Archive image from page 454 of Discovery reports (1932) Discovery reports discoveryreports06inst Year: 1932 GEOGRAPHICAL DISTRIBUTION 357 second barrier, that between the South Atlantic and the South Pacific, is situated at a Hne approximately level with Buenos Aires on the South American coast and passes in a south-easterly direction to the region of the West Wind Drift. It is formed by the junction of the Brazil current running down from the north and a cold current flowingup from the region of the Magellan Straits. Here again there is a considerable difference in temperature between the t
Archive image from page 454 of Discovery reports (1932) Discovery reports discoveryreports06inst Year: 1932 GEOGRAPHICAL DISTRIBUTION 357 second barrier, that between the South Atlantic and the South Pacific, is situated at a Hne approximately level with Buenos Aires on the South American coast and passes in a south-easterly direction to the region of the West Wind Drift. It is formed by the junction of the Brazil current running down from the north and a cold current flowingup from the region of the Magellan Straits. Here again there is a considerable difference in temperature between the two currents, nearly twice as great as that between the South African currents, and the fact that no South Atlantic species pass this barrier might be taken to mean that temperature was the deciding factor. But to my mind, a more im- portant factor than temperature is the relation of the currents forming the two barriers, namely, that in the South African barrier the currents run parallel with each other, and though in opposite directions, are not opposed, while in the South American barrier Fig. 46. Illustrating the two closed circulatory systems of currents in the southern hemisphere, in relation to the distribution of sponges in that area. they are opposed. In the first case, the mixing of the waters at the line of junction allows the migrating sponges to be carried from the southerly directed Agulhas current into the northerly flowing Benguela current, and thence shortly to be restored to a third current, the South Equatorial, in which the temperature is similar to that of the Indian Ocean currents, whence they have come. Once in the South Equatorial current, their passage to the West Indies and the coast of Brazil is only a matter of time, and we do, in fact, find that one at least of the species common to the West Indies and Australia is also found on the coast of Brazil. Assuming that the distribution of sponges is the result of transport by ocean currents, we should e
Size: 2125px × 941px
Photo credit: © Bookend / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: archive, book, drawing, historical, history, illustration, image, page, picture, print, reference, vintage
