Physical Geography Of The Sea 1855/1

 The Gulf Stream, § 1. — Its Color, 2. — Its Cause, 3-7. — Franklin’s Theory, 8. The Sargasso Sea, 13. — The Trade wind Agency refuted, 14. — Galvanic Properties of Gulf Stream Waters, 26. — Initial Velocity, 30. — Agents that make Water in one part of the Sea heavier than in another, 31. — Temperature of the Gulf Stream, 37. — It is Roof-shaped, 39. — Why the Drift Matter of the Gulf Stream is sloughed off to the right of its Course, 42. — Course of the Gulf Stream, 47. — Currents run along arcs of Great Circles, 49. — The Course of Currents counter to the Gulf Stream, 52. — The Force derived from Changes of Temperature, 53. — Limits of the Gulf Stream for March and September, 54. — Streaks of Warm and Cool Water in it, 55. — A Cushion of Cold Water between the Bottom of the Sea and the Waters of the Gulf Stream, 56. — It runs up hill, 57.

1. There is a river in the ocean. In the severest of droughts it never fails, and in the mightiest floods it never overflows. Its banks and its bottom are of cold water, while its current is of warm. The Gulf of Mexico is its fountain, and its mouth is in the Arctic Seas. It is the Gulf Stream. There is in the world no other such majestic flow of waters. Its current is more rapid than the Mississippi or the Amazon. 2. Its waters, as far out from the Gulf as the Carolina coasts, are of an indigo blue. They are so distinctly marked, that their line of junction with the common sea-water may be traced by the eye. Often one half of the vessel may be perceived floating in Gulf Stream water, while the other half is in common water of the sea; so sharp is the line, and such the want of affinity between those waters, and the reluctance, on the part of those of the Gulf Stream to mingle with the common water of the sea. PAGE 26 THE PHYSICAL GEOGRAPHY OF THE SEA. 3. What is the cause of the Gulf Stream has always puzzled philosophers. Modern investigations and examinations are beginning to throw some light upon the subject, though all is not yet clear. 4. Early writers maintained that the Mississippi River was the father of the Gulf Stream. Its floods, they said, produce it; for its velocity, it was held, could be computed by the rate of the current of the river. 5. Captain Livingston overturned this hypothesis by showing that the volume of water which the Mississippi River empties into the Gulf of Mexico is not equal to the one thousandth part of that which escapes from it through the Gulf Stream. 6. Moreover, the water of the Gulf Stream is salt — of the Mississippi, fresh; and those philosophers (§ 4) forgot that just as much salt as escapes from the Gulf of Mexico through this stream, must enter the Gulf through some other channel from the main ocean; for, if it did not, the Gulf of Mexico, in process of time, unless it had a salt bed at the bottom, or was fed with salt springs below — neither of which is probable — would become a fresh-water basin. 7. The above quoted argument of Captain Livingston, however, was held to be conclusive; and upon the remains of the hypothesis which he had so completely overturned, he set up another, which, in turn, has been upset. In it he ascribed the velocity of the Gulf Stream as depending “on the motion of the sun in the ecliptic, and the influence he has on the waters of the Atlantic.” 8. But the opinion that came to be the most generally received and deep-rooted in the mind of seafaring people was the one repeated by Dr. Franklin, and which held that the Gulf Stream is the escaping of the waters that have been forced into the Caribbean Sea by the trade-winds, and that it is the pressure of those winds upon the water which forces up into that sea a head, as it were, for this stream. 9. We know of instances in which waters have been accumulated on one side of a lake, or in one end of a canal, at the expense of the other. But they are rare, sudden, and partial, and for the most part confined to sheets of shoal water where the ripples are proportionally great. As far as they go, the pressure of the trade-winds may assist to give the Gulf Stream its initial velocity, but is it of itself adequate to such an effect? To my mind, the laws of Hydrostatics, as at present expounded, appear by no means to warrant the conclusion that it is, unless the aid of other agents also be brought to bear. THE GULF STREAM. PAGE 27 Admiral Smyth, in his valuable memoir on the Mediterranean (p. 162), mentions, that a continuance in the Sea of Tuscany of gusty gales from the southwest has been known to raise its surface no less than twelve feet above its ordinary level. This, he says, occasions a strong surface drift through the Strait of Bonifaccio. But in this we have nothing like the Gulf Stream; no deep and narrow channel-way to conduct these waters off like a miniature river even in the sea, but a mere surface flow, such as usually follows the piling up of water in any pond or gulf above the ordinary level. The Bonifaccio current does not flow like a river in the sea across the Mediterranean, but it spreads itself out as soon as it passes the Straits, and, like a circle on the water, loses itself by broad spreading as soon as it gets to sea. 10. Supposing the pressure of the waters that are forced into the Caribbean Sea by the trade-winds to be the sole cause of the Gulf Stream, that sea and the Mexican Gulf should have a much higher level than the Atlantic. Accordingly, the advocates of this theory require for its support “a great degree of elevation.” Major Rennell likens the stream to “an immense river descending from a higher level into a plain.” Now we know very nearly the average breadth and velocity of the Gulf Stream in the Florida Pass. We also know, with a like degree of approximation, the velocity and breadth of the same waters off Cape Hatteras. Their breadth here is about seventy-five miles against thirty-two in the “Narrows” of the Straits, and their mean velocity is three knots off Hatteras against four in the “Narrows.” This being the case, it is easy to show that the depth of the Gulf Stream off Hatteras is not so great as it is in the “Narrows” of Bemini by nearly 50 per cent., and that, consequently, instead of descending, its bed represents the surface of an inclined plane from the north, up which the lower depths of the stream must ascend. If we assume its depth off Bemini to be two hundred fathoms, which are thought to be within limits, the above rates of breadth and velocity will give one hundred and fourteen fathoms for its depth off Hatteras. The waters, therefore, which in the Straits are below the level of the Hatteras depth, so far from descending, are actually forced up an inclined plane, whose submarine ascent is not less than ten inches to the mile. PAGE 28 THE PHYSICAL GEOGRAPHY OF THE SEA. The Niagara is an “immense river descending into a plain.” But instead of preserving its character in Lake Ontario as a distinct and well-defined stream for several hundred miles, it spreads itself out, and its waters are immediately lost in those of the lake. Why should not the Gulf Stream do the same? It gradually enlarges itself, it is true; but, instead of mingling with the ocean by broad spreading, as the “immense rivers” descending into the northern lakes do, its waters, like a stream of oil in the ocean, preserve a distinctive character for more than three thousand miles. 11. Moreover, while the Gulf Stream is running to the north from its supposed elevated level at the south, there is a cold current coming down from the north; meeting the warm waters of the Gulf midway the ocean, it divides itself, and runs by the side of them right back into those very reservoirs at the south, to which theory gives an elevation sufficient to send out entirely across the Atlantic a jet of warm water said to be more than three thousand times greater in volume than the Mississippi River. This current from Baffin’s Bay has not only no trade-winds to give it a head, but the prevailing winds are unfavorable to it, and for a great part of the way it is below the surface, and far beyond the propelling of any wind. And there is every reason to believe that this polar current is quite equal in volume to the Gulf Stream. Are they not the effects of like causes? If so, what have the trade winds to do with the one more than the other? 12. It is a custom often practiced by seafaring people to throw a bottle overboard, with a paper, stating the time and place at which it is done. In the absence of other information as to currents, that afforded by these mute little navigators is of great value. They leave no tracks behind them, it is true, and their routes can not be ascertained. But knowing where they were cast, and seeing where they are found, some idea may be formed as to their course. Straight lines may at least be drawn, showing the shortest distance from the beginning to the end of their voyage, with the time elapsed. Captain Beechey, R. N., has prepared a chart, representing, in this way, the tracks of more than one hundred bottles. From it, it appears that the waters from every quarter of the Atlantic tend toward the Gulf of Mexico and its stream. Bottles cast into the sea midway between the Old and the New Worlds, near the coasts of Europe, Africa, and America, at the extreme north or farthest south, have been found either in the West Indies, or within the well-known range of Gulf Stream waters. THE GULF STREAM. PAGE 29 Of two cast out together in south latitude on the coast of Africa, one was found on the island of Trinidad; the other on Guernsey, in the English Channel. In the absence of positive information on the subject, the circumstantial evidence that the latter performed the tour of the Gulf is all but conclusive. Another bottle, thrown over off Cape Horn by an American master in 1837, has been recently picked up on the coast of Ireland. An inspection of the chart, and of the drift of the other bottles, seems to force the conclusion that this bottle too went even from that remote region to the so-called higher level of the Gulf Stream reservoir. 13. Midway the Atlantic, in the triangular space between the Azores, Canaries, and the Cape Verde Islands, is the Sargasso Sea. (Plate VI.) Covering an area equal in extent to the Mississippi Valley, it is so thickly matted over with Gulf weed (fucus natans), that the speed of vessels passing through it is often much retarded. When the companions of Columbus saw it, they thought it marked the limits of navigation, and became alarmed. To the eye, at a little distance, it seems substantial enough to walk upon. Patches of the weed are always to be seen floating along the Gulf Stream. Now, if bits of cork or chaff, or any floating substance, be put into a basin, and a circular motion be given to the water, all the light substances will be found crowding together near the centre of the pool, where there is the least motion. Just such a basin is the Atlantic Ocean to the Gulf Stream, and the Sargasso Sea is the centre of the whirl. Columbus first found this weedy sea in his voyage of discovery; there it has remained to this day; and certain observations as to its limits, extending back for fifty years, assure us that its position has not been altered since that time. This indication of a circular motion by the Gulf Stream is corroborated by the bottle chart and other sources of information. If, therefore, this be so, why give the endless current a higher level in one part of its course than another? PAGE 30  THE PHYSICAL GEOGRAPHY OF THE SEA. 14. Nay, more; at the very season of the year when the Gulf Stream is rushing in greatest volume through the Straits of Florida, and hastening to the north with the greatest rapidity, there is a cold stream from Baffin’s Bay, Labrador, and the coasts of the north, running to the south with equal velocity. Where is the trade-wind that gives the high level to Baffin’s Bay, or that even presses upon, or assists to put this current in motion? The agency of winds in producing currents in the deep sea must be very partial.  These two currents meet off the Grand Banks, where the latter is divided. One part of it under-runs the Gulf Stream, as is shown by the icebergs which are carried in a direction tending across its course. The probability is, that this “fork” continues on toward the south, and runs into the Caribbean Sea, for the temperature of the water at a little depth there has been found far below the mean temperature of the earth, and quite as cold as at a corresponding depth off the Arctic shores of Spitzbergen. 15. More water can not run from the equator or the pole than to it. If we make the trade-winds cause the former, some other wind must produce the latter; but these, for the most part, and for great distances, are submarine, and therefore beyond the influence of winds. Hence it should appear that winds have little to do with the general system of aqueous circulation in the ocean. The other “fork” runs between us and the Gulf Stream to the south, as already described. As far as it has been traced, it warrants the belief that it, too, runs up to seek the so-called higher level of the Mexican Gulf. 16. The power necessary to overcome the resistance opposed to such a body of water as that of the Gulf Stream, running several thousand miles without any renewal of impulse from the forces of gravitation or any other known cause, is truly surprising. It so happens that we have an argument for determining, with considerable accuracy, the resistance which the waters of this stream meet with in their motion toward the east. Owing to the diurnal rotation, they are carried around with the earth on its axis toward the east with an hourly velocity of one hundred and fifty-seven[6] miles greater when they enter the Atlantic than when they arrive off the Banks of Newfoundland. In consequence of the difference of latitude between the parallels of these two places, their rate of motion around the axis of the earth is reduced from nine hundred and fifteen[7] to seven hundred and fifty-eight miles the hour. [6] In this calculation the earth is treated as a perfect sphere, with a diameter of 7925•56 miles. [7] Or, 915 to 785. On the latter parallel the current has an east set of about one and a half miles the hour. Making the true velocity to the east, and on the axis

of the earth, about seven hundred and sixty miles the hour at the Grand Banks. THE GULF STREAM. PAGE 31