The evolution of climate

by C. E. P. Brooks

In western Europe the mammoth and woolly rhinoceros are regarded as indications of severe climate, but their presence in north-eastern Siberia in large numbers is evidence of a climate probably somewhat warmer than that of the present day, especially as regards the length of the vegetation period. Probably the winter snowfall also was less than now. It is difficult to see how the fauna could have moved from, say, the New Siberian islands into a warmer climate each winter, for the winter climate becomes markedly more severe as one penetrates south from the Arctic coast into the interior. It is possible that the mammoth and woolly rhinoceros hibernated during the winter.

After this interglacial there came a recrudescence of glacial conditions. In this case, however, the Stanovoi and Verkhoiansk mountains and the Patom highlands were not buried in an ice-sheet, but became the centre of great valley glaciers, which reproduced the well-known glacial phenomena—corries, glacial terraces, U-valleys, etc. The ice extended down the great river valleys, leaving a typical moraine landscape on either side, and again reached the New Siberian islands. In course of time the climate ameliorated, again commencing in the south, and again the ice of the glaciers was buried. In the New Siberian islands the happenings are summarized very expressively by a rock-section described by Vollossovitsch. The bottom of the section is formed by the older layer of “fossil ice.” Above this is a sandy clay with remains of meadow vegetation and shrubs, followed by a fine clay with remains of alder and white birch, and the bones of mammoth and rhinoceros. Above this comes another layer of “fossil ice,” followed by clay with the dwarf birch, Arctic willow, and bones of musk ox, horse and later mammoth. After this the coastal regions sank beneath the sea for a time and marine clays were formed in a climate somewhat warmer than the present. When the land rose again the conditions resembled those now prevailing.

Though not part of Asia, reference may be made here to the glaciation of Spitzbergen, which runs strictly parallel with that of northern Siberia. The first glaciation was of the “ice-sheet” type, originating in the region north of Storfjiord, filling the whole of that fiord and extending south of South Cape. Barentz Land and Stans Foreland were at least partially ice-covered. The ice-floor of Spitzbergen, which resembles that of Siberia, may have originated during this glaciation. This was followed by subsidence to 230 feet below present level, and the ice retreated, giving place to an “interglacial,” during which frost was very active and largely obliterated the traces of the ice-sheet. This “interglacial” was followed by a second extension of the ice, which affected the valleys and fiords only, leaving the plateaux free. This again was followed by subsidence and a warm period.

In southern Kamchatka there was a great development of ice, but in the form of a network of glaciers rather than of an inland ice-sheet. In the east the ice reached the sea, but on the west it left a zone forty to sixty miles broad, and up to a thousand feet high unglaciated, so that there was the same difference then as now between the rainy east side and the drier west side of the peninsula. The present snow-line in the centre of southern Kamchatka is about 5500 feet, and at the maximum of the glaciation it must have been fully 3000 feet lower.

This glaciation was followed after an interval by a second, which was confined to the mountains. The moraines of this glaciation are much fresher than are those of the earlier one.

In Japan the mountains were only just high enough for glaciers to develop in the north. The moraines are old and weathered, and their meaning has been disputed; but recent work by Simotomai and Oseki seems to have established their glacial origin. The depression of the snow-line necessary to produce them—about 3000 feet—fits in very well with that observed in adjoining parts of the continent. The phenomena were confined to small hanging glaciers in the Hida mountains which cut out corries and descended to a level of about 8000 feet, leaving small morainic ridges. This glaciation was probably contemporaneous with the earlier and greater glaciation of Siberia. To the succeeding interglacial may be attributed the marine deposits found near Tokio containing corals, at present living some distance further south. No trace of any subsequent glaciation of Japan has yet been found.

J. S. Lee has recently called attention to the existence of a glaciated area in northern China, the evidence for which consists of moraines and striated slabs found in southern Chi-li, and a glaciated valley with travelled boulders in the north of Shan-si. The glacial deposits in Chi-li are closely associated with a layer of quartzite pebbles which continues southward beneath the loess on the eastern side of the Tai-hang range, and is attributed to either torrential rain or the melting of glaciers. J. Geikie had long ago stated that there once existed ice-masses all over northern China, and considered that the ice came from the Himalayas. This origin is impossible, the probable source of the ice being the Yablonoi mountains in southern Mongolia.

In the Himalayas the glaciers formerly had a much greater extension. The glaciers at present extend downwards to 11-13,000 feet, but old moraines are found at 7000 feet, and near Dalhousie on the southern slopes of the Dholadar range to 4740 feet.

On the northern side of the Himalayas there was a great development of ice over Tibet, but there was not a real ice-sheet such as occurred further north. Oldham records three separate periods of glaciation in Kashmir, but it is not yet possible to discuss the glacial history of the Himalayas in detail. The latter is likely to prove complicated, since the range is still rising, and has probably been doing so either continually or intermittently throughout the Quaternary.