The distribution of dissolved copper in the Pacific

38

Earth and Planetary Science Letters, 37 (1977) 38-54 © Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

[41

THE DISTRIBUTION OF DISSOLVED COPPER IN THE PACIFIC E.A. BOYLE l, F.R. SCLATER and J.M. EDMOND Department of Earth and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Mass. 02139 (USA)

Received April 20, 1977 Revised version received July 25, 1977

The general form of Cu-depth profiles is unique. In the central North Pacific, values decrease from a surface maximum of about 3 nmol/kg to 1.5 nmol/kg in the upper thermocline. Below about 750 m there is an increase to over 6 nmol/kg in the bottom waters with no mid-depth extremum. The profiles in the boundary regions are similar in the deep water but do not have the surface maximum. This unique elemental distribution is maintained by aeolean input to the surface waters comparable in magnitude to the fluvial component, ubiquitous scavenging in the subsurface and deep water, and a strong bottom source. Apparently the scavenging agent, presumably sinking particles, loses its Cu-binding capacity during early diagenesis. The half-life with respect to scavenging is about 1100 years and the overall residence time with respect to input or final removal about 5000 years.

1. Introduction

2. Sampling and analytical procedures

Copper is enriched in deep-sea clays b y factors of between three and ten over near-shore sediments and shales [2] and is also a significant component of ferromanganese nodules and o f the metal-rich deposits at spreading centers. Considerable attention has been given to the sedimentary geochemistry of Cu and there is extensive information on the geographical distribution and accumulation rates of the element ([2] and references therein). A number o f detailed studies have attempted to distinguish among the several sources for the Cu in deep-sea sediments, i.e. detrital, hydrogenous, volcanogenic, and biogenous. However, little is known about the distribution of dissolved Cu in the water column which could constrain the choice of these components. F o r this reason we have determined the concentrations of Cu in six detailed vertical profiles from throughout the Pacific.

The samples were originally collected for Ba analyses as part of the GEOSECS program; the samplehandling procedure is described in detail elsewhere [3]. Copper was determined b y a 50 : 1 preconcentration from 100-ml samples by cobalt pyrrolidine dithiocarbamate coprecipitation [4] followed by redissolution of the precipitate and analysis of the concentrate by flameless atomic absorption using a Perkin-Elmer HGA 2100 graphite furnace, model 403 spectrophotometer, and model 56 chart recorder [5]. The precision o f the analysis is estimated to be +0.2 nmol/kg (1 o). The profiles (Fig. 1) show that most samples deviate from a smooth curve by no more than 2o confirming this estimate. The accuracy is probably comparable. An intercalibration was made with Dr. M.P. Bender (URI) on two deep-water samples from the Sargasso Sea analyzed [6] by the APDC coprecipitation me. thod with yield monitoring using reactor-produced 64Cu (tl/2 = 12.8 hours, E. r = 511 keV). The results are in good agreement [6]. As further confirmation, Moore and Burton [7] report similar values using concentra-

1 Present address: Grant Institute of Geology, University of Edinburgh, Edinburgh, Scotland.

39 tion on Chelex-100 [8] in profiles from the eastern North Atlantic. A major reason for the paucity of oceanographic Cu data is the difficulty involved in obtaining uncontaminated samples and in analyzing them at the extremely low concentration levels encountered (ca. 10 -9 mol/kg). This problem first became apparent from the analyses of a suite of carefully collected samples from the upwelling region south of New Zealand [9] and has subsequently been confirmed by other workers ([6,7] as pointed out above). Clearly, the criteria applied to establish the validity of the data are crucial. A priori arguments on the extent of precautions in sampling and analysis are not in themselves sufficient nor is the fact that the numbers are lower than previously reported. The primary criteria must be interlaboratory agreement [6,7] and the oceanographic consistency of the data themselves; detailed profiles should show smooth variations related to the hydrographic and chemical features displayed by conventionally measured properties. Regional variations should be compatible with what is known of the large-scale physical and chemical circulation of the oceans. The problems in sampling and analysis have not been completely overcome. Occasionally certain points fall high off the trends. Most of these samples have been re-run. Usually they then fall back onto the "smooth" distribution indicating contamination during the first analysis; the original analysis has therefore been disregarded and is not reported here. However in some cases, the re-run gives a value identical to the original analysis. This probably indicates sample contamination but in the absence of proof the data have been retained (although not plotted) and are indicated by asterisks in the tables. The numbers reported here are, by operational definition, "total dissolvable Cu"; that is, any Cu in the sample converted to a labile ionic form by acidification to pH 2 and storage for over one year. Reports on the particulate concentration of Cu in seawater ([ 10]; P. Brewer and D. Spencer, personal communication) and for additional Cu released by UV oxidation [7] suggest that these forms comprise much less than 10% of the total Cu. Hence the total dissolvable Cu concentrations are closely equivalent to the dissolved Cu in the original water.

3. The distribution of copper in the water column • The Cu measurements are listed along with the associated hydrographic data in Table 1 and are plotted as depth profiles in Fig. 1 along with oxygen, phosphate and silicate for comparison. The profiles all show a striking increase in concentration to the bottom; this is in contrast to the nutrients which (with the exception of Si at station 293) display the usual mid-depth maxima. In the case of stations 219 and 340 the deep-water curves are clearly concave up. The profiles differ markedly from one another in the upper kilometer. Station 293 in the Circumpolar Current southeast of New Zealand has a form very similar to that for silica; station 345 in the California Current at 22.5°N is depleted in the mixed layer with a sharp concentration increase through the upper thermocline similar to that for phosphate. The values are uniform between 200 and 1000 m, the region of the phosphate maximum and below this increase to the bottom. At station 219 in the Bering Sea there are no identifiable features in the upper-water column; the levels are high and uniform to a depth of 1000 m. The stations in the Central Pacific gyre, 202,226, and 340, are broadly similar and completely different from the others. The surface waters are enriched by as much as a factor of two over the upper thermocline; there is a pronounced subsurface minimum extending to between 500 and 750 m. The increase below is steep to a strong inflection around 1000 m. The profiles show no obvious points of similarity with the nutrients beyond the general increase with depth.

3.1. The deep and bottom waters At stations 202,219,340 and 345 the deep-water potential temperature-salinity (O-S) relationship is linear reflecting its origin by vertical advection of bottom water and diffusive mixing with the overlying intermediate water. These profiles can be modeled consistently (although not uniquely) by a steady state one-dimensional advection-diffusion model with constant coefficients [11-14]. The following differential equations describe this model for potential temperature (0) and the concentration of Cu with a zero-order (J) or first-order (if)

40 TABLE 1 Copper and associated hydrographic data from six Pacific GEOSECS stations Depth (m)

0 (°C)

8(%~,)

02 (umol/kg)

Station 202; 33" 66'N, 139 ° 34'W; 30 August 1973 0 21.750 34.646 230 77 17.116 34.564 254 227 10.943 34.160 223 351 8.693 34.046 208 502 5.572 33.968 122 697 4.645 34.188 23 820 4.134 34.286 11 1127 3.228 34.455 21 1216 3.040 34.482 24 1423 2.679 34.527 38 1616 2.335 34.561 49 1822 2.019 34.592 64 2235 1.664 34.627 85 2439 1.554 34.640 94 2645 1.458 34.650 104 2849 1.380 34.655 111 3051 1.306 34.663 119 3200 1.262 34.668 125 3497 1.200 34.675 138 3646 1.178 34.678 142 3794 1.160 34.676 143 3943 1.146 34.680 147 4090 1.140 34.681 149 4242 1.127 34.682 151 4392 1.121 34.683 153 4541 1.116 34.684 154 4686 1.110 34.683 155 4846 1.107 34.684 155 4983 34.685 156

PO4 (#mol/kg)

Si (umol/kg)

Cu (nmol/kg)

0.06 0.09 0.86 1.34 2.25 3.03 3.13 3.17 3.15 3.10 3.04 2.97 2.86 2.82 2.77 2.72 2.65 2.61 2.60 2.56 2.58 2.55 2.55 2.55 2.56 2.53 2.53 2.53 2.53

2.4 2.6 11.9 25.0 57.1 96.0 111.7 137.1 141.3 149.1 158.0 163.8 177.9 177.1 176.2 175.5 173.7 169.7 166.9 167.3 166.7 163.6 161.4 160.5 158.0 156.1 154.7 155.2 153.9

2,4, 2.5 1.6 1,6, 1.7 1.6 2.0 2.4 3.1 4.2 3.9, 4.9 7.2, 7.2 * 4.6 4.3, 4.7 4.5 4.8, 5.6 5.0 4.5, 4.9 5.1 5.6 4.7 5.4, 5.9 5.9, 6.1, 6.5 6.2 5.5, 5.6 5.7, 6.0 6.6 6.7, 6.8 6.3, 6.6 6.6 9.4, 10.7 *

1.60 2.42 2.90 2.97 3.03 2.89 2.89 3.04 2.95 3.05 3.01 2.99 2.91 2.86 .... 2.80 2.73

32.2 74.2 100.8 113.7 128.0 131.0 141.9 150.9 163.3 176.5 190.1 202.7 209.5 220.9 226.9 221.7

2.6 3.1 3.1 2.8 3.0 2.5 2.6 2.8 3.9 3.3 3.8 3.5 4.1 4.3 5.6 6.0

* Con.tamination suspected.

Station 219; 53°06'N, 1 77~1 7W," 8 October 1973 5 7.107 33.069 298 160 3.533 33.524 196 348 3.548 33.886 70 459 3.417 34.027 48 599 3.294 34.159 25 641 3.226 34.177 27 790 3.047 34.266 20 941 2.834 34.337 17 1188 2.531 34.413 22 1438 2.249 34.480 26 1676 1.983 34.536 39 1986 1.741 34.585 54 2285 1.594 34.613 66 2582 1.482 34.635 78 3479 1.310 34.665 100 3710 1.281 34.669 109

41 TABLE 1 (continued) Depth (m)

0(°C)

S(%o)

02 0zmol/kg)

PO 4 (#mol/kg)

Si (/~mol/kg)

Cu (nmol/kg)

219 213 229 216 208 200 178 170 119 67 33 26 29 36 46 55 76 83 106 130 143 151 160 164 168 168 174 177

0.02 0.01 0.02 0.49 0.88 1.16 1.61 1.75 2.27 2.72 2.95 3.00 3.01 2.98 2.91 2.88 2.78 2.74 2.66 2.56 2.50 2.46 2.42 2.37 2.34 2.36 2.32 2.31

3.3 2.7 3.2 7.2 16.0 23.8 38.5 45.6 68.5 98.8 121.6 135.3 145.0 153.7 159.6 165.1 169.0 168.1 163.5 154.7 152.5 149.7 145.7 143.3 139.9 139.1 136.0 135.8

3.5 3.1 1.6 1.5 2.2 1.7 2.2 5.8, 2.7 3.4, 3.9 6.7, 3.4, 4.2, 5.0, 3.9, 4.4 4.6 5.2, 5.2 5.2 5.3 6.5, 5.2 6.0 6.1 5.5, 5.8

274 257 273 259 217 205 195 178 176 176 184 191 196 198 202 208 211 212 212

0.73 1.28 1.40 1.63 2.00 2.13 2.24 2.28 2.28 2.20 2.12 2.08 2.10 2.11 2.13 2.13 2.15 2.16 2.17

2.7 5.2 6.6 13.1 30.8 44.8 53.8 68.9 73.4 80.3 83.7 88.5 95.8 98.3 108.7 116.6 120.5 124.5 125.3

1.6 1.1, 1.2 1.9 2.2, 2.0 1.8 2.3 2.2, 2.5 2.6, 2.6 2.4 3.1 3.3 4.0 3.9 4.1, 4.4

Station226;30°34'N, 170°36'E;9 November1973 8 36 82 207 382 457 555 591 688 834 983 1126 1274 1422 1617 1713 2004 2149 2443 3030 3422 3812 4389 4589 4783 4800 5183 5477

24.73 24.75 23.58 15.19 12.01 10.33 7.92 7.28 5.62 4.28 3.62 3.20 2.85 2.53 2.30 2.06 1.741 1.620 1.480 1.286 1.197 1.139 1.073 1.040 1.030 1.023 0.992 0.969

35.055 35.053 35.005 34.627 34.396 34.277 34.103 34.066 34.031 34.131 34.265 34.371 34.440 34.488 34.531 34.560 34.600 34.615 34.639 34.663 34.673 34.679 34.684 34.689 34.689 34.689 34.691 34.695

5.0 * 3.9 7.4 * 4.2 4.0 5.1 4.4

5.7

7.6 *

6.2

* Contamination suspected.

Station 293;52°40'S, 178°05'W;1March 1974 3 215 457 684 961 1142 1290 1586 1733 2030 2326 2622 2918 3066 3511 4008 4462 4913 5257

11.328 7.65 6.46 5.27 4.07 3.30 2.83 2.45 2.37 2.19 2.018 1.78 1.52 1.422 1.05 0.77 0.586 0.48 0.446

34.419 34.419 34.342 34.268 34..312 34.347 34.395 34.525 34.577 34.659 34.708 34.732 34.736 34.735 34.723 34.711 34.705 34.700 34.699

1.3

2.5

2.3 2.7, 2.9

4.6

TABLE 1 (continued) Depth (m)

0 (0C)

S(%o)

O2 (~mol/kg)

PO4 (~mol/kg)

Si (~mol/kg)

Cu (nmol/kg)

0.24 1.68 2.28 2.31 2.33 2.33 2.45 2.70 2.83 3.02 3.05 3.08 3.05 3.08 3.04 2.91 2.82 2.74 2.71 2.63 2.66 2.61 2.58 2.52 2.51 2.47 2.43 2.40 2.39 2.38 2.38 2.38

5.0 16.8 25.0 27.2 29.4 31.0 33.8 44.1 54.3 66.6 75.8 83.6 90.9 100.1 110.1 125.4 138.3 147.8 153.9 156.5 158.0 159.0 160.2 159.6 160.4 156.4 153.8 151.4 150.8 149.6 149.0 148.8

3.5 3.3 2.6 2.8, 3.2 2.3, 2.7 1.6 1.9 1.7 1.5 2.1 1.5 2.1 2.8 2.1 2.9, 3.5 3.5, 2.5 2.5 3.0, 3.1:3.6, 3.7 ** 3.5 3.7 3.3 3.3 3.8 5.4, 6.6 * 3.9 4.6 5.3 5.2 4.8 4.6 6.1 6.5 7.7, 8.4

0.25 0.26 0.69 1.57 2.30 2.49 2.79 2.89 2.99 3.10 3.12 3.04 2.96 2.80 2.75 2.66 2.52 2.51

5.2 5.8 10.4 23.4 38.8 50.8 62.8 75.7 81.3 100.3 117.8 135.2 146.0 156.1 161.4 164.9 165.6 164.7

1.4 1.1 1.9 2.8 2.5 2.6 3.6 * 5.1 * 2.4 7.0 * 2.8 2.8 3.3 3.3 7.7 * 4.8 5.7 5.5

Station 340; 10°28'N, 123°38'W; 1 June 1974 0 41 77 102 141 194 256 410 513 616 718 820 923 1025 1176 1431 1681 1929 2082 2284 2331 2732 2931 3128 3329 3530 3727 3920 4121 4121 4329 4329 4516

26.81 16.88 13.39 12.46 11.59 11.00 10.44 9.05 7.90 6.85 5.982 5.37 4.84 4.38 3.907 3.183 2.62 2.189 1.992 1.780 1.772 1.592 1.494 1.394 1.304 1.239 1.175 1.113 1.084 1.084 1.076 1.076 1.071

34.226 34.654 34.720 34.787 34.765 34.739 34.723 34.653 34.591 34.565 34.540 34.542 34.547 34.561 34.572 34.593 34.616 34.638 34.647 34.658 34.659 34.667 34.672 34.678 34.679 34.683 34.686 34.688 34.691 34.691 34.691 34.691 34.691

204 71 6 3 9 15 7 2 1 1 7 12 23 28 38 58 71 86 94 103 105 115 121 129 136 143 150 156 159 156 160 160

* Contamination suspected. ** Duplicate runs on two samples drawrL from the same Niskin

Station 345; 22°31 'N, 122°12'W; 6 June 1974 11 67 137 186 274 343 424 505 584 786 995 1291 1590 1888 2184 2582 3778 4206

18.418 16.910 12.511 10.702 9.590 8.275 7.424 6.364 6.102 4.997 4.114 3.251 2.638 2.140 1.787 1.536 1.205 1.193

34.157 33.958 33.775 33.885 34.296 34.286 34.364 34.328 34.417 34.469 34.511 34.561 34.596 34.622 34.646 34.661 34.681 34.681

239 247 213 136 57 45 16 13 8 10 19 36 55 76 95 111 138 139

* Contamination suspected (from dust on bottle caps and in threads)

43

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Fig. 1. Depth profiles of copper, oxygen (o), phosphate (o) and silicate for GEOSECS Pacific stations 202 and 219, Points connected by a dashed line are replicates of the same sample.

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Fig. 1 (continued). Depth profiles o f copper, oxygen (o), phosphate (e) and silicate for GEOSECS Pacific stations 226,293 (p. 44), 340 and 345. Points connected by a dashed line are replicates o f the same sample.

46 reaction term: ro"

-

(la)

I4/0 ' = 0

KCu" - WCu' + J = 0

(zero order)

(lb)

KCu" - WCu' + ~bCu = 0

(first order)

(lc)

where K is the vertical eddy diffusivity, and W is the vertical advection velocity (positive downwards). The general solutions to these equations are (z is the distance from the sea surface):

0 = A e t'z+C

(2a)

J Cu = Alebz + - ~ z + C1

(2b)

Cu = h 2 edz + C2 e(b-a)z

(2c)

where b = W/K and d=b(l_

VI

4t~/W)b

Rearranging (2a), substituting into (2b), and combining integration constants gives: J Cu=~ +--z+~ W

(3)

From (3), J/IV can be determined by a multiple linear

regression of Cu vs. 0 and z. The Cu, 0, and depth data were fit to (2a), (2c), and (3) (Table 2) using an iterative least squares method for (2a) and (2c). If Cu is conservative in the linear 0 - S region (J/W = ~/W = 0), the Cu-0 relationship must be linear. Instead, Cu deviates negatively from a linear relationship (Fig. 2) indicating that Cu is removed from the deep water. Zero- and first-order removal terms fit the data equally well (Table 2), so the functionality of the removal process is not constrained [ 14]. The absolute rates were estimated using the values for W determined from radioisotope distributions at GEOSECS stations adjacent to stations 202 and 345 (GEOSECS I 3.66 m/yr [14]; 204, 3 . 8 5 - 2 . 9 3 m/yr [16]). The zero-order removal rate at both stations is 3 × 1 0 - 3 nmol kg -1 yr -1 ; the removal alternatively can be described by a Cu "half-life" of 1100 years (Table 2). Craig [14] in the original adaptation of the advection diffusion model [11,12] to treat the problem of trace metal scavenging applied it to the data of Spencer et al. [15]. His conclusions regarding the deep-water chemistry of Cu are surprisingly similar to those presented here given that the levels reported [15] were about seven times higher. Since the reasons for the discrepancy in concentration levels are not understood (D.W. Spencer, personal communication),

TABLE 2 Parameter

Station 219

Station 345

K/W (m) A (°C) C (°C) J/W * (nmol kg-lyr-lm -l) a (nmol/kg) j3 (nmol kg-1 °C-l) ofit (nmol/kg) t~/W* (m -~) A 2 (nmol/kg) C2 (nmol/kg) afi t (nmol/kg) W ** (m/yr) J * (nmol kg-1 yr-1) • (yr -l) t 1/2 = -0.693/4 (yr)

540 13.88 1.33 1.64 X 10 -3 -1.7 1.24 0.20 3.1 × 10-4 2.19 2.43 0.24 -

780 10.84 1.14 0.85 × 10-3 2.4 -0.172 0.38 2.0 × 10-4 2.76 -3.00 0.07 -3.7 -3.2 × 10 -a -7.4 X 10-a 940

Station 202

Station 340

850 8.37 1.07 0.96 X 10 -3 1.3 0.71 0.25 1.8 X 10-4 3.15 3.72 0.27 -3.4 -3.1 X 10-3 -6.1 X 10-4 1130

850 11.38 1.04 1.37 X 10 -3 -1.0 0.61 0.45 2.7 X 10-4 2.07 -2.06 0.47 -

* J and ~0 are considered to be mutually exclusive: for the value given for J, ~0 = 0, and for the value given for 4, J = 0. ** Estimated from nearby stations [14,16].

47 I

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Cu n mol / kg

Fig. 2. Cu-O plots for stations 2 0 2 , 2 1 9 , 3 4 0 and 345 in the deep linear O-S region.

the significance of the earlier modeling study [14] can only be coincidental. Given the general increase of Cu with depth and the mid-depth scavenging process, Cu must be introduced into the deep water from the bottom. The flux (FB) can be crudely estimated by the method of Munk [12] as:

FB= -WCUB+ K (\S C~ Z u l]B ~ 2 . 5 nmol cm -2 yr -1 (4) Assuming an effective sediment diffusion coefficient of 10-6 cm-2 s-L, this flux requires a pore water gradient o f about 102nmol kg-' cm-i. Such high gradients should not extend very deep into the sediment as the solubility product of several Cu compounds

would be exceeded within a few centimeters [1]. The profile data thus require a very strong source of Cu near the sediment surface. The calculated diffusive flux out of the sea floor is comparable to the average

Cu accumulation rate in Pacific sediments, 1 nmol cm -2 yr -1 [2,17]. The suggestion [14] based on the previous data [15] that the high bottom values could be maintained advectively requiring "that Antarctic Bottom Water must forfn with a very high Cu concentration" [14] is discounted by the data from station 293 whose location was chosen to investigate this point. The bottomwater value (0 < 0.5 °) is 4.4 nmol/kg. Values in the North Pacific are generally 6 nmol/kg or higher, an increase of about 300. The equivalent increments for phosphate and silicate are about 15% (Table 1). However, the form of the latter profiles is completely different from that of Cu. Since the Antarctic Bottom Water at station 293 does not have an especially high Cu concentration and since profiles of all other tracers (with the exception of 226Ra with a known bottom source) show a mid-depth maximum, there must be a strong general flux of Cu from the sediment surface into the water column. The only other elements for which non-metabolic deep-water removal has been demonstrated are 2 ~opb and 2'°po [18-20]. For the latter there is no net removal from the water column, 10% on the average being associated with the suspended material [19]. For 2 ,opb the concentration anomaly is pronounced, ranging in excess of 50%, and ubiquitous in the deep sea [21]. There is considerable controversy as to the dominant mechanism of net removal of 2'°pb, whether one dimensionally by adsorption on sinking particles [21] or two dimensionally by bottom scavenging [19]. In the case of Cu where both scavenging in the deep water and release from the sea floor are prominent features of the profiles it is difficult to accept that bottom activity alone could account for both effects. It seems more likely that sinking particles do indeed scavenge Cu which is then remobilized during biological and chemical re-working of the freshly sedimented material. Such dualistic behavior is not necessarily contradictory; the time scales of sinking and of opensystem exposure at the sediment-water interface differ by 2 - 3 orders of magnitude and hence the Cu-binding capacity of the material can be altered at rates very much slower than the scavenging process. Since the primary flux to the sea floor has to be about twice the net accumulation rate, the uppermost layer of deep-sea sediments should be strongly enriched in Cu.

48 The influence of the ridge crests, either as sources or sinks, has commonly been invoked to explain the observed distribution of trace elements in sediments. The accumulation rate of Cu in the metal-rich sediments of the East Pacific Rise is about 1.2 nmol cm -2 yr -1 over a zone approximately 5000 km × 1000 km [17]. If this is distributed as a scavenging anomaly throughout the eastern Pacific below 1 km then the effective removal rate would be 3 × 10 -4 nmol kg -1 yr -a , an order of magnitude less than the model rates. Measurements of the Cu concentrations in the ambient water column above the Galapagos spreading center [22] indicate no obvious anomaly relative to other stations at the same potential temperature (Table 3). Preliminary measurements of hydrothermal solutions from the same area [23] show the Cu values to remain within about 25% of ambient over the temperature range sampled (13°C). It should be emphasized that this evidence does not discriminate between seawater and hydrothermal waters as the source for the Cu in metal-rich ridge-crest sediments but indicates rather that this incorporation is a minor component of the overall cycle of the element in the deep-water column. 3.2. The upper waters

The degree of enrichment of the mixed layer in Cu correlates well with that of 2 lOpb [24] ; stations which have high surface Cu concentrations lie within the 15 dpm/100 kg-contour equivalent to daughterparent activity ratios greater than two. The absence of a pronounced surface maximum (stations 219, 293,345) is indicative of regions of high biological TABLE 3 Comparison of copper concentrations in the eastern Pacific at a potential temperature of about 1.8°C Location

Galapagos spreading center (Pleiades Leg 2, station 82; 0° 34.6'N, 86°6.5'W) GEOSECS station 345 GEOSECS station 202

Depth (m)

Bottom Cu depth (nmol/kg) (m)

2500

2720

5.0 -+0.3

2100 2000

4221 5129

4.0 + 0.5 4.5 + 0.3

productivity associated with upwelling and correspondingly lower 21°pb levels. The only profile for which both Cu and 2a°pb data presently exist is 226 [19,24]. The two elements show very similar behavior in the upper 1500 m (Fig. 3). For both the levels drop off sharply through the uppermost thermocline. The 21°pb minimum at about 500 m is appreciably deeper and broader than that for Cu (225 m), however both increase steadily below 750 m. The 2 X0pb stations 201 (34°N) in the California Current [25] and Bartlett 3 (19°S) in the Peru Current [20] are in very similar oceanographic regimes to the Cu station 345 (22°N). At station 201 there are only three points in the upper kilometer; the surface point is low relative to that at 389 m which is identical to the value at 768 m, below which the levels increase to the bottom. The more detailed profile from Bartlett 3 (B-3) shows a very steep gradient between 32 m (3.1 dpm/lO0 kg) and 150 m (9.16 dpm/lO0 kg). Between this depth and 1200 m the increase is only to 11.7 dpm/100 kg. Below this again there is a more rapid increase to a deep maximum. The Cu profile at station 345 is remarkably similar showing a sharp increase between 75 and 200 m, a uniform region to 1275 m, and a continuous rise to the bottom. In the Circumpolar Current the 2 a0pb station 282 [25 ] is similar to the Cu station 293, each showing a steady increase from the mixed layer to depths of over 1500 m. A plot of all the available matched Cu and 2l°pb surface data shows two relationships (Fig. 4); in the Circumpolar Current where the atmospheric input of 2 lOpb is negligible there is a tight linear correlation with a slope of approximately 30 nmol Cu/dpm 2~°Pb. For the tropical North Pacific, stations 345, 202 and 226 lie on a straight line with station 340 falling to considerably higher Cu values. The slope of the line is about 10 nmol/dpm. It is clear that the relationship in the Circumpolar Current is maintained by the upwelling of water containing 226Ra-supported 21opb; this is consistent with the nutrient correlations displayed by Cu [9]. In the northern waters however, the high surface values for both species show no correlation to any other measured property and certainly cannot be maintained by upwelling. Since it is known that the high 2~opb concentrations are caused by wet and dry fallout from the atmosphere of the decay product of continentally derived 222Rn [24], it appears that

49 Pb- 210 dpm/IOOkg 20

I0

o

o

I

3O I

Pb-210 Cu nmol/kg dpm/lOOkg 2 3 4 0 I0 I

1° "

I

r

G

80

Cu nmol/kg

~

I

2

I•

I

3 I

Pb-210 dpm/lOOkg Cu nmol/kg 5 I0 I 2 I

o

I

I

"

I

o o

•

o o

×

o

500 o o o---o

o

o

1000

m

X

e-4

500

Fig. 3. Comparison of the distribution of Cu and 21°Pb in the upper waters at the same or similar stations. (a) Station 226 in the western central Pacific gyre. (b) Station 201 in the California Current (×), Bartlett 3 (B-3) in the Peru Current (o) for 2lOpb and Cu station 345 in the California Current (e). (c) 282 (21°pb) and 293(Cu, e) in the Circumpolar Current, north of the Polar Front in the extreme southwest Pacific.

I

I

e226 = 25 202 e-e

20

0 0 E

340

O. "o

o

H

15

Od i Q.

345

0286 o 287

I0 280 oo

285 o282

°290 o294 233

• 293

J 2 Cu nmol

J 3 / kg

Fig. 4. Plots of Cu vs. 2z°Pb for surface waters. All 2t°Pb data from Nozaki et al. [24]: Cu data from the Circumpolar Current (o) are taken from Boyle and Edmond [9].

the Cu levels are also maintained by atmospheric transport. The possibility of a lateral contribution of Cu from shallow-water sediments, as is the case for 228Ra can be examined using the published surface distribution map [26]. 228Ra has highest values close to the boundaries, 2'°Pb and Cu in the central gyre. Specifically station 345 in a region of high 22aRa has low surface Cu, the reverse being true for station 226. While more data is needed to establish the significance of this source, it is clearly of no importance at the stations under discussion. Estimates of the probable magnitude of the aeolian input of Cu (Table 4) can be derived only indirectly and with considerable uncertainty. The data on the composition of marine aerosols are striking in that they show an enrichment of Cu relative to A1 by several hundred over the values expected from "average continental crust" [27]. The same phenomenon is observed for Zn, Cd, Sb, Pb and Se and appears ubiquitous being present in the North Atlantic [28], on Hawaii [29] and also at the South Pole [30]. Since the absolute concentration levels at the Antarctic station are over three orders of magnitude lower than in the northern hemisphere while the relative enrichments are almost identical, it is difficult to believe that they are an artifact of contamination or sampling. The presence of the effect at the South Pole

50 TABLE 4 Estimates of the aeolian input of Cu Location/sample type

U.S. rain [32] U.K. rain [33] Greenland snow [ 31,34] 65°N 1966-1971 (average) 77°N 1945-1971 (average) 77°N [30] Antarctica [ 30,35 ] 70°S Base Roi Baudouin air snow South Pole air snow Japan rain [24] Marine rain [36,37] Bermuda air [27] model 1 model 2 Central North Pacific [24]

21°pb

Cu

concentration

flux

concentration

-

-

330 365

-

0.09

0.2 × 10-3 5 -

0.055 0.01 2 1.5

13.4 9.2

flux

0.6 0.3

0.006 + 0.003

.0.016 -

-

0.3 6.9

Concentration units are, rain and snow: dpm/kg, nmol/kg; air: dpm/m 3, nmol/m3. Fluxes are consistent: dpm cm -2 yr -1 and nmol cm-2 yr-1

suggests that its origin is not from industrial pollution of the troposphere but that stratospheric transport is involved. This is confirmed by the data of Weiss et al. [31] for the concentration in the Greenland ice cap where there is a pronounced seasonal cycle in the rate of accumulation. The observed winter maximum is consistent with a stratospheric source. The origin of the Cu aerosol is not known although it is thought likely t o b e volcanic [27]. There appear to be no reported data on the concentration of Cu in marine rain. The averages for land stations in the U.S. [32] and U.K. [33], 330 nmol/kg and 365 nmol/kg, are very high and may reflect proximity to pollution sources. The accumulation rates on the Greenland ice cap [31 ] are much lower and highly variable. At Dye-3 (65°N) data for 1966-1971 average 13.4 nmol/kg, equivalent t o ' an accumulation rate of 0.6 nmol cm -2 yr -~ . At Camp Centry (77°N) comparable values for the period 1945-1971 are 9.2 nmol/kg, 0.3 nmol cm -2 yr -1. At the latter station, the ice accumulation rate has been determined using 2 lopb [34] allowing calculation of the deposition rate of the radio-isotope,

0.09 dpm cm -2 yr -1, and of the Cu/21°Pb ratio, 3.3 nmol/dpm. There are no reports of Cu distributions in the Antarctic ice cap although, at the South Pole, there have been extensive measurements of the aerosol concentrations (0.006 + 0.003 nmol/m 3, [30]). The 21°pb accumulation rate at that location is 0.01 dpm cm -2 yr -l [35]. At the Belgian Base Roi Baudouin (70°S, 24°E), both the accumulation rate of 21°Pb (0.055 dpm cm -2 yr - l ) and the air concentration (0.2 × 10 -3 dpm/m 3) have been reported [35]; the latter shows no seasonal variation. Assuming that the deposition rate of 2 lOpb at the two sites is directly proportional to the air concentrations, then the computed aerosol Cu/2~°Pb ratio at the South Pole is 3 nmol/dpm. The reported values for 2 ~opb in marine rain average about 5 dpm/kg [36,37]. The precipitation rate over the central North Pacific is about 100 cm/yr [38] equivalent to a wet deposition rate for 22Opb of 0.5 dpm cm-2 y r - l . Accepting the Cu/210pb ratio of 3 nmol/dpm gives an estimated input of Cu of 1.5 nmol cm -2 yr -1 . The model results presented by

51 Turekian et al. [39] indicate a somewhat higher value for 21°Pb input, from 2 over Japan (measured) to 0.7 dpm cm -2 yr -l over San Diego. The central North Pacific average is about 1.5 dpm cm -2 yr -1 equivalent to a Cu flux of 4.5 nmol cm -2 yr -1 . Duce et al. [27] have estimated the aeolian flux of various trace metals into the mixed layer based on the data for the aerosol concentrations at Bermuda (33°N). They used two models; one assumes that the aerosol is uniformly distributed to 5000 m and is completely rained out 40 times per year; the other assumes washout factors - the ratio of rain to air concentrations - measured in the North Sea using a continuously open collector. The computed values are 0.29 and 6.9 nmol cm -2 yr-1 respectively. The chemical dynamics of Cu in the mixed layer can be represented by a simple box model similar to those used for 2 ~opb [24]. At steady state, regarding the effect of vertical mixing with the thermocline waters as negligible, the flux of Cu from the atmosphere must be balanced by its removal in particulate form. Assuming that scavenging is proportional to concentration, taking the average mixed layer concentration as 3 nmol/kg and the average thickness as 50 m, then the residence time for Cu ranges from 50 to 2.1 years (using the low and high model flux values of Duce et al. [27]) with the 2 ~Opb.based estimate giving 10 and 3.3 years, respectively. The residence

time o f 2~°pb itself in the mixed layer is rather well established at about 1.7 years in the central gyres and as low as a month in regions of very high biological productivity [24,40]. It appears reasonable to suggest therefore that the observed surface Cu maximum in the central North Pacific is maintained by a flux of the element from the atmosphere of about 3 nmol cm -2 yr -1 . The fact that the aerosol Cu/21°pb ratio is lower than in the mixed layer is consistent with these arguments. The pronounced minimum in the upper thermocline is coincident with the generally observed particle and productivity maximum [41] and is probably maintained by a combination of biological uptake and general scavenging with subsequent incorporation into and removal by zooplanktonic fecal material [41]. The specific nature of the carrier phase or phases is uncertain, however. In Table 5 the reported values are listed for Cu in various particulate materials along with the ratios CUdeep -- CUs,arface

Xdeep -- Xsurface where X is the characteristic element in the carrier phase and the values are for the mixed-layer and deep North Pacific. There is sufficient Cu in surface particulates and whole phytoplankton to account for the observed deep-water enrichments. However

TABLE 5 Comparison

of surface/deep

enrichments

with carrier

Sample Type/Ref.

Cu/Organic C *

Water column Atlantic surface particulates [ 10] Sargassum [43] Sediment foraminifera [44] Coccolith ooze [45] Pteropods (average) [46] Whole surface phytoplankton [47] (medians) group I group II group III Silica frustrules (medians) group I group It

1.3 x l0 -s 1.9 X 10 -5

elemental ratios "Cu/P 1.5X10 -3

Cu/Ca

Cu/Si

7

2.9 X 10 -5

X 10 -s

6.6 × 10-3 -

10-s

-

1.5 ×

-

2

-

2.2 X 10 -s

× 10 -s

3.0 X 10-5 4.7 X 10-5 1.3 X 10 -4 5.3 x 10 -6 8.5 × 10-6

* The water column "organic C" change is taken as the non-carbonate portion of the CO 2 increase.

52 TABLE 6 Calculation of the oceanic residence time for copper with respect to input and final removal

Ocean River input* Aeolian input ** Sediment output :[: Sediment output :~

Assumed average concentration

Total Cu (moles)

4 nmol/kg 18nmol/kg 250 ppm -

6 × 1012 -

Flux (moles/yr) -6 -6 2 3.4

× 10s × 108 X 109 X 109

Residence (time/yr) -1 × 104}5 × 103 1 x 104 3 × 103 1.7 x 103

* Based on net output of the Amazon Estuary, June, 1974 (E. Boyle, unpublished data) and assuming this value representative of the world average river input. ** See text. :~ "Typical" carbonate-free sediment value [ 1] multiplied by an assumed average sedimentation rate of 0.15 gcm -2 (103 yr) -1 multiplied by the area of the ocean, 361 × 106 km2. :~:~Integrated Cu sedimentation rate for the Pacific [2] assumed representative of the whole ocean.

neither of the carriers known to have deep regenera= tion cycles, carbonate and silicate, appears to be sufficient, individually or in combination to maintain these levels.

4. The oceanic residence time for copper Estimates of river input and sedimentary accumulation rates of Cu are given in Table 6. The contribution of the atmospheric flux is certainly significant but difficult to evaluate with any precision. If as an upper limit the estimated value for the central North Pacific is applied worldwide, the annual delivery rate to the mixed layer is 101° mol/yr, about four times the sedimentary accumulation rate and about a factor of twenty greater than the estimated river input (Table 6). It is well known that the 21°Pb flux is drastically reduced in the southern hemisphere due to the smaller continental source areas and is in general lower at high than middle latitudes [24,37]. However, the flux of Cu necessary to maintain the North Pacific surface maximum is itself about half the river input. It is clear therefore that atmospheric and fluvial transport of Cu to the oceans must be of comparable significance. The computed residence time of about 5000 years is one of the shortest known for water-soluble species (e.g. alkalinity 80,000 years; Cd 50,000 years [42 ] ; Si 18,000 years; Ba 10,000 years [ 16] ; and Ni 10,000 years [3]).

5. Conclusions The geochemical cycle of Cu in the oceans is one of the most complex reported to date. The primary input to the sea surface probably derives equally from fluvial and aeolian transport. The latter is expect. ed to be most important at northern middle latitudes; the estimated flux into the central North Pacific is 3 nmol cm -2 yr -1. Copper is actively removed from the upper waters, the mixed-layer residence time being about 5 years. In the central gyre there is a pronounced concentration minimum in the upper thermocline coincident with the particle and productivity maximum [41]. Below depths of about 600 m the profiles increase to the bottom at all stations analyzed. Where applicable, advection-diffusion models indicate scavenging of Cu from the deep water, presumably by sinking particles. The average scavenging rate is about 3 × 10 -3 nmol kg -1 yr -I equivalent to a "half-life" of 1100 years. The increasing form of the profiles requires a strong bottom source. It appears that the Cu-binding capacity of the scavenging material is destroyed during early diagenesis. The resulting release of Cu occurs at a rate similar to that of net accumulation in the sediment. There must therefore be a Cu-rich layer at the sediment surface and associated pore water gradients of order 100 nmol kg -1 cm -1 . The oceanic residence time of Cu is short, about 5000 years. The outstanding features of the Cu cycle - aeolian

53 input and deep-water scavenging - are consistent with w h a t is k n o w n about the atmospheric, aqueous and sedimentary chemistry o f the element. Copper is enriched relative to A1 in atmospheric aerosols b y a a factor of 100 over the crustal abundance. The p h e n o m e n a is ubiquitous, observed in all types of environments. Active scavenging o f Cu f r o m solution has been d e m o n s t r a t e d for a wide variety o f materials from standard m o n t m o r i l l o n i t e to dead p l a n k t o n [1 ]. Copper is enriched in deep-sea sediments by up to a factor o f ten over shales and c o n t e m p o r a r y shelf deposits. It is likely that this c o m p l e x o f properties is mechanistically related. The great chemical reactivity o f Cu, its very short residence time, means that its marine geochemical cycle should be strongly perturbed by the climatic oscillations associated with the ice ages.

5

6

7

8

9 10

11 Acknowledgements We thank A.E. Bainbridge and the G E O S E C S Operations G r o u p for their care in the collection and shipboard processing of the samples. We also thank J.B. Corliss for permission to use the preliminary hydrographic data from the Galapagos spreading center cruise P L E I A D E S . We are grateful to K.K. Turekian, M.L. Bender, D.W. Spencer, R. Collier, and R. Stallard for critical discussion and especially to P.G, Brewer for the hospitality o f his laboratory. H. Craig has urged us to acknowledge the c o n t r i b u t i o n o f J. R o t t e n in providing a style m o d e l for this paper. This w o r k has been supported by the O N R through C o n t r a c t N00014-75-C-0291, by the IDOE, and by a grant f r o m the D o h e r t y F o u n d a t i o n . C o n t r i b u t i o n No. 16 of the G e o c h e m i s t r y Collective at MIT.

12 13 14 15

16

17

18

19

References 1 K.H. Wedepohl, Copper, in: Handbook of Geochemistry II-2, K.H. Wedepol, ed. (Springer-Verlag, New York, N.Y. 1970). 2 S. Krishnaswami, Authigenic transition elements in Pacific pelagic clays, Geochim. Cosmochim. Acta 40 (1976) 425 -434. 3 F.R. Sclater, g. Boyle and J.M. Edmond, On the marine geochemistry of nickel, Earth Planet. Sci. Lett. 31 (1976) 119-128. 4 E.A. Boyle and J.M. Edmond, Determination of trace metals in aqueous solution by APDC chelate coprecipitation, in: Analytical Methods in Oceanography, T.R.P.

20

21

22

Gibb, Jr., ed., Adv. Chem. Ser., No. 148 (ACS, Washington, D.C., 1975) 44-55. E.A. Boyle and J.M. Edmond, Determination of copper, nickel, and cadmium in seawater, Anal. Chim. Acta 91 (1977) 189-197. M.L. Bender and C.L. Gagner, Dissolved copper, nickel and cadmium in ~he Sargasso Sea, J. Mar. Res. 34 (1976) 327-339. R.M. Moore and J.D. Burton, Concentrations of dissolved copper in the eastern Atlantic Ocean, 23°N to 47°N, Nature 264 (1976) 241-243. J.P. Riley and D. Taylor, Chelating resins for the concentration of trace elements from sea water and their analytical use in conjunction with atomic absorption spectrophotometry, Anal. Chim. Acta 40 (1968) 479-485. E.A. Boyle and J.M. Edmond, Copper in the surface waters south of New Zealand, Nature 253 (1975) 107-109. S. Krishnaswami and M.M. Sarin, Atlantic surface particulates: composition, settling rates and dissolution in the deep sea, Earth Planet. Sci. Lett. 32 (1976) 430-440. K. Wyrtki, The oxygen minimum in relation to ocean circulation, Deep-Sea Res. 9 (1962) 11-28. W. Munk, Abyssal recipes, Deep-Sea Res. 13 (1966) 7 0 7 730. H. Craig, Abyssal carbon and radiocarbon in the Pacific, J. Geophys. Res. 74 (1969) 5491-5506. H. Craig, A scavenging model for trace elements in the deep sea, Earth Planet. Sci. Lett. 23 (1974) 149-159. D.W. Spencer, D.E. Robertson, K.K. Turekian and T.R. Folsom, Trace element calibrations and profiles at the GEOSECS test station in the northeast Pacific Ocean, J. Geophys. Res. 75 (1970) 7688. L.H. Chan, J.M. Edmond, R.F. Stallard, W.S. Broecker, Y.C. Chung, R.F. Weiss and T.L. Ku, Radium and barium at GEOSECS stations in the Atlantic and Pacific, Earth Planet. Sci. Lett. 32 (1976) 253-267. K. Bostr6m, T. Kraemer and S. Gartner, Provenance and accumulation rates of opaline silica, AI, Ti, Fe, Mn, Cu, Ni and Co in Pacific pelagic sediments, Chem. Geol. 11 (1973) 123-148. H. Craig, S. Krishnaswami and B.L.K. Somayajulu, 210 Pb-2~26Ra: radioactive disequilibrium in the de e p sea, Earth Planet. Sci. Lett. 17 (1973) 295-305. M.P. Bacon, D.W. Spencer and P.G. Brewer, 2 1 0 Pb/ 2 2 6 Ra and 21°po/21°Pb disequilibrium in seawater and suspended particulate matter, Earth Planet. Sci. Lett. 32 (1976) 227-296. J. Thomson and K.K. Turekian, 21°po and 21°Pb distributions in ocean water profiles from eastern south Pacific, Earth Planet. Sci. Lett. 32 (1976) 297-303. B.L.K. Somayajulu and H. Craig, Particulate and soluble Zl°pb activities in the deep sea, Earth Planet. Sci. Lett. 32 (1976) 268-276. R.F. Weiss, J.E. Lupton, P.F. Lonsdale, A.E. Bainbridge and H. Craig, Hydrothermal plumes on the Galapagos spreading center, EOS Trans. Am. Geophys. Union 57 (1976) 935.

54 23 J.M. Edmond, L.I. Gordon and J.B. Corliss, Chemistry of the hydrothermal waters at the Galapagos spreading center, EOS Trans. Am. Geophys. Union 58 (1977) in press. 24 Y. Nozaki, J. Thomson and K.K. Turekian, The distribution of 21°pb and 21°po in the surface waters of the Pacific Ocean, Earth Planet. Sci. Lett. 32 (1976) 304-312. 25 M.D. Applequist, Lead-210 in the deep sea: Pacific Ocean investigations, M.S. Thesis, Univ. of California, San Diego, Calif. (1975) 127 pp. 26 A. Kaufman, R.M. Trier and W.S. Broecker, Distribution of 228Ra in the World Ocean, J. Geophys. Res. 78 (1973) 8827-8848. 27 R.A. Duce, G.L. Hoffman, B..I. Ray, I.S. Fletcher, G.T. Wallace, J.L. Fasching, S.R. Piotrowicz, P.R. Walsh, E.J. Hoffman, J.M. Miller and J.L. Heffter, Trace metals in the marine atmosphere: sources and fluxes, in: Marine Pollutant Transfer, H.L. Windom and R.A. Duce, eds. (Lexington Books, Lexington, Mass., 1976) Chapter 4, pp. 77-119. 28 R.A. Duce, G.L. Hoffman and W.H. Zoller, Atmospheric trace metals at remote northern and southern hemisphere sites: pollution or natural ?, Science 187 (1975) 5 9 - 6 1 . 29 G.L. Hoffman, R.A. Duce and E.J. Hoffman, Trace metals in the Hawaiian marine atmosphere, J. Geophys. Res. 77 5322-5329. 30 W.H. Zoller, E.S. Gladay and R.A. Duce, Atmospheric concentration and sources of trace metals at the South Pole, Science 183 (1974) 198-200. 31 H. ~eiss, K. Bertine, M. Koide and E.D. Goldberg, The chemical composition of a Greenland glacier, Geochim. Cosmochim. Acta 39 (1975) 1-10. 32 A.L. Lazarus, E. Lorange and J.P. Lodge, Jr., Lead and other metal ions in United States rain, Environ. Sci. Technol. 4 (1970) 5 5 - 5 8 . 33 D.H. Peirson, P.A. Cawse and R.S. Cambray, Chemical uniformity of airborne particulate material and a maritime effect, Nature 251 (1974) 6 7 5 - 6 7 9 . 34 G. Crozaz and C.C. Langway, Jr., Dating Greenland firn-

ice cores with 21°pb, Earth Planet. Sci. Lett. 1 (1966) 194-196. 35 G. Crozaz, E. Picciotto and W. DeBrenck, Antarctic snow chronology with 21°Pb, J. Geophys. Res. 69 (1964) 2597-2604. 36 Rama, M. Koide and E.D. Goldberg, Pb-210 in natural waters, Science 134 (1961) 9 8 - 9 9 . 37 Y. Nozaki and S. Tsunogai, Lead-210 in the north Pacific and the transport of terrestrial material through the atmosphere, Earth Planet. Sci. Lett. 20 (1973) 8 8 - 9 2 . 38 A. Baumgartner and E. Reichel, The World Water Balance (Elsevier, New York, N.Y., 1975) 179 pp. 39 K.K. Turekian, Y. Nozaki and L.K. Benninger, Geochemistry of atmospheric radon and radon products, Annu. Rev. Earth Planet. Sci. 5 (1977) 227-255. 40 K.W. Bruland, M. Koide and E.D. Goldberg, The comparative marine geochemistries of lead-210 and radium-226, J. Geophys. Res. 79 (1974) 3083-3086. 41 J.K.B. Bishop, J.M. Edmond, D.R. Ketten, M.P. Bacon and W.S. Silker, The chemistry, biology and vertical flux of particulate matter from the upper 400 m of the equatorial Atlantic Ocean, Deep-Sea Res. 24 (1977) 511-548. 42 E.A. Boyle, F.R. Sclater and J.M. Edmond, On the marine geochemistry of cadmium, Nature 263 (1976) 4 2 - 4 4 . 43 E.D. Goldberg, W.S. Broecker, M.G. Gross and K.K. Turekian, Marine chemistry, in: Radioactivity in the Marine Environment (U.S. National Academy of Science, New York, N.Y., 1971) 272 pp. 44 D . Krinsley, Trace elements in the tests of planktonic foraminifera, Micropaleontology 6 (1960) 297. 45 G. Thompson and V.T. Bowen, Analyses of coccolith ooze from the deep tropical Atlantic, J. Mar. Res. 27 (1969) 32. 46 D. Krinsley and R. Bieri, Changes in the chemical composition of pteropod shells after deposition on the sea floor, J. Paleontol. 33 (1959) 682-684. 47 J.H. Martin and G.A, Knauer, The elemental composition of plankton, Geochim. Cosmochim. Acta 37 (1973) 1639-1654.