462 



GULF STREAM 



GULL 



from the Japan and Yellow seas also ceases, which 

 causes the slackness of the Kuro Siwo, south of the 

 main island, in June, as it is then only due to the 

 equatorial current. Later on, in July and August, 

 wnen it is further augmented by the surface drift 

 from the China Sea in the south-west monsoon, it 

 runs again with great rapidity, and is wholly a 

 warm current. These peculiar effects are probably 

 not experienced to the eastward of the meridian of 

 140 E. ; there apparently the stream is always a 

 warm one. The current that runs from the Arctic 

 Ocean through Behring Strait is insignificant com- 

 pared with the Arctic currents of the Atlantic. 

 There is an ill-defined Sargasso Sea in the North 

 Pacific, in some respects resembling that of the 

 North Atlantic. The surface currents in the 

 Indian Ocean are, as is well known, changed with 

 the shifting of the monsoons. 



From the Challenger observations it appears 

 to be proved that the dense warm equatorial 

 waters which pass along the eastern snores of 

 South America, Africa, and Australia into the 

 Great Southern Ocean that surrounds the world 

 in latitudes beyond 40 S., become cooled in 

 these latitudes, and sink to the bottom through 

 the other waters on account of their greater 

 density. This water is then drawn slowly north as 

 a great indraught to supply the loss by surface 

 currents and evaporation in the equatorial regions 

 of the Atlantic, Pacific, and Indian oceans. It 

 appears then that by far the larger part of the 

 cold water that fills these great ocean-basins is 

 cooled and sinks to the bottom in about 50 S. 

 lat. A portion of this water seems also to be 

 drawn southward to supply the place of the 

 relatively light though cold surface currents that 

 flow north from the Antarctic in the regions of 

 floating ice. The great bulk of the ocean has a low 

 temperature below 45 F. ; it is ice cold in the 

 Atlantic at the bottom even under the equator. 

 The warm surface water is a relatively thin film, 

 but this film is much deeper towards the western 



Sirts of the oceans in the tropics than in the eastern. 

 n the other hand, in the regions of the westerly 

 winds of temperate latitudes the layer of warm water 

 is deeper in the eastern parts of the oceans, as has 

 been already noticed in referring to the deep-water 

 temperatures off' Britain and tropical Africa. These 

 facts are clearly shown on the Challenger maps, 

 showing the distribution of temperature at 10, 20, 

 50, 60, 100, and 300 fathoms. 



The surface currents may, as we have seen, 

 have a considerable velocity, but there is no 

 evidence that any such currents exist in the 

 deeper waters at the bottom of the ocean ; the 

 movements there must be slow and massive. It is 

 true that between oceanic islands and in positions 

 like the Wy ville-Thomson Ridge, between Scotland 

 and the Faroe Islands, where the tidal wave is con- 

 fined, the ridges are swept by currents at a great 

 depth ; but these are exceptional cases. In the 

 open ocean the temperature decreases with in- 

 crease of depth, except in the Arctic or Antarctic, 

 where there is melting ice on the surface. In 

 enclosed seas, like the Mediterranean, Caribbean 

 Sea, Gulf of Mexico, Sulu Sea, and many others, 

 there is a large body of water at the bottom of a 

 nearly uniform temperature ; the depth at which 

 this uniform temperature is reached depends on 

 the height of the ridges cutting enclosed seas off 

 from general ocean circulation. The deeper water 

 in these can only be renewed by vertical currents 

 set in motion by the winds or by convection 

 currents. The direct influence of ocean currents on 

 climate is undoubtedly great, but this influence is 

 most marked by the indirect effects of the prevail- 

 ing winds blowing from off these currents towards 

 the land, carrying with them heat and moisture. 



Gulfweed (Sargassum), a genus of seaweeds 

 (Algae) of the sub-order Fucaceae, of which two 

 species (S. vulgare and S. bacciferum) are found 

 floating in immense quantities in some parts of 

 the Atlantic, Pacific, and Indian oceans. They 

 are tropical plants, although sometimes carried by 

 winds and currents to the British coasts. The frond 

 is very long, and is furnished with distinct", stalked, 

 nerved leaves, and simple axillary stalked air- 

 vessels. The receptacles are linear, in small axillary 

 clusters or racemes. The trivial name bacciferum, 

 applied to one of the species, is derived from the 

 berry-like appearance of the air-vessels. The gulf- 

 weed is generally found floating, but there is reason 

 to think that it is at first attached to the bottom 

 of comparatively shallow parts of the sea. It floats 

 in large fields, or more frequently in long yellow 

 lines in the direction of the wind. In crossing the 

 Atlantic, its presence is regarded as a sure indi- 

 cation of the Gulf Stream, by which it is wafted 

 northward and eastward. Where the Gulf Stream 

 is deflected from the banks of Newfoundland east- 

 ward, and sends off its more southern branch 

 towards the Azores, is situated the Sargasso^ Sea, 

 ' that great bank of weeds, which so vividly 

 occupied the imagination of Christopher Columbus, 

 and which Oviedo calls the seaweed meadows' 

 ( Humboldt ). The quantity of floating seaweed is 

 often such as to impede the progress of ships. 

 Multitudes of small marine animals accompany it, 

 with fishes ready to prey on them. The gulf weed 

 is eaten in China ; and in other parts of the East 

 also it is used in salads and as a pickle. 



Gull (Larus), a genus of web-footed birds 

 belonging to the Laridae, a family of long- winged 

 sea-birds having the longitudinal nostrils placed 

 laterally and not covered by a cere, the three 

 anterior toes completely webbed, the hind-toe, when 

 present, small and not touching the ground. The 

 family includes the Scissor-bills or Skimmers 

 ( Rhynchopinae), the Terns or Sea-swallows (Ster- 

 ninau), and the true Gulls (Larinee). The true 

 gulls are of less slender build than their nearest 

 allies, the Terns ; their wings are not quite so long 

 and pointed, and they have the bill more hooked. 

 The most important genera are Stercorarius, the 

 voracious and predatory Skuas; Rissa, the Kitti- 

 wakes; Xema, the fork-tailed Gulls; and Larus. 



The genus Larus comprises sixty species, cosmo- 

 politan in their distribution, and includes many of 

 the larger gulls and most of those common in Great 

 Britain. The prevailing colour is 'white, with a 

 gray mantle varying in shade from the most delicate 

 pearl gray to a dark blackish slate or nearly black,' 

 and there are often black markings about the head, 

 which, however, vary in different seasons. The 

 two sexes are usually almost alike in colour, but 

 the young are dusky and brownish and have the 

 bill dark, while in adults the bill, legs, and feet are 

 bright red or orange. The legs are very powerful, 

 and are placed well forward so that the body is 

 carried horizontally, the bill is stout and curved, 

 with a prominent angle on the lower part and a 

 corresponding swelling on the upper. Though most 

 gulls are marine, they frequent, and even breed by 

 inland lakes not far from the sea, and large flocks 

 of them may often be seen following the plough 

 eagerly picking up the worms and grubs. They 

 are very voracious and will eat almost anything, 

 but feed chiefly on fish and molluscs. To break the 

 shells of the molluscs they sometimes carry them 

 high into the air and drop them upon a rock. 

 Audubon tells of a gull observed by htm which, 

 when the shell did not break the first time, carried 

 it a second time higher, and a third time higher 

 still. Some of the larger species e.g. the Great 

 Black-backed Gull (L. marinus), prey even upon 

 the eider-duck and other wild fowl, and very many 



