Volkman ,! K . Farringttm .i W , Gagosian R. B. and Wakeham S G. 11983~ Lipid composition of coastal marine sediments from lhe Peru upwelling region. In A&'ances in Organic Geoehemisto, 1981 (Edited by Bjoroy M. et al.), pp. 228 240. Wiley, Chichester. Volkman J K . Gillan F T.. Johns R. B. and Eglinton G, 11981) Sources of neutral lipid in a temperate intertidal sediment Geoehim. ('osmoehim. Acta 45. 1817 1828.
Pergamon
Origins and simulated thermal alteration of sterols and keto-aleohols in deep-sea marine sediments of the Okinawa Trough JIANG SHANCHUN,I TERESAO'LEARY,2 JOHN K. VOLKMAN,2 ZHANGHUIZHI,l JIA RONGFEN,1 YU SUHUA,l WANGYAN,1 LUAN ZUOFENG,3 SUN ZOOQING3 arid J1ANGRONGHUA3 tGuangzhou Institute of New Technology for Geology, Chinese Academy of Sciences, Guangzhou, P.R. China, 2CSIRO Division of Oceanography, Hobart, Tasmania, Australia and 3Institute of Oceanology, Chinese Academy of Sciences, Qingdao, P.R. China Abstract---Compositional data on the sterol and alcohol fractions isolated from deep-sea marine sediments from the Okinawa Trough were obtained to determine the relative contribution from marine and terrestrial inputs. Following extraction, the total saponifled neutral fraction was derivatized with BSTFA and then analysed by capillary GC and GC-MS. A suite of C2~--C29stenols and stanols and C30-C32keto-alcohols were identified in the sediments. Major sterols included 27-nor-24-methylcholesta-5,22E-dien-3fl-oland cholest-5-en-3fl-ol,which are most likely from marine fauna, and the C2s sterols 24-methylcholesta-5,22Edien-3fl-ol and 24-methylcholesta-5,24(28)-dien-3fl-ol,both of which are common in diatoms. C29 sterols were dominated by sterols with 24-ethyl substitution of higher plant origin, but 23,24-dimethyl sterols which are found in some marine phytoplankton were also quite abundant. The major 4-methyl sterol was 4~,23,24-trimethyl-5~-eholest-22E-en-3~-olwhich is considered a common indicator of dinoflagellates. Each sterol co-occurred with the corresponding 5~-stanol. Other indicators of terrestrial input such as a- and fl-amyrin were also identified. The sediments also contained significant amounts of the C30 keto-alcohol triacontan-15-one-l-ol, as well as smaller amounts of C3~ and C32 keto-alcohols. These unusual lipids are found in many marine sediments, and they may be formed by the oxidation of the corresponding C30-C32 alkyl diols found in some marine microalgae. The thermal stability of the compounds in these sediments was studied by heating portions of the surface sediment in glass tubes for 16 h at temperatures ranging from 100°C to 200°C. The C27 stanol/stenol ratio increased with increasing temperatures up to 140°C, as did the corresponding C28 and C29 stanol/stenol ratios. The keto-alcohols were more stable than sterols under these conditions. Key words----sterols, stanols, keto-alcohols, thermal alteration, Okinawa Trough
INTRODUCTION The Okinawa Trough is a back-arc basin which lies between the East China Sea shelf and the Ryukyu Islands in the marginal island arc of the West Pacific (Fig. 1). The sediments of the Okinawa Trough consist mainly of a calcareous brownish-grey ooze with abundant shell fossils. Sediments were sampled in order to obtain compositional data on the organic material present and to determine possible origins. Sterols occur in high concentrations in most recent sediments. They are comparatively stable and hence have a long geological record. Over the past two decades, extensive research has been carried out on the sterol distributions in sediments and seawater to investigate their potential as ecological markers for the contribution from t/;rrestrial and marine organisms to sediments (Nishimura and Koyama, 1977; Volkman et aL, 1983, 1987; Bang Shanchun et aL, 1992). The sterol distribution can also give an indication of early-stage diagenesis and microbial transformations. However, chemical, physical and microbial transformation of sterols produce complex
mixtures of diagenetic products that can limit their usefulness as source indicators. Sterol diagenesis in deeper sediments is expected to be controlled by physicochemical variables such as redox and temperature. The relative stabilities of various sedimentary sterols towards physical and chemical degradation has been studied. Dreier et al. (1988) concluded that 4-methyl sterols were more stable than 4-desmethyl sterols after heating a series of sterols in lacustrine sediments from 150 to 250°C. It is a common observation that the 5~-stanol/A5stenol ratio increases with depth in marine sediments. For example Jiang Shanchun et al. (1992) in their study of marine sediments from Beibu Gulf in the South China Sea, reported that the C27 5~-stanol/A5stenol ratio increased from 0.57 to 1.74 over the depth range 50-465 cm. The present study presents the first compositional data for sterols, and other neutral constituents, in marine sediments from the Okinawa Trough, off the coast of China. The sterol distribution of sediment sample Z-17-4 was analysed. As an adjunct to this study, simulated thermal alteration experiments were performed on the same sediment sample.
415
J1ANGSHANCHUNet al.
416
(80: 20 v/v) at 80°C for 2 h. The neutral fraction was treated with bis(trimethylsilyl)trifluoroacetamide (BSTFA) immediately before G C analysis to convert compounds containing free hydroxyl groups to their trimethylsilyl-ether derivatives•
E X P E R I M E N T A L
Sample collection Marine sediments were collected during an investigatory cruise of Oceangoing Science Ship No. 1 by researchers from the Institute of Oceanology, Chinese Academy of Science, Qingdao, P.R. China. Sediment grab sample No. Z-17-4 was obtained from 26°35'N, 125<~52'E in the Okinawa Trough at a water depth of 1670m (Fig. 1). The bottom sediments consisted of a brownish-grey ooze, which contained abundant shells and a considerable amount of calcium carbonate.
Simulated thermal maturation experiment The wet sediment was dried in an oven overnight at 50°C. Four 50 g portions of dry sediment were put into glass tubes, which were then sealed under nitrogen. Each tube was then placed in the oven and heated at 100, 140, 175 and 200~C respectively for 16 h. The sterol fraction was isolated using T L C and derivatized using B S T F A prior to analysis by G C and GC-MS.
Lipid extraction and fractionation Wet sediment was weighed and quantitatively extracted by the modified one-phase c h l o r o f o r m methanol Bligh and Dyer method (Bligh and Dyer, 1959). After phase separation, the lipids were recovered in the lower chloroform phase. The solvents were then removed under vacuum. The upper aqueous phase containing salts and water-soluble material was discarded• The total saponified neutral lipid (TSN) fraction was obtained by reducing an aliquot of the total solvent extract to near dryness under N2 followed by saponification in 5% K O H with methanol-water
1180 34° ,
,
,
120° , v
~
~ , l
122° , ,
!,
Analysis by capillary gas chromatography (GC) The TSN fractions were analysed with a Shimadzu 9A gas chromatograph equipped with an F I D and cool OCI-3 on-column injector (SGE, Australia). Samples were dissolved in chloroform to which a known amount of n-docosane (n-Cz2) was added as an internal standard• Samples were injected, at an oven temperature at 4 5 C . onto a fused-silica capillary column (nonpolar methyl silicone: 50 m × 0.32 mm i.d., Hewlett-Packard). After 1 min. the oven temperature was raised to 1 2 0 C at
124* ,! i
i,
126° I
i
128°
130°
132°
i ~ l
Yellow Sea 32* Shangh~
:;
..-'÷Dl/
30* Il/
P.R.C h i n a / L
.~
EastChinaSea
LFujii , 26 ° /
Z-17--4O
f"
II
ij
.
.
•
.
.!
.
~.~
'~
...,>
Taiwan" •
<>£
," ~" "';" ,"
,vincqtif'
d
° .
.
.
.~ ff .
.
.
.
.
.
.
.
.
.
.
24 °
Fig. 1. Map of East China Sea showing sample site 7.-17.4. Note the proximity of the sample to the edge of the continental shelf (marked by 201)m depth contour) even though it was collected at 1670 m water depth.
Sterols and keto-aleohols in deep-sea sediments 30°C/min and then to 320°C at 4°C/min, and then held for 20 min. Hydrogen was used as the carrier gas. The detector temperature was 330°C. Analysis by gas chromatography-mass spectrometry (GC-MS) G C - M S analyses were performed with an HP 5890 GC and 5790 MSD fitted with a direct capillary inlet. The nonpolar column, injector and chromatographic conditions were similar to those described above with the exception that helium was used as the carrier gas. Electron impact mass spectra were acquired and processed with an HP 59970A Computer Workstation. Typical MSD operating conditions were: electron multiplier 2200 V; transfer line 310°C; electron impact energy of 70eV; 0.8 scans/s; mass range 40--600 Da. Quantitation Peak areas were quantified from the GC traces using chromatography software (DAPA Scientific Software); however, due to the complexity of the sterol chromatogram and co-elution of some components, it was necessary to quantify some peaks using ratios obtained from GC-MS data. A5 sterols were identified using the following ions: m/z 129, 255, and 386. The 5~-stanols were identified from m/z 215, 257 and 388 mass fragmentograms. RESULTS AND DISCUSSION The organic carbon content in the surface sediment from sample site Z-17-4 is quite low (0.76%) when compared to highly productive marine areas. For example, in the upwelling region off Peru, organic carbon comprises between 3 and 5% of the sediment (Volkman et al., 1983, 1987). The organic carbon content reflects both the primary productivity in the water column (Henrichs and Farrington, 1984) and degree of preservation (e.g. Emerson and Hedges, 1988). Steroi abundances are low in the Okinawa Trough (2.3 gg/g dry wt) when compared to Peru ( ~ 1 3 0 # g / g dry wt) and more like concentrations found in intertidal sediments (2.0 gg/g dry wt; Volkman et al., 1981) reflecting low productivity in the water column, the effects of diagenetic processes such as dehydration to sterenes, oxidation to steroid ketones and reduction to 5~-stanols (e.g. Volkman et al., 1987). 4-Desmethyl sterols A complex distribution of sterols was found in the sediment (Fig. 2), which is characteristic of many marine sediments containing both marine and terrestrially-derived organic matter (e.g. Volkman et al., 1981, 1987; Jiang Shanchun et al., 1992). The major C27 sterols in the sediment are cholest-5en-3fl-ol and cholesta-5,22E-dien-3fl-ol and their corresponding stanols (Table 1). Cholest-5-en-3p-ol (cholesterol) is the most abundant sterol and corn0(3 21-3/4--N
417
prises 9.3% of the total identified sterols. Cholesterol is common in marine sediments, and is most likely derived from zooplankton (Gagosian et al., 1980) and benthic animals, although microalgal sources are also possible (Volkman, 1986). Sterols with 27-nor side-chains were also identified in the sediments from the Okinawa Trough. These sterols occur widely in the marine food web, and in sediments, but their origins are not well known (de Leeuw et al., 1983). C2s sterols comprised 23% of the identified sterols. These included 24-methylcholesta-5,22E-dien-3fl-ol and 24-methylcbolesta-5,24(28)-dien-3fl-ol and their corresponding stanols. 24-Methylcholest-5-en-3fl-ol is also present in significant amounts (Table 1). The presence of 24methylcholesta-5,22E-dien-3fl-ol, with cholesta5,22E-dien-3fl-ol and 23,24-dimethylcholesta5,22E-dien-3fl-ol suggests that diatoms are likely to be their major source (Volkman, 1986; Volkman et al., 1987). The 24-ethyl substituted sterols dominate the C29 sterol distribution and comprise 24% of the total identified sterols. The most abundant C29 sterols present are 24-ethylcholest-5-en-3fl-oi (8.0%), 24-ethylcholesta-5,22E-dien-3fl-ol (3.7%) and 24ethylcholesta-5,24(28)Z-dien-3fl-ol (3.8%). The corresponding stanols are also present in significant amounts (Table 1). The 23,24-dimethyl substituted sterol distribution is dominated by 5ct-stanols such as 23,24-dimethyl-5ct-cholest-22E-en-3fl-ol (4.9%) and 23,24-dimethylcholestan-3fl-ol (3.4%). The corresponding stenois constituted 2.3 and 0.77% respectively. The abundance of 23,24-dimethyl substituted sterols most likely reflect a dinoflageilate source as the 23,24-dimethyl substitution is a common feature of the 4-methyl sterols of these algae (Alam et al., 1979). For example, de Leeuw et al. (1983) attributed the presence of 23,24-dimethylcholesta5,22E-dien-3fl-ol, 23,24-dimethyl-5~-cholest-22E-en3fl-ol, 23,24-dimethylcholest-5-en-3fl-ol and 23,24dimethyl-5~-cholestan-3fl-ol in Black Sea sediments to dinoflagellates. Minor contributions from diatoms and prymnesiophytes are also possible (Volkman, 1986). The dominance of 24-ethyl substituted C29 sterols is unusual for a surface marine sediment. 24-Ethylcholesterol is commonly thought to derive from vascular plants of terrestrial origin, however several species of phytoplankton are now known to contain large amounts of this sterol (Volkman, 1986; Nichols et al., 1986). The two other common sterols in vascular plants are 24-ethylcholesta-5,22E-dien-3fl-ol and 24-methylcholest-5-en-3fl-ol (Volkman et ai., 1987) both of which occur in significant amounts in the Okinawa Trough sediments. The ratios of these three sterols is 2.9:1.3:1 respectively. This is similar to the ratio of these three sterols in sediments in the upwelling zone off Peru (3.5:1.8:1), where these
418
JL~qGSHANCltUNet al.
21
a) sterols (TMSi-ethers)
16
7
10
/ L7+lg
13
19
VI
tO r~
22
I
I
I
I
t
60
62
64
66
68
23+24
b) diols & keto-ols (TMSi-ethers)
25 26
.J [
I
I
I
t
70
72
74
76
78
Time (minutes) Fig. 2. Partial gas chromatogramsshowingdistributionsof (a) sterolsand (b) long-chaindiols and keto-ols (as TMSi-ethers)from sediment Z-17-4. Peaks are identifiedin Table 2. The peaks in 2(a) are enhanced by halving the attenuation compared with the peaks in 2(b). sterols were thought to be derived mainly from organic matter of terrestrial origin (Volkman et al., 1987).
cannot be excluded (Volkman et al., 1993). Small amounts of 4,24-dimethyl-5~-cholestan-3fl-ol were also observed.
4 - M e t h y l sterols
5~-Stanols / A 5-stenols
Among marine microalgae that have been studied, only the dinoflagellates (Alam et al., 1979) and a few prymnesiophytes (Volkman et al., 1990) produce large amounts of 4-methyl sterois. The major 4methyl sterol identified in the Okinawa Trough sediments is 4~,23,24-trimethyl-5,,-eholest-22E-en-3/1-ol (dinosterol), which comprised 9.1% of the total identified sterols (Table 1). The occurrence of such high concentrations of dinosterol is indicative of a dinoflagellate source (Boon et al., 1979), although the possibility of a minor contribution from diatoms
Previous reports have shown that stanols are more stable to oxidative degradation than stenols (Nishimura, 1977). Nishimura (1977) predicted that stanol/stenol ratios would be higher in more reduced sediment. Gagosian et al. (1980) reported stanol/stenol ratios ranging from 0.48 to 2.7 for anoxic sediments from Black Sea cores, whereas stanol/stenol ratios ranged from 0.21 to 0.50 for the more oxic sediments of the western North Atlantic. The 5~-stanols/AS-stenol ratios from the Okinawa
Sterols and keto-alcohols in deep-sea sediments Trough surface sediments ranged from 0.2 to 4.42 depending on which pair is examined. It is very likely that the high ratios may be attributable to a direct input o f 5~t-stanols such as 23,24-dimethyl-5ctcholestan-3fl-ol rather than from conversion of the corresponding stenol.
Triterpene alcohols Jiang Shanchun and Fu Jiamo (1984) previously noted that higher plant detritus is constantly transported by wind and surface currents from Fujian (Fig. 1) and Zhejiang provinces into the Okinawa Trough region. These authors identified several monoterpenes including cyclohexane, 1-methyl-5(1-methylethenyl)-cyclohexene and l-methyl-4-(1methylethylidene)-cyclohexanes which they attributed to terrestrial plant inputs. Biomarker evidence of this was also obtained in the present work from the identification of ~- and flamyrins. These were identified from their mass spectra (Volkman et al., 1987) and from comparison of retention times on the m / z 218 mass fragmentogram (Fig. 3) with authentic standards which were run separately. The concentrations of 0r- and [3-amyrin were 11 and 15 ng/g dry wt respectively. These concentrations are very low when compared to sediments from the Peru upwelling zone where the concentrations of ct- and
419
fl-amyrin were up to l0 times higher (Volkman et al., 1987).
C m and C~2 alkane diols and keto-alcohols The C30, Cal and C32 keto-alcohols were identified from their characteristic mass spectra and their retention times on the m / z 130 mass fragrnentogram (Fig. 4). The C30 c o m p o u n d is approximately four times more abundant than the C32 c o m p o u n d (Table l). These keto-alcohols have been identified in many aquatic sediments (e.g. de Leeuw et al., 1981; Smith et al., 1983; Nichols and Johns, 1986), but a biological source has still not been identified. The corresponding alkyl-1,15-diols have been identified in a natural bloom of the cyanobacterium Aphanizomenon flos-aquae (Morris and Brassell, 1988), but the same compounds were not found in studies of this species in laboratory culture (de Leeuw et al., 1992). The C30 diol is more abundant than the corresponding C30 keto-alcohol (Table l). Volkman et al. (1992) have identified C30-C32 diols in marine microalgae from the class Eustigmatophyceae, so an algal source for the diols seems likely. The keto-alcohols present in the sample may arise from oxidation of the diols, or perhaps they are synthesized by an algal species which has not yet been studied. Further research on the origins and diagenesis of these compounds is clearly still needed.
Table 1. Concentrations (ng/g dry wt of sediment) of sterols and long-chain diols and keto-ols identifiedin sediment sample from site Z-17-4 in the Okinawa Trough GC peak* Sterol identification ng/g dry wt % Total sterols I 27-nor-24-methylcholesta-5,22E-dien-3fl-ol 21 I. 1 2 cholesta-5,22E-dien-3fl -ol 110 5.7 3 27-nor-24-methyl-5~t-cholest-22E-en-3fl-ol 20 1.0 4 5ct-cholest-22E-en-3fl-ol 76 4.0 5 cholest-5-en-3/~-ol 179 9.2 6 5:t-cholestan-3fl-ol 85 4.4 7 24-methylcholesta-5,22E-dien-3fl-ol 147 7.7 8 24-methyl-5~t-cholest-22E-en-3fl-ol 77 4.0 9 24-methylcholesta-5,24(28)E-dien-3fl-ol 49 2.5 10 24-methyl-5ct-cholest-24(28)E-en-3fl-ol 86 4.5 l0 24-methylcholest-5-en-3fl-ol 54 2.8 I1 24-methyl-Sct-cholestan-3fl-ol 32 1.7 12 23,24-dimethylcholesta-5,22E-dien-3fl-ol 44 2.3 13 23,24-dimethyl-5~t -cholest-22E-en-3fl-ol 96 5.0 13 24-ethylcholesta-5,22E-dien-3fl-ol 71 3.7 14 24-ethyl-Sct-cholest-22E-en-3fl-ol 46 2.4 15 23,24-dimethylcholest-5-en-3fl-ol 15 0.8 16 24-ethylcholest-5-en-3fl -ol 154 8.0 16 24-ethylcholesta-5,24(28)E-dien-3fl -ol 26 1.4 16 23,24-dimethyl-Sct-cholestan-3fl-ol 65 3.4 17 24-ethylcholesta-5,24(28)Z-dien-3fl-ol 73 3.8 17 24-ethyl-5~t-cholest-24(28)E-en-3fl-ol 9 0.5 18 24-ethyl-5ct-cholestan-3fl-ol 67 3.5 19 4,24-dimethyl-5~t-cholestan-3fl-ol 30 1.6 20 24-ethyl-50t-cholest-24(28)Z-en-3fl-ol 16 0.8 21 4~t,23,24-trimethyl-5ct-cholest-22E-en-3fl-ol 175 9.0 22 C30-Sct-stanols 101 5.2 TOTAL 23 24 25 26
l,l 5-dihydroxytriacontane triacontan- 15-one-I-ol I,I 5-dihydroxydotriacontane dotriacontan-15-one-l-ol
TOTAL *Peak numbers refer to Fig. 2.
1923 231 121 63 27 442
100
420
JIANGSHANCHUNet al. Okinawa "/'rough Z-17-4 Tnterpeae alcohols (TMSi-ethers)
~-myrm
m/z218 a-amyrm
8 <
51
53
55
Time (minutes) Fig. 3. Mass fragmentogram fbr m/z 218, the base peak in mass spectra of ~-amyrin (urs-12-en-3fl-ol) and fl-amyrin (olean-12-en-3fl-ol).
S i m u l a t e d thermal alteration
Major changes to the sterol distributions were observed as the sediments were heated up to 175°C (Fig. 5). At 200°C the sterols are almost completely destroyed. The C27 and C 2 9 5~-stanol/Atstenol ratios increase with increasing temperature up to 175°C, as do the C27 and C28 A22 stanol/AS'n-stenol ratios (Table 2). Previous studies of thermal alteration have shown that the distributions of sterols in sediments are affected by temperature (Ikan et al., 1975; Sieskind et al., 1979; Dreier et al., 1988), although different results have been obtained. Ikan et al.
(1975) showed that cholesterol is released by heating sediment. Maximum yields were obtained by heating sediments at 100°C for 30 days, presumably due to the release of sterols from bound forms. Higher temperatures led to significant decreases in sterol concentrations as a result of thermal degradation. Dreier et al. (1988) also noted increasing yields of extractable sterols after heating lacustrine sediments up to a temperature of 20OC. Sieskind et al. (1979) demonstrated the conversion of cholestanol to a mixture of steranes (40%) and sterenes (35%) when heated with kaolinite at 140°C for 16h.
C3o Okmawa Trough Z-17-4 Alkan-15-one-1-ol (TMSi-ethers) m/z 130
C32
<
,
55
,
,
57 Time (minutes)
,
,
,
59
Fig. 4. Mass fragmentogram for m/z 130, showing the distribution of the C30~Cn long-chain alkan-I 5-one-l-ols.
Sterols and keto-alcohols in deep-sea sediments
was unaffected at temperatures up to 175°C, indicating that they are more stable than sterols under these conditions. However, at 200°C the ketoalcohols were also substantially degraded.
Room Temp.
7
24
CONCLUSIONS
Data on the distribution of sterols, and ketoalcohols, in a deep-sea marine sediment from the Okinawa Trough are presented for the first time. The sediments are low in total organic carbon, possibly reflecting either low productivity in the overlying water column or high relative accumulation rates of inorganic detritus. The predominance of C27 and C2s sterols is typical of marine sediments derived from autochthonous sources and such as zooplankton moults, carcasses and faecal pellets, and phytoplankton such as diatoms. The presence of dinosterol, and the high proportion of 23,24-dimethyl-substituted sterols (12%), is consistent with an input from dinoflagellates. The high proportion of 24-ethylcholest-5-en3fl-ol and the presence of g- and fl-amyrin provides clear evidence for terrigenous organic matter in these marine sediments, which is probably derived from aeolian inputs. C30-C32 keto-alcohols were present in comparable abundance to the major sterols, and are presumed to derive from the oxidation of the corresponding diols found in microalgae such as eustigmatophytes. Simulated alteration experiments carried out at 100, 140, 175 and 200°C show that the C27 and C29 5~t-stanol/AS-stenol ratios and C27 and C28 A22 stanol/AS.2:-stenol ratios increase with increasing temperature. The distribution of C30-'C32 keto-alcohols was unaffected by heating to 175°C indicating they are more stable than sterols. Sterols and ketoalcohols were destroyed by heating the sediment at 200°C.
26 __A__
100 *C 7
8
12
13
J
421
24
140"C 24
24
175"c
26
Tkne
Acknowledgements--We thank engineers Liu Zhi Chun and
Fig. 5. Partial chromatograms of sterol fraction after simulated thermal alteration experiments. Peak identification given in Table 2.
The chromatogram for the sample heated at 175°C (Fig. 5) shows a very strong predominance of the keto-ols relative to sterols. It is of interest that the distribution of C30-C32 keto-alcohols
Shao Min for assistance with obtaining mass spectra. These analyses were performed as part of a collaborative study between the National Laboratory of Organic Geochemistry (Guangzhou, China) and CSIRO Division of Oceanography (Hobart, Australia). This work was funded by the Chinese National Science Foundation, the Chinese National Laboratory of Organic Geochemistry and the CSIRO Division of Oceanography, Australia. Jiang Shanchun gratefully acknowledges the support provided by Dr Angus McEwan, Chief of the Division of Oceanography, during his visit to Hobart.
Table 2. 5,,-Stanol/A 5 stenol ratios in sediment from the Okinawa Trough after simulated thermal alteration experiments Temp. (°C)
50 100 140 175 200
5~-C27AX2E/C27A5"22E 0.46 0.55 0.85 0.31 .
.
5a-C27A°/C2~ As
50t-C2sA22E/C2sA5'22E
50t-C29A22E/C29A5'22E
0.35 0.53 0.93 2.11
0.49 0.44 1.06 --
0.41 0.44 0.73 0.27
.
*Ratios determined from GC-traces shown in Fig. 4.
.
422
JIANG SHANCHUN et al, REFERENCES
Atam M., Sansing T. B., Busby E. L., Martinez D. R. and Ray S. M. (1979) Dinoflagellate sterols. I. Sterols of the dinoflagellates of Gonyaulax species. Steroids 33, 197-203. Bligh E. G. and Dyer W. J. (1959) A rapid method of total lipid extraction and purification. Can. J. Bioehem. Physiol. 37, 912~917. Boon J. J., Rijpstra W. 1., de Lange F,, de Leeuw J. W., Yoshioka M. and Shimizu Y. (1979) Black Sea sterol--a molecular fossil for dinoflagellate blooms. Nature 277, 125 127. Dreier F., Buchs A. and Giilaqar F. O. (1988) The degradation rates of some sterols in a heated sediment. Geochim. Cosmochim. Acta 52, 1663 1666. Emerson S, and Hedges J. L. (1988) Processes controlling the organic carbon content of open ocean sediments. Paleoceanography 3, 621-634. Gagosian R. B., Smith S. O., Lee C., Farrington J. W. and Frew N. M. (1980) Steroid transformations in recent marine sediments. In Advances in Organic Geochemistry 1979 (Edited by Douglas A. G. and Maxwell J. R.), pp. 407-419. Pergamon Press, Oxford. Henrichs S. M. and Farrington J. W. (1984) Peru upwelling region sediments near 15S. 1. Remineralization and accumulation of organic matter. Limnol. Oceanogr. 29, 119. lkan R., Baedecker M. J. and Kaplan I. R (1975) Thermal alteration experiments on organic matter in recent marine sediments- -III. Aliphatic and steroidal alcohols. Geochim. Cosmochim. Acta 39, 195 203, Jiang Shanchun and Fu Jiamo (1984) Monoterpenes as terrigenous markers in Okinawa Trough sediments. Geochemistry 3, 342 345. Jiang Shanchun, Jia Rongfen and Luan Zuofeng (1992) The evolution of stenols and stanols in marine sediment core from Beibu Gulf of the South China Sea. Chin. J. Oeeanol. Limnol, 10, 92-96. de Leeuw, J, W., Rijpstra W. I. C. and Mur L. R. (1992) The absence of long-chain alkyl diols and alkyl keto-l-ols in cultures of the cyanobacterium Aphanizomenon flosaquae. Org. Geoehem. 18, 575 578. de Leeuw J. W., Rijpstra W. 1. C. and Schenck, P. A. ( 1981 ) The occurrence and identification of C~0, C~ and C3: alkan-l,15-diols and alkan-15-one-ols in Unit I and Unit II Black sea sediments. Geochim. Cosmochim. Acta 45, 2281 -2285. dc Leeuw J. W.. Rijpstra W. I. ('., Schenck P. A. and Volkman J. K. (1983) Free, esterified and residual bound sterols in Black Sea Unit 1 sediments. Geochbn. Cosmochim. Acta 4% 455-465.
Morris R. J. and Brassell S. C. (1988) Long-chain alkanediols: biological markers for cyanobacterial contributions to sediments, Lipids 23, 256-258. Nichols P. D and Johns R. B. (1986) The lipid chemistry of sediments from the St. Lawrence estuary. Acyclic unsaturated long chain ketones, diols and ketone alcohols. Org. Geochern. 9. 25 30. Nichols P, D., Palmisano A. C., Smith G. A. and White D. C (1986) Lipids of the Antarctic sea-ice diatom Nitzschia cvlindrus. Phytoehemistry 25, 1649-1653. Nishimura M. (1977) Origin of stanols in young lacustrine sediments. Nature, London 270, 711-712. Nishimura M. and Koyama T. (1977) The occurrence of stanols in various living organisms and the behaviour of sterols in contemporary sediments. Geochim. Cosmochim. ,4eta 41, 379 385. Sieskind O., Joly G. and Albrecht P (1979) Simulation oi the geochemical transformations of sterols: superacid effect of clay minerals. Geochim. Cosmoehim. Aeta 43, 1675 1679 Smith D. J , Eglinton G. and Morris R. J. (1983) Occurrence (~f long-chain alkan-diols and alkan-15-one-l-ols in a quaternary sapropel from the Eastern Mediterranean. Lipid~ 18, 902 905. Volkman J, K. (1986)A review ol sterol markers for marine and terrigenous organic matter. Org. Geochem. 9, 83 99. Volkman .I.K., Kearncy P and Jeffrey S. W. (1990) A ne,a source of 4-methyl sterols and 5:((H)-stanols in sediments: prymnesiophyte microalgae of the genus Pavlova. Org Geoclwm. 15, 489 497. Volkman J. K.. Farrington J. W. and Gagosian R. B. (19871 Marine and terrigenous lipids in coastal sediments from the Pcru upwelling region at 15 S: sterols and triterpene alcohols Org. Geochem. ! I, 463-477. Volkman ,1. K., Barrett S. M., Dunstan G. A. and Jeffie} S. W. ( 19921 C~0 C~: alkyl diols and unsaturated alcohols m microalgae of the class Eustigmatophyceae. Org. Geochem. 18, 131 138. Volkman J. K., Barrett S. M.. l)unstan G. A. and Jeff're.,, S. W. {1993) Geochemical significance of the occurrence ~,t" dinosterol and other 4-methyl sterols in a marine diatom Org. Geochem 20. 7 15 Volkman ,! K . Farringttm .i W , Gagosian R. B. and Wakeham S G. 11983~ Lipid composition of coastal marine sediments from lhe Peru upwelling region. In A&'ances in Organic Geoehemisto, 1981 (Edited by Bjoroy M. et al.), pp. 228 240. Wiley, Chichester. Volkman J K . Gillan F T.. Johns R. B. and Eglinton G, 11981) Sources of neutral lipid in a temperate intertidal sediment Geoehim. ('osmoehim. Acta 45. 1817 1828.