Interstitial water trace-metal chemistry of laminated sediments from the Gulf of California, Mexico

Marine Chemistry, 14 (1983) 89--106 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

89

I N T E R S T I T I A L WATER T R A C E - M E T A L CHEMISTRY OF LAMINATED SEDIMENTS FROM T H E G U L F OF C A L I FO RN IA , MEXICO HANS J. BRUMSACK* and JORIS M. GIESKES Scripps Institution of Oceanography, La Jolla, CA 92093 (U.S.A.) (Received February 22, 1983;revision accepted July 21, 1983) ABSTRACT Brumsack, H.J. and Gieskes, J.M., 1983. Interstitial water trace-metal chemistry of laminated sediments from the Gulf of California, Mexico. Mar. Chem., 14: 89--106. This report presents major and minor element profiles for interstitial waters recovered from the oxygen-minimum zone of the Gulf of California. The major elements and nutrients show concentration--depth profiles typical for anoxic, laminated sediments, with sulfate-reduction occurring close to the sediment--water interface, accompanied by increases in alkalinity and ammonia. Barium is solubilized near the sediment--water interface, but decreases below 10 cm depth, showing concentrations consistent with barite solubility. The dissolved concentrations of Mn, Fe, and Al are higher in the upper part of the sedimentary column; Mn and Fe due to reduction of oxides and A1 probably because of dissolution of siliceous material. In contrast, dissolved Mo, V, and Cr show concentrations increasing with depth. The strong correlation of the concentrations of Mo, V and Cr with "yellow substance" absorbance reflect the importance of dissolved organic matter for the mobility of these elements during early diagenesis. INTRODUCTION

Geochemists have always been puzzled by t he o f t e n - f o u n d unique traceelement composition o f black, bituminous sediments in t h e geological record (Brongersma-Sanders, 1966; Vine and T o u r t e l o t , 1970; Calvert and Price, 1970; Brumsack, 1980). Explanations for these metal enrichments have varied f r o m the supply of t h e metals b y p l a n k t o n in areas o f upwelling (Brongersma-Sanders, 1966; Brongersma-Sanders et al., 1980) to the upt ake o f metals b y th e sediments f r o m seawater under anoxic water conditions (e.g., Brumsack, 1980). Among those elements strongly enriched in m a n y organic carbon-rich sediments relative t o average shale are Mo, V, and Cr. Figure 1 shows t he mean values o f these elements in average shale (Wedepohl, 1970), cretaceous black shales f r om t h e Atlantic Ocean (Brumsack, 1980) and seawater. The plot o f th e e n r i c h m e n t o f these elements in black shales relative to average shale versus their seawater concentrations shows a strong relationship,

* Present address: Geochemisches Institut, Goldschmidtstrasse 1, D-3400 G6ttingen, West Germany.

0304-4203/83/$03.00

© 1983 Elsevier Science Publishers B.V.

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ppm 38 black sha|es

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ppb seawater

0.2

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2.2

6.9

22.7

7-12

B/A

Fig. 1. Correlation of the relative enrichment of Cr, V, U, and Mo in black shales with their abundance in seawater. (A. from Wedepohl, 1970 and personal communication; B from Lange et al., 1977 and Brumsack, 1980; C from Riley and Taylor, 1972;Morris, 1975; Burton, 1975; and Campbell and Yeats, 1981.)

suggesting that seawater should represent the ultimate source for the excess Mo, V and Cr in this sediment type. Studies of the association of trace metals with sedimentary phases, organic or inorganic, are pertinent for the understanding of metal accumulation processes. Calvert and Morris (1977) found high metal contents in organic fractions of diatomaceous oozes off Walvis Bay. They established that the enrichment of metals in fulvic and humic acids was the result of diagenetic alteration of organic and inorganic sediment components. In this report we emphasize our findings on the interstitial water chemistry of varved sediments from the oxygen minimum zone of the Gulf of California slope and will discuss the possible pathways of certain trace elements during early diagenesis. AREA OF STUDY

The Gulf of California is a long marginal sea of the Pacific Ocean, with an areal extent of about 25 × 104 km 2 and characterized by an exceptionally high primary productivity (Zeitschel, 1969). Laminated diatomaceous sediments are found mainly on the continental slopes of the central and southern Gulf (van Andel and Shot, 1964; Schrader et al., 1980), where the upwelling-induced oxygen-minimum zone impinges on the sediment-seawater interface at water depths ranging from 400--800 m (Calvert, 1966). The laminae result from changes in the proportion of the biogenous and terrigenous inputs. Generally, a laminae couplet is deposited annually; a light lamina with higher abundances of oceanic diatoms forms during the dry

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Fig. 2. Location of sampling sites, core numbers and water depths (DSDP Sites 479 and 480 are also shown).

winter season of NW winds and corresponding upwelling at the mainland side, a dark lamina is deposited during the wet summer season with SE winds accompanied by higher terrigenous input (Donegan, 1981). Because of the absence of bioturbation these sediments not only represent a unique paleoclimatic record but also are ideal for the study of early diagenesis. The site locations and depths are listed in Fig. 2. Sampling area E is located close to DSDP Sites 479 and 480 which were drilled in 1978/79 (Schrader et al., 1980). SAMPLING AND SAMPLE PREPARATION

Four box cores and one Kasten core were chosen for subsampling. Subcores were taken by inserting a 10-cm diameter PE tube into the center of the box cores under slight vacuum to prevent compaction. A set of subsamples was taken at 3-cm intervals and the interstitial water was recovered immediately or after storing (max. 36 h) of sediments in syringes and plastic bags at in situ temperatures until processing. Additional surface samples (0--5 mm), including the syphoned water and floating particles, were kept in sealed plastic bags. Subsampling of the Kasten core was conducted 12 h after recovery and only samples from the center of the core, which had not been in contact with the metal casings were taken. Acid cleaned plastic materials were used during all sampling procedures to prevent contamination. The pore waters were squeezed onboard ship in a simple, jack-operated squeezing device which contained no metal parts. The device is similar to that described by K~lil and Goldhaber (1973), but without the nitrogen atmosphere. Only acid-cleaned Teflon and PE materials came into contact with the samples and quartz-distilled water was used for all cleaning steps. As an added precaution the first drops of pore water were discarded, after

92 TABLE I Analytical parameters for direct-injection atomic absorption determinations (Drying t e m p e r a t u r e was 105°C for 6 0 s ; depending on the c o n c e n t r a t i o n 10 ~)r 2 5 p i were injected; pyro-tubes were used for all determinations. All parameters given may vary f r o m instrument to instrument; strong alteration effects of the graphite tubes also should be considered ) Element

Carrier-gas

(flow)

Setting

Ash (°C-s)

A t o m (°C-s)

Det. limit (ppb)

Fe

N2/Ar

(40)

Norm 3

1200-30

2500-5

~;

Mn

Ar

(50)

Norm 3

850-40

2500-5

2

A1 a

N2/H 2

(50)

Norm 3

1450-20

2700-5

2

Cr a'c

N2/H2

(80)

Stop 3

1150-70

2500Max-7

0.5

Va

Ar--N2/H2

(50)

Norm 3

1400-30

2700Max-7

10

Mo a,b

Ar--N2/H 2

(50)

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1300-40

2700Max-7

10

a Heinrichs (1979). b Nakahara and Chakrabarti (1979). c Matsusaki et al. (1981).

which a 5 0 c m 3 plastic syringe was used to retain the sample. After squeezing, a pre-cleaned filter holder was connected to the syringe and the water was filtered through a 0.45 p Nuclepore filter into precleaned 30 cm 3 PE screw-top bottles. An aliquot of 2 cm 3 was removed and spiked with cadmium nitrate for hydrogen sulfide determinations and another aliquot of 10 cm 3 was sealed in 3 dram plastic vials for alkalinity and major ion determinations. The remaining 2 0 - - 3 0 c m 3 were acidifed with 1 0 0 p l doubledistilled HC1 and sealed for trace-element analyses. Despite all these precautions sample contamination and alteration (i.e., release or scavenging of metals) cannot be completely excluded.

ANALYTICAL METHODS

The trace metals, Fe, Mn, A1, Mo, V, and Cr, were determined by direct injection flameless atomic absorption (Perkin-Elmer AA 403 equipped with a H G A 2200 graphite furnace and deuterium background correction). The temperature for the ashing step was chosen as high as possible to eliminate salt matrix effects (Nakahara and Chakrabarti, 1979, Matsusaki et al., 198I). The ashing temperatures, detection limits, etc., for the individual elements are shown in Table I. Calibration curves were obtained b y spiking filtered

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and acidified La Jolla Pier seawater. For A1, Cr, V, and Mo, a 10--20% hydrogen in nitrogen mixture was used as carrier gas (Heinrichs, 1979). Barium was analyzed using an ARL 3 5 0 0 0 C ICP with background correction. Artificial, sulfate-free, seawater spiked with Ba served as a calibration standard. A 1 cm 3 aliquot of sample (either interstitial water or calibration standard) was spiked with 25 #1 of a 10 000 ppm Fe solution (internal standard) and diluted with 8 cm 3 distilled wat'er in plastic vials to reduct salt evaporation effects in the plasma burner. Emission lines used were: Ba, 4 5 5 4 . 0 3 A; Fe, 2 5 9 9 . 4 0 A. RESULTS AND DISCUSSION

Major ions in interstitial waters The study of the distribution of the major-ion composition of interstitial waters as well as those of nutrients is important for the description of the environmental condition of the sediments. The results of the study of these constituents are presented in Fig. 3 (a and b). It should be noted that only core E-5 does not show any lamination and is bioturbated.

Sulfate In core E-5 sulfate remains constant to a depth of at least 55 cm. The same is true for the alkalinity and ammonia, except for the lowermost sample. The other cores in contrast show decreasing sulfate values with

94

depth as a result of bacterial sulfate reduction, which is also reflected in the increases in alkalinity and ammonia. The sulfate concentrations of the uppermost samples of the anoxic cores are higher than those of seawater by as much as 2 mM. This may be explained partly as a result of interference in the polarographic sulfate determination by dissolved organic carbon (DOC). On the other hand, Goldhaber and Kaplan (1980) reported a similar phenomenon on a Carmen Basin core, using a gravimetric method. This suggests that sulfide oxidation may account for this excess sulfate. The sulfate concentration is essentially zero at a depth of 290 cm in core E-17. According to Berner (1978) the initial sulfate gradient correlates with the rate of sedimentation, leading in this case to an estimated sedimentation rate of 0.10 cm y-1. The corresponding values for the other cores are: Core

E-9 E-13 E-17 G-32

Depth for SO~ - = 0

Sedimentation rate

(cm}

(cm y- I)

210 275 290 235

0.],l

0.11 0.10 0.13

These values are in agreement with a sedimentation rate of 0.15 cm y-1 obtained by Bruland (1974) using the 21°Pb dating method on sediments collected in the study area. Donegan (1981) confirms this result (0.13 cm y-1 ), but points out that varve-counting (based on a laminae couplet per year) leads to a sedimentation rate of 0.185 cm y-1. However, in general the data confirm t h a t a laminae couplet represents roughly one year.

Phosphate The phosphate concentration is < 10ttM in the bioturbated core (E-5), whereas it reaches values of well over 100 ttM in the core tops of the anoxic, laminated sediments.

Silica Dissolved silica increases downward in core E-5 from an initial value of less than 500 #M to values around 800 ttM. In contrast, the silica concentrations in the surface samples of the laminated sediments are often higher than in the deeper horizons. Dissolved silica in core G-32 is lower than in the other laminated cores, because of the much lower content of siliceous materials of this core. Apparently, in laminated sediments unaffected by bioturbation, maxima in silica as well as ammonia, phosphate and alkalinity are caused by intense biochemical activity in the surface sediments. Similar observations were made by Sholkovitz (1973) in the varved sediments of the Santa Barbara Basin.

95 Calcium and magnesium In the core tops of the laminated sediments, particularly those in the Guaymas Basin, slightly elevated concentrations of dissolved calcium are observed. These observations can be understood in terms of almost complete carbonate dissolution in the core tops. This is evident from the rapid decrease in calcium with depth in the solid phases (Brumsack, in preparation). At greater depths in the cores, carbonate precipitation accounts for the decrease in dissolved calcium. The decrease in magnesium with depth may be explained by complexation with DOC or the trapping at ion exchange positions of marine humic matter. Nissenbaum and Swaine (1976) reported high magnesium values for these materials. An alternative explanation may be found in the uptake of magnesium in exchange positions in clay minerals (Sholkovitz, 1973; Bischoff et al., 1975). On some samples, the hydrogen sulfide concentration was also determined. In core E-13 a maximum value of 3 1 0 p M was obtained, which may represent a minimum since the loss of hydrogen sulfide during the sampling procedure cannot be ruled out. The data on the major-ion composition of the interstitial waters clearly indicate that, with the exception of core E-5, reducing conditions characterize the sediments both on the Guaymas slope as well as in core G-32 o f f Mazatlan. Of interest are the core tops of cores E-9, E-13, and E-17. Alkalinities, ammonia, phosphate, and silica concentrations, as well as calcium concentrations, are higher than those of seawater and the interstitial waters immediately below the core tops. This suggests that rates of diagenesis of organic matter are enhanced near the sediment--water interface, probably due to the higher availability of organic substrate, whereas bioturbation obliterates such a record in core E-5. Minor elements in interstitial waters Barium The behavior of Ba in the ocean is relatively well understood. Chan et al. (1977) showed that Ba is almost entirely involved in the deep regeneration cycle and parallels that of silica. Marine plankton shows Ba levels of 17 to 59 ppm (Martin and Knauer, 1973). It should be noted that Ba belongs to those elements which are n o t rapidly mobilized soon after the initiation of decomposition o f plankton (Collier and Edmond, 1981). Barium concentration--depth profiles are presented in Fig. 3. At seawater sulfate concentrations the expected solubility of Ba with respect to barite at ~ 7°C is ~ 0 . 0 3 p p m (Church and Wolgemuth, 1972), i.e., the values at depths below 10 cm in cores E-9, E-13, G-32 and the upper part of E-17. The surface samples in these cores contain much higher Ba concentrations, suggesting regeneration of this element in the surface sediments, presumably in the zone of enhanced remineralization of organic matter and dissolution of biogenic silica and carbonate. Under these circumstances, barite solubility does not appear to control the Ba concentration.

In core E-5, Ba concentrations are all slightly in excess of the equilibrium concentration expected for barite. In core E-17, below a depth of 250 cm, a gradual increase in Ba is observed, i.e., below the depths where sulfate concentrations are < 2 mM. We submit that the actual sulfate concentrations below 250 cm are lower than those reported in the Appendix, mainly because of low precisions in the polarographic m e t h o d utilized at low sulfate concentrations. The gradual increase in Ba with depth can best be understood in terms of solubility control by barite (Church and Wolgemuth, 1972t~ Aluminum The behavior of A1 in the marine environment is still under discussion, especially the question of whether its concentration in seawater is controlled by biological or inorganic processes (Hydes, 1979; Caschetto and Wollast, 1979a). A1 data in interstitial waters are still relatively rare, partly due to analytical difficulties. Caschetto and Wollast (1979b) reported A1 values in interstitial waters of Mediterranean and North Sea sediments, which are considerably higher than in the overlying b o t t o m waters, but do not appear to correlate with dissolved silica concentrations. More recently, 8toffyn-Egli (1982) established a rather strong correlation between A1 and dissolved silica in interstitial waters obtained close to the sediment--seawater interface. She suggested that this may signal a close relationship between the geochemistry of A1 and that of biogenic silica. All samples analyzed for A1 in this investigation (Fig. 4,a and b) show higher values close to the sediment--seawater interface followed by a decrease with depth. This is particularly the case in cores E-5 and G-32. The data do not suggest a direct correlation with dissolved silica, particularly not in the core tops, in contrast to the observation of Stoffyn-Egli (1982). Martin and Knauer (1973) reported for their low-Ti p h y t o p l a n k t o n a median concentration of 100 ppm A1 in the organic fraction and 620 ppm A1 in the low Ti siliceous frustules. Even though contamination by terrigenous components cannot be completely excluded, A1 seems to be present at least at the 100 ppm level in marine plankton. These results have been confirmed by Collier and E d m o n d (1981), who reported that during their leaching experiments a significant fraction of A1 was dissolved which was presumably incorporated in biogenic material. Yet, though biogenic material undergoing decomposition near the sediment--seawater interface may act as a source for dissolved A1, there is no clear correlation with such indicators as dissolved silica. Perhaps the lower dissolved silica values in cores E-5 and G-32 cause slower rates of removal o f A1 from the interstitial waters, thus allowing relatively high concentrations in the surface sediments. In core E-17 the A1 concentrations reach values of ~< 7 ppb below 300 cm. These concentrations are considered to be steady-state values maintained by the clay mineral assemblage (Hydes, 1977). Authigenic clay mineral formation appears to be the ultimate sink for dissolved A1 in these sediments.

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Fig. 4a, b. A1, Mn, Fe, and Ba in interstitial waters from the Gulf of California. Iron and manganese Both elements are known to be easily mobilized under reducing conditions. Thermodynamic considerations predict that Mn(IV) reduction should occur prior to Fe(III) reduction (Froelich et al., 1979), and that the zone of Mn reduction occurs between the zones of catabolic nitrate reduction and sulfate reduction. In the sediments considered in this study, the sulfate reduction zone starts at or very near the sediment--water interface and thus the reduction processes involving Mn and Fe are initiated at the sediment-seawater boundary. This results in the high concentrations of Mn and Fe in the surface samples (Fig. 4,a and b). Similar findings have been reported in other hemipelagic sediments (Calvert and Price, 1972; Elderfield et al., 1981). At greater depths sinks for Mn are in carbonates and for Fe in Fesulfides (Berner, 1980; Elderfield et al., 1981 and references therein). In core E-5 Mn and Fe are also mobilized in the core top. Thus, notwithstanding the constancy in dissolved sulfate, alkalinity and ammonia as a result of bioturbation, conditions throughout core E-5 are reducing in nature. This implies that the rate of diagenetic reactions responsible for the Eh change, and therefore Fe and Mn solubility, is much faster than diffusion and mixing due to bioturbation. Molybdenum, vanadium and chromium Before proceeding with the discussion of interstitial water concentrations of these elements, it seems appropriate to present a very brief discussion of the distribution of these elements in the oceanic water column.

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Fig. 6a, b, c. Correlation of the yellow substance absorbance with Mo, V, and Cr in interstitial waters from the Gulf of California. Open circles -- suboxic core E-5, field circles = anoxic cores E-9, E-13, E-17 and Go32.

established V surface concentrations of 0.9 ppb which increase with depth and are closely correlated with nutrient concentrations in the upper water column, reaching a maximum concentration of 1.7 ppb at ~ 200 m. Huizenga and Kester (1982) report concentrations of 1 . 8 p p b below 9 0 0 m in the Sargasso Sea and variable concentrations, 1.4--2.3 ppb, in waters of the New York Bight. The interstitial water profiles for Cr, Mo, and V are shown in Fig. 5,aand b. The yellow substance (y.s. or " G e l b s t o f f " ) absorbance at 375 nm (Bricaud et al., 1981) is also shown. The y.s. absorbance correlates with DOC in core E-17 (r = 0.84, n = 17; V. Ittekkot, personal communication). In general the concentrations of all three elements increase with depth in all cores investigated. Of the three elements, Mo is the only one for which interstitial water data are available in the literature. Contreras et al. (1978) report an increase in the Mo concentration with depth to maximum values of -~ 2 0 0 p p b in samples from the Gulf of Maine. Even though this increase (about 20 times seawater) is not as pronounced as in the laminated sediments from the Gulf of California, the trend seems to be the same and the difference in Mo mobilization might be connected to the higher biogenic input in the high productivity environment of the Gulf of California. Several mechanisms have been proposed for the transfer and fixation of Mo into anoxic sediments. These include precipitation as Mo sulfides (Goldschmidt, 1954), sorption o n t o particulate organic matter, such as humic acids (Szilagyi, 1967), co-precipitation with Fe sulfides (Bertine, 1972), and scavenging by Mn oxides (Berrang and Grill, 1974). The mobilization of Mo into the interstitial water phase does not seem to be associated with the process of manganese mobilization or iron sulfide precipitation, especially in view of the opposite behavior of Mn and Fe in the interstitial waters when compared to the distribution of Mo. Similar conclusions were reached by Contreras et al. (1978). The relatively good correlation between y.s. absorbance and Mo {r = 0.75) shows that Mo seems to be b o u n d to a dissolved organic phase, possibly low molecular weight organic matter (Fig. 6a). The problem remains as to h o w to introduce Mo in large enough quantities

1O0 into the sediment, especially in organic-carbon-rich sediments. Marine plankton is low in Mo; Martin and Knauer (1973) report values <'. 2 p p m . Average shale, being comparable to the terrigenous input, shows concentrations of ~ 2 ppm as well (Wedepohl, 1970), whereas Corg.-rich sediments have concentrations of ~ 2 0 p p m . Since seawater concentrations of this element are relatively high (10 ppb level), this represents the most likely Mo source. The important step for Mo accumulation seems to be the reduction of Mo(VI) to Mo(V), which is easily sorbed (Szilagyi, 1967). Marine organic matter combines both the reducing agent and absorption or ion exchange sites. During the generation of dissolved humics a significant part of the Mo may be mobilized and transferred to the DOC pool which builds up during bacterial degradation of organic matter (Pilipchuk and Volkov, 1974}. Contreras et al. (1978) propose that the degradation of organic matter accounts for the majority of Mo in interstitial waters, a concept in agreement with the data presented here. Nissenbaum and Swaine (1976) reported unusually high trace metal contents of marine humic substances and state that most Mo is associated with this material. Calvert and Morris (1977) indicate similar trends. It is probable that redox processes at the sediment -~ water interface serve to scavenge Mo from the overlying waters. Subsequently the buildup of low molecular weight humic acids in the interstitial waters serves to mobilize this scavenged Mo. The V profiles look very similar to those of Mo (Fig. 5), suggesting that a comparable process leads to an enrichment in interstitial waters. Szalay and Szilagyi's (1967) experiments show that humic acids are able to reduce the mobile metavanadate anion (VO3) to the vanadyl (VO) 2+ cation, which can be fixed by organic matter. The ability of V to form metallo--organic complexes is geologically significant as demonstrated by the high V--porphyrin concentration of some crude oils. In contrast to Mo, V is less concentrated in seawater ( 1 - - 2 p p b ) and marine plankton has low concentrations ( < 3 ppm; Martin and Knauer, 1978). On the other hand, average shale has concentrations of ~ 120 ppm V. Therefore, the scavenging process for V by marine organic matter may be less important than for Mo. But in general the geochemical behavior of V seems to be closely related to Mo with the exception that incorporation into sulfide phases during a later stage of early diagenesis is less likely. The correlation between V and y.s. absorbanee (r = 0.89; Fig. 6b) is even more significant than for Mo. Most of the V should still be present in the sediments in the terrigenous fraction, a smaller part (represented by the mobile V in interstitial waters) may be bound to organic matter. Chromium shows the best correlation with y.s. absorbance (r = 0.95; Fig. 6e). It is not an element which is typically enriched to high levels in Corg.rich sediments. The concentration of Cr in marine plankton is relatively low ( < I ppm; Martin and Knauer, 1973), as is its abundance in seawater ( ~ 0 . 2 p p b ; Campbell and Yeats, 1981). On the other hand, the Cr redox chemistry is comparable to that of Mo and V. Under oxic conditions Cr(VI)

101

is the dominant species, whereas under reducing conditions the less mobile Cr(III) occurs (Cranston and Murray, 1978) and might well be adsorbed by organic matter. Yamazaki et al. (1980) show that Cr(III) forms uncharged and/or negatively charged organic complexes of various molecular weights in the presence of humic substances within the neutral pH-range. This observation would explain the good correlation between y.s. absorbance and Cr. Any excess Cr in the solids will be undetectable because terrigenous matter should be high in this element (average shale = 90 ppm; Wedepohl, 1970). In summary, we have demonstrated that the elements Mo, V, and Cr are very mobile during early diagenesis. The strong correlations with organic matter (y.s. absorbance) can be explained by the redox chemistries of these elements and corresponding sorption and/or complexation by dissolved organic matter, e.g., low molecular weight humic substances. Mo, V, and Cr are not the only elements being concentrated in marine humic matter, e.g., U has a similar redox chemistry. Therefore, this study is just a small step towards a better understanding of the behavior of trace metals during early diagenesis of Corg.-rich sediments. ACKNOWLEDGEMENTS

The authors thank the captain and crew of the Mexican R/V "Mariano Matamoros" for their assistance during shipboard operations. Thanks also to Hans Schrader for the generous support during the BAM-80 cruise. We thank Drs. G. Klinkhammer, H. Ohmoto and K.H. Wedepohl for their critical reading of a previous version of this manuscript and helpful comments by A.P. Lisitzin, P.J. Wangersky and an anonymous reviewer. Financial assistance was provided by a stipend from the Deutsche Forschungsgemeinschaft to the first author (HJB) and a grant from NSF, OCE78-27376 (MANOP). APPENDIX

Core

Depth (cm)

Akalinity 3 Ammonia ( m e q d m - ) (raM)

Silica (mM)

Phosphate (mM)

Ca (mM)

Mg (raM)

Sulfate (mM)

E-5

2.0 4.5 7.5 10.5 13.5 16.5 22.5 28.5 37.5 49.5 54.0

2.52 2.53 2.23 2.54 2.54 2.53 2.61 -2.57 2.81 3.31

0.479 0.539 0.638 0.652 0.717 0.763 0.787 0.785 0.792 0.781 0.812

0.0061 0.0052 0.0087 0.0052 0.0068 0.0060 0.0061 . . 0.0082 0.0083 0.0126

10.33 10.32 10.28 10.19 10.21 10.19 10.06 . . 10.27 10.06 9.69

51.93 51.55 52.02 51.68 51.92 51.55 51.68

28.1 28.2 29.2 28.0 28.4 28.2 28.5

51.54 51.94 51.55

27.9 28.4 28.5

0.014 0.021 0.028 0.024 0.022 0.016 0.021 0.032 0.086 0.192

l {} 2

APPENDIX

(continued)

Core

Depth (cm)

Alkalinity Ammonia ( m e q dm-:*) (mM)

Silica (raM)

Phosphate (raM)

Ca (raM)

Mg (raM)

Sulfate ,~mM)

E-9

1.5 4.5 7.5 10.5 13.5 19.5 25.5 34.5 48.5

5.76 4.01 4.36 5.10 5.64 6.86 7.53 8.53 10.54

0.84 0.41 0.41 0.48 0.57 0.65 0.71 0.80 0.96

1.273 1.035 0.970 0.937 0.983 0.959 0.940 0.849 0.974

0.310 0.107 0.090 0.085 0.081 0.087 0.080 0.089 0.072

10.90 10.67 10.57 10.53 10.59 10.58 10.41 10.43 10.36

52.44 51.52 51.57 51.37 51.07 51.30 51.62 51,87 51.36

30.8 29.6 28.7 29,1 28.5 27.0 26.9 26,2 23.5

E-13

1.5 4.5 7.5 10.5 13.5 19.5 25.5 34.5 45.5

4.63 4.28 4.90 5.63 6.54 7.48 8.24 9.34 10.11

0.60 0.35 0.43 0.54 0.65 0.71 0.79 0.89 1.06

0.982 0.934 0.904 0.884 0.848 0.870 0.869 0.885 0.864

0.316 0.205 0.198 0,196 0.204 0.174 0.159 0.141 0.123

10.20 10.24 10.30 10.37 10.33 10.32 10.30 10.30 10.26

52.36 52.03 51.60 51.89 52.01 51,91 52.00 51.80 51.55

30.0 29.6 28.2 28.8 28.4 27.8 27.1 26.4 25.1

G-32

2.5 5.5 8.5 11.5 14.5 20.5 26.5 32.5 40.0

3.58 4.24 4.65 4.88 5,88 7.02 7.77 9.21 10.09

0.13 0.23 0.30 0.41 0.46 0.59 0.72 0.87 1.00

0.477 0.516 0.513 0.546 0.540 0.555 0.545 0.583 0.565

0.118 0.130 0.109 0.109 0.120 0.121 0.144 0.133 0,139

10.53 10.62 10.68 10.59 10.61 10.56 10.37 10.24 9.98

51.83 51.43 50.93 50.64 51.05 50.71 50.56 50.19 50.02

30.6 28.9 28.7 28.3 28.1 27.5 26.4 26.0 25.5

E-17

2.5 6.5 13.5 22.5 33.5 46.5 61.5 78.5 97.5 118.5 141.5 166.5 193.5 222.5 253.5 286.5 321.5 358.5 397.5 421.5 448.5

7.24 4.54 6.40 7.61 9.10 9.98 12,18 14.45 15.19 18.44 20.25 22.99 25.10 28.58 27.78 29.39 32.24 36.05 34.98 34.46 36.33

0.81 0.50 0.62 0.75 0.95 1.07 1.28 1.45 1.61 1.87 2.11 2.33 2.60 2.83 3.04 3.35 3.55 3.77 3.98 4.27 4.24

0.920 0.816 0.774 0.784 0.897 0.774 0.768 0,772 0.765 0.761 0.706 0.683 0.679 0.676 0.550 0.528 0.502 0.521 0.420 0.484 0.424

0.140 (}.078 0.139 0.126 0.128 0.101 0.107 0.108 0.107 0.106 0.105 0.103 0.092 0.106 0.080 0.081 0.062 0.065 0.046 0.048 0.061

11.89 11.68 10.70 10.53 10.55 10.06 t0.35 10.14 10.00 9.74 9.42 9.26 8.97 8.80 8.09 7.52 5.99 5.63 5.30 4.48 4.95

53.98 53.24 52.37 52.85 52.77 52.49 52.46 52.28 51.9,1 52.34 51.65 51.74 51.31 51.69 50.79 48.60 51.31 51.35 51.27 50.02 51.211

28.6 29,3 28.0 27.2 25.5 24.3 22.0 19.8 17,7 16.1 113.2 I 1.8 9.8 6.4 4.9 1.8 2.1 0.9 1.0 1.4 1.8

103 APPENDIX

(continued)

Core

Depth (cm)

Mn (ppb)

Cr (ppb)

Mo (ppb)

V (ppb)

Fe (ppb)

Al (ppb)

y.s.

E-5

2 4.5 7.5 10.5 13.5 16.5 22.5 28.5 37.5 49.5 54

60 68 21 37 15 22 33 16 22 21 9

3.0 4.6 6.7 1.5 1.5 1.7 1.5 1.1 1.6 2.1 2.4

25 22 38 53 50 72 73 95 125 120 318

44 38 70 95 163 152 188 125 129 154 262

92 50 145 38 19 35 14 5 12 18 9

95 85 79 45 25 58 23 13 26 28 25

6 6 7 6 8 9 7 20 4 4 20

0.09 0.07 0.07 0.06 0.06 0.06 0.05 0.06 0.06 0.05 0.06

E-9

1.5 4.5 7.5 10.5 13.5 19.5 25.5 34.5 48.5

106 45 39 30 31 20 22 11 5

2.8 1.2 2.3 2.1 2.3 2.9 3.1 3.5 4.4

26 41 76 135 123 114 35 80 225

18 56 101 96 93 115 65 245 339

1025 290 110 42 33 9 15 9 9

140 17 59 40 44 87 45 43 31

50 72 32 36 40 43 45 50 65

0.46 0.12 0.09 0.04 0.03 0.03 ~ 0.03 ~ 0.03 ~ 0.03

E-13

1.5 4.5 7.5 10.5 13.5 19.5 25.5 34.5 45.5

93 20 42 11 7 12 9 3 < 2

1.3 2.0 2.2 2.7 2.4 3.0 3.0 3.9 4.1

16 22 31 30 88 88 97 33 148

28 45 95 98 90 148 106 95 221

26 24 31 45 32 45 49 57 59

0.39 0.04 ~ 0.03 0.03 0.03 ~ 0.03 0.03 ~0.03 ~ 0.03

G-32

2.5 5.5 8.5 11.5

33 36 38 50

2.1 1.3 1.1 1.8

15 16 21 35

83 126 100 100

2220 820 645 575

14.5

33

0.5

35

228

20.5 26.5 32.5 40

30 34 20 17

2.0 1.9 3.8 3.0

35 39 40 94

200 78 250 145

90 220 105 80 30 14 10 44? 8

42 68 41 48 34 32 30 90? 27

Ba (ppm)

265 132 110 --

-0.09 -~< 0.03 . . . . ---

345

--

--

~< 0 . 0 3

370 195 95 42

65 -. . . . --22 --

~< 0.03 ~< 0.03 ~< 0.03 ~< 0.03

104 APPENDIX (continued) Core

E-17

Depth (cm) 2.5 6.5 13.5 22.5 33.5 46.5 61.5 78.5 97.5 118.5 141.5 166.5 193.5 222.5 253.5 286.5 321.5 358.5 397.5 421.5 448.5

Mn (ppb) 35 5 <~ 3 4 ~ 3 ~ 3 ~ 3 ~ 3 5 <~ 3 ~3 ~ 3 4 ~ 3 <:3 ~3 6 ~ 3 5 11 ~3

Cr (ppb) 1.8 2.0 3.9 3.0 4.4 5.2 6.8 6.2 5.9 5.7 6.7 8.4 6.0 6.2 7.7 9.1 7.9 7.6 11.6 7.5 10.0

Mo (ppb) 95 200 478 822 447 785 631 708 596 457 617 955 575 565 668 617 617 525 569 447 570

V (ppb) 140 120 390 530 580 800 970 880 745 600 945 1290 590 505 1130 955 880 810 1240 575 1240

Fe (ppb)

A1 (ppb)

20 71 10 13 5 12 19 12 8 6 10 8 11 15 10 12 14 13 20 24 24

49 44 29 23 45 38 41 20 26 21 24 18 13 (51) 23 10 6 7 6 33 7

y.s,

33 33 66 73 64 76 82 73 87 73 100 115 92 98 136 120 132 124 162 121 147

Ba ~ppm} 0.16 0.05 ~ 0.03 ~ 0.03 ~ 0.03 ~ 0.03 0.04 ~ 0.03 ~< 0.03 0.01 0.03 0.03 0.07 0.13 0.12 0.74 1.18 3.06 5.63 7.31 7.80

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