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High-resolution glacial and deglacial record of atmospheric methane by continuous-flow and laser spectrometer analysis along the NEEM ice core

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Publication date 2013
Author Chappellaz J., Stowasser C., Blunier T., Baslev-Clausen D., Brook E. J., Dallmayr R., Fain X., Lee J. E., Mitchell L. E., Pascual O., Romanini D., Rosen J., Schuepbach S.,
Project Schweizerische Beteiligung an der Eis-Tiefbohrung in Nordwest Grönland NEEM (Teil 2)
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Original article (peer-reviewed)

Journal CLIMATE OF THE PAST
Volume (Issue) 9(6)
Page(s) 2579 - 2593
Title of proceedings CLIMATE OF THE PAST
DOI 10.5194/cp-9-2579-2013

Open Access

URL http://www.clim-past.net/9/2579/2013/
Type of Open Access Publisher (Gold Open Access)

Abstract

The Greenland NEEM (North Greenland Eemian Ice Drilling) operation in 2010 provided the first opportunity to combine trace-gas measurements by laser spectroscopic instruments and continuous-flow analysis along a freshly drilled ice core in a field-based setting. We present the resulting atmospheric methane (CH4) record covering the time period from 107.7 to 9.5 ka b2k (thousand years before 2000 AD). Companion discrete CH4 measurements are required to transfer the laser spectroscopic data from a relative to an absolute scale. However, even on a relative scale, the high-resolution CH4 data set significantly improves our knowledge of past atmospheric methane concentration changes. New significant sub-millennial-scale features appear during interstadials and stadials, generally associated with similar changes in water isotopic ratios of the ice, a proxy for local temperature. In addition to the midpoint of Dansgaard–Oeschger (D/O) CH4 transitions usually used for cross-dating, sharp definition of the start and end of these events brings precise depth markers (with ±20 cm uncertainty) for further cross-dating with other palaeo- or ice core records, e.g. speleothems. The method also provides an estimate of CH4 rates of change. The onsets of D/O events in the methane signal show a more rapid rate of change than their endings. The rate of CH4 increase associated with the onsets of D/O events progressively declines from 1.7 to 0.6 ppbv/yr in the course of marine isotope stage 3. The largest observed rate of increase takes place at the onset of D/O event #21 and reaches 2.5 ppbv/yr.
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