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Authigenic transition elements in Pacific pelagic clays
Geochimxa
et Cosmochimxa
Acta. 1976. Vol. 40. pp. 425 lo 434. Pergamon
Press Printed
in Great Britain
Authigenic transition elements in Pacific pelagic clays S. KRISHNASWAMI Physical Research Laboratory, Ahmedabad-380 009, India (Received 11 February 1975; accepted in revised form 16 October 1975) Abstract-The
concentrations of SC, Ti, Fe, Mn. Co, Ni, Cu, La, Th and U have been measured in several Pacific pelagic clays having widely different accumulation rates, 0.49.0 mm/lo’ yr. The authigenic fractions and deposition rates of these elements have been estimated from the measured concentrations using various models. The results show that in Pacific clays about 90% Mn, 80”/, Co and Ni and 50% Cu are authigenic whereas the major fraction (290%) of SC, Ti, Fe, La, Th and U are of detrital origin. Anticorrelation between the clay accumulation rates and the concentrations of Mn, Co, Ni and Cu is observed. This suggests a uniform authigenic deposition of these elements superimposed on varying amounts of detrital materials. The concentrations of SC, Ti and Th are almost independent of sedimentation rates, indicating that their authigenic deposition is small compared to their detrital contribution. Comparison of the authigenic deposition and river input rates shows that Mn, Co and Ni are accumulating in excess of their supply by factors of 2-10, whereas the converse is true for Cu and U. Additional sources to account for the budgetary discrepancies of Mn, Co and Ni are discussed, with particular reference to in situ leaching of detrital phases transported to the oceans via rivers.
INTRODUCTION
To DELINEATEthe geochemical cycle and balance of various elements in the marine environment it is essential to have a better knowledge of their authigenie concentrations and deposition rates on the ocean floor. Though various techniques to estimate the detrital and authigenic fractions of deep-sea sediments have been reported (GOLDBERG and ARRHJNUS, 1958; CHESIXR and HUGHES, 1967), available data on the authigenic deposition rates of elements are not abundant (BENDERet al., 1966; KRISHNASWAMI and LAL, 1972). Hence it was thought worthwhile to study systematically the distribution of a select group of elements in radiometrically dated Pacific pelagic clays, with a view to quantitatively estimate their authigenic deposition rates. The elements measured are Mn, Co, Ni, Cu, U, SC, Ti, Fe, La and Th. The selection of these elements was based on the observation that some of them (Mn, Co, Ni, Cu and U) exhibit marine budgetary discrepancies (B~STROU, 1967; TUREKIAN, 1968; RILEY and CHESTER, 1971) while for the others (SC, Ti, Fe, La and Th) no data on the authigenic deposition rates were available. The techniques of measurement and the models to estimate the authigenic concentrations are discussed. Based on the authigenic concentrations an attempt has been made to evaluate their marine geochemical balance.
MATERIALS
AND
METHODS
The relevant details of the sediment and nodule samples analysed are given in Table l(a) and (b), respectively. Since
the extent of incorporation or rejection of different elements by biogenic phases in marine sediments are not well understood, only clays were studied in this work. [The CaCO, conceptrations of all the cores listed in Table l(a) is
to
425
S.
426 Table 1 (a). Physical data and sedimentation deep-sea sediments studied Water
Core MSN-96+
L.xPtion
depth
(m)
Sh'S
KRISHNASWAMI
rates of the
Sedimentation rate*(mm/lO’y) (C) (a) 01
0.4
0. 6
4o%s
5120
0.5
1.4
4620
0.4
0. 9
TF-1 TF-2 TF-3 TF-4
13Z049’W DWBG-30++
19o5o’s 148O39’W
v-19-259**
11%2’S
5528
9’03~s
4960
0. 6
NOVA-I&16+
0°14.1’N
5160
1.7
6331
1.4
5100
1.9
176Y. 9’W NOVA-IU-13’
03’55.6’N
+
(mm/lo6
Y)
w
13O53’S
3623
1.0
3695
1.0
150°35’W 1
ZP-50++
13O53’S 150°35’W
2P-52++
9’57’N 131°47’W
4930
7.3
CARR-SD+
10’39’N 10845’W
5216
NM
DODO-SD+
1a016’N 161’5O’W
5500
1.0
6A**
19’39’N 113O44’W
4000
4.0
TRIPOD-2D+
20°45’N 112’47’W
3000
4.0
DH-2+
21’50’N 115’12’W
3430
NM
34O54’N 160’19’W
5400
4. 0
40’16’N 170°20’E
3000
1.4
1.6
174°52’E
Growth rate
4770
!xP s
1.6
165O45’W CAP-6 BG++
**
95O
98Ol’W DWBG-52++
and their
(m) E-17 -36
4350
nodules
Water depth
Location
Nodule code
2.3
4154
42oo2’s
I (b). Details of manganese growth rates
114O15’W DWHG -49++
Table
119°41. 3’W MSN-14x+
B020’N 145’24’W
CAP-49 BG++
9’1l’N
4410
1.6
2.4
124O9’W NOVA-III-lo+
O&3.
SN
1.0
6105
116°41. 3’W CAP-SOBG++
14’5S’N
4270
1. 0
2.1
4310
1.5
2.2
4400
1.0
2.0
124’12’W DWBG-Z++
21°2?.2’N 126’43’ W
WIG-5++
28°37.6’N
V21-D2
**
ZETES-3D+
124’25. VW v-21-71**
21°54’N
5660
2.4
162%1’E SOB-15++
28%.9’N
3455
9.0
13.0
3900
9.0
13.0
6360
1.5
3.0
117°31. 4’W FAN -BG-7++
30’43’N 119O5O’W
CK-4++
42’30’N 16Z”06. 2’W
’ TIFR collection. + + SIO collection, and ** LDGO collection. *All sedimentation rates are based on “‘Th chronology.
(a) GOLDBERG and KOIDE (1962). (b)/ KU et al. (1968). The sedimentation rates of all cores excluding V-18-258 and V-21-71 are recalculated values from the results of GOLDBERG and KOIDE(1962). The major correction factor is due to shortening of open barrel cores compared to piston cores. (c) AMINet al. (1975).
** LDGO collection, + TIFR collection and + + SIO collection. USGS reference rocks are similar to those reported in the literature (FLANAGAN, 1969; FLEISCHER, 1969). Duplicate measurements of the concentrations in the reference rocks and marine samples were in agreement within 210%. The average concentrations of SC, Ti. Fe, Mn, Co, Ni, Cu, La, Th and U in Pacific pelagic clays based on the present measurements are given in Table 5. The deduced averages are in moderate agreement with the data of CRONAN (1969) and KRISHNASWAMI and LAL (1972).
Table 2. Results of analysis of USGS reference samples Co”ce”tratton
W-l Present Reported values* work
Element
34.6
SC
Mn
Fe(74 model 303 atomic absorption spectrophotometer. Along with the samples USGS reference rocks and reagent blanks were also measured. RESULTS The results of the measurements of USGS rocks, sediments and nodules are given in Tables 2, 3 and 4, respectively. The measured concentrations of various elements in
33-37
13.50
1300-1400
7.1
7. 6-1.8
CO
49.5
41 -54
NL
61
TO-90
C”
117
112-122
La
11
10-21
In (ppm.
G-2 Present Rapotied rork “*“e&l* 3. 1 210 1. 6
3. 0
rock
wt)
ECR - 1 Present Reported aork vpluo~: 26.6
31-33
1950
265 1.66
-
ND
4. 3
36.2
-
13.7
-
9. 3 36-37 30
ND
10-11
-
15-27
89.6
80-64
22.5
23-24
* From FLANAGAN (1969) and FLEISCHER (1969). Results of measurements directly comparable to the techniques used in this study are given.
N-Not
detectable.
427
Authigenic transition elements in Pacific pelagic clays Table 3. Elemental concentrations
of Pacific pelagic clays
Depth Concentration of elementsInppm.dry weight;unlessstated
interval
Core
analyzed SC I___\
Ti
Mn
Fe(%)
3940
Co
Ni
Cu
La
Th+
U*
MSN-96
10-12.5
3980
4.2
-
64
67
15
1.4
DWHG-49
IO-20
la
3230 23000
a.5
ias
590
600
15
10.0
DWBG-62
20-30
23
3600
3.8
96
212
340
33
10.6
-
DWBG-30
20-25
20
a.3
-
306
335
102
-
14800
192 250
336
9.5 -
_
V-16-256
16-20
24
a900
la200
166 242
311
aa
50-53
_
_
13200
169 255
302
14.0 __
CAP-BBC
10-20
22
5600
10200
a.0
Qa 205
314
43
7.9
NOVA-la
16-16
25.5 5500
6200
5.3
91 350
519
64
7.0
-
NOVA-16
6-12
23
3960
6050
5.8
56
117
278
37
7.9
1.3
NOVA-13
5 -8.5
26
3540
5160
6.0
86
156
330
40
11.9
1.3
MSN 14lG
6-8
31
4000
1030
5.4
31
a3
256
34
12.3
1.6
STYX-5B
lo-la
31.5
3230
10920
3.6
-
516
455
129
6.2
-
CAP-4QBG
10-20
26
4400
5100
5.2
a.4
-
NOVA-10
10-12
26
4600
1100
5.2
-
CAP-5OBG
30-34
21
3150
4015
4.1
-
DWBG-2
10-20
-
5100
5550
5.4
WIG-5
10-13
14
5040
4670
4.6
SOB-15
10-14
16
5340
FANBG-7
10-15
17
5200
CK-4
16-20
-
5040
-
2-9.5
20-25 v-21-71
ia
55-62
5430
16400 10550
a.7
1.6 -
3.1
-
798
64
231
523
60
11.1
-
191
363
57
11.0
-
la1
la2
271
42
12.0
-
-
209
191
32
12.6
-
119 230
4.0
16 145
136
30
9.1
4.4
29
163
163
30
12.5
-
1600
4.0
31
94
163
32
11.0
-
5300
4600
4.3
52
162
172
36
5000
105 172
205
15.4 __
2.1
-
-
*Th and U data compiled from GOLDBERG and KOIDE (1962),Ku (1966),Ku et al. (1968) and AMIN et al. (1975). The reported *32Th values by La Jolla group were multiplied by 15 to correct for HCI leaching efficiency (GOLDBERG and KOIDE, 1962).
DISCUSSION Estimation of authigenic deposition rates The main aim of the present investigation is to estimate the authigenic deposition rates of various elements on the ocean floor, with a view to evaluate their marine geochemical balance. Since in the past
the main emphasis has been in studying the distribution of elements among the various components of deep-sea sediments, available data on the authigenic deposition rates are sparse. A systematic pattern between the clay accumulation rates and the concentrations of various elements in pelagic clays has emerged from the results
Table 4. Chemical composition of radiometrically dated Pacific manganese nodules Nodulecode sc
Ti
Concentrations inppm dry weight,unlessstated ?vlo La Th* Ni Cu Mn(k) Fe(X) Co
u*
ti20w**
E-11-36
NM
1200
36.0
15.6
1660
6000
2800
650
176
54.5
TF-2
il.8
11400
16.6
20.0
4200
3020
1940
NM
350
22.0
15.0
21.4
20.0
9.0
11.2
2P-50
14.4 13400
16.0
20.5
3900
3140
1450
160
232
10.5
20.5
2P-62
NM
2140
21.6
4.1
1720
14400
9500
940
76
NM
7.4
12.5
CARR-QD
11
6BOO
42
10.2
960
2400
6500
NM
131
NM
NM
11.8
DODO-QD
NM
20.4
5200
3100
618
1050
244
35.0
9.0
24.0 10.6
12000 39.8
6A
la. 9
2690
25.6
9.4
1210
11700
9210
1020
100
24.5
1.0
TRIPOD-2D
10.2
6450
16.9
23.0
3610
2530
211
590
370
38.0
16.0
6.9
NM
30.0
16.1
960
NM
6100
NM
200
NM
NM
16.2
1600
15.6
15.4
3220
5260
3680
660
229
122.0
5.6
13.1
6450
26.5
11.4
5450
455
2750
405
40.0
17.0
21.1
DH-2 V21-D2 ZETBS-3D
a.5 NM
6.5
NM-Not measured. *Data for U and Th concentrations are compiled from BHAT et al. (1973) and Ku and BROECKER (1969).For nodules 2P-50 and 2P-52 are determined in the present study. ** Represents weight loss of air dried nodule samples at 110°C for 2 hr.
428
S. KRISHNASWAMI Table 5. Average concentration
reliable results for those elements whose abundances in shales or near-shore sediments are small compared to that in pelagic clays. This case is realistic only for Mn. Co and Cu where the correction is less than Y,,. For Ni and SC. where C,C,, _ Z--3. the estimates may be only semi-quantitative. For Fe. Ti, La. Th and U where C, _ C, no reliable estimates of authigenie concentrations can be made. Since the chemical composition of the shales and the shelf sediments are similar, the deduced authigenic cmcentrations by both these models follow the same pattern.
of SC, Ti. Mn. Fe, Co, Ni, Cu, La, Th and U in Pacific sediments Concentration
Element
SC
Present study*
of element(ppm. wt) Reported averages** (a)
(b)
22.3
28
Ti
4v7a+
4548
4500
Mn
7430
4784
7800
Fe (% wt)
5.44
5.07
5.10
87
101
Ni
224
211
242
CU
338
323
430
CO
La
52
Th
10.4
U
2
132
115 12.3 2.2
*
Average of 20 clay sediments. **(a) CRONAN (1969) and (b) KRISHNAS-
WAMIand LAL (1972). +For estimating the mean Ti concentration the result of DWBG-30 is excluded (Table 3).
of this work. A model for the deposition of elements (henceforth designated as ‘constant flux model’) has evolved from this pattern. Based on this model the authigenic deposition rates and detrital fractions of elements can be evaluated directly. Additionally, the observed distribution of various elements in pelagic clays and the occurrence of deposits like manganese nodules can be understood in terms of this model. The reported methods to estimate the authigenic and detrital fractions of deep-sea sediments are based on a twocomponent system for pelagic clays. Thus the total concentration of any element, C,, in the sediment is the sum of the contributions from these two fractions, i.e. c, = c, + Cd.
(1)
where C is the concentration of the element and the suffixes t. a, and d represent total, authigenic and detrital phases. The problem is to ascertain the contributions of either C, or Cd to the total measured value, C,. For the sake of completeness the assumptions of the commonly adopted approaches for estimating the authigenic concentrations and the deduced results using them are discussed briefly below. The results of the ‘constant flux model’ and its implications are presented subsequently.
GOLDBERG and ARKHI-~\;I~Is(195X) observed that in the dissolution rate (g,‘m’ hr) of marine deposits (manganese nodule, calcite and apatite) in chelating agents like EDTA was faster than that of terrestrial minerals (feldspar, goethytc. glass and rutile). Using similar techniques. CHISTEK and Hucrq~s (1967) and CHESTER and MESSIHA-HANNA (1970) have estimated the lithogenous fraction of several Atlantic deep-sea sediments. The estimation of the authigenic fraction of elements using this technique is based on their preferential dissolution in selected chemicals. In this work, the leaching of the samples was done by boiling them under reflux with ammonium salt of EDTA at pH = X. The samples were repeatedly boiled to ensure complete leaching. The results of these measurements (Table 7) show that a large fraction of (3 70”,,) of Mn. Co and Ni in the Pacific clays can be preferentially dissolved in EDTA. The deduced authigenic fractions of various elements (Table 7) follow the same pattern as that observed for the North Pacific and Atlantic sediments measured using similar technique (CHESTER and HI~GHES. 1969: CHESTERand
Table 6. Estimated authigenic concentrations of element based on the shale and shelf sediment correction methods Element
Shales
ivln
7430
850
CU
338
45
3b
CO
87
1La
13
Ni
224
(iR
46
23
SC Ti
4679
Fe (% wt)
5.44
13 4600 4. 72
La
52
92
Th
10. 4
12
2
II
In this approach the value of Cd is obtained by assuming the composition of the detrital fraction of sediments to be the same as that of shales (BENDER et ul., 1966; KRISHNASWAMIand LAL, 1972) or of sediments collected from near-shore regions. Table 6 gives the estimated authigenic concentrations based on this model. This approach gives
C’uncentration (ppm. wt) Authigernc;:* Near shore sediments (b) (a)
Pat ifir* sedments
*
810
6580
il. 5 4085 4.8
293
68 156 10
6620 302
74 178 11.5
(78)
(593)
(0.72)
(0.64)
7”
::. 7
From Table 5. The data for shales and near-shore sediare from TUREKIAX and WEDEPOHL(1961) and
ments
KRISHNASWAMI
(1973). ** Using relation 1. (al and (b) represent the estimates based on shale and shelf sediment correction methods. respectively. The values in paranthesis could be in large error since they represent the difference of two approximately equal numbers.
Authigenic transition elements in Pacific pelagic clays Table 7. Average EDTA leachable concentrations ments in Pacific clays* Element
Mtl
%Element leachable in EDTA
78
of ele-
Detrital
5800
1830
CO
73
64
23
Ni
65
146
78
CU
43
145
193
Fe (% wt)
18
1
4.44
*Based on the analyses of 10 cores: MSN-96, DWHG-49, DWHG-52, DWBG-30, V-18-258, CAP-SBG, NOVA-18, NOVA-10 and V-21-71 (Table la). MESSIHA-HANNA,
Table 8. Comparison of the estimated authigenic concentrations of elements based on commonly adopted methods* Estimated authigenicconcentration(ppm. wt)
Mean concentration CUDI& .. . wt) Authigenic
1970).
Excluding Cu, the measured authigenic concentrations follow the same trend as that of the shale model. The detrital concentration of Cu deduced by the leaching technique is higher by about a factor of 2-3 than that estimated by the shale model, an observation similar to that of Ck~sTER and HUGHES (1969). The cause for the observed discrepancy is not clear. It is likely that the non-leachable fraction of Cu in deep-sea clays is of eolian or biogenous origin. Manganese nodule model The authigenic concentrations of elements are estimated using this model on the assumption that their authigenic precipitation rates on the pelagic clays and manganese nodules are the same (KRISHNASWAMI and LAL, 1972). The observation that the authigenic accumulation rates of Mn, Cu, Ni, Co. and of the radioisotopes “Be and 230Th in both sediments and nodules are similar within a factor of 2-3 (BENDER et al.. 1970; SOMAYAJULU et al., 1971; KRISHNASWAMI and LAL, 1972; BHAT et al., 1973) supports this assumption. In this model the authigenic concentrations are calculated using the fbllowing relation (KRISHNASWAMI and LAL, 1972; KRISHNASWAMI, 1973):
where S is the clay accumulation rate, p is the density, (subscripts s and n refer to sediments and nodules, respectively), E is the fraction of time for which the nodules grow on an average, G is time averaged growth rate of nodules and& is the geometry factor for the nodule exposure. The value of R is calculated to be about 10, using the following numerical values for the various parameters. S = 2-3 mm/lo3 yr, ps = 0.5 g/cm3, E = 0.1, G = 3 mm/lo6 yr, pn = 2.5g/cm3 and fw = 2. Considering the uncertainties in the values of p, K and fw the calculated ratio of 10 is considered to be in agreement with the mean observed ratio of 25 (range l&43) for elements with different degrees of chemical reactivities, Mn, Co, Ni,
429
Element
(i)
(ii)
SC
10
12
Ti
‘18
593
(iii)
(iv)
0. 5
Mont probable
authigenic concentration
0.5
310
3 00
Mn
6560
6620
5600
10900
7000
Fe
7200
6400
9600
6400
1500
CO
68
14
64
120
60
Ni
156
116
146
226
175
CU
293
302
145
160
225
La
9
10
Th
1.6
2
”
0.4
0.4
* (i) Shale method, (ii) shelf sediment method, (iii) leaching method and (iv) nodule method. The estimated authigenie concentration of SC, Ti and Fe by methods (i) and (ii) could be in large error (see text for method of calculation).
Cu, “Be and Th. In view of this agreement, the authigenie concentration of various elements have been calculated using a value of 25 for R. The estimated values are givenjn Table 8.
Comparison of the estimated authigenic concentrations based on various models The authigenic concentrations of Mn, Co, Ni and Cu are easily estimated by all the methods. The deduced values for Mn, Co, Ni, Cu, Fe and Ti by the various methods are in modest agreement. For SC, La, Th and U. only the manganese nodule method could give estimates of the authigenic concentrations. Though the estimates for Mn, Co, Ni and Cu by this method are in agreement with the results of other models, it is likely that some of these elements may be preferentially incorporated into the nodule matrix. It is therefore important to confirm the deductions obtained by this method by some independent approach. The most probable authigenic concentrations for the elements studied are also listed in Table 8. The estimates for SC, Ti, La, Th and U are based mainly on the nodule method, for the others it is the average of all the techniques. Constant Jlux model This model is based on the assumption of uniform authigenic deposition rate of an element over the ocean floor. An anticorrelation between the authigenie concentration, C,, and sedimentation rate, S, is expected, if the authigenic deposition rate of an element is uniform, i.e.:
c, = g s
430
S. KRISHNASWAMI
In such case the total concentration, ment would be:
C,, in the sedi-
C,=C,+C,=s:,+rd.
(4)
s
where K is the authigenic deposition rate (g/cm” yr), ps is the in situ density of the sediment (g/cm3) and S is the sedimentation rate (cm/yr). The assumption of this model is expected to hold good for elements which are homogeneously distributed in the ocean, i.e. whose residence times are comparable to or more than the oceanic mixing times. Mn. Co, Ni. Cu and U should fall in this category. For SC. Ti, La and Th. which are chemically more reactive and have short residence times, the assumption of uniform deposition may be questionable. The available data on the vertical and geographical distribution of these elements in sea water are sparse and hence it is dificult to make a critical judgement on the nature of their distribution. BENDER et u[. (1966) observed an almost constant accumulation rate for Mn in cores in which both the Mn concentrations and the sedimentation rates vary over an order of magnitude. Later work (BENDER et ul., 1970) on different types of pelagic sediments (red clays, calcareous and siliceous oozes) showed more scatter in the accumulation rate of Mn. It is likely that part of the scatter in their estimates may be due to the assumption that calcite and opal are Mn-free diluents (BLACK, 1965; BOSTROMand FISHER, 1972). Additional uncertainty in their estimates may result from the difficulty in assigning sedimentation rates by the magnetic reversal technique in which there is no accurate way of compensating for the loss of core tops.
The simplest correlation is expected for 130Th which is uniformly produced in the water by the decay of uranium and precipitated to the ocean floor. The terrigenous supply of 230Th is small compared to its in situ production from sea water, since its concentration in rivers (soluble and particulate) is very low (MOORE, 1967; SCOTT, 1968). Figure 1 shows the variation of the surface 13’Th concentration in sediments as a function of the inverse of sedimentation rate (only cores which have an integrated Z30Th activity of 2800 dpm/cm” and which show an undisturbed exponential decay of 230Th with depth are plotted). The data for Fig. 1 have been compiled from GOLDBERG and KOIDE (1962, 19631, GOLDBERG er (11. (1963.1964). GOLDBERGand GRIFFIN (1964), Ku (1966), Ku et ul. (1968) and AMIN et al. (1975). The 230Th concentrations published by the La Jolla group have been multiplied by a factor of I.5 to correct for incomplete recovery of thorium isotopes in the acid leaching procedure (GOLDBERGand KOIDE. 1962). It is evident from Fig. 1 that the surface 230Th concentration is anticorrelated with the sedimentation rate as expected from relation (2). It must be mentioned here that even if the sedimentation rates as recalculated by Ku et al. (1968) are used the anticorrelation pattern is still obtained. The precipitation rates of 13’Th in the Pacific, Atlantic and Indian oceans have been calculated from the slope of the line in Fig. 1 and using a value of 0.5 g/cm3 for in situ density. The estimated values range between 8.9-13.7 and 12%13.5 dpm/cm’ lo3 yr for the Pacific and Atlantic oceans. respectively, depending on the sedimentation rates used. The higher deposition rates are associated with the revised sedimentation rates of Ku et al.
ATLANTIC
and
INDIAN -
l ‘/S),
INVERSE
OF
SEDIMENTATION
RATE
400
IO’yr/cm
Fig. 1. Plot of surface 230Th concentration (dpm/g) vs inverse sedimentation rate (lo3 yr/cm) for cores from the Pacific, Atlantic and Indian oceans. Only cores showing exponential decay of 230Th with depth and having an integrated 230Th activity of 2 8OOdpm/cm’ are plotted. The anticorrelation between clay accumulation rate and surface 230Th concentration is clearly evident. The *30Th deposition rate deduced from thee slope of the line range between 8 and 13 dpm/cm’ 10” yr.
Authigenic transition elements in Pacific pelagic clays
0
(Vd*INVERSE
10
OF SEDIMENTATION
A “‘OO20 RATE
431
10 IO’,,~/~,,,
Fig. 2. Scatter diagrams of the concentrations of Fe, Ni, Cu, Mn, Co, SC, Ti and Th in dated Pacific pelagic clays against inverse sedimentation rates. For plotting the revised sedimeentation rates of Ku et al. (1968) have been used. The lines drawn are least square fits for the data points. As is evident, the concentrations of Mn, Co, Ni, Cu and Fe are anticorrelated with the sedimentation rates. The concentrations of SC,Ti and Th are almost independent of sedimentation rates. The deduced authigenic deposition rates and the detrital component of these elements in pelagic clays are given in Table 9.
(1968). The calculated deposition rate of 230Th on the ocean floor is in agreement with its production rate, 8-9dpm/cn? lo3 yr. The variation of the concentrations of Mn, Ni, Cu, Co, Fe, Ti, Th and SC, in 18 cores as a function of sedimentation rate is plotted in Fig. 2. The results show that the concentrations of Mn, Co, Ni, Fe and Cu are anticorrelated with the sedimentation rate. This is consistent with the model of uniform authigenie deposition superimposed on a background of detrital input. The concentrations of SC, Ti and Th are almost independent of sedimentation rates. The latter observation is expected for those elements whose authigenic concentrations are small compared to their detrital contributions. It is apparent from the data (Fig. 2) that in sediments with clay accumulation rates exceeding about 0.5 g/cm2 lo3 yr (corresponding to about 10 mm/lo3 yr) the authigenic concentrations of elements in them would be small, i.e. C, N Cd. In such cases the elemental abundances in sediments would be the same as that in the detrital component (shales) and would be independent of sedimentation rate. However, the total deposition rate of the element would be positively correlated with the sedimentation rate. The results of TUREKIAN and SHLJTZ(1965) who observed a positive correlation
between trace element and clay accumulation rates in Atlantic calcareous cores fall in this category. The other extreme, i.e. deposition of purely authigenic material would result when the detrital sedimentation rate, S, is very small. The occurrence of ferromanganese minerals in regions of low detrital sedimentation is consistent with this expectation. The authigenic deposition rates and detrital concentrations of these elements are estimated from the slope and intercept of the best fit lines in Fig. 2. These calculations are carried out using the sedimentation rates reported by various groups as well as using the revised rates of Ku et al. (1968) (Table 9). In general, for all elements studied, higher authigenic deposition rates and lower detrital concentrations are deduced using the revised sedimentation rates (Table 9). Marine geochemical balance of transition elements
Table 10 gives the calculated authigenic deposition ,rates of elements in pelagic clays along with their supply rates via rivers. The best estimates of authigenic deposition rates given in Table 10 is based mainly on the constant flux model. The results (Table 10) show that Mn, Co and Ni are depositing in excess of their supply by factors of 2-10 whereas the removal rate of Cu and U are
432
S. KRISHNASWAMI
RENARD(1891) suggested submarine volcanism as a source of elements to the oceans. Though a considerable amount of work has been reported on this subDetrital concentration Au thigenic precipitation ject, no quantitative estimates for input rates of eleElement (ppm. wt) unless stated rate ( fl g/J 103 yj* ments by submarine volcanism are available. The imib) (a) (a) (b) portance of eolian dust as source of trace elements to the deep-sea sediments has been discussed recently Mn 2067 240 650 (WINDOM, 1970; CHESTERand JOHNSON,1971). Based Fe@ wt) 4.33 3.8 640 1500 on the analyses of airborne dust over the Atlantic CO 46 31 2.3 5 and Pacific thev conclude that the concentrations of Ni 92 51 5.1 12.6 Mn. Co and NE in the dust material are not adequate cu 224 169 5.1 12.8 to account for their supply to pelagic clays. La 30.5 24.4 0. 9 1.9 Recently the significance of river suspended load SC 22.1 21 -+ 0. 07 as a source of trace metals to the oceans has been Ti 5262 5291 recognized. The major fraction of solids introduced Th 11.6 11.3 to the oceans are weathered materials from the continents. Elements present in these solids include those (a) and (b) refer to estimates deduced using the original in the lattice positions of the minerals and those and revised sedimentation rates (see text). which are retained on their surfaces by adsorptionion * Calculated from the slope of the least square lines (Fig. exchange processes, The available data on the elemen‘I. tal abundances in river suspended materials (T~IKEK+ In these cases the deposition rates could not be estimated since slopes were negative (Fig. 2). IA~Vand SCOTT, 1967; MARTIN rf ~rl.. 1973) suggest that many of the transition metals are enriched in them compared to shales and the detritai fraction of about an order of magnitude less than their input. deep-sea sediments. The fate of these adsorbed eleBased on the results of three Atlantic cores, TUREKIAN ments in the marine environment is not well under(1968) pointed out that the deposition rates of Co stood. They may be transported and deposited with and Ba are in excess of their stream supply, whereas the detritus, or may get desorbed in the estuarine for Ag its input is an order of ma~itude more than regions. its removal. The deductions of the present work are Attempts to understand the behaviour of these similar to those of TUREKIAN(1968). adsorbed elements while in contact with sea water The origin of ‘excess’ Mn, Co and Ni on the ocean have been carried out by KHARKARrr ul. (1968) and floor is intriguing. Various sources. e.g. submarine MARTINrt 111.(1973). Their results indicate that some volcanism, river detritus, eolian dust and postof the adsorbed trace elements in river detritus are depositional migration have been suggested to explain desorbed on contact with sea water. The fraction of the origin of these elements on the ocean Roor (ARRthe element reieased varies depending on the chemical HENWS et ul., 1964: CHESTER,1965; TUREKIAN,1965; reactivity of the element and the nature of the adsorRILEY and CHESTER,1971). Murray in MURRAYand bent. Further, the fraction of leached elements reaching the open ocean areas is uncertain. and probably Table IO. Estimated authigenic deposition and supply is governed by the organic productivity in the estuarrates of elements ine regions. To evaluate the significance of this source, experiments were carried out to estimate the amount Authigenic deposition rate* (#g/cm’ 103y) River+ I input Best estimate of Mn, Co, Ni, 12(j3[3aand U isotopes leached from Element II river suspended sediments by sea water. The leaching experiments were done using sediments collected from SC 0.05 - (0.07) 0.05 0. 04 Indian rivers and lakes. The samples were powdered Ti 30 _ 30 30 and separated into two size fractions (1) less than IJO Mn 700 240 (650) 500 70 pm and (2) less than 10 ,rlm. The feaching was done Fe 750 640 (1500) 800 6700@ either by passing the sea water through a column CO 8 2.3(5.0) 5 2 of the sediment or by stirring a suspension of the Ni 18 5.7(12.6) 10 3 mud in sea water. For each experiment about 50 g cu 22 J.l(l2.6) 8 70 La 1 0.9( 1.9) 1 2 sediment was used. The experiment was continued till Th 0.2 0.2 1 the concentrations of elements in leachates were close ti 0.04 0.04 I to or less than their detection limits. [For details see KRISHNASWAM~ (1973f.f * I. From the most probable authigenic concentration The input of Mn, Co. Ni, Ra and U to the oceans (Table 9) and a mean clay accumulation rate of 0.1 g/cm2 via ‘dissolved supply” and ‘in situ leaching’ is given 10’ yr, II. from the constant flux model. The values in in Table I I. The data in Table 11 suggests that there parenthesis are based on revised sedimentation rates. is a definite supply of trace elements to the ocean + From TUREKIAN (1969). by in s&r leaching of river-borne suspended matter. 11, Upper limit. Table 9. Deduced detrital concentrations and authigenic deposition rates of elements based on constant flux model
1,
433
Authigenic transition elements in Pacific pelagic clays Table 11. Input of Mn, Co, Ni, U and Ra by in situ leaching of river suspended material Element
M”
Leachableamount* (microgram/g sediment)
100
Input(/&!/cm2 1037) In situ leaching
Soluble**
70
(7.110)
400
CO
0.5 (0.1-2.5)
2
2
Ni
0
3
0
U
0.3 (0.1-O. 7)
1
1.2
Ra+
0.1 (0.06-O. 3)
1
0.4
of Physical Research Laboratory, Ahmedabad. Thanks are due to Profs. RAMA,B. L. K. S~MAYAJULU,N. BHANDARI, RICER HART and Mr. S. K. BHATTACHARYAfor helpful discussions and criticisms. The experimental work was carried out while the author was a member of the Tata Institute of Fundamental Research, Bombay. The help given by the various members of the Geophysics Group, TIFR during the different phases of the work is thankfully acknowledged.
REFERENCES AMIN B. S., LAL
* Most probable values and the ranges (in parenthesis) are given. ** From TUREKIAN(1969). + In units of dpm. This contribution exceeds the dissolved supply rate for manganese and equals these for cobalt and uranium. Similar conclusions were arrived at by TUREKIAN (1968) to account for the excess deposition rate of Co in Atlantic sediments.
D. and SOMAYAJULUB. L. K. (1975) Chronology of marine sediments using the “Be method: intercomparison with other methods. Geochim. Costnochim. Acta 39, 1187-l 192. ARRHENIUSG., MEXO J. and KORKISCH J. (1964) Origin of oceanic manganese minerals. Science 144, 17G173. BENDER M. L., Ku T. L. and BROECKER, W. S. (1966) Manganese nodules: their evolution. Science 151, 32_%328. BENDER, M. L., Ku, T. L. and BROECKER,W. S. (1970) Accumulation rates of manganese in pelagic sediments. Earth Planet. Sci. Lett. 8, 143-148. BHAT S. G., KRISHNASWAMIS., LAL D., RAMAand SOMAYAJULU B. L. K. (1973) Radioactive and trace elemental
studies of ferromanganese SUMMARY
AND
CONCLUSIONS
nodules. Proc. Symp. HydroVol. 1, pp. 443462.
geochemistry and Biogeochemistry,
The Clarke Company. The measurements of SC, Ti, Fe, Mn, Co, Ni, Cu, La, Th and U in dated Pacific pelagic clays and manganese nodules have led to the following conclusions : (i) Mn, Co, Ni and Cu are enriched by factors of 3-10 in pelagic clays compared to shales and nearshore sediments. The concentrations of SC, Ti, Fe, La, Th and U in clays, shales and near-shore sediments are similar. A major fraction of the ‘excess’ Mn, Co, Ni and Cu can be preferentially leached. (ii) The authigenic fraction of these elements in pelagic clays have been estimated using different models. The results indicate that Mn, Co, Ni and Cu are primarily of authigenic origin, whereas the concentrations of SC, Ti, Fe, La, Th and U in deepsea sediments are controlled by detrital materials. (iii) The authigenic precipitation rates of Mn, Co, Ni and Cu on the Pacific ocean floor are found to be nearly uniform, thus their variation in absolute concentrations in sediments probably reflect the local sedimentation rates. The authigenic precipitation rates of the elements, SC, Ti, La and Th are small compared to their detrital component. The data also suggest that in sediments whose clay accumulation rates exceed 0.5 g/cm2 lo3 yr the authigenic concentration of tiny element in them would be small.
BLACK M. (1965) quoted B~STROM K. (1967) The
in TUREKIAN(1965). problem of excess manganese in pelagic sediments. In Researches in Geochemistry, (editor H. Abelson), Vol. 2, pp. 421-452. John Wiley. BOSTROM K. and FISHERD. E. (1972) Lateral fluctuations in pelagic sedimentation during the Pleistocene glaciations. Boreas 1, 22752288. CHESTERR. (1965) Elemental geochemistry of marine sediments. In Chemical Oceanography, (editors J. P. Riley and G. Skirrow), Vol. 2, Chapter 15, pp. 23-80. Academic Press. CHESTERR.. and HUGHES M. J. (1967) A chemical technique for the separation of ferromanganese minerals, carbonate minerals and adsorbed trace elements from pelagic sediments. Chem. Geol. 3, 199-212. CHESTERR. and MESSIHA-HANNA R. G. (1970) Trace element partition patterns in North Atlantic deep-sea sediments. Geochim. Cosmochim. Acta 34, 1121-l 128. CHESTERR. and JOHNXIN L. R. (1971) Trace element geochemistry of North Atlantic aeolian dust. Nature 231, 176-178. CRONAN D. S. (1969) Average abundances of Mn, Fe, Ni, Co, Cu, Pb, MO, V, Cr, Ti and P in Pacific pelagic clays. Geochim. Cosmochim. Acta 33, 1562-1565. FLANAGAN F. J. (1969) U.S. Geological Survey standards --II. First compilation of data for the new U.S.G.S. rocks. Geochim. Cosmochim. Acta 31, 81-120. FLEISCHERM. (1969) U.S. Geological Survey standards-I. Additional data on rocks G-l and W-l 1965-67. Geochim. Cosmochim. Acta 31, 65-79. GOLDBERGE. D.
and ARRHENIUS G. 0. S. (1958) Chemistry of the Pacific pelagic sediments. Geochim. Cosmochim. Acta 13, 153-212.
AcknowledyementsI thank Prof. D. LAL for his guidance and encouragement provided throughout the investigation. Dr. M. SANKAR DAS of Analytical Division, B.A.R.C. and members of his group, provided necessary facilities for the analyses of sediment and nodule samples. This study would have been impossible without the generous supply of samples from Profs. G. ARRHENIUS,W. R. RIEDELAND D. MACDOUGALL of Scripps Institution of Oceanography, San Diego. Prof. W. S. BROECKERof Lamont-Doherty Geological Observatory, Palisades, and Prof. B. L. K. SOMAYAJULU
GOLDBERGE.
D. and GRIFFIN J. J. (1964) Sedimentation rates and mineralogy in the South Atlantic. J. Geophys. Res. 69, 42934309.
GOLDBERGE.
D. and KOIDE M. (1962) Geochronological studies of deep sea sediments by the ionium-thorium method. Geochim. Cosmochim. Acta 26, 417450. GOLDBERGE. D. and KOIDE M. (1963) Rates of sediment accumulation in the Indian Ocean. In Earth Science and Meteoritics, (editors J. Geiss and E. D. Goldberg), pp. 9@102. North Holland.
434
S. KRISHNASWAMI
GOLDBERGE. D., KOIDE M., GRIFFINJ. J. and PETERSON M. N. A. (1963) A sedimentary profile across the North Atlantic Ocean. In Isotopic and Cosmic Chemistry, (editors H. Craig, S. L. Miller and G. J. Wasserburg), pp. 21 l-237. North-Holland. GOLDBERGE. D., KOIDE M. and GRIFFIN J. J. (1964) Ionium/thorium geochronology on Miami core A 254-BR-C. In Recent Researches in the Fields of Hydrosphere, Atmosphere and Nuclear Geochemistry. pp. 117-126.Maruzen. KHARKARD. P., TUREKIANK. K. and BERTINEK. K. (1968) Stream supply of dissolved silver, molybdenum. antimony, selenium, chromium, cobalt, rubidium and cesium to the oceans. Geochim. Cosmochim. Acta 32, 285-298. KRISHNASWAMI S. (1973) Geochemistry of transition elements and radioisotopes in marine and freshwater environments. Ph.D. thesis, Bombay University, 224 pp. KRISHNASWAMI S. and LAL D. (1972) Manganese nodules and budget of trace solubles in the ocean. In Proc. The Changing Chemistry of Oceans, (editors D. Dyrssen and D. Jagner), pp. 307-320. Almquist & Wilksell. Ku T. L. (1966) Uranium series disequilibrium in deep sea sediments. Ph.D. thesis. Columbia University, 157 PP.
Ku T. L., BROECKER W. S. and OPDYKEN. (1968) Comparison of the sedimentation rates measured by paleomagnetic and the ionium methods of age determination. Earth Planet. Sci.
Lett. 4, 1-16.
Ku T. L. and BROECKERW. S. (1969) Radiochemical studies on manganese nodules of deep-sea origin. DeepSea Res. 16, 625-631. MARTIN J. M., KULBICKI G.
and DEGRO~TA. J. (1973) Terrigenous supply of radioactive and trace elements to the ocean. In Proc. Symp. Hydrogeochemistry and Biogeochemistry, Vol. 1, pp. 463-483. The Clarke Company. MOOREW. S. (1967) Amazon and Mississippi river concentrations of uranium, thorium and radium isotopes. Earth Planet. Sci. Lett. 2, 231-234.
MURRAYJ.. and RENARDA. F. (1891) Report on deep sea deposits. Rep. Sci. Results Voyage H.M.S. Challenger, Deep Sea Deposits, 525 pp. RILEYJ. P. and CHESTERR. (1971) Introduction to Marine Chemistry, 465 pp. Academic Press. SCOTT M. R. (1968) Thorium and uranium concentrations and isotopic ratios in river sediments. Earth Planet. Sci. Lett. 4, 245-252.
SOMAYAJULU B. L. K., HEATHG. R.. MOORET. C. and CRONAN D. S. (1971) Rates of accumulation of manganese nodules and associated sediments from the equatorial Pacific. Geochim. Cosmochim. Acta 31. 621-624. TUREKIANK. K. (1965) Some aspects of the geochemistry of marine sediments. In Chemicul Oceanography. (editors J. P. Riley and G. Skirrow), Vol. 2, Chapter 16. pp. 8 l-1 26. Academic Press. TUREKIANK. K. (1968) Deep sea deposition of barium, cobalt and silver. Grochim. Cosmochim. Acta 32, 603~~612.
TUREKIANK. K. (1969) The oceans. streams and atmosphere. In Handbook ofGeochemistry, (editor K. H. Wedepohl), Vol. 1. Chapter IO, pp. 297-323. Springer-Verlag. TUREKIANK. K. and SCHUTZD. F. (1965) Trace element economy in the oceans. Proc. Symp. Marine Geochemistry, October 1964. University of Rhode Island. Occasional Publ. 3, 41-89. TUREKIANK. K. and SCOTTM. (1967) Concentrations of Cr. Ag, MO, Ni, Co and Mn in suspended material in streams. Enoiron. Sci. Technol. I, 94&942. TUREKIANK. K. and WEDEPOHLK. H. (1961) Distribution of the elements in some major units of the Earth’s crust. Bull. Geol. Sot. Amer. 72, 175-192. WINDOM H. L. (1970) Contribution of atmospherically transported trace metals to South Pacific sediments. Geochim. Cosmochim. Actrr 34, 509 -5 14.
et Cosmochimxa
Acta. 1976. Vol. 40. pp. 425 lo 434. Pergamon
Press Printed
in Great Britain
Authigenic transition elements in Pacific pelagic clays S. KRISHNASWAMI Physical Research Laboratory, Ahmedabad-380 009, India (Received 11 February 1975; accepted in revised form 16 October 1975) Abstract-The
concentrations of SC, Ti, Fe, Mn. Co, Ni, Cu, La, Th and U have been measured in several Pacific pelagic clays having widely different accumulation rates, 0.49.0 mm/lo’ yr. The authigenic fractions and deposition rates of these elements have been estimated from the measured concentrations using various models. The results show that in Pacific clays about 90% Mn, 80”/, Co and Ni and 50% Cu are authigenic whereas the major fraction (290%) of SC, Ti, Fe, La, Th and U are of detrital origin. Anticorrelation between the clay accumulation rates and the concentrations of Mn, Co, Ni and Cu is observed. This suggests a uniform authigenic deposition of these elements superimposed on varying amounts of detrital materials. The concentrations of SC, Ti and Th are almost independent of sedimentation rates, indicating that their authigenic deposition is small compared to their detrital contribution. Comparison of the authigenic deposition and river input rates shows that Mn, Co and Ni are accumulating in excess of their supply by factors of 2-10, whereas the converse is true for Cu and U. Additional sources to account for the budgetary discrepancies of Mn, Co and Ni are discussed, with particular reference to in situ leaching of detrital phases transported to the oceans via rivers.
INTRODUCTION
To DELINEATEthe geochemical cycle and balance of various elements in the marine environment it is essential to have a better knowledge of their authigenie concentrations and deposition rates on the ocean floor. Though various techniques to estimate the detrital and authigenic fractions of deep-sea sediments have been reported (GOLDBERG and ARRHJNUS, 1958; CHESIXR and HUGHES, 1967), available data on the authigenic deposition rates of elements are not abundant (BENDERet al., 1966; KRISHNASWAMI and LAL, 1972). Hence it was thought worthwhile to study systematically the distribution of a select group of elements in radiometrically dated Pacific pelagic clays, with a view to quantitatively estimate their authigenic deposition rates. The elements measured are Mn, Co, Ni, Cu, U, SC, Ti, Fe, La and Th. The selection of these elements was based on the observation that some of them (Mn, Co, Ni, Cu and U) exhibit marine budgetary discrepancies (B~STROU, 1967; TUREKIAN, 1968; RILEY and CHESTER, 1971) while for the others (SC, Ti, Fe, La and Th) no data on the authigenic deposition rates were available. The techniques of measurement and the models to estimate the authigenic concentrations are discussed. Based on the authigenic concentrations an attempt has been made to evaluate their marine geochemical balance.
MATERIALS
AND
METHODS
The relevant details of the sediment and nodule samples analysed are given in Table l(a) and (b), respectively. Since
the extent of incorporation or rejection of different elements by biogenic phases in marine sediments are not well understood, only clays were studied in this work. [The CaCO, conceptrations of all the cores listed in Table l(a) is
to
425
S.
426 Table 1 (a). Physical data and sedimentation deep-sea sediments studied Water
Core MSN-96+
L.xPtion
depth
(m)
Sh'S
KRISHNASWAMI
rates of the
Sedimentation rate*(mm/lO’y) (C) (a) 01
0.4
0. 6
4o%s
5120
0.5
1.4
4620
0.4
0. 9
TF-1 TF-2 TF-3 TF-4
13Z049’W DWBG-30++
19o5o’s 148O39’W
v-19-259**
11%2’S
5528
9’03~s
4960
0. 6
NOVA-I&16+
0°14.1’N
5160
1.7
6331
1.4
5100
1.9
176Y. 9’W NOVA-IU-13’
03’55.6’N
+
(mm/lo6
Y)
w
13O53’S
3623
1.0
3695
1.0
150°35’W 1
ZP-50++
13O53’S 150°35’W
2P-52++
9’57’N 131°47’W
4930
7.3
CARR-SD+
10’39’N 10845’W
5216
NM
DODO-SD+
1a016’N 161’5O’W
5500
1.0
6A**
19’39’N 113O44’W
4000
4.0
TRIPOD-2D+
20°45’N 112’47’W
3000
4.0
DH-2+
21’50’N 115’12’W
3430
NM
34O54’N 160’19’W
5400
4. 0
40’16’N 170°20’E
3000
1.4
1.6
174°52’E
Growth rate
4770
!xP s
1.6
165O45’W CAP-6 BG++
**
95O
98Ol’W DWBG-52++
and their
(m) E-17 -36
4350
nodules
Water depth
Location
Nodule code
2.3
4154
42oo2’s
I (b). Details of manganese growth rates
114O15’W DWHG -49++
Table
119°41. 3’W MSN-14x+
B020’N 145’24’W
CAP-49 BG++
9’1l’N
4410
1.6
2.4
124O9’W NOVA-III-lo+
O&3.
SN
1.0
6105
116°41. 3’W CAP-SOBG++
14’5S’N
4270
1. 0
2.1
4310
1.5
2.2
4400
1.0
2.0
124’12’W DWBG-Z++
21°2?.2’N 126’43’ W
WIG-5++
28°37.6’N
V21-D2
**
ZETES-3D+
124’25. VW v-21-71**
21°54’N
5660
2.4
162%1’E SOB-15++
28%.9’N
3455
9.0
13.0
3900
9.0
13.0
6360
1.5
3.0
117°31. 4’W FAN -BG-7++
30’43’N 119O5O’W
CK-4++
42’30’N 16Z”06. 2’W
’ TIFR collection. + + SIO collection, and ** LDGO collection. *All sedimentation rates are based on “‘Th chronology.
(a) GOLDBERG and KOIDE (1962). (b)/ KU et al. (1968). The sedimentation rates of all cores excluding V-18-258 and V-21-71 are recalculated values from the results of GOLDBERG and KOIDE(1962). The major correction factor is due to shortening of open barrel cores compared to piston cores. (c) AMINet al. (1975).
** LDGO collection, + TIFR collection and + + SIO collection. USGS reference rocks are similar to those reported in the literature (FLANAGAN, 1969; FLEISCHER, 1969). Duplicate measurements of the concentrations in the reference rocks and marine samples were in agreement within 210%. The average concentrations of SC, Ti. Fe, Mn, Co, Ni, Cu, La, Th and U in Pacific pelagic clays based on the present measurements are given in Table 5. The deduced averages are in moderate agreement with the data of CRONAN (1969) and KRISHNASWAMI and LAL (1972).
Table 2. Results of analysis of USGS reference samples Co”ce”tratton
W-l Present Reported values* work
Element
34.6
SC
Mn
Fe(74 model 303 atomic absorption spectrophotometer. Along with the samples USGS reference rocks and reagent blanks were also measured. RESULTS The results of the measurements of USGS rocks, sediments and nodules are given in Tables 2, 3 and 4, respectively. The measured concentrations of various elements in
33-37
13.50
1300-1400
7.1
7. 6-1.8
CO
49.5
41 -54
NL
61
TO-90
C”
117
112-122
La
11
10-21
In (ppm.
G-2 Present Rapotied rork “*“e&l* 3. 1 210 1. 6
3. 0
rock
wt)
ECR - 1 Present Reported aork vpluo~: 26.6
31-33
1950
265 1.66
-
ND
4. 3
36.2
-
13.7
-
9. 3 36-37 30
ND
10-11
-
15-27
89.6
80-64
22.5
23-24
* From FLANAGAN (1969) and FLEISCHER (1969). Results of measurements directly comparable to the techniques used in this study are given.
N-Not
detectable.
427
Authigenic transition elements in Pacific pelagic clays Table 3. Elemental concentrations
of Pacific pelagic clays
Depth Concentration of elementsInppm.dry weight;unlessstated
interval
Core
analyzed SC I___\
Ti
Mn
Fe(%)
3940
Co
Ni
Cu
La
Th+
U*
MSN-96
10-12.5
3980
4.2
-
64
67
15
1.4
DWHG-49
IO-20
la
3230 23000
a.5
ias
590
600
15
10.0
DWBG-62
20-30
23
3600
3.8
96
212
340
33
10.6
-
DWBG-30
20-25
20
a.3
-
306
335
102
-
14800
192 250
336
9.5 -
_
V-16-256
16-20
24
a900
la200
166 242
311
aa
50-53
_
_
13200
169 255
302
14.0 __
CAP-BBC
10-20
22
5600
10200
a.0
Qa 205
314
43
7.9
NOVA-la
16-16
25.5 5500
6200
5.3
91 350
519
64
7.0
-
NOVA-16
6-12
23
3960
6050
5.8
56
117
278
37
7.9
1.3
NOVA-13
5 -8.5
26
3540
5160
6.0
86
156
330
40
11.9
1.3
MSN 14lG
6-8
31
4000
1030
5.4
31
a3
256
34
12.3
1.6
STYX-5B
lo-la
31.5
3230
10920
3.6
-
516
455
129
6.2
-
CAP-4QBG
10-20
26
4400
5100
5.2
a.4
-
NOVA-10
10-12
26
4600
1100
5.2
-
CAP-5OBG
30-34
21
3150
4015
4.1
-
DWBG-2
10-20
-
5100
5550
5.4
WIG-5
10-13
14
5040
4670
4.6
SOB-15
10-14
16
5340
FANBG-7
10-15
17
5200
CK-4
16-20
-
5040
-
2-9.5
20-25 v-21-71
ia
55-62
5430
16400 10550
a.7
1.6 -
3.1
-
798
64
231
523
60
11.1
-
191
363
57
11.0
-
la1
la2
271
42
12.0
-
-
209
191
32
12.6
-
119 230
4.0
16 145
136
30
9.1
4.4
29
163
163
30
12.5
-
1600
4.0
31
94
163
32
11.0
-
5300
4600
4.3
52
162
172
36
5000
105 172
205
15.4 __
2.1
-
-
*Th and U data compiled from GOLDBERG and KOIDE (1962),Ku (1966),Ku et al. (1968) and AMIN et al. (1975). The reported *32Th values by La Jolla group were multiplied by 15 to correct for HCI leaching efficiency (GOLDBERG and KOIDE, 1962).
DISCUSSION Estimation of authigenic deposition rates The main aim of the present investigation is to estimate the authigenic deposition rates of various elements on the ocean floor, with a view to evaluate their marine geochemical balance. Since in the past
the main emphasis has been in studying the distribution of elements among the various components of deep-sea sediments, available data on the authigenic deposition rates are sparse. A systematic pattern between the clay accumulation rates and the concentrations of various elements in pelagic clays has emerged from the results
Table 4. Chemical composition of radiometrically dated Pacific manganese nodules Nodulecode sc
Ti
Concentrations inppm dry weight,unlessstated ?vlo La Th* Ni Cu Mn(k) Fe(X) Co
u*
ti20w**
E-11-36
NM
1200
36.0
15.6
1660
6000
2800
650
176
54.5
TF-2
il.8
11400
16.6
20.0
4200
3020
1940
NM
350
22.0
15.0
21.4
20.0
9.0
11.2
2P-50
14.4 13400
16.0
20.5
3900
3140
1450
160
232
10.5
20.5
2P-62
NM
2140
21.6
4.1
1720
14400
9500
940
76
NM
7.4
12.5
CARR-QD
11
6BOO
42
10.2
960
2400
6500
NM
131
NM
NM
11.8
DODO-QD
NM
20.4
5200
3100
618
1050
244
35.0
9.0
24.0 10.6
12000 39.8
6A
la. 9
2690
25.6
9.4
1210
11700
9210
1020
100
24.5
1.0
TRIPOD-2D
10.2
6450
16.9
23.0
3610
2530
211
590
370
38.0
16.0
6.9
NM
30.0
16.1
960
NM
6100
NM
200
NM
NM
16.2
1600
15.6
15.4
3220
5260
3680
660
229
122.0
5.6
13.1
6450
26.5
11.4
5450
455
2750
405
40.0
17.0
21.1
DH-2 V21-D2 ZETBS-3D
a.5 NM
6.5
NM-Not measured. *Data for U and Th concentrations are compiled from BHAT et al. (1973) and Ku and BROECKER (1969).For nodules 2P-50 and 2P-52 are determined in the present study. ** Represents weight loss of air dried nodule samples at 110°C for 2 hr.
428
S. KRISHNASWAMI Table 5. Average concentration
reliable results for those elements whose abundances in shales or near-shore sediments are small compared to that in pelagic clays. This case is realistic only for Mn. Co and Cu where the correction is less than Y,,. For Ni and SC. where C,C,, _ Z--3. the estimates may be only semi-quantitative. For Fe. Ti, La. Th and U where C, _ C, no reliable estimates of authigenie concentrations can be made. Since the chemical composition of the shales and the shelf sediments are similar, the deduced authigenic cmcentrations by both these models follow the same pattern.
of SC, Ti. Mn. Fe, Co, Ni, Cu, La, Th and U in Pacific sediments Concentration
Element
SC
Present study*
of element(ppm. wt) Reported averages** (a)
(b)
22.3
28
Ti
4v7a+
4548
4500
Mn
7430
4784
7800
Fe (% wt)
5.44
5.07
5.10
87
101
Ni
224
211
242
CU
338
323
430
CO
La
52
Th
10.4
U
2
132
115 12.3 2.2
*
Average of 20 clay sediments. **(a) CRONAN (1969) and (b) KRISHNAS-
WAMIand LAL (1972). +For estimating the mean Ti concentration the result of DWBG-30 is excluded (Table 3).
of this work. A model for the deposition of elements (henceforth designated as ‘constant flux model’) has evolved from this pattern. Based on this model the authigenic deposition rates and detrital fractions of elements can be evaluated directly. Additionally, the observed distribution of various elements in pelagic clays and the occurrence of deposits like manganese nodules can be understood in terms of this model. The reported methods to estimate the authigenic and detrital fractions of deep-sea sediments are based on a twocomponent system for pelagic clays. Thus the total concentration of any element, C,, in the sediment is the sum of the contributions from these two fractions, i.e. c, = c, + Cd.
(1)
where C is the concentration of the element and the suffixes t. a, and d represent total, authigenic and detrital phases. The problem is to ascertain the contributions of either C, or Cd to the total measured value, C,. For the sake of completeness the assumptions of the commonly adopted approaches for estimating the authigenic concentrations and the deduced results using them are discussed briefly below. The results of the ‘constant flux model’ and its implications are presented subsequently.
GOLDBERG and ARKHI-~\;I~Is(195X) observed that in the dissolution rate (g,‘m’ hr) of marine deposits (manganese nodule, calcite and apatite) in chelating agents like EDTA was faster than that of terrestrial minerals (feldspar, goethytc. glass and rutile). Using similar techniques. CHISTEK and Hucrq~s (1967) and CHESTER and MESSIHA-HANNA (1970) have estimated the lithogenous fraction of several Atlantic deep-sea sediments. The estimation of the authigenic fraction of elements using this technique is based on their preferential dissolution in selected chemicals. In this work, the leaching of the samples was done by boiling them under reflux with ammonium salt of EDTA at pH = X. The samples were repeatedly boiled to ensure complete leaching. The results of these measurements (Table 7) show that a large fraction of (3 70”,,) of Mn. Co and Ni in the Pacific clays can be preferentially dissolved in EDTA. The deduced authigenic fractions of various elements (Table 7) follow the same pattern as that observed for the North Pacific and Atlantic sediments measured using similar technique (CHESTER and HI~GHES. 1969: CHESTERand
Table 6. Estimated authigenic concentrations of element based on the shale and shelf sediment correction methods Element
Shales
ivln
7430
850
CU
338
45
3b
CO
87
1La
13
Ni
224
(iR
46
23
SC Ti
4679
Fe (% wt)
5.44
13 4600 4. 72
La
52
92
Th
10. 4
12
2
II
In this approach the value of Cd is obtained by assuming the composition of the detrital fraction of sediments to be the same as that of shales (BENDER et ul., 1966; KRISHNASWAMIand LAL, 1972) or of sediments collected from near-shore regions. Table 6 gives the estimated authigenic concentrations based on this model. This approach gives
C’uncentration (ppm. wt) Authigernc;:* Near shore sediments (b) (a)
Pat ifir* sedments
*
810
6580
il. 5 4085 4.8
293
68 156 10
6620 302
74 178 11.5
(78)
(593)
(0.72)
(0.64)
7”
::. 7
From Table 5. The data for shales and near-shore sediare from TUREKIAX and WEDEPOHL(1961) and
ments
KRISHNASWAMI
(1973). ** Using relation 1. (al and (b) represent the estimates based on shale and shelf sediment correction methods. respectively. The values in paranthesis could be in large error since they represent the difference of two approximately equal numbers.
Authigenic transition elements in Pacific pelagic clays Table 7. Average EDTA leachable concentrations ments in Pacific clays* Element
Mtl
%Element leachable in EDTA
78
of ele-
Detrital
5800
1830
CO
73
64
23
Ni
65
146
78
CU
43
145
193
Fe (% wt)
18
1
4.44
*Based on the analyses of 10 cores: MSN-96, DWHG-49, DWHG-52, DWBG-30, V-18-258, CAP-SBG, NOVA-18, NOVA-10 and V-21-71 (Table la). MESSIHA-HANNA,
Table 8. Comparison of the estimated authigenic concentrations of elements based on commonly adopted methods* Estimated authigenicconcentration(ppm. wt)
Mean concentration CUDI& .. . wt) Authigenic
1970).
Excluding Cu, the measured authigenic concentrations follow the same trend as that of the shale model. The detrital concentration of Cu deduced by the leaching technique is higher by about a factor of 2-3 than that estimated by the shale model, an observation similar to that of Ck~sTER and HUGHES (1969). The cause for the observed discrepancy is not clear. It is likely that the non-leachable fraction of Cu in deep-sea clays is of eolian or biogenous origin. Manganese nodule model The authigenic concentrations of elements are estimated using this model on the assumption that their authigenic precipitation rates on the pelagic clays and manganese nodules are the same (KRISHNASWAMI and LAL, 1972). The observation that the authigenic accumulation rates of Mn, Cu, Ni, Co. and of the radioisotopes “Be and 230Th in both sediments and nodules are similar within a factor of 2-3 (BENDER et al.. 1970; SOMAYAJULU et al., 1971; KRISHNASWAMI and LAL, 1972; BHAT et al., 1973) supports this assumption. In this model the authigenic concentrations are calculated using the fbllowing relation (KRISHNASWAMI and LAL, 1972; KRISHNASWAMI, 1973):
where S is the clay accumulation rate, p is the density, (subscripts s and n refer to sediments and nodules, respectively), E is the fraction of time for which the nodules grow on an average, G is time averaged growth rate of nodules and& is the geometry factor for the nodule exposure. The value of R is calculated to be about 10, using the following numerical values for the various parameters. S = 2-3 mm/lo3 yr, ps = 0.5 g/cm3, E = 0.1, G = 3 mm/lo6 yr, pn = 2.5g/cm3 and fw = 2. Considering the uncertainties in the values of p, K and fw the calculated ratio of 10 is considered to be in agreement with the mean observed ratio of 25 (range l&43) for elements with different degrees of chemical reactivities, Mn, Co, Ni,
429
Element
(i)
(ii)
SC
10
12
Ti
‘18
593
(iii)
(iv)
0. 5
Mont probable
authigenic concentration
0.5
310
3 00
Mn
6560
6620
5600
10900
7000
Fe
7200
6400
9600
6400
1500
CO
68
14
64
120
60
Ni
156
116
146
226
175
CU
293
302
145
160
225
La
9
10
Th
1.6
2
”
0.4
0.4
* (i) Shale method, (ii) shelf sediment method, (iii) leaching method and (iv) nodule method. The estimated authigenie concentration of SC, Ti and Fe by methods (i) and (ii) could be in large error (see text for method of calculation).
Cu, “Be and Th. In view of this agreement, the authigenie concentration of various elements have been calculated using a value of 25 for R. The estimated values are givenjn Table 8.
Comparison of the estimated authigenic concentrations based on various models The authigenic concentrations of Mn, Co, Ni and Cu are easily estimated by all the methods. The deduced values for Mn, Co, Ni, Cu, Fe and Ti by the various methods are in modest agreement. For SC, La, Th and U. only the manganese nodule method could give estimates of the authigenic concentrations. Though the estimates for Mn, Co, Ni and Cu by this method are in agreement with the results of other models, it is likely that some of these elements may be preferentially incorporated into the nodule matrix. It is therefore important to confirm the deductions obtained by this method by some independent approach. The most probable authigenic concentrations for the elements studied are also listed in Table 8. The estimates for SC, Ti, La, Th and U are based mainly on the nodule method, for the others it is the average of all the techniques. Constant Jlux model This model is based on the assumption of uniform authigenic deposition rate of an element over the ocean floor. An anticorrelation between the authigenie concentration, C,, and sedimentation rate, S, is expected, if the authigenic deposition rate of an element is uniform, i.e.:
c, = g s
430
S. KRISHNASWAMI
In such case the total concentration, ment would be:
C,, in the sedi-
C,=C,+C,=s:,+rd.
(4)
s
where K is the authigenic deposition rate (g/cm” yr), ps is the in situ density of the sediment (g/cm3) and S is the sedimentation rate (cm/yr). The assumption of this model is expected to hold good for elements which are homogeneously distributed in the ocean, i.e. whose residence times are comparable to or more than the oceanic mixing times. Mn. Co, Ni. Cu and U should fall in this category. For SC. Ti, La and Th. which are chemically more reactive and have short residence times, the assumption of uniform deposition may be questionable. The available data on the vertical and geographical distribution of these elements in sea water are sparse and hence it is dificult to make a critical judgement on the nature of their distribution. BENDER et u[. (1966) observed an almost constant accumulation rate for Mn in cores in which both the Mn concentrations and the sedimentation rates vary over an order of magnitude. Later work (BENDER et ul., 1970) on different types of pelagic sediments (red clays, calcareous and siliceous oozes) showed more scatter in the accumulation rate of Mn. It is likely that part of the scatter in their estimates may be due to the assumption that calcite and opal are Mn-free diluents (BLACK, 1965; BOSTROMand FISHER, 1972). Additional uncertainty in their estimates may result from the difficulty in assigning sedimentation rates by the magnetic reversal technique in which there is no accurate way of compensating for the loss of core tops.
The simplest correlation is expected for 130Th which is uniformly produced in the water by the decay of uranium and precipitated to the ocean floor. The terrigenous supply of 230Th is small compared to its in situ production from sea water, since its concentration in rivers (soluble and particulate) is very low (MOORE, 1967; SCOTT, 1968). Figure 1 shows the variation of the surface 13’Th concentration in sediments as a function of the inverse of sedimentation rate (only cores which have an integrated Z30Th activity of 2800 dpm/cm” and which show an undisturbed exponential decay of 230Th with depth are plotted). The data for Fig. 1 have been compiled from GOLDBERG and KOIDE (1962, 19631, GOLDBERG er (11. (1963.1964). GOLDBERGand GRIFFIN (1964), Ku (1966), Ku et ul. (1968) and AMIN et al. (1975). The 230Th concentrations published by the La Jolla group have been multiplied by a factor of I.5 to correct for incomplete recovery of thorium isotopes in the acid leaching procedure (GOLDBERGand KOIDE. 1962). It is evident from Fig. 1 that the surface 230Th concentration is anticorrelated with the sedimentation rate as expected from relation (2). It must be mentioned here that even if the sedimentation rates as recalculated by Ku et al. (1968) are used the anticorrelation pattern is still obtained. The precipitation rates of 13’Th in the Pacific, Atlantic and Indian oceans have been calculated from the slope of the line in Fig. 1 and using a value of 0.5 g/cm3 for in situ density. The estimated values range between 8.9-13.7 and 12%13.5 dpm/cm’ lo3 yr for the Pacific and Atlantic oceans. respectively, depending on the sedimentation rates used. The higher deposition rates are associated with the revised sedimentation rates of Ku et al.
ATLANTIC
and
INDIAN -
l ‘/S),
INVERSE
OF
SEDIMENTATION
RATE
400
IO’yr/cm
Fig. 1. Plot of surface 230Th concentration (dpm/g) vs inverse sedimentation rate (lo3 yr/cm) for cores from the Pacific, Atlantic and Indian oceans. Only cores showing exponential decay of 230Th with depth and having an integrated 230Th activity of 2 8OOdpm/cm’ are plotted. The anticorrelation between clay accumulation rate and surface 230Th concentration is clearly evident. The *30Th deposition rate deduced from thee slope of the line range between 8 and 13 dpm/cm’ 10” yr.
Authigenic transition elements in Pacific pelagic clays
0
(Vd*INVERSE
10
OF SEDIMENTATION
A “‘OO20 RATE
431
10 IO’,,~/~,,,
Fig. 2. Scatter diagrams of the concentrations of Fe, Ni, Cu, Mn, Co, SC, Ti and Th in dated Pacific pelagic clays against inverse sedimentation rates. For plotting the revised sedimeentation rates of Ku et al. (1968) have been used. The lines drawn are least square fits for the data points. As is evident, the concentrations of Mn, Co, Ni, Cu and Fe are anticorrelated with the sedimentation rates. The concentrations of SC,Ti and Th are almost independent of sedimentation rates. The deduced authigenic deposition rates and the detrital component of these elements in pelagic clays are given in Table 9.
(1968). The calculated deposition rate of 230Th on the ocean floor is in agreement with its production rate, 8-9dpm/cn? lo3 yr. The variation of the concentrations of Mn, Ni, Cu, Co, Fe, Ti, Th and SC, in 18 cores as a function of sedimentation rate is plotted in Fig. 2. The results show that the concentrations of Mn, Co, Ni, Fe and Cu are anticorrelated with the sedimentation rate. This is consistent with the model of uniform authigenie deposition superimposed on a background of detrital input. The concentrations of SC, Ti and Th are almost independent of sedimentation rates. The latter observation is expected for those elements whose authigenic concentrations are small compared to their detrital contributions. It is apparent from the data (Fig. 2) that in sediments with clay accumulation rates exceeding about 0.5 g/cm2 lo3 yr (corresponding to about 10 mm/lo3 yr) the authigenic concentrations of elements in them would be small, i.e. C, N Cd. In such cases the elemental abundances in sediments would be the same as that in the detrital component (shales) and would be independent of sedimentation rate. However, the total deposition rate of the element would be positively correlated with the sedimentation rate. The results of TUREKIAN and SHLJTZ(1965) who observed a positive correlation
between trace element and clay accumulation rates in Atlantic calcareous cores fall in this category. The other extreme, i.e. deposition of purely authigenic material would result when the detrital sedimentation rate, S, is very small. The occurrence of ferromanganese minerals in regions of low detrital sedimentation is consistent with this expectation. The authigenic deposition rates and detrital concentrations of these elements are estimated from the slope and intercept of the best fit lines in Fig. 2. These calculations are carried out using the sedimentation rates reported by various groups as well as using the revised rates of Ku et al. (1968) (Table 9). In general, for all elements studied, higher authigenic deposition rates and lower detrital concentrations are deduced using the revised sedimentation rates (Table 9). Marine geochemical balance of transition elements
Table 10 gives the calculated authigenic deposition ,rates of elements in pelagic clays along with their supply rates via rivers. The best estimates of authigenic deposition rates given in Table 10 is based mainly on the constant flux model. The results (Table 10) show that Mn, Co and Ni are depositing in excess of their supply by factors of 2-10 whereas the removal rate of Cu and U are
432
S. KRISHNASWAMI
RENARD(1891) suggested submarine volcanism as a source of elements to the oceans. Though a considerable amount of work has been reported on this subDetrital concentration Au thigenic precipitation ject, no quantitative estimates for input rates of eleElement (ppm. wt) unless stated rate ( fl g/J 103 yj* ments by submarine volcanism are available. The imib) (a) (a) (b) portance of eolian dust as source of trace elements to the deep-sea sediments has been discussed recently Mn 2067 240 650 (WINDOM, 1970; CHESTERand JOHNSON,1971). Based Fe@ wt) 4.33 3.8 640 1500 on the analyses of airborne dust over the Atlantic CO 46 31 2.3 5 and Pacific thev conclude that the concentrations of Ni 92 51 5.1 12.6 Mn. Co and NE in the dust material are not adequate cu 224 169 5.1 12.8 to account for their supply to pelagic clays. La 30.5 24.4 0. 9 1.9 Recently the significance of river suspended load SC 22.1 21 -+ 0. 07 as a source of trace metals to the oceans has been Ti 5262 5291 recognized. The major fraction of solids introduced Th 11.6 11.3 to the oceans are weathered materials from the continents. Elements present in these solids include those (a) and (b) refer to estimates deduced using the original in the lattice positions of the minerals and those and revised sedimentation rates (see text). which are retained on their surfaces by adsorptionion * Calculated from the slope of the least square lines (Fig. exchange processes, The available data on the elemen‘I. tal abundances in river suspended materials (T~IKEK+ In these cases the deposition rates could not be estimated since slopes were negative (Fig. 2). IA~Vand SCOTT, 1967; MARTIN rf ~rl.. 1973) suggest that many of the transition metals are enriched in them compared to shales and the detritai fraction of about an order of magnitude less than their input. deep-sea sediments. The fate of these adsorbed eleBased on the results of three Atlantic cores, TUREKIAN ments in the marine environment is not well under(1968) pointed out that the deposition rates of Co stood. They may be transported and deposited with and Ba are in excess of their stream supply, whereas the detritus, or may get desorbed in the estuarine for Ag its input is an order of ma~itude more than regions. its removal. The deductions of the present work are Attempts to understand the behaviour of these similar to those of TUREKIAN(1968). adsorbed elements while in contact with sea water The origin of ‘excess’ Mn, Co and Ni on the ocean have been carried out by KHARKARrr ul. (1968) and floor is intriguing. Various sources. e.g. submarine MARTINrt 111.(1973). Their results indicate that some volcanism, river detritus, eolian dust and postof the adsorbed trace elements in river detritus are depositional migration have been suggested to explain desorbed on contact with sea water. The fraction of the origin of these elements on the ocean Roor (ARRthe element reieased varies depending on the chemical HENWS et ul., 1964: CHESTER,1965; TUREKIAN,1965; reactivity of the element and the nature of the adsorRILEY and CHESTER,1971). Murray in MURRAYand bent. Further, the fraction of leached elements reaching the open ocean areas is uncertain. and probably Table IO. Estimated authigenic deposition and supply is governed by the organic productivity in the estuarrates of elements ine regions. To evaluate the significance of this source, experiments were carried out to estimate the amount Authigenic deposition rate* (#g/cm’ 103y) River+ I input Best estimate of Mn, Co, Ni, 12(j3[3aand U isotopes leached from Element II river suspended sediments by sea water. The leaching experiments were done using sediments collected from SC 0.05 - (0.07) 0.05 0. 04 Indian rivers and lakes. The samples were powdered Ti 30 _ 30 30 and separated into two size fractions (1) less than IJO Mn 700 240 (650) 500 70 pm and (2) less than 10 ,rlm. The feaching was done Fe 750 640 (1500) 800 6700@ either by passing the sea water through a column CO 8 2.3(5.0) 5 2 of the sediment or by stirring a suspension of the Ni 18 5.7(12.6) 10 3 mud in sea water. For each experiment about 50 g cu 22 J.l(l2.6) 8 70 La 1 0.9( 1.9) 1 2 sediment was used. The experiment was continued till Th 0.2 0.2 1 the concentrations of elements in leachates were close ti 0.04 0.04 I to or less than their detection limits. [For details see KRISHNASWAM~ (1973f.f * I. From the most probable authigenic concentration The input of Mn, Co. Ni, Ra and U to the oceans (Table 9) and a mean clay accumulation rate of 0.1 g/cm2 via ‘dissolved supply” and ‘in situ leaching’ is given 10’ yr, II. from the constant flux model. The values in in Table I I. The data in Table 11 suggests that there parenthesis are based on revised sedimentation rates. is a definite supply of trace elements to the ocean + From TUREKIAN (1969). by in s&r leaching of river-borne suspended matter. 11, Upper limit. Table 9. Deduced detrital concentrations and authigenic deposition rates of elements based on constant flux model
1,
433
Authigenic transition elements in Pacific pelagic clays Table 11. Input of Mn, Co, Ni, U and Ra by in situ leaching of river suspended material Element
M”
Leachableamount* (microgram/g sediment)
100
Input(/&!/cm2 1037) In situ leaching
Soluble**
70
(7.110)
400
CO
0.5 (0.1-2.5)
2
2
Ni
0
3
0
U
0.3 (0.1-O. 7)
1
1.2
Ra+
0.1 (0.06-O. 3)
1
0.4
of Physical Research Laboratory, Ahmedabad. Thanks are due to Profs. RAMA,B. L. K. S~MAYAJULU,N. BHANDARI, RICER HART and Mr. S. K. BHATTACHARYAfor helpful discussions and criticisms. The experimental work was carried out while the author was a member of the Tata Institute of Fundamental Research, Bombay. The help given by the various members of the Geophysics Group, TIFR during the different phases of the work is thankfully acknowledged.
REFERENCES AMIN B. S., LAL
* Most probable values and the ranges (in parenthesis) are given. ** From TUREKIAN(1969). + In units of dpm. This contribution exceeds the dissolved supply rate for manganese and equals these for cobalt and uranium. Similar conclusions were arrived at by TUREKIAN (1968) to account for the excess deposition rate of Co in Atlantic sediments.
D. and SOMAYAJULUB. L. K. (1975) Chronology of marine sediments using the “Be method: intercomparison with other methods. Geochim. Costnochim. Acta 39, 1187-l 192. ARRHENIUSG., MEXO J. and KORKISCH J. (1964) Origin of oceanic manganese minerals. Science 144, 17G173. BENDER M. L., Ku T. L. and BROECKER, W. S. (1966) Manganese nodules: their evolution. Science 151, 32_%328. BENDER, M. L., Ku, T. L. and BROECKER,W. S. (1970) Accumulation rates of manganese in pelagic sediments. Earth Planet. Sci. Lett. 8, 143-148. BHAT S. G., KRISHNASWAMIS., LAL D., RAMAand SOMAYAJULU B. L. K. (1973) Radioactive and trace elemental
studies of ferromanganese SUMMARY
AND
CONCLUSIONS
nodules. Proc. Symp. HydroVol. 1, pp. 443462.
geochemistry and Biogeochemistry,
The Clarke Company. The measurements of SC, Ti, Fe, Mn, Co, Ni, Cu, La, Th and U in dated Pacific pelagic clays and manganese nodules have led to the following conclusions : (i) Mn, Co, Ni and Cu are enriched by factors of 3-10 in pelagic clays compared to shales and nearshore sediments. The concentrations of SC, Ti, Fe, La, Th and U in clays, shales and near-shore sediments are similar. A major fraction of the ‘excess’ Mn, Co, Ni and Cu can be preferentially leached. (ii) The authigenic fraction of these elements in pelagic clays have been estimated using different models. The results indicate that Mn, Co, Ni and Cu are primarily of authigenic origin, whereas the concentrations of SC, Ti, Fe, La, Th and U in deepsea sediments are controlled by detrital materials. (iii) The authigenic precipitation rates of Mn, Co, Ni and Cu on the Pacific ocean floor are found to be nearly uniform, thus their variation in absolute concentrations in sediments probably reflect the local sedimentation rates. The authigenic precipitation rates of the elements, SC, Ti, La and Th are small compared to their detrital component. The data also suggest that in sediments whose clay accumulation rates exceed 0.5 g/cm2 lo3 yr the authigenic concentration of tiny element in them would be small.
BLACK M. (1965) quoted B~STROM K. (1967) The
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AcknowledyementsI thank Prof. D. LAL for his guidance and encouragement provided throughout the investigation. Dr. M. SANKAR DAS of Analytical Division, B.A.R.C. and members of his group, provided necessary facilities for the analyses of sediment and nodule samples. This study would have been impossible without the generous supply of samples from Profs. G. ARRHENIUS,W. R. RIEDELAND D. MACDOUGALL of Scripps Institution of Oceanography, San Diego. Prof. W. S. BROECKERof Lamont-Doherty Geological Observatory, Palisades, and Prof. B. L. K. SOMAYAJULU
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