GULF STREAM 



461 



tin- Atlantic. This great txxly of warm water 

 indirrctly modifies the climate of western Europe, 

 an. I it in | io-.il, I,- to trace it* effects as far as the 

 coasts of Spit/bcrgen mill Nova Zembla. It is 

 essential in describing the (Julf Stream to take 

 into consideration tlie general question of oceanic 

 circulation, and the thermal condition* of the 

 ocean m'ade known from the explorations of the 

 ( '/tn/li-nifi-r, Make, and other recent expeditions. 



The prevailing winds of the globe are determined 

 by the distribution of atmospheric pressure, and 

 tin- |><)-it ion of barometric maxima and minima 

 are in turn determined by the distribution of 

 land- masses and water-surfaces. The wind blows 

 out of and around high-pressure or anticyclonic 

 an-as, ;iud into and around low pressure or cyclonic 

 iin-.-is (see ATLANTIC). By comparing the maps of 

 the prevailing winds with those or the oceanic 

 currents, it will be seen that the latter roughly 

 coincide with the winds blowing out of and around 

 tin- high -pressure areas in the Atlantic and Pacific 

 oceans. There have been many theories to account 

 for oceanic circulation, but recent researches show 

 that all the principal surface currents have their 

 origin in, and are maintained by, the action of the 

 prevailing winds of the globe, modified locally by 

 variations in temperature, density, evaporation, 

 gravity, and rotation of the earth. 



The phenomenon of oceanic circulation is to be 

 seen in its simplest form in the westerly wind- 

 driven currents of the trade-wind regions of the 

 Atlantic and Pacific. The heated surface waters 

 of the tropics are there driven to the west, and 

 banked up towards the eastern shores of America, 

 Africa, Asia, and Australia. On the other hand, 

 the cold deep water is drawn up along the western 

 shores of America and Africa to take the place of 

 the surface water driven before the trade-winds. 

 The temperatures of the water towards the western 

 parts of the oceans are thus higher and more uni- 

 form to considerable depths below the surface than 

 in the eastern, where they are lower and have a 

 wider range at different seasons or different states 

 of the wind. The writer has even measured this effect 

 of the wind in Loch Ness in Scotland ; he found 

 the cold water from the bottom drawn to the sur- 

 face in the course of a few hours, and the warm 

 surface water banked up to the north end of the 

 loch, during a southerly gale. Recent observations 

 show that similar effects are produced in the great 

 oceans during a continuance of winds off shore. 



In the Atlantic a large proportion of the waters 

 of the equatorial current are forced into the Carib- 

 bean Sea through the passages in the Windward 

 I-l.ui.U, ,-unl then into the Gulf of Mexico, princi- 

 pally through the Yucatan Channel. The amount 

 of accumulation or heaping up of water in the Gulf 

 of .Mexico, through the action of the trade-winds, 

 has been measured by the officers of the United 

 States Coast Survey ; it has leen found that the 

 Atlanti.- Ocean at Sandy Hook is 3 feet 4 inches 

 lower than the waters of the Gulf of Mexico at the 

 mouth of the Mississippi. This is partly the origin 

 of the force constantly at work to keep up the flow 

 of the Gulf Stream through the Strait of Florida. 

 The stream as it Hows through the narrowest part 

 of the strait is 50 miles wide, and has an average 

 depth of 350 fathoms. Iu the axis of the stream 

 the velocity is four or five knots an hour, two miles 

 an hour or even less along the edges, and probably 

 the same near the bottom. It is estimated to be 

 150 miles wide off Charleston, and 300 miles wide 

 off Sandy Hook ; it then spreads fan-like over the 

 surface of the North Atlantic. Off Cape Hatteras 

 the velocity is about three miles an hour, off the 

 banks of Newfoundland one and a half mile an 

 hour, then the rate slowly merges into that of 

 the north-easterly drift of the Atlantic four or 



five miles a day. The mean surface temperature 

 in the strait* is 81-5 F. ; oil Sandy Hook, 73"-4 F. 

 The average bottom temperature in the strait at 

 400 fathoms is 45" F. ; off Charleston, at 300 

 fathoms, 53 F. ; and off Sandy Hook, in 200 

 fathoms, 46 0> 5 F. The bottom in the strait, and 

 for some distance north on the ' Blake plateau,' 

 appears to I , swept by the current so that no fine 

 (X)/.e is allowed to form ; but the bottom, where hard, 

 is niiide up of the remains of surface and hottom- 

 living organisms, often cemented together into 

 nodules and phosphatic concretions. The diagram 

 in the article ATLANTIC shows the distribution of 

 temperature across the Gulf Stream between New 

 York and Bermuda. The Gulf Stream water of 

 the North Atlantic is carried towards the coasto 

 of Europe by the south-west winds ; one branch 

 passes on to the coasts of Norway, and another 

 south to the coasts of Spain and Africa. As this 

 water is carried into colder latitudes it sinks on 

 becoming cooled because of its greater density, so 

 that off the coasts of Britain warmer water is found 

 at a depth of three-fourths of a mile than at a like 

 depth off the tropical coast of Africa, where the 

 winds are off shore. While a warm current passes 

 to the Arctic Ocean along the coasts of Norway 

 and Lapland, a cold current from the Arctic comes 

 down the coasts of Greenland, and along the coasts 

 of Labrador and the United States, inside the Gulf 

 Stream, and ultimately sinks beneath it into the 

 deeper parts of the North Atlantic basin. The 

 passage from the green, cold, turbid waters along 

 the American coast into the deep blue, warm 

 waters of the Gulf Stream is sometimes sudden 

 and well marked, and is usually observed by all 

 who sail from the shore seaward. 



The winds blow out of and around an area situ- 

 ated in the North Atlantic, between the north of 

 Africa and America, and the surface currents of 

 water also circulate around this area, which is known 

 as the Sargasso Sea. Here are found immense banks 

 of floating Gulfweed (q.v.), covered with peculiar 

 species of animals : Crustaceans, Polyzoa, Annelids, 

 Molluscs, Hydroids, and Fishes, all the same colour 

 as the weed, presenting remarkable examples of 

 protective resemblance. 



A very similar, but not such a well-defined or 

 constant stream as the Atlantic one, is found in 

 the North Pacific, and is known as the Kuro Siwo 

 ( ' Black Stream ' ) or Japan Stream. On approach- 

 ing Japan in April from the south the Challenger 

 found a belt of water running to the eastward at 

 the rate of three miles per hour. In this stream the 

 temperature changed from 63 to 68 F. suddenly 

 several times without any alteration in the rate of 

 the current. In June no current was found 30 to 40 

 miles from the coast, but close to the south coast of 

 the main island there was a northward current of 

 two miles per hour and a mean temperature of 72 '5 

 F. Alternating bands of cold and warm water were 

 also found by the Challenger in the Gulf Stream near 

 its shore edge. The origin of these alternate belts 

 of water in the Japan Stream is probably due to the 

 monsoons. The northern equatorial current striking 

 against the eastern side or the Philippine Islands 

 is, as is well known, diverted to the northward, 

 along the eastern side of Formosa, after passing 

 which it appears gradually to lose its distinctive 

 character. During the north-east monsoon a cold 

 surface current is running to the southward from 

 the Japan and Yellow seas. It appears therefore 

 highly probable that the equatorial current, 

 instead of losing itself as is supposed, when it 

 meets with the cold water from the Japan and 

 Yellow seas, is diverted to the eastward along with 

 a cold northerly current, the two running together 

 side by side without intermingling their waters. 

 When the north-east monsoon ceases the current 



