High-resolution glacial and deglacial record of atmospheric methane by continuous-flow and laser spectrometer analysis along the NEEM ice core
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...
| Main Authors: | , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2013-11-01
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| Series: | Climate of the Past |
| Online Access: | http://www.clim-past.net/9/2579/2013/cp-9-2579-2013.pdf |
| Summary: | 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 (CH<sub>4</sub>) record covering the time period from 107.7 to
9.5 ka b2k (thousand years before 2000 AD). Companion discrete CH<sub>4</sub>
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 CH<sub>4</sub> 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) CH<sub>4</sub> 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 CH<sub>4</sub> 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 CH<sub>4</sub> increase associated with the onsets of D/O events progressively
declines from 1.7 to 0.6 ppbv yr<sup>−1</sup> 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<sup>−1</sup>. |
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| ISSN: | 1814-9324 1814-9332 |