水合物与湿地对晚第四纪大气甲烷浓度变化影响的模型比较

Model comparison of the effect of gas hydrates and wetlands on the atmospheric methane concentration variation in late Quaternary

对于冰芯记录的古大气甲烷含量的周期变化,存在普遍接受的湿地假说,还有近十几年提出的水合物假说。O’Hara建立了一级模型试图辨别湿地和水合物这两种源对气候影响的可能性。模拟结果显示水合物可能是引起大气甲烷变化的主要来源,而否定了湿地作为最大甲烷源的可能性。对其模型的数学推导和机制的合理性进行了检验,修正了模型中的错误,模拟得出与原文不同的观点。结果表明,海底水合物甲烷含量达到10kg.m–3(或湿地甲烷含量1600kg.m–3)才能与实际冰芯甲烷记录相吻合。而自然界中还未发现如此高含量的水合物或湿地甲烷资源。但这一结果并不能否定湿地或水合物对气候变化可能造成的巨大影响,因为模型中以指数衰减模式释放甲烷意味着甲烷源区为封闭系统,所以需要较大的初始浓度而海底水合物和湿地的演化均为一个开放系统。因此,O'Hara原文的模型和机制能否反映实际情况有待商榷。

There exist the widely accepted wetlands hypothesis and a new hydrate gun hypothesis, for the periodic changes of atmospheric methane concentration recorded in the Antarctic and Greenland ice cores. O＇Hara tried to identify the probability of methane sources between gas hydrate and wetlands by model simulations with first-order kinetics. The results suggested that it is not wetlands but gas hydrate that may be the major source of the atmospheric CH4. This paper checked the mathematical derivation and the model mechanism, then corrected the model and came up with distinguished new results. The best-fit modified model requires the methane concentration of 10 kg-m 3 for marine gas hydrates or that of 1600 kg＇m-3 for wetlands. But no methane source with so high content is found in gas hydrate or wetlands. The results did not eliminate gas hydrate or wetlands as the primary CH4 source, but reflected that the model was a closed system for the CH4 source, which so needs high initial methane concentration. This model mechanism conflicts with the fact that both gas hydrates and wetlands develop as open systems.