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Cochran, J. R., Stow, D.A.V., et al., 1990Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 116
13. PRELIMINARY DATA ON DISSOLVED HEAVY METALS IN INTERSTITIAL WATER FROMTHE BAY OF BENGAL, LEG 1161
Toshio Ishizuka,2 Yukio Kodama,2 Hodaka Kawahata,3 and Venugopalan Ittekkot4
ABSTRACT
Preliminary data are presented on dissolved heavy metals in interstitial water samples collected at Site 718 ofOcean Drilling Program Leg 118.
The heavy metals at this site are divided into three groups: Group I (B, K, Mn, Ni, Pb, total Si, total P, V)behaves like Mg, which decrease with depth; Group II (Ba, Cu, Sr, Ti) behaves like Ca, which increases with depth;and Group 111 (Cd, Co, Cr, Fe, Na, Mo, Zn) contains metals that are independent of depth.
Mg decreases with depth from 50 mM at the seafloor to 21 mM at 900 mbsf. Mn in the sulfate reduction zone (1.0to 2.8 ppm) is more highly concentrated than in the methane fermentation zone (0.23 to 0.50 ppm), except for Section116-718-1H-1. A similar behavior is also observed for V and Pb. Ni, B, and K decrease non-uniformly with depth.
Ca and Sr increase with depth at the same rates, indicating the dissolution of inorganic calcium carbonate byanaerobic oxidation of organic matter (Sayles, 1981). The distribution of Ba with depth is very similar to those ofCa and Sr. Cu and Ti profiles trend to increase non-uniformly with depth.
Fe is constant with depth. The sharp decrease in total silicate concentration at the seafloor probably indicates adecrease in the decomposition of siliceous biological matter (e.g., diatoms) and production of opal. The constantlevels of Group 111, except for Na and Fe, may reveal equal sources of supply from surface seawater and theHimalayas over time.
INTRODUCTION
Understanding the behavior of heavy metals in interstitialwater under conditions of sulfate reduction and methanefermentation is important in geochemical studies, especiallythose relating to early diagenesis of heavy metals. Decay andoxidation of organic matter (Emerson et al., 1980) leads to amanifold increase in Mn, Fe, Cu, Ni, and Zn contents ofmarine interstitial water (Hartmann and Mueller, 1979 andKlinkhammer, 1980). Although many studies have focusedattention on the major elements in interstitial water (e.g.,Berner, 1980; Gieskes, 1983; Gieskes and Lawrence, 1981;McDuff, 1981; Manheim, 1978; Manheim and Bischoff, 1989;Sayles and Manheim, 1975; Sholkovitz, 1973), only a few haveaddressed problems concerning the distribution of heavymetals (e.g., Brooks, et al., 1968, Klinkhammer, 1980, Saw-Ian and Murry, 1983). Within surficial sediments, oxidants arereduced sequentially: first O2, NO3, followed by MnO2 andFe2O3 and then by SO^~.
However, little is known about the effects of this reductionsequence on the distribution of metals deeper in the sedimentcolumn. Available data indicate that Ca in interstitial waterdecreases during sulfate reduction followed by a concomitantCa and Sr increase at greater depths. Following S θ | ~ reduc-tion, Mg decreases with depth in pelagic sediment during earlydiagenesis (Gieskes, 1983). The increase of both Ca and Sr andthe decrease of Mg at the depth in the sediment column ofinterstitial water implies recrystalization of carbonate (Saylesand Manheim, 1975) or reaction with clay minerals.
Preliminary results of both heavy metal and major cationanalyses in interstitial water samples collected at Site 718 in
1 Cochran, J. R., Stow, D.A.V., et al., 1990. Proc. ODP, Sci. Results, 116:College Station, TX, U.S.A. (Ocean Drilling Program).
2 Ocean Research Institute, University of Tokyo, Nakano, Tokyo, 164Japan.
Geological Survey of Japan, Tsukuba, 305 Japan.University of Hamburg, Geological-Paleontological Institute, Bundesstrasse
55, 200 Hamburg, Federal Repubic of Germany.
the Bay of Bengal are presented here. Site 718 is located in thecentral Indian Ocean approximately 800 km south of SriLanka and 200 km northwest of the Afanasiy Nikitin sea-mount group (Fig. 1).
METHODS
Interstitial water samples were obtained with an automaticstainless steel mechanical squeezer and sealed in polythenetubes, which were pre-washed with 2 M HN0 3 . Samples wereacidified to about 2 M with 14 M HNO3, which was made bysub-boiling distillation of guaranteed reagent (Mattinson,1972).
We analyzed the heavy metals in the interstitial watersamples using an inductively coupled plasma emission spec-trometry (ICP). The instrumental components and operatingconditions for the Seiko JY 48P(V) with cross-flow-typenebulizer are summarized in Table 1. The operating condi-tions were set according to recommended procedures. Theanalytical calibration curves were determined using theblank and mixed standard solutions of all the elementsinvestigated (analytical standard solutions for atomic ab-sorption analysis, Wako Chemical Co.). We could notmeasure three elements (Cd, Cu, Pb) due to the Ca effect ofinterstitial water on the ICP instrument. They were analyzedby graphite atomic absorption spectrophotometry on a Hi-tachi Z-8000. Na and K of interstitial water were measuredby flame atomic absorption spectrometry (Hitachi, Z-8000).Ca and Mg concentrations of the interstitial water that weremeasured by the ICP agree to within 5% of the titrationanalyses made on board ship (Table 2 and Shipboard Scien-tific Party, 1989). The analysis of heavy metals reportedbelow are accurate to within 5% (Table 3).
RESULTS
The stratigraphic section recovered at the Site 718 rangesfrom late Quaternary to early Miocene. The sediments aredominated by mud, silty mud, and silty turbidites, some ofwhich are characterized by relatively high organic carbon
145
T. ISCHIZUKA, Y. KODAMA, H. KAWAHATA, V. ITTEKKOT
20°N
15'
10c
5°S
π wr• iSwatch of no ground
AfanasiyNikitinSeamounts
80°E 85° 90° 95°
Figure 1. Location of ODP Site 718 in Bay of Bengal.
Table 1. Instrumental and Operating Conditions.
ICP spectrometerFrequencyOutput powerCoolant gasAuxiliary gasCarrier gasObservation highNebulizerPolycnromatorGratingReciprocal linear dispersionEntrance slit widthExit slit width
Seiko JY 48 P(V)27.12 MHz1.3 KWargon 16 L/min.argon 0.6 L/min.argon 0.4 L/min.16 mm above work coilcross-flow typePaschen-Runge type (100 cm focal length)2550 grooves/mm0.39 nm/mm at 270 nm20 µm38 µm
contents (0.2 to 2.5 wt %) in the sulfate reducing zoneextending down to about 200 mbsf, but display lower organiccarbon content (<0.5 wt %) in the methane fermentation zonebelow 200 mbsf.
Foraminifers are sporadic to absent throughout the sectionwith the exception of the top few meters, which have a moreabundant planktonic assemblage. However, the profile ofcalcium carbonate shows an increase on average from 5% to20% with depth (about 5% down to 250 mbsf, 10% between250 and 700 mbsf, and 10% to 20% below 700 mbsf) (Leg 116shipboard Scientific Party, 1989). This increase in calciumcarbonate may be the result of inorganic carbonate such asthat reported by Ishizuka and Mori (in press).
The Ca concentration of the interstitial water is approxi-mately constant (8.3-10 mM) with depth in the zone of sulfatereduction, but increases from 11.0 to 18.0 mM with depthwithin the zone of methane fermentation (Fig. 2A). Theconstant increase of Sr (6.1 to 7.9 ppm down to 200 mbsf and11.0 to 17.0 ppm below 200 mbsf) with depth shows a similarprofile to that of Ca (Fig. 2B). Dissolution of calcium carbon-
ate by anaerobic oxidation of organic matter (Sayles, 1981) isindicated by the fact that Ca and Sr increase at the same rate.The Ba profiles with depth closely match Ca and Sr inbehavior (Fig. 2C). The reasons for this similarity are notknown, but it may relate to the absorption of clay minerals orbiogenic residue. Cu and Ti profiles tend to increase non-uniformly with depth (Figs. 2D and 2E). Cu is typically closelyassociated with a labile solid phase, to which it becomesattached near the sea-sediment interface (Klinkhammer, 1980;Sawlan and Murry, 1983).
Mg concentration shows a constant level (46 to 46 mMexcept for the Section 118-718-1H-4) down to 10 mbsf, thendecreases with depth (46 to 21 mM) between 10 and 500 mbsf,and becomes constant again (21 to 27 mM) below 500 mbsf(Fig. 4). Goldberg and Arrhenius (1958) demonstrated that theMg content of biogenic carbonate is very low. Therefore, mostof the Mg is not in the lattice of carbonate, but probably Mgabsorbed onto clay minerals by cation exchange. This isindicated also by the difference between increase of calcium(ΔCa = 6 mM) and decrease of Mg-ΔMg = 25 mM). The Kcontent is constant 20 to 24 mM (down to 10 mbsf), anddecreases from 20 to 3.2 mM with depth between 100 and 400mbsf and then varies markedly from 5.4 to 18.0 mM below 400mbsf (Fig. 3A). By contrast the Na content shows an irregularvariation (370 to 410 mM) with depth (Fig. 3B). These resultsare different from those of Sayles (1981), in which Na releaseand K uptake are related to silicate reaction.
Both total phosphate and total silicate (Figs. 3C and 3D)decrease with depth down to 300 mbsf, from 1.4 to 0.17 ppmand from 13.0 to 3.8 ppm, respectively. This indicates eitherbiological reaction or reaction with calcium phosphate, inaddition to the silicate reaction. The B decrease in pore water(Fig. 3E) may reflect the replacement of K in illite as proposedby (Harder, 1959). However, as both B and K decrease withdepth at Site 718, this may suggest either replacement of otherelements in clay minerals or the authigenesis of illite.
Ni shows a general decrease with depth (Fig. 3F). Mnshows higher concentrations in the sulfate reduction zone (1.0to 2.8 ppm) than in the methane fermentation zone (0.23 to0.50 ppm), except for the Section 116-718 1H-1, even thoughthe MnO2 reduction occurs before Fe and sulfate reduction(Fig. 4A). V and Pb have similar behaviors to Mn with depth(Figs. 4B and 4C). V shows 53 to 64 ppb in the sulfatereduction zone, 27 to 39 ppb in the methane fermentationzone, and Pb ranges from 100 to 130 ppb in the sulfatereduction zone and 41 to 83 ppb in the methane fermentationzone. The Pb and V concentrations may depend on redoxconditions within the sediments.
Total silicate decreases with depth, 13 to 5.9 ppm, only innear-surface sediment. It is then approximately constant, 5.9to 6.8 ppm, in the sulfate reduction zone and fluctuates morewidely, 3.4 to 8.3 ppm, in the methane fermentation zone. Thesharp decrease of the total silicate just below the seafloor mayindicate a decrease in the rate of decomposition of siliceousbiological matter (e.g., diatoms) and authigenesis of opal.
Cd, Cr, Co, Fe, Mo, Zn, and Zr are approximately constantwith depth (e.g., Figs. 4D, 4E, and 4F). Cd, Co, Zn, and Fedecrease or increase with depth in the southern CaliforniaBorderland and Santa Barbara and Santa Cms Basins (Brookset al., 1968). These authors suggested that enrichment of Cd,Co, Cu, and Zn in surface sediments could be attributed tobiological concentration and release, as there was more thansufficient organic matter present to account for such a source.However, at Site 718 there is very little fresh organic matter insurface sediments so that the relatively low concentrations ofheavy metals are constant with depth. Fe content is constantwith depth because iron reduction occurs before sulfate re-
146
DISSOLVED HEAVY METALS
duction. The lack of variation of those concentrations exceptFe and Na may reveal a similar source of supply over timefrom surface seawater and the Himalayas.
ACKNOWLEDGMENTS
The authors acknowledge their gratitude and deep appre-ciation to the late E. T. Degens (Geological-PaleontologicalInstitute, University of Hamburg), who suggested and super-vised this work.
REFERENCES
Berner, R. A., 1980. Early Diagenesis: A Theoretical Approach:Princeton, NJ (Princeton Univ. Press).
Brooks, R. R., Presley, B. J., and Kaplan, I. R., 1968. Trace ele-ments in the interstitial waters of marine sediments. Geochim.Cosmochim. Ada., 32:397-414.
Emerson, S., Jahnke, R., Bender, M., Froelich, P., Klinkhammer,G., Bowser, B., and Setlock, G., 1980. Early diagenesis insediments from the eastern equatorial Pacific. I. Pore waternutrients and carbonate results. Earth Planet. Sci. Lett., 49:57-80.
Gieskes, J. M., 1983. The chemistry of interstitial waters of deep-seasediments: interpretation of deep-sea drilling data. In Riley, J. P.,and Chester, R. (Eds.), Chemical Oceanography (Vol. 8): London(Academic Press), 222-269.
Gieskes, J. M., and Lawrence, J. R., 1981. Alteration of volcanicmatter in deep-sea sediments: evidence from the chemical compo-sition of interstitial waters from deep-sea drilling cores. Geochim.Cosmochim. Ada, 45:1687-1703.
Goldberg, E. D., and Arrhenius, G.O.S., 1958. Chemistry of Pacificpelagic sediments. Geochim. Cosmochim. Acta, 13:153-212.
Harder, H., 1960. Einbau von Bor in detritische Ton-minerale.Geochim. Cosmochim. Acta, 21:284-294.
Hartmann, M., and Mueller, P. J., 1979. Trace metals in interstitialwaters from Central Pacific Ocean sediments. In Fanning, K. A.,and Manheim, F. (Eds.), The Dynamic Environment of the OceanFloor: Lexington, Mass. (Lexington Books), 285-301.
Klinkhammer, G. P., 1980. Early diagenesis in sediments from theeastern equatorial Pacific. II. Pore water metal results. EarthPlanet. Sci. Lett., 49:81-101.
Manheim, F. T., 1976. Interstitial waters of marine sediments. InRiley, J. P., and Chester, R. (Eds.), Chemical Oceanography(Vol. 6): London (Academic Press), 115-186.
Manheim, F. T., and Bischoff, J. L., 1989. Geochemistry of porewaters from Shell Oil Company drill holes on the continental slopeof the northern Gulf of Mexico. Chem. Geol., 4:63-82.
Mattinson, J. M., 1972. Preparation of hydrofluoxic, hydrochloric, andnitric acid at the ultralow lead levels. Anal. Chem., 44:1715.
McDuff, R. E., 1981. Major cation gradients in DSDP interstitialwaters: the role of diffusive exchange between seawater and upperocean crust. Geochim. Cosmochim. Acta, 45:1705-1713.
Sawlan, J. J., and Murry, J. W., 1983. Trace metal remobilization inthe interstitial waters of red clay and hemipelagic marine sedi-ments. Earth Planet. Sci. Lett., 64:213-230.
Sayles, F. L., 1981. The composition and diagenesis of interstitialsolutions-II. Fluxes and diagenesis at the water -sediment inter-face in the high latitude North and South Atlantic. Geochim.Cosmochim. Ada., 45:1061-1086.
Sayles, F. L., and Manheim, F. T., 1975. Interstitial solutions anddiagenesis in deeply buried marine sediments: results from theDeep Sea Drilling Project. Geochim. Cosmochim. Acta, 39:103-128.
Shipboard Scientific Party, 1988. Site 718: Bengal Fan. In Cochran,J. R., Stow, D.A.V., Proc. ODP, Init. Repts., 116: CollegeStation, TX (Ocean Drilling Program), 91-154.
Sholkovitz, E. R., 1973. Interstitial water chemistry of the SantaBarbara Basin sediments. Geochim. Cosmochim. Acta., 37:2043-2073.
Date of initial receipt: 18 April 1989Date of acceptance: 24 January 1990Ms 116B-136
Table 2. Major cation elements in the interstitial water at Site 718. Fl-AA is flame atomic absorption.
Section
116-718-
1H-011H-011H-031H-041H-051H-051H-061H-06
13X-0115X-0125X-0129X-0132X-0236X-0149X-0155X-0259X-0362X-0390X-01
Interval(cm)
40-50140-150140-150140-150130-140140-150
0-10140-150140-150140-150140-150128-138140-150130-140140-150140-150140-150140-150140-150
Analytical Method
Depth(mbsf)
0.451.44.45.97.37.47.58.9
125144239268307343467525565593856
Na(nM)
790810820810780820800770820740760790820770720820790
820
Fl-AA
K(mM)
20.023.023.023.020.021.020.020.018.013.07.99.9
10.03.25.7
16.05.4
15.0
Fl-AA
Mg(mM)
48484939464747464237283030262126212427
ICP
Ca(mM)
9.910.010.08.39.7
10.09.89.7
10.09.4
11.011.011.012.013.014.013.015.016.0
ICP
Sr(ppm)
7.27.57.76.17.17.37.17.07.97.9
11.012.011.013.013.013.016.016.017.0
ICP
Ba(ppm)
0.10.20.10.10.10.20.10.20.20.20.91.32.54.66.36.26.51.53.1
ICP
B(ppm)
5.47.26.96.55.95.95.85.86.56.24.53.42.84.53.92.72.33.54.9
ICP
Si(ppm)
11.013.09.25.96.56.16.36.66.15.94.14.83.86.38.35.03.45.76.7
ICP
P(ppm)
0.551.400.720.830.620.650.630.610.370.460.340.170.260.390.260.290.280.340.26
ICP
147
Table 3. Heavy metals in the interstitial water at Site 718. GF-AA is graphite atomic absorption.
Section
116-718-
1H-011H-011H-031H-041H-051H-051H-061H-06
13X-0115X-0125X-0129X-0132X-0236X-0149X-0155X-0259X-0362X-0390X-01
Interval(cm)
40-50140-150140-150140-150130-140140-150
0-10140-150140-150140-150140-150128-138140-150130-140140-150140-150140-150140-150140-150
Analytical Method
Depth(mbsf)
0.451.44.45.97.37.47.58.9
125144239268307343467525565593856
Pb(Ppb)
100110110100110120130130120120724178866886636569
GF-AA
Ti(PPb)
15151614161819181817141315191819161918
ICP
Zr(PPb)
0.8n.d.0.83.43.05.07.04.08.07.0n.d.n.d.n.d.4.06.04.0n.d.n.d.n.d.
ICP
V(PPb)
61565954586462615753353339363236273033
GF-AA
Cr(PPb)
3.12.61.8
52.05.2
11.04.22.61.32.4
13.050.05.28.83.03.12.04.77.5
GF-AA
Mo(PPb)
35353429253232313126282133292636242935
GF-AA
Mn(ppm)
0.221.402.801.701.701.501.601.701.501.000.230.480.500.390.450.340.250.500.30
ICP
Fe(PPb)
3254
760100420120
1500250
793534
240550
7431282980
3100
ICP
Co(PPb)
0.40.91.20.81.52.60.71.31.71.61.51.91.01.41.31.20.7
10.01.3
GF-AA
Ni(PPb)
1888795839
12030167260233811382726343115
GF-AA
Cu(PPb)
9941
17039
480280530180380830320150160540140320370780130
GF-AA
Zn(PPb)
19016051016015021019041027040085027099
400150300130310220
ICP
Cd(PPb)
12161410111614131514273111132014183016
GF-AA
DISSOLVED HEAVY METALS
Ca (mM)
1000
Sr (ppm)
Ba (ppm)
2 4 6 8u
200
400
Depth(mbsf)
600
800
1 nnn
a—i 1 1 1 1—-»-—
g
BB
BEl
B
BB
B
'.
B
200 -
400 -Depth(mbsf)
600 -
800
1000
8 10 12 14 16 18
Cu (ppb)D
0 200 400 600 800 1000u
200
400
Depth(mbsf)
600
800
1 nnn
Q • I£JI u• i
B
ElBB
B
-
B
BB
B
1 '
El
El
Figure 2. Profiles of interstitial water with depth at Site 718. A. Ca; B. Sr; C. Ba; D. Cu; E. Ti; F. Mg.
149
T. ISCHIZUKA, Y. KODAMA, H. KAWAHATA, V. ITTEKKOT
Ti (ppb)
200 -
400 -Depth(mbsf)
600
800 -
1000
Mg (mM)
200 -
400Depth(mbsf)
600
800 -
1000
Figure 2 (continued).
150
DISSOLVED HEAVY METALS
K (mM) Na (mM)
A10
200
600
800
1000
20LJLJ H
400
Depth(mbsf)
aa
a-
B
α
P (ppm)0.0 0.5 1.0
200-
400-
Depth(mbsf)
600-
800-
1000
o
0
200
400
Depth(mbsf)
600
800
1 nc\n
-B
B
Q
-
D
D
m
B
a
B
B
1.5D
Si (ppm)6 8 10 12 14
EIU u u
200 •
400 -Depth(mbsf)
600 -
800 -
1000
Figure 3. Profiles of interstitial water with depth at Site 718. A. K; B. Na; C. Phosphate; D. Silicate; E. B; F. Ni.
151
T. ISCHIZUKA, Y. KODAMA, H. KAWAHATA, V. ITTEKKOT
B (ppm)
2 3 4 5 6 7
200 -
400 -Depth(mbsf)
600 -
800 -
1000
Ni (ppb)
0 20 40 60 80 100 120 140u
200
400
Depth(mbsf)
600
800
1 nnn
• U I I • 1 • M • ii| — | • LJ
Dπ
-B
BB
B
-
B
BD
El
D
Figure 3 (continued).
152
DISSOLVED HEAVY METALS
Mn (ppm) V (ppb)
200-
400-Depth(mbsf)
600-
800-
1000
20 30
Pb (ppb)
200-
400-Depth(mbsf)
600-
800-
1000
200
400
Depth(mbsf)
600
800-
1000
Co (ppb)40 60 80 100 120 140 8 10 12
200 -
400 -Depth(mbsf)
600
800 -
1000Figure 4. Profiles of interstitial water with depth at Site 718. A. Mn; B. V; C. Pb; D. Co; E. Mo; F. Zn.
153
T. ISCHIZUKA, Y. KODAMA, H. KAWAHATA, V. ITTEKKOT
Zn (ppb)
0 200 400 600 800 1000u
200
400
Depth(mbsf)
600
800
1 nnn
• Q ui u Q i
BB
-
BB
B-
B
BB
B
B
• i •
D
200-
400-Depth(mbsf)
600-
800-
1000
Figure 4 (continued)
154
