Through the first Antarctic night, 1898-1899

THE BATHYMETRICAL CONDITIONS OF THE ANTARCTIC REGIONS

BY

HENRYK ARCTOWSKI

The scientific work of the Belgian Antarctic Expedition was commenced in the channels of Tierra del Fuego, and after the vessel left the pack they were concluded at Punta Arenas. It is thus impossible to discuss the physical geography of the antarctic regions in general without including the scientific results of the expedition of the Belgica.

The works of Murray, Neumayer, Fricker, and others,[2] give a general account of the previous state of our knowledge of the antarctic regions, and therefore I prefer to give a short summary of the results obtained by the Belgian Antarctic Expedition from the point of view of oceanography.

The Belgica had the advantage of navigating a region in which no previous bathymetric researches had been made, and her soundings have a special value (although their actual number was not great) because they were not taken at random. On the voyage from Staten Island to the South Shetlands, a line of soundings was run nearly from north to south, giving a transverse section of the “antarctic channel” which separates the Andes from one of the projecting angles of Murray’s hypothetical antarctic continent. In another place also, beyond the antarctic circle, and to the west of Alexander I. Land, we were able to obtain a series of soundings, some before entering the ice, the others on account of the drift of the vessel when imprisoned in the pack. The soundings on our way southward are given in the Table as Nos. 1–9, and those taken between 70° and 107° west as Nos. 10–56, while the results are represented chartographically in the two maps.

The first map shows the probable arrangement of the depths to the south of Cape Horn and in the antarctic regions. Soundings Nos. 1, 2, and 3 prove that south of Staten Island the continental shelf is very narrow, and terminates seaward in an abrupt slope, the greatest depth sounded (2209 fathoms) lying, in fact, very near the island. To the east, on the contrary, the continental shelf extends to a great distance as Burdwood Bank.

Between the southern versant of the Andes and the mountain system forming the framework of the antarctic lands visited by the expedition, there lies a deep, flat-bottomed depression, the floor of which rises gently towards the south, and not far from the South Shetlands an abrupt slope leads up to the rocky shallows near Livingstone Island. The last sounding taken gave a depth of 2625 fathoms in 56° 28′ south and 84° 46′ west, proving that the depth increases towards the Pacific Ocean. As, on the contrary, the Sandwich group, South Georgia, and Shag Rocks lie to the east, it seems probable that this great basin (called Barker Basin on the chart in the Challenger Reports) does not extend to the east of these islands. In a note on the interest which attaches to the geological exploration of the lands in the far south, which I published in December, 1895,[3] I suggested that “Grahamland is connected with Patagonia by a submarine ridge, which forms a great arc extending between Cape Horn and the South Shetland Islands, and that the tertiary chain of the Andes reappears in Grahamland.” I maintain this hypothesis, which demands for its satisfactory demonstration not only the geological study of the land, but also and chiefly a detailed bathymetrical map. The first step to this end has now been made.

The second map, showing soundings in the pack, is on a larger scale than the first, and shows the distribution of the soundings to the west of the land, and within the antarctic circle. It clearly demonstrates the presence of a continental shelf. The section along the line AB is extremely characteristic, showing distinctly that the submarine slope is discontinuous. The submerged bank, which terminates abruptly towards the ocean, has depths of from 200 to 300 fathoms, and farther south the depths are probably still less. I shall not discuss the configuration of this submarine elevation as one might imagine it to be from the soundings taken upon it, for the soundings are not numerous enough for this to be done profitably. But I cannot refrain from calling attention to one point which seems to me of great importance. The edge of the plateau is indicated by the isobath of 300 fathoms, beyond which the depths increase very rapidly. Now, it is the 100-fathom line which is generally accepted as the limit of the continental shelf, and it would appear possible that in the antarctic regions the continental shelf had been submerged. The discussion of this interesting question would, however, lead us too far.

It is noteworthy that the soundings carried out by the Erebus and Terror to the east of Victorialand, and north of the ice-barrier discovered by Ross, also indicate the existence of a continental shelf with much greater depths to the north. Between the two there still remains a space of 60° of longitude to explore before one can say whether they are connected.

All the positions were fixed by M. Lecointe, and I am indebted to the kindness of this accomplished astronomer for the exact place of each sounding. The sounding-machine of the Belgica was constructed by Le Blanc at Paris, and is similar to that employed on the Pola by the Austrian expedition. During the wintering in the ice, M. de Gerlache had a simple but effective arrangement constructed on board, which was fitted up on the ice close to the ship, and only required a hole to be cut in order to allow a sounding to be made. It consisted of a wooden drum carrying the sounding-wire, a brake consisting of a cord and a strong piece of wood serving as a lever to regulate the descent of the weight, and two cranks on the axle of the drum to heave in the wire. A wheel of one metre in circumference, with a counter from the Le Blanc machine, allowed the depth to be read off. The line ran through a block attached by a dynamometer to three poles arranged as a tripod. The soundings and temperature observations were laborious, and it is due to the co-operation of MM. Amundsen, Tollefsen, Johansen, Melaerts, Van Rysselberghe, and of M. de Gerlache himself, that it has been made possible for me to write these notes on the bathymetrical conditions of the antarctic regions.

TABLE OF SOUNDINGS.