Local artifacts in ice core methane records caused by layered bubble trapping and in situ production: A multi-site investigation

Deglaciations are characterized by the largest natural changes in methane (CH4) and nitrous oxide (N2O) concentrations of the past 800g€¯000 years. Reconstructions of millennial- to centennial-scale variability within these periods are mostly restricted to the last deglaciation. In this study, we present composite records of CH4 and N2O concentrations from the EPICA Dome C ice core covering the penultimate deglaciation at temporal resolutions of g1/4100 years. Our data permit the identification of centennial-scale fluctuations during the transition from glacial to interglacial levels. At g1/4134000 and g1/4129000 years before present (hereafter ka), both CH4 and N2O increased on centennial timescales. These abrupt rises are similar to the fluctuations associated with the Dansgaard-Oeschger events identified in the last glacial period. In addition, gradually rising N2O levels at g1/4130g€¯ka resemble a pattern of increasing N2O concentrations on millennial timescales characterizing the later part of Heinrich stadials. Overall, the events in CH4 and N2O during the penultimate deglaciation exhibit modes of variability that are also found during the last deglaciation and glacial cycle, suggesting that the processes leading to changes in emission during the transitions were similar but their timing differed. © 2021 Copernicus GmbH. All rights reserved.