Geochvnica rt Cosmochunica Acta. 1977. Vol. 41, pp. 2R9 fo 296. Pergamon Press. Printed in Great Brituin

Fatty wids and Pb210 geochronalogy of a sediment core from Buzzards Bay, Massachusetts*

JOHN W. FARRINGXIN, SUSAN M. HENRICHS and ROBERT ANDERXXV

Chemistry Department, Woods Hole Qceanographic ~nst~tutjon, Woods Hole, Massachusetts 02543, U.S.A.

Abstract-Four sections of a Pb-210 dated core of 62cm length from Buzzards Bay, Massachusetts, were analyzed for fatty acids. A comparison of fatty acids extracted by Soxhlet extraction (unbound fatty acids) with fatty acids extracted by subsequent saponification extraction of the same sample (bound fatty acids) showed the former did not undergo diagenetic loss any faster than the latter. However, compositional differences between bound and unbound fatty acids were apparent in the top section of l-2 cm and were less apparent in the 54-58 cm section. At least 14% of the bound fatty acids are esterified to non+olvent extractable material. The net conversion of fatty acids to other compounds is 32 pg/g dry weight sediment over the first 30 yr after deposition.

PARKER (1967) compared the fatty acid composition of phytop~ankton and surface sediments from the coast of the Gulf of Mexico. He summarized his find- ings with the statement, “Much of the geochemical modification of fatty acids takes place early”. The qualitative and quantitative changes in fatty acid dis- tribution with increasing depth in cores of recent sur- face sediments also document that early diagenesis of fatty acids takes place (PARKER and LEO, 1965; FARRINGTON and QUINN, 1971a; BRowrr et al., 1972; &XAKE et al., 1972, among others).

The importance of early chemical ar biochemical diagenesis of fatty acids deposited to surface sedi- ments was established un~uivocaIIy by the work of RWEAD et al. (1971). Their experiments with r4C and ‘II Xabelled oleic acid added to intertidal mud flat sediments showed rapid conversion of oleic acid to other fatty acids and to uncharacterized metabolites or chemical reaction products. In a recent report of fatty acids in a l-m core from the inner continental shelf off Walvis Bay, South-West Africa, BOON et a!. (1975) concluded that the acids had a microbial ori- gin, This conclusion is wefl supported by the Fact that marine phyto~~ankton are the overwhelmingly most important primary producers of organic matter in this area and their fatty acid compositions are markediy different from the composition of fatty acids in sedi- ments. JOHNS and ODNER (1975) suggest that a major portion of the 16-24 carbon diacids in an intertidal mud were contributed by microbial activity in the sediments.

In most of the above studies, fatty acids were extracted from the sediment samples by a single extraction procedure. Additional information about the biogeochemistry of fatty acids and other com-

*Woods FIofe ~~~no~a~hic Institution Contribution No. 3774.

pounds in surface sediments can be gained by using extraction procedures based on difIerent chemic& properties or chemical reactions during the extraction process. FARRINGIVX and QUINN (1971bf applied two extraction procedures sequentially to remove fatty acids from sediments. Solvent extraction aided by re- flux or Soxhlet apparatus yielded a fatty acid fraction which they designated as ‘unbound’ fatty acids, i.e. easily extractable. Further solvent extraction of the sediment samples gave negligible yields. The appli- cation of a saponification procedure to the previously extracted sediment yielded quantities of fatty acids equal to or greater than the unbound fatty acids. These were designated ‘bound’ fatty acids.

F~INGTON and QUINN (1973) suggested that bound fatty acids may be adsorbed onto mineral SUE” faces, esterified to humic materials in sediment, entrapped in humic materials, or some combination of the preceding. They further suggested that bound fatty acids would be more resistant to diagenetic alteration and would be expected to become an in- creasingly larger portion of the total fatty acids with increasing depth of burial.

The objectives of the present study were: (I) to investigate the qualitative and quantitative

distribution of bound and unbound fatty acids in a core of estuarine sediment.

(2) To determine if bound fatty acids were stabilized with respect to unbound fatty acids over a geotogi- tally short period of time.

(3) To determine if the bound fatty acids or some fraction thereof are esterified to some organic sub- stances in sediments or clathrated in an organic matrix.

A technique for dating cores up to 1OOyr of age has been described by KCNDE et al. (1973). We have applied this technique to a sediment core from Buz- zards Bay in order to provide a time scale against which changes in concentration and com~sition of fatty acids can be assessed.

289

290 J. W. FARRINGTON, S. M. HENRICHS and R. ANDERSOPJ

EXPERIMENTAL

Snrnpling

The sediment sampled was silt-clay, populated primarily by deposit feeders which generate a 2-3 cm thick biotur- bated surface layer (RHOADS, 1974). The coring station located at 41” 29.0’ N, 70” 52.5’ W in 17 m of water was sampled on November 11, 1974, using a 21 cm dia. sphincter corer (BURKE, 1968). Sediment samples were frozen following extrusion and stored at -4°C for 8 months before analysis. The sediments of Buzzards Bay, Massachusetts have been described in general terms by MWRE (1963).

Extraction and isolation of fatty acids

We generally followed procedures described by FARR- INGTON and QUINN (1971b) with the exception of substitut- ing pentane for petroleum ether. All solvents were reagent grade and 1 x distilled in an all-glass still.

Soxhlet extraction. The Whatman 43 x 123 mm extrac- tion thimbles were pre-extracted for 48 hr in 1: 1 benzene- methanol. About 100 g of wet sediment was extracted with 1: 1 benzene-methanol for 72 hr. The solvent was changed every 24 hr. The combined lipid extracts were twice extracted with pentane, and the pentane extracts were washed with saturated NaCl solution. The pentane extract was dried over NazSOB, and the solvent evaporated under reduced pressure. One-fifth of the total lipid extract was analyzed for fatty acids.

The Soxhlet-extracted lipids were placed in 13 ml centri- fuge tubes with 2ml 0.5N KOH in methanol. The tubes were flushed with Nz, sealed with Teflon lined screw caps and heated for 20min in a boiling water bath. The tubes were then cooled, 2 ml of 14% w/w BF, in methanol were added; the tubes were flushed with N2, sealed, and heated in a boiling water bath for five minutes. Fatty acid methyl esters were extracted into pentane from the reaction mix- ture in the tube using the procedures of FARRINGTON and QUINN (1971b). Fatty acid methyl esters were isolated from lipid or non-saponi~able lipid extracts by TLC on 20 cm x 20 cm 0.25 mm silica ael on aluminum (E. Merck). TLC plates were developed in -petroleum ether-ethyl ether- acetic acid (95:5: 1). A portion of the plate containing a standard methyl ester was sprayed with bromothymol blue reagent and visualized with NH3. A corresponding band on the sample portion of the plate was scraped off and the fatty acid methyl esters extracted with 1 x distilled CHCla.

Transesterijkation extraction. Following Soxhlet extrac- tion, the sediment samples were air-dried and weighed. The sediment was then transferred to a 500 ml round-bottomed flask with 200 ml of anvhvdrous 0.5 N KOH in methanol. The mixture was refluxed-for 1 hr, and then acidified with methanolic HCl to pH < 2. The lipids were extracted from the reaction mixture into pentane in the same manner as for the Soxhlet extraction. The free fatty acids and fatty acid methyl esters in the lipid extract were isolated by TLC as previously described.

SaponiJication extraction. This procedure was identical to the transesterification extraction except that 200ml of 0.5 KOH in methanol-water (1: 1) was substituted for an- hydrous 0.5 N KOH in methanol.

Structure determination and quantijication

Gas chromatographic analysis. The fatty acid methyl esters were analyzed on a 3-m 2.2-mm i.d. ss. 10% Silar IOC (Aoolar 1OCl on 1001120 mesh Gas Chrom 0 (Applied’ Science Laboratories, Inc., State College, P$ U.S.A.) column installed in a Varian Model 2700 gas chro- matograph equipped with a flame ionization detector. The

* Shorthand notation for fatty acids-number of carbon atoms ; number of double bonds.

column was temperature programmed from 150 to 200°C at 2”/min with He carrier gas flow of 2G30 ml/min. Injec- tor temperature was 200-210°C and detector temperature 300°C.

The following internal standards were used: 17:0* fatty acid added to sediment samples prior to extraction; 19:0 fatty acid methyl ester and 21:0 fatty acid added to saponi- fication or transesterification extracts. These fatty acids were chosen because they occur in only trace amounts in the sediments. Concentrations of fatty acids were deter- mined by ratios of peak areas to those of the internal stan- dards (area = height x width at i-height).

Replicate cores and replicate analyses for core sections were-not obtained. However, previous work by FARRING- TON and OUINN (197la. b: 1973) and FARRINGTON (1971) gave a range of variance up to 30% for fatty acid concen: trations in estuarine sediments from Narragansett Bay, Rhode Island. Applying the maximum variance we calcu- lated the 95?i, confidence interval for our analyses as +0.5 times the concentration of fatty acids. The 95% confidence interval for the ratios of fatty acids to 16:0 is about kO.05. Blanks for solvents and reagents carried through the entire procedure showed negligible concentrations of fatty acids. Resaponification of sediment samples gave less than 5:i/, of the amount of fatty acid from previous extracts.

Straight chain fatty acids were tentatively identified by comparison of retention times to a 14:O to 24:0 fatty acid methyl ester standard run periodically under the same con- ditions as the samples, Portions of the fatty acid methyl esters from the Soxhlet and transesterification extracted l-2 cm samples were hydrogenated for 1 hr over Adam’s catalyst. The unsaturated fatty acid peaks were identified by comparison of the gas chromatograms of hydrogenated and non-hydrogenated portions.

Gas chromatography-mass spectrometry. The fatty acids from the l-2 cm and 54-58 cm transesterification extracted samples were analyzed on a Finnigan 1015 SL gas chroma- tograph-mass spectrometer-computer system equipped with the Apolar 1OC column described above. The gas chromatograph conditions were those described above except that the starting temperature was 14o’C. The mass spectrometer operating parameters were: pre-amp- x IO-’ A/V; ionizer 500 PA, 70 eV; multiplier 2.3 kV. Mass spectra of the fatty acid methyl esters were interpreted according to MCCLOSKEY (1970).

Organic carbon measurements

Organic carbon concentrations were obtained by analy- sis of sediment samples on an F and M Model 185 CHN analyzer, after treatment of the sediment with phosphoric acid to remove carbonate and drying at 110°C to constant weight.

Pb-210 measurements

The core was sampled over continuous 1 cm intervals. Known portions of sediment from each interval were dried to constant weight at 110°C. The sediment was ground, mately 26dpm of PO-208 tracer was added as an inter- homogenized, and dried again to constant weight at 110°C. Samples of 2-5 g were weighed and placed in a beaker with 50ml of concentrated HNOa. The size of the sample used depended on the expected Pb-210 activity. Approxi- nal standard. The beaker with acid and sample was heated on a hot plate, but not boiled, for 4 hr. The acid was decanted through 11 cm Reeve angel glass fiber filters, the sediment rinsed twice with hot concentrated HCl for 10min each on the hot plate, and then rinses were also decanted through the filter. The combined acids were treated with 5 ml of 70% HClO, and solutions evaoorated on a hot plate until only HQG, fumes remained, along with a residue. The residue was dissolved in 20ml of con- centrated HCl and again the solution was evaporated on a hot plate to only a residue and HC104 fumes. The resi- due was then dissolved in 50 ml of 2 N HCl.

Fatty acids and Pb-210 geochronology 291

AST JF-4 STATION P CORE ,o,,,rPo - 210 ACTIVITY VERSUS DEPTH

LEAST SQUARES LINE

6.5cm/22yr=2.95mmlyr

r=-.94

The samples were adjusted to pH 2 with concentrated NH,OH and plating of PO-208 and PO-210 on silver disks was accomplished according to the technique of FLYNN (1968), except that plating was carried out for 4 hr to maximize plating efficiency (BACON, 1975). The PO-208 and PO-210 spectrum was counted without interference as de- scribed by BACON (1975). Pb-210 activity is measured as PO-210 since they are in secular equilibrium (CARPENTER, 1975).

RESULTS

Pb-210 measurements

The depth below which unsupported Pb-210 could not be accurately measured was determined from the slope of the Pb-210 depth profile to be 30cm. The Pb-210 activity values below 40cm were averaged and the average subtracted from the Pb-210 activities for sections above the 40cm depth. The plot of Pb-210 vs depth to 3Ocm is given in Fig. 1. A sedi- mentation rate of 2.95 mmjyr is obtained by deter- mining the slope of the line in Fig. 1 and applying the equations:

A, = &exp( - ;I/s)Z

In A, = -A/sZ + In AO,

or plotting on semilog paper A, vs Z, where

A, = Pb-210 activity at depth Z, A, = Pb-210 acti- vity at surface, Z = 0, A = decay constant for Pb-210, s = average sedimentation rate.

This sedimentation rate is also applied to lower core sections to obtain approximate ages of these sections.

Fatty acids and organic carbon

Concentrations of organic carbon and fatty acids decrease markedly with increase in depth from 1-2 cm to 8-12 cm sections (Tables 1 and 2). This de- crease coincides with the transition from the aerobic upper few centimeters which are rapidly mixed and populated with macrobenthos to the deeper sediment layers which are less oxic or anoxic. The exact depth at which oxygen disappears has not been determined for this depositional area. The organic carbon and fatty acid concentrations decrease less markedly

Table 1. Fatty acids in core from Station P, Buzzards Bay. Massachusetts (pg,/g dry wt)

---.- 14:Ob 15:01 15:Oa 15:0 14~' 16:O 17:Ot 16:l 17:0 18:O 18~1 19:0 20br 18" 20:0 22:0 Total

Total'

1-2 cm 12.3 1.8 7.6 2.4 7.8 30.8 1.4 7.7 0.8 6.9 6.5 1.3 1.1 0.7 3.1 1.4 93.6 8-12 cm :.: 1.6 4.9 1.4 4.7 21.6 1.0 2.8 1.0 4.6 3.8 trd 0.6 0.4 2.8 1.8 61.7 20-24 uo 54-58 cm 7:1

1.0 3.8 1.2 5.2 21.0 0.9 2.0 0.6 4.6 1.7 tr 0.6 0.3 2.8 1.6 56.5 0.6 2.4 0.7 4.5 17.2 0.6 2.2 0.8 4.0 1.2 tr tr tr 2.6 0.9 44.8

unbound (Soxhlet Extraction)

l-2 cm 2.9 0.5 3.6 0.5 1.6 10.0 tr 4.7 Xd 1.8 3.7 0.5 0.3 0.4 1.1 0.8 32.4 8-12 cm 1.9 0.7 2.2 0.6 0.8 6.6 tr 0.4 x tr 1.3 1.1 18.9 20-24 cn? 1.5 0.2 1.4 0.3 1.1 5.8 tr 0.5 x

;.; ;.; ;; ::: 1.2 1.0 14.8

54-58 cm 1.2 0.1 0.8 0.2 1.1 5.0 tr 0.4 x 1:2 0:7 tr ::: tr 1.2 0.9 12.8

Bound (SaponificatioR Extraction)

1-Z cm Transest. 1.4 0.2 0.4 0.5 tr 3.4 0.7 0.3 tr 1.4 0.2 x Total 9.4 1.3 4.0 1.9 6.2 20.8 1.4 3.0 0.8 5.1 2.8 0.8 &3 ;:3 !:: & 6::;

8-12 cm 6.8 0.9 2.7 0.8 3.9 15.0 1.0 2.4 1.0 3.3 1.8 X 0.6 0.4 1.5 0.7 42.8 20-24 cm Transest.e 1.2 0.1 0.3 0.2 0.1 2.1 0.4 0.1 tr 0.9 0.2 X tr tr 0.3 tr Total 7.7 0.8 2.4 0.9 4.1 15.2 0.9 1.5 0.6 3.5 1.0 tr 0.6 0.3 1.6 0.6 4::;

54-58 cm 5.9 0.5 1.6 0.5 3.4 12.2 0.6 1.8 0.8 2.8 0.5 X tr tr 1.4 tr 32.0

*The 95% confidence interval is +0.5 x concentration. “Fatty acids are designated # carbons: # double bonds, i = iso; a = anteiso,

br = branched chain; p = unsaturated. ’ Identification tentative. 14 /1 may be 14:2. d X = Fatty acid was used as internal standard. tr = trace, less than 0.05 pg/g dry wt. ’ Transesterified.

292 J. W. FARRINGTON, S. M. HENRICHS and R. ANDERSON

Table 2. Depth distribution of organic carbon, bound and unbound fatty acids

Depth in Core Fatty Acid Concentration Bound Fatty Acid mg/g dry wt. Total Fatty Fattya~rd2C~~ntration Total Fatty Acid of Acids

Organic Carbon Organic Carbon

1-2 cm -7 .65 23.8 3.93 x 10-3

8-12 cm .66 .69 15.5 3.98 x 10-3

20-24 cm .60 .74 16.3 3.47 x 10-3

54-58 cm .48 .71 11.7 3.83 x 10-3

throughout the remaining core sections (Tables 1 and 2). When comparing all core sections the percentage of organic carbon present as fatty acids does not vary significantly (Table 2). Also, bound fatty acids are not stabilized relative to unbound fatty acids over the 190 yr time span sampled (Table 2).

The distribution of fatty acids in all the core sec- tions differs from that of marine organisms (JEFFRIES, 1971; ACKMAN and HOOPER, 1969; PUGH, 1971) and the benthic animals Nepthys incisa and Yoldia limtula (FARRINGTON et al., 1973). Polyunsaturated acids which are the major types of the fatty acids in these organisms are not present in the sediment sample at a concentration level greater than 0.05 pg/g dry weight. The 18:2 and 18: 3 fatty acids which make up 30-50% of the fatty acids of several marsh grasses (JEFFRIES, 1971, 1972; MAURER and PARKER, 1967; SCHULTZ and QUINN, 1973) are also not major con- stituents. The presence of the branched chain iso and anteiso 15 carbon fatty acids indicates bacterial origin for some major fatty acids (LEO and PARKER, 1967; COOPER and BLUMER, 1968; KATES, 1967; CHO and SALTON, 1965; Boom et al., 1975).

In Table 3 fatty acid concentrations are given as fractions of the concentration of the most abundant acid, 16:0, in order to investigate changes in the rela- tive abundances of acids with depth in the core. The

proportion of 16:0 and other saturated, straight-chain acids increases slightly with depth. Monounsaturated acids decrease relative to 16:0 when comparing the top and bottom core sections. The branched-chain acid 15 :Oa also is relatively less concentrated at depth. Increased analytical errors at low concen- trations may obscure any trends for other acids.

In the l-2 cm section, the concentrations of the 16: 1 and 18: 1 monounsaturated fatty acids in the unbound fraction are much larger relative to 16:0 than in the bound fraction. This difference between the bound and unbound fractions decreases with depth. A partially characterized fatty acid designated here as 14 p was present in the sediment. Its concen- tration is fairly constant with depth relative to 16:0 and it is also present in higher relative abundance in the bound fraction. The 14~ is a fatty acid which has differing retention times for non-hydrogenated and hydrogenated samples and a mass spectrum con- sistent with a 14 carbon fatty acid with one or two double bonds. Unfortunately, due to sample size limi- tations the molecular ion in the mass spectrum obtained was not sufficiently distinct from the back- ground noise to assign unambiguously a molecular weight and permit positive identification.

The transesterification reaction gave about a 14% yield of total fatty acids as fatty acid methyl esters,

Table 3. Fatty acid concentrations relative to 16:0

Fatty Acid: 14:o

Sorhlet ExtractiOn

2 cm .29

8-12 cm .28

20-24 cm .26

54-58 cm .24

Saponification Extraction

2on .45

8-12 al .45

20-24 cm .51

54-58 cn .4a

Total

2cm .40

8-12 cm .4n

20-24 cm .44

54-58 cm .41

15:01 15:oa 14u 16:l 18:O

.OS .36 .16 .47 .18

.ll .33 .12 .06 .20

.03 .24 .19 .09 .19

.02 .16 .22 .08 .24

.06 .19 .30 .14 .25

.06 .18 .26 .16 .22

.05 .16 .27 .lO .23

.04 .13 .28 .15 .23

.06 .25 .25 .25 .22

.07 .23 .22 .I3 .21

.05 .18 .25 .lO .22

.03 .14 .26 .13 .23

18:l

.37

.30

.12

.14

.13

.lP

.07

.04

.21

.18

.08

.07

20:o 22:o

.ll .08

.20 .17

.21 .17

.24 .18

.I0

.lO

.ll

.ll

.lO

.13

.13

.15

.03

.05

.04

__

.05

.08

.oa

.05

95”4 confidence interval = +0.05. Data calculated from Table 1.

Fatty acids and Pb-210 geochronology 293

demonstrating that some of the bound fatty acids in the sediment sample react as esters or amides. How- ever, this is not a quantitative indication of the amount of esters present, and gives only a minimum value. GLASS (1971) reported that in anhydrous meth- anolic sodium hydroxide transesterification of fatty acid esters precede saponification, but is quantitative only for limited reaction times. Thus, esterified fatty acids in the bound fraction could be saponified after transesterification. SCHULTZ and QUINN (1973) used this type of reaction to differentiate free and esterified fatty acids in marsh detritus. We checked the transes- terification procedure using previously extracted sedi- ment spiked with cholesterol stearate, 19:0 fatty acid methyl ester, and 21:0 fatty acid and found that a reaction time of 1 hr produced complete saponifica- tion of the esters present. Shorter reaction times gave some transesterification, but 19:0 fatty acid methyl ester was partially saponified before cholesterol stear- ate was completely transesterified. This is probably due to inherent differences in reactivity (GLASS, 1971). No methylated 21:0 was detected, substantiating the fact that free fatty acids are not methylated by this procedure.

DISCUSSION

Pb-210 geochronology

The Pb-210 record shows that the upper 3cm is well mixed, having a uniform value for excess Pb-210. This depth of mixing is in accord with the studies by RHOADS (1974), which showed that the species present in the benthos of the area should mix or bio- turbate the upper 3 cm. There is an increased scatter of excess Pb-210 activity at depth intervals of 8-15 cm and 25-26 cm. An interesting correlation can be drawn between the time of deposition for these inter- vals, taking into account 3 cm of bioturbation, and periods when severe hurricanes passed through Buz- zards Bay in 1954, 1944 and 1938 (DUNN and MILLER, 1960). The lower depth interval where scattering occurs almost corresponds to hurricanes in the 1866 and 1869 time interval but occurs at 25-26cm, in- stead of 3c-31 cm as calculated from the sedimen- tation rate. Since these hurricanes were less severe than the later ones, they may not have caused a dis- turbance in the record. Rather, the disturbance at 25-26 cm may have resulted from a severe unrecorded winter storm.

Scatter in the Pb-210 vs depth record may occur during severe storm conditions due to extensive mix- ing of the sediment below the depth of bioturbation and/or a substantial change in Pb-210 input to sedi- ments due to increased runoff from land or deposition from the atmosphere.

Fatty acids

Sediments from Narragansett Bay, a nearby sedi- mentary regime, were analyzed for fatty acids by FARRINGTON and QUINN (1971a b; 1973). The con-

centrations of fatty acids in surface sediments from the Buzzards Bay station are within the range of those found in Narragansett Bay. However, fatty acid con- centrations decreased more rapidly with depth in Narragansett Bay. In general, the distribution of fatty acid species was similar for areas sampled in the two bays. The ratio of bound to total fatty acids in the top 8-1Ocm of sediment from Narragansett Bay ranged from 0.32 to 0.65 (FARRINGTON and QUINN, 1971b, 1973), as compared to 0.650.69 for the l-2 cm and 8-12cm sections of the Buzzards Bay core.

The fairly constant ratio of bound fatty acids to total fatty acids (Table 2) suggests either (i) there is not a significant net production and/or protection of bound fatty acids relative to unbound fatty acids with increasing depth and time, or (ii) bioturbation is rapid and penetrates deep enough to maintain the constant ratio. The latter would require the process controlling the fatty acid composition of both the bound and unbound fractions to be independent of and faster than the bioturbation processes in order to maintain the observed compositional differences between core sections (Tables 1 and 3). Bioturbation cannot be extensive throughout the depth of the core for the following reasons: (i) the Pb-210 record shows no extensive bioturbation below 4cm, (ii) NOSHKIN and BOWEN (1973) and BOWEN (1975) have reported that the fallout radionuclides 23g Pu and 13’Cs have not penetrated deeper than 25 cm, and (iii) RHOADS (1974) investigating the benthos of this area found that sedi- ments at this location have only a 223 cm bioturbated layer.

The processes which result in the formation of fatty acids into bound and unbound fractions evidently occur early in the diagenetic sequence. In the O-8 cm sediment samples from Narragansett Bay 32-65x of the fatty acids are in the bound fraction (FARRINGTON and QUINN, 1971 b). In the l-2 cm section of the Buz- zards Bay core we studied 65% of the fatty acids are in the bound fraction. SCHULTZ (1974) using solvent extraction and transesterification procedures similar to those we have used, found that about 46% of the fatty acids in the suspended detritus leaving a marsh are in the bound fraction. Thus, it is probable that some organic detritus transported from nearby marshes to the location of our sampling station will already contain bound fatty acids at the time of depo- sition.

Some insight into the nature of the phenomena re- sponsible for retaining the bound fatty acids in the sediment during solvent extraction is gained from our data. FARRINGTON and QUINN (1971b, 1973) suggested esterification to non-solvent extractable organic matter as one possibility. Our data (Table 1) from the trans- esterification experiments demonstrates that at least 14% of the bound fatty acids are linked via ester or amide bonds to non-organic solvent extractable material. Humic and fulvic acid materials are good candidates since they are a significant fraction of sedi- ment organic matter, contain hydroxyl and amine

294 J. W. FARRINGTON, S. M. HENRICHS and R. ANDERSON

groups, and are not extracted by organic solvents (SCHNITZER and KHAN, 1973). Indeed, recent studies of humic and fulvic materials from soil (SCHNITZER, 1976) show that 16:0 and 18:0 fatty acids are major constituents of humic and fulvic materials. The slower reaction of the bound fatty acids relative to choles- terol stearate may be due to steric hindrance resulting from incorporation in the fulvic-humicQrganic mat- ter-mineral matrix of the s~iments.

FARRINGTON and QUINN (1971b, 1973) also sug- gested that physical entrapment in the non-solvent extractable organic matter, similar to urea clathration, was a possible ‘binding’ mechanism. If this were the case we would expect n-alkanes to also be bound to some extent if n-alkanes and linear chain fatty acids are equally available for entrapment. FARRINGTON and TRIPP (in preparation) have determined hydro- carbon concentrations in the same core sections which we have analyzed for fatty acids. The same sequential extraction procedures were used as for fatty acids and the remainder of the analytical pro- cedures have been described (FARRINGTOX and TRIPP, in press). Qnfy 510% of the total n-alkanes in the range n-C,, to n-C3, was extracted by saponification extraction after first applying Soxhlet extraction. If n-alkanes and fatty acids are equally available for entrapment, this suggests that physical entrapment is not the most important ‘binding’ mechanism for fatty acids, There is some reason to think that this assump tion may be incorrect, as we will discuss at the end of this section. Thus, we cannot definitely rule out entrapment as the agent for ‘binding’ some of the bound fatty acids in these sediments.

We cannot tell from our data whether or not a significant fraction of the bound fatty acids are adsorbed onto sediment particles. Interactions between fatty acids R-COO- and clay surfaces =Si-O- or = AI-Q-, might produce a bond

0 0 = %-O-C-R or G Al-Q-C-R. Such a clay-fatty acid compound might be expected to undergo a transester- ification reaction in the anhydrous KOH-methanol similar to the reaction of the ester bonds of triglycer- ides, waxes, and sterol esters. MEYERS and QUINN (1973) adsorbed fatty acids onto clays from seawater and saline solutions of the pH of seawater, dried the clay and adsorbed fatty acids, and treated them with 0.5 N KOH in methanol-benzene (1: 1) for 5 min at 1OOC in a screw cap centrifuge tube (MEYERS, 1972). No methyl esters were produced under these trans- esterification conditions.

MEYERS and QUINN (1973) determined heats of adsorption and concluded that fatty acid-clay interac- tions under their laboratory conditions involved pri- marily hydrogen bonds and Van der Waal’s forces, We think that acid treatment of sediment samples and subsequent extraction with organic solvent should remove most fatty acids adsorbed onto clays by hy- drogen bonds or Van der Waal’s forces. Earlier exper- iments by FARRINGT~N and QUINN (1971b) involved

this type of extraction procedure, as described by PARKER and LEO (1965). Subsequent extraction of sediment samples with saponification extraction yielded the same proportion of bound fatty acids as without acid treatment prior to organic solvent extraction. This would probably not be the case for calcium carbonate-rich sediments. The sediments we have examined contain less than 2T.i carbonate based on comparison qf total carbon and organic carbon dete~inations.

Natural sediment is a much more complex chemi- cal mixture than clay-fatty acid mixtures in the labor- atory. However, the evidence to date as cited above argues that fatty acids transesterified in the extraction with anhydrous KOH-methanol are not originally present as free acids adsorbed or esterified onto clays,

0 0 i.e. z Al-UC-R or zz Si-O-C-R.

The combination of Pb-210 and organic geochemi- cal me~urements for the same core provided a means of ~lculat~g rates of diagenesis of fatty acids. The fatty acid concentration at 5458cm (Table 1) rep- resents a net loss of 52% of the fatty acids. We know from the Pb-210 data that the sedimentation rate is about 3.0mm/yr. From this data we calculate the conversion of fatty acids to other organic and inor- ganic compounds at a net rate of 32pg/g dry weight over the first 30 yr after deposition and at a much slower rate thereafter (Table 1 and Fig. 1). Appli- cation of similar measurements for other classes of compounds should provide further information on rates of organic geochemical processes in this deposit- ional environment.

We view our experiments as an initial attempt at characterization of the chemical interactions between fatty acids and other organic matter and mineral mat- ter in surface sediments. There are many complicating factors influencing the early diagenesis of fatty acids, This is exemplified by the recent work of JOHNSON

(1974). He has shown that there are at least 18 differ- ent types of organic-mineral particle types in the upper 2 cm of the sediments we have sampled. He also reported that 10-12’~ of the quartz grains in these sediments were encrusted with organic matter. Johnson’s interest in these parameters stemmed from their influence on the s~imentological properties of sediments, the nutrition of the benthos, and hence their influence on benthic ecology. However, his find- ings are important to biogeochemical studies, If each of the particle types have differing chemistries and micro-environments, then the diagenesis of fatty acids and other organic compounds will be different in each. The importance of the influence of these differ- ent particle types on the diagenesis of organic com- pounds is worthy of investigation. Conversely, the in- fluence of the chemical properties of organic com- pounds on the formation, m~nten~ce, and fate of these particles and on their nutritive value to benthic organisms is also of interest.

Fatty acids and Pb-210 geochronology 295

CONCLUSIONS CARPENTER R. (1975) Chemical and geochemical studies

(1) The processes which produce the bound fatty off the coast of Washington. Report Reference No. A75-56 RLO-2225-T24-18 May, 1975 from University of

acid fraction are operative either prior to or shortly Washington, Department of Oceanography to the U.S.

after deposition. Atomic Energy Commission.

(2) Bound fatty acids are not stabilized relative to CHO K. Y. and SALTON M. R. J. (1965) Composition of

unbound fatty acids over the approximately 200yr bacterial membrane and wall lipids. Biochim. Biophys. Acta 116, 73-79.

period following deposition in the sediments we sam- COOPER W. J. and BLUMER M. (1968) Linear, iso and ,.,Prl ant&o fatty acids in Recent sediments of the North

(3) Compositional differences between bound and Atlantic. Deep-Sea Res. 15, 535-540.

unbound fatty acids in the l-2 cm section are less DUNN G. E. and MILLER B. I. (1960) Atlantic Hurricanes.

Louisiana State University Press. annarent at a death of 54-58 cm. FARRINGTON J. W. (1971) Ph.D. thesis, University of Rhode

‘t4) At least 14% of bound fatty acids are esterified Island.

to non-solvent extractable materials in the coastal- FARRINGTON J. W. and QUINN J. G. (1971a) Fatty acid

estuarine sediments investigated. diagenesis in Recent sediments from Narragansett Bay,

(5) The bound fatty acids are less reactive towards Rhode Island. Nature Phys. Sci. 230, 67-69.

F ARRINGTON J. W. and OUINN J. G. (1971b) Comoarison transesterification-saponification than are sterol esters added to sediments and subjected to the same

\ I of sampling and extraction techniques for fatty kids in Recent sediments. Geochim. Cosmochim. Acta 35, “** -44

treatment. /53-/41.

(6) Fatty acids are converted to other compounds FARRINGTON J. W. and QUINN J. G. (1973) Biogeochemis-

at a net rate of 32 pg/g dry weight over the first 30 yr try of fatty acids in Recent sediment from Narragansett Bay, Rhode Island. Geochim. Cosmodhim. Acta 37,

of deposition and at a much slower rate thereafter. 259-268.

(7)^Some aspects of fatty acid biogeochemistry in FARRINGTON J. W., QUINN J. G. and DAVIS W. R. (1973)

surface sediments sampled in Buzzards Bay are simi- Fatty acids of Nepthys incisa and Yoldia limatula. J.

lar to that of nearby Narragansett Bay. Fish. Res. Bd. Can. 30, 181-185.

FARRINGTON J. W. and TRIPP B. W. (in press) A compari-

Acknowledgements-We thank GEORGE R. HARVEY, JAMES

G. QUINN, ROBERT B. GAGOSIAN, OLIVER C. ZAFIRIOU and PHILIP A. MEYER~ for valuable discussion of the manu- script, NELSON M. FREW for the gas chromatograph-mass spectrometer analysis, BRUCE W. TRIPP and NEIL MOSES- MAN for assistance in the laboratory. MICHAEL BACON and PETER G. BREWER provided valuable advice and discussion for the Pb-210 analyses. This work was supported by the Office of Naval Research Contract N00014-66C0241: NR083-004, and by fellowships to Susan M. Henrichs and

son of methods of analysis for hydrocarbons in surface sediments. In Marine Chemistry in the Coastal Enuiron- ment, American Chemical Society Symposium Series.

FLYNN W. W. (1968) The determination of low levels of polonium-210 in environmental materials. Analyt. Chim. Acta 43, 221-227.

GLASS R. L. (1971) Alcoholysis, saponification and the preparation of fatty acid methyl esters. Lipids 6,919-925.

JEFF~IES H. P. (1971) Seasonal composition of temperate plankton communities: fatty acids. Limnol. Oceanogr. 15, 419426.

Robert Anderson- from the- Massachusetts Institute of JEFFRIES H. P. (1972) Fatty acid ecology of a tidal marsh. Technology-Woods Hole Oceanographic Institution Joint Limnol. Oceanogr. 17, 433440. Graduate Program in Oceanography. The alpha counting JOHNS R. B. and ODNER 0. M. (1975) Biological diagenesis: equipment was provided by support from the Energy dicarboxylic acids in Recent sediments. Geochim. Cosmo- Research and Development Administration Contract No. chim. Acta 39, 129-136. AT (ll-l)-3566. JOHN~~N R. G. (1974) Particulate matter at the sediment-

water interface in coastal environments. J. Mar. Res. 32,

REFERENCES 313-330.

KATES M. (1967) Bacterial lipids. Ado. Lipid Rex 2, 17-90. KOIDE M., BRULAND K. W. and GOLDBERG E. D. (1973)

Th-228/Th-232 and Pb-210 geochronologies in marine and lake sediments. Geochim. Cosmochim. Acta 37,

ACKMAN R. G. and Hcopnn S. N. (1969) Analyses of fatty acid from Newfoundland copepods and seawater with remarks on the occurrence of arachidic acid. Lipids 6, 1171-1187. 417-421. LEO R. F. and PARKER P. L. (1966) Branched chain fatty

BACON M. (1975) Ph.D. thesis, Joint M.I.T.-Woods Hole acids in sediments. Science i52, 649-650. Oceanographic Institution Program in Oceanography. MAURER L. G. and PARKER P. L. (1967) Fatty acids in

BOON J. J., DE LEEUW J. W. and SCHENCK P. A. (1975) sea grasses and marsh plants. Contrib. Mar. Sci. 4, Organic geochemistry of Walvis Bay diatomaceous 113-119. ooz+I. Occurrence and significance of fatty acids. Geo- MCCLOSKEY J. A. (1970) Mass spectrometry of fatty acid chim. Cosmochim. Acta 39, 1559-1565. derivatives. In Topics in Lipid Chemistry, (editor F. D.

BCWEN V. T. (1975) Transuranic elements in marine envir- Gunstone), pp. 369-440. Wiley Interscience. oments. In U.S. Energy Research and Development MEYERS P. A. (1972) Ph.D. thesis, University of Rhode Administration Health-and Safety Laboratory Report, HASL-291, April 1, 1975, p. I-57-1-79.

BROWN F. S., BAEDECKER M. J., NISSENBAUM A. and KAP- LAN I. R. (1972) Early diagenesis in a reducing fjord, Saanich Inlet, British Columbia-III. Changes in organic constituents of sediments. Geochim. Cosmochim. Acta 36, 1185-1203.

BURKE J. (1968) A sediment coring device of 21 cm dia- meter with sphincter core retainer. Limnol. Oceanogr. 13. 714-718.

Island. MEYERS P. A. and QUINN J. G. (1973) Factors affecting

the association of fatty acids with mineral particles in seawater. Geochim. Cosmochim. Acta 37, 1745-1759.

MCI~RE J. R. (1963) Bottom sediment studies, Buzzards Bay, Massachusetts. J. Sediment. Petrol. 33, 511-558.

NOSHKIN V. E. and BOWEN V. T. (1973) Concentrations and distributions of long-lived fallout radionuclides in open ocean sediments. In Radioactive Contamination of the Marine Environment, pp. 671686. IAEA.

296 J. W. FARRINGTON, S. M. HEINRICHS and R. ANDERSON

PARKER P. L. (1967) Fatty acids in Recent sediments. Con- trib. Mar. Sci. 12, 135-142.

PARKER P. L. and LEO R. F. (1965) Fatty acids in blue- green algal mat communities. Science 148, 373-374.

PEAKE E.. CASAGRANDE D. J. and HODGS~N G. W. (1972) Fatty acids, chlorins, hydrocarbons, sterols and ‘car01 tenoids from a Black Sea core. The Black Sea. Amer. Assoc. Petrol. Geol. Mem. 20, 505-523.

PUGH P. R. (1971) Changes in the fatty acid composition of Coscinodiscus eccentricus with culture-age and salinity. Mar. Biol. 11, 118-124.

RHEAD M. M.. EGLINTON G.. DRAFFAN G. H. and ENG- LAND P. J. (‘1971) Conversibn of oleic acid to saturated fatty acids in Severn Estuary sediments. Nature 232. 327-330.

RHOADS D. C. (1974) Organism-sediment relations on the muddy sea floor. Oceanogr. Mar. Biol. Ann. Rev. 12, 263-300.

SCHNITZER M. (1976) The chemistry of humic substances. In Environmental Biogeochemistry, Vol. 1, (editor J. 0. Nriagu), pp. 89-107. Ann Arbor Science Publishers.

SCHNITZER M. and KHAN S. U. (1972) Humic Substances in the Environment. Marcel Dekker.

SCHULTZ D. M. (1974) Ph.D. thesis, University of Rhode Island.

SCHULTZ D. M. and QUINN J. G. (1973) Fatty acid compo- sition of organic detritus from Spartina alternipora. Estuarine Coastal Mar. Sci. I. 177-190.