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Tar ‘specks’ in the North Atlantic
Marine Pollution Bulletin L. L. Fancey and W. R. Squires often rendered assistance and W. R, Penrose provided fruitful discussion, l am also grateful to the Marine Sciences Research Laboratory, Memorial University for experimental facilities, and to Golden Eagle Canada Limited for co-operation. Contribution number 261 from the Marine Science Research Laboratory, Memorial University, Newfoundland. Note added in proof." AHH has recently been detected (PerkinElmer fluorimeter) in fresh sea-urchin homogenate prepared with protease inhibitor PMSF.
Adamson, R. H. (1967). Drug metabolism in marine vertebrates. Fed. Proc., 26, 1047-1055. Ahokas, J. T., Pelkonen, O. & K~rki, N. T. (1975). Metabolism of polycyclic hydrocarbons by a highly active aryl hydrocarbon hydroxylase system in the liver of a trout species. Biochem. Biophys. Res. Commun., 63,635-641. Ahokas, J. T. (1976). Metabolism of 2,5-diphenyloxazole (PPO) by trout liver microsomal mixed function monooxygenase. Res. Comrnun. Chem. Pathol. Pharm., 3,439-44" Bickel, M. H. & Baggiolini, M. (1966). The metabolism of imipramine and its metabolites by rat liver microsomes. Biochem. PharmaeoL 15, 1155-1169. Burns, K. A. (1976). Hydrocarbon metabolism in the intertidal fiddler crab Uca pugnax. Mar. BioL, 36, 5-11. Conney, A. H. (1967). Pharmacological implications of microsomal enzyme inductions. PharmacoL Rev., ! 9, 317-366. Corner, E. D. S., Kilvington, C. C. & O'Hara, S. C. M. (1973). Qualitative studies on the metabolism of naphthalene in Maia squinado(Herbst). J. mar. biol. Ass. U.K., 53,819-832. Corner, E. D. S., Harris, R. P., Kilvington, C. C. & O'Hara, S. C. M. (1976). Petroleum compounds in the marine food web: short term experiments on the fate of naphthalene in Calanus. J. mar. bioL Ass. U.K., 56, 121-133. Creaven, P. J., Parke, D. V. & Williams, R. T. (1965). A fluormetric study of the hydroxylation of biphenyl in vitro by liver preparations of various species. Biochem. J., 96, 879-885. Elmamlouk, T. H. & Gessner, T. (1976). Mixed function oxidases and nitroreductases in hepatopancreas of Homarus americanus. Comp. Biochem. PhysioL, 53, 57-62. Heidelberger, C. (1975). Chemical carcinogens. Ann. Rev. Biochem., 44, 79-121. Khan, M. A. Q., Coello, W., Khan, A. A. & Pinto, H. (1972a). Some characteristics of the microsomal mixed function oxidase in the freshwater crayfish, Cambarus. Life Sck, 11, Pt. 2,405-415. Khan, M. A. Q., Kamal, A., Wolin, R. J. & Runnels, J, (1972b). In vivo and in vitro epoxidation of aldrin by aquatic food chain organisms. Bull. Environ. Contam. ToxicoL, 8,219-228. Khan, M. A. Q., Stanton, R. H. & Reddy, G. (1974). Detoxication of foreign chemicals by invertebrates. In Survival in Toxic Environments(Khan, M. A. Q. & Bederka, J. P. eds.), pp. 177-201. London: Academic Press.
Khan, M. A. Q. (1976). In vitro metabolism of cyclodiene epoxides by freshwater fishes. Unpublished data. Lee, R. F., Sauerheber, R. & Benson, A. A. (1972). Petroleum hydrocarbons: uptake and discharge by the marine mussel, Mutilus edulis. Science, (Wash. DC), 177, 344-346. Lee, R. F. (1975). Fate of petroleum hydrocarbons in marine zooplankton. Proc. Joint Conf. on Prevention and Control of O i l Spills. API, EPA, USCG pp. 535-540. Lee, R. F., Furlong, E. & Singer, S. (1976). Detoxification systems in marine invertebrates. Aryl hydrocarbon hydroxylase from the tissues of the blue crab, Callinectes sapidus and the polychaete worm, Nereis sp. Biological effects program workshop, May 16-19 (1976). Texas A&M University, College Station, Texas. Lowry, O. M., Rosenbrough, N. J., Farr, A. L. & Randall, R. J. (1951 ). Protein measurement with the Folin phenol reagent..L Biol. Chem., 193,265-275. Matsumura, F. 0975). Metabolism of insecticides by animals and plants. In Toxicology o f Insecticides. pp. 165-251. London: Plenum Press. Medical Research Council. Special report no. 306. (1968). The carcinogenic action of mineral oils: A chemical and biological study. H.M.S.O. London. Neff, J. M. & Anderson, J. W. (1975). Accumulation release and body • • . ]4 . '. distribution of benzopyrene C m the clam Rangta cuneata. Proc. Joint Conf. on Prevention and Control oj Oil Spills. API, EPA, USCG pp. 469-471. Netter, K. J. & Seidel, G. J. (1964). An adaptively stimulated Odemethylating system in rat liver microsomes and its kinetic properties. J. Pharmacol. Expt. Ther., 146, 61-65. Payne, J. F. & Penrose, W. R. (1975). Induction of benzo(a)pyrene hydroxylase in fish by petroleum. Bull. Environ. Contain. Toxicol.,
14, 112-116. Payne, J. F. (1976). Field evaluation of benzopyrene hydroxylase induction as a monitor for marine petroleum pollution. Science, (Wash. DC), 191, 945-946. Pedersen, M. G., Hershberger, W. K., Zachariah, P. K. & Juchau, M. R. (1975). Hepatic biotransformation of environmental xenobiotics in six strains of rainbow trout (Salmo gairdneri). J. Fish. Res. Bd Can., 33,666-675. Pohl, R. J., Bend, J. R., Guarino, A. M. & Fouts, J. R. 0974). Hepatic microsomal mixed function oxidase activity of several marine species from coastal Maine. Drug Metab. Disposition, 2, 545-555. Scarpelli, G. (1974). Hepatic function in fish. In Marine Bioassays Workshop Proc. API, EPA, MTS, Marine Technology Society (Wash. DC), pp. 191-198. Vandermeulen, J. H. & Penrose, W. R. (1976). Absence of aryl hydrocarbon hydroxylase activity in chronically oiled marine bivalves: possible consequences. J. Fish. Res. Bd Can., (to be submitted). Zobell, C. E. (1971). Sources and biodegradation of carcinogenic hydrocarbons. Proc. Joint Conf. on Prevention and Control o f Oil Spills. A PI, EPA, USCG.
Tar 'Specks' in the North Atlantic ADAM
ZSOLNAY
D u k e U n i v e r s i t y M a r i n e L a b o r a t o r y , B e a u f o r t , N C 2 8 5 1 6 , U. S. A .
A n u m b e r o f dark specks retained o n filters, through w h i c h seawater had been filtered, c o n t a i n e d material that absorbed U V light very strongly. This material was m o s t likely s u n k e n pieces o f tar. T h e a m o u n t was 0 . 1 2 p g / ! on an average and was i n d e p e n d e n t o f hydrographic parameters. The average amount of floating tar in the Northwest A t l a n t i c is c o n s i d e r a b l e ( 1 - 1 0 m g / m 2) ( M o r r i s , 1971; 116
M o r r i s & B u t l e r , 1973). T h e u l t i m a t e f a t e o f t h i s m a t e r i a l is n o t yet f u l l y k n o w n , b u t it is r e a s o n a b l e t o a s s u m e t h a t a c e r t a i n a m o u n t o f it s i n k s a f t e r s u f f i c i e n t w e a t h e r i n g h a s t a k e n p l a c e . W h e n s e a w a t e r is f i l t e r e d , a l a r g e n u m b e r o f b l a c k s p e c k s a r e o f t e n f o u n d o n t h e f i l t e r . A s p e c k is d e f i n e d h e r e as a n y t h i n g t h a t r e m a i n s b e h i n d o n a G F C g l a s s f i b r e f i l t e r a n d c a n b e s e e n w i t h t h e n a k e d eye. T h e size o f 5 0 r a n d o m l y c h o s e n s p e c k s w a s d e t e r m i n e d u n d e r a microscope. Their depth dimension was made equal to
Volume 8/Number 5/May 1977 their w i d t h . T h e i r a v e r a g e v o l u m e was f o u n d to be 3.00___0.73 x 10-6cm 3. T h e q u e s t i o n is w h e t h e r o r n o t these specks a r e t a r ?
TABLE 1
Tar specks found at various water columns in the North Atlantic. Water column
Volume filtered (I.)
Analysed specks
No. tar
Tar specks ~ug/I)
1
120.0
677
13
0.33
(2)500/(2)1000/(7)1400/ (I)1800/(1)2400
2
36.8
343
3
0.24
(1)450/(1)500/(1)1055
3
20.8
245
0
0.00
--
4
66.5
245
1
0.05
( I )2600
5
118.8
235
1
0,03
(1)1500
6
80.7
105
1
0.04
(1)210
7
76.2
130
1
0.04
( 1)30
Methods T a r specks were l o o k e d for in seven w a t e r c o l u m n s on six d i f f e r e n t cruises in the N o r t h A t l a n t i c . T h e results are s h o w n in the table. E a c h speck was r e m o v e d f r o m the filter with a H a m i l t o n SS60-N solid s a m p l e r needle a n d injected into a high p e r f o r m a n c e liquid c h r o m a t o g r a p h i c system with a U V d e t e c t o r at 254 n m ( Z s o l n a y , 1973). A n unfilled 20 x 1.8 m m i.d. c o l u m n was used a n d the e l u a n t was n - h e x a n e . T h e resulting U V - a b s o r b a n c e o f the specks ( m i n u s c o n t r o l values) f r o m a n y one c o l u m n o f w a t e r was then p l o t t e d a g a i n s t f r e q u e n c y . A n e x a m p l e o f such a p l o t is s h o w n in Fig. 1. I n m o s t cases the a b s o r b a n c e was a r o u n d zero. T h e large n u m b e r o f small negative values were d u e to e x p e r i m e n t a l e r r o r . O n e value, h o w e v e r , has a far g r e a t e r a b s o r b a n c e a n d clearly results f r o m a d i f f e r e n t m a t e r i a l t h a n the rest o f the specks. This was d e t e r m i n e d by the use o f the D i x o n ' s test for outliers ( D i x o n , 1951). T h e p r o b a b i l i t y o f this e x t r e m e v a l u e b e l o n g i n g to the rest o f the p o p u l a t i o n is well u n d e r 0.005. This m a t e r i a l was m o s t likely s u n k e n tar, since m a t e r i a l o r i g i n a t i n g f r o m p e t r o l e u m w o u l d have a far g r e a t e r UV a b s o r p t i o n at 254 nm t h a n a n y biogenic material.
Results and Discussion A n a v e r a g e speck h a d a v o l u m e o f 3.00 × 10 -6 cm 3. I f a d e n s i t y o f 1 is a s s u m e d , the a v e r a g e weight o f each speck w o u l d then be 3 / t g . O n e o f the p r i m e r e a s o n s why this s t u d y was u n d e r t a k e n was to see if tar speck d i s t r i b u t i o n s reflect h y d r o g r a p h i c c o n d i t i o n s in the o c e a n . Specks s h o u l d t e n d to a c c u m u l a t e in a r e a s w h e r e there is a s t r o n g d e n s i t y g r a d i e n t such as in the p e r m a n e n t tliermocline. This was n o t f o u n d to be the case f o r the t a r specks s t u d i e d here. T h e p e r m a n e n t t h e r m o c l i n e o f all the w a t e r c o l u m n s s a m p l e d was b e t w e e n 500 a n d 1000 m. T h e d a t a in the table d o n o t i n d i c a t e a g r e a t e r a b u n d a n c e o f tar specks a b o v e these d e p t h s . This indicates that the
At each depth (no.) found
(1) 33 °40"N and 57°36"W. (2)37 ° 14.3"N and 11°20"W. (3) 22 ° 15"N and 17°4TW. (4-7) about 20 miles SW of Bermuda. p e r m a n e n t t h e r m o c l i n e does n o t serve as a n effective b a r r i e r t o these specks. This was a l s o s h o w n b y there being no m a j o r a c c u m u l a t i o n o f t a r specks in the M e d i t e r r a n e a n w a t e r as it leaves the S t r a i g h t s o f G i b r a l t a r . T h e M e d i t e r r a n e a n has been f o u n d to have 20 m g / m 2 o f t a r ( H o r n et al., 1970). This is far m o r e t h a n in a n y r e g i o n o f the A t l a n t i c a n d there s h o u l d be a g r e a t e r c o n c e n t r a t i o n o f tar specks in the M e d i t e r r a n e a n water. W a t e r c o l u m n 2 ( T a b l e 1), which h a d a very p r o n o u n c e d t o n g u e o f M e d i t e r r a n e a n w a t e r at a b o u t 1000 m , s h o w e d n o e x t r a large c o n c e n t r a tion o f t a r specks in :'t. In fact the overall view at all the w a t e r c o l u m n s is t h a t the d e p t h at which specks were f o u n d is r a t h e r r a n d o m . T h e i r t r a n s p o r t into the d e e p waters o f the N o r t h A t l a n t i c c o u l d be caused by grazing a n d m i g r a t i o n o f z o o p l a n k t o n . O n the o t h e r h a n d S t o k e ' s law shows t h a t even if the specks are o n l y 1°70 m o r e d e n s e t h a n the w a t e r b e l o w t h e m , t h e y w o u l d sink at a rate o f a b o u t 3000 m a year. P a s s i v e sinking a l o n e c o u l d a c c o u n t for their presence in the d e e p w a t e r . I n t e r e s t i n g l y there a r e no t a r specks f o u n d in the u p welling r e g i o n o f f N o r t h w e s t A f r i c a (water c o l u m n 3). This c o i n c i d e d with a n a b s e n c e o f t a r f l o a t i n g o n the s u r f a c e in this r e g i o n ( E r h a r d t , p e r s o n a l c o m m u n i c a t i o n ) . T h e a v e r a g e a m o u n t o f t a r specks f o u n d for all the s a m p l e s was 0.12 /~g/l. I f o n e t a k e s a v o l u m e o f 1.6 x 1017 m 3 f o r the N o r t h A t l a n t i c , the t o t a l a m o u n t o f t a r specks w o u l d be 1.9 x 107 m e t r i c tons. C a l c u l a t i o n s o f this t y p e s h o u l d be viewed with e x t r e m e c a u t i o n , b u t they d o serve to s h o w t h a t the a m o u n t o f tar in the f o r m o f specks b e l o w the o c e a n ' s s u r f a c e is c o n s i d e r a b l e .
12--
The research support of the Oceanography Section, National Science Foundation, NSF Grant GA-DES 74-18094, and the competent technical assistance of Ms C. Frohlichstein and Mr B. Moorfield are gratefully acknowledged.
I0--
8--
U4
2
-o15
-005
h
005
o15
025
U V - absorbance
035
0,*5
I10
1.15
(au. x 0.02)
Fig. 1 UV-absorbance (minus controls) by material eluated from specks in a water column of the North Atlantic plotted against frequency.
Dixon, W. J. (1951). Ratios involving extreme values. Ann. Math. Star., 22, 68-78. Horn, L. M., Teal, J. M. & Backus, R. H. (1970). Petroleum lumps on the surface of the sea. Science, 168, 245-246. Morris, B. F. (1971). Petroleum: tar quantities floating in the Northwestern Atlantic taken with a new quantitative neuston net. Science, 173,430-432. Morris, B. F. & Butler, J. N. (1973). Petroleum residues in the Sargasso Sea and on Bermuda beaches. Proc. Joint Conf. on Prevention and Control of O i l Spills, pp. 521-529. Zsolnay, A. (1973). Determination of aromatic hydrocarbons in submicrogram quantities in aqueous systems by means of high performance liquid chromatography. Chemosphere, 6, 253-260. 117
Adamson, R. H. (1967). Drug metabolism in marine vertebrates. Fed. Proc., 26, 1047-1055. Ahokas, J. T., Pelkonen, O. & K~rki, N. T. (1975). Metabolism of polycyclic hydrocarbons by a highly active aryl hydrocarbon hydroxylase system in the liver of a trout species. Biochem. Biophys. Res. Commun., 63,635-641. Ahokas, J. T. (1976). Metabolism of 2,5-diphenyloxazole (PPO) by trout liver microsomal mixed function monooxygenase. Res. Comrnun. Chem. Pathol. Pharm., 3,439-44" Bickel, M. H. & Baggiolini, M. (1966). The metabolism of imipramine and its metabolites by rat liver microsomes. Biochem. PharmaeoL 15, 1155-1169. Burns, K. A. (1976). Hydrocarbon metabolism in the intertidal fiddler crab Uca pugnax. Mar. BioL, 36, 5-11. Conney, A. H. (1967). Pharmacological implications of microsomal enzyme inductions. PharmacoL Rev., ! 9, 317-366. Corner, E. D. S., Kilvington, C. C. & O'Hara, S. C. M. (1973). Qualitative studies on the metabolism of naphthalene in Maia squinado(Herbst). J. mar. biol. Ass. U.K., 53,819-832. Corner, E. D. S., Harris, R. P., Kilvington, C. C. & O'Hara, S. C. M. (1976). Petroleum compounds in the marine food web: short term experiments on the fate of naphthalene in Calanus. J. mar. bioL Ass. U.K., 56, 121-133. Creaven, P. J., Parke, D. V. & Williams, R. T. (1965). A fluormetric study of the hydroxylation of biphenyl in vitro by liver preparations of various species. Biochem. J., 96, 879-885. Elmamlouk, T. H. & Gessner, T. (1976). Mixed function oxidases and nitroreductases in hepatopancreas of Homarus americanus. Comp. Biochem. PhysioL, 53, 57-62. Heidelberger, C. (1975). Chemical carcinogens. Ann. Rev. Biochem., 44, 79-121. Khan, M. A. Q., Coello, W., Khan, A. A. & Pinto, H. (1972a). Some characteristics of the microsomal mixed function oxidase in the freshwater crayfish, Cambarus. Life Sck, 11, Pt. 2,405-415. Khan, M. A. Q., Kamal, A., Wolin, R. J. & Runnels, J, (1972b). In vivo and in vitro epoxidation of aldrin by aquatic food chain organisms. Bull. Environ. Contam. ToxicoL, 8,219-228. Khan, M. A. Q., Stanton, R. H. & Reddy, G. (1974). Detoxication of foreign chemicals by invertebrates. In Survival in Toxic Environments(Khan, M. A. Q. & Bederka, J. P. eds.), pp. 177-201. London: Academic Press.
Khan, M. A. Q. (1976). In vitro metabolism of cyclodiene epoxides by freshwater fishes. Unpublished data. Lee, R. F., Sauerheber, R. & Benson, A. A. (1972). Petroleum hydrocarbons: uptake and discharge by the marine mussel, Mutilus edulis. Science, (Wash. DC), 177, 344-346. Lee, R. F. (1975). Fate of petroleum hydrocarbons in marine zooplankton. Proc. Joint Conf. on Prevention and Control of O i l Spills. API, EPA, USCG pp. 535-540. Lee, R. F., Furlong, E. & Singer, S. (1976). Detoxification systems in marine invertebrates. Aryl hydrocarbon hydroxylase from the tissues of the blue crab, Callinectes sapidus and the polychaete worm, Nereis sp. Biological effects program workshop, May 16-19 (1976). Texas A&M University, College Station, Texas. Lowry, O. M., Rosenbrough, N. J., Farr, A. L. & Randall, R. J. (1951 ). Protein measurement with the Folin phenol reagent..L Biol. Chem., 193,265-275. Matsumura, F. 0975). Metabolism of insecticides by animals and plants. In Toxicology o f Insecticides. pp. 165-251. London: Plenum Press. Medical Research Council. Special report no. 306. (1968). The carcinogenic action of mineral oils: A chemical and biological study. H.M.S.O. London. Neff, J. M. & Anderson, J. W. (1975). Accumulation release and body • • . ]4 . '. distribution of benzopyrene C m the clam Rangta cuneata. Proc. Joint Conf. on Prevention and Control oj Oil Spills. API, EPA, USCG pp. 469-471. Netter, K. J. & Seidel, G. J. (1964). An adaptively stimulated Odemethylating system in rat liver microsomes and its kinetic properties. J. Pharmacol. Expt. Ther., 146, 61-65. Payne, J. F. & Penrose, W. R. (1975). Induction of benzo(a)pyrene hydroxylase in fish by petroleum. Bull. Environ. Contain. Toxicol.,
14, 112-116. Payne, J. F. (1976). Field evaluation of benzopyrene hydroxylase induction as a monitor for marine petroleum pollution. Science, (Wash. DC), 191, 945-946. Pedersen, M. G., Hershberger, W. K., Zachariah, P. K. & Juchau, M. R. (1975). Hepatic biotransformation of environmental xenobiotics in six strains of rainbow trout (Salmo gairdneri). J. Fish. Res. Bd Can., 33,666-675. Pohl, R. J., Bend, J. R., Guarino, A. M. & Fouts, J. R. 0974). Hepatic microsomal mixed function oxidase activity of several marine species from coastal Maine. Drug Metab. Disposition, 2, 545-555. Scarpelli, G. (1974). Hepatic function in fish. In Marine Bioassays Workshop Proc. API, EPA, MTS, Marine Technology Society (Wash. DC), pp. 191-198. Vandermeulen, J. H. & Penrose, W. R. (1976). Absence of aryl hydrocarbon hydroxylase activity in chronically oiled marine bivalves: possible consequences. J. Fish. Res. Bd Can., (to be submitted). Zobell, C. E. (1971). Sources and biodegradation of carcinogenic hydrocarbons. Proc. Joint Conf. on Prevention and Control o f Oil Spills. A PI, EPA, USCG.
Tar 'Specks' in the North Atlantic ADAM
ZSOLNAY
D u k e U n i v e r s i t y M a r i n e L a b o r a t o r y , B e a u f o r t , N C 2 8 5 1 6 , U. S. A .
A n u m b e r o f dark specks retained o n filters, through w h i c h seawater had been filtered, c o n t a i n e d material that absorbed U V light very strongly. This material was m o s t likely s u n k e n pieces o f tar. T h e a m o u n t was 0 . 1 2 p g / ! on an average and was i n d e p e n d e n t o f hydrographic parameters. The average amount of floating tar in the Northwest A t l a n t i c is c o n s i d e r a b l e ( 1 - 1 0 m g / m 2) ( M o r r i s , 1971; 116
M o r r i s & B u t l e r , 1973). T h e u l t i m a t e f a t e o f t h i s m a t e r i a l is n o t yet f u l l y k n o w n , b u t it is r e a s o n a b l e t o a s s u m e t h a t a c e r t a i n a m o u n t o f it s i n k s a f t e r s u f f i c i e n t w e a t h e r i n g h a s t a k e n p l a c e . W h e n s e a w a t e r is f i l t e r e d , a l a r g e n u m b e r o f b l a c k s p e c k s a r e o f t e n f o u n d o n t h e f i l t e r . A s p e c k is d e f i n e d h e r e as a n y t h i n g t h a t r e m a i n s b e h i n d o n a G F C g l a s s f i b r e f i l t e r a n d c a n b e s e e n w i t h t h e n a k e d eye. T h e size o f 5 0 r a n d o m l y c h o s e n s p e c k s w a s d e t e r m i n e d u n d e r a microscope. Their depth dimension was made equal to
Volume 8/Number 5/May 1977 their w i d t h . T h e i r a v e r a g e v o l u m e was f o u n d to be 3.00___0.73 x 10-6cm 3. T h e q u e s t i o n is w h e t h e r o r n o t these specks a r e t a r ?
TABLE 1
Tar specks found at various water columns in the North Atlantic. Water column
Volume filtered (I.)
Analysed specks
No. tar
Tar specks ~ug/I)
1
120.0
677
13
0.33
(2)500/(2)1000/(7)1400/ (I)1800/(1)2400
2
36.8
343
3
0.24
(1)450/(1)500/(1)1055
3
20.8
245
0
0.00
--
4
66.5
245
1
0.05
( I )2600
5
118.8
235
1
0,03
(1)1500
6
80.7
105
1
0.04
(1)210
7
76.2
130
1
0.04
( 1)30
Methods T a r specks were l o o k e d for in seven w a t e r c o l u m n s on six d i f f e r e n t cruises in the N o r t h A t l a n t i c . T h e results are s h o w n in the table. E a c h speck was r e m o v e d f r o m the filter with a H a m i l t o n SS60-N solid s a m p l e r needle a n d injected into a high p e r f o r m a n c e liquid c h r o m a t o g r a p h i c system with a U V d e t e c t o r at 254 n m ( Z s o l n a y , 1973). A n unfilled 20 x 1.8 m m i.d. c o l u m n was used a n d the e l u a n t was n - h e x a n e . T h e resulting U V - a b s o r b a n c e o f the specks ( m i n u s c o n t r o l values) f r o m a n y one c o l u m n o f w a t e r was then p l o t t e d a g a i n s t f r e q u e n c y . A n e x a m p l e o f such a p l o t is s h o w n in Fig. 1. I n m o s t cases the a b s o r b a n c e was a r o u n d zero. T h e large n u m b e r o f small negative values were d u e to e x p e r i m e n t a l e r r o r . O n e value, h o w e v e r , has a far g r e a t e r a b s o r b a n c e a n d clearly results f r o m a d i f f e r e n t m a t e r i a l t h a n the rest o f the specks. This was d e t e r m i n e d by the use o f the D i x o n ' s test for outliers ( D i x o n , 1951). T h e p r o b a b i l i t y o f this e x t r e m e v a l u e b e l o n g i n g to the rest o f the p o p u l a t i o n is well u n d e r 0.005. This m a t e r i a l was m o s t likely s u n k e n tar, since m a t e r i a l o r i g i n a t i n g f r o m p e t r o l e u m w o u l d have a far g r e a t e r UV a b s o r p t i o n at 254 nm t h a n a n y biogenic material.
Results and Discussion A n a v e r a g e speck h a d a v o l u m e o f 3.00 × 10 -6 cm 3. I f a d e n s i t y o f 1 is a s s u m e d , the a v e r a g e weight o f each speck w o u l d then be 3 / t g . O n e o f the p r i m e r e a s o n s why this s t u d y was u n d e r t a k e n was to see if tar speck d i s t r i b u t i o n s reflect h y d r o g r a p h i c c o n d i t i o n s in the o c e a n . Specks s h o u l d t e n d to a c c u m u l a t e in a r e a s w h e r e there is a s t r o n g d e n s i t y g r a d i e n t such as in the p e r m a n e n t tliermocline. This was n o t f o u n d to be the case f o r the t a r specks s t u d i e d here. T h e p e r m a n e n t t h e r m o c l i n e o f all the w a t e r c o l u m n s s a m p l e d was b e t w e e n 500 a n d 1000 m. T h e d a t a in the table d o n o t i n d i c a t e a g r e a t e r a b u n d a n c e o f tar specks a b o v e these d e p t h s . This indicates that the
At each depth (no.) found
(1) 33 °40"N and 57°36"W. (2)37 ° 14.3"N and 11°20"W. (3) 22 ° 15"N and 17°4TW. (4-7) about 20 miles SW of Bermuda. p e r m a n e n t t h e r m o c l i n e does n o t serve as a n effective b a r r i e r t o these specks. This was a l s o s h o w n b y there being no m a j o r a c c u m u l a t i o n o f t a r specks in the M e d i t e r r a n e a n w a t e r as it leaves the S t r a i g h t s o f G i b r a l t a r . T h e M e d i t e r r a n e a n has been f o u n d to have 20 m g / m 2 o f t a r ( H o r n et al., 1970). This is far m o r e t h a n in a n y r e g i o n o f the A t l a n t i c a n d there s h o u l d be a g r e a t e r c o n c e n t r a t i o n o f tar specks in the M e d i t e r r a n e a n water. W a t e r c o l u m n 2 ( T a b l e 1), which h a d a very p r o n o u n c e d t o n g u e o f M e d i t e r r a n e a n w a t e r at a b o u t 1000 m , s h o w e d n o e x t r a large c o n c e n t r a tion o f t a r specks in :'t. In fact the overall view at all the w a t e r c o l u m n s is t h a t the d e p t h at which specks were f o u n d is r a t h e r r a n d o m . T h e i r t r a n s p o r t into the d e e p waters o f the N o r t h A t l a n t i c c o u l d be caused by grazing a n d m i g r a t i o n o f z o o p l a n k t o n . O n the o t h e r h a n d S t o k e ' s law shows t h a t even if the specks are o n l y 1°70 m o r e d e n s e t h a n the w a t e r b e l o w t h e m , t h e y w o u l d sink at a rate o f a b o u t 3000 m a year. P a s s i v e sinking a l o n e c o u l d a c c o u n t for their presence in the d e e p w a t e r . I n t e r e s t i n g l y there a r e no t a r specks f o u n d in the u p welling r e g i o n o f f N o r t h w e s t A f r i c a (water c o l u m n 3). This c o i n c i d e d with a n a b s e n c e o f t a r f l o a t i n g o n the s u r f a c e in this r e g i o n ( E r h a r d t , p e r s o n a l c o m m u n i c a t i o n ) . T h e a v e r a g e a m o u n t o f t a r specks f o u n d for all the s a m p l e s was 0.12 /~g/l. I f o n e t a k e s a v o l u m e o f 1.6 x 1017 m 3 f o r the N o r t h A t l a n t i c , the t o t a l a m o u n t o f t a r specks w o u l d be 1.9 x 107 m e t r i c tons. C a l c u l a t i o n s o f this t y p e s h o u l d be viewed with e x t r e m e c a u t i o n , b u t they d o serve to s h o w t h a t the a m o u n t o f tar in the f o r m o f specks b e l o w the o c e a n ' s s u r f a c e is c o n s i d e r a b l e .
12--
The research support of the Oceanography Section, National Science Foundation, NSF Grant GA-DES 74-18094, and the competent technical assistance of Ms C. Frohlichstein and Mr B. Moorfield are gratefully acknowledged.
I0--
8--
U4
2
-o15
-005
h
005
o15
025
U V - absorbance
035
0,*5
I10
1.15
(au. x 0.02)
Fig. 1 UV-absorbance (minus controls) by material eluated from specks in a water column of the North Atlantic plotted against frequency.
Dixon, W. J. (1951). Ratios involving extreme values. Ann. Math. Star., 22, 68-78. Horn, L. M., Teal, J. M. & Backus, R. H. (1970). Petroleum lumps on the surface of the sea. Science, 168, 245-246. Morris, B. F. (1971). Petroleum: tar quantities floating in the Northwestern Atlantic taken with a new quantitative neuston net. Science, 173,430-432. Morris, B. F. & Butler, J. N. (1973). Petroleum residues in the Sargasso Sea and on Bermuda beaches. Proc. Joint Conf. on Prevention and Control of O i l Spills, pp. 521-529. Zsolnay, A. (1973). Determination of aromatic hydrocarbons in submicrogram quantities in aqueous systems by means of high performance liquid chromatography. Chemosphere, 6, 253-260. 117