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| Titel |
Predictive modelling of terrestrial and sub-aquatic permafrost in Northern Eurasia: implications for the global carbon cycle and climate |
| VerfasserIn |
O. Anisimov, S. Reneva, V. Kokorev |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250063182
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| Zusammenfassung |
| Permafrost contains about 1670 Gt of carbon, which is nearly one half of the global soil
carbon pool. The concept of “methane bomb” associated with the rapid release
of significant amounts of methane from thawing permafrost and amplification of
the global climate change has been widely discussed in the scientific literature.
Particular concerns are associated with thawing Siberian wetlands, and with the East
Siberian Arctic Shelf (ESAS). Recent observations indicate high concentrations
of methane over ESAS, up to 7-8 ppm at selected locations over the Laptev sea,
while the latitude-mean atmospheric methane concentration equals 1.85 ppm. Some
researchers attribute it to the increased gas permeability of thawing sub-sea permafrost,
destabilization of hydrates and enhanced venting of methane to the atmosphere trough
taliks. In this study we use mathematical modelling to calculate the past, present
and future state of the Northern Eurasian terrestrial and sub-aquatic permafrost, to
quantify the contribution to the global methane balance, and to evaluate the climate
feedback.
GIS analysis of small-scale digital topographic maps indicated that the total area of Siberian
wetlands is approximately 0.7 million km2, of which ca 0.35 mln km2 are located
in permafrost regions. Estimated net flux of methane from the frozen wetlands
under the current climatic conditions is about 28.5 Mt/y. According to our model
results, projected by the mid-21st century changes in the volume of the seasonally
thawing organic-rich soils and higher soil temperatures may increase the methane
flux from Siberian frozen wetlands by 6-10 Mt/y, which is likely to increase the
atmospheric concentration by 100 Mt and lead to ca. 0.01 °C global temperature
rise.
We used a comprehensive model forced with the transient regional climatic scenario to
simulate the dynamics of permafrost and the depth to the boundaries of hydrate stability zone
(HSZ) at ESAS over the period from the last glacial maximum 18-20 Ky b.p. up to the end of
the millennium. The model is based on the heat transfer equation and explicitly accounts for
the effect of salt diffusion in the bottom sediments by coupling the thermal and mass fluxes.
We used a climate scenario suggesting that at the time of inundation (ca 8 Ky b.p.) the top
sediment layer warmed by ca. 12 °C from -13.5 °C (mean annual air temperature) to -1.5 °C
(bottom water temperature). Temperature was set to this constant value until 1985. Since then
in accord with modern observations we imposed 0.09°C/year trend until 2100, and
afterwards prescribed the temperature to constant value of 11.5 °C. The rate of
temperature change in the 21st century in this schematic scenario by far exceeds all IPCC
projections. It has been made intentionally to explore the likelihood of the so-called
“methane bomb” concept under most favourable, though highly unrealistic, climate
conditions.
Ultimately, our results do not support this hypothesis indicating that enhanced concentrations
of atmospheric methane at ESAS are not related to recent climatic changes. Our main
conclusion is that in the following 1000 years permafrost layer characterized by near-zero gas
permeability will remain at ESAS above the HSZ preventing the massive escape of methane
to the atmosphere except for the fault zones, where it seeps already under the current
conditions.
Acknowledgement. This study is supported by the German-Russian Otto Schmidt
Laboratory, project OSL-12-02, and the Russian Foundation for Basic Research, project
11-05-12011. |
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