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CHAPTER 5 THE EFFECTS OF THE ECOLOGICAL SYSTEM ON THE TRANSPORT OF ELEMENTS IN THE SEA ' BOSTWICK H. KETCHUM, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts SOME elements may be profoundly influenced by the biological cycle and their resulting dis- tribution in the sea may be quite different from the distribution of elements that are affected only by the circulation of the water. Numer- ous examples of the modification of distribution by biological activities could be given but it may suffice to review briefly the vertical distri- bution of phosphorus in the ocean. The photosynthetic fixation of carbon is lim- ited to the surface hundred meters or less of the sea by the penetration of light, and the plant nutrients, including phosphorus, are as- similated there. The surface concentration of these elements may be reduced to virtually zero. Below the photosynthetic zone, the con- centrations of these nutrients increase, reaching maximum values at depths of 200 to 1000 meters, the actual depth depending upon loca- tion and the oceanic circulation. These maxi- mum concentrations are produced by two proc- esses. The water at intermediate depths is formed by cooling at high latitudes in the ocean, where it sinks and spreads out. At the time of sinking, it contains some inorganic phosphorus and organic matter which is de- composed, liberating the plant nutrients and decreasing the oxygen content. Additions to the organic matter from the surface waters occur everywhere, increasing the nutrient maxi- mum concentration and decreasing the oxygen minimum. Below the nutrient maximum-oxygen minimum layer the concentration of phosphorus decreases again reaching values which are gen- erally constant and uniform from a depth of about 1500 meters to the bottom (Redfield, 1942). The general patterns of distribution of the elements important in plankton growth on an ocean-wide scale are thus quite different from 1 Contribution No. 871 from the Woods Hole Oceanographic Institution. the pattern of distribution of the major ele- ments. The processes which must be considered in order to evaluate biological effects on the ultimate distribution of radioisotope wastes or contaminants in the sea include (1) the assimi- lation or adsorption of the elements by the bio- logical populations, (2) the effects of gravity, (3) vertical migrations, (4) horizontal migra- tions, and (5) the effects of stationary popula- tions in flowing systems. It has been shown in another section of this report that biological populations may concen- trate by several orders of magnitude various elements and their radioisotopes. To evaluate the possible significance of this in the oceans, it is necessary to determine the quantity of living material present (the biomass) and the rate of production of the populations of the ecological system. The biomass, when combined with the known concentration factor, will indicate how much of an element in the water may be com- bined in the living organisms. The most active concentration of elements may occur during the rapid growth of populations; consequently it is also essential to know the rate of production of the various populations involved. A few data on both the biomass and the rate of production of various populations in the sea are given in Tables 1 and 2. The biomass figures indicate that concentra- tion factors of 12,500 or more would be re- quired, under static conditions, to incorporate half of an element in a cubic meter of water within the ecological system even in the high concentrations of living material found in red- tide blooms. However, the biological popula- tions are not static; those movements which are independent of the motion of the water can, by repetition, transport larger proportions of elements than is indicated by static equilibrium conditions. The productivity values in Table 2 indicate that several times the standing crop of phytoplankton is produced annually. Both 52
Chapter 5 53 Ecological Systems and Transport TABLE 1 ESTIMATES OF BIOMASS OF MARINE POPULATIONS. ALL VALUES HAVE BEEN CONVERTED TO VOLUME (WET WEIGHT) PER CUBIC METER (PARTS PER MILLION) Population Location and character Phytoplankton Maximum Atlantic Maximum Pacific Red Tide Blooms Long Island Sound Coastal Water Sargasso Sea Zooplankton Gulf of Maine Coastal Water Sargasso Sea N. African Upwelling Eastern North Pacific Eastern Tropical Pacific Peru Current Source ⢠a b c c c d e g 8 cc/m* 10 25 41 18.2 1.2 0.3 0.08 â 1.0 0.08 â 0.8 0.006 â 0.09 1.0 0.042 0.055 0.124 a. Complete utilization of maximum phosphorus concentrations; conversion P = 0.5 per cent of wet weight. b. Ketchum and Keen, 1948, 17-21, Table 1. Conversion as in a. c. Riley, Stommel and Bumpus, 1949, Table VI; conversion C = 10 per cent wet weight. d. Redfield, 1941, drained volumes, vertical tows, assumed mean depth 100 meters. e. Riley, et al., 1949, Table V, displacement weight. f. Unpublished data, W. H. O. I., surface tows at night, drained volumes. g. Unpublished data, S. I. O., oblique tows 200-300 meters to surface, wet plankton volumes. the depth of the photosysthetic zone and the production rate at various depths, are variable, thus the values for production cannot be re- duced without excess over-simplification to a volume basis which would permit direct com- parison with Table 1. However, Riley's (1941) maximum value for the standing crop of phyto- TABLE 2 ESTIMATES OF THE PRODUCTIVITY OF MARINE PHYTOPLANKTON POPULATIONS Location and gC/m*/ cc/m*/ character Source year year1 Sargasso Sea (Atlan- tic) a 18 180 Coastal Areas (Atlan- tic) a Open Ocean (Pacific) .. a Equatorial Divergence (Pacific) a Coastal Areas (Pacific) . a Oceanic Mean a Long Island Sound min b max N. Atlantic 3°-13°N. . b Oceanic Mean C a. Steemann Nielsen (1954). Carbon-14 method. This is given as gross production, but Ryther (1954) suggests that it may be net (gross minus respiration) production in nutrient poor areas. b. Riley (1941). Gross production, oxygen method. c. Riley (1944). 1 Conversion assuming one gram of carbon = 10 cc of wet plankton. 1100 11000 50 500 140 1400 200 2000 55 550 95 950 1000 10000 278 2780 340 ± 220 1200-5600 plankton in Long Island Sound, 1.82 gC/m2, showed a production of 0.187 gC/m2/day and the annual production was twenty times as great as the maximum standing crop observed at any one time. Estimates of the growth of zooplank- ton populations have given values ranging up to 5 per cent of the standing crop per day. It is a truism in ecology that the total quan- tity of living material which can be produced decreases as the trophic level of the organisms considered increases. In some ecological sys- tems the biomass reflects this progression, i.e., at any one time there will be a larger standing crop of plants than of herbivores and the stand- ing crop becomes progressively smaller as one goes through the various higher steps of the food web. In the oceans, however, this is not necessarily true. It is common to find rather high concentrations of the herbivorous zoo- plankton when phytoplankton are scarce. Large populations of herbivores will quickly decimate the plants on which they feed. A balance may be maintained as a result of the different lengths of the life cycle of the various parts of the food web. A population of phytoplankton can double in a period of time ranging from hours to days, whereas the life cycles of zooplankton are more commonly measured in terms of weeks or months and the life cycles of the higher elements of the food web, such as fish, are
54 Atomic Radiation and Oceanography and Fisheries measured in terms of seasons or years. A com- paratively small population of phytoplankton doubling rapidly can provide the energy and nutrients of an equivalent or even larger animal population which is increasing more slowly. The size of various populations and their rate of production in the English Channel has been evaluated by Harvey (1950) and his re- sults are given in Table 3. These illustrate the above conclusions, since the average biomass of animals exceed that of the plants, but the rate TABLE 3 AVERAGE QUANTITY, THROUGHOUT THE YEAR, OF PLANTS AND ANIMALS BELOW UNIT AREA OF SEA SURFACE IN THE ENGLISH CHANNELl Dry wt of organic matter Standing crop Production Organism g./m* g./m*/day Phytoplankton 4.00 0.4-0.5 Zooplankton 1.50 0.1500 Pelagic Fish 1.80 0.0016 * Bacteria 0.04 â Demersal Fish 1.25 0.0010 Bottom Fauna 17.00 0.0300» Bottom Bacteria 0.10 â 1 From Harvey (1950), depth equals 70 meters. 2 Based on estimated mortality of 30 per cent per annum. 3 Based on estimated mortality of 60 per cent per annum. of production of the plants exceeds that of the animal populations. The plankton organisms in the open sea pro- vide by far the largest quantity of living ma- terial and by even more the largest organic absorptive surface. Those radioisotopes which are adsorbed will become bound to the organ- isms, and they are as subject to the effects of gravitation and migration as if they had been assimilated and utilized. Gravity affects the organisms in a population and can thus modify the distribution of ele- ments which become incorporated in the bio- logical cycle. Ultimately only two fates await most of the plankton which grows in the sur- face layers. It may be eaten by the herbivores or it may sink out of the illuminated zone and decompose at greater depths. If the plankton is eaten by a herbivore, a proportion of the organic matter is incorporated into the herbivore body but an even larger proportion is returned to the water as excretion or faecal pellets. The excretions may be present in the water inhabited by the plankton and reused in situ. The faecal pellets settle into the deeper water where they decompose. Gravity thus imposes on elements which become incorporated in the biological system a modification of the distribution which would be produced by movements of the water alone, since they tend to accumulate at some intermediate depth in the water column, or on the bottom. One of the unsolved problems of marine biology is the definition of the proportion of organic matter which is decomposed by the time the particulate material sinks to various depths. This problem must be solved before an evalua- tion of the biological effects on the distribution of radioisotope contamination of the seas can be made. It may be worthwhile to summarize some of the present thinking on this problem. In the first place, everywhere that samples have been taken in the deep sea, living organ- isms have been found. Since we know of no mechanism other than photosynthesis at the sur- face which can provide the organic material necessary to support these populations, it is clear that some of the surface produced material must reach all depths of the ocean. It may be argued by some that the bacterial chemosyn- thetic processes are a source of fixed carbon which has not been considered, but the condi- tions in the deep sea are not suitable for the formation of organic matter by any of these processes. The presence of the nutrient maximum-oxy- gen minimum layer at intermediate depths in the sea has led to the conclusion that most of the organic matter formed at the surface must be oxidized by the time it has sunk to a depth of 1000 meters (Redfield, 1942). Analyses of organic phosphorus in the equatorial Atlantic Ocean showed considerable amounts in the waters above 1000 meters, but none at greater depths (Ketchum, Corwin, and Keen, 1955). There is no present evaluation of the quantity of organic carbon which can sink to greater depths, nor is it possible to evaluate whether this quantity would be sufficient to support the known populations of archibenthic organisms. These two extremes thus define the dilemma. Namely that some organic matter must reach the great depths, but, at the same time, most of the decomposition appears to occur above a depth of 1000 meters. The secular change of oxygen in the deep
Chapter 5 35 Ecological Systems and Transport sea which has been found by Worthington (1954) in the North Atlantic, provides one means of computing the total quantity of or- ganic matter required. Worthington observed a decrease of 0.3 milliliters of oxygen per liter in thirty years at depths between 2500 meters and the bottom. In the Atlantic Ocean this corresponds to an average thickness of 1500 meters and the total quantity of organic matter required to produce this change in oxygen is equivalent to the decomposition of 8 grams of organic carbon per square meter per year in this layer. This quantity of organic matter is nearly 15 per cent of the annual mean produc- tion according to Steemann Nielsen (1954) and from 1.4 to 7 per cent of the mean sug- gested by Riley (1944). Part of the secular change in oxygen may have been produced by eddy diffusion into the oxygen minimum layer, which would reduce the quantity of organic carbon reaching greater depths. The effects of gravity may be accentuated when the surface currents are opposed to the currents in the deeper layers. This type of circulation pattern is very common in estuaries, on continental shelves, and in those areas where offshore winds produce upwelling of the deeper waters. In all of these cases the nutrient rich deep water is carried inshore in a sub-surface drift, and brought to the surface by upwelling or vertical mixing. The nutrients are assimilated by the plankton in the surface layers and are carried offshore in the surface current. When the organisms sink, they again reach the on- shore sub-surface current where they decompose liberating more nutrients into water which is already relatively rich. Thus the elements in- volved in biological processes follow a different cycle from the circulation of the water and this cycle leads to an accumulation of elements greater than can be found in either of the source waters (Strom, 1936; Hulburt, In press). Nutrient elements are commonly concentrated by this type of mechanism in fjords. Where the deepest water is relatively stagnant and isolated from the intermediate and surface layers, con- siderable concentrations of organic derivatives can be developed. In the Norwegian fjords with a relatively shallow sill, for example, anaerobic conditions may be produced in the bottom water and the nutrients are five to ten times as concentrated as in either of the source waters (Strom, 1936). In the Black Sea the deep water is isolated from the surface by a strong density gradient and its average age has been estimated at 2500-5000 years (Sverdrup, Johnson and Fleming, 1942, p. 651). Very large accumulations of organic derivatives are found in this deep water. (Gololobov, 1949.) Opposed currents can, however, work in the opposite way and lead to a decrease in the concentration of elements involved in the bio- logical cycle. The classic example of this type of circulation is the Mediterranean, where the nutrients available for plant growth are less than half of the concentration available in the adjacent parts of the Atlantic. In the Mediter- ranean the supply comes from the surface wa- ters of the North Atlantic which are already impoverished by plant growth. Since evapora- tion exceeds precipitation in the Mediterranean the water becomes more saline, sinks and is lost as a deep outflow over the sill at Gibraltar (Thomsen, 1931). The accumulation of ele- ments in sinking organisms transfers these ele- ments from the inflowing surface water to the outflowing deep water. They are eventually lost from the Mediterranean. A similar process apparently applies to the entire North Atlantic. There is a large inflow of South Atlantic sur- face water which contains low concentrations of elements involved in the ecological cycle. The outflow from the North Atlantic required to balance the water budget occurs at depths and this water contains considerable quantities of the elements which had been returned to the water (Sverdrup et al., 1942). In summary the various peculiarities of dis- tribution which can be attributed to gravitational effects on the ecological cycle are therefore (1) the accumulation of elements at inter- mediate depths as a result of sinking and de- composition, (2) the concentration of elements in areas of opposed flow where the deep water is brought to the surface by upwelling or ver- tical mixing and (3) the impoverishment of areas where the supply of water is from the surface and the loss from greater depths. In addition to the passive gravitational effects on organisms, animal plankton forms exhibit vertical migrations. A considerable literature has developed in this field over the last ten years, but the effects of these vertical migrations on the distribution of elements has not been studied directly and must be inferred from our knowledge of the ecological system.
56 Atomic Radiation and Oceanography and Fisheries Historically, a few studies of the vertical migration of zooplankton had been made prior to the war. Great impetus was given these studies when a false bottom was repeatedly observed on echo sounding recorders (Dietz, 1948; Hersey and Moore, 1948). This has been called the scattering layer. Although there is still controversy as to which organisms are the principal scatterers in the sea, it has been established that one or more layers are com- monly found which migrate vertically over a depth of as much as 800 meters, being at or near the surface at night and at great depths at mid-day. No observations of the changes of elements involved in the biological cycle which may be associated with vertical migrations have been made. Most of our analytical techniques are too insensitive to detect the day to day changes which might be expected in biologically active elements if our present evaluation of the density of the populations and their respiration and excretion rates is correct. It is known, however, that direct assimilation of some elements is possible by invertebrate forms and vertical trans- port of radioisotopes might be expected to re- sult. Indeed, the transport of radioisotopes might prove an excellent tool for the study of vertical migrations if a source were provided at one depth within the range of the migration. Ecologically the following effects might be expected as a result of vertical migration. The zooplankton are certainly in the area of the most dense concentration of their food, the phytoplankton, when they are at the surface at night. During the hours of darkness they may therefore be expected to consume the living material in the water, and some of this, at least, would be excreted or passed as faecal pellets at depth in the day time. This process would thus augment the effects of gravity on those elements incorporated in the biological system. There is also evidence that the zooplankton can as- similate dissolved elements from sea water. If elements were assimilated at depth they might be excreted or exchanged near the surface and thus directly modify the vertical distribution in the sea. It should not be neglected that larger or- ganisms can certainly migrate vertically over greater distances than we have discussed above. Certainly whales, tuna and sharks, and pre- sumably the smaller forms upon which they feed are known to go to considerable depths in the ocean. Quantitatively, of course, these members high on the food chain are propor- tionally small compared to the plankton or- ganisms. However, their effects on vertical dis- tribution of materials may not be negligible over periods of several decades. Horizontal migrations of organisms may also result in the transport of material involved in the biological cycle and are also independent of the currents of the ocean. Here again man does not know enough to assess these quantita- tively, but their possible effects should not be ignored. The migrations of pelagic fishes may be of considerable interest in this regard. The salmon for example reach maturity in the open sea, then migrate in enormous numbers to coastal areas to breed. Such a horizontal migration could transport radioisotopes, since the salmon could accumulate materials from large volumes of the sea and, by their migration, concentrate them many thousand-fold in the rivers and estuaries. Many other fish also exhibit extensive migra- tions. Even though some of these do not enter the rivers to breed, they may enter the areas where they are available for commercial cap- ture, thus becoming some of the food supply of the nation. Unfortunately, in many of these species we do not know the complete life his- tory and most of our information concerning their occurrences and migrations is obtained only during the period of year when they are caught. The Atlantic tuna, for example, are caught in the early spring in the Caribbean and off the Bahama Banks. As spring and summer progresses they migrate northward along the coast, and maximum catches occur in New England in late summer and early fall. The winter habitat and breeding area of these large and important food fish is largely unknown, though preliminary data suggest that they prac- tically circumnavigate the North Atlantic Ocean (Mather and Day, 1954). Similarly the mack- erel catches are first concentrated in the south- ern part of the Atlantic coastline in the late spring and early summer. The large catches off New England occur in August and Septem- ber. This species breeds on the Atlantic con- tinental shelf during its summer northward migration (Sette, 1943, 1950). Additional examples of mass migrations into
Chapter 5 57 Ecological Systems and Transport the coastal regions are found in the Pacific sardine and the North Atlantic herring. In all of these cases materials assimilated at sea may be concentrated in inshore waters as a result of these migrations, which may cover thousands of miles. Such migrations certainly make it difficult to select any area in the oceans as being sufficiently remote and isolated from human interest to insure that the discharge of radio- isotope wastes might not be transported into those areas man is most interested in protecting. It should, however, be pointed out that this is a quantitative problem, and our knowledge is not sufficiently detailed to permit evaluating the quantity of radioisotopes which could be transported in mass migrations of fish. In addition to the movements of organisms which are independent of the circulation of the water resulting from gravity and vertical and horizontal migrations, many populations remain stationary in a flowing stream of water. The organism is thus able to concentrate remarkably the constituents of the water masses which pass by. Harvey (1950) estimated, for example, that the bottom population was nearly 70 per cent of the total population at a station in the English Channel (see Table 3). The most apparent of these stationary popu- lations are those which live on or in the bottom. Much of our knowledge concerning such popu- lations is confined to those which occupy shal- low waters such as the clams, the oysters, and other economically important species. Stationary populations may be exposed to and feed on populations in many cubic miles of sea water during the course of an active growing season. Although most of our knowledge is confined to shallow water forms, it is known that such stationary populations are a main source of food for many bottom-feeding commercial fishes. The haddock and cod fisheries of New England and the halibut fishery of the Pacific Coast, for example, are ground fisheries. These impor- tant species of fish feed on sedentary or sta- tionary populations. Even in the great depths of the ocean such sedentary populations have been found wherever man has had the oppor- tunity to search for them. Although little is known of their location in the food web and dynamics of the ocean, it seems certain that they play a part. The importance of such stationary popula- tions is that they can concentrate enormously the density of organic matter in those locations suitable for their survival. In unique situations they may concentrate by several orders of mag- nitude the available organic matter in the ocean. Less obvious stationary populations are plank- tonic and unattached, and one would expect them to be transported away from a given area by the currents. It has been found in some cases, however, that in spite of horizontal cur- rents of considerable velocity, the centers of some planktonic populations can remain rela- tively stationary. Presumably there is a con- stant drain from these populations as a result of the currents which carry away some of the organisms, but the rate of production of the population is sufficient to maintain the popula- tion in spite of this drain. Examples of such populations are to be found in almost all estu- aries which tend to maintain endemic species different from those commonly found in the adjacent sea (Ketchum, 1954; Bousfield, 1955). Even in the open ocean similar stationary popu- lations have been found (Redfield, 1939, 1940, 1941; Johnson and co-workers, unpublished observations). It is necessary to have a rate of reproduction of the population as a whole suffi- cient to balance the circulatory drain. This rapid rate of reproduction will, of course, lead to the concentration of materials from the water mass moving past. A special case of biological concentration of materials which probably involves several of the above phenomena is found in the "red tide." It has been shown that the concentration of total phosphorus in the colored water of these dinoflagellate blooms is commonly ten to twenty times as great as the concentration which can be found in any of the adjacent waters (Ketchum and Keen, 1948). Most of this phosphorus is combined in the living cells, and very little is present in the inorganic form. One of the explanations for these high concen- trations involves the accumulation of the organ- isms at the surface because of their buoyancy, and the subsequent further concentration of the surface film by convergence of water masses (Ryther, 1955). In the red tides which have occurred in recent years off the west coast of Florida, the organism involved, Gymnodinium brevis, produces a toxin which is lethal to the fish and other organisms in the water, and vast numbers of fish have been killed as a result of these dinoflagellate blooms (Gunter, et al.,
Atomic Radiation and Oceanography and Fisheries 1948). Recent evidence indicates that the or- ganisms are almost always present in the water (Collier, A., unpublished), but in such low concentrations that there is no marked fish mortality. It is only after the concentration produced by the biological and hydrographic system that mortalities result. In evaluating the discharge of radioisotope wastes at sea, the factor of safety must be sufficient so that safe levels of radioactivity can be maintained, even after the various mecha- nisms of biological accumulation. REFERENCES BOUSFIELD, E. L. 1955. Ecological control of the occurrence of barnacles in the Mira- michi Estuary. Nat. Mas. Canada Bull. No. 137, Biol. Ser. No. 46, pp. 1-69. DIETZ, R. S. 1948. Deep scattering layer in the Pacific and Antarctic oceans. /. Mar. Res. 7:430-442. GOLOLOBOV, Y. K. 1949. (Contribution to the problem of determining the age of the present stage of the Black Sea) in Russian. Dokl. Akad. Naak SSSR. 66:451-454. GUNTER, G., R. H. WILLIAMS, C. C. DAVIS, and F. G. WALTON SMITH. 1948. Cata- strophic mass mortality of marine animals and coincident phytoplankton bloom on the west coast of Florida, November, 1946 to August, 1947. Ecol. Monogr. 18:309- 324. HARVEY, H. W. 1950. On the production of living organic matter in the sea off Ply- mouth. /. Mar. Biol. Assoc. U. K. 29: 97-137. HERSEV, J. B., and H. B. MOORE. 1948. Prog- ress report on scattering layer observations in the Atlantic Ocean. Trans. Amer. Geophys. Union. 29:341-354. HULBURT, E. M. In press. The distribution of phosphorus in Great Pond, Massachu- setts. (Submitted to /. Mar. Res.) KETCHUM, B. H. 1954. Relation between cir- culation and planktonic populations in estuaries. Ecol. 35:191-200. KETCHUM, B. H., N. CORWIN, and D. J. KEEN. 1955. The significance of organic phos- phorus determinations in ocean waters. Deep-Sea Res. 2:172-181. KETCHUM, B. H., and D. J. KEEN. 1948. Unusual phosphorus concentrations in the Florida "red tide" sea water. /. Mar. Res. 7:17-21. MATHER, F. J., Ill, and C. G. DAY. 1954. Observations of pelagic fishes of the tropi- cal Atlantic. Copeia, 1954, no. 3:179-188. REDFIELD, A. C. 1939. The history of a popu- lation of Limafina retroversa during its drift across the Gulf of Maine. Biol. Bull. 76:26-47. 1941. The effect of the circulation of water on the distribution of the calanoid com- munity in the Gulf of Maine. Biol. Bull. 80:86-110. 1942. The processes determining the con- centration of oxygen, phosphate and other organic derivatives within the depths of the Atlantic Ocean. Pap. Phy. Oceanog. Meteorol. 9:1-22. REDFIELD, A. C., and A. BEALE. 1940. Fac- tors determining the populations of chae- tognaths in the Gulf of Maine. Biol. Bull. 79:459-487. RILEY, G. A. 1941. Plankton studies. III. Long Island Sound. Bingham Oceanog. Coll. Bull. 7(3): 1-93. 1941a. Plankton studies. V. Regional sum- mary. /. Mar. Res. 4:162-171. 1944. The carbon metabolism and photo- synthetic efficiency of the earth as a whole. Amer. Set. 32:129-134. RILEY, G. A., H. STOMMEL, and D. F. BUMPUS. 1949. Quantitative ecology of the plank- ton of the western North Atlantic. Bing- ham Oceanog. Coll. Bull. 12:1-169. RYTHER, J. H. 1954. The ratio of photosyn- thesis to respiration in marine plankton algae. Deep-Sea Res. 2:134-139. 1955. Ecology of autotrophic marine dino- flagellates with reference to red water con- ditions. Luminescence of Biological Sys tems: 387^14. SETTE, O. E. 1943. Biology of the Atlantic mackerel (Scomber scombrus) of North America. Part I: Early life history. Fish. Bull. 38:149-237. SETTE, O. E. 1950. Biology of the Atlantic mackerel (Scomber scombrus) of North America. Part II. Migrations and habits. Fish. Bull. 51:251-358.
Chapter 5 Ecological Systems and Transport 59 STEEMANN NIELSEN, E. 1954. On organic SVERDRUP, H. U., M. W. JOHNSON, and R. H. production in the oceans. /. Con. Internat. FLEMING. 1942. The Oceans, their physics, Explor. Mer. 19:309-328. chemistry and general biology, x+1087 ' ,. , , , , , TT PP-. Prentice-Hall. Inc., New York. STROM, K. M. 1936. Land-locked waters Hy- THO^E'N; H 1931.'Nitr'ate and phosphate drography and bottom deposits in badly contents of Mediterranean waterr D^sh ventilated Norwegian Fjords with remarks Oceanog. Exped. 1908-1910. 3:14 pp. upon sedimentation under anaerobic condi- WORTHINGTON, L. V. 1954. A preliminary tions. Norske Vidensk. Akad. 1. Mat. note on the time scales in North Atlantic Naturv. Klasse No. 7, 85 pp., Oslo. circulation. Deep-Sea Res. 1:244-251.
