Methane concentration and delta deuterium of methane from the NGRIP ice core

The causes of past changes in the global methane cycle and especially the role of marine methane hydrate (clathrate) destabilization events are a matter of debate. Here we present evidence from the North Greenland Ice Core Project ice core based on the hydrogen isotopic composition of methane [dD(CH4)] that clathrates did not cause atmospheric methane concentration to rise at the onset of Dansgaard-Oeschger (DO) events 7 and 8. Box modeling supports boreal wetland emissions as the most likely explanation for the interstadial increase. Moreover, our data show that dD(CH4) dropped 500 years before the onset of DO 8, with CH4 concentration rising only slightly. This can be explained by an early climate response of boreal wetlands, which carry the strongly depleted isotopic signature of high-latitude precipitation at that time.

全球甲烷循环既往变化的成因，尤其是海洋甲烷水合物（clathrate）失稳事件所扮演的角色，迄今仍存在学术争议。本研究基于北格陵兰冰芯计划（North Greenland Ice Core Project）冰芯的甲烷氢同位素组成[δD(CH₄)]，获得相关证据，证实第7、8次丹斯果-奥什格尔（Dansgaard-Oeschger，DO）事件发生初期，甲烷水合物并未导致大气甲烷浓度上升。箱式模型（box modeling）结果支持，北方湿地排放是此次间冰阶甲烷浓度升高的最合理解释。此外，我们的数据显示，在第8次DO事件启动前500年，δD(CH₄)便已下降，而同期甲烷浓度仅出现小幅上升。该现象可通过北方湿地的早期气候响应加以解释：彼时北方湿地的甲烷排放携带了当时高纬度降水所特有的强烈贫化同位素信号。