摘要
过去全球变化是全球变化研究的重要组成部分。探讨地球环境在地质时期的变化规律是人们预测未来气候变化、应对目前和将来日益严峻的环境问题的迫切需求。我国位于典型的季风气候区,夏季风带来的降水是我国人口最多、经济最发达的广大东部地区发展的重要基础。并且季风演化引起的气温、降水等气候指标的变化深刻影响着该地区的人类活动,因此季风的研究成为国内外的研究热点。重庆位于我们南部季风区,受到东南、西南季风的共同影响,受地形影响,“焚风效应”显著,夏季闷热,降雨集中,冬季寒冷多雨的气候,影响着重庆地区经济的发展。
温度和降水是影响水中氧同位素分馏的主要因素。随着海拔的升高,温度和降水会发生相应的变化。即温度随着海拔的升高会降低,海拔每升高100 m气温会减低0.6℃；降水随着海拔的升高会增多。海拔较高的洞穴,洞穴滴水中氧同位素也会因海拔的升高带来的温度和降水的变化发生改变。金佛山最高峰海拔在2251m,当海拔升高,气温降低,云层中水汽更易凝结,降水量增加,洞穴滴水中δ180值偏负。
通过对羊口洞的监测研究,发现在滴量、洞穴温度和水温三个指标中,滴量与洞穴滴水中氧同位素相关性最高,R在0.836-0.988之间；其次是滴水氧同位素与洞穴温度的相关性,R在0.513-0.84之间；相关性最小的是水温与滴水氧同位素的相关性,R在0.466-0.715之间。其中YK3#与YK4#的滴水氧同位素与滴量呈反相关关系,体现出“降水量效应”,即滴水中氧同位素与降水量呈负相关关系。由于冬季洞内温度为四季中最低,而且洞内4个滴水点滴水的氧同位素值均在冬季最偏负,体现出典型的“温度效应”,即滴水中氧同位素与温度呈正相关关系。对YK1石笋的生长速率研究发现：23.7-22.8 ka BP,沉积速率为53.6 mm/ka,此段沉积速率最高,可是氧同位素值却偏正。说明在石笋生长速率较快时,其氧同位素值不一定偏负,这与芙蓉洞中FR5石笋氧同位素值与其沉积速率的关系一样。
YK1石笋氧同位素的高分辨率记录,明确了H2和D-O 2事件结束的时间分别是23.57±0.047 ka BP和22.46±0.045 ka BP,H1事件开始的时间是16.63±0.05 kaBP。与我国同纬度地区石笋及南海海洋沉积物记录一致,早于格陵兰冰芯、青藏高原湖泊沉积物、印度洋低纬地区石笋记录,而晚于南半球高纬地区石笋记录。
YK1氧同位素记录与我国季风区、南亚季风地区石、南北半球高纬度对于古气候事件的记录存在时间上的不同步。但由于各个载体在年龄控制点和年龄误差各不相同,所以仍然需要更多分辨率更高的氧同位素记录来确定古气候事件的起止时间,从而明确古气候信息在各地区持续时间。
The past global change is one of the most important parts in the investigation of the global changes. Exploring how the climate changed in the geological period does benefit to the prediction of the climate change in the future which is necessary because of the serious environment crisis now. China locates in the typical monsoon region and the summer monsoon takes plentiful precipitation to the east of China which is the most populous and developed region of China. The evolvement of summer monsoon must lead to the variation of rainfall and temperature of east China and the deeply affect human lives in this region. Therefore, the researches of monsoon variation have been one of the most important hotpots in climate change. Chongqing locates in the south monsoon region of China, affected by southeast and southwest monsoon, and landform, remarkable"Burn wind effdct",the climate characteristic is muggy in summer, precipitation concentrated, cold and rainy in winter, which affect the develope of economy in Chongqing.
Temperature and precipitation are the major factors which influence the fractionation of the oxygen isotope. Temperature and precipitation will change relevantly when altitude rise. That is, temperature will be reduced with the rise of elevation; precipitation will be increased with the rise of altitude. The oxygen isotope of the drop water in the cave with the high altitude also will change because the rise of altitude can change of temperature and precipitation. The elevation of Jinfo Mountain peak is 2251m,when altitude rise, temperature will reduce, the vapor condensed easier in the cloud, precipitation will increase, and theδ18O of drip water in cave will change lower. The result show that among the volume of drip water, temperature in cave and temperature of drip, the volume of drip water and the oxygen isotope of drip water have the highest correlation, the value of R is between 0.988～0.836; temperature in cave and the oxygen isotope of drip water have the higher correlation, the value of R is between 0.513～0.84;the lowest correlation is between temperature of drip water and the oxygen isotope of drip water, the value of R is between 0.466～0.715. The relationship between the oxygen isotope and the volume in the drip water is opposite at the site of YK3# and YK4#, which present "precipitation effect"(that is the relationship between the oxygen isotope and precipitation is negative correlation). The value of oxygen isotope in four sites'drip water is the lightest in winter because the temperature is lowest in winter, and this is "temperature effect"(that is the relationship between the oxygen isotope and temperature is positive correlation)) We can found:23.7～22.8 ka BP, the stalagmite grew fastest with deposit rate is 53.6 mm/ka, but the value of oxygen isotope is increase It is show that the value of oxygen isotope is not light when stalagmite grew fast, and it is like the FR5 recorded.
High-resolution oxygen isotope record of YK1 recorded certainly the termination of H2 and D-O2 at 23.57 ka BP and 22.46 ka BP, the beginning time of H1 at 16.63 ka BP. The oxygen isotopic record of YKl is consistent with the stalagmite records of the same latitude region; and earlier than Greenland ice core records, lake sediments in Tibet Plateau, the stalagmite records in low latitude region of India Ocean; later than the stalagmite records in high latitude of South hemisphere.
Compared with monsoon region in China, monsoon region in South Asia, the high latitude region in South and North hemisphere, the record of YK1 and the records are not synchronous. Because of the different age point and age error, it is need more and higher-resolution oxygen records to determine the start and stop time of these paleoclimate events, so that to confirm the duration about paleoclimate information in different region.
引文
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