Ice Record of δ13C for Atmospheric CH4 during the Last Termination
Abstract
Methane (CH4) is the second most important anthropogenic greenhouse gas after CO2 with a stronger global warming potential. The changes of atmospheric methane concentrations are in phase with rapid climate changes in the past. The force that drives these processes is still unknown but can be constrained using methane isotopic information from ice cores. In this study, we report atmospheric methane carbon isotope ratios from North Greenland Eemian ice drilling (NEEM) ice, covering the last glacial-interglacial transition (9-32 ky BP). The results show that the carbon in atmospheric methane was isotopically enriched during the glacial period, in agreement with previous studies (Fischer et al, 2008). This implies stronger emissions from more 13C-enriched sources or a stronger 13C fractionation in the sink than assumed. Another hypothesis, recently investigated, suggests that the carbon isotopic signature is not stable over time, as was commonly assumed, but varies over time as a response to environmental changes (Schaefer and Whiticar, 2008). We investigate the role of the different processes using two-box model calculations, where we attempt to simulate natural variations in the underlying biogeochemical processes and the atmospheric composition of the past. For this, we use published emission estimates for the strongest contributing sources, emissions from wetlands and biomass burning, in order to better constrain source and sink strengths during the last glacial termination (Power et al, 2008; Ringeval et al, 2010; 2012; Hopcroft et al, 2011; Banda et al, 2012; Guangqi et al, 2013).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.B21A0479P
- Keywords:
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- 0414 BIOGEOSCIENCES Biogeochemical cycles;
- processes;
- and modeling