Organic matter preservation on the Pakistan continental ...directory.umm.ac.id/Data Elmu/jurnal/O/Organic Geochemistry/Vol31... · Sonja Schulte*, Kai Mangelsdorf, Ju¨rgen Rullko¨tter

Organic matter preservation on the Pakistan continentalmargin as revealed by biomarker geochemistry

Sonja Schulte *, Kai Mangelsdorf, JuÈ rgen RullkoÈ tter

Institute of Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg,

PO Box 2503, D-26111 Oldenburg, Germany

Received 18 January 1999; accepted 17 July 2000

(returned to author for revision 15 June 2000)

Abstract

In order to assess whether the oxygen-minimum zone (OMZ) in the Arabian sea has an e�ect on the preservation

and composition of organic matter in surface sediments we investigated samples from three di�erent transects on thePakistan continental margin across the OMZ. In addition to determining the total amount of organic carbon (TOC),we analyzed the extractable lipids by gas chromatography, combined gas chromatography/mass spectrometry, and

compound-speci®c stable carbon isotope measurements. The extractable lipids are dominated by marine organic matteras indicated by the abundance of lipids typical of marine biota and by the bulk and molecular isotopic composition.Sediments from within the OMZ are enriched in organic carbon and in several extractable lipids (i.e. phytol, n-alcohols,

total sterols, n-C35 alkane) relative to stations above and below this zone. Other lipid concentrations, such as those oftotal n-fatty acids and total n-alkanes fail to show any relation to the OMZ. Only a weak correlation of TOC withmineral surface area was found in sediments deposited within the OMZ. In contrast, sediments from outside the OMZ

do not show any relationship between TOC and surface area. Among the extractable lipids, only the n-alkane con-centration is highly correlated with surface area in sediments from the Hab and Makran transects. In sediments fromoutside the OMZ, the phytol and sterol concentrations are also weakly correlated with mineral surface area. Thedepositional environment of the Indus Fan o�ers the best conditions for an enhanced preservation of organic matter.

The OMZ, together with the undisturbed sedimentation at moderate rates, seems to be mainly responsible for the highTOC values in this area. Overall, the type of organic matter and its lability toward oxic degradation, the mineral sur-face area, the mineral composition, and possibly the secondary productivity by (sedimentary) bacteria also appear to

have an in¯uence on organic matter accumulation and composition. # 2000 Elsevier Science Ltd. All rights reserved.

Keywords: Organic carbon; Lipids; Preservation; Surface sediments; Oxygen-minimum zone; Biomarkers; Arabian sea

1. Introduction

The possible causes of organic matter enrichment inmarine sediments have already been a central issue ofnumerous organic geochemical investigations. Many of

these studies revealed concentration maxima of organic

carbon at intermediate water depths on continentalslopes (e.g. Premuzic et al., 1982) where an oxygen-

minimum zone (OMZ) in the water column impinges onthe sea¯oor. This contributed to the widely acceptedview that preservation of organic matter in marine

sediments is chie¯y controlled by low bottom-wateroxygen levels (e.g. Schlanger and Jenkyns, 1976; Thiedeand van Andel, 1977; Demaison and Moore, 1980; Par-opkari et al., 1992, 1993; van der Weijden et al., 1999).

In contrast to this, other investigators collected evi-dence for organic matter enrichment by other factorssuch as upwelling-induced high primary productivity,

0146-6380/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.

PI I : S0146-6380(00 )00108-X

Organic Geochemistry 31 (2000) 1005±1022

www.elsevier.nl/locate/orggeochem

* Corresponding author at present address: Geosciences,

University of Bremen, Postfach 330 440, D-28334 Bremen,

Germany. Tel.: +49-421-218-7108; fax: +49-421-218-3116.

E-mail address: [email protected] (S. Schulte).

winnowing, sediment texture, grain size, and mineralsurface area (Calvert, 1987; Pedersen and Calvert, 1990;Calvert and Pedersen, 1992; Calvert et al., 1995; Berga-maschi et al., 1997; Ganeshram et al., 1999). The role of

adsorption of organic matter on mineral surfaces wasemphasized in a number of studies (Keil et al., 1994 a, b;Mayer, 1994). Ransom et al. (1998) pointed out that

mineralogy and surface area of California margin sedi-ments play a more important role in preservation thanthe oxygen level of bottom waters and the organic mat-

ter origin (marine or terrestrial), whereas Hulthe et al.(1998) suggested that oxygen does have an in¯uence onorganic matter degradation in continental margin sedi-

ments. Hartnett et al. (1998) pointed out that ``the heartof the preservation controversy lies in the fact that nosingle factor seems to control preservation under allconditions''. The present organic geochemical investi-

gation of three series of surface sediments from di�erenttransects across the OMZ on the Pakistan continentalmargin in the northeastern Arabian sea, collected during

the SONNE-90 cruise in 1993, is a contribution to theongoing discussion on the parameters a�ecting organicmatter preservation. Besides determining bulk para-

meters like organic carbon content, stable carbon iso-tope composition of whole organic matter and mineralsurface area, we have placed particular emphasis on

possible e�ects of the OMZ on the composition andconcentration of selected extractable lipids in the surfacesediments.

2. Study area

The northern Arabian sea is characterized by strongseasonal variability of monsoonal upwelling (Slater andKroopnick, 1984) and high primary productivity

(Kabanova, 1968; Quasim, 1977, 1982) which, togetherwith the supply of oxygen-depleted intermediate-depthwater masses from the south (Swallow, 1984; Olson etal., 1993), favor the development of an exceptionally

broad and stable mid-water OMZ. This OMZ (200±1100 m; down to 0.5 mg O2/l) for the purpose of thisstudy was de®ned by laminated sur®cial sediments and

the absence of benthic organisms (Fig. 1; von Rad et al.,1995). Recently, Schulz et al. (1996) demonstrated thatthe OMZ was persistently present during the last 6

kyears.

3. Samples and analytical methods

3.1. Samples

During the SONNE-90 cruise in 1993, surface sedi-ments in, and adjacent to, the OMZ on the Pakistancontinental margin were collected, using box cores, on

three di�erent transects across the slope and at a distalreference site (Fig. 2). A preliminary description ofsediment characteristics including the enrichment oforganic carbon within and just below the OMZ was

published by von Rad et al. (1995).

3.1.1. The Makran transect (Area A)

The area o� the Makran coast south-west of Omara(Area A; Fig. 2) is an active continental margin slopewith sedimentation rates between 2.5 and 3 mm/year

over the last 90 kyear and a tendency of decreasingvalues with increasing water depth (Schulz and vonRad, 1997). The typical sediment in Area A is a hemi-

pelagic carbonate- and quartz-rich silty clay with abun-dant chlorite. The annual surface productivity in thisarea (64.5�E/24.5�N) is estimated to be around 480 g Cm2/year, with highest values in July during the SW

monsoon, from a digitized productivity atlas (developedby Denis Dollfus, CEREGE Aix-en-Provence, France)based on satellite chlorophyll observations and a model

of photosynthesis (Antoine et al., 1996). The mineralsurface area of Area A sediments varies between 10.8and 17 m2/g sediment and slightly increases with water

depth (Keil and Cowie, 1999; Fig. 3).

3.1.2. The Hab transect (Area B)

The Hab transect south-west of Karachi (Area B; Fig.2) has an extremely complicated slope morphology(Schulz et al., 1996). On the basis of varve counting and210Pb measurements, a sedimentation rate of 1.6 mm/

year was determined (core 39 KG) and considered repre-sentative for the whole transect (von Rad et al., 1999; U.von Rad and H. Schulz, personal communication). The

mass accumulation rates (MAR) for sediments from thistransect range from 333 to 1000 g m2 yearÿ1 with highervalues occurring within the OMZ (Sutho� et al., 2000).

As in the Makran transect, the sediments are also char-acterized by hemipelagic carbonate-rich, silty clays withchlorite as an abundant clay mineral. The estimatedprimary productivity (about 435 g C m2/year at 65.5�E/24.5�N) is only slightly lower than in Area A. The sur-face area of the sediments increase with water depthfrom 5.4 to 17.6 m2/g (Keil and Cowie, 1999; Fig. 3).

3.1.3. Murray Ridge (Area C)The Murray Ridge (Area C; Fig. 2) was selected as a

pelagic reference site una�ected by downslope sedimenttransport, which is still located below the extendedOMZ (Schulz et al., 1996). The estimated annual pri-

mary productivity in this area (64.5�E/23.5�N) is 375 gC m2/year. The reference sediment has a mineral surfacearea of 16.9 m2/g (Keil and Cowie, 1999).

3.1.4. The Indus transect (Area D)The Indus slope (Area D; Fig. 2) is a broad and gently

dipping passive continental margin which is signi®cantly

1006 S. Schulte et al. / Organic Geochemistry 31 (2000) 1005±1022

less a�ected by sediment redeposition than Areas A andB (Schulz et al., 1996). Based on 210Pb measurementsand varve counting, the sedimentation rate ranges from0.6 to 1.1 mm/year (U. von Rad and H. Schulz, unpub-

lished results; Crusius et al. 1996; Cowie et al., 1999).The hemipelagic carbonate-rich silty clays contain det-rital carbonate fragments and quartz. The estimated

primary productivity in this area (66.5�E/23�N) is about375 gCm2/year, i.e. closer to that on the Murray Ridgethan in Areas A and B. The mineral surface area of

sediments from the Indus transect (13.8±20.7 m2/g) arehigher than in the other areas and do not show a sys-tematic trend with water depth (Keil and Cowie, 1999;

Fig. 3).

3.2. Methods

We analyzed 32 surface samples (upper 2 cm) fromabove, within, and below the OMZ for bulk parameters.Based on these results, 22 samples where selected for

detailed studies of the molecular composition of theextractable organic matter.After freeze-drying and grinding, the sediments were

analyzed in duplicate or triplicate (when relative di�er-

ences were larger than 5% after duplicate measure-ments) for total carbon content by combustion in aLECO-SC-444 instrument. Carbonate contents were

determined in duplicate by acidi®cation using a UIC-Coulometrics CM 5012 device. A detailed description ofthe system as well as a discussion of the accuracy and

reproducibility of the method were provided by Engle-man et al. (1985) and Jackson and Roof (1992). Totalorganic carbon (TOC) contents were calculated as the

di�erence between total and inorganic carbon data.Solvent extractions were performed for 48h in a

Soxhlet apparatus with dichloromethane containing 1%methanol. After addition of internal standards (squa-

lane, erucic acid, 5a-androstan-17-one) and removalof the hexane-insoluble fraction by the addition of alarge excess of n-hexane (`asphaltene' precipitation), the

Fig. 1. Oxygen contents in the water column, nekton/epibenthos/bioturbation from photo sled observations, color and sediment facies

of core top sediments. Modi®ed after von Rad et al. (1995).

S. Schulte et al. / Organic Geochemistry 31 (2000) 1005±1022 1007

hexane-soluble portion of the extract was separated bymedium-pressure liquid chromatography (MPLC;Radke et al., 1980) into fractions of aliphatic hydro-

carbons, aromatic hydrocarbons, and polar hetero-compounds (NSO fraction). Subsequently, carboxylicacids were separated from the NSO fraction on a col-

umn ®lled with KOH-impregnated silica gel (63±200mm; a solution of 0.5 g KOH in 10 ml iso-propanol wasadded to 4 g silica gel). The nonacidic compounds wereeluted with 120 ml dichloromethane. Following this, 120

ml of a solution of formic acid (2% in dichloromethane)transformed the potassium salts of the acids back to theoriginal acids and eluted them from the column. For

molecular analysis, the acids were methylated with diazo-methane, and the nonacidic polar compounds weresilylated with N-methyl-N-trimethylsilyltri¯uoroacet-

amide (MSTFA).Gas chromatography was performed on a Hewlett

Packard 5890 Series II instrument equipped with a

Gerstel KAS 3 temperature-programmed cold injectionsystem and a fused silica capillary column (30 m length,inner diameter=0.25 mm, coated with DB 5 (J&W),®lm thickness=0.25 mm). Helium was used as the car-

rier gas, and the oven temperature was programmedfrom 60�C (1 min) to 305�C (50 min) at 3�C/min. Theinjector temperature was programmed from 60�C (5 s

hold time) to 300�C (60 s hold time) at 8�C/s. GC/MSstudies were performed under the temperature condi-tions given above with the same type of gas chromato-

graph interfaced directly to a Finnigan SSQ 710 B massspectrometer operated at 70 eV.Molecular isotope analyses were performed using the

same type of gas chromatograph (fused silica capillarycolumn; 30 m length, inner diameter=0.25 mm, coatedwith Ultra 2 (HP), ®lm thickness=0.17 mm; temperatureconditions as given above) attached to a Finnigan MAT

252 isotope ratio mass spectrometer via a combustioninterface. This instrument was calibrated with a CO2

standard at the beginning and the end of each analysis and

with compounds of known isotopic composition whichwere co-injected with each sample and served as internalisotopic standards. Isotopic ratios are expressed as d13Cvalues in per mil relative to the V-PDB standard.

4. Results

4.1. Composition of lipids

4.1.1. Gross molecular compositionThe aliphatic hydrocarbon fractions of the surface

samples are dominated by C17 and C43 n-alkanes in a

Fig. 2. Map of investigation area o� Pakistan. The area shaded gray indicates the OMZ impinging on the continental slope. Letters A±D

indicate study areas, with A=Makran transect, B=Hab transect, C=Murray Ridge (reference location), and D=Indus transect.


carbon number range between with components con-taining more than 40 carbon atoms being present onlyin small amounts (Fig. 4; Schulte, 1997). The n-alkane

distribution maximizes at n-C31 in eighteen of the ana-lyzed samples, and at n-C35 in the other four sampleswhich were all deposited within the OMZ. The long-

chain homologs (C25±C35) show an odd-over-even car-bon number predominance with a carbon preferenceindex (CPI) between 1.3 and 4 (Schulte, 1997). Besidesthe n-fatty acids, branched-chain (iso and anteiso) iso-

mers of the C15 and C17 acids were detected. Mono-unsaturated acids with 16 and 18 carbon atoms as wellas a diunsaturated C18 acid were also present. The fatty

acid distributions have a pronounced maximum in theshort-chain compound range (at C16:1, C16:0, or C18:0)and a second, lower maximum at C24:0 or C26:0 (Schulte,

1997). The even-carbon-numbered fatty acids are domi-nant in all samples.Sterols were detected between C27 and C30 among

which the C28 and C30 pseudohomologs dominate(Schulte, 1997). The most prominent sterol is dinosterol:24-ethylcholest-5-en-3b-ol, its saturated counterpart,and cholesterol also occur in high abundance (Schulte,

1997; Fig. 5).In the n-alcohol series ranging from 14 to 28, n-hexa-

decanol is the most abundant homolog. Furthermore,

phytol, alkandiols, keto-ols, hopanoic acids and alco-hols, and as well as C37 and C38 alkenones are sig-ni®cant constituents of the NSO fraction (Fig. 5;Schulte, 1997).

4.1.2. Isotopic composition of single compoundsTwo samples, one from above and one from within

the OMZ were investigated for the isotopic compositionof n-alkanes. Most importantly, the isotopic composi-tion of the n-C35 alkane signi®cantly di�ers from those

of the other long-chain n-alkanes (Schulte, 1997; Schulteet al., 1999). In the sample from above the OMZ, the n-C35 alkane has a d13C value of ÿ26.2% compared with a

mean d13C value of ÿ28.1% (n=8, S.D.=1.21%) forthe other long-chain n-alkanes (C27±C39). In the samplefrom within the OMZ, the n-C35 alkane (ÿ24.2%) isisotopically even 4% heavier than, on average, the other

long-chain n-alkanes (ÿ28.06%; n=9, S.D.=1.95%)(Schulte et al., 1999). Chromatographic coelution of anunknown component with the n-C35 alkane can be exclu-

ded on the basis of GC/MS and GC-irm-MS analyses(Schulte, 1997).For one sample from within the OMZ (12 KG, Table

1), the isotopic compositions of several fatty acids weredetermined. The d13C values vary between ÿ24.6% andÿ28.4% with a mean value of ÿ26.3% (n=9, standard

deviation=1.17%). The n-C24 and n-C26 acids have anisotopical composition that is 2% lighter than that ofthe other n-fatty acids (mean=ÿ25.8%, n=7, standarddeviation=0.73%; Schulte, 1997).

4.2. Organic matter abundance in relation to the OMZ

4.2.1. Total organic carbon (TOC)In a plot versus water depth, the TOC data exhibit

variations between 0.4 and 4 wt.% (Fig. 6). As was

noted in previous studies (e.g. Paropkari et al., 1992;Calvert et al., 1995), there is a broad mid-slope organiccarbon maximum, i.e. organic carbon values in surfacesediments are higher on the continental slope within the

present OMZ than above and well below (Table 1 andFig. 6). On the Pakistan continental margin, this max-imum is most pronounced for the Indus transect and

less so in Areas A and B. These regional di�erences arein general agreement with the measurements of Par-opkari et al. (1992). The shallow-water rise of the

organic carbon content at the top of the OMZ is fairlysharp, whereas the carbon values decrease graduallywith increasing water depth below the OMZ.

As can be seen from Fig. 6, the stable carbon isotopedata of the total organic matter vary slightly betweenÿ20.8% and ÿ19.2% (Cowie et al., 1999), i.e. the valuesare in the typical marine organic matter range of

ÿ20�2% (Hoefs, 1980). The d13C values of the sedi-ments deposited within the OMZ are isotopically 0.5%lighter (mean: ÿ20.5%; n=12; S.D.=0.3%) than those

Fig. 3. Mineral surface area of surface sediments versus water

depth. The area shaded gray denotes the depth range of the

OMZ. Letters indicate the transects A±D. MR corresponds to

the sample from the Murray Ridge.


of the sediments deposited outside the OMZ (mean:-

20.0%; n=12; S.D.=0.4%). No di�erence between thethree transects was observed. The two samples frombelow 2500 m water depth show d13C values that are

slightly lighter than those of the other samples frombelow the OMZ (Fig. 6).

4.2.2. Compound group concentrations

We analyzed a suite of biomarkers characteristic ofmarine and terrigenous organic matter to investigatewhether or not the low bottom-water oxygen con-

centrations within the OMZ have an in¯uence on thepreservation of these compounds. Because these com-pounds belong to di�erent chemical compound classes,

they should have di�erent sensitivities toward degrada-tion during early diagenesis.The C16±C42 n-alkane concentrations vary between 31

and 184 mg/g TOC, with the exception of sample 164KG, which has an n-alkane concentration of 385 mg/gTOC (Fig. 7). The extremely high n-alkane concentra-tion in this latter sediment may be related to the sam-

pling location south of the Indus Canyon. Other thanthe rest of the samples from Area D, the sedimentrepresented by 164 KG may have accumulated organic

matter supplied by the Indus River and de¯ected south

by the prevalent surface ocean current (Rao and Rao,1995). n-Alkane concentrations in sediments from AreasA and B increase with water depth (r2=0.93 and

r2=0.94, respectively), whereas the n-alkane concentra-tions in Area D sediments are less signi®cantly corre-lated with the water depth (Fig. 7; r2=0.61; sample 164KG south of the Indus Canyon not included).

The concentrations of n-fatty acids in the surfacesediments from the four sampling areas vary between460 and 2940 mg/g TOC and exhibit nearly the same

average values within and outside the OMZ (991 mg/gTOC within OMZ, n=12, and 884 mg/g TOC outsideOMZ, n=9; Fig. 7). However, there are di�erences

among the transects studied. In the sediments from theIndus transect, the fatty acid concentrations are almostinvariable over the entire range of water depth (164 KG

excluded). By contrast, the sediments from the Makrantransect show a strong decrease in fatty acid concentra-tion between 200 and 1000 m water depth, and thosefrom the Hab transect have slightly elevated concentra-

tions within the depth range of the OMZ (Fig. 7).n-Alcohols (C12±C28) were detected in concentrations

between 90 mg/g TOC for the reference sample (MR)

Fig. 4. Representative gas chromatogram of an aliphatic hydrocarbon fraction (110 KG; Table 1. Numbers indicate carbon numbers

of n-alkanes. S=internal standard.


and 2420 mg/g TOC for sample 164 KG (Fig. 8). With-out taking into account sample 164 KG, the concentra-

tions of the n-alcohols in sediments deposited within theOMZ on average are 1.6 times higher (430 mg/g TOC,n=10; Fig. 8) than outside the OMZ (273 mg/g TOC,n=10; Fig. 8). We note that three samples from within

the OMZ have comparatively low concentrations of n-alcohols.The concentrations of total sterols (C27±C30) vary

between 83 and 2070 mg/g (Fig. 8). The mean con-centration in samples deposited outside the OMZ is 415mg/g TOC (n=10), whereas the samples from within the

OMZ have a mean concentration (1020 mg/g TOC,n=11) almost 2.5 times higher with highest valuesbeing attributed to samples from Areas A and B. Sedi-

ments from Area D, with the exception of sample 164KG, fail to show elevated sterol concentrations withinthe OMZ.

4.2.3. Speci®c biomarkersThemajor source of phytol is chlorophyll a and released

from it by hydrolysis already in the water column

(Baker and Louda, 1983). Due to the highly reactiveallylic hydrogen atoms, phytol is rapidly degraded by

oxidation (Rontani et al., 1990). The phytol concentra-tions in the surface sediments from the Pakistan marginvary between 1.5 and 126 mg/g TOC with the highestconcentrations occurring within the OMZ (up to six

times higher than above and below; Fig. 9), especially insediments from the Hab transect (B) The phytol con-centration in several sediments within the OMZ on the

Makran (A) and Indus transects (D) are also sig-ni®cantly higher than the average value of samples fromoutside the OMZ.

Dinosterol, a speci®c marker for dino¯agellates (e.g.Boon et al., 1979; Nichols et al., 1984; Robinson et al.,1984) which were abundant organisms in plankton tows

from the overlying surface waters in the study areas(von Rad et al., 1999), was detected in a concentrationrange from 14 to 320 mg/g TOC. Concentrations ofdinosterol are two times higher in sediments from within

the OMZ (mean: 165 mg/g TOC, n=10) than in sedi-ments deposited outside the OMZ (mean: 85 mg/g TOC,n=10; Fig. 9). The higher abundance of dinosterol

Fig. 5. Representative gas chromatogram of an NSO fraction (110 KG; Table 1). Numbers denote carbon numbers of n-fatty acids.

Numbers-OH represent carbon numbers of n-alcohols. S=internal standard. A=cholesterol, B=24-ethylcholest-5-en-3b-ol+23,24-

dimethylcholest-5-en-3b-ol, C=24-ethylcholestan-3b-ol, D=dinosterol, E=17b,21b-homo-hopan-31-ol, F=17b,21b-dihomo-hopan-

32-ol, G=17b,21b-dihomo-hopanoic acid, H=C37:2 alkenone, I=C38:2 alkenone.


within the OMZ is most pronounced in sediments from

Areas A and B. By contrast, Area D sediments do notshow a remarkable variation of dinosterol concentrationas a function of water depth.

Because the stable carbon isotopic compositions ofthe C24 and C26 n-fatty acid di�er from those of theother fatty acids, they may have a distinct origin.

Sediments from within the OMZ have a 1.6 timeshigher concentration of C24 plus C26 fatty acids(mean: 130 mg/g TOC, n=11; Fig. 9) than sediments

which were deposited outside the OMZ (mean: 80 mg/gTOC, n=11; Fig 9). The maxima of C24 and C26 n-fattyacid concentrations cover the water depth range of theOMZ, with no obvious di�erences between the trans-

ects.Branched-chain fatty acids are more common in bac-

teria than in other organisms (Volkman et al., 1980;

Parkes and Taylor, 1983), and so they are useful indi-cators of bacterial contributions to sediments. The sumof C15 and C17 branched fatty acids versus water depthis shown in Fig. 10. Sediments within the OMZ are

richer in branched-chain fatty acids by a factor of up tonearly 3 (maximum about 260 mg/g TOC) relative tosediments which were deposited above or below the

OMZ (mean: 110 mg/g TOC, n=11).The C35 n-alkane is enriched within the water depth

range of the OMZ in all transects (up to more than 15

mg/g TOC) by a factor of about 2 on average relative tothe sediments deposited outside the OMZ (mean: 6 mg/gTOC) (Fig. 10). The molecular carbon isotopic compo-

sition of this component is signi®cantly more positivethan those of the other long-chain n-alkanes pointing toa distinct origin of the C35 homolog (Schulte, 1997;Schulte et al., 1999). In contrast to the C35 n-alkane, the

C31 n-alkane which is typically derived from higherplants (e.g. Eglinton and Hamilton, 1967; Rieley et al.,1991; Meyers and Ishiwatari, 1993) is not enriched

within the OMZ. The concentration, normalized toTOC, increases with increasing water depth in Areas Aand B similar to those of the C27 and C29 n-alkanes. In

the Indus transect, such an increase was not observed(Fig. 10).

4.3. Organic matter abundance in relation to mineralsurface area

It was suggested that organic matter settling through

the water column and in surface sediments may be pro-tected against oxidation and microbial degradation bysorption on mineral surfaces (Keil et al., 1994a; Mayer,

1994; Hedges and Keil, 1995, Bergamashi et al., 1997).For this reason, we compared published data on mineralsurface area for the surface sediments on the Pakistan

continental margin (Keil and Cowie, 1999) with organicgeochemical data generated in this study.

4.3.1. Total organic carbon (TOC)

The TOC contents of the investigated samples do notshow an overall signi®cant correlation with mineralsurface area (Fig. 11). However, within the OMZ, the

organic carbon content with a correlation coe�cient ofr2=0.49 may indicate an organic load on minerals ofabout 2.2 mg C/m2.

4.3.2. Extractable lipidsA strong correlation between n-alkane concentration

and mineral surface area was observed for sedimentsfrom Areas A and B (r2=0.83 and 0.84, respectively;Fig. 11). The concentrations of the other extractablelipids analyzed do not show any relationship with the

surface area, except for phytol and sterol concentrationsof sediments deposited outside the OMZ (Fig. 11) exhi-biting a weak to good correlation.

Table 1

Sample number, water depth, organic carbon content and C24/

C16 n-fatty acid ratio in sediments collected on the continental

slope o� Pakistan. (n.d.=not determined)a

Sample Area Water depth

(m)

TOC

(%)

C24/C16

fatty acids

18 KG A 228 1.1 0.08

34 KG A 667 1.1 0.26

23 KG A 690 1.7 0.19

12 KG A 789 2.1 0.38

20 KG A 993 1.8 0.63

28 KG A 1017 2.9 0.72

24 KG A 1204 1.6 0.44

1 KG A 2679 1.2 n.d.

65 KG B 119 2 0.14

69 KG B 134 1.6 0.18

39 KG B 704 2 0.21

142 KG B 865 2.3 0.25

79 KG B 1970 1.1 0.1

85 KG B 2882 0.9 0.29

87 KG C 1782 2 0.28

120 KG D 96 0.4 n.d.

124 KG D 136 1.7 0.15

129 KG D 185 0.7 n.d.

163 KG D 239 0.9 n.d.

113 KG D 287 2 n.d.

164 KG D 322 2.8 0.18

180 KG D 398 3.1 n.d.

96 KG D 483 2.5 0.36

110 KG D 776 3.1 0.38

107 KG D 992 4 0.43

173 KG D 1192 0.4 n.d.

103 KG D 1206 2.45 0.35

168 KG D 1283 2.9 n.d.

99 KG D 1506 2.1 0.19

115 KG D 1796 1.1 n.d.

95 KG D 2111 0.7 n.d.

a Samples from within the OMZ are in bold.


5. Discussion

5.1. Information on the origin of organic matter basedon straight-chain lipid distributions and the carbon

isotopic composition of individual components

The occurrence of long-chain n-alkanes with an odd-

over-even carbon number predominance in marinesediments is commonly interpreted as a contributionfrom higher land plants (e.g. Eglinton and Hamilton,1967; Rieley et al., 1991; Meyers and Ishiwatari, 1993).

Very long chain n-alkanes (>C35) with no carbonnumber preference were detected in a surface sedimentfrom the western Arabian Sea (Oman upwelling; Eglin-

ton et al., 1997), and they do occur in a number of othermarine sediments (Volkman, private communication1998). However, the origin of these very long-chain n-

alkanes is still unknown.The stable carbon isotope ratio of higher-plant n-

alkanes is lower by about 5±10% than the bulk plant

tissue (Collister et al., 1994; Lichtfouse et al., 1994). Asimilar di�erence (7 Ð 9%) between n-alkanes and totalbiomass was reported for a cyanobacterium (Sakata etal., 1997). Nothing has been reported so far about the

isotopic depletion of n-alkanes in marine organism, butassuming the same di�erence in marine organism as inother plants (about 7.5%), n-alkanes deriving from C3

and C4 land plants and from marine organism should

have d13C values of ÿ35.5%, ÿ19.5%, and ÿ27.5%,respectively. The carbon isotope ratios measured for then-alkanes from the Pakistan margin sediments (C27±C39

mean: ÿ28.1%; n=9, S.T.D.=2.0%) would be closestto those of marine organism, but these values could alsoresult from a mixed origin of the n-alkanes from C3 and

C4 plants or a mixture from all three sources. Thus, theorigin of the n-alkanes cannot be unambiguously deter-mined on the basis of their isotopic composition alone.The CPI of higher plant n-alkanes ranges from 3 to

40.3 (McCa�rey et al., 1991 and references therein;Collister et al., 1994), whereas CPI values of bacterialand phytoplankton n-alkanes generally are closer to

unity (McCa�rey et al., 1991). Accordingly, the CPIvalues between 1.3 and 4 of the Pakistan margin sam-ples point to a mainly marine origin of n-alkanes in the

sediments, which is in agreement with the molecularcarbon isotope data. Zegouagh et al. (1998) interpretedn-alkane CPI values of 1.4±2.7 in arctic surface sedi-

ments as a marine signal, and a marine origin was alsosuggested for n-alkanes showing a CPI of 3±4 in Per-uvian surface sediments (McCa�rey et al., 1991). Theabsence of an unresolved complex mixture in the sediment

extracts (Fig. 4) and the relatively low concentrations ofn-alkanes make a petrogenic origin of the n-alkanes inthe studied samples unlikely, except for possibly a minor

Fig. 6. Distribution of total organic carbon (TOC) and stable carbon isotopic composition of total organic matter (d13C; Cowie et al.,1999) in surface sediments as a function of water depth. The shaded area denotes the approximate depth range of the present OMZ.

Letters correspond to the investigation areas A±D. MR indicates the sample from the Murray Ridge.


portion as indicated by traces of saturated steranes and

hopanes in the extracts (Schulte, 1997).Short-chain fatty acids (C12±C18) are commonly pro-

duced by marine micro-organisms (Schnitzer and Kahn,

1978; Sargent and Whittle, 1981), whereas long-chainfatty acids mainly derive from higher land plants (Mat-suda and Koyama, 1977). For the Pakistan margin

sediments, this interpretation is supported by the iso-topic composition of the fatty acids with heavier d13Cvalues for the short-chain members and lighter valuesfor the C24 and C26 acids (Schulte, 1997). Because lipids

in general are depleted in 13C relative to the total bio-mass by around 4% (Monson and Hayes, 1982; Hayes,1993) and since C3 land plants commonly have a d13Cvalue of ÿ28% (Bird et al., 1995), one would expect ad13C value of around ÿ32% for a C3 plant-derived lipid.Therefore, the C24 and C26 acids may not be exclusively

contributed by C3 land plants, but also include an iso-topically heavier C4 land plants and/or marine compo-nent (ÿ12% and ÿ20%, respectively; Smith and

Epstein, 1971; Hoefs, 1980).Despite the vicinity to the Indus river, the proportion

of terrestrial organic matter is conspicuously small inthe sediments studied. This terrigenous contribution to

the sediments is most clearly re¯ected by long-chain n-alcohols (>C20) believed to derive from higher landplants (Eglinton and Hamilton, 1967; Kolattukudy,

1976). The biomarker evidence of a predominance of

the marine organic matter, however, is consistent withthe d13C values of bulk organic matter (Cowie et al.,1999) and microscopical observations indicating that in

the study area OM is mainly (75±95%) amorphouswith only a small fraction of terrigenous organoclasts(von Rad et al., 1995; Littke et al., 1997; LuÈ ckge et al.,

1999).

5.2. Factors in¯uencing the accumulation of organicmatter

5.2.1. Bottom water oxygen concentrationThe TOC pro®le across the OMZ on the Pakistan

margin shows a mid-slope maximum roughly coincidentwith the extension of the OMZ (Fig. 2). This result is ingood agreement with those of previous studies (Par-

opkari et al., 1992; Calvert et al., 1995; Cowie et al.,1999). As an exception to this general picture, theorganic carbon contents of two samples directly beneath

the OMZ on the Indus transect were found to be high.von Rad et al. (1995), on the basis of their Parasounddata, suggested that surface sediment, originally depos-ited within the OMZ, had been displaced down-slope by

slumping. This idea, however, is not compatible with theexcess 210Pb pro®les which, rather, indicate continuousin-situ sedimentation below the OMZ (Cowie et al.,

Fig. 7. Concentrations of n-alkanes (C17±C43) and n-fatty acids (C12±C30) in surface sediments versus water depth. The shaded area

denotes the approximate depth range of the present OMZ. Letters correspond to the transects A±D. MR indicates the sample from the

Murray Ridge. 164 KG is the only sample taken south of the Indus Canyon.


1999). Thus, although the organic carbon maximum inthe surface sediments appears to be related to the pre-sent position of the OMZ, not all of the organic carbon

accumulation pattern can be readily explained by water-column oxygen concentrations. The more complexorganic carbon patterns in the Hab and Makran trans-

ects, compared to the Indus transect, may be related tothe tectonic activity in those active margin areas, whichis also re¯ected in common turbidities found in deepercore sections from the same areas.

Among the individual lipids and lipid groups in thesediment extracts, the C35 n-alkane, the sum of the C24

and C26 n-fatty acids, phytol, the n-alcohols, and dinos-

terol have elevated concentrations relative to totalorganic carbon within the present depth range of theOMZ. This suggests that the oxygen content of the

overlying water column may be an important factorcontrolling the accumulation of these components. Fordinocysts, considered labile under normal marine con-

ditions, it was recently demonstrated that anoxic condi-tions controlled their preservation in Mediterranean Seasediments (Combrourieu-Nebout et al., 1998). Becausedinosterol is a common constituent of dino¯agellates

(Robinson et al., 1984), the relative extent of preserva-tion of this biomarker may well be controlled by thewater-column redox conditions.

Recent studies also demonstrated slower degradationof some sterols under anaerobic conditions (Teece et al.,1994; Sun and Wakeham, 1998). This slower degrada-

tion rate may be invoked for the concentration max-imum of the sum of sterols and of dinosterol within theOMZ of Areas A and B. On the other hand, elevated

sterol concentrations do not extend over the wholedepth range of the OMZ, and in Area D there is noenrichment of sterols at all within the OMZ. This alsoholds true for the other extractable lipids studied in

some detail (phytol, branched-chain C15 and C17 fattyacids, n-alcohols) which are enriched within the OMZ,but not over the entire depth range, and which also

show di�erences between the three transects. Thus,although oxygen depletion in the water columnmay havea favorable in¯uence on biogenic lipids in marine sedi-

ments, this parameter alone does not appear to be su�-cient.The concentrations of the sum of n-alkanes, the sum

of n-fatty acids, and of the C31 n-alkane fail to show anyrelationship with oxygen content in the overlying watercolumn on the Pakistan margin. It was demonstrated inincubation experiments that the n-alkane concentration

in sediments is not a�ected by di�erent redox conditions(Teece et al., 1994). The chemical inertness of saturatedalkanes may explain these observations, but it is less

Fig. 8. Concentrations of n-alcohols (C14±C28) and sterols (C27±C30, cf. Fig. 5; Schulte, 1997) in surface sediments versus water depth.

The area shaded gray indicates the approximate depth range of the present OMZ. The letters indicate the transects A±D. MR corre-

sponds to the sample from the Murray Ridge.


easy to conceive that this should also hold for the fattyacids.

5.2.2. Mineral surface areaA positive correlation between TOC content and

mineral surface area has previously been observed in

several studies of marine sediments and was invoked toemphasize that organic matter can be protected againstmineralization, and thus be preserved, by sorption onmineral surfaces (Keil et al., 1994a,b; Mayer, 1994;

Bergamaschi et al., 1997). In the Pakistan margin sam-ples of this study, there was no general signi®cant cor-relation between TOC and mineral surface area. Only

for sediments deposited within the OMZ, a weak posi-tive correlation was observed (r2=0.49; Fig. 11), whichsuggests that part of the organic matter within the OMZ

is associated with mineral surfaces at a relatively highlevel of loading (2.2 mg C/m2). Similarly high loadingswere determined in size fractions of a Peru Margin

sediment (Bergamaschi et al., 1997), but with a muchhigher correlation coe�cient between TOC and surfacearea. It should be noted, however, that the highest TOCcontents on the Pakistan margin occur in Area D in

sediments that also have the highest surface areasamong the samples studied (Figs. 3 and 6). Our resultsare in con¯ict with those of Ransom et al. (1998) and

van der Weijden et al. (1999) who reported a positivecorrelation between organic matter content and mineralsurface area for continental margin sediments from

outside the OMZ and no correlation between TOC andsurface area for sediments deposited within the OMZ.Among the investigated biomarker concentrations,

only those of the n-alkanes in Area A and B samplesshow a signi®cant positive correlation with mineral sur-face area (Fig. 11). This is in disagreement with theresults of Jeng and Chen (1995), who did not detect any

grain-size e�ect (which is indistinguishable from thee�ects caused by surface area; Jeng and Chen, 1995 andreferences therein) for the concentration of n-alkanes in

sediments o� Taiwan. By contrast, the lack of correla-tion between n-alkane concentrations and mineral sur-face area in Area D sediments (Fig. 11) is consistent

with the results of Jeng and Chen (1995).Phytol and the sum of sterols also are correlated with

mineral surface area, but in contrast to n-alkanes this is

true only for sediments from outside the OMZ. This isin accordance with the results of Jeng and Cheng (1995)who reported a pronounced grain-size e�ect for phytoland sterols in sediments o� northeastern Taiwan. The

investigation of the Pakistan margin sediments alsocorroborates the observation of Jeng and Cheng (1995)that n-alcohols do not correlate with mineral surface

Fig. 9. Concentrations of phytol, dinosterol, and the sum of C24 and C26 n-fatty acids in surface sediments versus water depth. The

shaded area denotes the approximate depth range of the present OMZ. Letters indicate the transects and MR the sample from the

Murray Ridge. �3 and �6 in the left-most column (phytol) mark three-fold and six-fold enrichment relative to the average value

outside the OMZ.


area. Apparently, the simple presence of a hydroxylgroup is not su�cient to explain the association of lipids

with mineral surfaces.Mineral composition may also play a role on the extent

of lipid adsorption. As was pointed out by Ransom et al.

(1998), organic matter appears to be preferentiallysequestered in smectite-rich sediments compared to thosewhose clay fractions are dominated by chlorite. The

relatively high abundance of chlorite in the investigatedPakistan margin sediments (particularly Areas A and B)may explain the weak correlation between organic mat-ter content and mineral surface area.

5.2.3. Type (origin) of organic matterRelative to marine organic matter, continentally

derived organic matter commonly includes a higherproportion of biologically resistant organic compoundsand a fraction already strongly degraded by soil

microbes (e.g. de Leeuw and Largeau, 1993; Berga-maschi et al., 1997). Furthermore, there is evidence thatterrigenous organic matter generally su�ers biological

degradation at a lower rate than marine organic matter(Huc, 1988; Littke and Sachsenhofer 1994) which leadsto a better preservation of this material.The isotopic composition of the C24 and C26 fatty

acids suggests that they are at least partly of terrestrialorigin. This may account for the pronounced enrich-ment of these compounds in sediments deposited within

the OMZ in all investigated areas (Fig. 8). Canuel andMartens (1996) demonstrated that the terrigenous C24

acid is degraded more slowly in coastal sediments thanmarine-derived short-chain fatty acids (e.g. C14 andC16:1). The C24/C16 fatty acid ratio was employed to

determine the relative contribution of fatty acids fromterrestrial and marine sources (Leenheer et al., 1984;LeBlanc et al., 1989). On the Pakistan margin, this ratio

in general is higher in sediments deposited within theOMZ (Table 1) possibly indicating a higher proportionof terrigenous fatty acids in sediments within the OMZ,although the non-terrigenous contribution (isotopic evi-

dence) to the same acid may have varied as well. As canbe seen by the n-alkane concentrations, which do notrelate to the OMZ, a terrestrial origin per se does not

lead to a higher accumulation rate within the OMZ.A better preservation of terrigenous organic matter

within the OMZ, however, is suggested by the lighter

(``more terrestrial'') d13C values of the total organicmatter in the corresponding sediments. A redox poten-tial related di�erence in organic matter preservation,

with heavier values above and below the OMZ, re¯ect-ing preferential remineralization of 12C compounds,would be an alternative explanation (Cowie et al., 1999).As a third hypothesis, the supply of isotopically light

organic matter by chemoautotrophic bacteria in oxygen-depleted water was suggested to explain the lighter d13Cvalues within the OMZ (Cowie et al., 1999). A speci®c in

Fig. 10. Concentration of branched C15+C17 fatty acids, the C35 n-alkane, and the C31 n-alkane versus water depth. The shaded area

corresponds to the depth range of the modern OMZ. Letters indicate the transects and MR the sample from the Murray ridge.


situ supply of organic matter by organism living withinthe OMZ might also explain the enrichment of the C35

n-alkane in sediments from within the OMZ, re¯ecting asecondary productivity signal (Schulte et al., 1999). Theisotopic composition of this compound is signi®cantly

di�erent from that of the other n-alkanes pointing toanother, yet unknown source. The higher concentra-tions of the bacterial branched fatty acids within theOMZ point to signi®cant bacterial activity and support

the suggestion of secondary productivity within theOMZ. This interpretation would be consistent with theresults of Lee (1992) who suggested that the production

of new organic matter by bacteria in sediments may be away of preserving carbon in anoxic sediments (regard-less of O2).

5.2.4. Reactivity toward oxic degradationAs mentioned above, phytol, the n-alcohols, and the

sterols all have higher organic-carbon-normalized con-centrations within the OMZ (Figs. 8 and 9). Chemically,all these compounds are alcohols, but the reactivitytoward oxidation of their hydroxyl groups decreases in

the order allylic>secondary>primary (March, 1992).Apparently, the relative degree of preservation underthe oxygen-depleted conditions of the OMZ increases

parallel to the reactivity of the hydroxyl group underoxic conditions (phytol>sterols>n-alcohols).

The relationship between preservation and reactivitycan also be demonstrated by di�erences in the preserva-tion of sterols with di�erent degrees of unsaturation. In

the Pakistan margin sediments, the concentration of thesum of sterols with two double bonds is three timeshigher within the OMZ (mean concentration: 170 mg/gTOC; n=11; Schulte, 1997) than outside the OMZ

(mean concentration: 55 mg/g TOC; n=9, Schulte, 1997).By comparison, the saturated and monounsaturatedsterols are only enriched by factors of 2.5 and 2.3 within

the OMZ (Schulte, 1997). This relationship betweenpreservation and the number of double bonds under-lines the in¯uence of the sensitivity to oxidation of a

lipid molecule on its preservation under suboxic condi-tions. This is in accordance with the conclusions of Sunand Wakeham (1998) who recently demonstrated that

cholesterol is more rapidly degraded under oxic thanunder anoxic conditions and that under anoxic condi-tions it is degraded faster than C26±C29 dienols. Allthese interpretations on speci®c compounds are con-

sistent with the statement of Hulthe et al. (1998) whosuggested that the e�ect of oxygen on the degradation oforganic matter depends on its lability.

Fig. 11. TOC, n-alkanes (C17±C43), phytol, and sum of sterols (C27±C30, cf. Fig. 5; Schulte, 1997) versus mineral surface area (Keil and

Cowie, 1999). Letters correspond to study areas. Letters in open circles indicate samples from within the OMZ. The regression lines

were calculated for sediments within the OMZ (TOC) and outside the OMZ (phytol, sterols) only.


On the other hand, the lack of enrichment of sterolsin sediments within the OMZ in the Indus transect(Area D) cannot be explained by reactivity alone. Themineral composition may be responsible for the higher

enrichment of sterols (and alcohols in general) in AreasA and B, where the sediments are dominated by chloritewith strong adsorptive properties. In contrast, sediments

of Area D are dominated by detrital carbonates.

5.2.5. Sedimentation rate and primary productivity

Sedimentation rate and primary productivity arerecognized as important factors controlling the quantityof OM buried in marine sediments (cf. RullkoÈ tter, 1999,

for an overview). The three transects on the Pakistanmargin di�er in primary productivity and sedimentationrate. Highest TOC values were observed within theOMZ of the Indus transect where primary productivity

and sedimentation rate are lowest, whereas lower TOCvalues occur in areas with higher primary productivityand sedimentation rate (Areas A and B; Fig. 6). This

disagrees with the empirical relationship between TOCcontent of sediments and primary productivity andsedimentation rate observed by MuÈ ller and Suess

(1979). On the basis of mean values of primary pro-ductivity and sedimentation rate (sedimentation ratemay, however, vary across the margin), the accumula-

tion of organic matter in the studied sediments appar-ently cannot be explained simply by di�erences inprimary productivity and sedimentation rate.

6. Conclusions

The composition of extractable lipids and the bulkstable carbon isotope data of organic matter in sedi-ments from the Pakistan continental margin indicate

that despite the vicinity of the Indus River the organicmatter is mainly derived from marine sources. Thisorganic geochemical evidence is in good agreement withthe results of organic petrographic analyses (Littke et al.

1997; LuÈ ckge et al., 1999).Supported by a biological marker approach we could

demonstrate that accumulation of organic matter in

marine sediments underlying an extended OMZ is acomplex process involving several di�erent mechanisms.Apparently, the OMZ plays a signi®cant role in the

accumulation and preservation of organic matter asindicated by a pronounced TOC maximum and theenrichment of single compounds within the OMZ in all

investigated areas.However, the low oxygen concentrations of the bot-

tom waters underlying the OMZ are not an exclusivefactor explaining all organic matter properties and their

variations on the Pakistan continental margin. The type(origin) of certain organic matter constituents and their(related) lability toward oxic degradation, the mineral

surface area, the mineral composition, and possibly thesecondary productivity by (sedimentary) bacteria alsoappear to have an in¯uence on the accumulation andcomposition of organic matter in this area and in some

cases to explain discrepancies with published observa-tions for other continental margin settings.Apparently, the depositional environment of the

Indus Fan (Area D) o�ers the best conditions forenhanced preservation of organic matter. The OMZtogether with the undisturbed sedimentation (slope

morphology) at moderate sedimentation rates seems tobe responsible for the high TOC values in this area.

Acknowledgements

We would like to thank Dr. Michael E. BoÈ ttcher for

carrying out GC±IR±MS analyses. We are grateful toDr. Barbara M. Scholz-BoÈ ttcher for her support duringGC/MS analyses. We also would like to thank Greg L.

Cowie for constructive comments and suggestions toimprove the manuscript. This study was ®nanciallysupported by the Bundesministerium fuÈ r Bildung, Wis-

senschaft, Forschung und Technologie (BMBF), grantno. 03G0090C. The authors carry the full responsibilityfor the content of this publication. Data are available on

http.//www.pangaea.de/home/sschulte.

Associate Editor ÐS.G. Wakeham

References

Antoine, D., AndreÂ , J.M., Morel, A., 1996. Oceanic primary

production 2. Estimation at global scale from satellite

(coastal zone color scanner) chlorophyll. Global Biogeo-

chemical Cycles 10, 57±69.

Baker, E.W., Louda, J.W., 1983. Thermal aspects in chlor-

ophyll geochemistry. In: Bjorùy, M. (Ed.), Advances in

Organic Geochemistry 1981. Wiley & Sons, Chichester, pp.

401±421.

Bergamaschi, B.A., Tsamakis, E., Keil, R.G., Eglinton, T.I.,

MontlucË on, D.B., Hedges, J.I., 1997. The e�ect of grain size

and surface area on OM, lignin and carbohydrate concentra-

tion, and molecular compositions in Peru Margin sediments..

Geochimica et Cosmochimica Acta 61, 1247±1260.

Bird, M.I., Summons, R.E., Gagan, M.K., Roksandic, Z.,

Dowling, L., Head, J. et al., 1995. Terrestrial vegetation

change inferred from n-alkane dp13C analysis in the marine

environment. Geochimica et Cosmochimica Acta 59, 2853±

2857.

Boon, J.J., Rijpstra, W.I.C., de Lange, F., de Leeuw, J.W.,

1979. Black sea sterol Ð a molecular fossil for dino¯agellate

blooms. Nature 277, 125±126.

Calvert, S.E., 1987. Oceanographic controls on the accumula-

tion of OM in marine sediments. In: Brooks, J., Fleet, A.J.

(Eds.), Marine Petroleum Source Rocks. Blackwell, Oxford,

pp. 137±151.


Calvert, S.E., Pedersen, T.F., 1992. Organic carbon accumula-

tion and preservation in marine sediments: how important is

anoxia?. In: Whelan, J.K., Farrington, J.W. (Eds.), Pro-

ductivity, Accumulation and Preservation of Organic Matter

in Recent and Ancient Sediments. Columbia University

Press, New York, pp. 231±263.

Calvert, S.E., Pedersen, T.F., Naidu, P.D., von Stackelberg, U.,

1995. On the organic carbon maximum on the continental

slope of the eastern Arabian sea. Journal of Marine Research

53, 269±296.

Canuel, E.A., Martens, C.S., 1996. Reactivity of recently

deposited organic matter: degradation of lipid compounds

near the sediment±water interface. Geochimica et Cosmo-

chimica Acta 60, 1793±1806.

Collister, J.W., Rieley, G., Stern, B., Eglinton, G., Fry, B.,

1994. Compound speci®c d13C analyzes of leaf lipids from

plants with di�ering carbon dioxide metabolism. Organic

Geochemistry 21, 619±627.

Combourieu-Nebout, N., Paterne, M., Turon, J.-L., Siani, G.,

1998. A high resolution record of the last deglaciation in the

central Mediterranian sea: paleovegetation and paleohy-

drological evolution. Quaternary Science Review 17, 303±

317.

Cowie, G.L., Calvert, S.E., Pedersen, T., Schulz, H., von Rad,

U., 1999. Organic content and preservational controls in

sur®cial shelf and slope sediments from the Arabian Sea

(Pakistan margin). Marine Geology 161, 23±38.

Crusius, J., Calvert, S., Pedersen, T., Sage, D., 1996. Rhenium

and molybdenum enrichments in sediments as indicators of

oxic, suboxic and sul®dic conditions of deposition. Earth and

Planetary Science Letters 146, 1996, 65±78.

Demaison, G.J., Moore, G.T., 1980. Anoxic environments and

oil source bed genesis. Organic Geochemistry 2, 9±31.

Eglinton, G., Hamilton, R.J., 1967. Leaf epicuticular waxes.

Science 156, 1322±1335.

Eglinton, T., Benitez-Nelson, B.C., Pearson, A., McNichol,

A.P., Bauer, J.E., Dru�el, E.R.M., 1997. Variability in

radiocarbon ages of individual organic compounds from

marine sediments. Science 277, 796±799.

Engleman, E.E., Jackson, L.L., Norton, D.R., 1985. Determi-

nation of carbonate carbon in geological material by coulo-

metric titration. Chemical Geology 53, 125±128.

Ganeshram, R.S., Calvert, S.E., Pedersen, T., Cowie, G.L.,

1999. Factors controlling the burial of organic carbon in

laminated and bioturbated sediments o� NW Mexico:

implication for hydrocarbon preservation. Geochimica et

Cosmochimica Acta 63, 1723±1734.

Hartnett, H.E., Keil, R.G., Hedges, J.I., Devol, A.H., 1998.

In¯uence of oxygen exposure time on organic carbon pre-

servation in continental margin sediments. Nature 391, 536±

572.

Hayes, J.M., 1993. Factors controlling 13C contents of sedi-

mentary organic compounds: principles and evidence. Mar-

ine Geology 113, 111±125.

Hedges, J.I., Keil, R.G., 1995. Sedimentary organic matter

preservation: an assessment and speculative synthesis. Mar-

ine Chemistry 49, 81±115.

Hoefs, J., 1980. Stable Isotope Geochemistry. Springer, Berlin.

Huc, A.Y., 1988. Aspects of depositional processes of organic

matter in sedimentary basins. In: Mattavelli, L., Novelli, L.

(Eds.), Advances in Organic Geochemistry 1987. Organic

Geochemistry Pergamon Press, Oxford, Vol. 13, pp. 263±

272.

Hulthe, G., Hulth, S., Hall, P.O.J., 1998. E�ect of oxygen on

the degradation rate of refractory and labile organic matter

in continental margin sediments. Geochimica et Cosmochi-

mica Acta 62, 1319±1328.

Jackson, L.L., Roof, S.R., 1992. Determination of the forms of

carbon in geological material. Geostandard Newsletters 16,

1992, 317±323.

Jeng, W.-L., Chen, M.-P., 1995. Grain size e�ect on bound

lipids in sediments o� northeastern Taiwan. Organic Geo-

chemistry 23, 301±310.

Kabanova, Yu, G., 1968. Primary production of the northern

part of the Indian Ocean.. Oceanology 8, 214±225.

Keil, R.G., Cowie, G.L., 1999. Organic matter preservation

through the oxygen-de®cient zone of the NE Arabian sea as

discerned by organic carbon: mineral surface area ratios.

Marine Geology 161, 13±22.

Keil, R.G., Tsamakis, E., Fuh, C.B., Giddings, J.C., Hedges,

J.I., 1994. Mineralogical and textural controls on the organic

matter composition of coastal marine sediments: Hydro-

dynamic separation using SPLITT-fractionation. Geochi-

mica et Cosmochimica Acta 58, 879±893.

Keil, R.G., MontlucË on, D.B., Prahl, F.G., Hedges, J.I., 1994.

Sorptive preservation of labile organic matter in marine

sediments. Nature 370, 549±552.

Kolattukudy, P.E., 1976. Chemistry and Biochemistry of Nat-

ural Waxes. Elsevier, New York.

LeBlanc, C.G., Bourbonniere, R.A., Schwarcz, H.P., Risk,

M.J., 1989. Carbon isotopes and fatty acids analysis of the

sediments of Negro Habour, Nova Scotia, Canada. Estuar-

ine and Coastal Shelf Science 28, 261±276.

Lee, C., 1992. Controls on organic carbon preservation: the use

of strati®ed water bodies to compare intrinsic rates of

decomposition in oxic and anoxic systems. Geochimica et


Leenheer, M.J., Flessland, K.D., Meyers, P.A., 1984. Compar-

ison of lipid character of sediments from the Great Lakes

and the northwestern Atlantic. Organic Geochemistry 7,

141±150.

de Leeuw, J.W., Largeau, C., 1993. A review of macromolecular

organic compounds that comprise living organisms and their

role in kerogen, coal and petroleum formation. In: Engel, M.,

Macko, S.A. (Eds.), Organic Geochemistry Ð Principles and

Applications. Plenum Press, New York, pp. 23±72.

Lichtfouse, E.A., Derenne, S., Mariotti, A., Largeau, C., 1994.

Possible algal origin of long chain odd n-alkanes in immature

sediments as revealed by distributions and carbon isotope

ratios. Organic Geochemistry 22, 1023±1027.

Littke, R., Sachsenhofer, R.F., 1994. Organic petrology of deep

sea sediments: a compilation of results from the Ocean Dril-

ling Program and the Deep Sea Drilling Project. Energy &

Fuels 8, 1498±1512.

Littke, R., LuÈ ckge, A., Welte, D.H., 1997. Quanti®cation of

organic matter degradation by microbial sulphate reduction

for Quaternary sediments from the northern Arabian sea.

Naturwissenschaften 84, 312±314.

LuÈ ckge, A., Ercegovac, M., Strauss, H., Littke, R., 1999. Early

diagenetic alteration of organic matter by sulfate reduction

in Quaternary sediments from the northeastern Arabian Sea.



March, J., 1992. Advanced Organic Chemistry: Reactions,

Mechanisms, and Structures. 4th Edition. Wiley, New York.

Matsuda, H., Koyama, T., 1977. Early diagenesis of fatty acids

in lacustrine sediments. I. Identi®cation and distribution of

fatty acids in recent sediments from a freshwater lake. Geo-

chimica et Cosmochimica Acta 41, 777±783.

Mayer, L.M., 1994. Surface area control of organic carbon

accumulation in continental shelf sediments. Geochimica et


McCa�rey, M.A., Farrington, J.W., Repeta, D.J., 1991. The

organic geochemistry of Peru margin surface sediments: II.

Paleoenvironmental implications of hydrocarbon and alco-

hol pro®les. Geochimica et Cosmochimica Acta 55, 483±498.

Meyers, P.A., Ishiwatari, R., 1993. Lacustrine organic

geochemistry Ð an overview of indicators of organic matter

sources and diagenesis in lake sediments. Organic Geochem-

istry 20, 867±900.

Monson, K.D., Hayes, J.M., 1982. Carbon isotope fractiona-

tions in the synthesis of bacterial fatty acids. Ozonolysis of

unsaturated fatty acids as a means for determining the intra-

molecular distribution of carbon isotopes. Geochimica et


MuÈ ller, P.J., Suess, E., 1979. Productivity, sedimentation rate

and organic matter in oceans Ð I: organic carbon preserva-

tion. Deep-Sea Research 26A, 1347±1362.

Nichols, P.D., Jones, G.J., de Leeuw, J.W., Johns, R.B., 1984.

The fatty acid and sterol composition of two marine dino-

¯agellates. Phytochemistry 23, 1043±1047.

Olson, B.D., Hitchcock, G.L., Fine, R.A., Warren, B.A., 1993.

Maintenance of the low-oxygen layer in the central Arabian

sea. Deep-Sea Research 40A, 674±685.

Parkes, R.J., Taylor, J., 1983. The relationship between fatty

acid distribution and bacterial respiratory types in con-

temporary marine sediments. Estuarine and Coastal Shelf

Science 16, 173±189.

Paropkari, A.L., Prakash Babu, C., Mascarenhas, A., 1992. A

critical evaluation of depositional parameters controlling the

variability of organic carbon in the Arabian Sea sediments.


Paropkari, A.L., Prakash Babu, C., Mascarenhas, A., 1993.

New evidence for enhanced preservation of organic carbon

in contact with the oxygen minimum zone on the western

continental slope of India. Marine Geology 111, 7±13.

Pedersen, T.F., Calvert, S.E., 1990. Anoxia vs. productivity:

What controls the formation of organic-carbon-rich sedi-

ments and sedimentary rocks? American Association of Pet-

roleum Geologists Bulletin 74, 454±466.

Premuzic, E.T., Benkovitz, C.M., Ga�ney, J.S., Walsh, J.J.,

1982. The nature and distribution of organic matter in the

surface sediments of world oceans and seas. Organic Geo-

chemistry 4, 63±77.

Quasim, S.Z., 1977. Biological productivity of the Indian

Ocean. Indian Journal of Marine Science 6, 122±137.

Quasim, S.Z., 1982. Oceanography of the northern Arabian

Sea. Deep-Sea Research 29A, 1041±1068.

von Rad, U., Schulz, H., SONNE 90 Scienti®c Party, 1995.

Sampling the oxygen minimum zone o� Pakistan: glacial-

interglacial variations of anoxia and productivity (preliminary

results, SONNE 90 cruise). Marine Geology 125, 7±19.

von Rad, U., Schaaf, M., Michels, K.H., Schulz, H., Berger,

W.H., Sirocko, F., 1999. A 5000 yr record of climate change

in varved sediments from the oxygen minimum zone o�

Pakistan, Northeastern Arabian Sea. Quaternary Research

51, 39±53.

Radke, M., Willsch, H., Welte, H.D., 1980. Preparative

hydrocarbon group type determination by automated med-

ium pressure liquid chromatography. Analytical Chemistry

52, 406±411.

Ransom, B., Kim, D., Kastner, M., Wainwright, S., 1998.

Organic matter preservation on continental slopes: impor-

tance of mineralogy and surface area. Geochimica et Cosmo-

chimica Acta 62, 1329±1345.

Rao, V.P., Rao, B.R., 1995. Provenance and distribution of

clay minerals in the sediments of the western continenal shelf

and slope of India. Continental Shelf Research 15, 1757±

1771.

Rieley, G., Collier, R.J., Jones, D.M., Eglinton, G., 1991. The

biogeochemistry of Ellesmere Lake, U.K. I. Source correla-

tion of leaf wax inputs to the sedimentary lipid record.

Organic Geochemistry 17, 901±912.

Robinson, N., Eglinton, G., Brassell, S.C., Cranwell, P., 1984.

Dino¯agellate origin for sedimentary 4a-methylsteroids and

5a(H)-stanols. Nature 308, 439±442.

Rontani, J.-F., Combe, I., Giral, P.J.-P., 1990. Abiotic degra-

dation of free phytol in the water column: a new pathway for

the production of acyclic isoprenoids in the marine environ-

ment. Geochimica et Cosmochimica Acta 54, 1307±1313.

RullkoÈ tter, J., 1999. Organic matter: the driving force for early

diagenesis. In: Schulz, H.D., Zabel, M. (Eds.), Marine Geo-

chemistry. Springer-Verlag, Heidelberg, pp. 129±172.

Sakata, S., Hayes, J.M., McTaggart, A.R., Evans, R.A., Leck-

rone, K.J., Togaski, R.K., 1997. Carbon isotopic fractiona-

tion associated with lipid biosynthesis by a cyanobacterium:

relevance for interpretation of biomarker records. Geochi-

mica et Cosmochimica Acta 61, 5379±5389.

Sargent, J.R., Whittle, K.J., 1981. Lipids and hydrocarbons in

the marine food web. In: Longhurst, A.R. (Ed.), Analysis of

Marine Ecosystems. Academic Press, London, pp. 491±533.

Schlanger, S.O., Jenkyns, H.C., 1976. Cretaceous oceanic

anoxic events: causes and consequences. Geologie en Mijn-

bouw 55, 179±184.

Schnitzer, M., Kahn, S.U., 1978. Soil Organic Matter. Elsevier,

Amsterdam.

Schulte, S., 1997. Erhaltung und fruÈ he Diagenese von orga-

nischem Material in Sedimenten vom pakistanischen Konti-

nentalrand. Thesis, University of Oldenburg, Germany.

Schulte, S., Rostek, F., Bard, E., RullkoÈ tter, J., Marchal, O.,

1999. Variations of oxygen-minimum and primary pro-

ductivity recorded in sediments of the Arabian Sea. Earth

and Planetary Science Letters 173, 205±221.

Schulz, H., von Rad, U., von Stackelberg, U., 1996. Laminated

sediments from the oxygen-minimum zone of the north-

eastern Arabian Sea. In: Kemp, A.E.S. (Ed.), Palaeoclima-

tology and Palaeoceanography from Laminated Sediments.

Geological Society Special Publication No. 116. Blackwell,

Oxford, pp. 185±207.

Schulz, H., von Rad, U., 1997. Sediment¯uÈ sse und Akkumula-

tion im Bereich der monsunbeein¯uûten Sauersto�-Mini-

mumzone vor Pakistan (PAKOFLUX). German JGOFS-

Indik Report 1995±1996, TP14, Bundesanstalt fuÈ r Geo-

wissenschaften und Rohsto�e, Hannover Germany, 28pp.

Slater, R.D., Kroopnick, P., 1984. Controls on dissolved oxygen


distribution and organic carbon deposition in the Arabian

Sea. In: Haq, B.U., Milliman, J.D. (Eds.), Marine Geology

and Oceanography of Arabian Sea and Coastal Pakistan.

Van Nostrand Reinhold, New York, pp. 271±303.

Smith, B.N., Epstein, S., 1971. Two categories of 13C/12C ratios

for plants. Plant Physiology 47, 380±384.

Sun, M.-Y., Wakeham, S.G., 1998. A study of oxic/anoxic

e�ects on degradation of sterols at the simulated sediment-

water interface of coastal sediments. Organic Geochemistry

28, 773±784.

Sutho�, A., Jennerjahn, T.C., SchaÈ fer, P., Ittekkot, V., 2000.

Nature of organic matter in surface sediments from the

Pakistan continental margin and the deep Arabian Sea:

amino acids. Deep-Sea Research II 47, 329±351.

Swallow, J.C., 1984. Some aspects of the physical oceano-

graphy of the Indian Ocean. Deep-Sea Research 31A, 639±

650.

Teece, M.A., Maxwell, J.R., Getli�, J.M., Parkes, R.J., Briggs,

D.E.G., Leftley, J.W., 1994. Laboratory degradation of

lipids of the marine prymnesiophyte Emiliania huxleyi and

signi®cance for sediment studies. In: Eglinton, G., Kay,

R.L.F. (Eds), Biomolecular Paleontology. Lyell Meeting

Volume; NERC Special Publication 94/1, pp. 58.

Thiede, J., van Andel, T.H., 1977. The paleoenvironment of

anaerobic sediments in the late Mesozoic South Atlantic

Ocean. Earth and Planetary Science Letters 33, 301±309.

van der Weijden, C.H., Reichart, G.J., Visser, H.J., 1999.

Enhanced preservation of organic matter in sediments

deposited within the oxygen minimum zone in the north-

eastern Arabian Sea. Deep-Sea Research I 46, 807±830.

Volkman, J.K., Johns, R.B., Gillan, F.T., Perry, G.J., Bavor

Jr., H.J., 1980. Microbial lipids of an intertidal sediment:

fatty acids and hydrocarbons. Geochimica et Cosmochimica

Acta 44, 1133±1143.

Zegouagh, Y., Derenne, S., Largeau, C., Bardoux, G., Mar-

iotti, A., 1998. Organic matter sources and early diagenetic

alterations in Artic surface sediments (Lena River delta and

Laptev Sea, Eastern Siberia). II. Molecular and isotopic

studies of hydrocarbons. Organic Geochemistry 28, 571±

583.


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Organic matter preservation on the Pakistan continental ...directory.umm.ac.id/Data Elmu/jurnal/O/Organic Geochemistry/Vol31... · Sonja Schulte*, Kai Mangelsdorf, Ju¨rgen Rullko¨tter