C & E N SPECIAL REPORT
CHEMISTRY AND THE OCEANS
The oceans are a complex water system in which many processes and events interact to affect
the system in unique and as yet largely unknown
ways. Oceanographers
are studying the seas and the information gaps are narrowing
he volume of the earth is about 800 times greater than the volume of the oceans, which is 1.37 billion cubic kilometers; the radius of the earth is about 1700 times greater than the average depth of the seas, which is 4 kilometers. Yet the oceans with an area of about 360 million square kilometers cover about 70% of the surface of the earth. The oceans, therefore, are a conspicuous feature of the planet. For this reason, the planet earth among all the other planets of our solar system is known as the water planet. These waters that we call the world ocean are known in history and literature as the Seven Seas. In antiquity the seven were the Mediterranean, Red, West African, East African, China, Indian Ocean, and Persian Gulf. Today, however, the seven are the Arctic, North Atlantic, South Atlantic, North Pacific, South Pacific, Indian, and the Antarctic. In one sense the divisions seem arbitrary and perhaps they are. A traveler can move from one body of water to another without changing vessels; also, the waters of the ocean are freely interchanged throughout, although the time involved for this exchange might be as long as 2000 years. In another sense, however, the divisions are not quite so arbitrary as they first appear. The Atlantic Ocean is characterized by a northward transfer of surface waters and a southward transfer of the deep waters. The Pacific Ocean and Indian Ocean surface and deep waters mix only at their southern extremities. Atlantic and Pacific Ocean waters mix in the Antarctic. The North Atlantic is the saltiest ocean, having about 37.9 parts per thousand salt. Also, the Atlantic Ocean, north and south together, is the wettest ocean system, getting about one half of all the rain that falls world-wide directly and from land run-off. The Arctic Ocean is a body of water almost completely surrounded by land; the Antarctic Ocean is a body of water surrounding a small land mass. These polar oceans are the least salty of the oceans, because melting ice constantly dilutes the salt solution; and no rivers feed these oceans with additional salts. The oceans are about 100 million years old and the water they contain is a complex solution of organic and inorganic components. The inorganic salts are derived from over two billion years of erosion of the earth's crust, the gaseous effusion of volcanoes, and meteoritic material. The organic materials are the products, byproducts, and decomposition products of the enormous
T
biological activity that occurs lit the $ e ^ ^ i f e t h # m$m itself, analyses of volcanic g ^ £ support^ free water on the earth's surface was ;hil^^['m^^\ the earth's geologic history from molten rp^k» WhîicKJ holds more water than rock which is cool and hard. The forces of gravity kept this moisture on the planet. The vastness of sea as it was known to them 25 centuries ago, and the ineluctable forces of the waters surrounding their lands, led the ancient Greeks to call these waters the oceans. Oceanus, the ancient Greek father of the gods as well as men, the beginning of alt things, was also the name given to the great outer stream that the ancient Greeks thought encircled the earth. The sea has always had an aura of mystery about it; its great expanse and peculiarities have always awed man; and the sea, for the most part, has always been an alien environment for man. Legends about the sea have persisted for time immemorial—the Flying Dutchman, mermaids, ships and men floating forever in the world ocean somewhere below the surface, never sinking to the sea floor. Even sea serpent mythology hangs on—the summer of 1963 brought reports of such a monster basking in the sun off the coast of New Jersey. However, the sea is slowly yielding its secrets to man. As a consequence, man is beginning to think of new ways to exploit the ocean, which has traditionally been a source of food, a place for recreation, a physical barrier to enemies, and a trackless transportation network. Man is turning to the sea even more today than ever before in his history. The sea still is an important source of food, but it is also a dumping ground for sewage and radioactive wastes, and a supplier of raw materials for paint, fertiliser, glue, and metals. From under the sea come sulfur, gas, coal, and oil. From the sea floor come metals, jewels, and raw materials used to extract some of the dissolved materials in the water. The sea water itself, through highly sophisticated techniques, is now being used as a source of fresh water. And, among other things, the sea is being studied by such men as Edwin A. Link and Jacques Yves-Cousteau as a place in which men can live and work for months at a time in special containers on the sea floor. Yet we know little about the world ocean. Today's maps of the ocean basins may be likened over-all in accuracy and detail to 18th Century maps of the land. Some oceanographers, the men who study the ocean and its
The Seven Seas Have Long Challenged
ri'Çy-.·
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phenomena, even go so far as to say that we know more about the surface of the moon than we do about our own oceans. Not only the basins of the seas, but the waters and the inclusions, living and nonliving, organic and inorganic, are little understood by man. The things that we do not know about the ocean's chemistry, biology, geology, hydrography, circulation, and the like make an imposing list. Fortunately, oceanographers are not fearsomely awed by the list, but instead are attacking these problems on a wide f r o n t . And the ocean is slowly yielding. Man has learned to predict the occurrence and path of t s u n a m i s (tidal waves) and can alert potentially affected areas; he can follow paths of hurricanes a n d , by studying these phenomena, has reasonable hopes of controlling t h e m ; he seriously sees the t i m e when fresh water for all the world's needs can be economically derived f r o m sea water; he plans to harness, at long last, the ocean's tides as a source of power; he foresees ways to control the world's climate by controlling or using the ocean currents; he finds the oceans an inexhaustible potential economic source of many of the metals that are rapidly becoming in short supply on l a n d ; and he looks to the sea to solve some of the world's food problems as he learns to harvest food f r o m the sea as a f a r m e r rather than a hunter. The promise of the oceans is as great as t h e i r vastness implies and the i m p o r t a n c e t h a t the ancient Greeks attached to the oceans no longer seems f a r f e t c h e d .
Mankind
The secrets of the sea are yielding to scientific studies I he oceans are a four-dimensional (time is the fourth dimension), interconnected, interdependent system that covers about 70% of the earth's surface. Man has long looked at the oceans as both friend and enemy, protector and provider, a place for fun and a place of danger. Throughout most of his civilized life he has made his home near the sea. Indeed, most of the world's major cities are at the water's edge. Life itself may have originated in the primordial ooze of some long-since vanished sea. Yet despite man's long familiarity with the seas, they remain largely a mystery to him. Except for making gross observations on the extent of the oceans, winds, and currents, man did not really undertake to study the ocean in any significant detail until about 100 years ago. This C&EN Special Report deals with the recent resurgence of interest in oceanography. Although primarily on chemical oceanography, the article includes discussions of some of the problems that are also biological, geological, physical, or meteorological because all of these things are interrelated and interdependent. The traditional subject distinctionschemistry, biology, hydrography, meteorology, geology, physics—are C&EN
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LORAN-C COVERAGE E f t » 3 MILE FIX ACCURACY % — — • USABLE FIX COVERAGE NAVIGATION. Loran-C stations permit ships' navigators to position their ships to within about three miles over parts of the earth's trackless seas. Supplementary systems are available in certain areas for precise positioning
rapidly disappearing in oceanography, just as they are in other fields. Biology and chemistry are inseparable in oceanography, and both add to the body of knowledge on the physical and dynamic processes in the oceans. For example, the close relationship between current systems and the geographic distribution of both organic and inorganic matter provides information on the movement of water masses in the ocean that otherwise would require extensive series of current measurements. Biological systems (fish, plants, microorganisms) use some of the elements in sea water and cause uneven, irregularly timed elemental distributions. Currents, winds, up welling and downwelling water, evaporation, rainfall, and runoff all affect the distribution of elements, as do changes in season, temperature, and depth (pressure ). Need for More and Better Ocean Data Brought Out by Thresher Sinking The nation was jolted into an awareness of how much it still has to learn about the sea by the tragedy of the Thresher about a year ago. The 4A
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sinking of that nuclear-powered submarine in April 1963 and the frenzied, essentially futile hunt for it that continued until September when the Navy called the search to a halt, pointed up how little we know about the oceans. The Thresher's approximate position at the time it sank with the loss of 129 men is known. The depth of the water in the area is only 8500 feet. Although undulating, the ocean bed there is relatively flat and almost featureless (although it does have housesized rocks). The area, however, is near the edge of the continental shelf where the continental slope begins and where the floor has a rugged topography, including steep inclines, deep canyons, and jagged peaks. Thousands of sorties were made across the area by many ships, and still the exact fate of the Thresher is unknown and may never be known. Although hundreds of photographs of the sea floor reveal debris from the Thresher, the main pressure hull was never sighted. Why, it might well be asked, should it be so difficult to "see" an object that is little more than 1.5 miles away? For one thing, the navigational aids THE
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available in the search area when the disaster occurred could determine the positions of the search ships probably /within about a mile or so, except with good radio reception during daylight, when it was possible to do better. (Where available, Loran-C under ordinary conditions permits fixes to an accuracy of 2 to 3 miles. For normal navigation purposes, such accuracy is perfectly satisfactory. To return to a precise spot in the ocean, however, where the position must be known to within a few yards, more precise techniques are necessary.) Sea Floor Topography Poorly Known For another thing, the ocean bottom in the search area, at least until the accident, had been poorly mapped (world-wide, only about 3% of the ocean bottom is reliably mapped). Still another is the lack of vehicles that can adequately navigate along the ocean floor and probe it. The problem of pinpointing the location of a ship on the surface is compounded by winds and ocean current drift, by weather and time of day and their effects on radio signal quality, by equipment malfunction, oper-
ator error, and the like. Further, the searchers on the ships generally have little more than an approximation of the position in the water of equipment attached to the end of several miles of cable and dangling "somewhere" in the ocean beneath their ships. The one vehicle that the U.S. possesses that can be considered even partially effective in scouting the ocean bottom is the bathyscaphe, Trieste, which is capable of diving with three men to depths of 36,000 feet. But even the Trieste had trouble on occasion at the 8500-foot depth. It developed shorts in its electrical circuits and lost control of both its ballast system and its starboard propulsion-control propeller. In one dive its lights failed. To a large extent these failures are attributable to the corrosive effects of sea water and the high pressures associated with depth. However, much of the damage to the Trieste came while the vessel was being towed through rough seas to the search area. Even while in good operational condition, the Trieste is limited to covering no more than one square mile on the ocean bottom per dive. Estimates by some of the investigators at the start of the search were that at least 100 dives would be needed to survey the suspect area. The Trieste, however, made only about 10 dives before being hauled off for repairs, other duties, and because of the onset of winter with its attendant bad weather. There were other problems, too. Cameras were towed about 20 feet above the sea floor, taking pictures at regular intervals. On one occasion, search authorities said that one of the search ships had taken pictures of the Thresher hull and diving planes. However, these pictures turned out to be photographs of the ballast attached to the camera to hold it down near the ocean floor (an "error," in some measure at least, attributable to the intense pressures on oceanographers on the scene "to publish something" because of the high public interest in the search ). The problems, errors, failures, and mistakes in judgment all involve people of high professional competence who were using machinery and equipment that in environments other than the ocean would have been reliable. To the question "Why is it so hard to find a large object only 1.5 miles from the surface?" the answer,
in a phrase, is that we know little about the mysterious ocean. It is this very lack of knowledge, however, that provides the challenge for today's océanographie research. Federal Government Pays for 90% of All US. Océanographie Research World War II and the Cold War period following brought home to the military services that they knew very little about the oceans. From an interest in antisubmarine warfare, the Federal Government's activities soon spread out to embrace and engulf the whole field of oceanography in the U.S. Now with $138 million in the President's budget for a federal océanographie program for fiscal 1965 for about 20 government agencies, the Federal Government is by far the major supporter of océanographie research in the U.S., according to James H. Wakelin, Assistant Secretary of the Navy for research and development. Easily 90% of all the money spent for océanographie research in the U.S. is from the Federal Government. For example, although private industry spends about $40 million each
search for fiscal 1963 for these private, state, and federal laboratories is about $100 million. All told private profit and nonprofit institutions spend perhaps only $2 million in funds that are derived from endowments and other private sources. The remainder and largest portion of the funds expended by these private groups comes from federal agencies, Mr. Vetter adds. In addition, the state governments (primarily of the coastal states ) altogether spend only from $7 to $10 million of their own state-derived funds on océanographie research on problems related largely, but not entirely, to industries along their shores and waterways. Here, too, the bulk of the money spent by the state governments for océanographie research comes from federal sources. Some of the present interest in the sea has been brought about by the attention focused in recent years on the hazards of using the oceans as unrestricted dumping grounds for waste fission products. Before the oceans can be safely used for the disposal of fission products, the possible effects of various oceanic systems—currents, mixing processes, geochemical factors,
THRESHER PIPE. The hull number of the Thresher (593 boat) is barely discernible near the dark crease area. This pipe was recovered from the sea floor by the bathyscaphe Trieste in its search for the sunken submarine
year on océanographie research, about $35 million comes directly from the Federal Government, principally for studies relating to antisubmarine warfare. (In all, federal funds to the tune of about $400 million each year are pouring into antisubmarine warfare projects. ) According to a recent survey of 81 major U.S. océanographie laboratories by Richard C. Vetter, executive secretary of the committee on oceanography of the National Academy of Sciences-National Research Council (Washington, D.C.), the total budgeted support for océanographie reCHEMISTRY
and biological systems—that are part of the world ocean must be adequately evaluated. Oceanography Is a Composite Science Oceanography, not one science but a mingling of many sciences oriented toward the seas, now gets more financial support than ever before. This support shows up as new facilities, new curriculums, new ships, new personnel, and new programs for organizations, both academic and industrial, profit and nonprofit, located near the shores and in land-locked areas. AND THE OCEANS
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Chemical oceanography is an old science recently revitalized As the field of oceanography grows, so too does the field of chemical oceanography. The chemical oceanographer may be a chemist who works on a ship, although he may also work on ocean problems in land-based laboratories. In either place he uses chemical tools and techniques to solve the problems of the oceans. He studies the complex chemistry of the oceans—the chemical species and isotopic composition of water and the reactivities and the distributions in time and space of these sea water components and their products. To understand what goes on in the oceans, one must first know what sea water is and what it contains. Indeed, the recognition of this particular need and the search to satisfy it marks the beginnings of chemical oceanography. Yet, despite more than 90 years of study of the chemistry of the oceans by workers from all parts of the world, an exact, universal description of ocean water cannot be made. Because of the size and complexity of the oceans, it is unlikely that any such description ever will be made. Thus, research on sea water and how it is affected by or how it affects the myriad of inclusions in the water must be a continuing program. Despite our lack of a complete understanding of what ocean water is, we do have enough information to discuss in a general way its properties, composition, behavior, and the like. We know that the oceans are a large but dilute electrolytic solution which probably contains all the naturally occurring elements known to man. If we include as "elements" the hydrogen and oxygen combined in the molecules of water, only 14 elements occur in concentrations of at least 1 p.p.m. in sea water. Most of the elements occur at considerably less than 1 p.p.m. Hence, analytical problems are enormous. Oceans Are Unique Chemical
Systems
Not only are the analytical problems difficult, but there are additional complications: The components of sea water have been in intimate contact for long, even geologic, times. Even when reactions occur and the elements combine and precipitate on the sea floor, the sea water still remains in contact with them. 6A
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Analytical problems are so great that what are known as Dittmar's 77 samples remain to this day as they have for the past 70 years the only set of world-wide water samples for which a complete analysis ( each of the major constituents) is available. From 1872 to 1876, H.M.S. Challenger, a British ship, carried scientific personnel on a round-the-world cruise to study the biology of the sea, collect water samples and bottom samples, and to measure water temperatures. A German-born chemist, Prof. William Dittmar, analyzed 77 water samples taken on this voyage. He determined the percentage composition of the dissolved solids (chloride, sulfate, sodium, calcium, magnesium, and potassium) in each of the 77 samples. The results of Prof. Dittmar's analyses, which took nine years to complete, supported the findings published by an English physician, Dr. Alexander Marcet, in 1819, and by the Danish chemist, Prof. Georg Forchhammer in 1865. Prof. Forchhammer took 20 years to complete the analysis of 200 samples of water collected for him by friends, ship captains, and naval officers. The three workers reached essentially the same conclusions: • Chloride, sodium, magnesium, sulfate, calcium, and potassium make up 99% of the dissolved salts in sea water. • The ratio of any one of the major constituents to the total dissolved solids is nearly constant in the sea even though the total concentration of dissolved solids may vary from place to place. These efforts by Dr. Marcet, Prof. Dittmar, and Prof. Forchhammer mark the beginnings of the study (mostly science, but sometimes art) known as chemical oceanography. Chemical oceanography is the application of chemical techniques and principles to the study of the sea and to the various isolated, yet interrelated, processes—biological, chemical, geological, meteorological, and physical—that make the oceans truly dynamic systems. A cynic has more succinctly described chemical oceanography as chemistry done from* the deck of a ship on the high seas, although this is a much too limited view to deserve serious attention.
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These rich beginnings of modern chemical oceanography were soon lost as a neglectful attitude toward chemical oceanography permeated the field. The chemical oceanographer analyzed water samples for such things as dissolved materials, especially chloride, oxygen, and plant nutrients. The physical oceanographer took some of these data and constructed density charts from which he attempted to construct tables relating pressures to ocean depths. He used these and other data to try to explain the "why" of ocean currents and the relation between oceans and the weather. The biological oceanographer also borrowed from the chemical oceanographers such data as were needed to understand and describe the biological mechanisms in the sea. Chemical Oceanography Temporarily Lost Its Distinctive Character Meanwhile, the science of chemical oceanography practically ceased to exist as a separate entity. According to Dr. Norris W. Rakestraw of Scripps Institution of Oceanography of the University of California (San Diego), the océanographie chemist for many years was little more than an assistant to the biologist, for the principal problem oceanographers worried about was that of the fertility of the sea—why certain parts are productive and others barren. Despite the antiquity of the . data on which it is based, the nearly constant ratio of the major constituents to each other as described by Marcet, Dittmar, and Forchhammer has been demonstrated over and over again. This very nearly constant ratio shows the effectiveness of both the mixing processes and the biological cycling of elements within the oceans on a worldwide basis. It can also be used to explain some of the known current systems. As water evaporates from the surface of a body of sea water, the density of the surface water increases. This dense water sinks, causing currents and water circulation. Such conditions occur, for example, on a large scale in the Mediterranean Sea. More often, oceanic circulation is the result of cooling and ice formation. Cooling of waters in the polar regions and the subsequent increase in den-
the valves W , feeing kept open fry means of a: weighty W, and closing them selves when ^ e weight reaches the bottom. Ulie valves in this machine are made of solid brass, and β&% fall ky their own weight* so as to dose die cylinder, the moment that the square FDE, which turns freely upon a pivot in P, is depressed in E, where it preponderates, the pieces, which supports the valves, thus becoming unhooked f«)mthei«ecessionofthehook,orclicket, in F. This may be effected in two ways; either fey the weight W no longer pressing on the square in F, so as to keep it faet in its place, u and therefore suâèring it to recede» so as to disengage ce; or by letting down along the line a weight B, that shall fall uporm BINbiy the rope A, and diseegage the valves by die jerk it occasions*' Uns «mstitutes the improvement by which water is now expected to he raised from any given depth, as well as *> * from the bottom, . ' # * , f%» a. This figure does not require any particular references. & represents the instrument in 'm natural Hts&e» which simply consists in a glass bulb of moderate thicknlts, «a* pableof holding 844,6 grains of distilled water, with a neck or tube issuing from it, md containing a delicate merwml thermometer, the elongated b lb of which is represented in dotted lines in the centre of the large bulb. To the end of * this neck ( the diameter of which is near half an inch), a long tofce having rather a small bore, is ground air-tight, and
j , *!
% %>Μ>ά > ^
CENTURY-OLD EQUIPMENT LITTLE CHANGED TODAY Both the thermometer and water-sampling devices used by Dr. Marcet almost 150 years ago to obtain data about the sea show striking similarities to some of the more sophisticated ones used today Source: "Philosophical Transactions of the Royal Society of London—1819", page 207 and plate X I I , reproduced by the express permission of the Royal Society, which retains full copyright privileges
sity are the primary reasons for deep oceanic circulation. The brine left after ice formation has greater density than the water in which the ice forms, the brine being both colder and higher in salt content than the original water. Nearly Constant Ratio of Major Salts in Sea Water Is Useful Concept Therefore, to understand and ex plain the movement of water within the ocean system, density is at least one sea water property that must be measured. But the analytical balance and the hydrometer used to measure density in the land-based laboratory do not function well on a rocking, pitching ship. Thus, the very nearly constant ratio of the major con stituents becomes useful. Measure ment of only one major component gives, by proportion, the amount (to about one part in 10,000) of other components present; and from this, density can be determined. Dr. Dayton E. Carritt of Massachu setts Institute of Technology (Cam
bridge), and Dr. James H. Carpenter of Johns Hopkins University (Balti more, Md.), and others point out that an extremely important qualification must be borne in mind in this concept of the nearly constant ratio of the ma jor constituents of sea water. The term "very nearly" has frequently been taken by oceanographers to mean that the ratios are constant. In fact, the early literature and many of the later works on the constituents of sea water emphasize that slight variations do occur. One of the major océanographie problems is determining the magnitude of these slight variations and estimating the subsequent variations (about three parts in 100,000) in the density of sea water. The density of sea water is a function of three variables—temperature, pressure, and composition (or salinity)—and it may be computed from measurements of them. Although sea water density can be measured directly, in practice it is usually derived from measurements of the three variables. CHEMISTRY
The relationships between temperature, pressure (one atmosphere), salinity, and density were determined in 1902 by Martin Knudsen and were published as Hydrographical Tables by the International Council for the Exploration of the Sea. These tables also give data for converting salinity to chlorinity (defined at that time as the equivalent amount of halogens as measured by volumetric titration with silver nitrate). Auxiliary tables provide corrections for thermal expansion. Thus, from a single titration for halogens, the oceanographer can derive salinity, density, and specific gravity at any desired temperature. Although Knudsen's tables are in wide use even today, some oceanographers object to them because they were derived from a comparison of only 24 samples. The samples, moreover, were not world-wide in origin, but were chiefly from the Baltic and North Seas—regions of prime interest to the International Council. However, the dilute waters of these two seas, isolated and influenced by a parAND
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AUTOMATED BUOY LINES CAN PROVIDE YEAR-ROUND DATA ON OCEANS
This line of buoys stretches from Woods Hole to Bermuda, automatically recording data for three months after buoy placement. At the sea surface, wind direction and speed are detected and recorded. Below the surface as many as 11 separate instrument clusters record such data as water current speed and direction and instrument depth. These data are recorded on photographic film by means of a batterypowered light coupled to the sensors. At about three-month intervals the buoy and its instruments are fished from the sea and the film is recovered for developing and readout ashore. Recovery of the instruments is often made difficult or impossible by bad weather, which tears the buoys from their deep-sea moorings
ticular set of rivers, are hardly representative of other dilute seas or of the world's oceans, these oceanographers feel. All the water samples were taken from the surface. Knudsen's tables do not take into account the possible changes in composition that might be a function of depth or the interaction between the water and the ocean floor. The tables also do not take into account the varying concentrations and types of materials that are biologically precipitated at the surface and regenerated in the depths. Further, some oceanographers are uncertain about the accuracy of the corrections for thermal expansion that are included in the tables. Be that as it may, these tables are used by oceanographers for computing density from chlorinity. Starting in 1902, Normal Water (Eau de mer normale) to be used as a standard reference for chlorinity measurements was prepared by the Hydrographical Laboratories in Copenhagen, Denmark. This water was adjusted to a chlorinity of about 19.4 parts per thousand, carefully analyzed in terms of the original 1902 standard to a precision of a few parts per million. This standard solution was distributed to océanographie laboratories throughout the world. Standard Sea Water Independent of Changes in Primary Standard However, such precision meant that any redefinition of atomic weights of silver, chlorine, sodium, potassium, or the other elements involved directly or indirectly in the chlorinity determination and preparation of primary standards introduced significant changes in the standards. To overcome this difficulty, chlorinity was redefined in 1937 in terms of a special batch of isotopically pure atomic weight silver: The equivalent weight of silver required to precipitate all the halides in a kilogram of Normal Water is equal to chlorinity times 1/0.3285233. Chlorinity is now defined as 0.3285233 times the weight of silver required to precipitate the halides from a kilogram of sea water. All new batches of Copenhagen water are standardized against this silver by gravimetric titration. Deriving the electrolyte concentration of sea water by determining electrical conductivity was first suggested before the turn of the century. For the past 35 or 40 years the Coast
CHECKING METER. Dr. William Richardson, who set up the buoy lines shown on the opposite page, watches the operation of flow meters as he peers through the viewing port in a raft moving across a water tank
Guard has been using the method routinely with some success. Its iceberg survey workers use electrical conductivity to determine salinity, and from this they calculate density. The density data are then used to determine the dynamic topography (ocean currents) that affects the movement of icebergs. Although density data derived in this manner are satisfactory for plotting ocean currents as related to the movement of icebergs, the data are not good enough where precise measurements are needed. Within recent years, Australian, English, and American oceanographers have developed laboratory type salinometers that make use of the electrical conductivity property of sea water and which are now in widespread use. These instruments are able to determine concentrations reproducible to about 2 p.p.m. in chlorinity units in a fraction of the time required for classical titration, which is reproducible to about 20 p.p.m. Furthermore, these salinometers very readily can be used at sea, and the precision attainable is practically the same whether operated on the deck of a rolling ship or in a shore based laboratory. The conductivity method also lends itself extremely well to measuring the concentration of constituents in sea water in situ. In situ conductivity instruments have been used for some time now (at least for 15 to 20 years) CHEMISTRY
with varying success. Until very recently, however, these instruments were designed for inshore or estuary work. They had rather shallow depth capabilities and gave results not precise to better than about 50 p.p.m. chlorinity. Today, in situ salinometers are being developed that can perform at great depth (6000 meters or more) with the precision obtainable with laboratory titrations (20 p.p.m.). One tremendous advantage the in situ salinometer has, of course, is its ability to give a continuous record of chlorinity or salinity with depth. Even where the chlorinity values obtained by the in situ salinometer may be much less precise than those obtained with a laboratory salinometer, the use of the in situ instrument can yield details of information concerning the water column that could be missed in the discrete sampling of the usual hydrographie technique. In theory, at least, densities derived from conductivity are more accurate than densities derived from chlorinity, since the chief ions affecting changes in the total salt composition, such as calcium and bicarbonate, are not involved in the chlorinity titration. However, measurements permitting a direct conversion from conductivity to density are not yet possible. If oceanographers from different laboratories wish to compare their conductivity-derived density data, they must AND THE OCEANS
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Temperature, depth, and salinity are used to delineate water masses calibrate conductometers in terms of Copenhagen standard sea water. They calculate density by first measuring chlorinity or salinity and then using Knudsen's tables for the conversion. Some oceanographers don't find these manipulations particularly burdensome, however, because they find "salinity" a helpful concept. Dr. R. A. Cox and co-workers at England's National Institute of Oceanography propose that Standard Sea Water be standardized for conductivity as well as chlorinity. The precision of density values derived from conductivity measurements is perhaps 10 times greater than the precision of density data obtained from chlorinity
data from measurements of electrical conductivity, some oceanographers propose dropping the derived terms and retaining only the directly measured ones. At the moment, most oceanographers are not likely to take such a step; so conductivity measurements are thus being added to the collection of other data. Salinity, another widely used term in oceanography, is a defined quantity that approximates the total salt concentration of sea water: S (parts per thousand) = 0.030 + 1.805 chlorinity (in parts per thousand). Salinity as a concept can be objected to by chemists as an imprecise composite. Indeed, a few oceanog-
CALIBRATING. Reversing thermometers are used both to determine temperature and to provide data for calculating the depth at which instruments are positioned. Readings are routinely made with the aid of magnifying lenses
determinations, Dr. Cox points out. To help speed the acceptance of the conductivity approach, Dr. Cox and co-workers are developing an instrument that measures conductivity in absolute units to five significant figures. Dr. Cox cautions that conductivity measurements should not be allowed to replace chlorinity measurements in identifying and tracing water masses throughout the ocean system. It is possible that changes in the deep water, such as changes in the rate of solution of calcium carbonate, could alter the water's density and conductivity but not its chlorinity. Rather than go through what they consider the waste motion of deriving 10A
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raphers hold salinity in disrepute, although many believe the term is useful because it is close to the actual salt content responsible for density. Salinity approximates the weight in grams, under vacuum, of the solids in 1 kilogram of sea water, weighed in vacuum (the solids dried to a constant weight at 480° C , the organic matter completely oxidized, the bromide and iodide replaced by an equivalent amount of chloride, and the carbonates converted to oxides). Hydrowire Is Oceanographers' Main Tool for Collecting Ocean Data The beginnings of chemical ocea-
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nography or, for that matter, the beginnings of oceanography itself are associated with plumbing the ocean depths. This was first done with devices attached to the hemp lines common to the days of the clipper ships. Later these hemp lines gave way to single-strand piano wire. This in turn gave way to braided or twisted steel cables of various designs, compositions, and sizes. Known as "hydrowires" ( for hydrographie wires ), these lines provide the vital link between the oceanographer and the ocean. He uses these lines to lower his instruments into the ocean for in-place readings or to remove water samples from specific depths. Indeed, the collection of water samples and the determination of the temperatures at which the samples are taken are still cornerstones of oceanography. Water samples for chemical analyses are usually collected with devices known as Nansen bottles. These bottles, often made of brass, are attached at intervals along a hydrowire, which is weighted and dropped over the side of the ship. The bottles are open at the top and bottom and are flushed with sea water as they are lowered. Finally, when all bottles have been lowered to the desired depth, they are allowed to equilibrate for a few minutes. Then a brass weight (a messenger) is dropped along the hydrowire, triggering a release mechanism that permits the bottles to invert. As the bottles invert, their self-contained valves close, thus sealing in the water sample at the sampling depths. The depth of the bottle is determined from two thermometers (called reversing thermometers) attached to the Nansen bottle. One thermometer is housed in a glass case and is pressure insensitive; the other is in direct contact with the sea and thus affected by the pressure. The protected (pressure-insensitive) thermometer gives the temperature of the water at the sampling level. The unprotected thermometer reads higher, however, because of pressure on the bulb. The elevation of "temperature" with pressure is unique for each thermometer, and each is calibrated in special pressure vessels located in some océanographie laboratories. The difference in readings between protected and unprotected thermometers is calculated
T E M P E R A T U R E (degrees C.)
2000
3000
6000
6000 70°
66°
60°
55°
50°
SALINITY (parts per 1000)
2000
3000
4000
5000
25°
20°
15°
10°
Source: Woods Hole Océanographie Institution
TEMPERATURE AND SALINITY PROFILES IN THE NORTH ATLANTIC (40°N) ARE TYPICAL OCEANOGRAPHIC DATA During the International Geophysical Year (1957-58), ships from many nations made surveys across the North and South Atlantic Oceans. These two profiles were made along the heavy track shown on the small map (left); the lighter lines show the tracks of other surveys made during the same period. The horizontal elements in the profiles are exaggerated to accentuate the sea floor topography CHEMISTRY
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KNOWN ABUNDANCES IN SEA WATER The large number of known elements in sea water indicates that probably all of earth's naturally occurring elements exist in the sea
Element
Chlorine Sodium Magnesium Sulfur Calcium Potassium Bromine Carbon Oxygen Strontium
Milligrams per liter 9,000 0,600 1,300 900 400 380 65 28 8 8
Boron Silicon Fluorine Nitrogen Argon Lithium
4.8 3.0 1.3 0.8 0.6 0.2
Rubidium Phosphorus Iodine Barium Indium Aluminum Iron
0.12 0.07 0.05 0.03 0.02 0.01 0.01
( b y taking t h e actual readings a n d applying necessary corrections because of differences b e t w e e n t e m p e r a t u r e s as registered a n d as read on ship b o a r d ) , a n d tables, slide rules, or pro g r a m e d c o m p u t e r s are used to convert the t e m p e r a t u r e difference to pressure, which, in turn, is converted to d e p t h . W i t h properly functioning ther mometers, this t e c h n i q u e for deter mining d e p t h is reliable to within 5 meters for d e p t h s of less t h a n 100 meters a n d to within a b o u t 0 . 5 % for greater d e p t h s . As w i t h any m e c h a n i c a l device, t h e r m o m e t e r s m a y fail in use, al though p r o b a b l y not more t h a n 2 % of t h e time a n d often not t h a t m u c h , especially at stations (as ocean sam pling locations are k n o w n ) worked d u r i n g good w e a t h e r . T o boost re liability as high as possible, t h e r m o m eters are c h e c k e d rather carefully. Woods Hole for one, for instance, on occasion rejects nine out of 10 sup plied by vendors. Of those accepted, generally two consecutive malfunc tions at sea m a k e it essential to repair a n d recalibrate t h e t h e r m o m e t e r in t h e laboratory ashore. A t t e m p t s h a v e been m a d e to sample water from specific d e p t h s in t h e ocean by d r a w i n g t h e w a t e r directly 12A
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Element Zinc Molybdenum Selenium Copper Arsenic Tin Lead Uranium Vanadium Manganese Titanium Thorium Cobalt Nickel Gallium Cesium Antimony Cerium Yttrium Neon Krypton Lanthanum Silver Bismuth Cadmium
Milligrams per liter
0.01 0.01 0.004 0.003 0.003 0.003 0.003 0.003 0.002 0.002 0.001 0.0007 0.0005 0.0005 0.0005 0.0005 0.0005 0.0004 0.0003 0.0003 0.0003 0.0003 0.0003 0.0002 0.0001
onto t h e ship by m e a n s of a circulat ing p u m p a t t a c h e d to a t u b e placed over t h e ship's side. A t h e r m o m e t e r in t h e line records t e m p e r a t u r e . A m o n g others, Dr. D o n a l d H o o d a n d co-workers of Texas A&M Uni versity (College Station) devised such a system. L o c a t e d on t h e deck of t h e ship is a p u m p w h i c h forces w a t e r u n d e r high pressure t h r o u g h a jet t h a t is placed below t h e sea surface. Theoretically, t h e system is capable of p r o d u c i n g pressure drops at t h e jet d e p t h e q u a l to t h e hydrostatic h e a d of w a t e r at t h e jet. A pressure d r o p of a b o u t 10 atmospheres can b e d e veloped with t h e jet 300 feet below t h e sea surface. Such a p i e s s u r e d r o p is sufficient to raise w a t e r from t h e d e e p e s t regions of t h e sea. Dr. H o o d is able to p u m p substan tial quantities of w a t e r to reservoirs on b o a r d ship for later analyses. For example, h e has gotten t h e following p u m p i n g rates p e r m i n u t e : 25 liters at 10 meters below t h e surface, 20 liters at 600 meters, 15 liters at 1000 meters, a n d 10 liters at 3 4 0 0 meters. T h e effective use of such a system m a y help t h e o c e a n o g r a p h e r by freeing him from a d e p e n d e n c e on sampling bottles while allowing him to take large w a t e r samples for evaluation. THE
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Milligrams per liter
Element Tungsten Germanium Xenon Chromium Beryllium Scandium Mercury Niobium Thallium Helium Gold Praseodymium Gadolinium Dysprosium Erbium
1 1 1 5 5 4 3 Ι Ι 5 4 2 2 2 2
X X X X X X Χ Χ Χ Χ Χ Χ Χ Χ Χ
10 4 10 4 10 4 10 -β 10 5 10 - 5 ΙΟ ΙΟ 10 δ 10 « 10 6 10 7 10 7 10 ' 10 7
Ytterbium
2 Χ 10
Samarium
2 Χ 10
7
Holmium
8 Χ 10
8
Europium
4 Χ ΙΟ-8
Thulium
4 Χ 10
Lutetium
4 Χ 10~8
7
8
Radium
3X10""
Protactinium
2 Χ 10
12
9 Χ ΙΟ"
15
Radon
Submersible p u m p s h a v e also been used, b u t they suffer from t h e effects of pressure w h e n lowered m u c h more than 100 meters below the surface. Additionally, they require an electrical , cable to provide power. T h e cable is not only difficult to h a n d l e at mod erate-to-great d e p t h s b u t is also sub ject to the corrosive effects of the w a t e r a n d to t h e s n a p p i n g a n d tug ging caused by t h e ship's pitching a n d rolling.
Hydrowire
Has Serious
Faults
T h e hydrowire itself poses many problems for the oceanographer. T h e r e are such obvious difficulties as t h e t e n d e n c y of t h e wire to kink, the task of keeping the wire from fouling in the ship's propeller, and the corro sive action of the sea water. T h e main difficulties generally bear in some way on time. For example, the round trip for a plankton net to sample at 5000 meters may take five or so hours, as can water sampling to this same depth. O n e of t h e reasons for the long times involved in the sampling is that t h e wire with its e q u i p m e n t cannot b e allowed to fall freely. In a free fall the motion of the ship may pro d u c e kinks in t h e cable. But an-
other reason is that the hydrowire must be stopped at intervals so that the water sampling devices can be at tached and the releasing mechanisms set. This operation, particularly in bad weather and rough seas, may take several minutes per device. Taking the bottles off takes almost as much time, perhaps even more, because the hydrowire must be hauled in care fully so as not to snap the wire or to foul it in the supporting pulley system.
Equipment malfunctions may on occasion add to the time required for a cast. For example, if the release mechanisms don't work properly, or if squid or jellyfish get caught in the releases, the messengers do not trip all the bottles. In such cases, a recast is needed. Finally, there is the simple matter of caution. The hydrowire loading platform hangs out over the side of the ship; the ship itself is an unsteady
support; and the bottles are both heavy and wet. If oceanographers are not to be faced with tangled hydrowires, there is a limit to the number that can be out at one time at any given station. For sampling near the surface, two lines may be out at once. For sam pling at greater depths—5000 meters and more—usually only one hydrowire can be out. While making such a deep probe, however, the scientists may also carry on other work at shallower levels of, say, a few hundred meters, so that proper planning can reduce the time the ship must stay at any one station when a number of stations are to be worked on the cruise. Many Measurements May Be Made from One Water Sample Offsetting whatever disadvantage the limit on the number of hydrowires imposes is the fact that water from each sample may often be used for a variety of experiments, not simply one single determination. The hydrowire has at least one other major shortcoming: It cannot handle great loads. For example, a wire cord 4 mm. in diameter has a break ing point of about 3200 pounds. The weight in water of 5000 meters of this line plus the customary 100-pound weight used to carry the line down is about 650 pounds. Sometimes on deep casts a gravity-operated coring device is used as the hydrowire weight, so that bottom samples may be obtained as a dividend in the op eration. Since, as a rule, the hydrowire is loaded only to one third to one fifth of its breaking point, the actual sampling load on this wire may be only 400 pounds ( 1 / 3 times 3200 pounds equals about 1050 pounds; subtracting 650 pounds deadweight in water leaves about 400 pounds working weight). The most widely used water sampling device is the Nansen bottle, which weighs about 7.5 pounds in water. Thus only about 50 bottles may be used on a deep cast of 5000 meters. A further restriction is that in bad weather when the ship's motion is in-
CORINGS. Clues to the sedimentary history of the sea floor are gained by studying samples of the floor gotten with coring devices such as this one being lowered over the side of a Woods Hole research vessel C&Ε Ν
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tensified and the strain on the hydrowire increased, fewer than the maximum number of bottles have to be used. As the ship rolls, the hydrowire is subject to rapid accelerations and the extra load added to the system as the wire is dragged through the water. These forces limit the working load that can be placed on the hydrowire. Because of time and weight restrictions, the sampling bottles are widely spaced on the hydrowire with the result that the data are discontinuous. Furthermore, the problem promises to get more acute as the need for larger bottles for larger samples for trace-element or other microquantitative studies develops. One proposal by oceanographers is that plastic lines having about the same density as water be used. Such lines have not yet proved feasible for deep casts. Until new concepts, materials, or equipment evolve, the oceanographer makes the most of the water sampling devices already at hand. From the water samples he collects, the oceanographer makes a whole host of measurements of the concentrations and kinds of inorganic and organic compounds, including gases and solids. Oxygen in Sea Water Is the Most Often Measured Dissolved Gas The amount and kind of gaseous components in sea water are related to the solubility of the gases in the water, and all are relevant to a number of océanographie phenomena such as the accumulation of gases in the swim bladders of deep sea fishes, the metabolic . processes of marine organisms, deep-sea currents, water turbulence, air-water surface exchange, and the like. Knowledge of the gaseous components can be used in identifying the masses of water or in understanding the environment in which chemical and biochemical reactions occur. The most frequently measured gas is oxygen, because it is essential in many biological processes. Furthermore, oxygen levels can be used to trace various bodies of water as they move intact through the ocean systems. In fact the oxygen content of sea water ranks third behind temperature and salinity *as the most often measured hydrographie variable. The measurement of oxygen concentration in sea water is not easy.
For one thing, oxygen reacts with the brass linings of Nansen bottles at high pressures and during the long time needed to haul the bottles from deep casts to the surface. Plastic-lined j?r even all-plastic bottles are often used to overcome this problem. Another problem is that bacteria and other biological systems in the water sample can easily alter the oxygen content of the sample if it is stored for any appreciable time before analysis. Even more basic is the lack of a precise knowledge of the solubility of oxygen in sea water, according to Dr. James Carpenter. This factor is important, for example, in understanding the mass transport of oxygen through the air-water interface of the ocean. The mass transfer of oxygen into the sea is driven by the very small difference in oxygen content between the near-surface waters and those beneath them. Since the near-surface waters of the ocean show only a few per cent deviation from the equilibrium saturation values, inaccuracies in the saturation values may make these waters appear to be oversaturated or undersaturated with respect to oxygen, when the opposite, in fact, may be so. To understand the extent and effectiveness of the movement of oxygen from the atmosphere to the surface water, the equilibrium between the two regions must be determined to within 0.1%. This can be done only if the solubility of oxygen in sea water is precisely known. Winkler Method Widely Used for 02 Most oceanographers use a modified Winkler method to determine the oxygen content of water samples aboard ship as the samples are collected. During the International Geophysical Year (IGY) of 1957-58 the measurements of the oxygen content of sea water ran consistently a few per cent higher on British vessels than on Woods Hole Océanographie Institution vessels working side by side. The British workers used potassium hydrogen iodate to standardize their sodium thiosulfate for the analyses; Woods Hole workers used potassium dichromate. The end result of the analytical method is to titrate iodine released during the reaction and thus to calculate the oxygen content from the io-
dine value. Studies undertaken because of the foregoing discrepancies showed that iodide may be oxidized to iodine during the standardizing of the thiosulfate solution with a standard potassium dichromate solution. This formation of iodine is a photochemical reaction that is enhanced by the highly acid conditions pertaining in the standardization when using potassium dichromate but does not occur when using potassium hydrogen iodate. Since this discovery, Woods Hole routinely uses both methods, partly to give data equivalent to that gotten by others, partly to have a way of comparing its new data with that gotten previously. For many years the choice of the proper standardizing solution has been wrapped in controversy. Some workers have proposed potassium dichromate, some make a case for potassium hydrogen iodate, and still others call for potassium iodate. In an attempt to solve the problem of different oxygen readings in future operations, Dr. Dayton Carritt invited 15 chemical oceanographers from all over the U.S. to come to Woods Hole for one week in December 1962. They were to bring their own equipment, just as though they were going to sea. Under Dr. Carritt's direction they carried out a series of three experiments—one in which each supplied his own standard for standardizing thiosulfate, one in which Dr. Carritt furnished a known standard, and one in which each carried out a complete Winkler analysis of a sea water sample of known oxygen content. In each experiment, the analysts showed good precision individually but rather poor accuracy. From these data and from additional tests, Dr. Carritt feels he can now furnish all chemical oceanographers with evidence that will show how the results of their procedures will compare with results of others and in most cases explain how the differences come about. As a result of his work, the National Academy of Sciences plans to recommend a procedure that will be as free from analyst bias as possible and as precise Scientifically as it is now possible to achieve. Then it will be up to each chemical oceanographer to decide whether to adopt the method himself. Similar programs on the intercalibration and standardization of ocean-
Oceanographer loads sampling gear on the hydrowire while standing in the "bucket," an unsteady perch over the ship's side CHEMISTRY
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Biological systems have a marked effect on element distribution in the ocean
the assumption falls within the precision and accuracy with which nitrogen can be determined. The difference may become significant at some future date when improved techniques permit greater accuracies to be achieved than are possible at present.
WINKLER STANDARDIZATION. Chemical oceanographers, using the equipment they take to sea, compare their procedures for oxygen determination to develop standard procedures of high accuracy
ographic techniques have been sponsored by such organizations as the United Nations Educational, Scientific and Cultural Organization; the Food and Agricultural Organization of the U.N.; the National Institute of Oceanography; the Scientific Committee for Océanographie Research; the Intergovernmental Océanographie Commission, and others. These programs have involved many countries and many methods, including those for oxygen, phosphate, nitrate, photosynthetic pigments, carbon-14 productivity, zooplankton, temperature, salinity, and radiant energy. Values for Gaseous Content of Sea Water Are Generally Unsatisfactory Meanwhile, the accepted values for the gaseous contents as well as other chemical constituents of sea water are usually combinations of the values obtained from the analyses of water samples by many workers from many countries who have used different standards, techniques, and calibrations. For such fundamental parameters as the solubilities in distilled and saline waters of the common atmospheric gases—nitrogen, oxygen, and argon—the data are generally unsatisfactory, according to Dr. Cornelius E. Klots and Dr. Bruce B. Benson in the department of physics at Amherst College. Perhaps, says Johns Hopkins' 16A
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Dr. Carpenter, the real hope for determining gases in sea water, especially oxygen and nitrogen, lies in the effective application of gas chromatography, and, in special situations, mass spectrometry. Already moving in this direction, the U.S. Naval Océanographie Office, the Naval Research Laboratory, and others use gas chromatography to determine both oxygen and nitrogen in the same sea water sample. Sea water samples as small as 2 to 3 ml. are used, and the technique is both precise and accurate. Moisture and carbon dioxide could interfere with detection of oxygen and nitrogen. However, both moisture and carbon dioxide are easily removed from the gas stream. A correction must be applied for argon, which diffuses out of the water sample and forms a peak on the gas chromatogram with oxygen. In an air-saturated sea-water sample the argon content may account for only 5% of the area under the 0 2 -Ar peak. However, where oxygen levels are low or depleted, argon could account for 50 to 100% of the area. Correction is made by assuming that the ratio of argon to nitrogen in sea water is a constant at a specific temperature. This assumption isn't 100% valid, since dissolved nitrogen in sea water may be affected by biological and chemical action. However, the difference in the oxygen value introduced by making
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Electrodes Can Follow
Photosynthesis
Another technique for determining oxygen uses the Kanwisher electrode. This is a platinum electrode separated from the water medium by a layer of polyethylene or Teflon that is permeable to molecular oxygen. Oxygen diffuses through the plastic layer and reacts at the platinum surface to form hydroxyl ions. The hydroxyl ions in turn diffuse through the film of electrolyte behind the membrane to react with silver to form silver oxide. The current passing through the electrode is proportional to the partial pressure of oxygen in the system. The electrode is stable for short periods of time and can be used for either fresh or salt water, in small volumes (1 ml.) or large (55 gallons). The electrodes may also be used in the open sea. In general, oxygen-sensing electrodes must be standardized for nearly every sample. These electrodes, furthermore, have a short life. The electrodes also can be used to follow the extent of photosynthetic activity and respiration in whole plants or plant parts and other organisms. Aerobic plants and other organisms in the dark reduce the oxygen level of their environment as they use up oxygen in respiration. However, photosynthesizing plants evolve oxygen, part of which they use for respiration and the rest of which they release to the environment. Therefore, base-rate respiration may be determined by measuring the oxygen uptake of nonphotosynthesizing organisms at any time and of photosynthesizing organ-
OXYGEN EVOLUTION. The leaf of a Sargasso weed exposed to light generates oxygen which is measured with a Kanwisher electrode to determine photosynthetic capabilities of the plant
isms when they are in the dark. The approximate extent of photosynthesis in photosynthesizing organisms is determined by measuring the net change in oxygen level of the environment and by adding to this net change the baserate oxygen uptake of respiration. Determination of photosynthetic activity in this kind of a system can only be approximate, largely because it cannot include precise corrections for the effects of such things as light, temperature, and carbon dioxide concentration on photosynthesizing organisms, and length of time the organisms have been photosynthesizing. Usually, photosynthesizing organisms are allowed to reach a steady state of respiration in the dark. Light is made available for a short time, the net change in the oxygen level of the environment is measured, and light is removed. Several cycles such as this are averaged, and the approximate photosynthetic rate is calculated from the average figures. An accurate determination of photosynthetic rates requires a more sophisticated approach. Although the Kanwisher electrode may be used to follow the approximate extent of photosynthesis and respiration» in organisms, the data derived from the use of the electrodes must be corrected for the effects of such things as a decrease in current through the electrodes brought about by increased hydrostatic pressures. The curve showing the decrease of current
through the electrode caused by increasing pressure is linear for the first 5000 pounds of pressure, decreasing about 3 % for each 500 pounds or 1000 feet of depth. The curve is no longer linear beyond 5000 pounds, where the rate of change is less than 3 % . The changes due to pressure are related mostly to changes in dissociation constants, solubilities, viscosities, volumes, and the size of the pores in the membrane of the electrode rather than to changes in the permeability of the membrane to oxygen. The electrode can be lowered over the side of the ship at a hydrographie station to record the oxygen profile of the water column. In this use it could supplant Nansen bottle water samples for oxygen analysis. At the very least, the oxygen profile from the Kanwisher or similar electrode could be used as a guide for placing Nansen bottles in all the different regions in the water column. Gaseous Content of Sea Water Is Affected by Biological Processes Oxygen, however, is only one of several dissolved gases in sea water that have biological significance. The sum of the biological processes in sea water can be viewed grossly in terms of photosynthesis (oxygen evolution) and respiration ( oxygen utilization ). Actually, the biochemical processes are considerably more complicated CHEMISTRY
than such a gross view implies. The purely chemical reactions and the metabolic activities of plants, animals, and microorganisms yield a wide variety of end products that result in the consumption of oxygen or, as the case may be, to the restoration of oxygen to the life cycle. End products of oxygen utilization in the sea are mainly carbon dioxide or carbonates, water, sulfate, and nitrate. Oxygen restoration in the euphotic or photosynthetic zone of the sea is mainly through photosynthesis. Some direct oxygen restoration occurs as plants and other organisms take up such nutrients as sulfates and nitrates and release oxygen in the combined form to the life cycle by either aerobic or anerobic processes. There is reason to believe that sulfate-reducing bacteria help to regulate the amount of oxygen in sea water, according to Dr. Claude ZoBell of Scripps Institution of Oceanography. For example, acid production (hydrogen ion release ) by bacteria on the sea floor causes oxygen in limestone and other insoluble carbonates to be released to the sea as carbon dioxide. As the carbon dioxide content of sea water changes, so does the pH of the water system. Thus, in addition to oxygen content, carbon dioxide content of sea water is an important oceanic property. In the open oceans near the surface of the sea, total carbon dioxide (mainly as HC0 3 ~ and to a lesser extent as C03~~) occurs at levels of about 45 ml. per liter compared to about 5 ml. per liter for oxygen. Total carbon dioxide as molecular carbon dioxide plus carbonic acid occurs in the surface waters at levels of about 0.2 ml. per liter. The partial pressure of carbon dioxide in sea water may be measured by equilibrating sea water with a gas phase (helium) and then measuring the carbon dioxide in the equilibrating gas. The partial pressure of carbon dioxide in the equilibrating gas is equal to the partial pressure of carbon dioxide in the water if equilibration is gentle and complete. An infrared analysis gives good resolution down to 1 p.p.m. carbon dioxide in 300 p.p.m. of gas. Surface sea water is generally near equilibrium with air. Because of its Text continues on page 20 A. Overleaf is an artist's sketchbook of typical shipboard océanographie operations AND THE OCEANS
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/
Sketchbook of Some Typical Oceanographi
&->%χΛ
Κ
•^
FRANK MULLINS
^ ^
\%^ A Nansen bottle is at tached to the hydrowirë; (left); a phojtoelectrjfc cell for measuring limit penetration in (the see is readied (lower center); a device to measure photosynthesis /stands by (upper rioht); the hydrowire inclination is checked, oxygejn content of water is determined, the hydrographie winch gets inspected (eight, top to bottom)
t :\
10 ' '
)peratians anjd Equipment Aboard Ship
Υ***?*.. : :•*
physical and chemical properties, carbon dioxide is 25 to 30 times as concentrated in sea water relative to oxygen as it is in air, under near equilibrium conditions. Because of this greater concentration and because carbon dioxide exchanges from sea water to the atmosphere at a rate 1 / 1 5 as fast as does oxygen, some oceanographers think that carbon dioxide may be a better and more stable indicator of recent biological change than is oxygen. Unfortunately, carbon dioxide concentration is influenced by pH and inorganic conditions or processes such as calcium carbonate precipitation and dissolution. 0.1
Greenhouse Effect May Be Causing an Over-All Warming of the Earth Another reason for the oceanographer's interest in the exchange of carbon dioxide between the air and the sea is that the air may contain more C 0 2 because we are burning more fossil fuels. Although data on the greenhouse effect (the warming of the earth because of the heat-trapping effects of increased carbon dioxide in the air) are not yet fully developed, two factors relating to the exchange of carbon dioxide between air and sea are known: • The rate of transfer of carbon dioxide from air to sea is controlled by turbulent processes (wind), evaporation, and radiant cooling in the water, according to Dr. Donald W. Hood and co-workers. The extent of control is exemplified by the fact that turbulent diffusion of carbon dioxide into the sea is about one million times greater than molecular diffusion. • The transfer of carbon dioxide from air to sea is not the limiting factor controlling the residence time (about seven years) of carbon dioxide in the air. However, the relation between the greenhouse effect and the carbon dioxide content and distribution in sea water is not known. In any discussion of the greenhouse effect and its relation to the solubility of carbon dioxide in water, one must also consider the ratio of the naturally occurring isotope of carbon (C 1 4 ) to carbon (C 1 2 ) which is largely supplied from the combustion of fossil fuels. (About 1% of the world-wide total of the carbon isotope C 14 is a byproduct of atom bomb tests; the concentration of C 14 in the surface waters 20A
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0.2
0.3 0.4 0.5
Source:
1 2 3 4 5 Wavelength (microns)
10
20
30 40 50
Von Arx, "Introduction to Physical Oceanography," 1962, Addison-Wesley, Reading, Mass.
GREENHOUSE EFFECT. The earth, warmed by solar radiation, emits infrared radiation which is partially trapped by C02, 03> and water vapor. Increases in atmospheric C0 2 from burning fossil fuels could cause earth's average temperature to increase
of the oceans may be as much as 10% higher than prebomb concentrations.) The burning of fossil fuels adds to the supply of C 12 (as C 1 2 0 2 ) in both the atmosphere and the sea. Yet the amount of C 14 added to the oceans or the atmosphere has been probably nearly constant in both time and space. Thus, a change in the ratio C 1 4 0 2 / C 1 2 0 2 is indicative of the change in atmospheric carbon dioxide attributable to the burning of fossil fuels. Such a change in the ratio was noted by Dr. H. E. Suess of Scripps Institution of Oceanography about eight years ago. The ratio, C 1 4 0 2 / C 1 2 0 2 , has decreased over the 100year period ending in 1950, according to Dr. Suess. However, the values for the Suess Effect, as it is now known, are subject to wide interpretation. For one thing, the exchange of either C 1 4 0 2 or C 1 2 0 2 with organic matter stored in the world's soils has not been evaluated. For another, no acceptable values exist for the differences in the solubility of C 1 4 0 2 and C 1 2 0 2 in sea water. The whole concept of the greenhouse effect is bound up in controversy. Not the least imposant part of the controversy lies in the lack of understanding of how carbon dioxide moves between the ocean reservoir and the atmosphere. The seas contain vast quantities of dissolved gases, and the waters release these gases as bubbles under certain conditions. Bubbles can form in the THE
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surface layer of sea water when the water is saturated with air and when temperature, pressure, salinity, and level of biological activity change. Bubble formation and growth in the surface layer are related primarily to only one gas: oxygen. Visible bubbles probably develop in sea water from invisible microbubbles of oxygen, whose presence is inferred, for example, from the ease with which bubbles form behind a ship's propellers (cavitation). Various Water Movements Affect Bubble Growth The incidence of bubble growth is probably increased by the occurrence of three common ocean phenomena: • The upward movement of subsurface water during the passage of internal waves (although similar to ocean surface waves, internal waves move below the surface and are not visible on it). • Turbulence in the region of a thermocline (the boundary between two layers of water of different temperatures ). • The downward movement of water caused by gravity. Supersaturation of the sea water by oxygen is probably needed for existing microbubbles to grow at depths exceeding a few feet, although not necessary for bubble formation in the surface layer. Such supersaturation
has been reported as high as 170% of the saturation level in the upper 10 feet of sea water (in July and August in shallow water off San Diego, Calif.). Although the true solubility of oxygen in sea water is probably known only to within 5%, the 170% saturation level indicates the magnitude of oxygen supersaturation possible in sea water. As large bubbles form and rise to the surface, a great amount of oxygen may be lost from the surface waters to the air, affecting the biological and chemical systems. It is possible in an area of downwelling that, as gas-saturated water sinks from the surface, the water becomes more than 100% saturated. In sea water, oxygen contents exceeding 100% saturation are commonly found at 10 meters below the surface layer, which itself may be 95 to 100% saturated with respect to oxygen. Also, photosynthetic activity in these lower regions could further increase the degree of saturation. The vertical gradient that then exists leads to an upward molecular diffusion of the excess gas. Océanographie Tools, Techniques, and Instruments Have Evolved Slowly Unfortunately, the difficulty in finding answers to the problems about mass transport, gas solubility, and the like in the sea has been compounded in chemical oceanography by a creeping evolution in tools, techniques, and instrumentation. Chemical oceanography has lagged 50 years behind
other sciences in this regard, Dr. Carritt says. Almost every standard laboratory instrument must be modified in some way for work at sea. However, chemical oceanographers are now beginning to use such modern tools as gas chromatography, neutron activation analysis, mass spectrometry, and the like, so that the gap is narrowing. Our knowledge of the distribution in time and space of many of the trace elements in the sea has been severely limited by sampling techniques available, the lengthy time needed for sampling, the inability to carry out all analyses on the ship, the difficulty in returning to the same spots in the ocean, and the ever-changing nature of the sea. For the most part, the chemical oceanographer does not have any instruments available for in-place measurements—from ocean surface to ocean bottom—of such variables as dissolved gas, pH, nutrient concentration, or salinity. Instead, he must often make his studies on water samples hauled to the surface. These samples, taken hundreds of meters apart on casts to depths of 4000, 6000, or even 10,000 meters, do not give the oceanographer the exact profile of the column of water. Two things militate against the use of submersible instruments: the high accuracy and precision required on the one hand and the low concentrations of dissolved or suspended materials in sea water on the other. What instruments have been developed for in-
place work are mostly for the physical oceanographer, who measures temperature, salinity, density, water depth, wave motion and height, current speed and direction, and the penetration of light and sound. The geological oceanographer uses undersea cameras, corers, and echo sounders to study the ocean floor. And almost by tradition, the biological oceanographer uses various plankton nets, trawls, and sampling bottles to obtain samples of living organisms from the sea. However, the chemical oceanographer is tied either to his ship or shore laboratory. His connection with the sea is through a hydrowire and watersampling devices that are frequently inadequate. He is further restricted by the unusually high accuracy required for routine analysis. This is a restriction which the average chemist does not often have to accept but which is an everyday problem for the chemical oceanographer. Salt Content of Sea Water Continues to Challenge Oceanographers The dissolved salts in the oceans have always been a challenging target for the oceanographer. This is perhaps simply because saltiness is the most obvious sea water quality. Or perhaps it is because the sea is a dilute electrolyte, containing probably every naturally occurring element known or perhaps because the elements in sea water have been in intimate contact for geologic time, reacting in unique or unsuspected ways. The oceans contain, on the average, about 35 parts per thousand (3.5%) dissolved salts. In large part, these dissolved materials have been carried for millions of years into the oceans by rivers draining the land. Although it is not possible to know exactly the rate of chemical denudation of the land masses over the geologic times or even at present, some estimates have recently been made. The present annual rate of chemical denudation from the continents of the world ranges from about six tons per square mile for Australia to about 120 tons per square mile for Europe. On a world-wide basis, the rivers deliver
FILTERING. Sea water is filtered aboard ship to collect biological samples for later C14 determinations
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The precise chemical analysis of sea water is a difficult task about 4.0 billion tons of dissolved material to the sea each year. There is some evidence that a like amount is deposited as sediment; so that insofar as total content is concerned, the oceans are in a steady state with respect to input and outgo. The average concentration of the major constituents in these river waters is ( in parts per million ) : bicarbonate 58.4; calcium 15.0; silica 13.1; sulfate 11.2; chloride 7.8; sodium 6.3; magnesium 4.1; potassium 2.3; nitrate 1.0; and iron 0.67. This represents a total of about 120 p.p.m. for the major dissolved solids. Except for sulfur and carbon, the top 10 elements are so abundant in sea water that biological or physical processes change their concentrations only slightly. So, to measure the effects of these processes, chemists often must perform analyses with precisions at the part-per-10,000 level. The next group of elements—ranging from boron at 4.8 p.p.m. to lithium at 0.2 p.p.m.—are called by some oceanographers the meso-abundant elements. They are affected by biological, chemical, and physical processes in the ocean to the extent that their concentrations can be reduced temporarily anywhere from 10 to 100% (or perhaps more properly to the detection limit for present analytical procedures). The meso-abundant elements occur at such low levels to begin with that the effects of the processes in the sea simply make the analytical problems more difficult. Most difficult of all to determine are the remaining elements, which exist at such low concentrations that analytical techniques must be carefully developed especially for sea water. This problem is illustrated by a story of what went on in a German laboratory after World War I. Germany, saddled with reparation payments and short of gold, thought perhaps it irr'ght extract gold from the sea. With an average concentration of only 0.000004 p.p.m. gold in sea water, the expense of extracting the gold was too great. However, German workers found that samples from an area in the North Sea appeared to have twice the normal content of gold. The hopes of the German chemists were dashed when they learned that the samples were badly contaminated by gold from the frames of the eyeglasses 22A
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worn by the technician when performing the analyses. Although the story may be apocryphal, it is illustrative of the barriers facing chemical oceanographers in their attempts to learn the chemical nature of the oceans. Neutron activation analysis is becoming an important analytical tool of the chemical oceanographer. The method is extremely sensitive and can be used to determine the concentration of elements at levels as low as several parts per billion. The method involves irradiating a sea water sample with neutrons and measuring the resulting radioactivity. The technique is effective for measuring many elements, as elements or in combined form, alone, or in mixtures, and is especially useful to determine trace elements in sea water. Activation analysis has been used with some success to determine the concentration of such trace elements in sea water as arsenic, cesium, gold, manganese, rubidium, strontium, zinc, and the halogens. Biological Systems Vlay Important Role in Movement of Ocean Inclusions The dissolved components become part of the sea water and are moved about by mass transport, diffusion, and biological transportation. Although physical factors (currents, evaporation, and sedimentation) and geochemical factors (volcanic action and chemical reactions) account for much of the changes in concentration of the constituents of sea water, certainly the biological factors are also important. Biologically active materials may move from one water layer to another as particulate organic matter sinks under the force of gravity or rises with upwelling water. Organisms selectively use many of these sea water constituents. As the organisms move about within the water system, the constituents suffer a kind of fractionation. This biological fractionation is distinct from any that may result from water circulation, yet the over-all effects of biological fractionation are conditioned by the gross movements of the water. Organisms affect the constituents of sea water both by synthesis (assimilation) and decomposition (metabolism or fecal deposition, either directly or through predators). This
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passage of elements from the water through living organisms and back to the water is termed the biomass cyclic system. However, the biomass is not static in either time or place because of the mobility of the organisms or because of marked or rapid environmental changes. Thus, considerations of the effect of the biomass on the sea are based on studies of biologic activity in large masses that are statistically uniform. The total concentration of dissolved organic compounds in sea water ranges between 10 mg. per liter near the shores and 0.1 mg. per liter in the isolated water masses of intermediate to great depth. These organic compounds range from the nonpolar aliphatic hydrocarbons to the highly polar polyfunctional acids or alcohols. They range in size from such small molecules as methane to large polymers such as enzymes and polysaccharides. The problems of sampling, low concentration, and contamination are major hurdles to chemical oceanographers in their studies on the components of sea water. Thus the major part of the dissolved organic material in the ocean, but especially in the deep water has still not been identified. Soluble organic materials (the organic matter that passes through a 0.45-micron Millipore filter) have chemical and biological importance for at least the following reasons: • They are a source of energy for algae, bacteria, and invertebrates. • They are growth stimulators ( vitamin B 32 , thiamine, auxins) in part for larvae, algae, and bacteria. • They may be toxins or growth inhibitors, killing or inhibiting entire populations or, perhaps, excluding one or two species. • They may serve as complexing materials for iron, manganese, phosphate, zinc, and other such trace elements. X The photosynthetic processes take place largely in the euphotic zoneusually the top 100 meters of the ocean—probably the maximum depth to which sufficient light penetrates for photosynthesis to equal the respiration of the biomass even in very clear Text continues on page 26A
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PLANKTON NET. Large, fine-mesh nets are lowered to sampling depth where a messenger triggers an open ing mechanism. The net is pulled through the sampling zone, then closed before be ing hauled to the surface
FRANK MULLIN'S
SHIP'S LAB. (Overleaf) This painting gives the artist's im pressions of the arduous jobs of sampling, analyzing, record ing, and calculating in a crowded and hot lab aboard a rocking, pitching ship
