MARINE BIOLOGY
Marine Biology 44, 223-226 (1977)
9 by Springer-Verlag 1977
5 Fe in Pacific Ocean Plankton C.D. Jennings Oregon College;Monmouth, Oregon, USA
Ab~
The specific activity of 55Fe in plankton increased from below detectable limits at 2OON to a m a x i m u m of 130 nCi/g Fe at 2OoS and then decreased to 5 nCi/g Fe at 50os. Along an east-west track near 15os a peak of 90 nCi/g Fe occurred at 135ow. It is suggested that this m a x i m u m is the result of fallout from French nuclear tests at Mururoa Atoll (22os; 139ow). The increase in 55Fe at high latitudes observed in previous studies in the North Atlantic Ocean and North Pacific Ocean did not occur in the South Pacific Ocean which supports the suggestion that belts of high tropospheric fallout accounted for the increase in the Northern oceans.
In~odu~ion
Iron-55 has been one of the major radionuclides in fallout since the atmospheric tests by the USSR and the United States in 1961-1962, and more recently the smaller atmospheric tests by France and China. In the ocean, where iron is in short supply, organisms have been found to concentrate 55Fe more than fresh water or terrestrial organisms (Palmer a n d B e a s l e y , 1967), and especially high concentrations have been noted in oceanic fish from both the North Pacific Ocean (Palmer and Beasley, 1967; Jennings, 1968; Jennings and Osterberg, 1973) and the North Atlantic Ocean (Jennings, 1969; Preston, 1970). Variations of 55Fe from place to place in plankton should correspond closely to variations in the water itself because they assimilate 55Fe quickly (Lowman, 1960) and have a fairly short life span as well as a rapid excretion rate for iron (Fowler, unpublished data). Consequently, concentrations of 55Fe in plankton should follow closely those in the water which surrounds them. Preston (1970) aptly pointed out that such is not the case for fish, especially migratory fish, in which the 55Fe concentrations may well represent uptake at a different time and/ or from a different region from which they were caught. Gamma-emitting radionuclides were reported in euphausiids from the North Pa-
cific Ocean shortly after the 1961-1962 tests (Osterberg, 1962a, b) and, around the time of the onset of nuclear testing by the French in the South Pacific, in euphausiids collected off the coast of Chile (Antezana and Fowler, 1972). Also, some measurements of 55Fe in plankton have been reported from the North Pacific Ocean (Lowman, 1960; Jennings, 1968), but I know of no reports published recently of 55Fe in plankton from the South Pacific Ocean. The paucity of data on radioactivity in marine organisms from the Southern Hemisphere is a serious deficiency because atmospheric nuclear tests are actively being carried out there. The "Southtow" expedition of Scripps Institution of Oceanography in 1972 collected plankton samples over a large part of the eastern South Pacific Ocean, and this paper reports the 55Fe concentrations in these samples.
Materials and Methods
Samples analyzed in this study were collected in a 3-m (IO-ft) Isaacs-Kidd midwater trawl on Legs I and 2 of the "Southtow" expedition at about 1OO latitude intervals from 20ON to 50os at longitude 120~ (Stations I-9, Figs. 1 and 2) and in a 1-m plankton net on Leg 8 at approximately 10 ~ longitude intervals from 85ow to 145ow at Latitude 12o16os between Callao, Peru and Papeete,
C.D. Jennings: 55Fe in Pacific Ocean Plankton
224
45
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Fig. i. Specific activity of 55Fe (nCi/g Fe) in plankton from Pacific Ocean. Error terms represent counting errors at • la
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T a h i t i (Stations 10-17). The s a m p l e s w e r e t a k e n from the nets w i t h as m u c h care as p o s s i b l e , to p r e v e n t c o n t a m i n a tion by stable iron f r o m the deck of the ship, and p r e s e r v e d in 10% b u f f e r e d f o r m a l i n for later a n a l y s i s in the laboratory. The s a m p l e s w e r e d r i e d at IO0OC and a s h e d for 24 h in a m u f f l e f u r n a c e at 6OOOC. The a s h e d s a m p l e s w e r e d i s s o l v e d in 6 M HC1, an a l i q u o t was r e m o v e d for s p e c t r o p h o t o m e t r i c d e t e r m i n a t i o n of stable iron, and the r e m a i n d e r of the sample was a n a l y z e d for 55Fe. I r o n - 5 5 was m e a s u r e d by first e x t r a c t i n g iron from the d i s s o l v e d s a m p l e w i t h 10% A l a m i n e - 3 3 6 in xylene, e l e c t r o p l a t i n g the iron by the m e t h o d of M a l e t s k o s and I r v i n e (1956), and c o u n t i n g the K x - r a y s of the 55Mn d a u g h t e r of 55Fe in an a n t i c o i n c i d e n c e shielded gas-flow proportional counter d e s c r i b e d e l s e w h e r e (Jones et al., 1975). A n a l y s e s of t o t a l iron w e r e c a r r i e d out c o l o r i m e t r i c a l l y w i t h I, 10 p h e n a n throline.
i
I 75 ~
Fig. 2. Concentration of 55Fe (pCig d r y w e i g h t -I) in plankton from Pacific Ocean. Error terms represent counting errors at + IO
variations of 55Fe with Latitude
I r o n - 5 5 has b e e n shown to i n c r e a s e w i t h l a t i t u d e in fish f r o m the N o r t h A t l a n t i c O c e a n (Preston, 1970), and the same t r e n d s e e m e d a p p a r e n t in the N o r t h P a c i f ic O c e a n in m e a s u r e m e n t s of 55Fe in the coho s a l m o n Oncorhyncus kisutch (Jennings, 1968). T h e s e o b s e r v a t i o n s run c o u n t e r to the u s u a l f a l l o u t m a x i m a m e a s u r e d at m i d l a t i t u d e s in s u r f a c e air (Volchok and K l e i n m a n , 1969) that r e s u l t f r o m stratos p h e r i c inputs to lower levels in the a t m o s p h e r e at the d i s c o n t i n u i t i e s in the t r o p o p a u s e o c c u r r i n g in t h e s e regions. Both a u t h o r s s u g g e s t e d n a r r o w b e l t s of t r o p o s p h e r i c f a l l o u t at h i g h l a t i t u d e s as a p o s s i b l e cause of the h i g h 55Fe content of fish c a u g h t there. This interp r e t a t i o n was b a s e d on the s u g g e s t i o n of P i e r s o n and C a m b r a y (1965) that such dep o s i t s h a d o c c u r r e d at t h e s e latitudes. M e a s u r e m e n t s of 55Fe in fish f r o m h i g h s o u t h e r n l a t i t u d e s at the same time as the s t u d i e s by J e n n i n g s (1968) and P r e s t o n (1970) w o u l d h a v e i n d i c a t e d w h e t h e r the p h e n o m e n o n o c c u r r e d only in the N o r t h e r n H e m i s p h e r e or in the S o u t h ern H e m i s p h e r e as well. If the i n c r e a s e at h i g h l a t i t u d e o c c u r r e d only in the N o r t h e r n H e m i s p h e r e , the h y p o t h e s i s that it r e s u l t e d f r o m b e l t s of t r o p o s p h e r i c f a l l o u t w o u l d be s u p p o r t e d , w h e r e a s if it o c c u r r e d in the S o u t h e r n H e m i s p h e r e as w e l l some a l t e r n a t i v e , m o r e g e n e r a l e x p l a n a t i o n , w o u l d be r e q u i r e d to e x p l a i n the i n c r e a s e at h i g h n o r t h e r n latitudes.
C.D. Jennings: 55Fe in Pacific Ocean Plankton
U n f o r t u n a t e l y , such s a m p l e s w e r e n o t collected, b u t the m e a s u r e m e n t s in p l a n k t o n in this r e p o r t m a y shed light on the question. A l t h o u g h p r e s e n t m e a s u r e m e n t s in p l a n k t o n c a n n o t be c o m p a r e d d i r e c t l y w i t h m e a s u r e m e n t s in fish in the 1960's, if some g e n e r a l a t m o s p h e r i c or o c e a n i c p r o c e s s w e r e the c a u s e of large c o n c e n t r a t i o n s at h i g h latitudes, it s h o u l d o p e r a t e in the S o u t h e r n H e m i s p h e r e as w e l l b e c a u s e of the s i m i l a r i t i e s in circ u l a t i o n in the two h e m i s p h e r e s . In this case, c o n c e n t r a t i o n s of 55Fe s h o u l d be h i g h e r in p l a n k t o n f r o m h i g h l a t i t u d e s than from m i d - l a t i t u d e s in the S o u t h e r n H e m i s p h e r e . F r o m my m e a s u r e m e n t s of 55Fe in e u p h a u s i i d s c o l l e c t e d f r o m 20ON to 50os, s h o w n in Figs. I and 2, it can be seen that the i n c r e a s e at high l a t i t u d e s d e c i d e d l y does not a p p e a r in the Southern H e m i s p h e r e . The p e a k of 55Fe s p e c i f ic a c t i v i t y is 130 nCi/g Fe, w h i c h occurs n e a r 20os, w i t h m u c h lower concent r a t i o n s b o t h at the low n o r t h e r n latitudes (below d e t e c t a b l e limits at 20ON) and at h i g h s o u t h e r n l a t i t u d e s (a low of 5 n C i / g Fe at 50os). T h e s e m e a s u r e m e n t s lend a d d i t i o n a l s u p p o r t to the n o t i o n that n a r r o w b a n d s of t r o p o s p h e r i c fallout a c c o u n t e d for the o b s e r v a t i o n s of h i g h c o n c e n t r a t i o n s of 55Fe in fish caught at h i g h l a t i t u d e s in the N o r t h P a c i f i c and N o r t h A t l a n t i c Oceans. A similar e x a m p l e of a s i n g l e m a j o r input of f a l l o u t has b e e n s u g g e s t e d for C h i l e a n w a t e r s by A n t e z a n a and F o w l e r (1972) from their o b s e r v a t i o n s of 65Zn in eup h a u s i i d s f o l l o w i n g the first F r e n c h nuclear tests in the P a c i f i c in 1966. Z i n c - 6 5 was e a s i l y m e a s u r e d in euphausiids in July 1966, but was not d e t e c t able in e u p h a u s i i d s c a u g h t only 6 w e e k s later. The m a x i m u m s p e c i f i c a c t i v i t y of 55Fe at 20os in this study c o r r e s p o n d s c l o s e ly w i t h the l a t i t u d e of the F r e n c h nuclear tests at M u r u r o a (22os; 139oE), and it is s u g g e s t e d that the o b s e r v e d m a x i m u m r e s u l t s f r o m the f a l l o u t from those tests. E v e n t h o u g h the f a l l o u t from r e c e n t t e s t i n g m i g h t c o n f u s e somew h a t the d i s t r i b u t i o n of 55Fe w i t h latitude, it is clear from the e x t r e m e l y low v a l u e of 55Fe in e u p h a u s i i d s c a u g h t at 50os that t h e r e is no i n c r e a s e o c c u r r i n g at h i g h s o u t h e r n l a t i t u d e s to m i r r o r the i n c r e a s e o b s e r v e d at high n o r t h e r n latitudes.
vacations of 55Fe with Longitude S i n c e the c o l l e c t i o n s of p l a n k t o n between Callao, P e r u and P a p e e t e , T a h i t i w e r e t a k e n w i t h a 1-m p l a n k t o n net, the
225
small b i o m a s s o b t a i n e d r e q u i r e d that m e a s u r e m e n t s of 55Fe be m a d e on the m i x e d s a m p l e s from each s t a t i o n w h i c h contained m a n y s p e c i e s but p r e d o m i n a n t l y c o p e p o d s and c h a e t o g n a t h s . In the r e g i o n from the P e r u v i a n coast to 117ow, the s p e c i f i c a c t i v i t i e s of 55Fe w e r e 13 n C i / g Fe or less, but at 125 ~ and 135ow the s p e c i f i c a c t i v i t i e s w e r e 80 and 90 n C i / g Fe, w i t h a d e c r e a s e to 2 n C i / g Fe near T a h i t i at 146ow (Fig. I). Since M u r u r o a lies a l o n g the l o n g i t u d i nal b a n d of the m a x i m u m , it is t e m p t i n g to s u g g e s t that the d e c r e a s e near T a h i t i occurs b e c a u s e of its d i s t a n c e from the test site. This seems u n l i k e l y , h o w e v e r , b e c a u s e the l o c a t i o n of the F r e n c h nuclear tests is in the zone of the southeast t r a d e w i n d s and the s o u t h e q u a t o r i a l current, so that f a l l o u t f r o m the tests s h o u l d be c a r r i e d to the. w e s t of the area sampled. C o n s e q u e n t l y , high c o n c e n t r a t i o n s of 55Fe w o u l d be e x p e c t e d in p l a n k t o n c o l l e c t e d f a r t h e r to the west. F o l l o w i n g the n u c l e a r test in the N o r t h ern H e m i s p h e r e at the E n i w e t o k t e s t i n g site, L o w m a n (1960) found that the w e s t w a r d drift of the r a d i o a c t i v i t y in p l a n k ton of the north e q u a t o r i a l c u r r e n t was a p p r o x i m a t e l y e q u a l to that of the current speed. A m o r e l i k e l y e x p l a n a t i o n for the low s p e c i f i c a c t i v i t y of 55Fe at 146ow is that s t a b l e iron may h a v e o c c u r r e d in the r e g i o n w h e r e the s a m p l e was taken, p e r h a p s b e c a u s e of input of iron into the w a t e r in r u n o f f f r o m the v o l c a n i c i s l a n d of Tahiti, w h i c h d i l u t e d the fallout 55Fe. This s u g g e s t i o n is s u p p o r t e d by the h i g h s t a b l e iron c o n c e n t r a t i o n (1OO0 ~g g dry weight-l) o b s e r v e d in the p l a n k t o n f r o m that c o l l e c t i o n . It has b e e n d o c u m e n t e d by Davies (1967) and disc u s s e d by P r e s t o n (1970) that f r e s h l y p r e c i p i t a t e d iron is m o r e a v a i l a b l e for u p t a k e by p h y t o p l a n k t o n in sea w a t e r than is aged iron, so that fresh inputs around Tahiti, if they occurred, could affect the c o n c e n t r a t i o n of 55Fe in p l a n k t o n in n e a r s h o r e w a t e r s . F u r t h e r s a m p l i n g in the w e s t e r n S o u t h P a c i f i c O c e a n s h o u l d be u n d e r t a k e n to see w h e t h er r e l a t i v e l y high c o n c e n t r a t i o n s of 55Fe o c c u r due to t r a n s p o r t into the region by the p r e v a i l i n g w i n d s and currents.
Acknowledgements. I should like to thank the staff of Scripps Institution of Oceanography and the officers and crew of the R.V. "Thomas Washington" for allowing me to participate in the "Southtow" expedition and for their help in sample collections. R. Ewing assisted in analysis of the samples and Dr. S. Fowler made helpful comments on the manuscript, and I thank them.
226
This work was supported by the U.S. Energy Research and Development Administration under Contract AT(45-I) 2231. Task Agreement i.
Literature Cited
Antezana, T.J. and S.W. Fowler: Gamma emitters in euphausiids from the southeast Pacific Ocean. Hlth Phys. 22, 201-205 (1972) Davies, A.G.: Studies of the accumulation of radio-iron by a marine diatom. In: Radioecological concentration processes, pp 983-991. Ed. by B. Alberg and F.P. Hungate. Oxford: Pergamon Press 1967 Jennings, C.D.: Iron-55 in Pacific Ocean organisms, 81 pp. Ph.D. Thesis, Oregon State University 1968 - Iron-55 in the North Pacific and North Atlantic Oceans. Rep. Bur. comml Fish. radiobiol. Lab. i, 40-48 (1969) - and C.L. Osterberg: Specific activity of 55Fe in Pacific salmon. In: Radionuclides in ecosystems, pp 703-708. Ed. by D.J. Nelson. Oak Ridge, Tenn.: USAEC Division of Technical Information 1973 Jones, "W.M., C.D. Jennings and N.H. Cutshall: Cycling of 55Fe and 65Zn in the Columbia River carp following reactor shutdown. In: Combined effects of radioactive, chemical and thermal release to the environment, pp 309318. Vienna: International Atomic Energy Agency 1975 Lowman, F.G.: Marine biological investigations at the Eniwetok test site. In: Proceedings of
C.D. Jennings: 55Fe in Pacific Ocean Plankton
the Conference on Disposal of Radioactive Wastes, Monaco, pp !O6-138. Vienna: International Atomic Energy Agency 1960 Maletskos, C.J. and J.W. Irvine, Jr.: Quantitative electrodeposition of radiocobalt, zinc and iron. Nucleonics 14 (4), 84-93 (1956) Osterberg, C.L.: Fallout radionuclides in euphausiids. Science, N.Y. 138, p. 529 (1962a) 65Zn content of salps and euphausiids. Limnol. Oceanogr. 7, 478-479 (1962b) Palmer, H. and T.M. Beasley: 55Fe in the marine environment and in people who consume ocean fish. In: Radioecological concentration processes, pp 259-262. Ed. by B. Alberg and E.P. Hungate. Oxford: Pergamon Press 1967 Pierson, D.H. and R.S. Cambray: Fission-product fallout from the nuclear explosions of 1961 and 1962. Nature, Lond. 205, 433-440 (1965) Preston, A.: Concentrations of iron-55 in commercial fish species from the North Atlantic. Mar. Biol. 6, 345-349 (1970) Volchok, H.L. and M.T. Kleinman: Radionuclides and lead in surface air. USAEC Health and Safety Laboratory, HASL Fallout Program. Quarterly Summary Report No. 214. App. D. pp DID7OO. Ed. by E.P. Hardy and J. Rivera. New York, N.Y.: Health and Safety Laboratory, USAEC 1969 -
Dr. C.D. Jennings Department of Natural Sciences Oregon College Monmouth, Oregon 97361 USA
Date of final manuscript acceptance: July 15, 1977. Communicated by J.M. P~r~s, Marseille