Chemical fractionation of transition elements in Pacific pelagic sediments

00167037:81~071141-06so2.00 0 CopyrIght 0 1981 Porgamon Press Lid

Chemical fractionation of transition elements in Pacific

sediments

pelagic

ULRICH F&sand F%IER STOPPERS lnstitut fir Sedimentforschung der L!niversit;it Heidelberg Im Neuenheimer Feld 236, D-69 Heidelberg, West Germany (Receiued 4 December 1979; accepted in revisedform

19 February 1981)

Abstract-Partitioning of transition elements in Pacific pelagic sediments (35 samples) was performed by sequential chemical leaching with barium chloride/triethanolamine (easily extractable fraction), acidic cation exchange resin (carbonate phases), and hydroxylamine hydrochloride and dilute hydrochloric acid solutions (hydrous oxides). Residual metal percentages are highest in red-brown clays and siliceous ooze, intermediate in calcareous materials and low in micronodules (2 samples, > 125 pm): residual metal contents seem to be controlled predominantly by the rate of admixture of volcanoclastic materials. At higher bulk metal concentrations, the non-residual fractions of Mn, Cu. Ni and Zn generally increase both in red-brown pelagic clays and in siliceous ooze. Mn, Ni. and Co concentrations are mainly associated with the easily reducible fraction (0.1 M NH,OH.HCl), whereas Fe, Cu. and Zn exhibit higher percentages in the hydrochloric acid soluble fractions (0.3 M HCl); Zn and Cu are associated to some extent with the carbonate phase, copper with the easily extractable fraction.

INTRODUCTION

studies served to help ascertain the sources of metals

THE PAannomNcr of metals in sediments is useful for the recognition of diagenetic reactions in pelagic deposits. By chemical leaching with EDTA, dilute hydrochloric and acetic acid, GOLDBERG and ARRHENIUS (1958) and ARRHENIUS and KORKISH (1959) determined the distribution of elements in detrital igneous minerals and authigenic phases (mainly the oxide minerals and microcrystalline apatite) in pelagic sediment. CHESTERand HUGI-W (1967) introduced a combined acid-reducing agent of 1 M hydroxylamine hydrochloride and 25% acetic acid for the separation of ferromanganese minerals, carbonate minerals, and adsorbed trace elements from pelagic deposits. The latter technique has been widely used on marine sediment samples, e.g. from the North Atlantic (CHESTER and MESSIHA-HANNA,1970: HOROWITZ,1974; HOROWITZ and CRONAN, 1976), the North Pacific (CHESTER and HUGHES,1969) and the East Pacific (SAYLESet al., 1975). HEATH and DYMOND (1977) compared various leaching methods. but favored the ammonium oxalate extraction technique originally introduced by SCHW~SWANN(1964) for soil analysis. Bowsza et al. (1979) have recently performed a series of specific extraction experiments on sediments associated with manganese nodule-rich areas of the eastern equatorial Pacific Ocean. Time-dependent differences during treatment with hydroxylamine hydrochloride, buffered citrate-dithionite and hydrochloric acid indicate that different phases may control the release of Fe, Cu, and Ni. In the present work on Pacific pelagic deposits, we have employed an extraction sequence which had been previously tested on polluted coastal marine and limnic sediments (PAJCWNEELAM and F~RSTNER,

1977; F~RSTNER and

in sediments as well as their availability for biological uptake. MATERIALS During the RV Sonne cruise SO-O6-l/2 from August 8 to October 15, 1978, five ocean areas were studied in detailtwo north of the equator (C, D) and three (F, G, K) in the southern Pacific (Fig. 1, Table 1). Area C is situated Table 1. Type and location of the core samples in the present study Core No. 5 10 26 27 28 34 45 47 51 73 79 92 96 97 110 114 123 124 125 172 200 210

PATCHINEELAM.1980). These 1141

Type KG KG KAL KAL KG KG KG KG KG KG KG

KG KG & KG KG KG SL KG KG KG

Water depth (m)

Lat.

Long.

4774 4916 4779 4801 4656 4750 4321 4687 4913 4851 4769 4529 4887 4753 4583 4189 4557 4387 4377 4944 4697 4667

ll”31’59N. ll”30’40 N. 11”3(YlON. 11’34’70 N. ll”30’30 N. 04”03’30 N. 07”00’76 S. 06”59’89 S. 06’59’65 S. 06’50’65 S. 06”49’38 S. 06’59’75 s. 06’58’98 S. 06”58’70 s. 09”32’22S. 09”48’39 s. 09”50’75s. 09”55’09 s. 09L54’72S. 18”59’47S. 21-12’50s. 21”34’64S.

133”47’42W.

KG = short box corer (Reineck type). KAL = large box corer. KL = piston corer. SL = gravity corer.

133”42’30w. 133”49’80W. 133’4460 w. 133”44’32W. 134”06’40w. 131’52’83 W. 132”01’13W. 132”09’65W. 132”08’59W. 132”o(y94W. 131”55’65W. 132”07’94W. 132”08’48W. 134”OOl7 w. 134”05’42W. 133”59’46W. 133”59’97w. 134”00’35w. 161’40’76W. 160”17’48W. 160”29’81W.

ULRICH FGRSTNER and PETER STOFFERS

I142

AREAD31-36 SOUTH WCFK:

,

OCEAN

AREA F 37-W

l AREA 0 99-149 ,TAHITI

,-FIJI

AREA K 190 - 250

I

12i0°

1

I

100°

I

I

140°

Fig. 1. Sampling

Table 2. Sedimentary

C

areas and station

numbers

contents

Core No.

Core depth

Carbonate 0, ‘0

Pelagic clay

10 28

Siliceous ooze

5 10 26 27

lo-20 o-2 lo-12 30-32 surface O-10 a-20 O-20

5 5 5 5 10 2 2 2

4.21 6.26 * 7.46 7.18 3.00 3.44 3.45 3.43

Nannoiforam ooze

34

O-2 23-25

72 87

Nanno/foram ooze

45

73 79 96 97

Cl 11-15 25-30 O-l surface O-1 35-40 surface surface surface O-20

Foram/nanno ooze (marly)

110 114 123 124 125

Volcanoclastics Pelagic clay

Siliceous ooze Marly siliceous ooze

eoO

of SO/O6 cruise.

carbonate

Sediment area facies

facies distribution,

loo0

120’

(%) and total metal concentrations Fe “/,

of the samples

studied

Mn

cu

Ni

Co

Zn

ppm

ppm

ppm

ppm

ppm

22.560 37,815 26.110 25,725 3,840 6.380 1,350 470

913 1,240 745 680 357 515 370 335

961 1,302 420 257 141 252 85 72

149 76 44 33 60 105 33 18

258 394 331 337 133 170 205 176

0.70 0.34

3,130 940

169 62

85 12

21 9

57 21

89 92 85 86 86 28 0

0.44 0.34 0.60 1.39 0.85 3.17 4.22

1,690 1.325 2.500 6,450 2,685 26,680 15,200

112 52 78 244 98 1,067 582

24 29 42 166 45 822 406

9 9 16 50 26 141 156

48

2.20

10,285

336

239

102

50 31 29

1.90 2.78 2.99

8,ooo 10,700 13,500

274 394 553

196 288 312

69 99 110

20 27 31 58 36 202 158 101 79 102 117

surface surface surface surface O-2

64 87 69 75 79

2.39 1.25 2.34 2.50 I .49

8,840 3,900 8,315 10,340 5.470

253 113 236 260 159

140 48 119 153 70

59 20 50 65 31

86 39 72 97 49

172 200

surface O-l 10-12 20-22 3638

0 0 0 0 0

10.49 8.15 7.82 7.95 8.12

4,100 8.490 9,040 8.870 8,260

441 271 267 240 226

83 189 201 173 164

96 148 147 142 146

347 225 213 211 216

210

O-2 lo-12 20-22 30-32

0 0 0 0

8.04 7.97 8.23 7.95

8.460 9,520 11,530 7.064

248 272 269 217

177 210 211 140

148 159 248 135

218 215 222 285

47 92 51

Chemical fractionation of transition elements in Pacific pelagic sediments between the Clarion and Clipperton Fracture zones at water depths ranging between 4650 and 4920m and contain red-brown clay and siiiaous muds in Recent deposits. Area D is located at the northern boundary of the high productivity equatorial zone and is characterized by a high sedimentation rate (calcareous ooze). Area F lies north of the Marquesas Fracture Zone; samples from water depths between 4331 and 4913 m contain nanno/foram ooze and siliceous ooze. Area G is located within the Marquesas Fracture Zone; samples taken from water depths 3400-4189m exhibit nanno/foram ooze materials and mariy siliceous ooze. Area K is situated in the Aitutaki Passage; samples taken from about 460&5200m water depth contain red-brown clays. One sample (No. 172) consists of voicanociastic material. Most of the samples were recovered with a box grab samples with maximum sediment depths of 40m; samples from sites Nos 26 and 27 (Area C), No. 97 (Area F) and No. 124 (Area G) were taken with other sampling devices, for example, a box or piston corer. Thirty-five sediment samples from 22 stations (from different sediment depths) were selected for the present study on metal partitioning and 2 samples of micronodules (> 125 pm) from red-brown clays of Areas C and K were analyzed in the same manner. Five sedimentary facie types were thus studied for their chemical phases of transition metals: (a) uolcanoclostic muterids, a single sample from Area K; (b) red-brown pelagic clay, samples from Areas C and K; (c) siliceous ooze from Areas C and F; (d) morlr sediments, in Area F more siiiaous, in Area G more caicareous (at an average of 75% carbonate on the borderline to ‘caicareous ooze’); (e) nunnofloram ooze in Area D and F (usually more than 85% carbonate). Bulk samples from the various areas show a wide range of chemical composition (Table 2). Carbonare contenrs vary between 0 and 92% (low concentrations in Areas C and K, higher contents in Areas D, F, and G). Mangcrnese varies between 470 ppm (No. 27) and 37,815 ppm (No. 28), &. by a factor of 80; nickel concentrations lie between 12ppm and 1,302ppm; cob& between 9 and 248ppm; iron between 0.347; and 10.49”“; zinc between 20 and 347 ppm; and copper between 52 and 1.240 ppm. A statistical evaluation of the data given in Table 2 (bulk chemical analysis; n = 35) shows a distinct positive correiation between manganese, copper, and nickel (Mn-Cu +0.896. Mn-Ni +0.883. Cu-Ni +0.919), as well as betwee& iron and zinc (+0.865). Lowest values for ‘r’ are found with cobalt (Cu +0.270, Mn +0.316, Ni +0.334, Zn +0.490, Fe +0.681) indicating a different distribution of this metal compared to the other elements studied. Cobalt is relatively poor in Area C, but very high in Area K. The correlations further show that ail transition elements are diluted by higher carbonate concentrations; the decrease is particularly strong for zinc and iron (-0.862 and -0.846, respectively), but is also significant for cobalt (-0.669) nickel ( - 0.438), manganese ( -0.430) and copper ( - 0.494). When the various facies types are considered separately, however, specific developments can be seen: red-brown clays, for example, indicate a strong positive correlation between Zn and Fe, Mn, Cu. and Ni, which is not present in the carbonate-rich nanno/foram samples. METHODS Successive extraction of transition element associations was performed according lo a scheme similar to those developed for the determination of chemical forms of maninduced metal pollutants in aquatic sediments (ENGLERer al., 1974; GUPTA and CHEN, 1975), in the form proposed by F~STNER and PATCHINEELAM (1980): (1) Easily extractable metal fraction (EEF) with 0.2 M BaCl,-triethanoiamine, pH 8.1.

(2) Carbonate exchanger, pH 5.

phases

(CO1)

1143 with

acidic

cation

(3) Easily reducible fraction (ERP) with a 0.1 M hy droxyiamine hydrochloride 0.01 N HNOa, pH = 2. (4) Hydrochloric acid soluble fraction (HCi) extracted with 0.3 N HCi, pH = 1. (5) Residual metal phases (Res.) with HF/

HCiO,-digestion. (The extraction of humate associations by 0.1 N NaOH was not employed here due to an expected high conantration of labile siliaous compounds which would be attacked to an appreciable degree; see BURIQN, 1978). The analyses were performed with atomic absorption spectroscopy. Method (I) was originally introduad by JACKSON(1958) for the determination of exchangeable cations in carbonate-bearing samples; here for reasons of comparability, carbonate-free samples were investigated with the same method. Method (2) forms the only ‘seiective’ extraction step in the present sequence, since this technique should exclusively dissolve carbonate phases (LLOYD, 1954; DEIJRER et al., 1978). Extraction step (3). modified from CHESTERand HUGHES’(1967) acid-reducing agent, was first employed in soil science for analysis of the easily reducible phases (Mn-oxides and amorphous Fe-oxyhydrates) by CHAO (1972). The more stable oxides and hydroxides (e.g. poorly crystalline hydrous Fe-oxides) are dissolved with 0.3 N HCI (step 4), a method proposed by MALO (1977) after comparison of various leaching techniques used for reducible metal compounds. One major advantage of the present leaching sequence is that the carbonate fraction is extracted before dissolution of the remaining acid-reducible phases. Otherwise, the carbonate contents buffer the extractive solutions. RESULTS AND DISCUSSION

In Table 3, the data of our chemical partition studies are given for different sedimentary facies (see section entitled ‘Materials’) and are arranged in the order of decreasing iron concentrations. The volcanoclastic materials are represented only by a single sample from Area K, whereas the data for the other facies show the average contents of several samples (n = number of samples) from two different areas each. In addition, data for micronodules from Area C and Area K are given in the last two columns in Table 3. Chemical fractionation

Treatment with BaCl,-triethanolamine solution does not release significant amounts of metal from the sediment particles except for copper (and nickel in the samples of red-brown clay from Area C). Release of iron by this reagent could only be determined in carbonate-rich sediments from Area F. It cannot be assumed that copper and iron are mobilized from carbonates or Fe/?vIn-oxides due to partial dissolution by BaCl,-triethanolamine, since zinc (which is characteristically associated with carbonate phases) is not found in the leachate and both copper and iron occur in less easily reducible phases. Sorption/desorption experiments with copper and clay minerals using BaCl,-solutions without triethanolamine suggest that simple cation exchange is relatively insignificant. 11 is concluded that the high degree .of remobilization of copper is either due to specific interactions with the

ULRICH F~RSTNERand PETER SCOFFERS

1144

Table 3. Percentages of metal forms in samples from different sedimentary environments Vol~n~iasti~

Facies

Red-brown

Marly sediment

Siliceous ooze

silic.

Nanno/fo~am

mud

.pelagic clay

10.45 -

8.03 3 20 77

333 1 12 87

3.70 _ 5 38 57

2.46 2 3 43 52

i.Yi 2 3 55 40

0.52 3 3 30 64

0.56 2 3 4 47 44

3.02 1 81 18

7.30 3 78 19

Cd.?.

Micronodules

ooze

Area “= Carbonate Fe “‘,

Res. “0

12

6.28 _ 3 17 80

Mn s; co* 4, ERP 9; HCl :a Res. %

0.4 I 64 29 7

2.81 89 10 1

0.89 80 12 8

030

2.09

1.06

0.72

0.20

U.?1

X86

16.59

84 7 9

s; 10

8: 9

8; 10

1

1

1

9: 7 1

8; 9 1

79 20 1

93 6 1

Cu ppm EEF 9’ co1 9 ERP O0 HCl “;, Res. ‘4

441 5 3 29 63

895 6 24 29 41

251 12 14 29 45

394 8 13 29 50

825 8 I 31 42 19

389 11 11 16 37 25

210 15 7 17 47 14

I16 20 8 78 ‘8 16

85 19 7 24 29 21

12.665 1.465 2 _19 77 2

4 14 76 6

Ni ppm EEF 0; ERP “3, HCI ‘0 Res. p,,

83 -. 47 29 24

735 5 81 10 4

183 56 11 33

138 43 18 39

614 -83 13 4

259 73 14 5

116 75 20 5

49 -80 5 15

34 87 3 10

14.465 1 45 53 2

5.080 1 64 32 3

Co ppm ERP “,,

96 65 27 8

‘h

i?Y

34

13Y

Y?

40

79 17 1

68 11 21

61 5 34

83 13 4

77 19 -1

16 ‘0 4

n.a. n.a. n.a.

il.& n.a. n.a.

45 54

59 39

1

1

347 9 41 50

330 _ 26 24 50

226 17 21 62

171 -_ 20 22 58

180 35 33 32

~~~ 16 16 37 31

67 ii 19 46 24

39 28 15 29 28

?Y 27 18 35 20

I.309 11 86 3

405 -30 60 10

EEF x+ co* ‘:, ERP “;,

2:

HCl “,;

HCl I’,> Res. ‘I,,

Zfi mm co* “; ERP ‘0

HCI “; Res. ?,

15

i?

I .YX.i

?.f,jS

* EEF = easily extractabb fraction. CO, = carbonate fraction. ERP = easily reducible phases. HCI = hydrochloric acid soluble. Res. = residual fraction.

triethanolamine component or that it exhibits characteristic forms which can be easily stripped from the particle’s surface. Zn and Cu are associated to some extent with the carbonate phase-28% and 1IT/, respectively in the calcareous sediments from Areas D and F. For Mn in the same areas an amount of 40,; has been determined. This is a characteristic difference in respect to the data from other environments (e.g. near-shore marine and lacustrine deposits; PATCHWELAM and F~RSTNER, 1977; SCWMOLL and F~~RSTNER,I979), where bonding of Mn by carbonate is often predominant. It becomes evident that iron is mainly associated with the residual fraction and. to a Iesser extent, with the HCI-sotubie phases. Enr~cbment of copper and

zinc equally takes place in the rusilv reducibIe and hydrochloric acid phases as well as in the residuul jmrion. That this occurs suggests that a considerable portion of the higher concentrations of the latter three elements locally occurring in pelagic sediments is affected by detrital influences. At higher bulk concentrations of Cu and Zn (particularly in nodules and micronoduies), the accumulative phases are in the 0.3 N HCI soluble fraction. On the other hand. even small enrichments of manganese. nickel, and cobalt are mainly associated with the easily reducible fractions (cobalt can also be enriched to a certain extent in the HCl fraction), i.e. with authigenic phases. Large differences between the minimum and maximum concentrations of Mn. Ni, an’d Co in the easily reducible fraction and of Mn and Co in the HCI extractable

Chemical fractionation of transition elements in Pacific pelagic sediments fraction may primarily be explained as characteristic infiuences of the sedimentary environment, e.g. dissolution of siliceous and calcareous shells of organisms (GLASBY et al., 1980) on the authigenic enrichment of these elements. Area1 variations Volcanoclastic material from Area K exhibits rela-

tively higher percentages of residually-bound metals and lower proportions of Fe, Mn, Cu, Ni, Co, and Zn in the easily reducible fractions than in the red-brown pelagic clays from the same area. Comparison of redbrown pelagic clu_vs from two provinces show that bulk concentrations of Mn. Cu, Ni, and Zn in Area C are higher and that percentages of these metals in the residual fractions are lower than in Area K, suggesting a distinct detrital influence on the distribution of the metal concentrations in the latter region. Even more significant than for this facies are the differences of both bulk composition and chemical associations of siliceous ooze in Areas C and F; the much higher concentrations of Mn, Cu, Ni, and Co in the siliceous muds from Area F coincide with significantly lower percentages of the residual fractions of these elements. With respect to the chemical forms of Mn and Ni, the siliceous ooze samples from Area F resemble the redbrown clays from Area K. These effects may be a result of varying admixtures of volcanoclastic components to both red-brown pelagic clays and siliceous muds in the different areas studied. On the other hand, there are relatively small area1 differencts in the chemical fractions of the calcareous sediments, both for marly sediments in Areas F and G and for the nannolforam ooze deposits in Areas D and F. These facies differ in that higher percentages of easily reducible phases and smaller proportions of HCl soluble phases of copper and nickel are established in the nanno/foram ooze. Except for the higher percentages of carbonate associations of Fe, Mn, Cu, and Zn, the distribution of the other metal fractions in carbonate-rich deposits is not significantly different from those in the red-brown clay, despite the much lower (l/5 to l/20) total metal concentrations. Metal enrichment in authigenic phases

In earlier studies on the geochemistry of pelagic sediments, a separation of ‘residual’ from ‘hydroge-

1145

neous’ metal forms is undertaken , usually with the aid of the acid-reducing agent (e.g. CHESTERand HUGHES.1967). Generally, the hydrogeneous character of trace metals was found to decrease in the order: Mn > Co > Ni > Cu > Zn > Fe The percentages of the hydrogeneous fraction, however, is mostly higher in the Pacific samples (CHFSTER and HUGHES, 1967; SAYLES et al., 1975) than in the pelagic sediments from the North Atlantic (CHESTER and MESSHA-HANNA,1970; HOROWITZ,1974; HOROWITZ and CRONAN, 1976), as there is less input of detrital material into the North and South Pacific pelagic areas. Our data confirm this sequence of decreasing non-residual fractions for the different sedimentary facies and for the samples of micronodules (Table 4). Diugenetic effects

Approximately 30”/, of the metals in the volcanoelastic sediment is associated with the HCl soluble fraction; in the other sedimentary facies, i.e. redbrown clays, siliceous ooze, marly sediments and nanno-foram ooze a distinct difference is indicated between the elements Fe, Cd, and Zn on the one hand, and Mn, Ni, and Co on the other, in that the former group contains characteristically higher percentages of HCl soluble associations (2o-400/,) compared to the elements in the latter group (5-20”/,). For the micronodules the respective percentages of HClsoluble phases are ?O-80”/, for Fe, Cu and Zn, and 20-45x for Mn, Ni and Co. Whereas the percentages of Ni and Co indicate a significant increase in the easily reducible extructunt compared to the HCI treatment for the above-mentioned sedimentary facies, the same is not valid for the micronodule samples. One possible explanation for this effect (which is also clearly seen for Cu in relation to the nodules of Area K) is the mechanism of recrystallization of minerals in the nodule material, which likely effects a lower leachability of the less acid, easily reducing agent than is the case for the amorphous oxides and hydroxides in the red-brown clays, siliceous and foraminiferous oozes. We have tried to confirm these findings by studying sediment samples taken from different depths of short cores. However, the method of differentiating the

Table 4. Metals in non-residual fractions (percent of total sediment) in different sedimentary facies of Pacific pelagic deposits Facies

Volcanoclastic material (n = 1J Red-brown pelagic clay (n = 12) Siliceous ooze (n = 6) Marly sediments (n = 9) Nannoiforam ooze (n = 7) Micronodules (n = 2)

Mn 0, 10

Co 0, /0

Ni %

Cu x

Zn %

Fe %

93 94 94 99 99 99

92 85 76 96 n.a. 98

76 77 73 95 89 97

37 56 60 81 80 96

50 42 51 73 78 93

28 22 23 55 50 81

ULRICHF~RSTNERand PETXRSTOFFERS

1146

easily and moderately acid soluble phases by chemical leaching seems to be as yet too inaccurate to establish the latter effects discussed. There is, however, a general decrease of the residual bonding, i.e. of the acidic leachability, of Cu in all cores investigated and of Mn, Ni. Zn, Co, and Fe in many examples with core

depth, which could suggest that diagenetic processes affect chemical associations of transition elements subsequent to deposition. Acknowlrdgemenrs-We are grateful to the German Research Society for its financial support, and we are indebted to our colleagues and the crew of the RV Sonne during the cruise SO-O&l/2 (chief scientist Professor Dr FRIEDRICH) for their help. G.P. GLASBYreviewed the manuscript and provided valuable suggestions. Mrs M. HILB~G did the chemical analyses and D. GODFREYkindly assisted in the preparation of the manuscript.

REFERENCES

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