Radioactivity in the Marine Environment (1971)

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Chapter Three OCEANIC DISTRIBUTIONS OF RADIONUCUDES FROM NUCLEAR EXPLOSIONS H. L. Volchok, V. T. Bowen, T. R. Folsom, W. S. Broecker, E. A. Schuert, G. S. Bien Bomb-produced radionuclides are of interest to ocean sci- entists for two primary reasons: (a) as potential contami- nants of the ocean biosphere that could have a profound influence on the future development of some life forms and that might even present a hazard to man, and (b) as radioac- tive tracers for studies of water masses, sediment movement, and various biological parameters. In either case, the practi- cal usefulness of fallout isotopes is limited by the precision of our knowledge of their temporal and spatial distribution in the oceans. The magnitude of the difficulty of determining the dis- tribution of bomb-produced radionuclides in the sea is in no way reflected by the amount of money or effort expended or the number of analyses performed to date. This is per- haps best illustrated by comparison with the scope of the studies of continental fallout. In 1966, for example, in the United States alone, approximately 2,000 land deposition samples were collected for 90Sr analysis. The United King- dom processed more than 800 precipitation samples for 90Sr or l37Cs in that year, and other European countries and Australia probably analyzed a similar number; thus, up- wards of 3,500 samples of deposition on the land areas of the world were collected and analyzed in 1966. From the oceans, on the other hand, we find that since 1954, account- ing for all samples from all countries a total of less than 3,000 analyses of 90Sr or l37Cs have been made. The rate has certainly increased in the last few years; in 1966, about 650 samples of ocean water were collected for fallout study, almost 20 percent of the number on land. Thus, we might reasonably conclude that, considering the area of the ocean surface (nearly three times that of the land) and the added dimension of depth, the data available for revealing the dis- tribution of fallout radioisotopes in the oceans are indeed scant. For this report, we have chosen to concentrate primarily on the distribution of 90Sr in the sea and to make only brief mention of 14C, 3H, and other radionuclides. Based on a survey, reported in the section on the ratio of 137Cs to 90Sr in seawater (p. 71) 137Cs is assumed to have remained well mixed with the 90Sr after entering the oceans, in the more or less constant ratio generally observed in atmospheric sam- ples. For convenience, we have approximated this ratio to be 1.5 and converted all 137Cs data to 90Sr accordingly. Thus, in this report, unless specifically referred to otherwise, all seawater l37Cs values are expressed as the equivalent 90Sr. The motives for directing the major portion of this study to the distribution of the 90Sr isotope are almost entirely dictated by very practical considerations: availability of sea- water analyses and the preponderance of land data for com- parison. Since the very earliest days of nuclear fallout stud- ies, 90Sr has been regarded as the fission product of greatest potential hazard to living things because of the unique com- bination of its relatively long 28-year half life, the very ener- getic beta particle of its 90Y daughter, and its general re- semblance to calcium in metabolic processes. For these 42

Oceanic Distributions of Radionuclides from Nuclear Explosions 43 reasons, great emphasis was put on 90Sr analysis in biologi- cal as well as environmental samples, including seawater, in attempting to assay its current levels in the biosphere and to develop methods of predicting future levels. A rather large body of 90Sr data has been accumulated over the last 15 years, resulting in good documentation of the distribution of that nuclide on the earth's land surfaces. Other geophysi- cal parameters of nuclear fallout, such as its relationship to precipitation and season have also developed from these data. Consequently, for any type of synoptic analysis of de- posited nuclear debris in the ocean and for comparison with land fallout, only 90Sr offers enough information to be of use. Strontium-90 also has the advantage of probably being useful as a water tracer through the apparent constancy of stable strontium in the sea at the relatively high concentra- tion of about 8 mg per liter of water. If the fallout 90Sr enters the sea in a soluble form, it must be a valid tracer of surface water. Under the impetus of producing this chapter, many of the foremost investigators in the field were requested to contribute their data, often unpublished, for 90Sr and 137Cs in seawater. Practical considerations dictated that this chap- ter be limited to data summaries, and, therefore, in order to provide a viable reference to the original 90Sr results and supporting data, they have virtually all been reported in a single volume of the Health and Safety (HASL) Quarterly Summary Report No. 197, dated July 1, 1968 (Bowenera/., 1968b; Folsom era/., 1968; Broecker and Simpson, 1968; Shirasawa and Schuert, 1968). Early in the preparation of this report, it became appar- ent that certain areas of disagreement between some of the authors were not resolvable. The disputes concern interpre- tation of oceanic 90Sr concentration data and, in some cases, the validity of analytical results; consensus on many of the interesting aspects and implications was impossible. Hence, in order to avoid embarrassment or withdrawal of any author, or a compromising of his views, we have re- mained neutral on a number of subjects. While this may ap- pear less than satisfactory as a purely scientific endeavor, we consider the overall benefit derived from maintaining this group of authors to be of greater value. 90Sr IN SURFACE OCEAN WATER Strontium-90 has been measured in surface water samples since 1954 in the Atlantic Ocean and starting in 1957 in the Pacific Ocean. In total, almost 2,600 analyses of samples from the oceans and major seas have been performed and reported; the results are summarized in the following pages. The concentrations of 90Sr vary in the surface ocean as a function of latitude, longitude, and time in fairly complex ways, and thorough interpretation of the data is simply not possible within the scope of this volume. The two primary objectives, therefore, have been to summarize all of the available measurements in tables of practical and useful form and to provide as complete referencing as possible to the original published data and methodology. Secondarily, a few of the outstanding and noncontroversial features have been described briefly. Detailed interpretive reports on 90Sr in the Atlantic surface waters (Bowen et al., 1968b) and 137Cs in the Pacific (Folsom et al., 1968) have been in- cluded with the data compilations in the Health and Safety Laboratory Quarterly Report mentioned earlier. The vari- ation of the ratio 137Cs/90Sr in surface ocean water is dis- cussed in a later section of this chapter. Tables 1-4 list the yearly averages of all known measure- ments of 90Sr in surface ocean water, grouped by 10° bands of latitude, for the Atlantic, Pacific, and Indian oceans. In order to point up the striking concentration differences that have been observed, the Pacific Ocean was divided into east- ern and western regions (east and west of 180°) in Tables 2 and 3. Table 5 summarizes the mean annual surface water 90 Sr concentrations in the major seas. Intercomparison of Laboratory Results Until very recently, no organized intercomparison program existed for laboratories engaged in radiostrontium analyses of seawater. Hence, for most of the period covered by Tables 1 through 5, and for most of the laboratories repre- sented, we can compare the quality of the analyses only by comparing samples from similar areas and times. Recog- nizing the variability undoubtedly present over the course of a year, and within the oceanic area of a 10° latitude band, one is nevertheless virtually forced to group data in this manner, in order to observe a reasonable number of com- parisons. In Tables 6, 7, and 8, examples were selected for the purpose of intercomparing both individual laboratories and countries of origin. Tables 6, 7, and 8 are not easily interpreted without ac- cess to the original data that were averaged. The best exam- ple of a misleading case is the North Sea comparison, in Table 8. In the 22 values making up the German average of 146, several were about equivalent to the Finnish value of 392. This is, of course, partially reflected in the mean de- viation error term. On balance, the agreement between labo- ratories seems to be quite acceptable in most cases, although a few, such as the North Atlantic Polish data and eastern Pacific equatorial data of 1961, may be exceptions. Since 1966, the Health and Safety Laboratory (HASL) has sponsored a 90Sr analysis laboratory intercomparison program. The program consists of providing any interested

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46 Radioactivity in the Marine Environment TABLE 2 Mean Annual 90Sr Concentrations" in Western Pacific Surface Water by 10° Bands of Latitude Latitude 1957 1958 1959 1960 1961 Band Ref.6 Conc.c Ref.6 Conc.c Ref.6 Conc.c Ref.6 Conc.c Ref.6 Conc.c 60°-70°N 1 369±40 (7) 1 21±1 (2) - - 50°-60°N - - - - — - - - 40°-50°N - - - - 1 266 (1) - 3 36±6 (1) 30°-40°N - - - - 1,2 366±163(3) - 3,5 37±7 (13) 20°-30°N 1 688 (1) 2 222 (1) - 3,5 62±26(9) 10°-20°N 1,2 121±57(2) 2 102 (1) - 3,4,5 35±18(14) 0°-10°N 1 355 (1) — 3 16 (1) 5 60±23(5) 0°-10°S - - - - — 3 19±7(5) 5 44±18(2) 10°-20°S - - - - 3 17±6(3) 4,5 16±1 (2) 20°-30°S - - - - - - - 30°-40°S - - - - — - - — 40°-50°S - - - - — 3 7±3 (4) 50°-60°S - - - - — 3 3 (1) 60°-70°S - - - - - - - - - Total No. of Analyses 7 4 8 9 52 Latitude 1962 1963 1964 1965 1966 Band Ref.6 Conc.c Ref.6 Conc.c Ref.6 Conc.c Ref.6 Conc.c Ref.6 Conc.c 60°-70°N - - - - - 3 61±9 (13) 50°-60°N - - - - 3 65 ±8 (40) 40°-50°N 6,7 118 (1) - 3 59±12(42) 30°'40°N 3,6,7,8 70±15(7) 7 107(1) 9 48±3(3) 3 69±7 (32) 20°-30°N 3,6,7 64±15(10) - 7 83(1) 3 44 ±6 (8) 10°-20°N 3,6,7 47±8 (10) - 7 108(1) 3 28±11 (14) 0°-10°N 3,6,7 27±4 (14) - 7 45(1) 3 21±3 (10) 0°-10°S 3 12±1 (11) - - 3 16±3 (15) 10°-20°S 3 12±2 (6) - 3 16±2 (7) 20°-30°S 3 llil (2) - - 3 22±8 (11) 30°-40°S - - - - - 3 43±14(3) 40°-50°S - - - - 3 34±17(4) 50°-60°S - - - - - 3 9±0 (1) 60°-70°S - - - — — - - - Total No. of Analyses 61 4 3 200 a * ?*j on Cs measurements were converted to *"Sr by the factor 0.67. 6C11 Mivakr r t at (\ '.,,,., I.iN Mi,..,,,,, -•,l S1n,,,. ,1 , (1 ,).,!> 1' t1l !,-,i., 1,111 i 1**r,s: nprcnnn1 mmm**nirat)nn^: *.ii Mionnrt ftnl ;' 1 'M, V* :n,,l hi. (5) Popov etal. (1964b);(6) Popov et al. (1966a); (7) Tchumitchev (1966); (8) Sarahushi et al. (1962); (9) Shuert (1968, personal communica- tion). cdpm/100 liters + mean deviation; numbers in parentheses are numbers of analyses.

Oceanic Distributions of Radionuclides from Nuclear Explosions 47 TABLE 3 Mean Annual 90Sr Concentrations" in Eastern Pacific Surface Water by 10° Bands of Latitude 1959 1960 1961 1962 1963 Latitude Ref.6 Conc.c Ref.6 Conc.c Ref.6 Conc.c Ref.6 Conc.c Ref.6 Conc.c 70°-80°N 4 35 (1) - -_ - - - -- 60°-70°N 1 21±1 (2) 4 41±1 (2) 4 54±4 (2) - - 50°-60°N 3 32±1 (3) - — - - 40°-50°N 3 34±6 (14) - - - 30°-40°N 3 20±6 (7) 1,2 18±6 (24) 3,5 36±12(24) 3,9 54±6 (13) — - 20°-30°N 1,3 26±6 (12) 3,5,6 36±9 (23) 3,9 45 ±6 (6) - - 10°-20°N 3 21 ±4 (7) 3,6 34±12(13) 10,12,13 48 ±7 (7) - - 0°-10°N 3 12±3 (4) 3,6,7 32±10(13) 10, 12, 13 49±16(16) - - 0°-10°S 3 6±1 (2) 3,6 19±10(11) 11,12,13 68±15(3) 14 10±0(2) 10°-20°S 3, 5, 6 24 ±8 (8) 12,13 73 (1) 14 7 ±3 (2) 20°-30°S 3,7 11 ±5 (2) — - - - 30°^0°S 3 11±1 (2) - - - - 40°-50°S — — — — 37 8±1 (3) - — - — 50°-60°S - - 3' 12 (1) - — - - 60°-70°S 3 7 (1) - - - - Total No. of Samples 9 50 120 48 4 1964 1965 1966 1967 Latitude Ref.6 Conc.c Ref.6 Conc.c Ref.6 Conc.c Ref.6 Conc.c 70°-80°N -. _ _- _- 6(f-70°N - - - - — - - - 50°-60°N 15 99±1 (2) 15 95±11(12) 3,15 89±18(8) — — 40°-50°N 3,15 97±17(5) 15 99±11 (11) 3,15 113±21 (17) 3 117±7 (8) 30°-40°N 3,15 78±30(19) 3,15 103±17(25) 3,16 128±20(124) 3,15 126 ±14 (6) 20°-30°N 3 60±11(11) 3,15 104 ±40(110) 3 107 ±27 (24) 10°-20°N — — — — 3 47±9 (21) 3 45 ±13 (38) f/-10°N 3 29 ±4 (9) 3 24 ±3 (29) 0°-10°S 3 22±8 (12) 3 15±2 (33) 10°-20°S 3 19±3 (14) 3 16 ±2 (30) 20°-30°S — - - - 3 29±7 (10) — - 30°^0°S - - 3 21 ±4 (30) - — 40°-50°S 3 24 ±7 (4) — - 50°-60°S - - - - - - — — 60°-70°S - - - - Total No. of Samples 37 38 359 168 ~Cs measurements were converted to Sr by the factor 0.67. 6(1) Folsom etal. (1960); (2) Folsom and Mohanrao (1960); (3) Folsom (1968, personal communication); (4) Bowen and Sugihara (1964); (5) Higano etaL (1963a and b); (6) Popov etal. (1964b); (7) Rocco and Broecker (1963); (8) Mauchline (1963); (9) Saruhashi etal. (1962); (10) Higano era/. (1962); (11) Shiozaki etal. (1964); (12) Popov et aL (1966); (13) Tchumitchev (1966); (14) Broecker etal. (1966a); (I5) Shirasawa and Schuert (1968); (16) Robertson and Perkins (1966b). cdpm/100 liters ± mean deviation; numbers in parentheses are numbers of analyses.

48 Radioactivity in the Marine Environment TABLE 4 Mean Annual 90Sr Concentrations" in Indian Ocean Surface Water by 10° Bands of Latitude 1959 1960 1961 1962 Latitude Band Ref.* Conc. c Ref.* Conc.c Ref.6 Conc.c Ref.b Conc. c 20°-30°N 10°-20°N - 2 13±1 (2) 25 + 11 (11) - - l. 2 2 34±6 (2) 0°-10°N - - 1, 2 26±8 (8) 2 14 (1) - — 0°-10°S 1 24 ±6 (2) 1, 2,3 23 ±4 (11) 2 34±9 (7) 4 13±4 (3) 10°-20°S 1 33±6 (4) 1, 2,3 18±5 (19) 2 24±13(4) 4 22 (1) 20°-30°S 1 28 (1) 2, 3 18±6 (6) - 4 29±5 (3) 30°-40°S 1 15 (1) 2, 3 11 ±4 (6) 3 18±6 (2) 4 24 (1) 40°-50°S - 3 4 (1) - - - Total No. of Analyses 8 64 16 8 Cs measurements were converted to 9"sr by the factor 0.67. *(1) Baranov et al. (1964); (2) Popov et al. (1964a);(3) Kolsom (1968, personal communication); (4) Popov and Orlov (1967). cdpm/100 liters ± mean deviation; numbers in parentheses are numbers of analyses. analytical group with a series of "standard" seawater sam- ples for 90Sr assay. The samples are aliquots of a large vol- ume of seawater obtained from a deep well at the Coney Island Aquarium, to some of which known amounts of 90Sr were added. The basic Coney Island water contains about 40 dpm 90Sr per 100 liters. The sample size is about 55 li- ters. By mid-1970, some 16 different laboratories from four countries had participated, and most had completed the analyses. In general, the participating laboratories repre- sented by data in Tables 1 through 5, including the contrac- tor organizations that carried out a portion of the Bowen et al. (1968; Bowen, personal communication) analyses, are proving to be in good calibration, almost all within 10 per- cent of the expected values. This program will be continued and hopefully expanded to include additional investigators. Seasonal Variations The spring peak of 90Sr fallout deposition on land has been extensively documented and is generally attributed to sea- sonal meteorological phenomena that give rise to substantial interchanges of air between the stratosphere and tropo- sphere. On the sea, neither direct measurements of 90Sr in precipitation nor surface water samples seem to systemati- cally reflect this annual fallout maximum at most sites. In the North Atlantic, four weather observation ships, operated by the U.S. Coast Guard and the Environmental Sciences and Services Administration (ESSA), have been utilized as fallout collection platforms for the past several years (USAEC Health and Safety Laboratory, 1968). Simi- larly, in the North Pacific, the Naval Research Defense Lab- oratory (NRDL) has maintained a number of fallout obser- vation posts on radar picket and weather ships. The data from these collections (Volchok, 1967; Volchok and Kleinman, 1968; Hammond et al., 1966) do not uniformly indicate higher 90Sr deposition during spring months, and, in several instances, suggest enhanced fallout during the winter. At the North Atlantic weather stations, systematic monthly collections of surface seawater have been carried out for over 5 years (Bowen, personal communication; Bowen et al., 1968). The 90Sr concentrations from these collections, reported in Bowen et al. (1968), suggest the tendency for the maximum annual concentration to occur in the second half of each year, with a median peaking month of September. The authors conclude, based on de- tailed study of frequency and intensity of precipitation, as well as on oceanographic experience, that significant amounts of fallout are deposited in the ocean by means other than precipitation. Schuert (1968, personal communication) reports the re- sults of measurements of 90Sr concentration in surface waters from the eastern North Pacific made periodically since late 1964 and states that no significant seasonal varia- tion was observed. Bainbridge (1963b), reporting on surface water concentrations of tritium in the northern Pacific, presented a curve of average monthly specific activity for the years 1960 and 1961. Here the maximum tritium con- centration occurred in the period December-January. The evidence brought forth by the investigations briefly summarized above strongly indicates that the commonly ob- served spring peak in deposition of stratospheric 90Sr on the land masses may be largely absent or substantially displaced in time on the sea. The authors cannot agree on whether or not this observation implies a difference in the basic fallout

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50 Radioactivity in the Marine Environment TABLE 6 Atlantic Ocean 90Sr" Comparisons Year Latitude Band Country 90Sr Conc.* Reference 1959 30°-40°N United States Soviet Union 16±3 (5) 17 ±7 (2) Bowener al., 1968b Popov era/., 1962 1960 40°-50°N Poland* Soviet Union 137±53(3) 27±22(3) Deraera/., 1962 Popov et al., 1962 1961 50°-60°N United States Soviet Union 12±2 (5) 12 (1) Bowener a/., 1968b Shvedov er al., 1963b 1961 40°-50°N United States United States Soviet Union Soviet Union Poland6 15±2 (2) 18 (1) 19±4 (3) 9 (1) 65 (2) Bowener al., 1968b Rocco and Broecker, 1963 Patinera/., 1966 Shvedov et al., 1963b Deraera/., 1962 1965 60°-70°N United States West Germany Denmark 29±5 (7) 38±11(9) Bowener a/., 1968b Kautsky, 1968, private communication Aarkrog er al., 1966b Cs measurements were converted to "Sr by the factor 0.67. dpm/100 liters ' mean deviation; numbers in parentheses are numbers of analyses. cThese were sampled near shore, perhaps accounting for the high value. 41 (2) TABLE 7 Pacific Ocean 90Sra Comparisons Year Latitude Band Country 90SrConc.6 Reference Western Pacific 1961 20°-30°N United States Soviet Union 47 ±9 (4) 75 ±40 (5) Folsomef0/., 1968 Popov etal., 1964b 1961 10°-20°S Japan Soviet Union 16 (1) 15 (1) Higano et al., 1 963a and b Popov etal., 1964b Eastern Pacific 1961 0°-10°N United States United States Soviet Union 17±1 (2) 6 (1) 45±12(10) Folsomefa/., 1968 Rocco and Broecker, 1963 Popov et al., 1964 1962 20°-30°N United States Japan 43±6 (5) 53 (1) Fohometal., 1968 Saruhashi et al., 1962 1967 30°^0°N United States United States 124 ±14 (5) 134 (1) Folsom et al., 1 968 Shirasawa and Schuert, 1968 al37Cs measurements were converted to 90Sr by the factor 0.67. dpm/100 liters ± mean deviation; numbers in parentheses are numbers of analyses.

Oceanic Distributions of Radionuclides from Nuclear Explosions 51 TABLE 8 90Sr" Comparisons in the Indian Ocean and Other Seas Year Comparison Country 90Sr Conc.6 Reference 1960 Indian Ocean United States Soviet Union Soviet Union 23 ±1 (4) 29±8 (3) 19±3 (4) Folsomera/., 1968 Baranovef a/., 1964 Popov etal., 1964 1963 Tyrrhenian Sea Soviet Union Italy Italy Italy 101 (1) 76±16(2) 108 ±48 (3) 92 (1) Ankudinovera/., 1967 Cigna etal., 1963 Argiero et al., 1965 Schreiber, 1966b 1963 Mediterranean Italy Soviet Union 88±22(2) 84±17(9) Argiero et al., 1965 Ankudinovef al., 1967 1963 North Sea Finland Denmark West Germany 392 (1) 122±6 (3) 146±70(22) Paakola and Voipio, 1965b Aarkrog and Lippert, 1964a Umweltradioaktivitat und Strahlenbelastung, 1964 Cs measurements were converted to "Sr by the factor 0.67. dpm/100 liters ± mean deviation; numbers in parentheses are numbers of analyses. mechanism for deposition on land and sea. A hypothesis dealing with these data and explaining the relationships has been advanced by Bowen et al. (1968) and in summary sug- gests more frequent and less geographically confined pene- trations of the over-ocean tropopause than believed to be the case over land. 90Sr IN OCEAN WATER FROM SURFACE TO 700 METERS Atlantic Ocean Measurements of 90Sr in water samples from depths of 700 m or less in the Atlantic Ocean have been collected; they are summarized in Tables 9 and 10. In the section of this chapter on the inventory of 90Sr in the ocean (p. 62), these data were used to compute the total 90Sr deposit in the oceans. Other features of these profiles also deserve emphasis-their average shape; their trend with time, when the data are expressed as fractions of the surface water con- centration; and the correlation of shape with latitude. The average shape of the curves of 90Sr versus depth to 700 m is relatively smooth, with the maximum at the sur- face and rarely falling below 10 percent of the surface value at 700 m. Figure 1 shows the mean profiles for samples from north of 30°N, and between 30°N and 20°S. The ap- parent secondary maximum at 250 m is very probably an artifact of the averaging; very few samples are available from this depth. Compared to the shape,discussed below (p. 75), of depth profiles for 95Zr-Nb, 144Ce, or l47Pm (each be- lieved to move vertically largely as particulate material), the scarcity of subsurface concentration maxima is striking. In those cases that are well established (Rocco and Broecker, 1963; Bowen and Sugihara, 1960, 1965), the hydrographic situation has commonly indicated subsurface lateral advec- tion along isopycnal surfaces outcropping to the surface further north or south. These curves appear to be clearly in- consistent with the idea that significant amounts of fallout 90Sr sink by association with particles. In this context, es- pecially convincing is the lack of any evidence for 90Sr 100 200 300 400 500 600 700 -30°N-70°N -20°S-30°N 20 40 60 80 100 % 0F SURFACE C0NCENTRATI0N FIGURE 1 Mean profiles of relative 90Sr in surface and intermediate Atlantic Ocean water.

52 Radioactivity in the Marine Environment TABLE 9 Mean 90Sr" Concentrations in Atlantic Ocean Surface to 700-m Profiles-Northern Hemisphere 1957 1958 1959 1960 1961 Depth (m) Ref.* Conc.c Ref.6 Conc.c Ref.6 Conc.c Ref.6 Conc.c Ref.* Conc.c 60°-70°N Surface 1 18±2 (1) — 30 - - - - - - — 100 - - - - — 300 1 67% (1) — 700 1 45% (1) - 50°-60°N Surface - - - - - - - - 100 - - - - - - - - 300 - - - - - - - - 500 - - - - - - - - 700 - - - 40°-50°N Surface 9,10,11 82±61(6) — 30 10 184% (1) — 50 10 184% (1) — 60 - - - - - - - 100 - - - - - - - - 200 - - - - - - - — 250 - - - - - - - 300 10 132% (1) — 500 - - - - - — 600 - - - - - - - — 700 — - - - - — - — 30°-40°N Surface 3,15 11 ±2 (8) 15 16±5(8) 3,9,11 16±3(7) 3,11,19,20 22±7(19) 50 3, 17 55% (2) 8 114% (1) 100 16 70% (1) 16, 17 57% (6) 8,18 57% (3) 8 36% (2) 300 16,17 50% (3) 8,18 91% (2) 8 27% (2) 400 16 35% (1) - - - - - - - - 500 15 35% (1) 16,17 28% (3) 8, 18 53% (2) 8 41% (1) 600 - - — 700 16 21% (1) 17 22% (1) 8 20% (1) 8 20% (1) 20°-30°N Surface 3,11,19,20,21 16±5(17) 50 11 94% (1) 100 21 70% (3) 200 - - - - - - — 300 8,21 30% (2) 400 - - - - - - — 500 8,21 10% (3) 700 8 5% (1) 10°-20°N Surface 3,15 8±2(5) - - - 26 18±4(4) 11,19,21,25 13±3(18) 50 11 107% (2) 100 16 68% (1) 25 100% (3) 11,25 42% (2) 250 25 55% (1) - - - - - - - - 300 25 35% (1) 400 16 27% (1) - - - - - - — 500 25 50% (1) 25 15% (1) 700 25 20% (1) 25 15% (1)

Oceanic Distributions of Radionuclides from Nuclear Explosions 53 1962 1963 1964 1965 1966 1967 Ref.6 Conc.c Ref.6 Conc.c Ref.6 Conc.c Ref.6 Conc.c Ref.6 Conc.c Ref.6 Conc.c 2, 3, 4, 5 78±18(24) 3, 6, 7 35±8 (16) - - - - - 7 89% (2) - — - - 5 48% (4) 7 100% (2) - - 3 22 ±6 (34) 3 40±8 (34) 3 28 ±2 (24) 8 46% (5) - - 8 48% (1) - - — - - 8 39% (3) - - 8 50% (2) - - - - - 8 28% (4) - — 9 14% (2) - - - — - - 8 31% (2) - - 8 30% (2) 8 65% (1) - - - 3 42±10(13) 3, 12, 13 43±12(29) 3 29 ±4 (9) — — — — : : 14 115% (1) — — - - - - - - 12,14 105% (3) 8 120% (2) - - - - - - 14 85% (1) - - - — - - - — 14 91% (2) - - - - - - 8 28% (2) 12, 14 71% (2) 8 105% (2) - - - 8 13% (2) 14 60% (2) - - - - - - — - 12,14 41% (4) - - — — - - 8 17% (1) — — 14 29% (1) - - 3,21,22 41±10(19) 3,23 46±9 (14) 3, 12 39±4 (12) — - - - 8 83% (2) 3 105% (1) - - • - - - 8 71% (1) 3,12 116% (1) - - - - - 8 36% (1) 3, 12 67% (1) - - — - 8 54% (1) - - - - - - - — — - — - - 3 14% (1) — - - - - - - 12 26% (1) - - — - - 8 18% (1) — - - — — - 3,21 28 ±6 (3) 22,24 26 ±9 (6) 3,23 39 ±3 (6) 3 35 ±2 (2) — - - - - - 8 117% (1) - - 8 76% (1) 24 131% (1) 8 115% (1) — — 8 130% (1) - — - 24 90% (1) - - - - - - - 8 44% (1) 24 41% (1) 8 74% (2) 8 74% (1) - - — - 24 33% (1) - - - - - - 8 18% (1) 24 15% (1) 8 54% (1) 8 16% (1) - - 8 11% (1) 24 4% (1) 8 36% (2) - — - — - - 3,22 27±6 (10) 3 21 ±2 (4) - - 8 42% (1) — - - - - - — - 8 57% (4) - - - - - - - 8 25% (4) - - - - - - - — 8 14% (4) - — 8 5% (1) - - — — 8 13% (4) — — — — — — — - continued overleaf

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Oceanic Distributions of Radlonuclides from Nuclear Explosions 61 TABLE 12 90Sra Concentration Profiles in the Western Pacific Ocean, 0-700 m 1961 1963 1964 1965 1966 Depth (m)6 Ref.c Conc.d Ref.c Conc.d Ref.c Conc.d Ref.c Conc.d Ref.c Conc.d 30°-40°N 0 3,7 37±7 (13) - 11 48±5(3) 4 69±7(32) 30 11 106% (1) - - 50 - - - - - - 13 92% (1) 70 11 94% (1) — - 80 - - - - - 13 103% (1) 100 - - - - - - 13 129% (1) 150 11 85% (1) 13 107% (2) 200 - - - - - 13 135% (6) 250 - - - - - 13 102% (5) 300 11 80% (1) 13 107% (5) 350 - - - - - - 13 82% (4) 400 - - - - - - 13 79% (4) 450 - - - - - 13 76% (1) 500 15 95% (l)e 11 48% (1) 13 77% (2) 600 - - - - - - 13 68% (2) 700 - - - - - - 13 41% (2) 20°-30°N 0 12 83 (1) - - 100 12 117% (1) - - 10°-20°N 0 4,5,7 35±18(14) - - 12 108 (1) - - 100 12 58% (1) - - 200 6,7,9 49% (1) - - - - - 350 6,7,9 57% (1) - - - - - - - - 500 6,7,9 29% (1) — — — — — - - - 0°-10°N 0 7 60±23 (5) 12 127±0(1/ 12 47±5(6/ - - 100 12 57% (I)/• 12 87% (1) - - 150 12 121% (2) - - 200 6,7,9 32% (1) - - - - - — 12 36% (2/ - - 250 - - 500 6,7,9 45% (1) - - - - - - - - o°-1o°s 0 7 44 + 18 (2) - - - - - - - 200 6,7,9 75% (1) — — — — — — — — "137Cs values converted to 90Sr by the factor 1.5. Depths are rounded off to nearest 10 m for 0-100 m and nearest 50 m for deeper samples. ' (I) Folsom and Mohanrao (1960); (2) Bowen and Sugihara (1964); (3) Folsom era/. (1968); (5) Higanoera/. (1963a); (6) Popov et al. (1963a); (7) Popov etal. (1964b); (8) Rocco and Broecker (1963); (9) Popov et al. (1966a); (10) Broecker et al. (1966a);(ll) Shirasawa and Schuert (1968); (12) Tchumitchev (1966); (13) Folsom (1968); (14) Robertson and Perkins(1966); (15)Miyake etal. (1964); (16) Saruhashi etal. (1962); (17) Higano era/. (1962); (18) Popov etal. (1966a). Surface values are dpm/100 liters ± mean deviation; subsurface values are percent of surface values; parentheses indicate number of analyses. ^Coastal sample. •'Samples obtained from 180°00' long.

62 Radioactivity in the Marine Environment 90Sr IN DEEP OCEAN WATER As briefly outlined and extensively referenced in earlier sections, the observations of 90Sr in the surface and inter- mediate depths of the oceans have been usefully applied to oceanography, meteorology, and related fields. The 90Sr data from deep ocean water, however, while less abundant because of the expense and difficulty in obtaining good samples, have become a source of considerable debate in the scientific literature. The core of the dispute lies in the find- ings (Bowen and Sugihara, 1958, 1960, 1965; Bowen etal., 1966;Miyakeefa/., 1961b, 1962a) of low but measurable concentrations of 90Sr at depths of greater than 1,000 m in virtually all parts sampled of both major oceans. These data TABLE 13 Mean 90Sr Concentrations in Atlantic Ocean and Caribbean Sea Deep Water 1957 1958 1959 1960 1961 Depth (m) Ref.a Conc.6 Ref." Conc.6 Ref.a Conc.6 Ref.a Conc.* Ref.a Conc." 60°-70°N 1,000 2,000 1 10±1(1) 50°-60°N 1,000 2,000 3,000 ------- 40°-50°N 1,000 2,000 3,000 ------- 4,000 5,000 30°-40°N 1,000 1 1 ±1 (1) 2,000 1,3 2 ±0.9(4) 1 3.5±0.3(1) 1 0.9 ±0.1 (3) 1 6.6±0.6(1) 1 1.5±0.5(2) 11 ±0.5 (2) 3,000 4,000 1 3.8±0.4(1) 1 4.1 ±0.6(1) 1 2.6 ±0.3(1) 20°-30°N 1,000 2,000 3,000 4,000 5,000 1 3 ±1 (1) 1 2 ±1 (1) 5 1.4±0.3(1)

Oceanic Distributions of Radionuclides from Nuclear Explosions 63 are in direct conflict with conclusions concerning the rates of vertical mixing based on 14C measurements (Broecker et al., 1960; Bien era/., 1963) and also with other investiga- tors' deep water 90Sr and 137Cs analyses (Rocco and Broecker, 1963; Broecker et al., 1966a). All the available deep water analyses of 90Sr are summarized in Tables 13 (Atlantic Ocean and Caribbean Sea) and 14 (Pacific Ocean). A consensus was impossible among the authors of this section, regarding the subject of 90Sr or 137Cs in the deep ocean. Hence, to obtain the most current views of the con- cerned scientist, each was invited to submit an essay of ap- proximately 500 words to be published unabridged in this volume. The three submitted papers, plus tabulations of deep water profiles in both the Atlantic and Pacific oceans follow. 1962 1963 1964 1965 1966 1967 Ref.a Conc.* Ref.a Conc.6 Ref.a Conc.6 Ref.a Conc.6 Ref.a Conc.6 Ref.a Conc.6 ----- ----- -- 1 8 ±3 (4) 1 3 ±1 (3) — - - - — — - - 1 1.5 ±0.5 (3) 1 1.5±0.5(1) — — - - 1 2 ±1 (1) — - - - — — - - - - - - 1 1.5 ±0.6(1) - - - - 1 4 ±1 (1) - 1 <1 (1) — - - - 1 4.5 ±2.5 (2) 2 3.1±0.3 - - - - 1 3 ±3 (3) 2 4.5±1.1 (4) - - - - - - 1 3 ±2 (2) 2 2.7 ±0.8 (2) - — - - - - — - - - 2 1.8 ±0.3 (2) — — - - - - 1 1 ±0.4 (4) 2 2.9±0.1 (2) - - - - - - 1 2.3±0.4(1) - - - - - - - — - - - 2 3.4±1.1 (4) - - — — - — 1 4 ±1 (1) 2 3.8±2.0(4) — - 4 4.2±1.7 (2) - - - - 1 1 ±0.3(1) - - - - - - - - 1 6 ±2 (1) 4 2.8±1.7(2) - - - - - - 1 1 ±1 (1) — - - - - - - - - - - - 4 2.8 ±1 (2) - - 1 1 ±2 (1) 1 2.5±3.6(1) 1,6 0.5±1 (2) 1 1 14 ±0.5(1) 0.5 ±0.3 (2) 1 1.3±0.0(1) - 1 1.5±1.4(1) 1,6 0.5±1 (2) — - - - 1 4.2±0.0 (1) - 6 0.7±1.5(1) 1 10 ±0.5(1) - - - 1,6 1.1±1.3(3) 1 <0.5 (1) 1 1.5 ±0.0(1) - - 1 1.5±2 (1) 1 0.5 ±0.2(1) — - - - 6 4 ±2 (1) — - - - 1 2.5 + 0.4(1) - - 6 1.2±0.5 (1) — - - - - - - - 6 1.4±0.6(1) — - - - 1 1.1 ±0.0(1) - - continued overleaf

64 Radioactivity in the Marine Environment TABLE 13 (Continued) 1957 1958 1959 1960 1961 Depth (m) Ref.a Conc.6 Ref.a Conc.6 Ref.a Conc.6 Ref.a Conc.6 Ref.a Conc.6 10°-20°N 1,000 - 5 0 ±0.4(1) - - - - - - 1 3 ±0.3(1) 7 1.6±0.8(1) - - 5 0.5 ±0.4(1) - - - - - - - - 1 4.5±0.4(1) 2,000 - - - - - - - - - - 7 2.8±0.3 (1) 3,000 - — 5 5 ±1 (2) 4,000 - - - 5,000 - - - 0°-10°N 1,000 7 <0.3 (2) - 7 3.5±0.3(1) . 2,000 - - - - - - 7 0.3±0.6 (2) - - - 3,000 — — — — 4,000 - - - - - - 7 <0.5 (2) - - - - 5,000 — — — — 0°-10°S 1,000 7 <0.6 (1) 7 2.5 ±0.3 (2) - 7 4.2±0.2(1) - - - - - - 7 3.2±0.2(1) 2,000 7 2.4 ±0.3 (2) - - - - 7 <0.4 (2) - - 7 3.2±0.5 (1) 3,000 — — - — 4,000 7 <0.9 (1) - — - - 7 <0.6 (1) - - - - 5,000 — — - — 20°-30°S ' 1,000 7 1.5 ±0.6(1) - - - 2,000 - - - - - 7 <1 (1) - - - 3,000 7 <1.6 (1) — — — — 30°^0°S 1,000 - 5 2.6±1 (1) 2,000 - - - 40°-50°S 1,000 - 5 15 ±1 (1) - - - 5 2.2±0.5 (1) 2,000 — — — — "(1) Bowen et al. (1968); (2) Kautsky (1968); (3) Bowen and Sugihara (1963); (4) Aarkrog (1968); (5) Rocco and Broecker (1963); (6) Broecker era/. (1966a); (7) Bowen and Sugihara (1965); (8) Gedeonov et aL (1967); (9) Ankudinov et al. (1967).

Oceanic Distributions of Radionuclides from Nuclear Explosions 65 1962 1963 1964 1965 1966 1967 Ref.a Conc.6 Ref.a Conc.6 Ref.a Conc.6 Ref.a Conc.6 Ref.a Conc.6 Ref.a Conc.6 - 1 3.5±0.5(2) 1 0.8± 0.4(1) - 1 2 ±0.6(2) 1 1.5 ±0.2(1) - 1 5 ±1 (2) 1 5 ±0.3(1) 1 0.5±0.2(1) — - — 1 <0.7 (1) - - 1 1.5±0.5 (1) 1 0.4±0.3 (1) — — 1 2 ±2 (1) - - 1 0.6 + 0.5 (1) - 1 3.5±3c (6) 8 10 ±7 (2) 1 0.3±0.4(2) — - 1 5 ±3 (1) - - - - - - 1 4 ±2 (2) — - 1 1 ±1 (1) 1 0 ±0.4(1) - - 1 3 ±4 (1) - - - - - - - - - - - 1 1.1 ±0.4(1) — — 1 7 ±1 (1) 1 1 ±4 (3)c 8 5.5±0.5(4) 1 0.6±0.4 (1) - - 1 0.5 ±1 (1) - - 1 1 ±0.5(1) 8 4 ±1 (3) 1 0.9±0.7(1) - - 1 2 ±3 (1) - 1 5 ±2 (1) 1 0 ±0.6(1) - 1 0 ±1 (1) 10 ±0.6(1) - - 9 5 (1) ----- ----- -- ----- ----- -- "Values are dpm/100 liters ± mean deviation or reported error if only one analysis; numbers in parentheses are number of analyses. ' I ).*t.* omitted from average, 2 values in 0°-10°N, 1 value in 0°-10°S. ,

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68 Radioactivity in the Marine Environment Evaluation of Deep Water Data Wallace S. Broecker If, as reported by Bowen and Sugihara (1960) and Miyake etal. (1962a), a significant fraction of the 90Sr and 137Cs added to the oceans by fallout of nuclear test debris have reached depths greater than 1,000 m in the ocean, then both the generally accepted rates of vertical mixing and the in- ventories of fallout production must be seriously in error. As I consider both of these estimates to rest on firm self- consistent evidence, I cannot accept the validity of any deep-water results that require this conclusion. The follow- ing paragraphs are a defense of this position. The most difficult aspect of any measurements involving trace amounts of any radioactivity is the estimation of the blank. Errors due to other sources, such as chemical yield and counter efficiency, are relatively easy to pin down. The fact that the surface-water data from various laboratories is reasonably consistent rules out the possibility that disagree- ment on the analytical results for deep waters stems from any analytical error other than the blank. I feel that the in- vestigations that yielded the most anomalous results (Bowen and Sugihara, 1960; Miyake et al., 1962) did not adequately demonstrate that the deep-water results were not solely the result of contamination. Such obvious checks as running 90Sr-free water, analyzing duplicates, and reanalyzing pro- cessed seawater were not reported. Indeed, in the case of the Woods Hole group who initially claimed to have no mea- surable blank, it was subsequently found that one of the reagents used in their analyses indeed contained enough 90Sr to give a few dpm/100 liters. Another reason for doubting the deep-water data is its lack of internal consistency. If 90Sr is being rapidly carried to the deep sea, then the deep-water values should rise roughly in accord with the total amount of fallout added to the oceans. In 1960, Bowen and Sugihara reported finding several dpm/100 liters in samples collected in 1958 over a wide range of depth in the deep equatorial Atlantic. Their values reported here for samples collected in 1965 and 1966 from the same latitude bands average less than 1 dpm/100 liters. Other investigators have obtained similar low deep- water results. It is easier for me to believe that this marks a reduction in blank rather than a severalfold decrease in the deep-water 90Sr inventory. Although the significance of the fraction of a dpm/100 liter values found in 1965 and 1966 can still be disputed, they are not nearly as difficult to live with as the earlier data. The roughly threefold increase in the surface values reduce by an order of magnitude the in- equity between the mixing rates required to explain the fall- out results and those based on natural radiocarbon. The inventory problem is also reduced to more manageable proportions. In June 1965, the Lamont group took a series of samples in the area studied by Miyake and his co-workers. Instead of finding tens of dpm of 90Sr and 137Cs, we found almost no measurable activities for these isotopes. Thus, even if his analyses were valid, they reflect no more than a local anom- aly and therefore cannot be used to calculate either oceanic mixing rates or fallout inventories. I think it is safe to say that any finite amounts of 90Sr and 137Cs found prior to 1965 on samples from below 1,500 m are almost certainly due to undetected blanks. In fact, for this period, I feel that the best estimate of an in- vestigator's blank is his results on deep-water samples. If they are reasonably consistent, they serve as a fair correc- tion for the near-surface-water results. If they show a large spread, the validity of even the surface values for that in- vestigator are open to serious question. Penetration of Fallout Strontium-90 into Deep Water of the Atlantic Ocean Vaughan T. Bowen In Table 13 are collected and averaged 188 measurements of the concentration of strontium-90 in samples from 1,000 m or deeper in the Atlantic Ocean and Caribbean Sea; of the data available, four numbers only are omitted, all from Ankudinovetal. (1967), whose 1963 1,000-m samples are so high as to indicate probable sample contamination or, possibly, pretripping of the sampler. In two other instances, conflicting data points have been presented without aver- aging: in 1961, Rocco and Broecker (1963) found negligible 90Sr at 1,000 and 1,500 m in the Caribbean Sea, whereas Bowen and Sugihara (1965) found measurable amounts at these depths in the eastern Sargasso. Of the laboratories reporting these analyses, most have shown that they can extract from some seawater samples strontium containing less strontium-90 than they can detect; this is true for Ankudinov et al. and Gedeonov et al., as it is for Bowen and his co-workers or for Broecker and his. In the excepted cases-Aarkrog (Denmark) and Kautsky (Ger- many)—the considerable bodies of data include enough analyses, 50 percent or less of their means for deep samples, to convince me they are not suffering seriously from "blank" problems. In spite of this, we have only one report (Broecker et al., 1966a) in which a majority (4 of 7) of the samples were below detection limits; even in this case, no 137Cs value was found to be zero! Although much has been made of them, Rocco and Broecker (1963) found only two below-detection 90Sr values, of eight 1,000-m or deeper samples. Reference to Table 1 shows that other bodies of data show smaller proportions still. Clearly, the data avail- able are consistent only with the view that most samples

Oceanic Distributions of Radionuclides from Nuclear Explosions 69 withdrawn from the deep Atlantic Ocean contain measur- able amounts of strontium-90. Since the depth of mixing during severe winter storms at high latitudes in both the North and the South Atlantic often exceeds 1,000 m, and since isotherms found much deeper than this at low latitudes reach depths from surface to only a few hundred meters, the mechanism for the ob- served penetration of 90Sr is reasonably clear. Wiist and Defant, Stommel and Arons have described, either from geostrophic analysis of oceanographic density profiles or from theoretical considerations, patterns of narrow, rapidly moving deep currents capable of transporting down-mixed 90Sr from high latitudes of either ocean to the equator in periods measurable in years or even months. It is of interest in this context that the data from 1957 show measurable 90Sr at 1,000-1,500 m in both oceans at latitudes above 10°, but none about the equator; this was the last time so considerable a mass of deep Atlantic water was shown to be unlabeled. The apparent contradiction between this data and that for the carbon-14 concentration of deep-ocean water has caused much concern, enough to induce others to suggest that 90Sr, contrary to the extensive published predictions of its behavior as a solute in seawater, may be sinking with some unknown population of particles, as Schuert has sug- gested may be the case for 137Cs. In the absence of positive evidence for this, the arguments already published appear conclusive, especially reinforced with the facts that rainfall 90Sr is collectible with high efficiency on ion-exchange col- umns, that high 90Sr has never coincided with the interme- diate depth peaks of cerium-144 or promethium-147, which appear to represent real populations of labeled sinking par- ticles, and that in the Baltic Sea, Salo and Voipio (1966, personal communication) have seen no evidence for deep penetration of 90Sr except as a consequence of obvious in- jections of new labeled seawater. This seems especially con- vincing since the depths involved are so small (about 200 m), the halocline limiting down-mixing is so excessively steep, and the only-brackish surface water provides the smallest concentrations of stable Sr as "hold-back carrier" available in any well-studied marine situation. It seems to me unavoidable to conclude that strontium- 90 has penetrated deep Atlantic and Caribbean waters and that in doing so, it must have acted as a tracer of real water movements. That this same conclusion also follows from analysis of our extensive body of surface water 90Sr values, I have demonstrated elsewhere (Bowen etal., 1968b). 90Sr and 137Cs in Deep Ocean Water Edward A. Schuert The existence of trace quantities of the global fallout radio- nuclides 90Sr and 137Cs in deep ocean water has been re- ported by a number of investigators. In most cases, the quantities observed have been at such low levels that they have challenged the analytical techniques available. Never- theless, enough positive evidence has been reported to form a consensus in favor of the existence of 90Sr and 137Cs at depths as great as 5,000 m. Recent research by the author and T. Shirasawa of the NRDL may shed light on this problem. An in situ pump- adsorber system was developed and was used off the coast of California (32°N, 130°W) to extract 137Cs from large vol- umes of seawater using the inorganic ion-exchange material KCFC. Profiles taken to 2,000 m, well into the deep water, were analyzed for both stable cesium and 137Cs. This tech- nique permitted the acquisition of uncontaminated samples from effective volumes of over 1,000 liters and further per- mitted an absolute error estimate to be placed on the results. Two profiles taken in January and June of 1967 showed positive evidence of 137Cs to 340 m. Samples taken at 380 m, 450 m, 700 m, 970 m, 1,200 m, and 1,800 m con- tained no 137Cs within the limits of detection (0 ± 0.2 dpm/ 100 liters). Water samples taken at the same time and pro- cessed in the laboratory showed trace amounts of 137Cs existing as deep as 1,000 m. The above unpublished results suggest that ionic 137Cs is not mixing across the intermediate waters into the deep domain. The question of translocation by particulate or by the biomass remains to be evaluated. However, it should be pointed out that if 137Cs or 90Sr are to be exploited as tracers of ocean water masses, only the ionic component should be measured. I feel that ionic 137Cs and 90Sr are excellent tracers for studying ocean circulation and mixing processes and that in the absence of advective processes, as in the case studied above, there has been no exchange between surface and deep waters in the time frame represented by the history of global fallout. Data reporting the existence of global fallout at depth should be reviewed from the point of view of advective and other translocation mechanisms such as particulate and bio- mass activity.

70 Radioactivity in the Marine Environment THE INVENTORY OF 90Sr IN THE OCEAN Because of the limited number of 90Sr and 137Cs measure- ments and the disagreement regarding the validity of the deep water values, any overall oceanic inventory is bound to be subject to rather large uncertainties. For this reason, we have chosen an approach that lends itself to a variety of as- sumptions regarding the distribution of fallout. The 90Sr concentration Cx, at any depthx, in the ocean can be approximated by the following equation: 0.693 X Cx=(Cs-CD)e -D. (0 where Cs and CD are, respectively, the concentrations of 90Sr at the surface and in the deep water mass. The parame- ter x1/2 (called the half mixing depth) is the depth at which the surface water excess (i.e., Cs - CD) decreases by a factor of two. Figure 3 diagrammatically represents the parameters of Eq. (1). Note that, for flexibility in computation, this method defines any parcel of water as consisting of both a "surface" and "deep" component. The surface concentra- tion, Cs -CD, decreases as described above; the deep con- centration CD remains constant throughout the depth of the sea. Signifying the mean depth of the ocean by x, and recog- nizing that x is large compared tox1/2, Eq. (1) can be inte- grated with the following result: (2) 0.693 Since CD and Cs are generally in units of dpm/100 liters and x andx1/2 are in meters, the integrated activity would come out in the unit, dpm meter/100 liters. This is readily con- vertible to the commonly used fallout unit mCi/km2 by the factor 4.5 X10~3. Taking x to be 3.8 X103 m, we then have (in units of mCi/km2) (3) Before doing any detailed calculation, it is worthwhile to get some feeling for the relative magnitude of the two terms in the integration. To do this, we will consider the ocean as a whole. Regardless of how the deep water data are inter- preted, a reasonable maximum for the oceanwide average for CD would be 3 dpm/100 liters (see Table 12). Hence, the upper limit on the inventory of the deep component is given by CDxA0 < 17X3X3.6X108 < 18X109 mCi 0CEAN SURFACE -MEAN DEPTH, 3800 METERS FIGURE 3 Diagrammatic representation of the parameters for computing oceanic ^Sr inventories. or CDxA0 ^ MCi, where Ao equals the area of the entire world ocean, 3.6X 108 km2. In estimating the surface component of the total inven- tory of 90Sr (from Table 1 and Figures 1 and 2), if we take X1/2 to be 200 m (it probably ranges from 50 m to at least 500 m) and Cs - CD to be 30 dpm/100 liters (it ranges from 7 to at least 100 dpm/100 liters) we obtain = 6.5 XI 0~3X 30X200 X 3.6 XI 08 = 14X109mCi = 14 MCi. Clearly, both terms must be considered! Complete inventories of 90Sr in the oceans have been carried out for 1961 and 1966. These years were picked be- cause substantial data are available at almost all regions and depths. It seems quite clear, based upon the information de- veloped in the earlier sections, that the surface 90Sr values, Cs, are high enough in concentration and well enough cross- checked as to be open to very little question. The half mix-

Oceanic Distributions of Radionuclides from Nuclear Explosions 71 TABLE 15 Oceanic Areas and Half Mixing Depths Area (108 km2) Latitude Atlantic Pacific Total x1/2(m) >30°N 0.23 0.41 0.64 200 0-30° N 0.30 0.61 0.91 100 0-30° S 0.26 0.72 0.98 100 >30°S 0.26 0.80 1.06 200 TABLE 16 Surface Concentrations of 90 Sr (dpm/100 liters) Weighted Atlantic Pacific Average Latitude 1961 1966 1961 1966 1961 1966 >30°N 22 37 40 95 34 74 0-30° N 14 22 39 91 31 68 0-30° S 7 18 22 23 18 22 >30°S 12 18" 8 21 9 20 "Estimated value. ing depth, jC1/2, and the average deep water concentration, CD, are somewhat in doubt; hence, to establish limits on the inventories, "reasonable" limits for these two parameters were used. For the deep water, values of 0 and 3 dpm per 100 liters were chosen. While the intermediate depth pro- files of Tables 9 and 10 and Figures 1 and 2 do not really permit definition of a systematic geographic variation, we have divided the main ocean bodies of each hemisphere into regimes north and south of 30° and assigned values for the half mixing depths of 100 m for the low-latitude regions and 200 m for the high latitudes. The areas used in the compu- tation and the assigned half mixing depths are listed in Table 15. The values of the surface water concentrations of 90Sr were obtained from the data in Tables 1, 2, and 3. These are listed in Table 16 along with the averages, weighted by the appropriate areas. The computed 90Sr inventories for 1961 and 1966 are shown in Table 17 for the two cases of deep water concen- trations mentioned. Also listed are the values calculated by extrapolating the land fallout observations, assuming no dif- ference between land and sea. It is very striking that even under the most conservative assumptions used in this calcu- lation, the results are double the land fallout per unit area. The overwhelming evidence, it must be pointed out, sug- gests that the deep ocean samples do contain small but mea- surable concentrations of 90Sr and further that the half mix- ing depth chosen for the computation is lower than most of the observational data would suggest. Hence, these consid- erations lead one to conclude that the oceanic fallout ap- pears to have been at least three, and perhaps more, times that on land, in agreement with the conclusion reached by Bowen et al. (1968b, 1969). We cannot reconcile this conclusion with the best esti- mates of the total 90Sr inventory (Volchok and Krey, 1967), which at most could accommodate about 50 percent more fallout on sea than on land. The additional 90Sr sug- gested in this computation, more than 7 MCi in 1966, seems to be much more than can be attributed to either measure- ment errors or underestimates in the total 90Sr production, and we are consequently left with no reasonable explanation for this inconsistency. THE RATIO OF 137Cs TO 90Sr IN SEAWATER Radiochemical analysis of most environmental samples studied in the investigations of nuclear fallout (stratospheric air, tropospheric air, and precipitation) yielded 137Cs/90Sr ratios generally ranging between values of about 1 and 3 (Friend etal., 1961; United Nations Scientific Committee on the Effects of Atomic Radiation, 1964, 1966; Hardy and Chu, 1967). Since both of these nuclides have inert gaseous precursors in their fission chains and generally similar non- refractory chemical characteristics, substantial fractionation from the time of their creation in the nuclear burst is con- sidered unlikely. Hence, the major part of the variation in observations of the ratio of 137Cs to 90Sr in environmental samples has been thought to reflect errors in analysis. The expected value of this ratio in global fallout, com- puted by Harley et al. (1965), based upon measured fission product yields of debris from megaton weapons and current data on half-lives and decay schemes, is 1.45. Thus, all of the fallout entering the sea is assumed to carry this ratio of I37Cs to 90Sr. Tables 18 and 19 summarize data on the ratio of 137Cs to 90Sr for both the Atlantic and Pacific oceans, subdivided by depth regions. The overall weighted average for all of these data is 1.6 ± 0.3. It seems reasonably clear that no sig- nificant trends in the ratio have been manifested, either with time or depth in the sea. All of the apparent anomalous val- ues (such as in the 1965 deep water Pacific) are readily ex- plainable, generally due to the extremely low activities and consequent greater uncertainties encountered in these samples. A limited amount of data is available for both 137Cs and 90Sr from the Black Sea. Gedeonov et al. (1966) reported a number of analyses on samples taken in mid-1965 from the surface to 500 m deep. The 137Cs/90Sr was extremely con- stant, averaging 1.7 ± 0.1. A substantial number of samples from the Baltic Sea were analyzed for these isotopes covering the period 1960 through 1967 (Kautsky, 1968 personal communication; Paakkola and Voipio, 1965a; Salo and Voipio, 1966 and

72 Radioactivity in the Marine Environment TABLE 17 Calculated Oceanic Inventories of 90Sr in 1961 and 1966 (in MCi) Measured Deep Water Calculated Calculated Concentration Surface Deep (dpm/ 100 liters) Component Component Total Land Extrapolation 1961 0 7.0 0 7.0 3.2 3 6.1 18.4 24.5 1966 0 14.3 0 14.3 7 fi 3 13.1 18.4 31.5 TABLE 18 Ratio of 137Cs to 90Sr in the Atlantic Ocean Year Reference Surface Water 1961 1.5 ±1.0 (6) Kautsky, 1968, personal communication .7±0.2(2) Rocco and Broecker, 1963 1962 .5±0 (2) Rocco and Broecker, 1963 1963 .8±0.1 (2) Kautsky, 1968, personal communication .8±0.5 (54) Ankudinov et al., 1967 .9±0.3 (2) Broecker et al., 1966a 1964 .5 ±0.2 (8) Umweltradioaktivitat und Strahlenbelastung, 1965 .7±0.3(30) Gedeonov et al., 1967 1966 .5 ±0.1 (6) Umweltradioaktivitat und Strahlenbelastung, 1966; Kautsky, 1968 Intermediate Water 1961 .6 ±0.2 (5) Rocco and Broecker, 1963 1963 .7±0.5 (5) Broecker et al., 1966a .7±0.5(21) Ankudinov et al., 1967 1964 .5±0.2(7) Gedeonov et al., 1967 1966 .6±0.1(14) Umweltradioaktivitat und Strahlenbelastung, 1966; Kautsky, 1968 Deep Water 1961 1 ).5±0 (1) Rocco and Broecker, 1963 1963 .7±0.6(5) Ankudinov et al., 1967 1964 .7±0.3(6) Gedeonov et al., 1967 1966 1.9±0.6(20) Umweltradioaktivitat und Strahlenbelastung, 1966; Kautsky, 1968 "Average value ± mean deviation; numbers in parentheses are numbers of analyses. personal communication, 1968). The ratio in the Baltic is found to be not nearly as constant as was seen for the oceans and generally is significantly lower, averaging some- what less than 1.0. Evidently, conditions in the Baltic Sea encourage the fractionation of these nuclides after deposi- tion, probably by changes in the 137Cs concentration rather than the 90Sr (Salo and Voipio, 1966). This brief discussion and the summaries of ratio data presented in the tables strongly indicate that barring the most unusual coincidence of some geochemical or biological process moving both nuclides in the sea in the same ratio of their supply, 90Sr and 137Cs (and hence their stable natu- rally occurring isotopes) must move by ocean circulation processes and are therefore valid tracers of the water movements. TRITIUM IN THE OCEANS The global inventory of bomb-produced tritium, primarily from the megaton hydrogen weapons tests of the late 1950's and early 1960's (Martell, 1963), far outweighs the amount present from natural production by cosmic interaction with air. Further, substantially all of the tritium, both natural and bomb-produced, combines to form tritiated water in

Oceanic Distributions of Radionuclides from Nuclear Explosions 73 TABLE 19 Ratio of i 37Cs to 90Sr in the Pacific Ocean Year 137Cs/90Sr" Reference Surface Water 1957 .2±0.4 (7) Miyakeetal., 1962a 1958 .2±0.3(3) Miyakeera/., 1962a 1959 .1±0.3(4) Miyakeefa/., 1962a 1961 .6±0.2(3) Rocco and Broecker, 1963 1963 .5 ±0.2 (4) Broecker et al., 1966a 1964 .5 ±0.3 (8) Shirasawa and Schuert, 1968 1965 .5±0.2(15) Shirasawa and Schuert, 1968 1966 .4 ±0.1 (2) Shirasawa and Schuert, 1968 Intermediate Water 1963 .9±0.5 (5) Broecker et al., 1966a 1964 .7±0.2(10) Shirasawa and Schuert, 1968 1965 .5 ±0.2 (26) Shirasawa and Schuert, 1968 1966 .4 ±0.1 (8) Shirasawa and Schuert, 1968 Deep Water 1958 .2±0.2 (4) Saruhashi et al., 1962 1959 .4 ±0.5 (4) Saruhashi et al., 1962 1960 .4±0 (1) Saruhashi et al., 1962 1964 .1±0.1(2) Shipman, 1966 1965 : 1.5 ±1.9 (6) Shirasawa and Schuert, 1968 "Average value ± mean deviation; numbers in parentheses are numbers of analyses. the stratosphere, and is subsequently brought down into the troposphere, where both precipitation and molecular ex- change serve to transfer the tritium into the surface ocean water. Hence, tritium could probably be called the ideal tracer for ocean water movements, and in light of the time elements involved since the major injections into the atmo- sphere and the probable concentrations in the sea from natural sources, it should be extremely useful in studies of rates and mechanisms of surface water movements. In all, the data and application of the data on tritium in ocean water is sparse. Some 350 samples of surface water from the North Pacific collected between 1959 and 1966 were analyzed for tritium (Bainbridge, 1963a, b; Dockins et al., 1967). They showed that the response of the ocean water to a pulsed input of tritium, such as the spring fallout high, is an instantaneous rise that decreases rather quickly, presumably due to distribution downward into the mixed layer. In addition, it was pointed out that since the peak surface concentration in 1963, the levels remained about constant through 1964 and 1965 and have subsequently de- creased, although the decrease has not been as abrupt as that of the tritium concentration in precipitation in the northern hemisphere. In the Atlantic Ocean, Ostlund and Rinkel (1967) studied mixing and movement of water in the equatorial current sys- tems by use of a series of profiles of tritium concentration, temperature, and salinity as a function of depth. The sam- ples were obtained in March of 1964 from an area between about 2°N and 2°S of the equator, and about 7°W to 15°W longitude. Their data strongly indicate that no measurable tritium penetrated below the thermocline (at approximately 100-200 m), and they conclude that the thermocline is an effective barrier for water. A typical tritium profile from this paper is shown in Figure 4. Additional Atlantic Ocean depth profiles for tritium have been reported on samples taken over a year later from the Atlantic, over a range of about 8°S to 52°N latitude (Munnich and Roether, 1967; Roether and Munnich, 1967). The latitude of these was from about 20°W to 30°W. Some examples of the profiles from these studies are reproduced in Figure 4. Generally, the equatorial samples, to 15°N, show a rapid decrease of tritium with depth, although measurable values seem to persist somewhat deeper than was seen in the Ostlund and Rinkel profiles. Whether this deeper penetra- tion of tritium can be attributed to the additional year be- tween the samplings, or perhaps to the particular longitudes of the profiles, is not apparent. Further north, as Figure 4 clearly illustrates, the pene- tration of tritium occurs to even greater depths; it is easily measurable at 100 m at all latitudes north of 38°N. In Table 20 are presented parallel data for tritium and 90 Sr analyzed separately on samples collected simulta- neously in July of 1967 from four stations in the North At- lantic. The tritium was analyzed by Roether and Munnich (1968, personal communication) and the 90Sr by Bowen et al. (1968, unpublished data). The two stations marked

74 Radioactivity in the Marine Environment TRITIUM C0NCENTRATI0NS 1N TRIT1UM UNITS 05 0 5 10 05 0 5 10 0 5 10 15 0 5 10 15 FIGURE 4 Tritium profiles in the Atlantic Ocean. (Profiles A, C, D, E, and F after Roether and Munnich, 1967; profile B after Ostlund and Rinkel, 1967.) 500- 1000-1 8'S 2'S VH 0 "Eastern" lay between 15°W and 30°W longitude, and the two marked "Western" lay between 35°W and 40°W. Al- though the actual 90Sr and tritium results in some cases show significant differences with respect to both surface and "mixed layer" concentrations, remarkable agreement is seen when the data are expressed as percent of surface value. The eastern stations show essentially uniform 3H to 200 m and 90Sr to 300 m, and only about 80 percent of the surface 90Sr at 300 m. Even at 500 m, the eastern stations show about 60 percent of the surface 90Sr or 3H, while the western fraction is only about 40 percent, both nuclides agreeing well. At 1,000 m, on the other hand, the eastern stations show less than 5 percent of the surface 90Sr and less than 10 percent of 3H, whereas the western pair show 20- 25 percent of the surface value, both nuclides again agreeing. The few samples in the 2,000-2,500 m range show no E-W dichotomy, the two nuclides again agreeing at 7-8 percent of the surface values. Clearly, the data show no systematic vertical discrepancy between 90Sr and 3H, as was suggested by Ostlund and TABLE 20 Tritium and 90Sr in Atlantic Ocean Profiles, July 1967,40°-50°N (percent of surface concentration) Western Eastern Depth (m) Tritium" 90Sf6 Tritium" 90Sr6 1 100 100 100 100 100 — 85.5 — 100 200 80.7 — 96 — 300 - 79 - 100 400 75.8 — - - 500 45 39 60 64 600 23.8 — 50 - 700 11 15.7 — — 800 17.3 - 18.2 — 1,000 26.6 21 7.4 3.4 1,500 9.5 — — — 2,000 — 7.6 - 8.8 2,500 - — 7.8 — "Tritium analyses from Roether and Munnich (personal communica- tion). Sr analyses from Bowen et al. (unpublished data). Rinkel (1967) for equatorial samples; Rooth (personal com- munication) has found their data consistent with the hy- pothesis that in 1963 no 3H had penetrated the 10° iso- therm about the equator. At the stations reported in Table 20, the 10° isotherm lay between 700 and 1,000 m on the eastern side, and between 500 and 600 m on the western; clearly, the data show penetration of this "barrier" in every case, but more extensively when the isotherm lies closer to the surface. The noncorrespondence of absolute concentrations of 3H and 90Sr in both surface and deep water samples is taken as evidence that these nuclides are introduced to the ocean with differing efficiencies by rain or other processes. A de- tailed examination of this relationship might be expected to be quite illuminating with respect to mechanisms of over- ocean fallout. 14C IN THE PACIFIC OCEAN The distribution of radiocarbon in the Pacific Ocean is best discussed under three headings: in the deep water, in the surface water, and in vertical profiles. The investigations of radiocarbon in deep Pacific Ocean water confirmed the theory that the only source of deep water is from the south, flowing northward, and the stron- gest movement in deep water is along the western boundary (Bien et al., 1965). Unfortunately, no 14C measurements of Pacific Ocean surface water were made prior to substantial contamination by radiocarbon from nuclear weapons tests. Broecker and Walton (1959) reported that approximately 10 percent of the bomb-produced radiocarbon had entered the ocean. This material served as a tracer of downward mixing, and Bien and Suess (1967) concluded that no penetration could be observed beyond a depth of 200 m in the Pacific Ocean. The horizontal distribution of 14C in the surface water of the Pacific Ocean is apparently very dependent upon lati- tude. In areas of known upwelling, where the water temper- ature is very obviously affected, the radiocarbon content follows the simple qualitative rule postulated by Burling and

Oceanic Distributions of Radionuclides from Nuclear Explosions 75 20 15 J 1 20 19 10 52-N 50* 45* 40* 35* LATITUDE 3O* 27*N FIGURE 5 Seasonal characteristics of 14C content in the surface water of the North Pacific Ocean, 155°W. Garner (1959), i.e., that the warmer the surface water, the higher its radiocarbon content. The colder, 14C-poor subsur- face water acts to cool and dilute the warmer 14C-rich sur- face water. The seasonal characteristics of the 14C content in the North Pacific is very well illustrated by the samples collected in a pair of traverses made in 1964 and 1966. During the summer of 1964, when the sea was calm and surface activity was at a minimum, samples were obtained along the 155° west meridian, from 27°N to 52°N. The 14C concentration reached a peak at about 35°N, the center of the so-called subtropical gyre in the North Pacific Ocean. At about 42°N, the 14C showed a minimum, indicating dilution by subsur- face water, also confirmed by temperature measurements. In midwinter of 1966, in rough seas and maximum surface activity, the same traverse was repeated. The resultant curve followed the same general trends but was measurably damped, possibly because of the effects of increased advec- tion and/or horizontal mixing in winter. In Figure 5 these results are illustrated in units of relative 14C concentration. OTHER FALLOUT RADIONUCLIDES IN OCEAN WATER In a later section of this chapter, Table 21 lists all artificial radionuclides known to have been measured in seawater, with a key to the literature references in which these have been reported. The data fall into two classes: reports of oc- currence, without enough detail of sampling either vertically or horizontally to support oceanographic or geochemical in- terpretation; and careful examinations of the vertical or horizontal distributions of a few nuclides, undertaken either by analysis of series of water samples or by the use of in situ gamma-ray spectrometers. Reports of Occurrence Some of these observations refer to radionuclides definitely not originating in fallout. There are a number of reports dealing with the Columbia River outflow, which carries cooling water radionuclides from the Hanford works into Northeast Pacific coastal water, and another series dealing with the outflow into the Irish Sea from the British fuel- reprocessing plant at Windscale. It should be noted that there are no reports of 32P, 46Sc, 51Cr, 60Co, 65 An, i iom^g; or 140ga in seawater, except from the Columbia River outflow. Of these, 60Co, 65Zn, and 110mAg are known to be disseminated in worldwide fallout, and others must be introduced to the oceans in course of the opera- tions of nuclear-powered ships as well as in marine disposal of radioactive wastes (see Chapter 1), but their concentra- tions in seawater have not reached levels detectable by the methods so far used. There is a much smaller number of reports in which the results are surprising: Nelepo (1960b), on the basis of in situ gamma spectrometry, reported both 85Kr and 155Eu. Con- sideration of their gamma spectra in relation to the relative insolubility in seawater of the former and to the quite low fission yield of the latter leads to the conclusion that each represents a misidentification of a gamma peak of 144Ce that Nelepo did not report, in spite of its known consider- able abundance, even though 155Eu is shown by its demon- stration, unequivocally, in marine sediments (Cerrai etal., 1967) to have been present in seawater. A similar case is the report (Nulman and Vasquez Barete, 1967) of 131I in coastal seawater from the eastern Pacific, Gulf of California, and Gulf of Mexico. The amounts reported are very high, a mean about 65 percent of the 90Sr in five samples for 1966, and show no systematic change with time in the months from March to October. There is no question that for brief periods following any atmospheric test explosion, 131I is a measurable constituent of fallout, and its identification in marine organisms has been made frequently; however, its presence in seawater had not been clearly demonstrated before. Another small group (54Mn and 125Sb) of radionuclides, well known from reports of their presence in aerosols and in marine sediments to have been introduced as fallout to the oceans, have only rarely been reported from the open ocean. Antimony-125 was found in 1963-1964 samples from the Gulf of Mexico (Hood et al., 1964; Slowey et al., 1965) by gamma spectrometry on material concentrated from 1,000- liter samples; Bowen and Sugihara (1958) had been unable to detect this nuclide in 55-liter samples from the open At- lantic. Slowey et al. (1965), from the fact that 125Sb con- centrations were highest in near-shore samples, suggest the seawater reflected land run-off as well as direct fallout to the ocean; very little 125Sb was found in other than "solu- ble" forms. Manganese-54 was found both in the Gulf of Mexico (Hood et al., 1964; Slowey et al., 1965) and in east-

76 Radioactivity in the Marine Environment ern Pacific coastal waters (Folsom et al., 1963); Slowey et al. found much less than the expected 54Mn in particulate forms, but they nevertheless found that this nuclide was moving downward in the water column at a rapid rate com- parable to that of 144Ce. Other radionuclides about which we have very little in- formation include 89Sr (Cigna etal., 1963),239Pu and 240Pu (Pillai era/., 1964; Bowen ef al., 1971), and 91Y (Miyake, 1963a). In the case of 91Y, Bowen and co-workers have a large number of still unpublished analyses of North Atlantic surface water samples taken early in 1962; by about June of that year, they found 91Y no longer determinable in 55-liter samples. In the case of plutonium-239, Pillai et al. (1964) found, surprisingly, no evidence for separation of this nu- clide from either 90Sr or 137Cs after reaching the sea surface. It seems likely that this was the result of their observing at a time when arrival of new fallout was so rapid as to obscure the effects of marine fractionation processes, since unpub- lished data of Pillai (Noshkin, Bowen, and Pillai, personal communication) showed that in shallow-water marine sedi- ments the relative 239Pu content was comparable to 144Ce, indicating, as discussed below, considerable separation from 90Sror137Cs. Nuclides Whose Vertical and Horizontal Distribu- tions Have Been Extensively Studied This group is seen by elimination to comprise 95Zr-95Nb, i03Ru i06Ru 141Ce) 144Ce and 147Pm of these, 147Pm has been reported by only one group (Bowen, 1961; Bowen and Sugihara, 1958, 1963, 1964, 1965; Sugihara and Bowen, 1962; Bowen et al., personal communication), although its fallout onto the sea surface in determinable amounts has been confirmed by analyses of marine biota (Cerrai et al., 1964a;Schreiber, 1966) and sediments (Cerrai etal., 1964b, 1967; Schreiber, 1966b). As seen in Table 21, the others have each been studied by a number of investigators, both in open-ocean samples and, in the cases of 95Zr-95Nb and 106 Ru, in the effluent from the Windscale works. It had been predicted by Bowen and Sugihara (1958) that lantha- nides in fallout should be largely associated with particulate matter in the oceans; the same conclusion was indicated by the studies of Greendale and Ballou (1954) and Freiling and Ballou (1962), although their data may not be applicable to "world-wide fallout" geochemistry. In the cases of 95Zr- 95Nb, 106Ru and 141Ce and 144Ce measurements by Chesselet and co-workers (Chesselet and Lalou, 1964a, b, 1965a, b; Chesselet et al., 1965) and by Hood et al. (1964) and Slowey et al. (1965) have shown this prediction to be largely correct, although the last-named authors reported unexpectedly large percentages of each to be "soluble" at some depths sampled in the Gulf of Mexico. Both 95Zr- 95Nb and 106Ru appear to be largely particulate also in Irish Sea waters contaminated by Windscale effluent (Mauchline, 1963). As might have been expected from this agreement of behavior, the vertical profiles of concentration of these four radionuclides agree in principal but not in detail. Curves are "wavy," with secondary maxima at depth and often even the maximum concentration at appreciable depth. In cases where sampling was close enough to show this detail, espe- cially profiles by Chesselet, there is a tendency for the curve to peak at a depth just shallower than the top of the ther- mocline. With the exception of this regularity, the actual depths of subsurface concentration maxima vary widely (Bowen and Sugihara, 1965; Sugihara and Bowen, 1962; Higanoera/., 1963b; Riel, 1966); although no systematic examination of this question has yet been made, enough data are available to show that it is very unlikely that these subsurface maxima coincide with depths characterized by stable high concentrations of suspended particles as de- scribed by Jerlov (1955) or by Lisitsyn (1961). It appears rather that those fallout-labeled particles that penetrate the thermocline have quite rapid vertical velocities. An important question about vertical transport referred to by Bowen and Sugihara (1965) as "populations of sinking particles" is whether these have significance for the geo- chemistry of the elements whose radionuclides are analyzed or whether they represent fallout nuclides locked into the debris of atmospheric tests (as "glassy spherules" condensed from the explosion cloud, for instance) and not equilibrating with elements in other phases of the ocean water column. Briefly, it is at least the majority opinion that little, if any, of the fallout analyzed in the oceans can be geochemically inert. We have discussed above the evidence that 90Sr and 137Cs are largely present in seawater in soluble form. Bowen and Sugihara (1963, 1965) and Sugihara and Bowen (1962) have discussed the evidence that 144Ce and 147Pm are phys- ically separated after they enter the water column. Similar separations are seen for 95Zr-95Nb versus 106Ru in the ver- tical profiles published by Chesselet and co-workers (1965), by Slowey et al. (1965), and by Riel (1966). That each of these radionuclides has been separated also from 90Sr or 137Cs is clear; this was explicitly discussed by Sugihara and Bowen (1962) and by Higano et al. (1964). Separations such as these appear possible only by solution of the fallout debris [the low pH conditions often operative in evaporat- ing rain drops (Ericsson, 1957) must not be lost sight of] and entry of the individual radionuclides into appropriate radionuclides into appropriate geochemical cycles in the oceans. This is not to say that one can be confident that the fall- out radionuclides come into isotopic equilibrium with their stable elements in seawater and so act as "good" tracers geo- chemically. In most cases, we have no evidence appropriate to considering this question—no stable element concentra-

Oceanic Distributions of Radionuclides from Nuclear Explosions 77 tion data for zirconium, ruthenium, or antimony, and really too little in such a case as manganese. The fact that fallout radionuclides enter the ocean largely by penetration of the sea surface, with its attendant organic chemical complexities still being unraveled, should surely raise suspicions in our minds. No evidence has yet appeared either in the Irish Sea or along the United States Pacific coast that uptake by or- ganisms is different when particular nuclides are introduced either as fallout or as "Windscale effluent" or "Columbia River outfall." This is encouraging, but experiments have not been planned specifically to explore this question, and often the fallout nuclides have had to be studied at great di- lution, producing large experimental uncertainties. Should later study bear out the hypothesis (Slowey era/., 1965) that a large fraction of near-shore antimony-125 represents land runoff (and, by inference, is isotopically equilibrated with land-supplied stable antimony), this situation would appear very favorable for confirming the usefulness of 125Sb as a geochemical tracer in seawater. In the case of the lanthanides (144Ce, 147Pm, and, when measured, 155Eu), recent evidence has further complicated the picture: H^gdahl et al. (1968) report that the relative abundance pattern of lanthanide elements appears to be a conservative property and to distinguish in the Atlantic such water masses as North Atlantic Deep Water, Antarctic Inter- mediate Water, and Antarctic Bottom Water from each other. Constituents of this degree of conservatism, bearing in mind that the Antarctic Intermediate Water mass is only about 700 m thick about the equator (Defant, 1961), could not have vertical velocities of the orders suggested for fall- out 144Ce or 147Pm, and they probably could not have oceanic residence times as short as those estimated by Goldberg et al. (1963). In discussion of this latter discrep- ancy, Goldberg has suggested, as had others, that the short- residence-time elements undoubtedly represent two con- stituents: one that is removed very rapidly after its introduction from river outflow by geochemical processes peculiar to the continental shelves; the other that, after reaching the pelagic environment, has a very long residence time. It is clear that this latter portion has the geochemical properties to be a conservative constituent of major water masses. It does not, however, appear that fallout lanthanides are tracing, or, by inference, equilibrating with, either postu- lated constituent. Further examination, in the case of each traceable fallout radionuclide, of the relationship between their behavior in the marine environment and that of the various forms of their related elements, should be a major task of students of fallout geochemistry in the oceans. One final point should be emphasized: Studies of shallow vertical profiles of such relatively short-lived nuclides as 95Zr-95Nb, 103Ru, 106Ru, 141Ce,and 144Ce (Chesselet et al., 1965) yielded very convincing evidence that for these fallout nuclides the deposit per unit ocean surface has con- siderably exceeded that per unit land surface at comparable latitude. Chesselet and his co-workers found a significant in- crease over land in fallout per unit area. The range of "over- ocean excess," on the Bay of Biscay or Mediterranean, was from twofold to sevenfold. Since in each case these integra- tions represent only the upper 150-300 m, they must be viewed as underestimating by whatever amounts have pene- trated to deeper levels. Considerable interest attaches to this demonstration of the same order of magnitude of over- ocean fallout excess as has been described from measure- ment of vertical profiles of 90Sr discussed earlier in this chapter (Bowen and Sugihara, 1960, 1963, 1965) or from study of the changes with time of surface ocean 90Sr con- centrations (Bowen et al., 1968a, b). NUCLIDE REFERENCE TABLE Table 21 lists all of the known publications that either re- port results or describe methods of analysis for radioiso- topes in seawater of particular interest to this chapter. In all, 26 radionuclides are represented, with more than 170 references; 90Sr and 137Cs are, naturally, the most prominent. TABLE 2 1 Seawater References to Radionuclides Analyzed in Nuclide Reference United Nations Scientific Committee on the Effects of Atomic Radiation (1966) Bainbridge(1963a, b) Begemann and Libby (1957) Dockinsefa/. (1957) Giletti(1957) Martell(1963) Munnich and Roether (1967) Ostlund and Rinkel (1967) Roether and Munnich (1967) 14C 32r United Nations Scientific Committee on the Effects of Atomic Radiation (1966) Bien and Suess ( 1967) Wienetal. (1963, 1965) Broecker (1963) Broecker et al. (1960) Broecker and Rocco (1963) Broecker and Walton (1959) Burling and Garner (1959) Munnich and Roether (1967) Rafter and Ferguson (1957) Roether and Munnich (1967, personal communication) Thommertef al (1965) Chakravarti et al. (1964)

78 Radioactivity in the Marine Environment TABLE 21 (Continued) TABLE 21 (Continued) Nuclide Reference Nuclide 46Sc Perkins el al. (1966) 51Cr Chakravarti ef al. (1964) Osterberg et al. (1965) Perkins et al. (1966) 54Mn Fohometal (1963) Hood and Slowey (1964) Slowey etal. (1965) 60Co Chakravarti et al. (1964) Perkins etal (1966) 65Zn Chakravarti et al. (1964) Perkins et al. (1966) 85Kr Nelepo(1960b) 89Sr United Nations Scientific Committee on the Effects of Atomic Radiation (1966) Cigna etal. (1964) Miyake and Sugiura (1955) 90Sr Aarkrog (1963;1968, personal communication) Aarkrog and Lippert (1964a, b, c; 1965a, b, c; 1966a, b,c;1967a,b, c) Aarkrog et al. (1963a, b, c) Agnedahlefa/. (1962) Ankudinov et al. (1967) USAEC Health and Safety Laboratory (1958, 1968) Umweltradioaktivitat und Strahlenbelastung (1962, 1964, 1965, 1966,1967a, b) Comitato Nazionale de 1'Energia Nucleare (1963, 1964, 1965,1966a,b) Rudjer Boskovic Institute (1964, 1965, 1966) United Nations Scientific Committee on the Effects of Atomic Radiation (1964, 1966) Ministry of Agriculture, Fisheries and Food (1967) Argieroefa/. (1963, 1965) Azhazha and Chulkov (1964) Baranov and Khitrov (1964) Baranovefa/. (1964) Blinovera/. (1965) Bowen(1961) Bowen and Sugihara (1957, 1958, 1960, 1963, 1964, 1965) Bowen et al (1968a, b, c) Broecker(1966) Broecker and Simpson (1968) Broecker et al. (1968a, b) Cerraiefa/. (1963a) Chakravarti et al. (1964) Cigna et al. (1963,1964) Deraefa/. (1962) Gedeonov et al. (1966, 1967) Hammond et al (1966) Higano(1959) Higanoefa/. (1962, 196 3a) Higano and Shiozaki (1960) Hishida and Yamamoto (1958) 125 95 Reference 90Sr Hiyama and Ichikawa (1957) Hollstein(1959) Kautsky (1962; 1968, personal communication) Mahmondefa/. (1961) Mauchline (1961, 1962, 1963) Mauchline and Templeton (1963, 1964) Miyake (1958a,1963a) Miyake etal. (1960; 1961a, b, c; 1962a, b; 1964) Miyake and Sugiura (1955) Nulman and Vasquez Barete (1967) Paakola and Voipio (1965a, b) Parkefa/ . (1965) Patin(1965) Patinefa/. (1966) Petersen(1962) Popov (1966) Popov etal. (1962; 1963b; 1964a, b; 1966a, b, c) Popov and Orlov (1967) Popov and Patin (1966a, b) Rocco and Broecker (1963) Salo and Voipio (1966; 1968, personal communication) Saruhashi (1963) Saruhashi et al. (1962) Schreiber (1967) Schreiber ef a/. (1962, 1964, 1965) Schreiber and Tassi-Pelati (1965) Shiozaki etal. (1965) Shvedover al. (1963a, 1964) Shvedov and Shirokov (1962) 91Y Miyake (1963b) Miyake and Sugiura (1955) Sb Bowen and Sugihara (1958) Hood and Slowey (1964) Slowey ef al (1965) Zr Ministry of Agriculture, Fisheries and Food (1967) Chakravarti et al. (1964) Chesselet ef al (1964a, b; 1965) Chesselet and Nordemanne (1962c) Cigna etal. (1963, 1964) Mauchline (1963) Mauchline and Templeton (1963) Miyake (1963a) Miyake and Sugiura (1955) Reil (1966) Reilef al (1965) Slowey etal (1965) Yamagata and Iwashima (1965) 103Ru Chakravartiera/ . (1964) Chesselet etal (1964a, b) Cigna etal. (1963,1964) Mauchline (1963) Miyake and Sugiura (1955) Slowey etal (1965) 106Ru Ministry of Agriculture, Fisheries and Food (1967) Chesselet etal. (1964a, b; 1965)

Oceanic Distributions of Radionuclides from Nuclear Explosions 79 TABLE 21 (Continued) TABLE 21 (Continued) Nuclide 106 110m 131, 137Cs 140Ba 141Ce 144Ce Reference Ru Cigna et al. (1964) Hood and Slowey (1964) Mauchline and Templeton (1963) Miyake and Sugiura (1955) Perkins et al (1966) Reiletal (1965) Slowey etal. (1965) Ag Perkins et al (1966) Nulman and Vasquez Barete (1967) Ankudinov et al. (1967) Umweltradioaktivitat und Strahlenbelastung (1962; 1964; 1965;I 966 ;1967a,b) Comitato Nazionale de 1'Energia Nucleare (1964; 1965; 1966a,b) United Nations Scientific Committee on the Effects of Atomic Radiation (1964, 1966) Ministry of Agriculture, Fisheries and Food (1967) Argieroef al (1963, 1965) Bainbridge (1963b) Baranov and Khitrov (1964) Broecker(1966) Broecker and Simpson (1968) Broecker et al. (1966a) Broecker and Rocco (1963) Chulkov and Gorbunov (1963) Cigna etal. (1963) Folsom (1968, personal communication) Folsom and Mohanrao (1960; 1962a, b) Folsom etal (I960, 1961, 1965, 1968) Folsom and Saruhashi (1963) Folsom and Sreekumaran (1966a, b) Gedeonovefa/ . (1967) Kupferman(1971) Hammond etal (1966) Higano era/. (1962, 1963) Higano and Shiozaki (1960) Kamedaer al. (1962) Kautsky (1962; 1968, personal communication) Miyake (1958a, 1963a) Miyake etal (1961a, b, c; 1962a, b; 1964) Mohanrao and Folsom (1963a, b) Nelepo (1960b) Nulman and Vasquez Barete (1967) Parkefa/ . (1965) Perkins and Robertson (1970, personal communication) Robertson and Perkins (1966b) Rocco and Broecker (1963) Perkins etal (1966) Chesselet etal. (1964a, b) Miyake and Sugiura (195 5) Slowey ef al (1965) Bo wen 1961 Bowen and Sugihara (1958, 1963, 1964, 1965) Chakravarti et al. (1964) Nuclide Reference 144Ce Chesselet etal. (1964a, b; 1965) Cigna etal. (1963) Higano et al (1962, 1963a) Hood and Slowey (1964) Kamedaera/. (1962) Mauchline (1963) Mauchline and Templeton (1963) Miyake and Sugiura (1955) Perkins etal (1966) Shiozaki et al (1964) Slowey etal (1965) Sugihara and Bowen (1962) 147Pm Bowen (1961) Bowen and Sugihara (1958, 1963) 155Eu Nelepo (1960b) 239Pu and Pillai et al. (1964) 240Pu Bowen et al. (1971) SUMMARY In this chapter we have endeavored to bring together all known measurements of fallout radionuclides in seawater, with special emphasis on 90Sr and 137Cs, and to discuss a number of important implications of these data. Addition- ally, an extensive bibliography has been compiled, covering measurements, analytical methodology, data reports, and applicable interpretive studies. By far the major emphasis in seawater analysis has been on 90Sr and 137Cs. The ratio of 137Cs to 90Sr was relatively constant regardless of depth, time, or location of sample collection, averaging about 1.5. Hence for simplicity in com- paring data, all 137Cs were converted to 90Sr by the fac- tor 0.67. This report summarizes the results of surface water analyses of 779 samples from the Atlantic Ocean, 1,181 from the Pacific Ocean, 96 from the Indian Ocean, and 543 from various seas. These results were reported by more than 20 different investigators from 8 different countries. The interlaboratory agreement on 90Sr analyses, based on samples taken in reasonably close proximity, was found to be satisfactory. The nonuniformity of observed seasonal variations of 90Sr in fallout over the oceans and also in sur- face water concentration, compared to the common spring peak on land, is not understood, and may reflect differences in the fallout mechanism. Depth profiles of 90Sr concentration, down to 700 m in the Atlantic, generally show regular decreases, with values

80 Radioactivity in the Marine Environment in this stratum rarely falling below 10 percent of the surface value, and no significant trend with time. No correlation of these profiles with inferred fallout rates to the surface can be discerned. In the Pacific, much greater geographic vari- ability is shown in the depth profiles; in the northwestern regions, the 700-m samples averaged about 35 percent of the surface concentration, while northeastern and California coastal profiles indicate much lower concentrations at depth. A consensus of opinion by the authors of this chapter could not be reached concerning interpretation of the deep water 90Sr concentration data and the total oceanic inven- tory. The conclusions drawn from these subjects have direct implications on the rate of mixing in the ocean, the age of deep water, and the global 90Sr budget. Tritium concentrations in the surface Pacific Ocean peaked in 1963 and have been decreasing since. In the east- ern equatorial Atlantic, the thermocline appears to com- pletely insulate the deeper layers from tritium penetration; however, north of about 15°, tritium was found at depths in excess of 2,000 m, with no systematic vertical discrepancy from 90Sr. Radiocarbon, studied in the northeastern Pacific Ocean, indicates no penetration below 200 m and a very strong latitude dependence in surface water. Interesting sea- sonal patterns of 14C in surface water suggest a relationship between weather and mixing. Studies of other artificial radionuclides in the sea have shown that the lanthanides, as well as zirconium and nio- bium, are largely associated with particles and exhibit gen- erally similar profiles with depth, in spite of the probability that the fallout debris is initially in solution on entering the ocean. The relationship between these nuclides and their stable isotopes in the sea is complex and, in the main not well understood. REFERENCES Aarkrog, A. 1963. In S. H. 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OECD Review, p. 15. Watari, K., T. Koyanagi, and M. Izawa. 1964. Concentration of radionuclides in sea water by ferric hydroxide type resin, p. 17. In 1963 Annual report of National Institute for Radiological Services. Watari, K., T. Koyanagi, and M. Izawa. 1965. Concentration of radionuclides from sea water by metal sulfides-Ion exchange resins, p. 16. In 1964 Annual report of National Institute for Radiological Services. Yakovleva, G. V. 1967. The effect of trade-winds air transport on the water pollution by strontium-90 and cesium-137 of the Equatorial Atlantic. Okeanologiya 7(4):617-622. Yamagata, N. 1959. Concentration of cesium-137 in the coastal waters of Japan. Nature (London) 184:1813. Yamagata, N. 1963. Gamma-ray spectrometric determination of cesium-137 in sea water by using ammonium molybdophosphate as scavenger. Nature (London) 200:157. Yamagata, N., and K. Iwashima. 1963. Monitoring of sea water for important radioisotopes released by nuclear reactors. Nature (London) 200:52. Yamagata, N., and K. Iwashima. 1965. Environmental contamination with 95Zr, 95Nb in Japan. Koshu Eiseiin Kenkyu Hokoku 14(3): 137-147. Yamagata, N., and S. Matsuda. 1959. Cesium-137 in the coastal waters of Japan. Bull. Chem. Soc. Japan 32:497. Yoshikawa, et al. 1961. Annu. Rep. Radiat. Center, Osaka Prefect. 2:20. APPENDIX Following is a listing of references to literature pertinent to this chapter which have appeared too late for inclusion in the bibliography, or which have only very recently come to our attention. These papers are not included in the Nuclide Reference Table (Table 21) in this chapter.

Oceanic Distributions of Radionuclides from Nuclear Explosions 89 We acknowledge the wonderful cooperation of many col- leagues who helped in supplying unpublished and unavail- able data, and in providing literature listings to enhance the bibliography. In particular: Dr. I. L. Karol (USSR), Dr. H. Kautsky (Germany), Dr. A. Voipio (Finland), Mr. A. Aarkrog (Denmark), and Mr. B. W. Schroeder (WHOI). Chesselet, R. 1969. Etude de la radioactivity artificielle du milieu marin par spectrometric gamma (1962-1969), p. 117. In Comm. Energie Atomique (Gif-sur-Yvette). Rep. CEA-R-3698. Doshi, G. R., and C. Sreekumaran. 1968. A simplified procedure for the estimation of 90Sr in sea-water. Curr. Sci. 37:554-555. Gilat, E., and N. Steiger-Shafrir. 1969. Radioactive contamination in marine environment and biota in the Eastern Basin of the Medi- terranean Sea. Technion 4. (Prog. Rep.) Hanya, T., A. Tadashi, and N. Kazuko. 1964. Behavior of 90Sr in Lake Haruna, Japan, p. 335-347. In Recent researches in the fields of hydrosphere, atmosphere and nuclear geochemistry. Ken Sugawara Festival Volume. Maruzen, Tokyo. Kalninya, Z. K., and G. G. Polikarpov. 1969. The concentration of 90Sr in plankton in various kinds of reservoirs. UN Document No. A/AC. 82/G/L. 1243. Lai, D., and H. E. Suess. 1968. The radioactivity of the atmosphere and hydrosphere. Annu. Rev. Nucl. Sci 18:407-434. Machta, L., K. Telegadas, and D. L. Harriss. 1970. 90Sr Fallout over Lake Michigan. J. Geophys. Res. 75:1092-1096. Noshkin, V. E. 1968. Ratios of 95Nb to 95Zr in over-ocean fallout. Nature (London) 219:1241-1243. Ostlund, H. G. 1969. Expedition Odysseus 65: 3H and radiocarbon in the Mediterranean and Black Seas. Univ. of Miami, Inst. of Marine Sci., Tech. Rep. ML69167. (Coral Gables, Fla.) Ostlund, H. G., M. O. Rinkel, and C. Rooth. 1969. Tritium in the Equatorial Atlantic current system. J. Geophys. Res. 74:4535- 4543. Polikarpov, G. G., V. I. Timoshchuk, J. A. Sokolova, and V. P. Parchevsky. 1969. 90Sr in the Danube River and the adjacent international zone of the Black Sea. UN Document No. A/AC. 82/G/L. 1243. Shirasawa, T. H. 1969. In situ oceanic 137Cs sampling technique. USNRDL-TR-69-13. (U.S. Naval Radiological Defense Labora- tory, San Francisco.) Shirasawa, T. H., and E. A. Schuert. 1968. Fallout radioactivity in the North Pacific Ocean: Data compilation of 90Sr and i 37Cs con- centrations in seawater. USNRDL-TR-68-93. (U.S. Naval Radio- logical Defense Laboratory, San Francisco.) Sokolova, I. A., V. P. Parchevsky, and N. V. Sokolova. 1968. Meth- ods and data on the study of contamination of the hydrosphere with 90Sr. Oceanology (USSR) 8(6):858-859 (Abstr.) Sreekumaran, C., S. S. Gogate, G. R. Doshi, V. N. Sastry, and R. Viswanathan. 1968. Distribution of 137Cs and 90Sr in the Ara- bian Sea and Bay of Bengal. Curr. Sci. 37:629-631. Timoshchuk, V. I. 1968. An improved water sampling system for 90Sr and other radioecological determinations. Oceanology (USSR) 8:439-441. Welander, A. D. 1969. Distribution of radionuclides in the environ- ment of Eniwetok and Bikini Atolls, Aug. 1964, p. 346-354. In Proceedings of the second symposium on radioecology. CONF- 670503. (Available from National Technical Information Service, U.S. Dep. of Commerce, Springfield, Va. 22151.) Yamagata, N. S., S. Matsuda, and K. Kodaira. 1963. Run-off of 137Cs and 90Y from rivers. Nature (London) 200:668-669.

Chapter Four PHYSICAL PROCESSES OF WATER MOVEMENT AND MIXING * D. W. Pritchard, R. O. Reid, A. Okubo, H. H. Carter INTRODUCTION Radioactive isotopes introduced into the marine environ- ment are subjected to the same physical, chemical, and bio- logical processes that affect nonradioactive isotopes in the same physical state. The additional factor influencing the distribution of an introduced radionuclide is radioactive decay. For very short-life isotopes, radioactive decay influ- ences distribution at all scales of space and time. For inter- mediate-life isotopes, decay is unimportant for space and time scales below some critical values and becomes increas- ingly important for space and time scales larger than these critical values. For long-life isotopes, decay influences the distribution in the ocean only for relatively large time and space scales. The fate of a radioactive substance introduced into the ocean depends on the physical and chemical state of the substance, the manner of introduction, and the location of introduction. This chapter considers the physical processes that advect the introduced material away from the source and those *Contribution No. 152 of the Chesapeake Bay Institute, The Johns Hopkins University. This chapter represents in part work carried out by the Johns Hopkins Unviersity under contract with the U.S. Atomic Energy Commission, and in part work carried out by Texas A&M University under contract with the Office of Naval Research. This chapter represents the joint effort of the listed authors. D. W. Pritchard served as chairman of the group. that disperse the material by nonadvective mechanisms. Motion in the ocean can be regarded as a continuous spec- trum encompassing scales ranging from that of the molecu- lar free path up to that of the ocean-wide circulation. For that part of the motion assigned to advective processes, the spatial and temporal distribution of the velocity field must be known; for that part of the motion assigned to the non- advective, or diffusive processes, only certain statistical properties are required. The division between advective and nonadvective motion depends upon how much detail, in time and space, we require in our effort to determine the distribution of the concentration of a constituent of sea- water or of an introduced material such as radioactive isotopes. The general concepts are most conveniently explained by describing the fate of radioactive materials introduced into the sea by several different methods and under several different conditions of physicochemical state. The situation most amenable to description is that in which the radioac- tive substance is introduced as a local source over a short period of time and in a chemical and physical state such that complete and immediate solution in the receiving wa- ters takes place. Further, the mass of introduced material is taken to be sufficiently small that no significant difference in density exists between the initial contaminated volume and the surrounding receiving waters. From a practical standpoint, the introduction of the contaminant will result in some initial mechanical dilution. The initial contaminated 90

Physical Processes of Water Movement and Mixing 91 volume resulting from this mechanical mixing is termed the initial cloud. The local current pattern will advect the contaminated cloud away from the point of introduction, and the small- scale turbulent motion will produce diffusion of the cloud, causing it to grow in volume and the concentrations within it to decrease. As the cloud increases in size, the scale of motion producing an advection of the cloud as a whole in- creases, as does the upper limit of the scales of motion that produce diffusion of the cloud. If our interest centers only on certain statistical properties of the spreading cloud, we may consider them with respect to scales of motion: eddies larger than the cloud produce an advection of the cloud as a whole, while eddies smaller than the cloud produce internal shearing and stirring, which together with processes produc- ing uniformity are described mathematically under the general term "turbulent diffusion." In such an approach the energy available for diffusion is considered to increase in proportion to some measure of the size of the cloud, though the relationship may not be linear. This manner of treating the problem permits us to describe the time varia- tion in the average root mean square spread of the cloud and the time-rate of decrease in peak concentration. With an adequate mathematical model, the area contained within the various isolines of concentration is also determined. However, the shapes of the cloud and of individual isolines of concentration are not described by this approach. The above discussion deals primarily with the horizontal spread of the cloud. It is tacitly assumed that the cloud is bounded vertically either by the surface and bottom, by the surface and a boundary of large vertical stability (such as the thermocline), or by an upper and lower boundary of high stability. If the vertical density structure permits significant vertical fluxes to take place, then the spread and the concen- tration distribution within the cloud will be influenced by processes of vertical advection and diffusion. Scale will be less important in regard to the vertical processes than to the horizontal processes. If we desire greater information about the moving and dispersing cloud, such as the general shape of the cloud and of the individual isolines of concentration and the probable positions of the points of maximum concentration and of the center of mass of the cloud (these may not be at the same position), then we need to look at the field of motion in greater detail. Eddies much larger than the cloud are then considered to be responsible for the advection of the cloud as a whole, and eddies much smaller than the cloud produce dispersion by turbulent diffusion. However, eddies approxi- mately the same size as the cloud significantly influence the shape of the cloud and contribute to the dispersion as well. Essentially, eddies about the same size as the cloud produce shear, or spatial variation in the velocity field. The shear in the velocity field will tend to advect one part of the cloud faster than another, producing an elongated, somewhat elliptical shape. Shears in both the horizontal and vertical planes are effective in producing this elongation, but the process is most easily envisioned by considering vertical shear. Consider the cloud as initially shaped like a vertical cylinder. The vertical shear in the horizontal current pattern will produce a tilting of the cylinder, as the upper portion is moving at a different speed than the lower portion. Large vertical-concentration gradients are therefore produced by this shearing advective motion, which, when acted on by vertical diffusion, produces an elongated cloud in the hori- zontal plane with the axis of elongation in the direction of the shear. As the patch grows in size, changes occur in the portion of the spectrum of motion that contributes to the diffusion process, the portion that produces the shear effects, and the portion that advects the cloud as a whole, with the bound- aries between these various portions of the spectrum always moving toward larger scale. Consequently, any model in- tended to describe the changing shape and concentration distribution for any considerable length of time must take into account the changes in the scales of the motion con- tributing to the various aspects of the movement and mix- ing of the contaminated cloud. If the material is introduced as a suspension of small par- ticles rather than in solution, the same processes of move- ment and mixing will still act to advect and disperse the initial cloud. However, there will also be a motion of the individual particles due to their settling velocity. A mathe- matical model of the process would therefore include an added term to account for this added vertical flux. If the material is introduced into the marine environment in a solution having significantly different density than the receiving waters, then the early fate of the radioactive ma- terial may be influenced to a considerable degree by the manner of introduction. If the initial solution is less dense than the receiving waters and the introduction is made at some depth belo\y the surface, then the cloud will ascend as a result of the buoyant forces. As the cloud ascends, it will mechanically entrain diluting water from the environment, thus providing for an initial mechanical decrease in concen- tration and also for a reduction in the difference in density between the cloud and the receiving waters. If the point of introduction is deep enough, and if a vertical gradient in density occurs in the receiving waters, then the cloud will ultimately entrain sufficient water to bring it to the density of the surrounding water and will cease to rise. At this point the physical processes discussed above begin to act on the cloud. If the cloud reaches the surface with a significant density difference remaining, the processes of further dilu- tion by turbulent mixing are somewhat inhibited. If the cloud is initially denser than the receiving waters, it will sink, entraining diluting water enroute. A sequence of events similar to that described above for the ascending cloud of lower density will then occur.

92 Radioactivity in the Marine Environment If the radioactive material is introduced as a large planar source, such as fallout on the surface of the ocean, then our concern with scale depends only on how detailed a descrip- tion we wish of the subsequent fate due to physical pro- cesses. The physical processes that are most important in determining the time history of the spatial distribution of the radioactive material introduced into the sea as a planar source at the sea surface are vertical diffusion; vertical ad- vection; and sinking at source regions for intermediate and deep water and subsequent horizontal movement of the radioactive materials within the intermediate and deep water masses. Hence, the large-scale ocean-wide circulation patterns, particularly those involving vertical motion, as distinguished from small-scale turbulent-diffusion processes, must play a major role in the long-term distribution of the introduced radioactive materials. In the early period after initiation of introduction, the vertical distribution at a given location will most likely depend primarily upon the vertical pro- cesses of turbulent diffusion and vertical advection. The length of time covered by this early period, during which the local vertical processes are of prime importance, is likely to be several decades. In the remainder of this chapter, the physical processes briefly mentioned above are described in greater detail. In addition to discussions of the general ocean-wide circula- tion, turbulent diffusion processes, and the special features of inshore and estuarine environments, one part of the chap- ter is devoted to the oceanographic implications of the ob- served distributions of natural tracers and of fallout-derived radioactive isotopes. OCEAN CHARACTERISTICS AND CIRCULATION This discussion summarizes the essential features of the cir- culation of the oceans in relation to the associated distribu- tion of properties. The density of seawater depends upon its temperature and salinity at a given pressure. In turn, through the geostrophic balance relation, the density governs in large measure the rate of change of current velocity with depth, excluding Ekman boundary layers (cf. Sverdrup et al., 1942). The distribution of properties, on the other hand, is governed by currents and turbulent mixing pro- cesses. Accordingly, one must have a knowledge of both in order to achieve a proper understanding of either. Our knowledge of the distribution of properties in the sea is at present much more complete than our knowledge of its circulation, with the possible exception of the surface currents. However, there have been particularly significant advances during the past 16 years in the development and application of methods for measuring the elusive interme- diate and deep currents (Swallow, 1955; Volkmann et al., 1956;Knauss, 1960;Metcalf et al., 1962; Richardson et al., 1963; Webster, 1963; Richardson and Schmitz, 1965; Pochapsky, 1966; Kolesnikov et al., 1966;Maloney, 1967). Direct measurements in deep water are still sparse, but those available seem to support qualitative deductions based upon theory (Stommel, 1957; Stommel and Arons, 1960a, 1960b). The latter studies, and those of Lineykin (1955) and Robinson and Stommel (1959), represent major advances in our understanding of the dynamics and thermal convec- tion of the ocean. A reasonably up-to-date and comprehensive treatment of the subject is given in general texts on physical oceanog- raphy, such as those of Defant (1961) and Neumann and Pierson (1966), as well as in more specialized texts such as that of Stommel (1965). Property Statistics A very thorough statistical treatment of the temperature and salinity of the oceans has been presented in a series of papers by Cochrane (1958), Pollak (1958), and Montgomery (1958). These workers have examined the bivariate distribu- tions of potential temperature and salinity in the Pacific, Indian, and Atlantic oceans, respectively. The potential tem- perature is the temperature that a seawater sample would have if it were brought adiabatically to the surface (atmo- spheric pressure) without change of its salinity. It differs from the in situ temperature of the sample by not more than 1.5°C (cf. Sverdrup et al., 1942, p. 64). Salinity is es- sentially the total dissolved salts (in grams) in 1 kg of sea- water (i.e., mass fraction in parts per mille). A summary of some of these property statistics is given in Table 1. The statistics for the potential specific volume of seawater are given in the table, along with those of poten- tial temperature and salinity. The potential specific volume 'is the specific volume a sample would have if brought adia- batically to atmospheric pressure. These values are presented in the form of an anomaly (expressed in centiliters per metric ton) from the specific volume of seawater at the standard conditions of 0°C, 35 per mille, and 1 atm. This standard specific volume has the value 97,264 cl/ton (Sverdrup et al., 1942). Thus, from Table 1 it is seen that the mean specific volume of the world ocean is 97,320 cl/ton (or 0.097320 cl/g). This specific volume, in turn, cor- responds to a density of 1.027538 g/ml (or a density anom- aly from 1 g/ml of 27.538 mg/ml). Table 1 indicates that 90 percent (by volume) of the water of the world ocean has potential temperatures lying in the range 0.0°C to 12.6°C, with a median value of 2.1°C and a mean value of 3.52°C (indicating a highly skewed dis- tribution). Moreover, 50 percent of the world ocean has

Physical Processes of Water Movement and Mixing 93 TABLE 1 Statistics of Potential Temperature, Salinity, and Potential Specific Volume Anomaly for the Pacific, Indian and Atlantic Oceans and for the World Ocean as a Whole" Ocean Mean 5% 25% (Lower Quartile) 50% (Median) 75% (Upper Quartile) 95% Potential temperature, °C Pacific 3.36 0.8 1.3 1.9 3.4 11.1 Indian 3.72 -0.2 1.0 1.9 4.4 12.7 Atlantic 3.73 -0.6 1.7 2.6 3.9 13.7 World 3.52 0.0 1.3 2.1 3.8 12.6 Salinity, per mille Pacific 34.62 34.27 34.57 34.65 34.70 34.79 Indian 34.76 34.44 34.66 34.73 34.79 35.19 Atlantic 34.90 34.41 34.71 34.90 34.97 35.73 World 34.72 34.33 34.61 34.69 34.79 35.10 Potential specific-volume anomaly, cl/ton Pacific 62 22 31 39 66 162 Indian 56 21 25 31 63 145 Atlantic 45 8 22 28 46 137 World 56 20 26 36 62 149 Reprinted with permission from Montgomery, 1958. potential temperatures in the narrow range of 1.3°C to 3.8°C (primarily associated with the deep water of the oceans). The total range of oceanic temperature is from about -2°C to 30°C (not indicated in the table). The 90 percent range for salinity in the world ocean is 34.33 to 35.10 per mille. Its extreme range is about 30.0 to 40.0 per mille, excluding estuaries and lagoons but including the arctic seas and the Red Sea. The statistical and physical differences between the Atlantic, Pacific, and Indian oceans are small but significant. Montgomery (1958) points out that the joint statistical dis- tribution of potential temperature and salinity in the world ocean shows a dominant mode at 1.5°C and 34.7 per mille, which he calls the "Common Water." This mode corresponds closely to the mode for the joint statistical distribution for the Pacific and Indian oceans individually. The Atlantic Ocean, on the other hand, has a dominant mode centered at a potential temperature of 2.25°C and salinity of 34.95 per mille. This is primarily associated with the North Atlantic Deep Water. A secondary mode occurs at 0°C and 34.65 per mille for the South Atlantic and is associated with the Antarctic Bottom Water. The relative volumes of the Pacific, Indian, and Atlantic oceans are, respectively, 53.0, 21.2, and 25.8 percent of the world ocean. Ninety percent of the water in the world ocean has a range in potential specific volume of only about 130 parts out of 10s. Nevertheless, such variations of specific volume are indeed important in computing currents related to the distribution of mass. The ranges of temperature (in situ) and salinity for vari- ous water classes of the oceans are given in Table 2, accord- ing to Defant (1961). The water classes referred to are delineated geographically in Figure 1, and the temperature- salinity relations for these classes are shown graphically in Figure 2. The Common Water would be represented by a point at the base of the curves in Figure 2. Spatial Distribution of Properties Typical vertical profiles of temperature and salinity are shown in Figures 3 and 4, respectively, for ten different latitudes in the Atlantic Ocean. In the Arctic and Antarctic, the water column is nearly isothermal and isohaline below about 200 m. The minimum surface temperature in these regions is controlled by the freezing point of seawater, which is about -1.8°C at normal salinities (Sverdrup et al., 1942). Surface salinities in the polar regions, particularly near the continents, vary considerably from summer to winter (being dependent upon the amount of meltwater). At mid-latitudes and in the tropical belt, the temperature distributions are characterized by a nearly isothermal, sur- face mixed layer (ranging in thickness from 10 to 200 m), a nearly isothermal abyssal region below the 1,000-m depth, with a transitional intermediate region of great stability (the thermocline). Below about 500 m, the field of temperature shows little seasonal variation.

o4 so sO ^ OO ON 5 -; ^ ^ so r^ >• >• JJ} JJJ ^ J3J J3I | 1 1 1 1 1 so '5 fO ' fO - . ' a ro ^^ oo r~* lo *o CO S5SS S on C NO 1« (^ ^ fN O *>J T o ~ o. D, ro 1 *J . . *J IO *- Tf E ^H ^H r- r- £ ???°oo (2 i i I i *- ON t** Tf ro ^H 1 Cq 0 a M 3 4 o 0) *S> H ^ ^_, (N ^ r.^ so r^ U E X jo J£J J* •* J* o 0 •M I I 1 1 1 ^ »4 *-* *_ *•• .s OO IO '^ •— * (*- l/•> u. J-j S u Bo C/3 ssssss .^ M V ' South Atlantic Central V Antarctic Intermediate \ Subantarctic Water Antarctic Circumpolar V South Atlantic Deep anc Antarctic Bottom Water C Eastern South Pacific W; Western South Pacific W Antarctic Intermediate > Subantarctic Water Pacific Deep Water and / Water Mith Atlantic ex NO v> 7 V -r s> op v> auth Pacific Oceans0 H i 1 1 1 1 o on — r 1 .'.'. -f '^ '.£ M CO — •" * ''•, -f *rj 2 * H ,s D 0 g, O •7 3 4 c/5 1^, ON fN O CT* ^ r > '^ rN so 'O -H r^ C >•1 M^ IX X? <?> » o y « X.? 2> r^. ro ro o •a [c 1 1 1 1 1 c •g [E i I i i i i u m 10 O ^^ O so £ Tf Tf 1O Tf Tf 10 u S 5 •a co £ js; ^; S ^ ^ CO o 3 O •^ ^ 00 •f **. 4-* .a C c u cs 10 r- ^f ro o B .2 « M +1 T — 2 T3 >- Q, Osososcort; sa d 000000 B £ E « » a u « « d 5 1 ~H fO Tf fO ^H sO (** 3 I o 1 3 £ •a M ^ " V Asiiriso:: 1 + + + + + o o V 'S U '3 a O cd ]S is liii1l s •« u UJ _ , < V3 « * &, rt C/J M ^ J T3 ^ -H oi fO ^ g*j sO M so 9s rt a 1 u E C 3 3 *aj o 13 c •H Q hrt m rt u ABLE 2 Ranges of Tempe ater masses of the Atlantic Oce orth Atlantic North Polar Water Subarctic Water North Atlantic Central Water North Atlantic Deep Water North Atlantic Bottom Water Mediterranean Water ater masses of the Pacific Oceai o C Subarctic Water Pacific Equatorial Water Eastern North Pacific Water Western North Pacific Water Arctic Intermediate Water Pacific Deep Water and Arctic Reprinted with permission from H fik C 0 H f Z -* fM fO Tf 1O *O > Z -H (N rO ^ >O sO a 94

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