Light hydrocarbons in Red Sea brines and sediments

Light hydrocarbons in Red Sea brines and sediments ROGERA. BURKE,JR,* JAMESM. BROOKSand Wan

M. SACKE'IT*

Department of Oceanography, Texas A & M University, College Station, TX 77843, U.S.A. (Received

1 August 1980; accepted in revisedform

3 December

1980)

Abstract-Light hydrocarbon (C,-Cs) concentrations in the water from four Red Sea brine basins (Atlantis II, &akin, Nereus and Vafdivia Deeps) and in sediment pore waters from two of these areas (Atlantis II and Suakin Deeps) are reported. The hydrocarbon gases in the Suakin Deep brine (T = . 25°C. Cl - = _ 857, CH, = _ 71/l) are apparently of biogenic origin as evidenced by C,/(C2 + Cs) ratios of _ 1000. Methane concentrations (6-8 ~11) in Suakin Deep sediments are nearly equal to those in the brine, suggesting sedimentary interstitial waters may be the source of the brine and associated methane. The Atiantis II Deep has two brine layers with significantly different light hydrocarbon concentrations indicating separate sources. The upper brine (T = - SO%, Cl- = w 73?&, CH. = - 155 &I) gas seems to be of biogcnic origin [C&Z, + Cs) = c IlOO], whereas the tower brine (T = -6l”C, Cl- = * lSSy&,,CH, a: c 120&l) gas is apparently of thermogcnic origin [C,/(C, + Cs) = + SO). The thermogenic gas resulting from thermal cracking of organic matter in the sedimentary column apparently migrates into the basin with the brine, whereas the biogenic gas is produced in situ or at the seawater-brine interface. Methane concentrations in Atlantis II interstitial waters underlying the lower brine. are about one half brine concentrations; this difference possibly reflects the known temporal variations of hydrothe~l activity in the basin.

INTRODUCX’ION TXE CENTIULrift valley of the Red Sea is known to

contain at least a dozen basins filled with water having elevated temperatures (2441°C) and/or salinities (Cl- = 73-156&J (MUSTY and AMANN, 1978; BACKERand %XELL, 1972). Associated with many of the brines ttre rn~~~ous sediments which arc predominantly oxides, sulfides and silicates rich in Fe and Mn, and with high concentrations of Zn, Cu, Pb, Cd and Ag. These sediments represent some of the most sign&ant examples of submarine hydrothermal mineralization so far discovered (BIGNELL,1978) and are of potential economic importance. The distribution, origin and fate of light hydrocarbons in the marine environment has received considerable attention (LAMOKTAONE et al., 1973; Broods and S~cruz’rr, 1977; SC!RA~N and Bw 1977, and others). Sources of fight hydrocarbons to the marine enviromnent include ~thro~~nic inputs (i.e. offshore oil and gas production), natural seepage, runoff, and possibly biological production in the water column. Two potential sources of light hydrocarbon gas frequently associated with hydrothermal systems are: (1) thermal degradation of organic material such as kerogen, and (2) chemical reaction of carbon dioxide and molecular hydrogen to form methane (GUNTEFL1978). BROOKS et al. (1979) and SACKETTet al. (1979) have reported the gaseous hydrocarbon geochemistry in the anoxic, hypersaline * Present address: Department of Marine Science, University of South Florida, 830 First Street South, St Petersburg, FL 33701, U.S.A.

brines of the Gulf of Mexico. The East Flower Garden Brine has pr~omi~tely thermogenic gas while the Orca Basin brine is biogenic in origin. Both of these anoxic brines showed evidence of in situ methane production. The dissolved gas geochemistry of the Red Sea brines and sediments has received iittk attention; information about light hydrocarbon d~butions is essentially nonexistent. SwINNERTON and LINNENB~M (1969) report one measurement of hydrocarbon gas in the Atlantis II Deep brine and two measurements of the waters above it. There are no pore water dissolved gas rn~u~en~ of the brine associated sediments in the literature. In this study, light hydrocarbon (C&s) concentrations in the waters from four of the Red Sea brine basins (Atlantis II, Suakin, Nereus and Valdivia Deeps) and in sediment pore waters from two of the areas (Atlantis II and Suakin Deeps) are reported. Locations of the brine areas sampled are shown in Fig. 1.

MATERIALS

AND METHODS

Samples for light hydrocarbon rn~ur~en~ were obtained aboard the RV Melv~fle in June 1978. Sediment samples retrieved by standard box coring techniques were stored, prepared, and analyzed as described by BERNARDet al. (1978). The technique involved scaling a OS-cm core section in a 0.5-l jar with sodium azide poisoned seawater and flushing the headspace with helium. The headspace is equilibrated on a high speed shaker with the interstitial water and the headspace analyze-d by gas chromato~aphy. Water samples were obtained by standard Niskin bottles attached to a hydroline and by 9-&r bottles attached to the deep tow geophysical vehicle of the Scripps Marine

627

R. A. BURKE et al.

628

26 REUS

DEEP

ATLANTIS VALDIVIA

II DEEP

DEEP

2d

UAKIN

DEEP

1d

Fig. I. Locations of brine basins sampled aboard the RV Meloillr, June 1978. Physical Laboratory (WEISSet al., 1977).Immediately after retrieval, the water samples were overflowed into 0.3-l bottles, poisoned with sodium azide, and capped carefully with no bubble. The samples were then refrigerated and stored in the dark until analysis. The water samples were prepared for gas chromatographic analysis in one of two ways. For samples of normal Red Sea Deep Water with expected nl/l gaseous hydrocarbon concentrations, a purge and trap method was used (BROOKS and SACKETT,1977). Brine samples containing &I quantities of methane were analyzed by the MCAUL~E (1971) multiple phase equilibrium method. However, special precautions were necessary since although the hot brines had cooled considerably from their in situ temperatures upon ascent from the depths, they were still very warm at the time of sampling. Further cooling caused a ‘bubble’ or headspace to form in the sample bottle due to contraction of the water. Substantial quantities (see Results and Discussion section) of hydrocarbon gas are contained in this bubble depending upon the temperature and dissolved gas concentration of the water. An Alltech Associates Headspace Sampler No. 8017 was usedto sample this headspace.. After headspace analysis, the bottle was opened and three 25ml aliquots of the water were drawn into gas tight syringes. Twenty-five ml of ultra-pure helium were then added to each syringe and the syringes were shaken on a wrist-action shaker to partition the hydrocarbon gases from the water into the headspace prior to analysis. Duplicate analyses of methane in the brine yielded a precision of 23% and a total average uncertainty in analysis of approximately & 5% (uncertainty in analysis of standard was + 2%).

RESULTS AND DISCU!+SION Suakin Deep The Suakin Deep contains two separate brine pools (see BACKER and SCHOELL, 1972, for bathymetric

map); a circular West Basin with a brine surface area of about 2.5 km2 and an elongate East Basin extend-

ing in a northwestern direction with an area of about 10 km* (BAUMANNet al.. 1973). The brines in the two basins have very similar chemical characteristics and temperature structures, suggesting that either the brines have a common source, or there is communication between them (BAUMANN et al., 1973). Samples from the Suakin Deep included two box cores (designated BC76 and BC79) from the East Basin and one hydrocast from the West Basin. Methane, ethane, oxygen and chloride ion concentrations are plotted versus water depth for the Suakin hydrocast in Fig. 2. Methane concentrations in the normal Red Sea Deep Water above the brine range from 40 to 50nl/l. These values are slightly higher than the predicted (WIESENFIURG and GLXN,USO,1979) atmospheric equilibrium value (- 35 nl,/l) and substantially higher than normal deep ocean concentrations (LAMONTAGNE et al., 1973). Across the brineseawater interface (somewhere between 2500 and 2770 m) methane concentrations increase approximately two orders of magnitude and the dissolved oxygen concentration decreases from normal Red Sea Deep Water values ( - 2 ml/l) to less than 0.1 ml/l. Ethane, undetectable above the brine, averages 5-7nl/l in the brine. Interstitial Cl-C3 hydrocarbon concentrations versus depth are presented for the Suakin box cores in Table 1. Methane concentrations for the two cores average 6-8 &‘I, about the same as in the brine. The higher than atmospheric equilibrium concentrations of methane above the brine are probably the result of diffusion from the brine. Alternatively, the high concentrations may result from advection off shelf and slope regions as suggested by SCRANTONand

629

Light hydrocarbons in Red Sea brines and sediments

1

2

tdETHANE(IIvL1and OXYCiEN(mllL) 5 6 7 3 4

6

CH4 (nlk)

Fig. 2. Methane, ethane. oxygen and chloride ion concentrations in the West Basin of the Suakin Deep. BREWER(1977) for the western subtropical North Atlantic. The molecular composition of the hydrocarbon gas in the brine is indicative of a biogenic origin as evidenced by a methane to ethanc (C&J ratio (no propane was detected) of c 1000. BERNARDet ol., (1977) characterized biogenic hydrocarbon gases (formed by m~h~ogenic bacteria) as having C,,& + C,) ratios greater than 1000 while thermogenic gases (formed from thermal degradation of organic matter) have C,/(C2 + C,) ratios smaller than 50. Although no specific attempts to isolate methanogenic bacteria in Suakin brines or sediments were found in the literature, HE~TZERand Orrow (1976) did isoiate denitrifying bacteria from the sediments, proving that at least the sediments are not sterile. The similarity of sediment and brine methane concentrations suggests that sedimentary interstitial water may be the source of the brine as well as methane. SCHOELLand FABER (197X) found that the Suakin brine and interstitial waters sampled during DSDP have similar oxygen

isotopic compositions and concluded that the brine could be interpreted as an a~mulation of ‘expelled interstitial waters.’ Consumption of the olefins, ethene and propene, by large populations of bacteria living in the upper l-2 cm of the sediments probably explains their absence in the brine. Hxrrzx~ and OTTOW (1976) report that the population of denitrifiers decreases from some IO&/gin surface material to only a few in the subsediment. Atlantis II deep The Atlantis II deep contains about 5 km3 of geothermally heated brines, stratified in two essentially homog~eous anoxic layers of differing salt content and temperature (SCHOELL,1975). The Atlantis II Deep can be divided into four separate basins (see BACKERand SCHOELL(1972) for bathymetric map); Southwest, West, North and East Basins. Since the 1971 cruise of the RV Vu/oidiviu,when detailed temperature me~urem~ts were made over the entire area1 extent of the Atlantis II Deep (SCHOELLand

630

R. A. BURKEer ul.

Cl-C3* Hydrocarbon Concentrations in Sediments of the East Basin, Suakin Deep

Table 1.

Depth (cm)

Methane (!Jl/L)

Ethene (nl/L)

Ethane (nl/L)

Propene tnl/L)

Propane (nl/L)

cl/K2+C3)

Box Core d76 - Water Depth = 2633m o-5 s-10 10-1s 15-20 20-25 25-30 30-35 35-40 40-4s 45-50 AVERAGE

124 139 375 282 151

4.7 6.8 6.3 6.1 5.9

ma

5.7 7.5

103 88 70 49

6.7 6.7 -5.9 6.2

157

26 42 12 9 43 55 33 12 9 -7 25

14 11 20 14 13 38 28 9 11 -a 17

180

: 1

3

160 530 680 140 100 220 560 740 590 390

60x Core /!7Y- [daterDepth = 2608m O-S 5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 AVERAGE

4.9 4.8 8.3 6.7 7.4 8.6 8.0 8.8 7.6 -7.5 7.5

60

134 61 133 221 154 191 174 96 ___ -272

79 50 a4 75 167 71 83 20 --49

21 16 9 20 a 30 33 5 _63 -

140 100 90 40 120 90 440 ___ -150

160

76

23

140

* The ratio C,/(C+C?) is methane/(ethane + propane) it does not include ethene or propene. Uncertainty in these ratios is estimated to be +a%. Also applies to Tables 2 and 3. 4

-*

HARTMANN, 1973), it has been generally accepted that active discharge of brine occurs in the Southwest Basin and spreads late&y to the others. As a result, the Southwest Basin exhibits the highest temperature, while the North and East Basins are the coolest (SCHOELLand HARYMANN, 1973). Samples from the Atlantis II Deep analyzed in this study include two box cores, one from the Southwest Basin and one from the edge of the East Basin (designated BCSL and BC84, restively) and one hydrocast from the Southwest Basin. Methane, ethane, propane, oxygen and chloride ion concentrations are plotted vs water depth for the Atlantis II hydroczrst in Fig. 3. As in the case of the Suakin Deep, the Red Sea Deep Water above the brine exhibits much higher methane concentrations than normal deep ocean water. Methane concentrations increase from _ 40 m/l at 1650 m to _ 80 &/I at 2OOOm. SWINNERTON and LINNENB~M (1969) reported a methane concentration of 40 nl/l at 1880 m above the North Basin. Methane concentrations in the upper brine layer (T = _ 5O”C, Cl- = SO?&,)are relatively constant at 155 &‘l, more than three orders of magnitude higher than overlying water concentrations. Methane, ethane and propane averaged 1IS, 2 and 75 nl/l, respectively. in the lower brine (7’ = _ 61°C. Cl- = 156?&,).Interstitial C,--Cs hydrocarbon concentrations vs depth are presented for the

Atlantis II Deep box cores in Table 2. The average methane concentration of Box Core No. SI from the Southwest Basin is 63 @l/l. Box Core No. 84. on the edge of the East Basin averaged only 26 HI/I of methane. The C,/(Cz + C,) ratio in the upper brine layer is approximately ItOO(Fig. 3) suggesting the hydrocarbon gas has a biogenic origin. This presents difficulties, as previous studies (WATSONand WATERBURY. 1969; HEITZERand OTTOW, 1976) have faiIed to detect bacteria in Atlantis II brine or sediments. The combination of high temperature, salinity, and metal concentrations and low availability of oxidizable organic material is apparently enough to render the brine unsuitable for microbial activity, whereas any one of those factors acting alone would not prevent bacterial life (WATSONand WATERBURY,1969). One possible explanation of the convicting evidence is that microbial methane production occurs in a thin transition layer between the brine and overlying seawater. WAJY~N and WATERBIIRY (1969) cultured many sampb in an attempt to isolate sulfate-r~ucing bacteria from the Atalntis II Deep brine layers. Results were always negative when pure brine from either brine layer was used as a culturing medium, but were positive with a mixture of upper layer, lower layer and brine-seawater interface water. They concluded that the bacteria must have come from a thin. l-2 m

Light hydr~rbons

in Red Sea brines and sediments

631

METHANE(nl/L)

00

D i 0

20

1

METH~E 4

(pi/L),

t

t

PROPANE

W;‘s

~,2~HL~~~

(xbf

,

,

*

1.0

2.0 OXYGEN(ml/L)

3.0

Fig, 3. Methane, athane, propane, oxygen and chloride ion ~n~ntrations Atlantis II Deep.

layer of anoxic water situated above the brine, since sulfate-reducing bacteria are strict anaerobes. This hypothetical layer should occur in the transition zone between 2015 and 2030m where the oxygen content decreases from 0.2mIjl to zero, the chlorinity increases from 40 to 700/&,and the methane concentration increase-s from 63 to 155 $/l (Fig. 3). While it is true that the study of WATSON and WATERBURY(1969) attempted to isolate sulfate-reducing bacteria and not methanogenic bacteria, there is no obvious reason why methanogens should be better transition

80

60

40

20

0

4.0

in the Southwest Basin of the

suited to the harsh conditions of the brines than sulfate reducers (J. SCHWARZ, personal communication). In the lower brine, methane concentrations are significantly lower (KM-132 &I), ethane concentrations are a factor of 15 greater, and propane is detectable in quantities of 60-80nI/l as compared to the upper brine (Fig. 3). The C,(C2 -I- C,) ratio around 50 in the lower brine suggests the hydrocarbon gas in the lower brine has a thermogenic origin. Nydrogen and oxgyen isotopic data suggest that the Atlantis II Deep brine is Red Sea paleowater, at least 5000 yr old (SCHOJZLL and

632

R. A. BURKE etal. Table 2.

Depth (cm)

cl-C3 Hydrocarbon Concentrations in Sediments of the Atlantis II Deep

Methane (ul/L)

Ethene (nl/L)

Ethane Propene (Ill/L) (nl/L)

c1uc2+c3)

Box Core H81 - Water Depth = 2145111 15-20 20-25 25-30 30-35 40-45 45-50 50-5s

66.8 57.7 58.5 6C.3 60.4 66.5 64.7

AVEI?&GE 63.3

116 il.0 92 122 180 - 44

121 125 136 109 80 127 - 62

2 3 2 12 -39 -5

550 460 430 630 750 520 1040

119

109

11

630

167

Box Core j/84- Water Depth = 2OlOm 5-10 15-20 25-30 35-40 45-50

22.4 21.5 22.8 33.5 31.1

AVERAGE 26.3

224 144 97 87 120 134

-__ --_ --_ _-_ ---

FABER, 1978), that has acquired its increased salinity

from contact with or circulation through Miocene evaporites that underlie the most recent sediments (MANHEIM, 1974; GIRDLER and STYLES, 1974). The brine is believed to be discharged through open fissures in the sediment (SCriOnLLet al., 1974) in the form of narrow plumes (TURNER, 1969) at an estimated temperature of I lO-210°C (SCHOELL and HARTMANN, 1978). The brine would have ample opportunity to concentrate hydrocarbon gases from thermal cracking of organic matter (SACKRT, 1978; and others) during its long subsurface burtal. CLAYPOOLer al. (1973) found that sediments containing relatively larger proportions of ethane (taken to indicate thermogenesis) were found in areas of higher heat flow (-4 ~cal/cm’/sec) for the Aleutian Trench-Arc System. For comparison, heat flow in the Atlantis II Deep ‘hot spot’ approaches IOficaI/crn2/sec (SCHOELL. 1975). If the above hypotheses concerning hydrocarbon gas genesis are correct, the 6i3C of methane should be significantly more negative in the upper Table 3.

_____ --

____ ____ ____ ______-

layer than in the Iower layer based on the model of BERNARD et al.(1977). Unfortunately, because of the small amounts of gases in the samples, these data could not be obtained. The average interstitial methane concentration in the core from the Southwest Basin (BC81) is about half that found in the brine (Fig. 3, Table 2). Since methane must be very unreactive in the sterile sediments and lower brine of the Atlantis II Deep, it should behave conservatively. Assuming diffusion across a planar surface from an infmite reservoir one can write the simple equation: Lz = DT;

where L is sediment depth, D is the molecular diffusion coefficient and T is time. For L equal to 15 cm (approximate depth BC81 super-penetrated) and D equal to 3.0 x 10-6cm2/sec, it should take about 2.5 yr for methane to diffuse from the brine to the top sediment interval sampled. The difference in brine and sediment methane concentrations could be due to the

Light Hydrocarbon and Hydrographic Data for Valdivia and Nereus Deeps

Sample I

Location (ON)

Location ('El

Temp. ("Cl

4 5 6

21°20.2' 2lO20.5 21O20.3'

37O56.8' 37"56.9' 37O56.8'

30.09 30.80 30.30

4 5

23O11.3' 23O12.9'

37O13.0' 37O13.0'

29.95 26.20

(%

Methane Ethene (!Jl/L) (nl/L)

Ethane (nl/L)

c1'c2

Valdivia Deep 139.6 137.5 137.2

140 119 129

7 3 2

3 3 1

40 40 130

5 8

1 2

llnl/L 6nllL

470 130

Nereus Deep 131.9 124.9

Lighthydrocarbons inRed Sea brines and sediments Table 4.

633

Methane Analysis of Atlantis II Deep Brines

Sample Depth (m)

CH4(ul/L) Brine Only

CH4(Ul/L) Brine + Headspace

Brine + Headspace Brine Only

2030 (upper brine)

62

156

2.5

2045 (upper brine)

63

158

2.5

2065 (lower brine)

32

104

3.2

2080 (lower brine)

37

115

3.1

2100 (lower brine)

45

132

2.9

changing conditions of brine discharge (temperature, flow rate) noted by several investigators over the last several years (BREWER et al., 1971; SCHOELLand HARTMANN, 1978). Assuming the water column hydrocarbon distribution in the East Basin is similar to that in the Southwest Basin, the methane concentration in BC84 is roughly equivalent to expected overlying brine methane concentrations (Fig. 3, Table 2). The fact that no ethane was detected in BC84 (Table 2) suggests that the methane was produced biologically. Other basins Light hydrocarbon, hydrographic and location data are given for the %sh’ samples from Valdivia and Nereus Deeps in Table 3. The data are too few for any detailed interpretation, but deserve some mmment. Methane concentrations in the Valdivia Deep are of the same order as those in the Atlantis II Deep (Fig. 3). The C,/Cz ratio of samples 4 and 5 are indicative of a thermal origin for the hydrocarbon gases in those samples. The C,/C2 ratio in sample 6 could be due to a mixture of thermogenic and biogenic gases. This similarity to the Atlantis II Deep is interesting since the Valdivia brine has such dilfnent characteristics and apparently a different origin. Isotopic measurements by SCHOELLand FABER (1978) showed the Valdivia brine to be the only one with an isotopic composition identical to present day Red Sea Deep Water. It was therefore proposed that the brine is simply the result of dissolution of exposed salt deposits with no thermal influence. Methane concentrations in the Nereus Deep (Table 3) are of the same order as those in the Suakin Deep (Fig. 2). The C,/C2 ratios of 471 and 129 suggest a mixture of thermogenic and biogenic gas. The Nereus brine is believed to have a paleowater origin similar to that of the Atlantis II Deep (SCHOELLand FABER, 1978) although the hydrographic properties are not as extreme (Table 3). The importance of performing headspace sampling on the brine samples is demonstrated by the methane

concentration data presented in Table 4. As can be seen, failure to analyze the headspace can lead to a concentration that is lowered by a factor of 2.5-3.2 (Table 4). SCRAN'TON (1977) found that Cariaco Trench samples analyzed immediately after collection had a higher methane concentration by a factor of 5 1.5 than did duplicates of the same samples analyzed three weeks later, presumably after bubble formation occurred. The bubble or storage effect would be expected to be larger for the Red Sea samples (50-61”C) than for the Cariaco Trench samples (17°C) since the former are much hotter.

SUMMARY Analysis of samples for light hydrocarbons from two hydrographic and four coring stations in the Atlantis II and Suakin Deeps revealed interesting features of their respective light hydrocarbon geochemistries. Based on molecular composition ratios, hydrocarbon gas in the Suakin Deep is believed to have a biogenic origin. Brine and sedimentary methane concentrations are nearly identical suggesting that sedimentary interstitial waters could be the source of brine and associated methane. The situation is more complex in the Atlantis II Deep where the two brine layers apparently have different hydrocarbon gas origins. Molecular composition ratios in the upper brine are indicative of a biogenic or@. The bacteria responsible most likely inhabit a layer in the pycnocline above the brine. The gas in the lower brine appears to have resulted from thermal degradation of organic matter. The brine probably acquired the gas during its presumed residence in underlying Miocene evaporite deposits.

Acknowledgements-We would liketo thank Dr CARL BOWSER (University of Wisconsin) for providing shiptime from his NSF Grant (OCE-78-08689) for sample collection and HUSSEIN ABDEL-REHEM, who actually collected the samples analyzed. Preparation of the manuscript was made possible by NSF Grant OCE-80-02455.

634

R. A. BURKEet al. REFERENCES

tection of the marine environment in the Red Sea. Ofi shore Technology Conjerence. OTC 3188, pp. 1199-1214.

BACKERH. and SCHOELLM. (1972) New Deeps with brines and metalliferous sediments in the Red Sea. Nat. Phys.

Sci. 240. 153-158. A., RICHTERH. and SCHOELLM. (1973) Suakin Deep: brines and hydrothermal sediments in the deepest part of the Red Sea. Geol. Rundschau 62, 684-694. BERNARDB. B., BROOKSJ. M. and SACKETTW. M. (1977) A neochemical model for characterization of hydrocarbon gas sources in marine sediments. Ofishore -Technology Conference, OTC 2934, pp. 435-438. BERNARDB. B., BROOKSJ. M. and SACKETTW M. (1978) Light hydrocarbons in Recent Texas continental shelf and slope sediments. J. Geophys. Res. 83, 4053-l. BIGNELLR. D. (1978) Genesis of the Red Sea: metalliferous sediments. Mar. Mining 1, 209-235. BREWERP. G.. WILSONT. R. S.. MURRAYJ. W., MUNNS R. G. and DENSMORE C. D. (1971) Hydrographic observations on the Red Sea brines indicate a marked increase in temperature. Nature 231, 37-38. BROCNUJ. M. and SACKERSW. M. (1977) Significance of low molecular weight hydrocarbons in marine waters. In Proceedings of the 7th International Meeting on Organic Geochemistry. (eds R. Campos and J. Soni), pp. 4454%. Espanola de Micropaieontologia. BRINKS J. M., BRIGHTT. J., BERNARDB. B. and SCHWAB C. R. (1979) Chemical aspects of a brine pool at the East Flower Garden Bank, northwestern Gulf of Mexico. Limnol. Oceanagr. 24 735-745. CLAYPOOLG. E.. F%SLEY B. J. and KAPLAN I. R. (1973) Gas analvses in sediment samoles from Legs 10. II, 13, 14. 15. 18 and 19. In Initial ‘Reports of txe Deep Sea Drilling Project XIX (eds J. S. &eager, b. W. Scholl et a/.\. DD. 879-884. U.S. Government Printing Office. GIRDLERR. W. and STYL& P. (1974) Two siage Red Sea floor spreading. Nature U7, 7-l I. GUNTERB. D. (1978) C,-C‘ hydrocarbons in hydrothermal gases. Geochim. Cosmochim. Acta 42, 137-139. HEITZERR. D. and Orrow J. C. G. (1976) New denitrifying bacteria isolated from Red Sea Sediments. Mar. Biol. 37, BAIJMANN

I-10.

LAMONTAGNE R. A., SWINNERTON J. W.. LINNENBOM V. J. and SMITH W. D. (1973) Methane concentrations in various marine environments. J. Geophys. Res. 78. 5317-5324. MANHEIMF. (1974) Red Sea geochemistry. In Initial Reports ofthe Deep Sea Drilling Project XXIII (eds R. B. Whitmarsh, 0. E. Weser et al.), pp. 975-988. U.S. Government Printing Office. MCAULIFFEC. (1971) Gas chromatographic determination of solutes by multiple phase equilibration. Chem. Technol. 1,46-51.

MUSTAFFIZ. and AMMANH. (1978) Ocean mining and pro-

SACKER W. M. (1978) Carbon and hydrogen isotope effects during the thermocatalytic production of hydrocarbons in laboratory simulation experiments. Geochim. Cosmochim. Acta 42, 571-580. SACKETTW. M., BROCIKS J. M., BERNARDB. B., SCHWAB

C. R., CHUNG H. and PARKERR. A. (1979) A carbon inventory for Orca Basin brines and sediments. Earth Planet. Sci. Lett. 44, 73-81. SCHOELLM. (1975) Heating and convection within the Atlantis II Deep geothermal system of the Red Sea. Proc. 2nd UN Geothermal Symposium, San Francisco, pp.

583-590.

SCHOELLM. and HARTMANNM. (1973) Detailed temperature structure of the hot brines in the Atlantis II Deep areas (Red Sea). Mar. Geol. 14. I-14. SCHOELLM. and FABERE. (1978) New isotopic evidence for the origin of Red Sea brines. Nature 275. 436-438. SCHOELLM. and HARTMANNM. (1978) Changing hydrothermal activity in the Atlantis II Deep geothermal system. Nature 2%. 784785. SCHIXLLM., BACKERH. and BAUMANNA. (1974) The Red Sea geothermal systems--new aspects on their brines and associated metalliferous sediments. 4rh IAGOD Symposium, Varna. pp. 303-314. SCRANM)NM. I. (1977) The marine geochemistry of methane. Ph.D. Dissertation, WHOIF(IT, Woods Hole. SCRANTONM. I. and BREWERP. G. (1977) Occurrence of methane in the near-surface waters of the western subtropical North Atlantic. Deep Sea Res. 24, 127-138. SWINNERTONJ. W. and LINNENWMV. J. (1967) Determination of the C, to C, hydrocarbons in seawater by gas chromatography. J. Chromatogn. Sci. 5, 576573. SWINNERTONJ. W. and LINNEN~~MV. J. (1969) Lowmolecular weight hydrocarbon analyses of Atlantis II waters. In Hot Brines and Recent Heavy Metal Deposits in the Red Sea (cds E. T. Degens and D. A. Ross), pp. 251-253. Springer-Verlag. TURNERJ. S. (1969) A physical interpretation of the observations of hot brine layers in the Red Sea. In Hot Brines and Recent Heavy Metal Deposits in the Red Sea (eds E. T. Dcgens and D. A. Ross), pp. 164-173. Springer-

Verlag. WATSONG. W. and WATERBURY J. B. (1969) The sterile hot brines of the Red Sea. In Hot Brines and Recent Heavy Metal Deposits in the Red Sea (eds E. T. Degens and

D. A. Ross), pp. 272-281. Springer-Verlag. WEEP R. F., L~NSDALEP., LUP~ONJ. E., BAINBRIDGE A. E. and CRAK; H. (1977) Hydrothermal plumes in the Gala-

pagos Rift. Nature 267, 600-603. WIE~ENBURG D. A. and GUIN.U~ON. L. (1979) Equilibrium solubilities of methane, carbon monoxide, and hydrogen in water and seawater. J. Chem. Eng. Data 24, 356360.