Antarctic Ocean.— The depths of the Ant arctic Ocean have been explored in various parts by Ross, Wilkes, Nares (Challenger ex pedition) and Gerlache. Ross sounded in 4,000 fathoms in the vicinity of South Georgia with out reaching bottom. The Challenger found depths of from 1,300 to 1,950 fathoms near the Antarctic Circle, south of Australia, while farther north the soundings ranged from 950 to 2,600 fathoms. Between the Cape of Good Hope and Kerguelen Islands depths of 2,500 to 3,100 fathoms have been reported. There seems to be a gradual shoaling of the waters toward the Pole, for Wilkes sounded in 500 to 800 fathoms off Adelie Land, and in 100 to 500 fathoms off Victoria Land, while Gerlache recorded less than 200 fathoms west of Palmer Land. The bottom in the extreme south is covered with a layer of diatom ooze. Farther northward the bottom is covered with deposits of globigerina ooze made up of the casts of Foraminifera, and in still deeper water the characteristic red clay, found at great depths in all the oceans, occurs. The temperature of the surface waters of the ocean range from a few degrees below to a few degrees above the freezing point.
Antarctic Continent.—The question whether there is a large land area of continental char acter within the Antarctic Circle has not yet been definitely settled, although most geog raphers and explorers express an affirmative opinion. Land areas of indefinite extent have been sighted and form an interrupted ring about the Pole. The mountain ranges and peaks discovered by Ross in Victoria Land are apparently of continental character. Granite andgneiss were found by D'Urville near Adelie Land, and Borchgrevinck states that the rock at Cape Adare is micaschist; these are distinctly continental types. Indirect evidence is fur nished by the materials transported from the far south by the icebergs, sandstone, basalt, boulders of massive rocks, and fragments of gneiss, granite, diorite and sedimentary rocks. The great icebergs which drift far into the region of the Southern Ocean are difficult to account for on any other theory than that they have been broken off from a vast sheet of land ice like that covering Greenland.
Antarctic Ice.— The conditions of ice formation in the Antarctic differ materially from those of the Arctic region. In the north ern hemisphere the polar ocean is enclosed by land, so that sea ice is much more important than land ice, the latter occurring only on the edge of the area, while in the Antarctic the reverse is true. Enormous masses of floating ice, flat-topped with perpendicular walls and oftentimes measuring many miles in width and length, are found throughout the Antarctic Ocean. The newly-formed bergs have evi dently been broken off from the edge of a thick ice-cap covering the Antarctic lands and grad ually pushed over the surface toward the sea. The thickness of the ice near the Pole is esti mated by Croll upon theoretical grounds at from 12 to 14 miles, but off the coast of Vic toria Land the ice-wall is only 10 to 20 feet high.
Climate,— The climatic conditions of the Antarctic are imperfectly understood, but tem perature is extremely severe. Compared with the Arctic the region is placed at a disadvan tage in having its summer during perihelion and winter in aphelion. Observations made by Ross in the vicinity of Victoria Land from 60 to S. showed a mean summer temperature of 28.85° F. for the sea and 28.31° for air; in lat. 66° 29' S. the maximum temperature in the month of December was 45.52 F. Wilkes found the mean temperature for January and February near Wilkes Land to be 302° F.,
with extremes of 34.52° and 23°, while Gerlache reported a winter minimum in 71° 30' S. of The German station in South Georgia gave a mean temperature of 37.52°. The glaciation of the land areas, the great ice-floes and the saturated condition of the atmosphere, producing heavy fogs, are influen tial in producing the extreme cold. Barometric observations by Ross indicate a gradual in crease in pressure south of 75° S., and it is believed that an area of extreme high pressure exists around the Pole, producing a permanent anticyclone with winds blowing in a south easterly direction toward the higher latitudes. No estimate of the precipitation has been made, but the atmosphere is probably comparatively dry over the land areas in the extreme south and the precipitation is in the form of fine ice crystals. Farther north there is a heavy precipitation of snow and sleet; rain seldom falls within the ice-bound region.
Fauna and Flora.— The largest of the Ant arctic mammals are the whales which frequent the cold waters in great numbers. Many of the species are similar to if not identical with those inhabiting the Arctic seas; rorquals, humpback whales, pilot whales, grampuses and dolphins are known, also a small whalebone whale (Bo len° australis), but the right whale does not exist in the Antarctic. There are 13 species of seals, including four of fur seals, which are closely related to those found in the north Pa cific, the sea-lion and the sea-elephant. Among birds the penguins are most abundant, their rookeries found on the borders of all lands free from ice. The largest species is the kings penguin; a specimen captured by Wilkes measured 4 feet 6 inches in height and weighed 65 pounds. A gull-plover (Chionis) is found exclusively in the Antarctic. A small teal fre quents Kerguelen, and stormy petrels, alba trosses, gulls, skuas and terns breed on most of the islands. Borchgrevinck found 11 species of fish in Antarctic waters, most of them new to science. Explorers have usually reported that fishes were scarce. A few species of insects have been described by Arctowslci and Borch grevinck. It is believed that no land animals exist in the extreme south. Of plant and in vertebrate life inhabiting the Antarctic Ocean there is a great abundance. The pelagic ani mals include cephalopods, brachiopods and gastropods, which furnish food for the whales, ccelenterates and Protozoa. The deep-sea fauna is much more strongly developed than the shallow-water fauna living in the vicinity of the Antarctic lands. Thirteen species of phanerogamous and numerous cryptogamous plants have been found near South Georgia. Hooker obtained from Cockburn Island four species of marine alga, three of fresh-water plants and 12 land plants, the last-named mostly lichens and mosses.
Bibliography.—Murray