depletion of cadmium and nickel was found for the surface waters that could be ... the storage bottles from a rubber boat about 200 m upwind from the main ship. Shallow ..... for North Atlantic Deep Water (NADW) through the sinking of cooled.
Marine Chemistry, 17 (1985)23--41 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
23
CADMIUM, COPPER, IRON, NICKEL AND ZINC IN THE NORTH-EAST ATLANTIC OCEAN
LARS-GORAN
D A N I E L S S O N , BERTIL M A G N U S S O N
and STIG W E S T E R L U N D *
Department of Analytical and Marine Chemistry, Chalmers University of Technology and University of Gothenburg, S-412 96 Gothenburg (Sweden) (Received February 27, 1984; revision accepted January 29, 1985)
ABSTRACT Danielsson, L.-G., Magnusson, B. and Westerlund, S., 1985. Cadmium, copper, iron, nickel and zinc in the north-east Atlantic Ocean. Mar. Chem., 17: 23--41. The concentrations of cadmium, copper, iron, nickel and zinc have been determined on 105 water samples from the north-east Atlantic Ocean. Three rather different areas were sampled in this investigation. The first area is the Norwegian Sea, the birthplace for North Atlantic Deep Water (NADW), bordering the Arctic. Second, the relatively shallow Iceland-Faroe Ridge area where the newly formed deep water spills over into the northeast Atlantic. The third area sampled is the north-east Atlantic, further south, with less pronounced seasonal variations in temperature and light conditions. In the Norwegian Sea no surface depletion was found for cadmium, copper, nickel or zinc. The mean concentrations were (for unfiltered samples): Cd, 0.20rim (22 ng l-1 ); Cu, 1.4 nM (90 ng l-1 ); Ni, 3.5 nM (200 ng 1-1 ); and Zn, 1.5 nM (130 ng 1-1 ). For iron the concentration in the surface water was 4.4nM (250 ngl-1), with a slight increase towards the bottom. In the warm surface waters of the north-east Atlantic a depletion of cadmium and nickel was found for the surface waters that could be correlated to a depletion of nutrients. For copper and zinc the slight depletion found could not be correlated with any of the nutrients. In the deep waters of the north-east Atlantic, higher concentrations of cadmium, copper, nickel and zinc were found than at similar depths in the Norwegian sea. For iron, on the other hand, the concentrations were higher in the Norwegian Sea.
INTRODUCTION
During recent years a significant improvement in our understanding of the trace-metal chemistry of ocean waters has been achieved. Concurrently, present-day baseline levels of many trace elements have been established for various areas of the oceans. This has been made possible by the development of more accurate and precise methods of sampling and measurement of metals at the ng 1-1 level in seawater. The work on lead by Patterson and co-workers paved the way for this evolution by pointing out the importance of contamination during sampling and analysis (Patterson and Settle, 1976). *To w h o m correspondence should be addressed.
0304-4203/85/$03.30
© 1985 Elsevier Science Publishers B.V.
24 On applying more appropriate sampling procedures, lower concentrations of metals were found, requiring the development of more sensitive analytical methods. A number of new methods with the necessary capability have bee~:~ published (Boyle and Edmond, 1977; Danielsson et al., 1978; Bruland et al.~ 1979; Mart, 1979). The application of refined methods has given deeper insight into the processes governing the internal cycling of trace metals in the oceans. For cadmium, nickel and zinc a close association with biogenic cycles has been found (Bruland, 1980; Boyle et al., 1976; Sclater et al., 1977; Danielsson, 1980; Boyle et al., 1981; Bruland and Franks, 1983; Danielsson and Westerlund, 1983). Similarly for copper, a close association with the cycling of micronutrients can be seen combined with a deep-water scavenging process (Boyle et al., 1976; Bruland, 1980). In contrast to this, the iron distribution seems to be largely governed by inorganic precipitation and adsorption processes (Gordon et al., 1983). Recent intercalibration exercises organised by ICES have shown that the results obtained by different groups using different methods are approaching each other (Bewers et al., 1981; Berman et al., 1983). These improved analytical capabilities have also led to the detection of important variations in trace metal concentrations in ocean waters both in time and space (Danielsson and Westerlund, 1983, 1984; Boyle and Huested, 1983; Bruland and Franks, 1983; Kremling, 1983). Most of the more recent work on trace metals in the oceans has been performed in tropical or subtropical areas with high biological activity throughout the year. Relatively few data are available for the -more temperate regions with their distinct seasonal variations. In this paper we present results from a cruise on the north-eastern Atlantic Ocean and the North Sea. These areas are of special interest because the extensive, highly productive shelf areas involved supply an important fishery. The most northerly stations are, furthermore, situated in the Norwegian Sea, the area where North Atlantic deep water is formed.
SAMPLING AND ANALYTICAL PROCEDURES Seawater samples were collected during a cruise with R/V "Alexander von H u m b o l d t " , belonging to the Academy of Sciences of the G.D.R., in June 1981. The cruise track and sampling stations are given in Fig. 1, The North Sea, the Norwegian Sea, the Iceland-Faroe Ridge and the North East Atlantic are included in the cruise track. Surface samples were collected directly in the storage bottles from a rubber boat a b o u t 200 m upwind from the main ship. Shallow water samples were obtained from the rubber boat with the aid of 2.5-1 modified Go-Flo samplers hung on a polyester line. Samples from greater depths (~> 20 m) were obtained from the main ship using the Go-Flo samplers hung on a stainless-steel wire. Subsamples were transferred, unfiltered, into carefully cleaned polyethylene bottles and acidified in a
25
oN '65
76
'55
~iii:iii%i~i~ii~7i~i~. 50
20
oW
10
0
10
° E
Fig. 1. Map showing the cruise track and the sampling stations.
clean bench with 1 ml 1-1 of purified nitric acid. The bottles were then wrapped in plastic bags and stowed in wooden boxes for transport. The analyses were carried out a few months later under clean-room conditions. The metals were extracted as dithiocarbamate complexes into Freon 113 and back-extracted into an acidic aqueous solution prior to determination with a graphite furnace AAS (Danielsson et al., 1978, 1982). A more detailed treatment of the sampling and analysis procedures, e.g., precision, blanks, metal leaching from storage bottles and sampling accuracy, can be found elsewhere (BriJgmann et al., 1982). Salinity and temperature readings were obtained from a CTD sond, and nutrients were determined by standard spectrophotometric procedures (Rhode and Nehring, 1979). RESULTS AND DISCUSSION
The complete data set from the expedition has been collected in a report (Briigrnann et al., 1982) available from the authors. The results of lead determinations on the same samples have been reported (Briigraann et al., 1985), as has the o u t c o m e of a methodological intercomparison (Briigmann et al., 1983). Trace metal, phosphate and hydrographical data are presented in Table I. The trace metal results represent the total acid-leachable metal content. However, investigations on North Sea and Skagerrak waters (Eisma
26 TABLE i Vertical profiles o f salinity, t e m p e r a t u r e , p h o s p h a t e a n d trace m e t a l (ng 1 - i } da~;a Depth (m)
Salinity (%o)
Temp. (°C)
PO4 (]lN~)
Cd
Cu
},'e
Ni
Zn
6.9
0.21 0.10
28 24
520 220
2600 1400
600 325
4.5 6.3 5.8 5.8 5.1
0.01 0.10 0.68 0.72 0.90 0.84
28 31 31 18 43 19
420 390 170 140 600 120
590 380 2200 1900 1800 6300
510 8 1 0 525 840 250 5 0 0 225 350 505 1 1 0 0 210 320
8.4 6.3 6.2
0.]2 0.14 0.18 0.59
13 27 46 43
114 150 920 112
530 500 5400 1300
205 195 360 195
210 300 520 480
8.8 6.7 7.9 7.4
0.03 0.01 0.50 0.85 0.82
24 28 20 19 20
270 320 150 96 88
260 310 300 300 560
385 395 245 195 190
520 540 280 170 91
9.0 7.1 6.0 0.9 --0.9
0.41 0.40 0.92 0,94 1.06 1.1]
18 17 21 20 25 21
85 76 86 76 96 92
90 114 2900 580 1100 1300
185 175 195 190 195 200
52 90 280 87 180 200
S t a t i o n 74 57°32'N, 11°19'E Date: 810524
0 30
-33.33
--
S t a t i o n 75 58°00'N, 09°00'E Date: 810525
0 10 50 100 200 530
-31.64 34.82 34.96 35.07 35.04
--
S t a t i o n 76 58°00'N, 02°30'E Date: 8 1 0 5 2 6
0 10 30 50
-34.98 35.05 35.06
--
S t a t i o n 77 60°00'N, 02°30'E Date: 810527
0 10 30 50 100
-32.03 34.81 35.26 35.30
--
S t a t i o n 78 62°30'N, 00°30'E Date: 8 1 0 5 2 8
0 20 100 200 400 800
-35.28 35.21 35.14 34.88 34.88
--
S t a t i o n 79 65°00'N, 01°00'W Date: 810529
0 20 100 200 500 1000
-35.06 35.04 34.95 34.88 34.89
-6.6 4.3 3.2 0.2 --0.7
0.28 0.32 0.85 1.20 1.05 1.05
24 21 18 18 23 22
83 93 81 81 85 85
230 450 350 350 370 440
185 190 180 180 180 190
84 110 67 58 110 115
2000 2800
34.91 34.91
--0.9 --0.9
1.10 1.08
21 21
88 93
840 650
190 200
105 96
Station 80 64°10'N, 05°40'W Date: 8 1 0 5 3 1
0 20 100 200 500 1000 2000 3400
-34.92 34.95 34.90 34.87 34.90 34.89 --
--
0.53 0.50 0.83 0.87 1.03 1.04 1.04 --
18 19 20 19 25 25 24 24
86 100 97 97 95 95 99 103
167 240 260 310 300 300 230 330
190 56 205 105 235 84 205 93 200-195 135 210 110 205 170
S t a t i o n 81 63°28'N, 07°00'W D a t e : 810602
0 20 100
-35.17 35.18
0.41 0.51 0.98
25 20 22
79 83 86
180 125 450
190 195 195
4.8 2.9 1.9 0.4 --0.6 --0.9 --7.9 6.6
970 500
56 83 94
27 TABLE I
(Continued) Depth (m)
Salinity (%)
Temp. (°C)
PO4 (pM)
Cd
200 500 1200
35.07 34.87 34.90
5.0 0.6 --0.8
0.92 0.96 1.07
21 21 22
S t a t i o n 82 62°45'N,08°20'W Date:810604
0 20 100 200 450
-35.23 35.23 35.21 34.93
-8.5 7.8 7.7 2.1
0.64 0.68 0.73 0.89 1.00
S t a t i o n 83 62°02rN, 09°35'W Date:810608
100 200 400 600
35.23 35.21 35.20 35.07
7.9 7.7 7.4 6.6
S t a t i o n 84 60°47'N, 14°00'W Date:810609
50 100 200 500 1000 1650
35.20 35.22 35.22 35.18 35.03 --
S t a t i o n 85 59°00'N,20°00tW Date:810610
0 20 100 200 500 1000 2000 2800
Station 86 5 3 ° 0 0 ' N , 20°00rW Date:810613
Cu
Fe
Ni
Zn
92 91 96
1600 860 1040
205 195 195
70 89 170
20 22 22 22 23
76 110 81 99 95
200 100 180 120 1440
200 210 195 210 205
75 150 105 78 115
0.94 1.03 1.04 1.05
22 23 23 24
82 128 123 82
83 194 88 360
195 200 200 195
97 480 93 170
9.2 8.3 8.2 7.7 5.5 --
0.68 0.90 0.93 0.98 1.30 --
16 18 20 24 27 28
79 93 80 88 116 87
57 89 51 70 330 200
185 195 195 195 2O5 215
62 105 93 78 120 115
-35.17 35.12 35.16 35.14 34.99 34.91 34.95
-10.2 9.0 8.9 8.0 5.3 3.6 3.1
0.43 0.53 0.87 0.95 1.08 1.36 1.20 1.21
15 17 21 19 24 26 28 26
85 103 84 103 89 96 93 101
89 70 100 140 115 390 150 190
190 185 190 195 195 220 215 210
34 105 62 71 180 115 140 162
100 200 500 1000 2000
35.31 35.32 35.19 35.00 --
11.0 10.4 8.8 4.7 --
0.63 0.90 1.20 1.22 --
9 15 20 31 27
79 88 85 92 92
1060 660 250 200 240
165 190 2OO 240 225
49 86 87 150 150
S t a t i o n 87 48°30tN, 20°00'W Date:810615
0 20 100 200 500 1000 2000 2700 3500
-35.65 35.65 35.64 35.35 35.13 34.92 34.92 --
-13.9 13.2 12.9 10.6 6.5 3.6 3.2 2.8
0.08 0.30 0.45 0.54 0.99 1.31 1.22 1.22 --
4.5 5.5 7 11 23 32 29 25 38
69 85 74 82 76 90 94 103 156
500 150 260 240 140 250 220 220 230
135 145 150 165 235 230 230 225 275
32 125 51 75 80 180 140 180 210
S t a t i o n 88 40°30rN, 15°00'W D~e: 810616
0 20 100 200
-35.50 35.50 35.49
-13.2 11.8 11.4
0.10 0.26 0.54 0.70
6.0 7.0 8.5 14
74 77 76 77
290 110 140 180
135 135 170 155
23 82 48O 7O
28 TABLE I (Continued) Depth Salinity (m) (%)
Station 89 48°30'N, 09°46'W Date: 810617
Temp (°C)
PO 4 (pM}
Cd Cu
Fe
Ni
Zn
105 ]85
500 1000
35.37 35.36
10.3 7.7
0.95 1.30
19 25
79 77
190 230
180 215
0 20 100 180
-35.47 35.49 35.50
-12.6 11.6 11.2
0.22 0.47 0.60 1.08
12 12 12 14
79 82 74 79
170 265 340 810
155 125 150 200 155 82 1170 160
Station 90 O r 50 06.8 N, 00°39.6'W Date: 810620
0 20 48
-34.78 34.78
-11.9 11.9
0.05 0.09 0.09
25 20 19
200 200 190
1450 5500 6700
245 305 215
260 420 370
Station 91 52*09'N, 03°30'E Date: 810620
0 20
-33.87
-13.6
0.44 0.27
20 32
340 330
29000 29000
400 390
660 600
Station 92 55°00'N, 05°00'E Date: 810621
10 36
34.37 34.14
10.1 8.0
0.06 0.17
28 290 26 100
1300 1400
300 340
520 580
Station 93 58°00'N, 09°00rE Date: 810622
0 10 50 100 200 530
27.62 34.64 34.90 34.99 35.10
12.7 5.9 5.9 5.5 5.5
0.05 0.06 0.82 0.88 0.94 0.95
31 32 18 35 18 19
1400 1900 1700 1900 3700 6400
480 490 255 520 215 185
390 510 200 560 300 220
-
400 790 170 750 120 120
et al., 1 9 8 4 ) s h o w t h a t t h e t o t a l acid-leachable f r a c t i o n represents t h e t o t a l trace m e t a l c o n t e n t in m o s t samples. F u r t h e r m o r e , this investigation s h o w e d t h a t f o r the metals c a d m i u m , c o p p e r , nickel and zinc less t h a n 10% o f the t o t a l was f o u n d in the p a r t i c u l a t e f r a c t i o n , while f o r iron t h e particulateb o u n d f o r m c o n s t i t u t e d the m a j o r fraction. With the c o n s i d e r a b l y l o w e r a m o u n t o f p a r t i c u l a t e s u s p e n d e d m a t t e r in t h e Atlantic waters ( B d i g r n a n n et al., 1 9 8 2 ) t h e acid-leachable f r a c t i o n is c o n s i d e r e d t o be very close to t h e dissolved or t o t a l f r a c t i o n in this area, e x c e p t f o r iron.
Surface waters T h e c o n c e n t r a t i o n s o f c o p p e r , nickel a n d zinc s h o w large variations i n t h e surface waters o f t h e N o r t h Sea, as can be seen f o r nickel in t h e section given in Fig. 2. High surface-water c o n c e n t r a t i o n s o f these metals are, h o w e v e r , a c c o m p a n i e d b y low salinities. A p l o t o f nickel c o n c e n t r a t i o n s in surface waters versus salinity is given in Fig. 3. Results f r o m o t h e r investigations in t h e S k a g e r r a k - - K a t t e g a t area are also i n c l u d e d in this figure (Magnusson a n d
29
ng I"
nM
c
0'3 0,2t 01
;'
20
lO ng 14
nM Ni
.4oo
~ -30o -
200
-I00
uM 1.0t 0.5
pM P
O
4
NorthSea
~E .C ~. C~4
Norwegian Sea
NorlhEasl Atlanlie
| | | i | | | 787980 81898384 85 8=68=78=8 899~0 9=19127~67=7 Station
Fig. 2. Horizontal profiles of c a d m i u m , nickel and phosphate in surface water. A mean value from 0 to 100 m is used. The b o t t o m topography in the investigated sea area is also shown.
Westerlund, 1983). These data suggest conservative mixing in the northeastern part of the North Sea between two water masses of 31 and 35 °/00 salinity. This is reasonable in this area where the Baltic current makes its impact. However, surface waters from the southern parts of the North Sea and the English Channel also fit fairly well into the plot. In general, the concentrations in this area are slightly higher than would be expected from the mixing plot. This is plausible, the Rhine and neighbouring polluted rivers being the source of the freshwater in this area. Metal--salinity plots for the other metals investigated did not show any indications of conservative mixing for those elements. The concentration levels in offshore surface water in this part of the Atlantic Ocean for Cu, Ni and Zn are around 3.3 nM (200 ng 1-1 ), 4.3 nM (250 ng 1-1 ) and 6.7 nM (400 ng 1-1 ), respectively.
30
ng I
nM
Ni -12
600-
i ~-
17.30eY~
-8 400-
!
1
=4
Salinity ')~,,
Fig. 3. Nickel concentration versus salinity for surface water and water sampled at 20 m depth. (e) Stations 76--92. (o) Stations 74, 75, 93. (~) Baltic outflow, Kattegat (Magnusson and Westerlund, 1983).
Cadmium concentrations in North Sea surface waters are of the same magnitude as those found in neighbouring areas of the Atlantic (Fig. 2). This is explained by the low concentration of cadmium in the Kattegat surface waters (0.21nM, 2 3 n g l - 1 ; Magnusson and Westerlund, 1983). Similarly, rivers like the G~ta River on the Swedish west coast have very low cadmium concentrations (Danielsson et al., 1983). For the river Rhine, which has a considerable load of cadmium and other metals, the large a m o u n t of suspended particles might facilitate trapping of metals in the estuary (Duinker, 1983)• A conspicuous feature of the plot of surface water cadmium concentrations is the low values around stations 87 and 88. A similar but smaller decrease can be seen for copper, nickel and zinc. These variations in trace metal concentrations are evidently related to the phase of the primary production in the different areas. During winter, cooling o f the surface water results in a turnover penetrating deep into the water column deeper at the northernmost stations due to more intense cooling. With improved light conditions in spring, surface water warms up and a stratification is developed. This process, which is essential for the start of a spring bloom, occurs earlier at the more southerly stations 87 and 88. However, the depth of the water column also influences the development of stratified conditions giving rise to early spring blooms in the shallow parts of the North Sea {Cushing, 1973). The extent of the spring production can be seen from the concentrations of phosphate and nitrogen. Concurrently with the depletion of the micronutrients there is a depletion o f trace metals, especially of cadmium.
31 The normal relationship between micronutrients and the trace metals cadmium, copper, nickel and zinc does not hold for the surface waters of the North Sea sampled here. Samples with low salinity and high concentrations of trace metals were generally very low in nutrients. In these waters, spring production starts early and had, at the time of sampling, consumed most of the nutrients available. However, the trace metal concentrations are still relatively high due to a high rate o f supply swamping the uptake by plankton. The supply can be either direct, through rivers and rain, or indirect through intense recycling from the sediments. Similar results were obtained for samples from the Baltic obtained one week before the start of this cruise. In the Baltic surface waters the peak of the spring bloom had passed and the nutrients were exhausted, but levels of cadmium, copper, nickel and zinc were of the same order of magnitude as those found in the Kattegat (Danielsson and Westerlund, 1984). Similar results were also obtained from consideration of the mixing of U.S. east-coast shelf water and Saragasso Sea water (Bruland and Franks, 1983). These authors found non-conservative behaviour for nutrients in this mixing zone while trace metals seemed to behave conservatively. The iron data show considerable scatter. This can be partly explained by contamination problems, b u t probably to a larger extent by the fact that unfiltered acidified samples were used. Thus, inhomogeneous distribution of particle-bound iron will show up in the results. The lowest concentrations (around 1 nM, 55 ng1-1) were found at stations 83--85. This might be explained by the fact that these stations should have the least continental influence. Somewhat higher concentrations (around 4 nM, 220 ng 1-' ) were found at most other stations while much higher concentrations were found in the English Channel and south-western North Sea.
Depth profiles Three different deep water regions were sampled during this cruise and the trace metal profiles shown in Figs. 4--8 have been grouped accordingly. Group 1, the Norwegian Sea, comprises stations 78--80. In this area, depths down to 3400 m were sampled. The area is known as one of the birthplaces for North Atlantic Deep Water (NADW) through the sinking of cooled surface water. Group 2, the Iceland-Faroe Ridge area comprises stations 81--84. This relatively shallow area constitutes the link between the Norwegian Sea and the central basins of the Atlantic. Group 3, constituting stations 85--88, is in the eastern central basin o f the Atlantic. Water depth in this area can exceed 4000 m. In Figs. 4 and 7 phosphate and temperature profiles characteristic for the Norwegian Sea and for the eastern central Atlantic basin are also shown.
Cadmium The cadmium profiles for the group 1 and 2 stations show only a weak depletion in the surface waters as discussed earlier (Fig. 4). The profile for
32 Cd 0;1
0.2
10
20
i
i
i
0;3
i
i
30
aM ng I i
I
011
0.21
10
20
0.31 30
nM
01
02
ng I '
1o
2o
i
O3
i - -
30
C4 40
!IM mJ I '
0-
7 /// "~
"
-o
-4
/
.*
\PO4 M
~o
".5'
i
o o, , ,,o , r°c
T=C
lio pM PO4
0.5 I
1 o )JM P O 4
I
••
A Group
1
, 78 •
Stations
Group
79
• so
2
81 82 • 83
Group
:. 8 4
3
s5 •
•
Stations
Stations
86
.8z ,~ 8 8
Fig. 4. Vertical profiles of Cd in the North East Atlantic. Group 1 stations: The Norwegian Sea. Group 2 stations: Faroe Ridge area. Group 3 stations: North East Atlantic. In this figure PO~- and temperature are also included for the two major different areas: station 80 in the Norwegian Sea and station 86 in the North East Atlantic.
the group 3 stations shows the normal behaviour with extensive depletion of surface waters. The surface water at station 85, however, bears in this respect a closer resemblance to the group 2 stations. This is explained by the lower surface temperatures and, therefore, less pronounced thermal stratification at this station. The later start of the production can also be witnessed by the high concentration of PO4 (0.5pM). Results for the three most shallow depths sampled at station 85 have therefore been excluded from the correlation calculation. With these three points excluded, a good correlation between cadmium and phosphate was found for the group 3 stations (Fig. 9). The best fit was obtained for a line with the equation Cd (nM) = 0.19 PO4 (pM) + 0.001. This is similar to the relationship calculated for data from other parts o f the Atlantic. Less efficient uptake or more efficient regeneration of cadmium relative to phosphorus was found in Arctic waters. However, for the Pacific the reverse behaviour has generally been found. The reasons for variations in the cadmium/phosphate transformation ratio have been discussed (Boyle et al., 1981). Variations in Cd/PO4 uptake ratio
33
Cu 0.5
1.5
1.0
(
nM
i
~00
5o
=
i
i
0,5 I
1.0
I
ng I'1
o-
1,5 100
i
i
e;~e=, ,t, e,
^
•
nM
I
50
I
1 .O
0.5
I
I
rig I "1
150
1.5
2.0
=
nM
=
100 I
ng I "1
150 o
• •
r I &
1-
2-
4Group
1
78 •
Stations
Group
79
• 80
Stations
2
81 82 83 84
Group Stations
3
o 85 • 86 • 87 ~ 88
Fig. 5. Vertical profiles of Cu in the North East Atlantic. Group 1 stations: The Norwegian Sea. Group 2 stations: Faroe Ridge area. Group 3 stations: North East Atlantic.
between different plankton communities seem to be the most plausible explanation. In temperate waters this might also lead to seasonal variations in uptake rate. Furthermore, as cadmium uptake varies with the availability of phosphate, ratios may be different in depleted waters compared to newly upweUed waters or temperate waters where spring production has just started. The cadmium concentration of Atlantic deep waters, below 1000 m, north of the Equator increases from north to south. From values of 0.18nM (20 ng1-1 ) at 88°N (Moore, 1978) and 0.18 nM (20ng1-1 ) at 82°N {Danielsson and Westerlund, 1983), the concentration increases slightly to 0.20 nM ( 2 3 n g l - ] ) in group 1 stations at 62--65°N and further to 0.25nM (29 ng 1-1 ) at group 3 stations at 48--59°N. These values are consistent with data from other authors. Bruland and Franks (1983) found 0.29nM (32ng1-1 ) at 34°N in the Sargasso Sea. Further south Statham (1983) found 0.33 nM (37 ng 1-1 ) for a group of stations at 25--34°N and 0.41 nM (46 ng 1-1 ) at 0--19°N. This increase of cadmium concentration with age of
34
Fe 11° 05
20
30
$
I
10
1.5
I
I
riM ugl I
lO
29()0 '7 ~
?
2oj
0~5
10
3L) 15
r~M
10
ksg i '
~(:
05
10
~¢,
•
nM !5
~ !'
•
5203 Q .
]
2-
3-
4
Group 1 Stations
78 • 79
Group
• 80
Stations
2
o
81 • 82
Group
• 83
Stations
84
3
:
85
• 8S , 87 = 88
Fig. 6. Vertical profiles of Fe in the North East Atlantic. Group 1 stations: The Norwegian Sea. Group 2 stations: Faroe Ridge area. Group 3 stations: North East Atlantic. deep water can be observed on a larger scale in the high deep-water concentrations found in the Indian Ocean (Danielsson, 1980) and in the Pacific (Bruland et al,, 1979).
Copper In contrast to cadmium, the profiles for copper are almost featureless (Fig. 5 ). The mean copper concentrations found in surface waters (0--100 m) at stations 85--88 (1.3 nM, 8 0 n g 1-1 ) are similar to those found for the Sargasso Sea (1.7 nM, 7 3 n g 1-1; Boyle et al., 1977). Moore ( 1 9 8 3 ) f o u n d slightly higher values (1.48 nM, 94 ng 1-1 ) in the eastern Atlantic at 20--25°N. At the other stations, only one sample (station 87, 3500 m) showed elevated concentration at the deepest level that could be caused by release from bottom sediments. On the other hand, significant release o f copper from bottom sediments was shown by Moore (1978) to take place only from slowly accumulating red clay sediments. In the areas sampled here, more rapid sediment accumulation would be expected.
35
Ni
J
1O0
•
200
i
i
o- % "~ IIII
}
k ngl'
100
200
,~. • ,,,,"
1
,
2
,
3
I
ng] ~
,
100
200
ngl ~
%
"" /
/
I P04 2-
•
•
3- i
1 o
,J
lo
Group
o
T°C
o.5
1:0 D M P O 4
t
Stations
o 78
Group
• 79 • 80
1o o.5,
Stations
2
~ 81
Group 3
• 82 * 83
Stations
84
Fig. 7. Vertical profiles of Ni in Norwegian Sea. Group 2 stations: Atlantic. In this figure PO~- and different areas: station 80 in the Atlantic.
T°C
Iio
~JM P O 4
~ 85 • 86
.87
~ 88
the North East Atlantic. Group 1 stations: The Faroe Ridge area. Group 3 stations: North East temperature are also included for the t w o major Norwegian Sea and station 86 in the North East
The deep waters sampled in this investigation showed copper concentrations only about 10% higher than the surface waters. Similar profiles were obtained in the Arctic (Danielsson and Westerlund, 1983). In profiles obtained further south in the Atlantic a clear increase in copper concentration with depth can be seen (Moore, 1978; Bruland and Franks, 1983). This is most likely due to the varying ages of the deep waters and consequent variations in the amount of sunken debris collected. Iron
The iron profiles shown in Fig. 6 display a relatively large scatter, especially for group 1 and 2 stations. This is to be expected from the use of acidified, unfiltered samples stored for some months before work up. Thus, particulate iron will be included in the results to a large degree. Samples taken in areas with significant input of terrestrial material or close to shallow shelf areas can therefore be expected to show higher concentrations, but also
36
Zn 1
2
I
nM
I
k
200
100
i
nM ng
i
•
I
~, 200
100
~71
:
200
s
•
280
-
Ill
i
7
;
~-
i
ngl
i
0-
3
i
100
J
i
lo
3-
Group
1
o 78 •
Stations
Group
2
79
:, 81 •
• so
Stations
Group
3
82
,83 84
