Page:The American Cyclopædia (1879) Volume II.djvu/90

 78 ATLANTIC OCEAN deeper impression in the Gulf stream in sum- mer than in winter, fi. In winter the Gulf stream is out in upon much less. The polar streams are then less powerful, the polar ice being fast in the north. This is shown by Mr. RednehTs observations on the drift ice off Newfoundland. Of 100 cases of ice seen, 87 occurred in April, May, June, and July ; of the remaining 13, there were 7 in March, 3 in August, 2 in February, and 1 in January ; none at all in September, October, November, and December. 7. The relations of temperature within the Gulf stream itself are about the same in winter and in summer; the fluctua- tions between its maximum and minimum would be only about 9. The thermometrical results of the deep-sea expeditions in the Eu- ropean seas in the steamers Lightning and Por- cupine in 1868, '69, and '70, have been used by Prof. Carpenter, under whose charge the ob- servations were made, for a theory of ocean cur- rents based on the heating and cooling of the wa- ter at the equator and pole respectively. The re- markable fact was brought out during the first cruise that in the channel between the Faroe islands and the N. coast of Scotland a warm nrea exists on the bottom in close proximity to a very cold one. The warm area, S. W. of the Faroe islands, had a temperature of 41 '4 at a depth of 767 fathoms ; the cold area, only 20 m. distant, between the Faroe and Shetland islands, only 29'7 at 640 fathoms, the surface temperature being the same. Near the Rock- all bank off the W. coast of Ireland the tem- perature of 41 was found to extend to 775 fathoms, with a bottom temperature of 37'4 at 1,400 fathoms, and oft' the bay of Biscay to 800 fathoms, with a bottom temperature at 2,435 fathoms of 36-5. Prof. Carpenter remarked on these results that the elevation of temperature in the warm area above the isotherm of its latitude could only be attrib- uted to a supply of water from the south- west ; and that the Gulf stream, meaning the warm water coming through the narrows of Florida, if it reached this locality at all, which he considers very doubtful, could only affect the most superficial stratum; and that the same could be said of the surface drift caused by southwesterly winds. He comes to the conclusion that the presence of the body of water ranging from 100 to 600 fathoms in depth, and the range of temperature of which is frqm 48 to 42, can scarcely be accounted for on any other hypothesis than that of a great general movement of equatorial water toward the polar area, of which the Gulf stream con- stitutes a peculiar case modified by local con- ditions. The arctic stream in the cold area is also a peculiar case of the general movement of the polar water toward the equator ; for it is forced to pass through this, the deepest channel between Iceland and Europe, and pressed toward its S. E. shore on account of the channel's oblique position with regard to the N. and S. flow of the water. Prof. Car- i penter is inclined to think that the Arctic ocean is insufficient to supply cold water enough for so great a reduction of tempera- ture as is found in the body of water below 1,000 fathoms in the Atlantic basin, and thinks that antarctic water may also flow in past the equator as far PS the tropic of Cancer ; a ques- tion rather difficult to settle in the present state of our knowledge, since all we know is that under the equator bottom temperatures havo been observed of 35 - 2 at 1,806 fathoms, and 33-(> at 2,306 fathoms. The best evidence adduced by Prof. Carpenter for the flow of polar water on the bottom toward lower lati- i tudes is based on his deep-sea temperatures of the Mediterranean. This closed body of water i communicates with the Atlantic through the strait of Gibraltar alone, and that is too shal- low to allow of a communication between the deep waters of the two basins. The Mediter- ranean goes down in some parts to 2,000 fathoms. The surface is hot in summer, as high as 78 sometimes, but the hot layer is shallow, 10 or 15 being lost in the first 30 fathoms. At 100 fathoms the temperature is generally 54 or 55 ; beyond that depth no further reduction was observed ; " whatever the temperature was at 100 fathoms, that it was at the bottom;" and this temperature is found to be the permanent temperature of the surface of the earth in that latitude. The same observer concludes that the ocean is subjected to two different circulations : a horizontal one produced by the action of the wind, the Gulf stream being an example of it ; and a vertical circulation dependent on opposition of tem- perature. V. LIFE IN THE ATLANTIC OCEAN. 1. Vegetation. The flora of the ocean, or nereis, as it has been called, is confined to a narrow belt along the shores and to the surface layer of water in mid-ocean, a strong light being necessary to its existence. With the ex- ception of a few species of the family of zoste- racecE (eelgrass, turtlegrass, grasswrack), the whole submarine vegetation belongs to the algse, plants of low organization. The limits of depth to which certain families, genera, or species are confined, are much more definite than they are for animals ; they have been called zones by Edward Forbes, characterized by the prevailing types growing in each. Com- mencing at the surface, he called littoral zone the region between high and low water, which on rocky shores is characterized by a luxuriant growth of fucaceas principally, of which dif- I ferent species form further subdivisions of the I zone, according to their preferences for a" j longer or shorter exposure to the air. Below l low-water mark the laminarian zone begins, and extends to 4 or 5 fathoms : in it are found in abundance the chondrm cri-spiis or carra- geen, the thong weed (himanthalia), and the tangle or devil's apron (laminaria). In the ! lower part of this zone are found the red and purple seaweeds, many of them of great dfli-
 * cacy and beauty. The next zone is that of the