36. PRELIMINARY LIPID ANALYSIS OF SECTION 481-2-21

I. D. Thomson, S. C. Brassell, G. Eglinton, and J. R. Maxwell, Organic Geochemistry Unit, University of Bristol,School of Chemistry, Cantock's Close, Bristol BS8 1TS, United Kingdom

ABSTRACT

We investigated the solvent-extractable lipids of a Quaternary diatomaceous ooze (Section 481-2-2) from the Guay-mas Basin. The section contained high concentrations of lipids, principally derived from algae. We also recognizedcomponents derived from bacterial and terrestrial sources. Major dinoflagellate blooms were indicated by the presenceof dinosterol as the major component. The lipid composition was typical of that of Recent marine sediments and re-flected a very early stage of lipid diagenesis.

INTRODUCTION

We investigated several classes of solvent-extractablelipids (hydrocarbons, alcohols, and acids) of a latePleistocene diatomaceous ooze from the GuaymasBasin, Gulf of California (Section 481-2-2; 7.5 m sub-bottom; TOC = 1.4%). We evaluated the lipid distribu-tions to determine their source, conditions of sedimentdeposition, and diagenetic alteration.

METHODOLOGY

The experimental procedure used to extract "free" lipids has beenreported in our previous DSDP investigation (Brassell et al., 1980a).We performed gas chromatography (GC) on a Carlo Erba 2150 gaschromatograph equipped with a 17-meter OV-1 glass capillary column(0.25-mm i.d.); the carrier gas was helium. Mass spectra were recordedwith a Finnigan 4000 gas chromatograph-mass spectrometer (GCMS), equipped with a 20-meter OV-1 glass capillary column. Data ac-quisition and processing were controlled by an INCOS 2300 datasystem. We made compound assignments from individual mass spec-tra and GC retention times—with reference to literature spectra andauthentic standards—where possible. Mass fragmentography (MF)was used to characterize homologous and pseudohomologous series(Wardroper et al., 1977; Brassell et al., 1980b) and to aid compoundidentification. Where possible, we quantitated individual compoundsfrom their GC response or by MF. The problems associated withquantitation are discussed elsewhere (Brassell et al., 1980a).

RESULTSThe detailed compound distributions of aliphatic

hydrocarbons, alcohols, and acids are reported herein.A brief description of the ketone fraction is given inTable 5. Aromatic components, although present, arenot reported.

Aliphatic Hydrocarbons

Acyclic Components

The n-alkanes of Section 481-2-2 ranged from «C17 tonC35 with an odd/even carbon preference index (CPI)of 7.2. The absolute concentration of individual homo-logues (quoted in ng/g dry-sediment weight) are shownin Figure 1A. In the C23 to C35 range, the overall dis-tribution is dominated by odd-numbered homologues in

189

Curray, J. R., Moore, D. G., et al., Init. Repts. DSDP, 64: Washington (U.S. Govt.Printing Office).

1i

2 31 , ! l I ,1, _L 1

5i

Jl

A

20 25 30 35

728

. . 1

1

. I I2

| j

B

15 20 25 30

317

. I

c

1 .15 20 25

Carbon Number30

Figure 1. Lipid concentrations in Section 481-2-2. A. Principal acyclicalkanes (solid lines = n-alkanes; dashed lines = acyclic isopre-noids in GC-elution positions. Bar numbers correspond as follows:1. pristane, 2. phytane; 3. 2,6,10,15,19-pentamethyleicosane, 4.squalane, 5. lycopane). B. Acyclic alcohols (solid lines = /i-alka-nols; dashed lines = 1. phytol, 2. C24., n-alken-1-ol, 3. C26:1 n-al-ken-l-ol. C. /i-alkanoic acids.

the C23 to C35 range and maximizes at nC29. No /i-al-keiles or branched alkanes or alkenes were detected. Theconcentrations of acyclic isoprenoid alkanes, pristane,phytane, 2,6,10,15,19-pentamethyleicosane (I), squa-lane (II), and lycopane (III) are given in Figure 1. Nounsaturated isoprenoid hydrocarbons were detected.

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I. D. THOMSON, S. C. BRASSELL, G. EGLINTON, J. R. MAXWELL

Cyclic Components

No diterpenoid alkanes, alkenes, tetracyclic alkanes,or alkenes derived from 3-oxytriterpenoids (Corbet etal., 1980) were detected.

Steranes were recognized as trace components, butthe low intensity of diagnostic ions in MF and individualmass spectra precluded compound assignment. No 4-methylsteranes, diasteranes, or 4-methyldiasteranes weredetected by MF. A complex mixture of mono-, di-, tri-,and tetra-unsaturated sterenes (C27-C29) occurs in Sec-tion 481-2-2; Table 1 shows the concentrations of themajor components. We recognized C27 to C29 ster-2-enesand stera-3,5-dienes from their characteristic mass spec-tra and GC-retention times (Wardroper, 1979); the C2 7compounds predominate. Lack of standard spectra pre-vented the assignment of nuclear double-bond positionsin steradienes (except stera-3,5-dienes), steratrienes, andsteratetrenes, but several components have been tenta-tively assigned as monoaromatic steroids by comparisonwith literature spectra (Spyckerelle, 1975; Schaeffle etal., 1978). In general, the C27 sterenes are the mostabundant (C27>C2 8>C2 9), and the C28 sterenes showthe greatest diversity of individual components. No4-methylsterenes, diacholestenes, or 4-methyldiacholes-tenes were detected.

The major triterpanes and triterpenes of Section481-2-2 are listed in Table 2 and are shown in a partialMF of m/z 191 (Fig. 2). Their distribution is limited toC27, C30, and C3i carbon numbers, and hop-22(29)-eneis the most abundant. We recognized several triterpenes(Components D, E, I, J, L and M) and a triterpadiene

Table 1. Concentrations of sterenes in Section 481-2-2.

Table 2. Concentrations of triterpenoid hydrocarbons in Section 481-2-2.

Assignment8 Formula StructurecConcentration0

(ng/g)

C28 3 n (aromatic), s c d

C28 3 n (aromatic), s c d

C28 3 n (aromatic)d

C27 n , Δ 2 2

C27 n , Δ24

C 2 7 Δ2

C27 2 n , s c

C28 n , Δ 2 2

C27 A3.5C 2 8

2 n , Δ24C 2 8

n , A24C28

n , Δ24C28 2

C 2 8 n , Δ24

C29 n , Δ 2 2

C 2 8 2 n Δ 2 4

35C 2 8C28

2 n , Δ 2 4

C 2 9 Δ2

C 2 9 3 ΔC 2 9 Δ

2

C27 3 n (aromatic)e

C27 3 n (aromatic)e

C29 n , Δ 2 4

C29 3.5C28 3 n (aromatic), s c e

C28 2 n , Δ 2 4

C27 4Δ (aromatic)e

C29 4ΔC29 3 n (aromatic)e

C28H42C28H42C28H44C27H44C27H44C27H46C27H42C28H46C27H44C28H44C28H46C28H46C28H48C28H46C 2 9 H 4 8C28H44C28H46C 28 H 44C29H50C29H46

C27H42C27H42C29H48

C 2 8 H 1 2C28H44c 27 H 40C29H44C29H46

IVIVIVIVIV

IV R! = R2 = HIVIV

IV Rl = R2 = HIVIVIV

IV Ri = H,R2 = CH3IVIVIV

IV Ri =H,R2 = CH3IV

IV R! = R 2 = C H 3IV

IV Ri = H,R2 = C2H5IVIVIV

IV Ri = H,R2 = C2H5IVIVIVIVIV

L1PID ANALYSIS

m/z 191

Elution Time

Figure 2. Total alkanes of Section 481-2-2. Gas chromatographic-mass spectrometry analysis:partial mass fragmentogram for m/z 191 diagnostic for triterpenoid hydrocarbons (Table 2).

Table 3. Concentrations of sterols in Section 481-2-2.a

Assignment*3 Structure0Concentration

cholesta-5,22-dien-3/3-ol5α-cholest-22-en-3/3-olcholest-5-en-30-ol5α-cholestan-3j3-ol24-methylcholesta-5,22-dien-3/3-ol24-methyl-5α-cholest-22-en-3j3-olC28 stanol24-methylenecholest-5-en-3|3-olC28 stanol24-methylene-5α-cholestan-3/3-ol24-methylcholest-5-en-3j3-ol24-methyl-5α-cholestan-3|3-ol23,24-dimethylcholesta-5,22-dien-3ß-ol23,24-dimethyl-5α-cholest-22-en-3/3-ol24-ethylcholesta-5,22-dien-3(3-ol24-ethyl-5α-cholest-22-en -3(3-ol23,24-dimethylcholest-5-en-3|8-ol23,24-dimethyl-5α-cholestan-3|8-ol24-ethylcholest-5-en-3l8-ol24-ethyl-5α-cholestan-3/3-ole

4,23,24-trimethyl-5α-cholest-22-en-3j3-olC30 4-methylsterolC30 4-methylsterolC30 4-methylstanol4,23,24-trimethyl-5α-cholestan-3i3-ol

XI VaXVaXlVbXVbXIVcXVc

—XlVd

—XVd 1

XlVe JXVeXlVfXVfXlVgXVgXI VhXVhXlViXViXVIf

———

XVIh

8447

201104275

78429718

115

4269

135224

9512783

331633

1933815495

309

a Sterols analyzed as TMS ethers." Based on mass spectral interpretation, comparison with literature

spectra, and GC-retention times.c See Appendix." Dry-weight of sediment.e Concentration of this component greatly enhanced by coelution with

an unknown C29 4-methylsterol.

Table 4. Concentrations of long-chain hydroxy ketones ("15-keto-l-ols") in Section 481-2-2.

Assignment2 Formula StructureConcentration

(ng/g)C

l-hydroxytriacontan-15-onel-hydroxyhentriacontan-15-onel-hydroxydotriacontan-15-one

C31H62O2C32H64O2

XVII, n = 14XVII, n = 15XVII, n = 16

107030

520

a Based on comparison with compounds assigned by de Leeuw et al. (personalcommunication) from comparison with synthetic homologues.

b See Appendix.c Dry-weight sediment.

imizing at «C 1 6 and /2C24, with an even over oddpreference of 4.3. Minor amounts of unsaturated (C 1 6 : 1and C1 8 : 1) and branched (iso- and anteiso-Cl5 and C17)components were also detected, ßß-bishomohopanoicacid (XVIIIc) also occurs as a minor component.

DISCUSSION

The high amount of extractable lipids in Section481-2-2 is similar to that obtained from anoxic bottomsediments in areas of high productivity, such as WalvisBay (Wardroper, 1979).

Paleoenvironment

Acyclic Components

The distributions of straight-chain components («-alkanes, /i-alkanols, and π-alkanoic acids) suggest alloch-thonous and autochthonous contributions to the sedi-

915

I. D. THOMSON, S. C. BRASSELL, G. EGLINTON, J. R. MAXWELL

merit. The «-alkane maximum at «C29 and the prominentodd/even preference in the C22 to C35 range suggest thatthe origins of the w-alkanes are predominantly terres-trial (Simoneit, 1975). The absence of major concentra-tions of short-chain components—particularly nC1 7, amajor alkane of phytoplankton (Oro et al., 1967; Gelpiet al., 1970; Blumer et al., 1971; Brassell et al.,1978)—may reflect preferential degradation of thesecomponents in the water column or sediment ratherthan low productivity (Johnson and Calder, 1973).

The origin of /2-alkanols in marine sediments is notwell understood. Their distribution in the Guaymas Ba-sin (Fig. IB) differs from that of the Japan Trench—where the predominant source of «-alkanols (maximiz-ing at ΛC2 4) has been assigned as terrestrial (Brassell etal., 1980a; Brassell, 1980)—and Walvis Bay, where phy-toplankton have been suggested as the source of the/7-alkanols (maximizing at nCl6) (Wardroper, 1979). Zoo-plankton wax esters may be the source of the w-alkanolsof the Guaymas Basin, as indicated by the predomi-nance of nC2o and nC22, which are major fatty-alcoholmoieties of wax esters (Sargent et al., 1976; Boon and deLeeuw, 1979). But the minor concentrations of/zC16 and«C18 in the sediment argue against a wax-ester origin forthe w-alkanols, as they are major alcohol components ofthese compounds (Boon and de Leeuw, 1979).

The bimodal distribution of the «-alkanoic acids(Fig. IC) provides evidence of a mixed contributionfrom terrestrial and bacterial/algal sources (Simoneit,1978; Brassell et al., 1980a, 1980b). It is also possiblethat the shorter-chain compounds may originate fromsaponified wax esters. We found trace amounts of iso-and anteiso-Cl5 and C17 acids, whose origins are prob-ably bacterial (Simoneit, 1975, 1978; Brassell et al.,1980a, 1980b).

Two major sources for the production of the iso-prenoids pristane and phytane have been suggested:They may result from the degradation of plant phytol(also recognized in this sample) or they may be directcontributions from methanogenic bacteria (Holzer etal., 1979). But the recognition of 2,6,10,15,19-penta-methyleicosane (I) and squalane (II) in Section 481-2-2(which are constituents of archaebacteria [Holzer et al.,1979]) and other evidence for methanogenic bacterialactivity in this hole (Oremland et al., this volume) sug-gest that methanogens are a source of these lipids. Theorigin of lycopane (III) in sediments is unclear, but a di-rect bacterial origin from methanogens (Brassell et al.,1981) seems more likely than diagenetic hydrogenationof lycopene, a constituent of marine algae.

The source of the l-hydroxyalkan-15-ones is un-known. They are probably of direct biological originbut have not yet been recognized as constituents of or-ganisms. A marine source of these components in Sec-tion 481-2-2 seems likely because of their occurrence inother Quaternary and Neogene marine sediments fromthe Black Sea (de Leeuw et al., personal communica-tion), the Cariaco and Japan trenches, and the Cali-fornian continental borderland (University of Bristol[England], Organic Geochemistry Unit, unpublished).

Cyclic Components

The wide range of sterols and stanols in Section481-2-2 is typical of areas of high productivity such asWalvis Bay and the Japan Trench (Wardroper et al.,1977; Brassell et al., 1980a).

Although C27 to C29, Δ5, Δ5 22, and Δ22 sterols are

widespread in organisms, their source probably is phy-toplankton (Boutry and Jacques, 1970; Boutry and Bar-bier, 1974; Orcutt and Patterson, 1975; Ballantine et al.,1979; Volkman et al., 1980). Certainly 23,24-dimethylsterols have been recognized only in marine sediments(Wardroper, 1979; Brassell et al., 1980b). Dinosterol(XVIf) is the predominant sterol in this section. It is theprincipal sterol of dinoflagellates (Shimizu et al., 1976)and a marker for major dinoflagellate blooms (Boon etal., 1979). Other 4-methylsterols may also derive fromdinoflagellates (Withers et al., 1978) or, perhaps, frommethanotrophic bacteria (Bird et al., 1971).

The hopanoids are probably an original bacterialcontribution to the sediment (De Rosa et al., 1971; Roh-mer, 1975). Hop-17(21)-ene (VIII) and neohop-13(18)•ene (X) are probably isomerization products of hop-22(29)-ene (Ensminger, 1977). But the absence in Section481-2-2 of hop-21-ene, the proposed intermediate of thisisomerization, suggests that these hopanoids also mayhave a primary origin from bacteria. The recent reportof the presence of several hopenes and fernenes in aphotosynthetic anaerobic bacterium (Howard, 1980)supports this view and suggests that, in the marine envi-ronment, fernenes, as well as hopenes, may originatefrom bacteria as well as from terrigenous sources (e.g.,from ferns; Berti and Bottari, 1968). Since no isomeri-zation of hopenes has occurred, the unknown triterpe-noid hydrocarbons in Section 481-2-2 are probablyderived directly from bacteria, rather than from the dia-genetic alteration of other triterpenes.

Diagenesis

The study of a single section precludes the evaluationof major diagenetic trends in Hole 481. But the lipiddata for Section 481-2-2 can be related to proposed dia-genetic pathways, which enables us to assess the matu-rity of the sediment. The odd/even preference of the/i-alkanes, although an insensitive indicator, and thepresence of n-alkanols and «-alkanoic acids as majorcomponents are characteristic of immature Deep SeaDrilling Project (DSDP) sediments (Simoneit, 1978;Brassell et al., 1980a, 1980b). The predominance ofsterols over their defunctionalized counterparts also at-tests to the immaturity of the section. The wide range ofsterenes, including Δ2-sterenes, Δ3>5-steradienes, andpartially characterized Δ22- and Δ^-steradienes and Δ24-steratrienes, is similar to that of other QuaternaryDSDP sediments from the Japan Trench (Brassell, 1980;Brassell et al., 1980a) and the California continentalborderland (McEvoy et al., in press). The absence ofΔ4-and Δ5- sterenes, thought to be acid-clay catalyzeddiagenetic products of Δ2-sterenes (Rubinstein et al.,1975) is characteristic of immature sterene distributions,

916

LIPID ANALYSIS

although they do occur in immature Quaternary sedi-ment elsewhere (Simoneit, 1975; Brassell, 1980; Dastil-lung and Albrecht, 1977). This observation may reflectthe high alkalinity in Hole 481 (see site chapter, thisvolume) when compared with other environments. Orthese other sediments may receive rederived material.

The absence of 4-methylsterenes is surprising in viewof the presence of 4-methylsterols, particularly of 4,23,24-trimethyl-5α-cholest-22-en-3|8-ol (dinosterol; XVIf).This concurs with data from other marine sedimentsand suggests steric hindrance by 4-methyl substitution inthe defunctionalization of 4-methylsterols and 4-methyl-stanols. Thus, it appears that microorganisms effectsterol-to-sterene conversion, since a geochemical path-way would not be expected to exhibit such selectivity be-tween 4-methyl- and 4-desmethyl-sterols.

In Section 481-2-2, the presence (in minor concentra-tions) of steranes, which are of anomalous maturity forRecent sediments, suggests a contribution of rederivedmaterial or, perhaps, minor core contamination from"pipe-dope" (drilling lubricant) (Brassell and Eglinton,1981; Thomson et al., in press).

The distribution of hopanoids is characteristic ofRecent aquatic sediment. The hopanoid alcohols, ßß-homohopan-31-ol (XVIIIa), j3ß-bishomohopan-32-ol(XVIIIb), and ßß-bishomohopanoic acid (XVIIIC), areprobably early-stage diagenetic products of polyhydrox-ybacteriohopanes (Rohmer, 1975) and are widespread inimmature marine sediments. Hop-22(29)-ene (XII) isoften the major triterpene of contemporary sediments(Brooks, 1974). In Section 481-2-2, its isomerization hasnot yet occurred to any significant extent. The absenceof ßa- and αß-hopanes is consistent with the section'simmaturity and precludes major pipe-dope contamina-tion of cores and contributions from thermally maturereworked material.

CONCLUSIONSTable 5 summarizes the results and discussion of the

lipid classes and gives the concentration of the majorcomponent of each class. We draw the following conclu-sions:

1) 4,23,24-trimethylcholest-22-en-3|S-ol (XVIIf) is thesingle most-abundant lipid, and its concentration is ap-proximately four times that of any other sterol. Hence,dinoflagellate blooms may have been important contri-butors to the sedimentary biomass.

2) The activity of methanogenic bacteria is indicatedby the presence of particular acyclic isoprenoid hydro-carbons.

3) Hydroxyalkanones are major components, which,although as yet unrecognized in organisms, are prob-ably of marine origin.

4) Contributions from terrestrial, algal, and bacte-rial sources are indicated by marker lipids; the algal con-tribution predominates.

5) The lipid data are typical of those sedimentsunderlying highly productive water columns.

6) Lipid distributions are characteristic of Recent ma-rine sediments, and typify a very early diagenesis stage.

Thus, the lipid composition of older sediment in Hole481 will determine the constancy of paleoenvironmental

conditions of deposition in the Guaymas Basin. It willespecially enable us to evaluate the sources of the sedi-mentary organic matter, the activity of methanogenicbacteria, and the history of water column productivity,especially dinoflagellate blooms. The changes in thelipid distributions with depth will also enable us toassess diagenetic trends and processes in an environmentof rapid sedimentation.

ACKNOWLEDGMENTS

We thank the Natural Environment Research Council (GR3/2951and supplement GR3/3758) for support. I. D. Thompson acknowl-edges a research studentship from the Science Research Council. Weare grateful to A. P. Gowar for help with C-GC-MS analyses and toP. A. Comet, J. McEvoy and B. R. T. Simoneit for useful discussionsand manuscript review.

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Table 5. Summary of lipids from Section 481-2-2 (7.5 m sub-bottom; late Pleistocene diatomaceous ooze).

Lipid Class Results Comments

π-alkanes

n-alkanols

n-acids

hydroxyalkanones

acyclic isoprenoid hydrocarbonssteranés

steroidal alkenes

sterols

triterpanes

triterpenes

hopanols

hopanoic acidketones

Long-chain components predominant;C29 major (189 ng/g); high CPIC20-C24 predominant; C20 major (728 ng/g);high CPIBimodal distribution; C]6 and C24 major (317and 155 ng/g); high CPIMajor components; C30 predominant(1030 ng/g)Lycopane major (68 ng/g)Very minor components (compound< 1.0 ng/g)Minor components: wide range; C27 Δ J 'predominant (74.6 ng/g); sterenes all Δ^Major components; wide range; 4,23,24-trimethyl-5α-cholest-22-en-3/3-ol predominant(1933 ng/g)Minor components; only (3/3-homohopane(29 ng/g) and ß-trisnorhopane detected;no α/3-hopanesMinor components; hop-22(29)-ene major(100 ng/g); several unidentified componentsMinor components; /3j3-bishomohopanolmajor (180 ng/g)Minor component; 0/3-homohopanoic acidComplex mixture of steroidal and triterpenoidalketones; no major amounts of long-chainunsaturated ketones; minor components dino-sterone and Ciβ isoprenoid ketone

Terrestrial origin; immature

Marine(?) origin; immature

Terrestrial and marine origin; immature

Unknown origin but probably marine

Methanogenic bacterial origin

Rederived material or minor pipe-dopecontaminationTypical of Recent sediment; immature; nomonosterene isomerizationTypical of highly productive marine environmentsand dinoflagellate blooms

Bacterial origin; immature; argues againstpipe-dope contamination

Bacterial origin; no apparent hopeneisomerization; immatureCharacteristic of Recent sediments; bacterialcontribution; immature

Fraction not examined in detail

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APPENDIX

LIPID ANALYSIS

X V I " X ^ A:R=CH9CH20H;B: R =2^" 2

CH3(CH2)nC(CH2)14OH

XVII

OH; C: R = CH2CH2CO2H

919