Bubble enclosures in polar ice cores represent the only direct paleoatmospheric archive. Ice core reconstructions of atmospheric methane concentrations show significant increases for both glacial/interglacial transitions as well as for rapid warming events (Dansgaard/Oeschger events).The source for these emissions is still a matter of debate with terrestrial wetlands, permafrost and marine gas hydrates being potential candidates. Additionally terrestrial plants producing methane under aerobic conditions could play a major role.By means of stable carbon and hydrogen isotope analysis of methane in ice core air bubbles we are able to distinguish between different methane sources. To this end a high-sensitivity, high precision mass spectrometric technique is currently developed.