从钻孔温度看气候变化──方法介绍及实例

READING PALEOCLIMATE FROM BOREHOLE TEMPERATURE PROFILES:PRINCIPLES AND EXAMPLES

地壳浅层的地温分布与过去一定时期的地表温度变化之间有着内在的联系，地温场记录着地表温度变化的历史。由于地表温度是描述气候变化的重要参数，通过对钻孔地温数据进行分析处理，可以达到研究古气候变化的目的。美国东北部、加拿大东南部和中国四川攀西地区若干钻孔地温剖面的反演结果一致表明，这些区域在过去数百年间地表温度均有不同程度的升高。与研究古气候的其他方法相比，地热方法具有理论基础牢固和现成数据基础庞大的突出特点，这一研究方法在世界范围的广泛应用必将有助于揭开全球气候变化的奥秘。

Temperature at the surface, determined principally by climate, serves as a boundary condition for establishing the thermal regime at shallow depths. The past changes of temperature at the surface transmitted down to subsurface by thermal conduction and were recorded as transient perturbations to a steady state temperature field. Recent efforts made by the international geothermal community in reconstructing the surface temperature history have demonstrated that borehole temperatures comprise valuable information about climate changes over the past few centuries.Both forward and inverse methods have been developed and employed by various authors in deriving climate information from borehole temperatures.Compared to other techniques in paleoclimate studies, the geothermal method of climate reconstruction has its limitations, such as lower resolution and shorter recoverable climate history. But it also has many remarkable advantages:(1) it is based on the well developed analytical theory of heat conduction rather than on an empirical relationship; (2)its concrete theoretical foundation makes the use of both forward and inverse methods possible;(3)it can directly reconstruct surface temperature, and therefore is free of uncertainties arising from conversion of proxy data to temperatures; (4) climate signals preserved in subsurface temperatures are usually less disturbed by anthropogenic sources; (5) the existing archives of borehole temperature data endow the geothermal technique with great potential for a world-wide study; and (6) the time interval for which this method displays its best resolving power covers both the industrial and preindustrial periods, facilitating an assessment of the greenhouse effect in global warming.Results from northeast United States, southeast Canada, and the Panxi area of southwest China are presented as examples of the application of this geothermal method. Investigations of the borehole temperature profiles selected from these areas show a warming with amplitudes of 0.6-2.1℃ typically over the last 300 years.The results inferred from the geothermal data are in general agreement with regional and global meteorological records, which significantly extend our knowledge about the surface temperature history.