Rivers in the Sea
( Originally Published Early 1900's )
Actual Rivers in the Ocean; distinct streams of water, flowing over a bed of water, with banks of water. Not merely one or two such rivers, but scores of them, hundreds of them, great and small, in all parts of the world.
Chief perhaps in importance is the Gulf Stream, that vast flood which pours out of the Gulf of Mexico, and acts as a winter heating apparatus for the west of Europe. Though by no means the largest of ocean streams, it is one of the most useful to man.
After quitting the Gulf, it hurries at speed through the Straits of Florida; then spreads out into a river, about fifty miles wide and over two thousand feet deep, journeying at a rate of some sixty miles in twelve hours.
For a while it hugs the American coast; but, happily for Europe, it forsakes this friend of its youth, and wanders to the northeastward across the Atlantic.
To call it a "river" is no mere fiction of speech. Near Halifax the separation between warm and cold water is so sharp, that those on board a ship may know what latitude they have reached, on entering or leaving the stream, by simply dipping a bucket in the water and taking the temperature. Literally the Gulf Stream is a warm river, flowing over a bed of cold water, with cold-water banks.
So far as Cape Hatteras the stream clings to its early friend; and after that the American coast knows it no more, being left to the mercies of a very different acquaintance. An icy stream flows southward from the far north, clinging to the coast of North America, while those in western Europe benefit by the presence of the warm current which travels over to them. This stream has been described as forming a "cold wall" to the mild Gulf Stream.
Fan-like, the Gulf Stream spreads as it journeys, growing gradually wider and wider, shallower and shallower, cooler and cooler—yet the last so slowly that, even off the coast of Scotland, water nine hundred fathoms deep is found to be at 40° F.
How strongly this mass of warm water affects the air above it is well known to sailors. When passing from the stream to the outside ocean, or from the ocean to the stream, they often change in a few hours from a warm to a cool or from a cool to a warm climate. The atmosphere is ever ready to tune its mood sympathetically to that of the ocean over which it sweeps.
But for the immense stores of heat carried northward, and given over to it, the English climate would be different indeed from what it now is. That is why their fellow-subjects in eastern and central Canada, living no farther from the equator than do the English, suffer from an intensity of cold in winter which they never endure. It is difficult to realize that parts of ice-bound Labrador and of Canada, where the thermometer often drops to 40° below zero, are no farther north than London and Paris ; while Newfoundland lies actually more to the south than Erin's green Isle.
Turning to the Pacific Ocean, we find there a corresponding river, again flowing to the northeast. Just as the Gulf Stream wanders across the Atlantic, so this river wanders over the Pacific, carrying stores of tropical warmth to opposite coasts. At its quickest, it is less rapid than the Gulf Stream, and about three times as wide. It too, as it journeys, becomes gradually broader, shallower, slower, colder.
This "Kuro Sivo" or "Black Stream," so named from its dark color, flows outside Japan, and then strikes freely for the northern coasts of North America. And because of its work as a winter heating apparatus in Alaska, the humming-bird is found at a latitude which, on the other side of the American Continent, means, not the play and whirr of humming-birds in a soft air, but the disporting of walruses among ice floes.
As in the Atlantic, so in the Pacific, the warm northward-travelling current is balanced by a cold southward-travelling current. The Arctic stream of the Pacific is not so marked as that of the Atlantic, perhaps partly because of the much shallower outlet' from the Arctic Ocean ; still it is quite chilly enough in its effects upon the Siberian climate. Here again the cold stream acts as a "wall" to the warm river flowing the other way.
More reasons than one may help to explain why these two currents slant off to the eastward instead of pouring due north. The shape of the various coastlines has some-thing to do with it; also the presence of ridges and hollows in the ocean-beds, and the resistance of other con-tending currents. A river, either on land or in the sea, will always travel where it finds least opposition.
One main cause, however, is the whirl of our Earth upon its axis. This, which greatly affects the directions of prevailing winds, alters also the lines followed by ocean rivers.
A current starting from near the equator for the north shares in the rapid rush of the Earth's surface, which at the equator spins eastward at a rate of about one thou-sand miles each hour. As the volume of water gets farther north, it reaches parts of the Earth which are whirling more slowly, while it has not lost much of its own eastward whirl. A sideways flow is the result, changing the northward into a northeastward direction.
But a stream starting from the far north for the south is affected in the opposite way. Near the north pole the Earth's surface hardly moves at all; and the southward-flowing current, being weighted with northern inertia, takes a contrary course to the current flowing north. It lags more and more behind the faster-revolving surface, and so wanders westward instead of eastward. Or, if prevented by the land from so doing, it hugs the coast which hinders it.
So the pull of the two great streams in the Atlantic is exactly opposed, each to the other. That of the Gulf Stream is towards the east; that of the Labrador Stream is towards the west; and the resolute manner in which the two refuse to mingle may be partly due to this fact.
If our Earth could be made to change the present whirl from west to east, and to revolve instead from east to west, those two great currents would alter their directions. The Gulf Stream would hug the American coasts, and the Labrador would find its way over to Europe. Then the British Isles in winter would know a temperature of 30° or 40° below zero, and the Canadians would experience soft damp winters and moderate summers. Perhaps they would no more welcome the exchange than would the English.
Then, too, the Black Stream would cling to the Asiatic side, transforming the climate of western Siberia, and the cold Arctic river would put a speedy end to humming-birds in Alaska. But abundance of ice floes would soon be awaiting the walruses, which would have to emigrate from the other side of the continent.
A good deal of discussion has been held as to whether England owes its mild climate to the Gulf Stream alone, or whether that Gulf Stream is merely a part of a general northward movement of Atlantic waters from the tropics towards the pole. The question has been warmly con-tested; and no doubt on both sides, as generally is the case, truth has been mixed with error.
The Gulf Stream cannot be viewed as a separate entity. Its very birth in the Gulf of Mexico depends on a great mass of water ever flowing from the southeast into the Caribbean Sea. Since so much water pours in, the same volume must pour out, and as it does so it gains the name of the "Gulf Stream."
But after quitting the Gulf of Mexico the stream does not exist alone. It becomes a leading part of the North Atlantic circulation. The whole surface of that ocean is slowly turning round and round—"whirling as if stirred in the direction of the hands of a watch,' and the Gulf Stream occupies one side or more of the vast maelstrom. In the centre of this revolving mass of water lies a district where the motion is slight, and at that centre floats an enormous collection of drift and seaweed called the Sargasso Sea.
Suppose we pour some water in a large basin, drop into it a handful of small leaves and chips, and make the whole spin gently with one hand. We shall then see how the chips and leaves will collect at the centre, and will float there, almost stationary. That is what happens, on a large scale, in the North Atlantic Ocean.
Other Oceans also have this steady circular movement, not of the whole body of water, but of the surface-water, down to a greater or less depth—precisely how deep one cannot say; it lessens gradually with increasing depth. The same is found also in the South Atlantic, in the North and South Pacific, and doubtless in the Indian Ocean.
To find its direction in any part, one need only lay a watch, face upwards, upon a map of the North Atlantic or the North Pacific. In both cases the water travels round with the watch-hands. In the South Atlantic and the South Pacific the flow is just in the opposite direction.
So both the Gulf Stream and the Black Stream are merely parts of a big oceanic whirlpool. Each ocean on Earth has its own system of circulation; and that system is part of a world-wide system. The waters are in perpetual and complicated motion. Streams pour incessantly hither and thither, to north and south, to east and west.
Two vast streams, known as the Equatorial Currents, nominally pour round the world, but really are best seen in the open Pacific, where for long distances no land meddies with their career. They flow steadily westward, one to the north and one to the south of the equator.
Between them flows a reverse stream, called the "Equatorial Counter Current." If a certain amount of water travels north, an equal quantity must travel south. Or if, as in this case, so much water runs in a westerly direction, a corresponding quantity has to run in an east, erly direction. Water may be marvellously piled up here or there, by influences of land or of wind, but it cannot remain piled up, without efforts on the part of the ocean to restore the equilibrium.
Were the whole Earth covered by a single unbroken sheet of water, these drift currents might circle round and round the globe for ever, undisturbed in their working. But the Earth has lands as well as oceans; and when a current strikes a coast its course is altered, part at least being turned in a fresh direction.
Much discussion has taken place about the causes which bring these great Drift Currents into being.
Disturbing elements, many in number, may have had a hand in the matter. So soon as one part of the sea-surface becomes warmer than another part, movements are set going; the heavy cold water sinks, the light warm water rises, and streams are started from the one place to the other. There are also countless rivers pouring into the ocean, each helping to upset its equilibrium. Heavy downpours of rain raise the level of the sea here or there, inducing more currents.
But these are lesser causes. It is now recognized, as a fact beyond question, that the main power in starting and sustaining ocean-currents is that of Wind.