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Pelagic tar in the Caribbean and equatorial Atlantic, 1974
Deep-Sea Research, 1976, Vol. 23, pp. 467 to 474. Pergamon Press, Printed in Great Britain.
NOTE
Pelagic tar in the Caribbean and equatorial Atlantic, 1974" THOMAS D . SLEETER,~'.~ BYRON F. MORRIS~ a n d JAMES N . BUTLER++
(Received 10 February 1975; in revisedform 17 July 1975; accepted 17 August 1975) Abstract--Pelagic tar was sampled at 61 stations in the Caribbean region and 31 stations in the eastern north and equatorial Atlantic. In the Caribbean, tar densities averaged 1-4 mg m-I, confirmingearlier reports. Tat' densities in the Canary Current region (2.0 mg m-a) were also similar to previously recorded densities, but in the equatorial Atlantic densitieswere significantlylower (0.16 mg m-a) than others have found. Caribbean beach transects showed substantial amounts of tar on windward shores. The data suggest that although the Caribbean has a lower standing stock of tar than the more slowly circulating Sargasso Sea, comparable quantities of tar probably pass through the former in unit time. INTRODUCTION W-14 of the R.V. Westward on a circumnavigaPELAGIC tar lumps have been quantitatively tion of the Caribbean Sea and Gulf of Mexico. surveyed in the North Atlantic since 1969. In July, on Cruise TR-155 of the R.V. Trident, 31 Compared to the extensively sampled western stations were occupied in a transect extending North Atlantic, the equatorial and eastern sub- along 26 to 28°W from the Azores southward tropical North Atlantic have been poorly studied. across the equatorial current region. Information Knowledge of tar densities in the latter regions gathered on these cruises is reported here to comes from limited sampling programs of four extend our knowledge of oceanic pollution from previous investigations: (1) the area between pelagic tar. Gibraltar and the Azores--HORN, TEAL and Recent beach tar surveys have been reported BACKUS (1970), 4 stations; SLEETER, MORRIS and from only a few localities, i.e. Bermuda (MORRIS BUTLER (1974), 14 stations; (2) the North and BUTLER, 1973; BUTLER,MORRIS and SASS,1973 Equatorial region--PoLIKARPOV, YEGOROV, and Golden Beach, Florida (SANER and CmtTIS, IVANOV, TOKAREWi and FELEPPOV (1971), 26 1974). The R.V. Westward cruises visited several consecutive tows along an 8-km drift track; islands throughout the Caribbean and conducted POLIKAm'OV and BENZmTSKV(1974), 6 stations. beach transects for tar pollution on many of these Several pelagic tar surveys have been reported islands. from the Caribbean Sea and the Gulf of Mexico (JEFFREY, FRANK, POWELL, BANTZ, VOS and MAY, METHODS 1973; SHERMAN, COLTON, KNAPP, DRYFOOS and The surface sampling on the R.V. Trident IOn, 1973; POLIICARPOV and BENZrIn'SKY, from the Azores to Brazil was identical to that 1974). *Contribution No. 607 from the Bermuda Biological During 1974, it was possible for us to extend Station. tBermuda Biological Station, St. George's 1-15, quantitative sampling of pelagic tar into the Bermuda. above regions. From January to March, 61 ~:Pierce Hall, Division of Engineering and Applied stations were occupied aboard cruises W-13 and Physics, Harvard University, Cambridge MA 02138, U.S.A. 467
468
THOMASD. SLEETER,BYRONF. MORRtSand JAMESN. BUTLER
employed by the MARMAP* program (COLTON, KNAPP and BURNS,1974). At all stations the ship steamed a 1-kin diameter circle, and the net was towed in undisturbed water. Typical tows were for 10 mEn at 5 knots,I" covering an area of ~ 3000 mE In the Caribbean, the net used was of U.S. Coast Guard design, 0.515-mm mesh, and consisted of a 1-m × l/2-m fiberglass frame with lateral floats (McGOWAN, SANER and HUFFORD, 1974). Typical tows were made for 30 men at 3 to 4 knots. The length of tow was determined by correlation of the ship log with a flowmeter attached to the net. Tar quantities from both cruises were determined as wet weights with an accuracy to
,o.+
0.1 g per sample. Beach transects were conducted according to the methods of MORRIS and BUTLER (1973). All tar within a 1-m wide strip of beach from the water level to the highest water mark was gathered. This method is more representative of tar input to shore than a tar per square meter comparison. The latter would be influenced by tidal variation and beach slope, and would make intercomparisons between beaches difficult. Transect sites along a beach were selected to be as representative of that *Marine Resources Monitoring Assessment and Prediction Program (a program of the United States National Marine Fisheries Service). "1"1knot = 0.51 m s -1.
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Fig. 1. Cruise track of the R.V. Trident. Numbers at stations give tar concentration in mg m -I.
Pelagic tar in the Caribbean and equatorial Atlantic, 1974
Table 1.
469
R.V. Trident station data.
......................... DATE STATION LOCATION NUMBER
TAR (mg/m 2 )
5 July
1 2
30*01'N, 26"28'W 28* N, 26"29'W
0.81 1.88
COMMENTS
6 July
3
26o36'N, 26°49'W
2.72
Misc. plastic, 3.7g
7 July
4 5
25o13'N, 26o58'W 23o23'N, 27o05'WI
0.76 0.68
Misc. plastic, 0.6g Misc. plastic, 0.4g
8 July
6 7
21*43'N, 27o21'W 19o56'N, 27o31'W
2.87 7.69
Misc. plastic, 0.4g 17 man diam. plastic marble, 3.6g
9 July
8 9
18*lS'N, 27*39'W 16°28'N, 27°52'w
0.71 0.09
l0 July
i0 ii 12
14°59'N, 27°59'W 12"57'N, 28*04'W 12*00'N, 28°OO'W
0.15 0.10 0.10
ii July
13
10"58'N, 28"00'W
0.27
12 July
14 15
9=21'N, 28°02'W 8=00'N 28°00'W
0.035 0.027
13 July
16 17
6=59'N, 28000'W ~=I3'N, 27°56'W
0.017 0.011
14 July
18 19
4°08'N, 27"58'W 2"57'N, 28*01'W
0.022 0.046
15 July
20
l*01'N, 27°58'W
0.020
19 July
21 22
0*48'N, 26°57'W I°58'N, 28°03'W
0.025 0.011
20 July
23 24
I*00'N, 28°01'W 0"I3'N, 28*01'W
0.049 trace
New net installed one speck 0.5 mm dia.
Water color changed from deep-blue to greyish green.
21 July
22 July
23 July
25
0*41'N, 28°02'W
none
26
I°41'S, 28°03'W
0.037
27
2°30'S, 28°00'W
0.i0
28 29
4°01'5, 28*01'W
0.019 0.52
30 31
5°02'S, 28°02'W 6*02'S, 28e05'w
0.57 0.078
particular beach as was subjectively possible. Whenever noticeable differences in the tar quantities occurred, multiple transects were taken.
Three lumps.
Only one speck of tar, 2ram in diam.
Halobates sp. larvae on tar lumps
Green algae on tar.
Atlantic equatorial currents as given by LONGHURST (1962) and PERLROTH (1966), tar densities (arithmetic means) in each current can be given:
RESULTS
The quantity of tar collected at 31 stations in the northeast and equatorial Atlantic by the R.V. Trident is given in Fig. 1 and Table 1. Almost all the tar was fresh, i.e. black, sticky, and soft, in contrast to the varying textures and colors of samples collected from the Canary Current region (SLEETER, MORRIS and BUTLER, 1974). Large amounts of tar were collected at Stas. 1 to 8, but from Sta. 9 southwards, the quantities decreased by more than an order of magnitude. Using the approximate locations of the various
.,Y(mg m - 9
Range
n
Canary Current (Stas. 1-9)
2"02
0-09-7.69
9
North Equatorial Current (Stas. 10-13)
0"16
0.10-0.27
4
Equatorial Countercurrent (Stas. 14-18)
0'02
001-0.04
5
South Equatorial Current (Stas. 19-31)
0"11
0.00-0.57
13
470
THOMAS D. SLEETER, BYRON F. MORRlS a n d JAMES N. BUTLER
The higher densities of fresh tar encountered at the early stations caused some soiling of the net and it is possible that some of the very small tar quantities recorded for several later stations were at least partially due to contamination from the soiled net. A clean net was attached prior to Sta. 23. Plastic particles often occur in surface samples (CARPENTER and SMITH, 1972; COTTON, KNAPP and BURNS, 1974). Plastic fragments were found in samples from Stas. 1 to 10 but were only weighted separately when appreciable quantities occurred. This is noted in Table 1. In the samples from Sta. 11 to 31 no plastic particles were found. The tar concentrations found at 61 stations during the R.V. Westward cruises to the Caribbean Sea and Gulf of Mexico are given in Fig. 2 and Table 2. On a regional basis, densities averaged
as follows: .X(mg In-~)
Region
Range
n
Atlantic side of LesserAntilles (Stas. 1-14) 1.12
0.02-8-37
14
Caribbean Sea (Sta. 15-49)
0.00-13-4
35
0-01-6"00
12
1"62
Gulf of Mexicoand Straits of 1'12 Florida (Stas. 50-61)
In all three regions, tar densities were similar not only in average concentration but also in range and variability. Lowest densities occurred in the region of the Dutch Antilles ( < 0.1 mg m -2) and the highest amount (13.4 mg m -2) occurred in the Mona Passage between Puerto Rico and Hispaniola.
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~..7,o.':i r ,,AWS Fig. 2. Cruise track of the R.V. Westward. Numbers at stations give tar concentration in mg m-L
Pelagic tar in the Caribbean and equatorial Atlantic, 1974
Table 2. ~A~
R.V. Westward station data.
SrAT~3N
LOCATIO~
NUAIBER
tAR
(mg/m2)
21 Jan. 74
1
33°35'N, 59°50'W
8.37
22 dan. 74
2 3 4 5
13°34'N, 14"10'N, 14°31'N, 14°55'N,
60*05'W 60"10'W 60°30'W 60°50'W
1.27 1.24 0.17 0.19
23 .]an. 74
6 7
15°13'N, 61°II'W 15°37'N, 60°56'W
0.03 0.32
24 ,/an. 74
8 9
16~05'N, 60°47'W 16°49'N, 61031'W
0.30 0.27
16 .]~1%. 71
]~ 13 12
17°28'N, 62°32'W 18°12'N, 63°26'W 18°55'N, 64"15'W
0.37 0.02 2.87
27 .fan. 74
13 14
19°07'N, 65°05'W 18°50'N, 65"28'W
0.23 0.07
9 Feb. 74
15 16
18°01'N, 67"28'W 17°45'N, 67033'W
13.4 0.31
I0 feb. 74
37 18 19
16°44'N, 67018'W 15057'N, 67019'W 15°22'N, 67o18'w
0.34 1.9 0.96
31 V'eb. 74
20 21 22
14023'N, 66050'w 13°42'N, 66041'W 13°03tN, 66°39'W
0.39 1.62 0.23
12 feb. 74
23
12"08'N, 66036'W
0.004
3~ ~'eb. 74
24
12"02'N, 67°47'W
0.023
20 feb. 74
25
II°55'N, 68°32'W
0.09
22 Feb. 74
26
If°IS'N, 69°18'W
0.043
23 feb. 74
27 28
31°38'N, 69°46'W 13*O0'N, 70°32'W
0.002 0.0
24 Feb. 74 25 Feb. 74
29 30 31
12*32'N, 70"22'W 12°52'N, 71°48'W 13*23'N, 73°13'W
0.0 0.002 0.36
26 ieb. ?'4
32 33
13°29'N, 74°13'W 13°39'Nt 75033'W
0.25 3.63
27Feb.
74
34 35
J3°49'N, 76*40'W 13033'N, 77058'W
28 Feb. 74
36
14~20'N, 80015'W
4 ~lar. 74
37
14a18'N, 8Go27'W
4.9
6 Max. 74
38 39
15°ll'N, 81005'W 15 °40'N , 81°23'W
0.67 0.06
7 31at. 74
40 41
16013'N, 82000'W 16°28'N, 83004'W
0.64 0.37
8 Mar. 74
42 43 44
16°36'N, 83053'W 16 ~40'N , 85005'W 16" 17'N, 85"55'W
8.5 1.43 O.0i
12 Mar. 74
45
16°03'N, 86*46'W
0.014
13 Mar. 74
46 47
17006'N, 86930'W 18°18'N, 86730'W
0.16 0.61
1.7 10.5 2.43
14 Mar. 74
48
18055'N, 86°27'W
0.45
15 Mar. 74
49
20°48'N, 86"49'W
0.41
16 Mar. 74
50 51
22°17'N, 86019'W 22°48'N, 85°17'W
0.18 0.06
17 Mar. 74
52
24"00'N, 84*30tW
6.0
18 Mar. 74
53 54
23°21'N, 84005'W 23"45'N, 84°14'W
3.0 0.I1
19 Mar. 74
55 56
23*45'N, 83011 'W 24°15'N, 81°13'W
0.043 0.023
20 Mar. 74
57 58
24048'N, 80e22'W 25°25'N# 79~33'W
2.82 0.03
22 Mar. 74
59
24°14'N, 79"59'W
0.009
24 Mar. 74
60
24" 09'N, 79"48W
0.14
25 Mar. 74
61
25"30'N, 80~02'W
1.02
471
All Caribbean beaches examined showed effects of chronic pollution by tar. In general, beaches facing east, i.e. exposed to the prevailing winds and currents within the Caribbean Sea, had substantially higher levels than those on a leeward (western) shore. The beaches surveyed and their tar densities are identified in Table 3. DISCUSSION Tar concentrations encountered in the Canary Current region (X = 2.0 mg m -2) are similar to the levels reported by earlier workers. HORN, TEAL and BACKUS (1970) reported values of 2, 3, 5, and 480 mg m -2 from the region between the Azores and Gibraltar, and SLEETER, MORRIS and BUTLER (1974) reported an average of 6 mg m -* in the same region. The tar concentrations found in the equatorial current region are decidedly lower than levels reported by POLIKARPOV, YEGOROV, IVANOV, TOKOREVA and FELEPPOV (1971), and by POLIKAgPOV and BENZHITSKY (1974). These workers found average contaminations of 12.7 mg m -2 (range 0.0 to 63.6) and I1.6 mg m -2 (2.7 to 25-9), respectively. The highest density we encountered in this region was 0.6 mg m-Z; our average value was 0.16 mg m -2. HEYERDAHL (1970, 1971) observed the variable nature of tar within the equatorial Atlantic during his Ra expeditions. Heavy concentrations were encountered on 6 days out of 52 on his first crossing, and on 40 of 36 days of his second expedition. At other times the waters were relatively devoid of tar. PRICE (1973) encountered floating tar during almost all of a crossing between the Canaries and Antigua. Major currents, with their rapid one-way transport of surface waters, should show considerably more temporal and spatial fluctuations in tar concentration than enclosed seas or central oceanic gyres. In a current system, the amount of tar found along the current would reflect the changes in input rates of new tar. Concentrations in central oceanic gyres, however, result from accumulation over time, and are probably less variable. We beiieve that the only significant source of
472
THOMASD. SLEETER,BYRONF. MORRISand JAMESN. BUTLER
Table 3. Beach tar concentrations found at several Caribbean locations. LOCATION Barbados: Bathsheba Gibbs Bay
DATE
TAR (g/~ of shore)
18 Jan 74 18Jan
74
Puerto Rico: E1 Condado, San Juan 2 Feb 74 Luquillo Beach 2 Feb 74 Dorado Beach 3 Feb 74 Rincon Beach 3 Feb 74 Los Roques Islands
15 Feb 74
40 62 4.5 52 112 83 12 2O 25 2.2
Isles de Ayes: Isla de Sotavente
19 Feb 74
Serrana Bank: South Cay
5 Mar 74
La Cieba, Honduras
9 Mar 74
13 230 47 0 0.2 0.0
NOTES
Windward shore " Leeward shore North shore West shore Windward shore-leeward side of lagoon Leeward shore Windward shore " Leeward shore
range 50-1000 Tar not weighed, est. mean 150-200 very soft, mixed with beach litter and seaweed. Maximum at windward corner of cay. 90 127
Windward shore
Note: the tar in a l-m wide transect of the beach was collected by hand and weighed. Provided the transect extended from the water line to above the high-water mark, its length and the state of the tide had little influence on the amount of tar collected. See BtrrLER, MORRISand Sins (1973) for details. pelagic tar is in the routine operations (deballasting, tank and bilge cleaning) of oil tankers involved in crude oil transport. Temporal changes in the input of tar along the equatorial West African sector of this shipping lane would likely be reflected in the changes in the tar concentrations within the equatorial current system. The apparently fresh nature of all the tar lumps collected in the equatorial region indicates a recent origin, supporting the hypothesis that the West African shipping lanes are the source. This is also evidenced in the higher tar concentrations of the westward-flowing Equatorial Current (e.g. Stas. 8 to 13) than in the eastward-flowing Equatorial Countercurrent (e.g. Stas. 14 to 19). Tar concentrations in the Caribbean Sea and Gulf o f Mexico are more in accord with reported levels. We found a slightly higher average concentration of tar in the Caribbean (1-6 mg m-9 than in the Gulf of Mexico (1.1 mg m-2), as did the M A R M A P surveys (SHERMAN, COLTON, KNAPP, DRYFOOS and KINNEAR, 1973)---0"5 and
0.16 mg m -z, respectively. JEFFREY, FRANK, POWELL, BANTZ, VOS and MAY (1973) found slightly higher concentrations of tar in the Gulf of Mexico--0.74 and 1-2 rng m -z. Since the latter group reported benzene-extractable dry residues rather than wet weights, these values should be increased by a factor of about 1.37 to convert to wet weight, giving 1-0 and 1.6 mg m -2 for their Caribbean and Gulf of Mexico averages. All these values are well within the normal variation that seems to be inherent in the sampling: approximately a factor of ten for single samples and a factor of two for averages of 20 or more samples (BUTLERand MORmS, 1974). POLIKARPOV and BENZHITSKY(1974) sampled l0 stations in the Caribbean. Omitting one station with an unusually large amount of tar (38 mg m-2), their average value (2.9 mg m -2) is also within the expected variability. During Ra L HEYERDAHL(1970) observed large quantities of tar east of Barbados, but in the later journey of Ra II he found these waters to be
Pelagic tar in the Caribbean and equatorial Atlantic, 1974
473
relatively clean (HEYERDAHL, 1971). The purpose than in regions where the residence time of of sampling the windward side of the Lesser surface material is longer. Antilles was to investigate Heyerdahl's initial observation of large mounts of tar in that area. Acknowledgements--This work was supported by the National Science Foundation International Decade of With the exception of one sample off Barbados, Ocean Exploration, Grant No. GX-32883, and by the however, we found relatively low levels of tar National Marine Fisheries Service (NOAA) MARMAP program. The authors thank JACK JoSSl for his help and on the Atlantic side of the islands. initiative in planning the cruise of the R.V. Trident and the Although the concentration of pelagic tar in captains and crews of the Trident (University of Rhode the Caribbean is about one tenth that of the Island) and the R.V. Westward(Sailing Education AssociaSargasso Sea, beach pollution on Caribbean tion) for their exceptional help during the cruises. Special thanks are due to JAN TUTTLEMANand PAULDESLAURIERS islands approaches the levels found on Bermuda for their assistance aboard the Westward. beaches (MORRIS and BUTLER, 1973; BUTLER, MORRIS and SASS, 1973). We attribute this to the REFERENCES fact that although the standing stock of tar in BUTLER J. N. and B. F. MORRIS (1974) Quantitative monitoring and variability of pelagic tar in the Caribbean surface waters is less, the rate of water North Atlantic. Proceedings of the Pollution movement past a point (i.e. an island) is greater. Monitoring (Petroleum) Symposium and Workshop, Per unit of time, an island shore in the Caribbean National Bureau of Standards Special Publication No. 409, pp. 75-78. will entrain tar from a considerably greater area of BUTLER J. N., B. F. MORRIS and J. SASS(I 973) Pelagic sea surface, and beach loadings will approach tar from Bermuda and the Sargasso Sea. Special those of more heavily polluted but more sluggish Publication No. 10, Bermuda Biological Station, 346 pp. systems. Beaches on the windward side of the E. J. and K. L. SMITH (1972) Plastics on islands consistently had higher levels of tar, while CARPENTER the Sargasso Sea surface. Science, 178, 1240-1241. leeside shores were often relatively clean. This COLTON J. F., F. D. KNAPP and B. R. BURNS (1974) Plastic particles in surface waters of the northcontrasts with Bermuda, where wind does not western Atlantic. Science, 185, 491~,97. consistently blow from one direction, and there HEYERDAHL T. (1970) Atlantic Ocean pollution is little correlation of tar accumulation with observed by Expedition 'Ra'. Biological Conservation, 2, 221-222. wind direction. T. (1971) Atlantic Ocean pollution and The tar on Caribbean beaches is often quite HEYERDAHL biota observed by the 'Ra' expeditions. Biological soft (fresh) in contrast to the hard (aged) tar Conservation, 3, 164-167. lumps commonly found in Bermuda. This may HORN M. H., J. M. TEAL and R. H. BACKUS (1970) Petroleum lumps on the surface of the sea. Science, indicate a more recent origin of the Caribbean 168, 245-246. tar, but these qualitative observations should be JEFFREY L. M., D. J. FRANK,N. POWELL,A. BANTZ, A. Vos and L. MAY (1973) Progress report on pelasupported by chemical analyses. The fresher gic, beach and bottom tars of the Gulf of Mexico appearance is also consistent with a relatively and controlled weathering experiments. Dept. of short residence time within the region. Significant Oceanography, Texas A. & M. University, 86 pp. inputs into the Caribbean region are the major LONGHURSTA. R. (1962) A review of the oceanography of the Gulf of Guinea. Bulletin IFAN, series A, tanker routes from Venezuela to North America, Vol. 24, no. 3. tar from the eastern Atlantic via the Equatorial McGowAN W. E., W. A. SANER and G. L. HUEFORD 0974) Tar ball sampling in the Western North Current, and possibly from natural seeps in the Atlantic. Marine Pollution Monitoring (Petroleum) local region. Again, these hypotheses should be Symposium and Workshop, National Bureau of tested by detailed chemical analyses of the floating Standards, Special Publication No. 409, pp. 83-84. See also U.S. Coastguard Report C G R & D 24/74, tar and correlation with known crude oil sources. 30 pp. The ultimate fate of tar in the Caribbean Sea MORmS B. F. and J. N. BUTLER (1973) Petroleum is probably on its shorelines, or it may eventually residues in the Sargasso Sea and on Bermuda be transported out of the region and into the Beaches. Proceedings (~f the Joint Conference on Prevention and Control of Oil Spills, American Sargasso Sea. Disintegration and biodegradation Petroleum Institute, pp. 521-529. will also play their part, but will be less important PERLROTH I. (1966) The distribution of water type
474
THOMAS D. SLEETER, BYRON F. MORRIS and JAMES N. BUTLER
structure in the first 300 feet of the equatorial SANER W. A. and M. CURTIS(1974) Tar bali loadings on Golden Beach, Florida. Pollution Monitoring Atlantic. Proceedings of the Symposium on the (Petroleum) Symposium and Workshop, National Oceanography and Fisheries Resources of the Bureau of Standards, Special Publication No. 409, Tropical Atlantic, UNESCO, pp. 185-191. POUKAm'OV G. G. and A. G. BENZrnTSKV (1974) pp. 79-81. Naphthic aggregates--biotope of neustonic SHERMANK., J. B. COLTON,F. D. KNAPP, R. DRYFOOS and B. S. KINNEAR (1973) Oil and Plastics Conperiphyta (in Russian). Visnek Akademii Nauk tamination and Fish Larvae in Surface Waters of Ukraninskoi RSR, Kiev, 4, 89-92. the Northwest Atlantic. Unpublished report of the POLIKARPOV G. G., N. YEGOROV, V. N. IVANOV, National Marine Fisheries Service, M A R M A P A. V. TOKAREVAand I. A. FELEPPOV (1971) Oil Field Office, Narrangansett, R.I. areas as an ecological niche (in Russian). Priroda No. 11. (Pollution Abstracts translation No. 72- SLEETERT. D., B. F. MORRISand J. N. BUTLER(1974) Quantitative sampling of pelagic tar in the North 5TC-0451 .) Atlantic Ocean: 1973. Deep-Sea Research, 21, PRICE A. R. G. (1973) A further look at pollution in the Atlantic Ocean. Biological Conservation, 35(4). 773-775.
NOTE
Pelagic tar in the Caribbean and equatorial Atlantic, 1974" THOMAS D . SLEETER,~'.~ BYRON F. MORRIS~ a n d JAMES N . BUTLER++
(Received 10 February 1975; in revisedform 17 July 1975; accepted 17 August 1975) Abstract--Pelagic tar was sampled at 61 stations in the Caribbean region and 31 stations in the eastern north and equatorial Atlantic. In the Caribbean, tar densities averaged 1-4 mg m-I, confirmingearlier reports. Tat' densities in the Canary Current region (2.0 mg m-a) were also similar to previously recorded densities, but in the equatorial Atlantic densitieswere significantlylower (0.16 mg m-a) than others have found. Caribbean beach transects showed substantial amounts of tar on windward shores. The data suggest that although the Caribbean has a lower standing stock of tar than the more slowly circulating Sargasso Sea, comparable quantities of tar probably pass through the former in unit time. INTRODUCTION W-14 of the R.V. Westward on a circumnavigaPELAGIC tar lumps have been quantitatively tion of the Caribbean Sea and Gulf of Mexico. surveyed in the North Atlantic since 1969. In July, on Cruise TR-155 of the R.V. Trident, 31 Compared to the extensively sampled western stations were occupied in a transect extending North Atlantic, the equatorial and eastern sub- along 26 to 28°W from the Azores southward tropical North Atlantic have been poorly studied. across the equatorial current region. Information Knowledge of tar densities in the latter regions gathered on these cruises is reported here to comes from limited sampling programs of four extend our knowledge of oceanic pollution from previous investigations: (1) the area between pelagic tar. Gibraltar and the Azores--HORN, TEAL and Recent beach tar surveys have been reported BACKUS (1970), 4 stations; SLEETER, MORRIS and from only a few localities, i.e. Bermuda (MORRIS BUTLER (1974), 14 stations; (2) the North and BUTLER, 1973; BUTLER,MORRIS and SASS,1973 Equatorial region--PoLIKARPOV, YEGOROV, and Golden Beach, Florida (SANER and CmtTIS, IVANOV, TOKAREWi and FELEPPOV (1971), 26 1974). The R.V. Westward cruises visited several consecutive tows along an 8-km drift track; islands throughout the Caribbean and conducted POLIKAm'OV and BENZmTSKV(1974), 6 stations. beach transects for tar pollution on many of these Several pelagic tar surveys have been reported islands. from the Caribbean Sea and the Gulf of Mexico (JEFFREY, FRANK, POWELL, BANTZ, VOS and MAY, METHODS 1973; SHERMAN, COLTON, KNAPP, DRYFOOS and The surface sampling on the R.V. Trident IOn, 1973; POLIICARPOV and BENZrIn'SKY, from the Azores to Brazil was identical to that 1974). *Contribution No. 607 from the Bermuda Biological During 1974, it was possible for us to extend Station. tBermuda Biological Station, St. George's 1-15, quantitative sampling of pelagic tar into the Bermuda. above regions. From January to March, 61 ~:Pierce Hall, Division of Engineering and Applied stations were occupied aboard cruises W-13 and Physics, Harvard University, Cambridge MA 02138, U.S.A. 467
468
THOMASD. SLEETER,BYRONF. MORRtSand JAMESN. BUTLER
employed by the MARMAP* program (COLTON, KNAPP and BURNS,1974). At all stations the ship steamed a 1-kin diameter circle, and the net was towed in undisturbed water. Typical tows were for 10 mEn at 5 knots,I" covering an area of ~ 3000 mE In the Caribbean, the net used was of U.S. Coast Guard design, 0.515-mm mesh, and consisted of a 1-m × l/2-m fiberglass frame with lateral floats (McGOWAN, SANER and HUFFORD, 1974). Typical tows were made for 30 men at 3 to 4 knots. The length of tow was determined by correlation of the ship log with a flowmeter attached to the net. Tar quantities from both cruises were determined as wet weights with an accuracy to
,o.+
0.1 g per sample. Beach transects were conducted according to the methods of MORRIS and BUTLER (1973). All tar within a 1-m wide strip of beach from the water level to the highest water mark was gathered. This method is more representative of tar input to shore than a tar per square meter comparison. The latter would be influenced by tidal variation and beach slope, and would make intercomparisons between beaches difficult. Transect sites along a beach were selected to be as representative of that *Marine Resources Monitoring Assessment and Prediction Program (a program of the United States National Marine Fisheries Service). "1"1knot = 0.51 m s -1.
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Fig. 1. Cruise track of the R.V. Trident. Numbers at stations give tar concentration in mg m -I.
Pelagic tar in the Caribbean and equatorial Atlantic, 1974
Table 1.
469
R.V. Trident station data.
......................... DATE STATION LOCATION NUMBER
TAR (mg/m 2 )
5 July
1 2
30*01'N, 26"28'W 28* N, 26"29'W
0.81 1.88
COMMENTS
6 July
3
26o36'N, 26°49'W
2.72
Misc. plastic, 3.7g
7 July
4 5
25o13'N, 26o58'W 23o23'N, 27o05'WI
0.76 0.68
Misc. plastic, 0.6g Misc. plastic, 0.4g
8 July
6 7
21*43'N, 27o21'W 19o56'N, 27o31'W
2.87 7.69
Misc. plastic, 0.4g 17 man diam. plastic marble, 3.6g
9 July
8 9
18*lS'N, 27*39'W 16°28'N, 27°52'w
0.71 0.09
l0 July
i0 ii 12
14°59'N, 27°59'W 12"57'N, 28*04'W 12*00'N, 28°OO'W
0.15 0.10 0.10
ii July
13
10"58'N, 28"00'W
0.27
12 July
14 15
9=21'N, 28°02'W 8=00'N 28°00'W
0.035 0.027
13 July
16 17
6=59'N, 28000'W ~=I3'N, 27°56'W
0.017 0.011
14 July
18 19
4°08'N, 27"58'W 2"57'N, 28*01'W
0.022 0.046
15 July
20
l*01'N, 27°58'W
0.020
19 July
21 22
0*48'N, 26°57'W I°58'N, 28°03'W
0.025 0.011
20 July
23 24
I*00'N, 28°01'W 0"I3'N, 28*01'W
0.049 trace
New net installed one speck 0.5 mm dia.
Water color changed from deep-blue to greyish green.
21 July
22 July
23 July
25
0*41'N, 28°02'W
none
26
I°41'S, 28°03'W
0.037
27
2°30'S, 28°00'W
0.i0
28 29
4°01'5, 28*01'W
0.019 0.52
30 31
5°02'S, 28°02'W 6*02'S, 28e05'w
0.57 0.078
particular beach as was subjectively possible. Whenever noticeable differences in the tar quantities occurred, multiple transects were taken.
Three lumps.
Only one speck of tar, 2ram in diam.
Halobates sp. larvae on tar lumps
Green algae on tar.
Atlantic equatorial currents as given by LONGHURST (1962) and PERLROTH (1966), tar densities (arithmetic means) in each current can be given:
RESULTS
The quantity of tar collected at 31 stations in the northeast and equatorial Atlantic by the R.V. Trident is given in Fig. 1 and Table 1. Almost all the tar was fresh, i.e. black, sticky, and soft, in contrast to the varying textures and colors of samples collected from the Canary Current region (SLEETER, MORRIS and BUTLER, 1974). Large amounts of tar were collected at Stas. 1 to 8, but from Sta. 9 southwards, the quantities decreased by more than an order of magnitude. Using the approximate locations of the various
.,Y(mg m - 9
Range
n
Canary Current (Stas. 1-9)
2"02
0-09-7.69
9
North Equatorial Current (Stas. 10-13)
0"16
0.10-0.27
4
Equatorial Countercurrent (Stas. 14-18)
0'02
001-0.04
5
South Equatorial Current (Stas. 19-31)
0"11
0.00-0.57
13
470
THOMAS D. SLEETER, BYRON F. MORRlS a n d JAMES N. BUTLER
The higher densities of fresh tar encountered at the early stations caused some soiling of the net and it is possible that some of the very small tar quantities recorded for several later stations were at least partially due to contamination from the soiled net. A clean net was attached prior to Sta. 23. Plastic particles often occur in surface samples (CARPENTER and SMITH, 1972; COTTON, KNAPP and BURNS, 1974). Plastic fragments were found in samples from Stas. 1 to 10 but were only weighted separately when appreciable quantities occurred. This is noted in Table 1. In the samples from Sta. 11 to 31 no plastic particles were found. The tar concentrations found at 61 stations during the R.V. Westward cruises to the Caribbean Sea and Gulf of Mexico are given in Fig. 2 and Table 2. On a regional basis, densities averaged
as follows: .X(mg In-~)
Region
Range
n
Atlantic side of LesserAntilles (Stas. 1-14) 1.12
0.02-8-37
14
Caribbean Sea (Sta. 15-49)
0.00-13-4
35
0-01-6"00
12
1"62
Gulf of Mexicoand Straits of 1'12 Florida (Stas. 50-61)
In all three regions, tar densities were similar not only in average concentration but also in range and variability. Lowest densities occurred in the region of the Dutch Antilles ( < 0.1 mg m -2) and the highest amount (13.4 mg m -2) occurred in the Mona Passage between Puerto Rico and Hispaniola.
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Pelagic tar in the Caribbean and equatorial Atlantic, 1974
Table 2. ~A~
R.V. Westward station data.
SrAT~3N
LOCATIO~
NUAIBER
tAR
(mg/m2)
21 Jan. 74
1
33°35'N, 59°50'W
8.37
22 dan. 74
2 3 4 5
13°34'N, 14"10'N, 14°31'N, 14°55'N,
60*05'W 60"10'W 60°30'W 60°50'W
1.27 1.24 0.17 0.19
23 .]an. 74
6 7
15°13'N, 61°II'W 15°37'N, 60°56'W
0.03 0.32
24 ,/an. 74
8 9
16~05'N, 60°47'W 16°49'N, 61031'W
0.30 0.27
16 .]~1%. 71
]~ 13 12
17°28'N, 62°32'W 18°12'N, 63°26'W 18°55'N, 64"15'W
0.37 0.02 2.87
27 .fan. 74
13 14
19°07'N, 65°05'W 18°50'N, 65"28'W
0.23 0.07
9 Feb. 74
15 16
18°01'N, 67"28'W 17°45'N, 67033'W
13.4 0.31
I0 feb. 74
37 18 19
16°44'N, 67018'W 15057'N, 67019'W 15°22'N, 67o18'w
0.34 1.9 0.96
31 V'eb. 74
20 21 22
14023'N, 66050'w 13°42'N, 66041'W 13°03tN, 66°39'W
0.39 1.62 0.23
12 feb. 74
23
12"08'N, 66036'W
0.004
3~ ~'eb. 74
24
12"02'N, 67°47'W
0.023
20 feb. 74
25
II°55'N, 68°32'W
0.09
22 Feb. 74
26
If°IS'N, 69°18'W
0.043
23 feb. 74
27 28
31°38'N, 69°46'W 13*O0'N, 70°32'W
0.002 0.0
24 Feb. 74 25 Feb. 74
29 30 31
12*32'N, 70"22'W 12°52'N, 71°48'W 13*23'N, 73°13'W
0.0 0.002 0.36
26 ieb. ?'4
32 33
13°29'N, 74°13'W 13°39'Nt 75033'W
0.25 3.63
27Feb.
74
34 35
J3°49'N, 76*40'W 13033'N, 77058'W
28 Feb. 74
36
14~20'N, 80015'W
4 ~lar. 74
37
14a18'N, 8Go27'W
4.9
6 Max. 74
38 39
15°ll'N, 81005'W 15 °40'N , 81°23'W
0.67 0.06
7 31at. 74
40 41
16013'N, 82000'W 16°28'N, 83004'W
0.64 0.37
8 Mar. 74
42 43 44
16°36'N, 83053'W 16 ~40'N , 85005'W 16" 17'N, 85"55'W
8.5 1.43 O.0i
12 Mar. 74
45
16°03'N, 86*46'W
0.014
13 Mar. 74
46 47
17006'N, 86930'W 18°18'N, 86730'W
0.16 0.61
1.7 10.5 2.43
14 Mar. 74
48
18055'N, 86°27'W
0.45
15 Mar. 74
49
20°48'N, 86"49'W
0.41
16 Mar. 74
50 51
22°17'N, 86019'W 22°48'N, 85°17'W
0.18 0.06
17 Mar. 74
52
24"00'N, 84*30tW
6.0
18 Mar. 74
53 54
23°21'N, 84005'W 23"45'N, 84°14'W
3.0 0.I1
19 Mar. 74
55 56
23*45'N, 83011 'W 24°15'N, 81°13'W
0.043 0.023
20 Mar. 74
57 58
24048'N, 80e22'W 25°25'N# 79~33'W
2.82 0.03
22 Mar. 74
59
24°14'N, 79"59'W
0.009
24 Mar. 74
60
24" 09'N, 79"48W
0.14
25 Mar. 74
61
25"30'N, 80~02'W
1.02
471
All Caribbean beaches examined showed effects of chronic pollution by tar. In general, beaches facing east, i.e. exposed to the prevailing winds and currents within the Caribbean Sea, had substantially higher levels than those on a leeward (western) shore. The beaches surveyed and their tar densities are identified in Table 3. DISCUSSION Tar concentrations encountered in the Canary Current region (X = 2.0 mg m -2) are similar to the levels reported by earlier workers. HORN, TEAL and BACKUS (1970) reported values of 2, 3, 5, and 480 mg m -2 from the region between the Azores and Gibraltar, and SLEETER, MORRIS and BUTLER (1974) reported an average of 6 mg m -* in the same region. The tar concentrations found in the equatorial current region are decidedly lower than levels reported by POLIKARPOV, YEGOROV, IVANOV, TOKOREVA and FELEPPOV (1971), and by POLIKAgPOV and BENZHITSKY (1974). These workers found average contaminations of 12.7 mg m -2 (range 0.0 to 63.6) and I1.6 mg m -2 (2.7 to 25-9), respectively. The highest density we encountered in this region was 0.6 mg m-Z; our average value was 0.16 mg m -2. HEYERDAHL (1970, 1971) observed the variable nature of tar within the equatorial Atlantic during his Ra expeditions. Heavy concentrations were encountered on 6 days out of 52 on his first crossing, and on 40 of 36 days of his second expedition. At other times the waters were relatively devoid of tar. PRICE (1973) encountered floating tar during almost all of a crossing between the Canaries and Antigua. Major currents, with their rapid one-way transport of surface waters, should show considerably more temporal and spatial fluctuations in tar concentration than enclosed seas or central oceanic gyres. In a current system, the amount of tar found along the current would reflect the changes in input rates of new tar. Concentrations in central oceanic gyres, however, result from accumulation over time, and are probably less variable. We beiieve that the only significant source of
472
THOMASD. SLEETER,BYRONF. MORRISand JAMESN. BUTLER
Table 3. Beach tar concentrations found at several Caribbean locations. LOCATION Barbados: Bathsheba Gibbs Bay
DATE
TAR (g/~ of shore)
18 Jan 74 18Jan
74
Puerto Rico: E1 Condado, San Juan 2 Feb 74 Luquillo Beach 2 Feb 74 Dorado Beach 3 Feb 74 Rincon Beach 3 Feb 74 Los Roques Islands
15 Feb 74
40 62 4.5 52 112 83 12 2O 25 2.2
Isles de Ayes: Isla de Sotavente
19 Feb 74
Serrana Bank: South Cay
5 Mar 74
La Cieba, Honduras
9 Mar 74
13 230 47 0 0.2 0.0
NOTES
Windward shore " Leeward shore North shore West shore Windward shore-leeward side of lagoon Leeward shore Windward shore " Leeward shore
range 50-1000 Tar not weighed, est. mean 150-200 very soft, mixed with beach litter and seaweed. Maximum at windward corner of cay. 90 127
Windward shore
Note: the tar in a l-m wide transect of the beach was collected by hand and weighed. Provided the transect extended from the water line to above the high-water mark, its length and the state of the tide had little influence on the amount of tar collected. See BtrrLER, MORRISand Sins (1973) for details. pelagic tar is in the routine operations (deballasting, tank and bilge cleaning) of oil tankers involved in crude oil transport. Temporal changes in the input of tar along the equatorial West African sector of this shipping lane would likely be reflected in the changes in the tar concentrations within the equatorial current system. The apparently fresh nature of all the tar lumps collected in the equatorial region indicates a recent origin, supporting the hypothesis that the West African shipping lanes are the source. This is also evidenced in the higher tar concentrations of the westward-flowing Equatorial Current (e.g. Stas. 8 to 13) than in the eastward-flowing Equatorial Countercurrent (e.g. Stas. 14 to 19). Tar concentrations in the Caribbean Sea and Gulf o f Mexico are more in accord with reported levels. We found a slightly higher average concentration of tar in the Caribbean (1-6 mg m-9 than in the Gulf of Mexico (1.1 mg m-2), as did the M A R M A P surveys (SHERMAN, COLTON, KNAPP, DRYFOOS and KINNEAR, 1973)---0"5 and
0.16 mg m -z, respectively. JEFFREY, FRANK, POWELL, BANTZ, VOS and MAY (1973) found slightly higher concentrations of tar in the Gulf of Mexico--0.74 and 1-2 rng m -z. Since the latter group reported benzene-extractable dry residues rather than wet weights, these values should be increased by a factor of about 1.37 to convert to wet weight, giving 1-0 and 1.6 mg m -2 for their Caribbean and Gulf of Mexico averages. All these values are well within the normal variation that seems to be inherent in the sampling: approximately a factor of ten for single samples and a factor of two for averages of 20 or more samples (BUTLERand MORmS, 1974). POLIKARPOV and BENZHITSKY(1974) sampled l0 stations in the Caribbean. Omitting one station with an unusually large amount of tar (38 mg m-2), their average value (2.9 mg m -2) is also within the expected variability. During Ra L HEYERDAHL(1970) observed large quantities of tar east of Barbados, but in the later journey of Ra II he found these waters to be
Pelagic tar in the Caribbean and equatorial Atlantic, 1974
473
relatively clean (HEYERDAHL, 1971). The purpose than in regions where the residence time of of sampling the windward side of the Lesser surface material is longer. Antilles was to investigate Heyerdahl's initial observation of large mounts of tar in that area. Acknowledgements--This work was supported by the National Science Foundation International Decade of With the exception of one sample off Barbados, Ocean Exploration, Grant No. GX-32883, and by the however, we found relatively low levels of tar National Marine Fisheries Service (NOAA) MARMAP program. The authors thank JACK JoSSl for his help and on the Atlantic side of the islands. initiative in planning the cruise of the R.V. Trident and the Although the concentration of pelagic tar in captains and crews of the Trident (University of Rhode the Caribbean is about one tenth that of the Island) and the R.V. Westward(Sailing Education AssociaSargasso Sea, beach pollution on Caribbean tion) for their exceptional help during the cruises. Special thanks are due to JAN TUTTLEMANand PAULDESLAURIERS islands approaches the levels found on Bermuda for their assistance aboard the Westward. beaches (MORRIS and BUTLER, 1973; BUTLER, MORRIS and SASS, 1973). We attribute this to the REFERENCES fact that although the standing stock of tar in BUTLER J. N. and B. F. MORRIS (1974) Quantitative monitoring and variability of pelagic tar in the Caribbean surface waters is less, the rate of water North Atlantic. Proceedings of the Pollution movement past a point (i.e. an island) is greater. Monitoring (Petroleum) Symposium and Workshop, Per unit of time, an island shore in the Caribbean National Bureau of Standards Special Publication No. 409, pp. 75-78. will entrain tar from a considerably greater area of BUTLER J. N., B. F. MORRIS and J. SASS(I 973) Pelagic sea surface, and beach loadings will approach tar from Bermuda and the Sargasso Sea. Special those of more heavily polluted but more sluggish Publication No. 10, Bermuda Biological Station, 346 pp. systems. Beaches on the windward side of the E. J. and K. L. SMITH (1972) Plastics on islands consistently had higher levels of tar, while CARPENTER the Sargasso Sea surface. Science, 178, 1240-1241. leeside shores were often relatively clean. This COLTON J. F., F. D. KNAPP and B. R. BURNS (1974) Plastic particles in surface waters of the northcontrasts with Bermuda, where wind does not western Atlantic. Science, 185, 491~,97. consistently blow from one direction, and there HEYERDAHL T. (1970) Atlantic Ocean pollution is little correlation of tar accumulation with observed by Expedition 'Ra'. Biological Conservation, 2, 221-222. wind direction. T. (1971) Atlantic Ocean pollution and The tar on Caribbean beaches is often quite HEYERDAHL biota observed by the 'Ra' expeditions. Biological soft (fresh) in contrast to the hard (aged) tar Conservation, 3, 164-167. lumps commonly found in Bermuda. This may HORN M. H., J. M. TEAL and R. H. BACKUS (1970) Petroleum lumps on the surface of the sea. Science, indicate a more recent origin of the Caribbean 168, 245-246. tar, but these qualitative observations should be JEFFREY L. M., D. J. FRANK,N. POWELL,A. BANTZ, A. Vos and L. MAY (1973) Progress report on pelasupported by chemical analyses. The fresher gic, beach and bottom tars of the Gulf of Mexico appearance is also consistent with a relatively and controlled weathering experiments. Dept. of short residence time within the region. Significant Oceanography, Texas A. & M. University, 86 pp. inputs into the Caribbean region are the major LONGHURSTA. R. (1962) A review of the oceanography of the Gulf of Guinea. Bulletin IFAN, series A, tanker routes from Venezuela to North America, Vol. 24, no. 3. tar from the eastern Atlantic via the Equatorial McGowAN W. E., W. A. SANER and G. L. HUEFORD 0974) Tar ball sampling in the Western North Current, and possibly from natural seeps in the Atlantic. Marine Pollution Monitoring (Petroleum) local region. Again, these hypotheses should be Symposium and Workshop, National Bureau of tested by detailed chemical analyses of the floating Standards, Special Publication No. 409, pp. 83-84. See also U.S. Coastguard Report C G R & D 24/74, tar and correlation with known crude oil sources. 30 pp. The ultimate fate of tar in the Caribbean Sea MORmS B. F. and J. N. BUTLER (1973) Petroleum is probably on its shorelines, or it may eventually residues in the Sargasso Sea and on Bermuda be transported out of the region and into the Beaches. Proceedings (~f the Joint Conference on Prevention and Control of Oil Spills, American Sargasso Sea. Disintegration and biodegradation Petroleum Institute, pp. 521-529. will also play their part, but will be less important PERLROTH I. (1966) The distribution of water type
474
THOMAS D. SLEETER, BYRON F. MORRIS and JAMES N. BUTLER
structure in the first 300 feet of the equatorial SANER W. A. and M. CURTIS(1974) Tar bali loadings on Golden Beach, Florida. Pollution Monitoring Atlantic. Proceedings of the Symposium on the (Petroleum) Symposium and Workshop, National Oceanography and Fisheries Resources of the Bureau of Standards, Special Publication No. 409, Tropical Atlantic, UNESCO, pp. 185-191. POUKAm'OV G. G. and A. G. BENZrnTSKV (1974) pp. 79-81. Naphthic aggregates--biotope of neustonic SHERMANK., J. B. COLTON,F. D. KNAPP, R. DRYFOOS and B. S. KINNEAR (1973) Oil and Plastics Conperiphyta (in Russian). Visnek Akademii Nauk tamination and Fish Larvae in Surface Waters of Ukraninskoi RSR, Kiev, 4, 89-92. the Northwest Atlantic. Unpublished report of the POLIKARPOV G. G., N. YEGOROV, V. N. IVANOV, National Marine Fisheries Service, M A R M A P A. V. TOKAREVAand I. A. FELEPPOV (1971) Oil Field Office, Narrangansett, R.I. areas as an ecological niche (in Russian). Priroda No. 11. (Pollution Abstracts translation No. 72- SLEETERT. D., B. F. MORRISand J. N. BUTLER(1974) Quantitative sampling of pelagic tar in the North 5TC-0451 .) Atlantic Ocean: 1973. Deep-Sea Research, 21, PRICE A. R. G. (1973) A further look at pollution in the Atlantic Ocean. Biological Conservation, 35(4). 773-775.