环流效应：中国季风区石笋氧同位素短尺度变化的气候意义-古气候记录与现代气候研究的一次对话

CIRCULATION EFFECT: CLIMATIC SIGNIFICANCE OF THE SHORT TERM VARIABILITY OF THE OXYGEN ISOTOPES IN STALAGMITES FROM MONSOONAL CHINA DIALOGUE BETWEEN PALEOCLIMATE RECORDS AND MODERN CLIMATE RESEARCH

根据最近的研究结果,中国季风区同一洞穴或同一区域的晚全新世石笋氧同位素序列具有较好的重复性,表明中国季风区的石笋氧同位素短尺度(10～100年尺度,后同)变率所具有的信号强于噪音。通过进一步比较分析发现,一些石笋氧同位素记录虽然来自距离上千公里之遥的不同区域,但它们的波动形式在年代际至世纪尺度极其相似,说明它们是一致的大区域信号,但多数石笋氧同位素序列未能校准到本区器测的降水或温度记录上。通过与中国气候学家建立的各类季风指数比较,发现这些具有一致大区信号的中国石笋氧同位素序列与海平面气压差指数或海陆温差指数关系最好。再通过与印度洋-太平洋海域海平面气压差、以及许多海、气环流观测记录对比,发现中国季风区石笋氧同位素序列记录了20世纪后期最强的一次全球海、气环流年代际均值突变,由此初步确认了中国季风区石笋氧同位素短尺度变化的环流意义:当印度洋海水和中东太平洋海水温度偏低时,西太平洋副热带高压偏北东缩而弱,中国季风区内来自印度洋的水汽份额增大,由于这些水汽的输送路程很远,导致中国季风区的雨水氧同位素及石笋氧同位素较轻;而当印度洋海水和中东太平洋海水温度偏高时,西太平洋副热带高压偏南西伸而强,中国季风区内来自印度洋的远源水汽份额减少,而来自西太平洋的水汽份额增大,由于后者输送路程较近,导致中国季风区的雨水氧同位素及石笋氧同位素较重。由此命名瑞利分馏原理所决定、反映印度洋/太平洋海、气环流转变且大区域一致的中国季风区石笋氧同位素10～100年尺度变化为"环流效应"。

According to recent research, Late Holocene stalagmite oxygen isotope sequences from the same cave or the same region situated in the monsoon zones of China have good reproducibility, Which is indicative of a common short-term signal. Also oxygen isotope records from different regions, often located thousands of kilometers apart, are found to possess similar fluctuations on decadal to century scales, indicating that they share the same large scale signal. However, most of these records can not be calibrated with local observed precipitation or temperature data. Comparing with various types of monsoon index represented by Chinese climatologists, the author has found that the common signal embedded within these stalagmite oxygen isotope sequences has a strong correlation with the sea level pressure difference or the index of temperature difference between the land and the sea.By comparing the sea-level pressure difference of the Indian-Pacific Ocean, as well as the many oceanatmosphere general circulation observations, with the stalagmite oxygen isotope sequences from the monsoonal area of China,the isotopic variations are found to correspond to the abrupt change in the average of the air-sea decadal circulation in the late 20th century. This confirms that the short-term changes in the stalagmite oxygen isotopes from Monsoon zones in China have significance for understanding changes in atmospheric circulation.When the temperature of the Indian Ocean and the Middle East Pacific is low, the West Pacific subtropical high becomes weak, and retreats northeastward. In this period, Monsoonal China is mainly controlled by the tropical monsoon trough i.e. the Intertropieal Convergence Zone（ITCZ）. The water vapor from the Southern Indian Ocean increases,which results in the lighter oxygen isotope in the precipitation, and subsequently in the stalagmite, because of the long trajectory associated with the water vapor. When the temperature of the sea water of the Indian Ocean and the middle-East Pacific is high, the Western Pacific subtropical high becomes strong and subsequently extends southwestward. The Chinese monsoon zone is then controlled by the Meiyu front, which results in the reduction of the water vapor from the Indian Ocean. In contrast, the water vapor from the Western Pacific, which is near Monsoonal China, increases. This implies that the heavier isotopic composition of the precipitation, due to the short transmission distance, is found in the stalagmite oxygen isotope record. Therefore, the author suggests that the changes in the stalagmite oxygen isotope records are due to the Chinese monsoon “circulation effect”,which agrees with the Rayleigh fractionation principle and reflects the changes in the Indian/Pacific Ocean circulation.