『Abstract
Reconstructions of past atmospheric concentrations of greenhouse
gases provide unique insight into the biogeochemical cycles and
the past radiative forcing in the Earth's climate system. We present
new measurements of atmospheric nitrous oxide along the ice cores
of the North Greenland Ice Core Project and Talos Dome sites.
Using records of several other ice cores, we are now able to establish
the first complete composite nitrous oxide record reaching back
to the beginning of the previous interglacial about 140,000 yr
ago. On the basis of such composite ice core records, we further
calculate the radiative forcing of the three most important greenhouse
gases carbon dioxide, methane and nitrous oxide during more than
a full glacial-interglacial cycle. Nitrous oxide varies in line
with climate, reaching very low concentrations of about 200 parts
per million by volume during Marine Isotope Stages 4 and 2, and
showing substantial responses to millennial time scale climate
variations during the last glacial. A large part of these millennial
time scale variations can be explained by parallel changes in
the sources of methane and nitrous oxide. However, as revealed
by high-resolution measurements covering the Dangaard/Oeschger
events 17 to 15, the evolution of these two greenhouse gases may
be decoupled on the centennial time scale. Carbon dioxide and
methane concentrations do not reach interglacial levels in the
course of millennial time scale climate variations during the
last glacial. In contrast, nitrous oxide often reaches interglacial
concentrations in response to both, glacial terminations and Dansgaard/Oeschger
events. This indicates, from a biogeochemical point of view, similar
drivers in both temporal cases. While carbon dioxide and methane
concentrations are more strongly controlled by climate changes
in high latitudes, nitrous oxide emissions changes may mainly
stem from the ocean and/or from soils located at low latitudes.
Accordingly, we speculate that high latitudes could play the leading
role to trigger glacial terminations
Keywords: greenhouse gas; radiative forcing; carbon dioxide; methane;
nitrous oxide; paleo』
1. Introduction
2. Data records
3. N2O artefacts
4. Results
4.1. Glacial N2O variations
4.2. N2O during the DO events 17 to 15
5. Discussion
5.1. Radiative forcing during the last 140 kyr
5.2. Comparison of millennial time scale climate variations and
glacial terminations
6. Conclusions
Acknowledgments
Appendix A
A.1. Measurement technique for N2O and
CH4
A.2. Offset corrections for N2O and CH4 measurements
A.3. Measurement technique for dust
A.4. Time scale synchronisation
Appendix B. Supplementary data
References