过去2000 年大气甲烷含量与气候变化的冰芯记录

温室气体与气候变化的关系是当前全球变化研究中的一个核心内容。目前关于大气温室气体含量变化只有几十年的实测资料, 而冰芯包裹气体中的CH4 不仅能反映过去大气CH4 含量随时间的变化, 而且能很好地揭示陆地CH4大气中的释放随时间及空间的分布。

ATMOSPHERIC METHANE CONCENTRATION AND CLIMATE CHANGE RECORDED IN ICE CORES OVER THE PAST 2000 YEARS

The relationship between greenhouse gases and climatic change is a pivotal task for the research of global change at present. Greenhouse gas concentrations in the atmosphere have been documented directly only since several decades ago, but they can be reconstructed through ice core analysis. The combined analyses of ice cores from Greenland and Antarctica, have allowed to quantify a remarkable difference of methane mixing ratio between the two polar regions in the past, revealing that there existed a large pole to pole methane gradient, and the methane concentration in north latitudes was higher than in Antarctica. It is suggested that the tropical area was the source area for global methane in pre-industrial time. However, the lacking of constraint on methane mixing ratio in tropical to low-middle latitudes becomes the major limitation for the reconstruction of global methane concentration in the past. This study was designed to solve this problem by analyzing ice cores from the Dasuopu in the Tibetan Plateau. The Dasuopu record shows an obvious methane concentration increase in the low-middle latitudes since industrialization, revealing a similar trend of methane concentration fluctuation recorded in polar ice cores. The high resolution of details of the Dasuopu record over the last century reveals a significant period between the two World Wars when the methane increase caused by human being activities was halted. This sub-tropical methane record also allows quantifying for the first time the difference of methane mixing ratio between polar and sub-tropical latitudes during the pre-industrial time. The average methane concentration in the Dasuopu record is 782nmol /mol in the time interval of 0 ～1850A. D., and the maximum temporal variation exceeded 200nmol /mol which has never been found in polar ice records. In average it is 66nmol /mol higher than Greenland and 109nmol /mol higher than Antarctica, agreeing with the former suggestion that the lower latitude areas are the source areas of global methane in pre-industrial time. Our data shows however that for the past 1000 years, the emission of methane in mid-high latitudes increased largely. During the past 2000 years, the latitudinal difference of climate change in the North Hemisphere had a crucial impact on the terrestrial methane emissions.