中国北方上新世降温事件及其对温度纬度梯度变化的影响

中晚上新世是现代气候形成过程根据在同一地区(剖面)获得的古地磁年代资料,发现山西榆社及河北泥河湾的孢粉资料记录了在松山/高斯极性事件界线附近(约2.5 Ma)的一次明显的降温事件.山西榆社的孢粉资料还记录了在约2.7 Ma-2.8 Ma的一次降温事件.这些降温事件主要是因为全球性气候变化引起的,北极圈附近和西伯利亚的冷高压大大地降低了我国,特别是我国北方的冬季气温.与此同时,位于北极圈附近的阿拉斯加发生了更为强烈的降温事件.比较两地相当时期的降温幅度,可以发现因为不同纬度的降温幅度不同使得温度的纬度变化梯度比降温事件发生前大大增加了,由原来的纬度每增加一度降低约0.3℃增大到约0.5℃.

PLIOCENE COOLING BEFORE THE ICE AGES IN NORTH CHINA

The development of an Ice Age climate meant a cooling of the polar regions. We used fossil pollen to estimateshifts in paleovegetation and climate, and our geologic sections were dated by magnetic stratigraphic studies in two basins ofNorth China (Yushe at 37° N and Nihewan at 40° N Lat.). Our study reveals a drying and cooling in mid Pliocene (ca 2.7 Ma-2.8 Ma) and later a sharp cooling of about 2 ℃ (mean annual temperature) at ca 2.5 Ma. The cooling was the result of a loweredwinter temperature, probably due to increased strength of the Arctic Front and winds from the high North Latitudes. A similarbut stronger cooling at about 2.5 Ma is recorded at pollen sites near the Arctic Circle. By comparing the two areas we calculatethat latitudinal temperature gradient steepened by a factor of about 1.5 × from mid Pliocene (ca. 3.1 Ma) to the end of the Gaussinterval at about 2.5 Ma. These significant changes marked the initial development of the modem climate in the NorthernHemisphere.