上越平標山の埋没泥炭層からみた完新世後期の気候変化

抄録

Mt. Tairappyo (1, 983m) is a snowy mountain against which the strong winter monsoon blows from the Sea of Japan. Gentle slopes are dominant in this mountain. Due to much snow, tall trees which usually form subalpine conifer forest are not able to grow on the upper part above 1, 600m. Therefore, no subalpine zone exists in this mountain. Instead of tall trees there excel meadows, Sasa fields or scrubs. The result of soil survey in this area showed that the buried peat is widely distributed under the Sasa fields or Graminea-herb meadows. The peat layers are 20_??_30cm thick and are buried under the Kuroboku (Ando) soil or alpine meadow soil (wet type), both with a thickness of about 15cm.
The accumulation of the present peat is limited at the bottom of nivation hollows. In these hollows snow patches exist till late June or middle July and supply enough melt water. The wide distribution of the buried peat layer indicates that there was an age when the remaining snow existed more widely in summer season as compared with the present. It seems that the delay of the snow melting is due to first the cool climate in that age. Perhaps it was low temperature at that age, especially in summer season. However, that age seems also to have had a heavier snowfall than the present situation. At present heavy snowfall occurs only in the year when the special strong cold waves hit Japan; it occurs in every ten and odd years. At the age when the buried peat layer was formed due to low temperature in winter, the frequency of the heavy snowfall must have increased, so that much snow existed comparing to the present. The buried peat layers probably accumulated owing to the delay of the snow melting caused by the increase of winter snow and the low temperature in summer. The ¹⁴C age of the bottom of the buried peat layer was 3, 100 y. B. P., suggesting that this cool and snowy age would correspond to the Neoglaciation.