Physical Geography Of The Sea 1855/8
CHAPTER VIII. — THE SALTS OF THE SEA.
What the Salt in Sea Water has to do with the Currents in the Ocean, § 289. — Reasons for supposing the Sea to have its system of Circulation, 290. — Arguments furnished by Coral Islands, 293. — What would be the Effect of no system of Circulation for Sea Water? 295. — Its Components, 297. — The principal Agents from which Dynamical Force in the Sea is derived, 300. — Illustration, 302. — Sea and Fresh Water have different Laws of Expansion, 308. — The Gulf Stream could not exist in a Sea of fresh Water, 309. — The effect of Evaporation in producing Currents, 310. — How the Polar Sea is supplied with Salt, 323. — The Influence of this under Current upon open Water in the Frozen Ocean, 326. — Sea Shells: The Influence exerted by them upon Currents, 330. — Order among them, 335. — They assist in regulating Climates, 336. — How Sea Shells and Salts act as Compensations in the Machinery by which Oceanic Circulation is conducted, 339. — Whence come the Salts of the Sea? 344.
288. IN order to comprehend aright the currents of the sea, and to study with advantage its physical adaptations, it is necessary to understand the effects produced by the salts of the sea upon the equilibrium of its waters; for wherever equilibrium be destroyed, whether in the air or water (§ 276), it is restored by motion, and motion among fluid particles gives rise to currents, which, in turn, constitute circulation. This chapter is therefore added as a sort of supplement, which will assist us in elucidating what has been advanced concerning the currents of the sea.
289. The question is often asked, “Why is the sea salty?” I think it can be shown that the circulation of the ocean depends, in a great measure, upon the salts of sea water; certainly its influences upon climate are greatly extended by reason of its saltness. As a general rule, the sea is nearly of a uniform degree of saltness, and the constituents of sea water are as constant in their proportions as are the components of the atmosphere. It is true that we sometimes come across arms of the sea, or places in the ocean, where we find the water more salt or less salt than sea
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water is generally; but this circumstance is due to local causes of easy explanation. For instance: when we come to an arm of the sea, as the Red Sea (§ 238), upon which it never rains, and from which the atmosphere is continually abstracting, by evaporation, fresh water from the salt, we may naturally expect to find a greater proportion of salt in the sea water that remains than we do near the mouth of some great river, as the Amazon, or in the regions of constant precipitation, or other parts where it rains more than it evaporates. Therefore we do not find sea water from all parts of the ocean actually of the same degree of saltness, yet we do find, as in the case of the Red Sea, sea water that is continually giving off to evaporation fresh water in large quantities; nevertheless, for such water there is a degree, and a very moderate degree, of saltness which is a maximum; and we moreover find that, though the constituents of sea water, like those of the atmosphere, are not for every place invariably the same as to their proportions, yet they are the same, or nearly the same, as to their character.
290. When, therefore, we take into consideration the fact that, as a general rule, sea water is, with the exceptions above stated, every where and always the same, and that it can only be made so by being well shaken together, we find grounds on which to base the conjecture that the ocean has its system of circulation, which is probably as complete and not less wonderful than is the circulation of blood through the human system.
In order to investigate the currents of the sea, and to catch a glimpse of the laws by which the circulation of its waters is governed, hypothesis, in the present meagre state of absolute knowledge with regard to the subject, seems to be as necessary to progress as is a corner-stone to a building. To make progress with such investigations, we want something to build upon. In the absence of facts, we are sometimes permitted to suppose them; only, in supposing them, we should take not only the possible, but the probable; and in making the selection of the various hypotheses which are suggested, we are bound to prefer that one by which the greatest number of phenomena can be reconciled. When we have found, tried, and offered such an one, we are entitled to claim for it a respectful consideration at least, until we discover it leading us into some palpable absurdity, or until some other hypothesis be suggested which
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will account equally as well, but for a greater number of phenomena. Then, as honest searchers after truth, we should be ready to give up the former, adopt the latter, and to try it until some other better than either of the two be offered.
291. With this understanding, I venture to offer an hypothesis with regard to the agency of the salts or solid matter of the sea in imparting dynamical force to the waters of the ocean, and to suggest that one of the purposes which, in the grand design, it was probably intended to accomplish by having the sea salt, and not fresh, was to impart to its waters the forces and powers necessary to make their circulation complete.
In the first place, we do but conjecture when we say that there is a set of currents in the sea by which its waters are conveyed from place to place with regularity, certainty, and order. But this conjecture appears to be founded on reason; for if we take a sample of water which shall fairly represent, in the proportion of its constituents, the average water of the Pacific Ocean, and analyze it, and if we do the same by a similar sample from the Atlantic, we shall find the analysis of the one to resemble that of the other as closely as though the two samples had been taken from the same bottle after having been well shaken. How, then, shall we account for this, unless upon the supposition that sea water from one part of the world is, in the process of time, brought into contact and mixed up with sea water from all other parts of the world? Agents, therefore, it would seem, are at work, which shake up the waters of the sea as though they were in a bottle, and which, in the course of time, mingle those that are in one part of the ocean with those that are in another as thoroughly and completely as it is possible for man to do in a vessel of his own construction.
292. This fact, as to uniformity of components, appears to call for the hypothesis that sea water which to-day is in one part of the ocean, will, in the process of time, be found in another part the most remote. It must, therefore, be carried about by currents; and as these currents have their offices to perform in the terrestrial economy, they probably do not flow by chance, but in obedience to physical laws; they no doubt, therefore, maintain the order and preserve the harmony which characterize every department of God’s handiwork, upon the threshold of which man has as yet been permitted to stand, to observe, and to comprehend.
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293. Nay, having reached this threshold, and taken a survey of the surrounding ocean, we are ready to assert, with all the confidence of knowledge, that the sea has a system of circulation for its waters. We rest this assertion upon our faith in the physical adaptations with which the sea is invested. Take, for example, the coral islands, reefs, beds, and atolls with which the Pacific Ocean is studded and garnished. They were built up of materials which a certain kind of insect quarried from the sea water. The currents of the sea ministered to this little insect — they were its hod carriers; when fresh supplies of solid matter were wanted for the coral rock upon which the foundations of the Polynesian Islands were laid, they brought them; the obedient currents stood ready with fresh supplies in unfailing streams of sea water from which the solid ingredients had not been secreted. Now, unless the currents of the sea had been employed to carry off from this insect the waters that had been emptied by it of their lime, and to bring to it others charged with more, it is evident the little creature would have perished for want of food long before its task was half completed. But for currents, it would have been impaled in a nook of the very drop of water in which it was spawned; for it would have soon secreted the lime contained in this drop of water, and then, without the ministering aid of currents to bring it more, it would have perished for the want of food for itself and materials for its edifice; and thus, but for the benign currents which took this exhausted water away, there we perceive this emptied drop would have remained, not only as the grave of the little architect, but as a monument in attestation of the shocking monstrosity that there had been a failure in the sublime system of terrestrial adaptations — that the sea had not been adapted by its Creator to the well-being of all its inhabitants. Now we do know that its adaptations are suited to all the wants of every one of its inhabitants — to the wants of the coral insect as well as to those of the whale. Hence we say we know that the sea has its system of circulation, for it transports materials for the coral rock from one part of the world to another; its currents receive them from the rivers, and hand them over to the little mason for the structure of the most stupendous works of solid masonry that man has ever seen — the coral islands of the sea.
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294. And thus, by a process of reasoning which is perfectly philosophical, we are irresistibly led to conjecture that there are regular and certain, if not appointed channels, through which the water travels from one part of the ocean to another, and that those channels belong to an arrangement which may make, and, for aught we know to the contrary, which does make the system of oceanic circulation as complete, as perfect, and as harmonious as is that of the atmosphere or the blood. Every drop of water in the sea is as obedient to law and order as are the members of the heavenly host in the remotest regions of space. For when the morning stars sang together in the almighty anthem, “the waves also lifted up their voice;” and doubtless, therefore, the harmony in the depths of the ocean is in tune with that which comes from the spheres above. We can not doubt it; for, were it not so, were there no channels of circulation from one ocean to another, and if, accordingly, the waters of the Atlantic were confined to the Atlantic, or if the waters of the arms and seas of the Atlantic were confined to those arms and seas, and had no channels of circulation by which they could pass out into the ocean, and traverse different latitudes and climates — if this were so, then the machinery of the ocean would be as incomplete as that of a watch without a balance-wheel; for the waters of these arms and seas would, as to their constituents, become, in the process of time, very different from the sea waters in other parts of the world, and their inhabitants would perish for the want of brine of the right strength or of water of the right temperature.
295. For instance, take the Red Sea and the Mediterranean by way of illustration. Upon the Red Sea there is no precipitation; it is a rainless region; not a river runs down to it, not a brook empties into it; therefore there is no’ process by which the salts and washings of the earth, which are taken up and held in solution by rain or river water, can be brought down into the Red Sea. Its salts come from the ocean, and the air takes up from it, in the process of evaporation, fresh water, leaving behind all the solid matter which this sea holds in solution (§ 239).
296. On the other hand, numerous rivers discharge into the Mediterranean, some of which are filtered through soils and among
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minerals which yield one kind of salts or soluble matter, another river runs through a limestone or volcanic region of country, and brings down in solution solid matter — it may be common salt, sulphate or carbonate of lime, magnesia, soda, potash, or ironeither or all may be in its waters. Still, the constituents of sea water from the Mediterranean and of sea water from the Red Sea are quite the same. But the waters of the Dead Sea have no connection with those of the ocean; they are cut off from its channels of circulation, and are therefore quite different, as to their components, from any arm, frith, or gulf of the broad ocean. Its inhabitants are also different from those of the high seas.
297. “The solid constituents of sea water amount to about 32 per cent. of its weight, or nearly half an ounce to the pound. Its saltness may be considered as a necessary result of the present order of things. Rivers which are constantly flowing into the ocean contain salts, varying from ten to fifty, and even one hundred grains per gallon. They are chiefly common salt, sulphate and carbonate of lime, magnesia* soda, potash, and iron; and these are found to constitute the distinguishing characteristics of sea water. The water which evaporates from the sea is nearly pure, containing but very minute traces of salts. Falling as rain upon the land, it washes the soil, percolates through the rocky layers, and becomes charged with saline substances, which are borne seaward by the returning currents. The ocean, therefore, is the great depository of every thing that water can dissolve and carry down from the surface of the continents; and, as there is no channel for their escape, they of course consequently accumulate.”
298. “The case of the sea,” says Fowner, “is but a magnified representation of what occurs in every lake into which rivers flow, but from which there is no outlet except by evaporation. Such a lake is invariably a salt lake. It is impossible that it can be otherwise; and it is curious to observe that this condition disappears when an artificial outlet is produced for the waters.”
299. How, therefore, shall we account for this sameness of compound, this structure of coral (§ 293), this stability as to animal life in the sea, but upon the supposition of a general system of circulation in the ocean, by which, in process of time, water from one part is conveyed to another part the most remote, and *
- See Appendix E.
- Youmans’s Chemistry
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by which a general interchange and commingling of the waters take place? In like manner, the constituents of the atmosphere, whether it be analyzed at the equator or the poles, are the same. By cutting off and shutting up from the general channels of circulation any portion of sea water, as in the Dead Sea, or of at mospheric air, as in mines or wells, we can easily fill either with gases or other matter that shall very much affect its character, or alter the proportion of its ingredients, and affect the health of its inhabitants.
300. The principal agents that are supposed to be concerned in giving circulation to the atmosphere, and in preserving the ratio among its components, are light, heat, electricity, and magnetism (§ 231). But with regard to the sea, it is not known what office is performed by electricity and magnetism, in giving dynamical force to its waters in their system of circulation. The chief motive power from which marine currents derive their velocity has been ascribed to heat; but a close study of the agents concerned has suggested that an important — nay, a powerful and active agency in the system of oceanic circulation is derived from the salts of the sea water, through the instrumentality of the winds, of marine plants, and animals. These give the ocean great dynamical force.
301. Let us, for the sake of illustrating and explaining this force, suppose the sea in all its parts — in its depths and at the surface, at the equator and about the poles — to be of one uniform temperature, and to be all of fresh water; and, moreover, that there be neither wind to disturb its surface, nor tides nor rains to raise the level in this part, or to depress it in that. In this case, there would be nothing of heat to disturb its equilibrium, and there would be no motive power (§ 288) to beget currents, or to set the water in motion by reason of the difference of level or of specific gravity due to water at different densities and temperatures.
302. Now let us suppose the winds, for the first time since the creation, to commence to blow upon this quiescent sea, and to ruffle its surface; they, by their force, would create partial surface currents, and thus agitating the waters to a certain depth, would give rise to a feeble and partial aqueous circulation in the supposed sea of fresh water.
303. This, then, is one of the sources whence power is given to the system of oceanic circulation; but, though a feeble one, it is one which exists in reality, and, therefore, need not be regarded as hypothetical.
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304. Let us next call in evaporation and precipitation, with heat and cold — more powerful agents. Suppose the evaporation to commence from this imaginary fresh-water ocean, and to go on as it does from the seas as they are. In those regions, as in the trade-wind regions, where evaporation is in excess of precipitation (§ 126), the general level of this supposed sea would be altered, and, immediately, as much water as is carried off by evaporation would commence to flow in from north and south toward the trade-wind or evaporating region, to restore the level.
305. On the other hand, the winds have taken this vapor, borne it off to the extra-tropical regions, and precipitated it (§ 129), we will suppose, where precipitation is in excess of evaporation. Here is another alteration of sea level by elevation instead of by depression; and hence we have the motive power for a surface current from each pole toward the equator, the object of which is only to supply the demand for evaporation in the trade-wind regions — demand for evaporation being taken here to mean the difference between evaporation and precipitation for any part of the sea.
306. Now imagine this sea of uniform temperature (§ 301) to be suddenly stricken with the invisible wand of heat and cold, and its waters brought to the various temperatures at which they at this instant are standing. This change of temperature would make a change of specific gravity in the waters, which would destroy the equilibrium of the whole ocean, upon which (§ 275) a set of currents (§ 277) would immediately commence to flow, viz., a current of cold and heavy water to the warm, and a current of warm and lighter to the cold. The motive power of these would be difference of specific gravity due to difference of temperature in fresh water.
307. We have now traced (§ 303 and 306) the effect of two agents, which, in a sea of fiesh water, would tend to create currents, and to beget a system of aqueous circulation; but a set of currents and a system of circulation which, it is readily perceived would be quite different from those which we find in the salt sea. One of these agents would be employed (§ 305) in restoring, by means of one or more polar currents, the water that is taken from one part of the ocean by evaporation, and deposited in another by
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precipitation. The other agent would be employed in restoring, by the forces due difference of specific gravity (§ 306), the equilibrium, which has been disturbed by heating, and of course ex panding, the waters of the torrid zone on one hand, and by cooling, and consequently contracting, those of the frigid zone on the other. This agency would, if it were not modified by others, find expression in a system of currents and counter currents, or rather in a set of surface currents of warm and light water, from the equator toward the poles, and in another set of under currents of cooler, dense, and heavy water from the poles toward the equator.
308. Such, keeping out of view the influence of the winds, which we may suppose would be the same, whether the sea were salt or fresh, would be the system of oceanic circulation were the sea all of fresh water. But fresh water, in cooling, begins to expand near the temperature of 40º, and expands more and more till it reaches the freezing point, and ceases to be fluid. This law of expansion by cooling would impart a peculiar feature to the system of oceanic circulation were the waters all fresh, which it is not necessary to notice further than to say it can not exist in seas of salt water, for salt water (§ 31) contracts as its temperature is lowered to its freezing point. Hence, in consequence of its salts, changes of temperature derive increased power to disturb the equilibrium of the ocean.
309. If this train of reasoning be good, we may infer that, in a system of oceanic circulation, the dynamical force to be derived from difference of temperature, where the waters are all fresh, would be quite feeble; and that, were the sea not salt, we should probably have no such current in it as the Gulf Stream.
So far we have been reasoning hypothetically, to show what would be the chief agents, exclusive of the winds, in disturbing the equilibrium of the ocean, were its waters fresh and not salt. And whatever disturbs equilibrium there may be regarded as the primum mobile in any system of marine currents.
Let us now proceed another step in the process of explaining and illustrating the effect of the salts of the sea in the system of oceanic circulation. To this end, let us suppose this imaginary ocean of fresh water suddenly to become that which we have, viz., an ocean of salt water, which contracts as its temperature is lowered (§ 308) till it reaches 280 or thereabout.
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310. Let evaporation now commence in the trade-wind region, as it was supposed to do (§ 304) in the case of the fresh-water seas, and as it actually goes on in nature — and what takes place? Why; a lowering of the sea level, as before. But as the vapor of salt water is fresh, or nearly so, fresh water only is taken up from the ocean; that which remains behind is therefore more salt. Thus, while the level is lowered in the salt sea, the equilibrium is destroyed because of the saltness of the water; for the water that remains after the evaporation takes place is, on account of the solid matter held in solution, specifically heavier than it was before any portion tf it was converted into vapor.
311. The vapor is taken from the surface water; the surface water thereby becomes more salt, and, under certain conditions, heavier; when it becomes heavier, it sinks; and hence we have, due to the salts of the sea, a vertical circulation, viz., a descent of heavier — because salter and cooler water from the surface, and an ascent of water that is lighter — because it is not so salty from the depths below.
312. This vapor, then, which is taken up from the evaporating regions (§ 126), is carried by the winds through their channels of circulation, and poured back into the ocean where the regions of precipitation are; and by the regions of precipitation I mean those parts of the ocean, as in the polar basins, where the ocean receives more fresh water in the shape of rain, snow, &c., than it returns to the atmosphere in the shape of vapor.
313. In the precipitating regions, therefore, the level is destroyed, as before explained, by elevation; and in the evaporating regions, by depression; which, as already stated (§ 305), gives rise to a system of surface currents, moved by gravity alone, from the poles toward the equator. But we are now considering the effects of evaporation and precipitation in giving impulse to the circulation of the ocean where its waters are salt.
314. The fresh water that has been taken from the evaporating regions is deposited upon those of precipitation, which, for illustration merely, we will locate in the north polar basin. Among the sources of supply of fresh water for this basin we must include not only the precipitation which takes place over the basin itself, but also the amount of fresh water discharged into it by the rivers of the great hydrographical basins of Arctic Europe, Asia, and America.
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315. This fresh water, being emptied into the Polar Sea and agitated by the winds, becomes mixed with the salt; but as the agitation of the sea by the winds extends to no great depth (§ 302), it is only the upper layer of salt water, and that to a moderate depth, which becomes mixed with the fresh. The specific gravity of this upper layer, therefore, is diminished just as much as the specific gravity of the sea water in the evaporating regions was increased. And thus we have a surface current of saltish water from the poles toward the equator, and in under current of water salter and heavier from the equator to the poles. This under current supplies, in a great measure, the salt which the upper current, freighted with fresh water from the clouds and rivers, carries back.
316. Thus it is to the salts of the sea that we owe that feature in the system of oceanic circulation which causes an under current to flow from the Mediterranean into the Atlantic (§ 252), and another (§ 245) from the Red Sea into the Indian Ocean. And it is evident, since neither of these seas is salting up, that just as much, or nearly just as much salt as the under current brings out, just so much the upper currents carry in.
317. We now begin to perceive what a powerful impulse is derived from the salts of the sea in giving effective and active circulation to its waters.
318. Hence we infer that the currents of the sea, by reason of its saltness, attain their maximum of volume and velocity. Hence, too, we infer that the transportation of warm water from the equator toward the frozen regions of the poles, and of cold water from the frigid toward the torrid zone, is facilitated; and consequently here, in the saltness of the sea, have we not an agent by which climates are mitigated by which they are softened ard rendered much more salubrious than it would be possible for them to be were the waters of the ocean deprived of their property of saltness?
319. This property of saltness imparts to the waters of the ocean another peculiarity, by which the sea is still better adapted for the regulation of climates, and it is this: by evaporating fresh water from the salt in the tropics, the surface water becomes heavier than the average of sea water (§ 127). This heavy water
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is also warm water; it sinks, and being a good retainer, but a bad conductor of heat, this warm water is employed in transport ing through under currents heat for the mitigation of climates in far-distant regions. Now this also is a property which a sea of fresh water could not have. Let the winds take up their vapor from a sheet of fresh water, and that at the bottom is not disturbed, for there is no change in the specific gravity of that at the surface by which that at the bottom may be brought to the top; but let evaporation go on, though never so gently, from salt water, and the specific gravity of that at the top will soon be so changed as to bring that from the very lowest depths of the sea speedily to the top.
320. If these inferences as to the influence of the salts upon the currents of the sea be correct, the same cause which produces an under current from the Mediterranean, and an under current rom the Red Sea into the ocean, should produce an under current from the ocean into the north Polar basin. In each case, the hypothesis with regard to the part performed by the salt, in giving vigor to the system of oceanic circulation, requires that, counter to the surface current of water with less salt, there should be an under current of water with more salt in it. That such is the case with regard both to the Mediterranean and the Red Sea, has been amply shown in other parts of this work (§ 252 and 239), and abundantly proved by other observers.
321. That there is a constant current setting out of the Arctic Ocean through Davis’s and other straits thereabout, which connect it with the Atlantic Ocean, is generally admitted. Lieutenant De Haven, United States Navy, when in command of the American expedition in search of Sir John Franklin, was frozen up with his vessels in the main channel of Wellington Straits; and during the nine months that he was so frozen, his vessels, holding their place in the ice, were drifted with it bodily for more than a thousand miles toward the south. The ice in which they were bound was of sea water, and the currents by which they were drifted were of sea water — only, it may be supposed, the latter were not quite so salt as the sea water generally is. The same phenomenon is repeated in the Sound, where (§ 252) an under current of salt water runs in, and an upper current of brackish water (§ 36 and 51) runs out.
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322. Then, since there is salt always flowing out of the north polar basin, we infer that there must be salt always flowing into it, else it would either become fresh, or the whole Atlantic Ocean would be finally silted up with salt. It might be supposed, were there no evidence to the contrary, that this salt was supplied to the Polar seas from the Atlantic around North Cape, and from the Pacific through Bering’s Straits, and through no other channels.
323. But, fortunately, Arctic voyagers, who have cruised in the direction of Davis’s Straits, have afforded us, by their observations (§ 281), proof positive as to the fact of this other source for supplying the Polar seas with salt. They tell us of an under current setting from the Atlantic toward the Polar basin. They describe huge icebergs, with tops high up in the air, and of course the bases of which extend far down into the depths of the ocean, ripping and tearing their way, with terrific force and awful violence, through the surface ice or against a surface current, on their way into the Polar basin.
Passed Midshipman S. P. Griffin, who commanded the brig Rescue in the American searching expedition after Sir John Franklin, informs me that, on one occasion, the two vessels were endeavoring, when in Baffin’s Bay, to warp up to the northward against a strong surface current, which of course was setting to the south; and that while so engaged, an iceberg, with its top many feet above the water, came “drifting up” from the south, and passed by them “like a shot.” Although they were stemming a surface current against both the berg and themselves, such was the force and velocity of the under current, that it carried the berg to the northward faster than the crew could warp the vessel against a surface but counter current. Captain Duncan, master of the English whale-ship Dundee, says, at page 76 of his interesting little narrative:*
“December 18th (1826). It was awful to behold the immense icebergs working their way to the northeast from us, and not one drop of water to be seen; they were working themselves right through the middle of the ice.”
And again, at page, &c.
Arctic Regions; Voyage to Davis’s Strait, by Dorea Duncan, Master of the Ship Dundee, 1826,1827.
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“February 23d. Latitude 68º 37’ north, longitude about 63º west.
“The dreadful apprehensions that assailed us yesterday, by the near approach of the iceberg, were this day most awfully verified. About three P.M., the iceberg came in contact with our floe, and in less than one minute it broke the ice; we were frozen in quite close to the shore; the floe was shivered to pieces for several miles, causing an explosion like an earthquake, or one hundred pieces of heavy ordnance fired at the same moment. The iceberg, with awful but majestic grandeur (in height and dimensions resembling a vast mountain), came almost up to our stern, and everyone expected it would have run over the ship.....
“The iceberg, as before observed, came up very near to the stern of our ship; the intermediate space between the berg and the vessel was filled with heavy masses of ice, which, though they had been previously broken by the immense weight of the berg, were again formed into a compact body by its pressure. The berg was drifting at the rate of about four knots, and by its force on the mass of ice, was pushing the ship before it, as it appeared, to inevitable destruction.”
“Feb. 24th. The iceberg still in sight, but driving away fast to the northeast.”
“Feb. 25th. The iceberg that so lately threatened our destruction had driven completely out of sight to the northeast from us.”
324. Now, then, whence, unless from the difference of specific gravity due sea water of different degrees of saltness, can we derive a motive power with force sufficient to give such tremendous masses of ice such a velocity?
325. What is the temperature of this under current? Be that what it may, it is probably above the freezing point of sea water. Suppose it to be at 32º. (Break through the ice in the northern seas, and the temperature of the surface water is always 28º. At least Lieutenant De Haven so found it in his long imprisonment, and it may be supposed that, as it was with him, so it generally is.) Assuming, then, the water of the surface current which runs out with the ice to be all at 28º, we observe that it is not unreasonable to suppose that the water of the under current, inasmuch as it comes from the south, and therefore from warmer latitudes.
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is probably not so cold; and if it be not so cold, its temperature, before it comes out again, must be reduced to 28º, or whatever be the average temperature of the outer but surface current. Moreover, if it be true, as some philosophers have suggested, that there is in the depths of the ocean a line from the equator to the poles along which the water is of the same temperature all the way; then the question may be asked, should we not have in the depths of the ocean a sort of isothermal floor, as it were, on the upper side of which all the changes of temperature are due to agents acting from above, and on the lower side of which, the changes, if any, are due to agents acting from below?
326. This under Polar current water, then, as it rises to the top, and is brought to the surface by the agitation of the sea in the Arctic regions, gives out its surplus heat and warms the atmosphere there till the temperature of this warm under current water is lowered to the requisite degree for going out on the surface. Hence the water-sky of those regions.
327. And the heat that it loses in falling from its normal temperature, be that what it may, till it reaches the temperature of 28º, is so much caloric set free in the Polar regions, to temper the air and mitigate the climate there. Now is not this one of those modifications of climate which may be fairly traced back to the effect of the saltness of the sea in giving energy to its circulation? Moreover, if there be a deep sea in the Polar basin, which serves as. a receptacle for the waters brought into it by this under current, which, because it comes from toward the equatorial regions, comes from a milder climate, and is therefore warmer, we can easily imagine why there might be an open sea in the Polar regions — why Lieutenant De Haven, in his instructions, was directed to look for it; and why both he and Captain Penny, of one of the English searching vessels, found it there.
328. And in accounting for this polynia, we see that its existence is not only consistent with the hypothesis with which we set out, touching a perfect system of oceanic circulation, but that it may be ascribed, in a great degree at least, if not wholly, to the effect produced by the salts of the sea upon the mobility and circulation of its waters. Here, then, is an office which the sea performs in the economy
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of the universe by virtue of its saltness, and which it could not perform were its waters altogether fresh. And thus philosophers have a — clue placed in — their hands which will probably guide them to one of the many hidden reasons that are embraced in the true answer to the question, “Why is the sea salty?”
329. SEA SHELLS. — We find in sea water other matter besides common salt. Lime is dissolved by the rains and the rivers, and emptied in vast quantities into the ocean. Out of it, coral islands and coral reefs of great extent — marl-beds, shell-banks, and infusorial deposits of enormous magnitude have been constructed by the inhabitants of the deep. These creatures are endowed with the power of secreting, apparently for their own purposes only, solid matter, which the waters of the sea hold in solution. But this power was given to them that they also might fulfill the part assigned them in the economy of the universe. For to them, probably, has been allotted the important office of assisting in giving circulation to the ocean, of helping to regulate the climates of the earth, and of preserving the purity of the sea.
330. The better to comprehend how such creatures may influence currents and climates, let us suppose the ocean to be perfectly at rest — that throughout, it is in a state of complete equilibrium — that, with the exception of those tenants of the deep which have the power of extracting from it the solid matter held in solution, there is no agent in nature capable of disturbing that equilibrium — and that all these fish, &c., have suspended their secretions, in order that this state of a perfect aqueous equilibrium and repose throughout the sea might be attained. In this state of things — the waters of the sea being in perfect equilibrium — a single mollusk or coralline, we will suppose, commences his secretions, and abstracts from the sea water (§ 293) solid matter for his cell. In that act, this animal has destroyed the equilibrium of the whole ocean, for the specific gravity of that portion of water from which this solid matter has been abstracted is altered. Having lost a portion of its solid contents, it has become specifically lighter than it was before; it must, therefore, give place to the pressure which the heavier water exerts to push it aside and to occupy its place, and it must consequently travel about and mingle with the waters of the other parts of the ocean until its proportion of solid matter is returned to it, and until it attains the exact degree of specific gravity due sea water generally.
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331. How much solid matter does the whole host of marine plants and animals abstract from sea water daily? Is it a thousand pounds, or a thousand millions of tons? No one can say. But, whatever be its weight, it is so much of the power of gravity applied to the dynamical forces of the ocean. And this power is derived from the salts of the sea, through the agency of sea-shells and other marine animals, that of themselves scarcely possess the power of locomotion. Yet they have power to put the whole sea in motion, from the equator to the poles, and from top to bottom.
332. Those powerful and strange equatorial currents (§ 270), which navigators tell us they encounter in the Pacific Ocean, to what are they due? Coming from sources unknown, they are lost in the midst of the ocean. They are due, no doubt, to some extent, to the effects of precipitation and evaporation, and the change of heat produced thereby. But we have yet to inquire, How far may they be due to the derangement of equilibrium arising from the change of specific gravity caused by the secretions of the myriads of marine animals that are continually at work in those parts of the ocean? These abstract from sea water solid matter enough to build continents of. And, also, we have to inquire as to the extent to which equilibrium in the sea is disturbed by the salts which evaporation leaves behind. Thus, when we consider the salts of the sea in one point of view, we see the winds and the marine animals operating upon the waters, and, in certain parts of the ocean, deriving from the solid contents of the same those very principles of antagonistic forces which hold the earth in its orbit, and preserve the harmonies of the universe. In another point of virw, we see how the sea-breeze and the sea-shell, in performing their appointed offices, act so as to give rise to a reciprocating motion in the waters; and thus they impart to the ocean dynamical forces also for its circulation.
333. The sea-breeze plays upon the surface; it converts only fresh water into vapor, and leaves the solid matter behind. The surface water thus becomes specifically heavier, and sinks. On the other hand, the little marine architect below, as he works upon his coral edifice at the bottom, extracts from the water
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there a portion of its solid contents; it therefor, becomes specifically lighter, and up it goes, ascending to the top with increased velocity, to take the place of the descending column, which, by the action of the winds, has been sent down loaded with fresh food and materials for the busy little mason in the depths below.
334. Seeing, then, that the inhabitants of the sea, with their powers of secretion, are competent to exercise at least some degree of influence in disturbing equilibrium, are not these creatures entitled to be regarded as agents which have their offices to perform in the system of oceanic circulation, and do not they belong to its physical geography? It is immaterial how great or how small that influence may be supposed to be; for, be it great or small, we may rest assured it is not a chance influence, but it is an influence exercised — if exercised at all — by design, and according to the commandment of Him whose “voice the winds and the sea obey.” Thus God speaks through sea-shells to the ocean.
335. It may therefore be supposed that the arrangements in the economy of nature are such as to require that the various kinds of marine animals, whose secretions are calculated to alter the specific gravity of sea water, to destroy its equilibrium, to beget currents in the ocean, and to control its circulation, should be distributed according to order.
336. Upon this supposition — the like of which nature warrants throughout her whole domain — we may conceive how the marine animals of which we have been speaking may impress other features upon the physical relations of the sea by assisting also to regulate climates, and to adjust the temperature of certain latitudes. For instance, let us suppose the waters in a certain part of the torrid zone to be 70º, but, by reason of the fresh water which has been taken from them in a state of vapor, and consequently by reason of the proportionate increase of salts, these waters are heavier than waters that may be cooler, but not so salt (§ 35). This being the case, the tendency would be for this warm, but salt and heavy water, to flow off as an under current toward the Polar or some other regions of lighter water. Now if the sea were not salt, there would be no coral islands to beautify its landscape and give variety to its features; sea
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shells and marine insects could not operate upon the specific gravity of its waters, nor give variety to its climates; neither could evaporation give dynamical force to its circulation, and they, ceas ing to contract as their temperature falls below 40º, would give but little impulse to its currents, and thus its circulation would be torpid, and its bosom lack animation.
337. This under current may be freighted with heat to temper some hyperborean region or to soften some extra-tropical cli mate (§ 64), for we know that such is among the effects of ma rine currents. At starting, it might have been, if you please, so loaded with solid matter, that, though its temperature were 70º, yet, by reason of the quantity of such matter held in solution, its specific gravity might have been greater even than that of extra-tropical sea water generally at 28º.
338. Notwithstanding this, it may be brought into contact, by the way, with those kinds and quantities of marine organisms that shall abstract solid matter enough to reduce its specific gravity, and, instead of leaving it greater than common sea water at 28º, make it less than common sea water at 40º; consequently, in such a case, this warm sea water, when it comes to the cold latitudes, would be brought to the surface through the instrumentality of shell-fish, and various other tribes that dwell far down in the depths of the ocean. Thus we perceive that these creatures, though they are regarded as being so low in the scale of creation, may nevertheless be regarded as agents of much importance in the terrestrial economy; for we perceive that they are capable of spreading over certain parts of the ocean those benign mantles of warmth which temper the winds, and modify, more or less, all the marine climates of the earth.
339. The makers of nice astronomical instruments, when they have put the different parts of their machinery together, and set it to work, find, as in the chronometer, for instance, that it is subject in its performance to many irregularities and imperfectionsthat in one state of things there is expansion, and in another state contraction among cogs, springs, and wheels, with an increase or diminution of rate. This defect the makers have sought to overcome; and, with a beautiful display of ingenuity, they have attached to the works of the instrument a contrivance which has had the effect of correcting these irregularities, by counteracting
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the tendency of the instrument to change its performance with the changing influences of temperature. This contrivance is called a compensation; and a chronometer that is well regulated and properly compensated will perform its office with certainty, and preserve its rate under all the vicissitudes of heat and cold to which it may be exposed.
340. In the clock-work of the ocean and the machinery of the universe, order and regularity are maintained by a system of compensations. A celestial body, as it revolves around its sun, flies off under the influence of centrifugal force; but immediate]y the forces of compensation begin to act; the planet is brought back to its elliptical path, and held in the orbit for which its mass, its motions, and its distance were adjusted. Its compensation is perfect.
341. So, too, with the salts and the shells of the sea in the machinery of the ocean; from them are derived principles of compensation the most perfect; through their agency the undue effects of heat and cold, of storm and rain, in disturbing the equilibrium, and producing thereby currents in the sea, are compensated, regulated, and controlled.
342. The dews, the rains, and the rivers are continually dissolving certain minerals of the earth, and carrying them off to the sea. This is an accumulating process; and if it were not cormpensated, the sea would finally become as the Dead Sea is, saturated with salt, and therefore unsuitable for the habitation of many fish of the sea. The sea-shells and marine insects afford the required compensation. They are the conservators of the ocean. As the salts are emptied into the sea, these creatures secrete them again and pile them up in solid masses, to serve as the bases of islands and continents, to be in the process of ages upheaved into dry land, and then again dissolved by the dews and rains, and washed by the rivers away into the sea.
343. The question as to whence the salts of the sea were originally derived, of course has not escaped the attention of philosophers. Some have advanced the idea — Darwin, the poet, among others — that they came originally from the land, and were washed into the sea by the rivers and the rains. There seems to be plausibility in this idea; but there is reason for questioning it, as will
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be seen by the arguments advanced and the facts stated in the Appendix to the second edition.—See Appendix F.)
344-a. Thus we behold sea-shells and animalcule in a new light. In every department of nature there is to be found this self-adjusting principle — this beautiful and exquisite system of compensation, by which the operations of the grand machinery of the universe are maintained in the most perfect order.
[For another view of the origin of the salts of the sea, adopted upon more matured reflection, see Appendix F.]
344-b. Thus we behold sea-shells and animalcule in a new light. May we not now cease to regard them as beings which have little or nothing to do in maintaining the harmonies of creation? On the contrary, do we not see in them the principles of the most admirable compensation in the system of oceanic circulation? We may even regard them as regulators, to some extent, of climates in parts of the earth far removed from their presence. There is something suggestive, both of the grand and the beautiful, in the idea that, while the insects of the sea are building up their coral islands in the perpetual summer of the tropics, they are also engaged in dispensing warmth to distant parts of the earth, and in mitigating the severe cold of the Polar winter.
Surely an hypothesis which, being followed out, suggests so much design, such perfect order and arrangement, and so many beauties for contemplation and admiration as does this, which, for the want of a better, I have ventured to offer with regard to the solid matter of the sea water, its salts and its shells — surely such an hypothesis, though it be not based entirely on the results of actual observation, can not be regarded as wholly vain or as altogether profitless. (See Appendix G.)