Download - Vulnerability of frozen carbon
Vulnerability of frozen carbon
D.V. Khvorostyanov1,2, G. Krinner2, P. Ciais1,
S.A. Zimov3
1Laboratoire des Sciences du Climat et l'Environnement,
Gif-sur-Yvette, France2Laboratoire de Glaciologie et Géophysique de l'Environnement,
St Martin d’Hères, France3Northeast Science Station, Cherskii, Russia
Permafrost
22.8 millions km2 or 23.9% NH land area Continuous permaforst as far as 50-60oN to the northeast of Lake Baikal 63% mainly in Siberia, Russian Far East, Northern Mongolia, Northeastern China
Continuous (90-100% area)Discontinuous (50-90% area)Sporadic (10-50% area)Isolated Patches (<10% area)
Permafrost melting
•12-22% all types•12-34% continuous
Area decrease by 2050:
Anisimov&Nelson 1997
Oelke et al, GRL 2004:Active layer depth increase1980 – 2002
NH Cryosols7.8 mln km2 268 Gt (16% world soil organic C)Soil C estimates:
top 1m only!
North America:
3.6 mln km2
(46%)
107 GtC (40%)Mean C content:31 kgC m-2
Eurasia:
4.2 mln km2
(54%)
162 GtC (60%)Mean C content:39 kgC m-2
Tarnocai et al, 2003
Yedoma Ice: Northeast Siberia
• 1-million km2 area of carbon-rich loess sediments
• Presumably 400 GtC at mean depth of 12 m and 33 kgC m-3 density
Zimov et al,Science 1997
Alekseev et al, Soil Science Society of America Journal (2003)
Temperature dependence of biomass decomposition
One C pool (Glardina&Ryan 2000)
Three C pools (Knorr et al 2005)
«One question, two answers»D.Powlson, Nature 2005
Goulden et al (1998) measurements: permafrost thaw =>
10-fold increased decomposition
Atmospheric warming feedbacks
Soil Model Processes
Heat conduction with freezing/thawing
Hydrology
Soil carbon consumptionOxic decompostion
Methanogenesis
Methanotrophy
Diffusion of O2 and CH4
Transfer of gases due to pressure difference
Methane ebullition
Holocene configuration: comparison with observations
Methane fluxes Cherskii, summer 2003
One point in Siberia...
• First we test the model sensitivity and study in some detail the key processes providing the feedback
• These are local climate conditions that matter for this part of the study
So we choose a point in the central southern Siberia but with soil configuration of Yedoma Ice
The region of interest is Northeast Siberia, but…
The surface forcing: 1000 + 1000
Present-day climate
2xCO2
Soil carbon balance
Indefinite integrals over time:
How much of the soil carbon has been transformed in one of these processes at a given time
Some details
Step forcing and soil response
3 types of simulations: No oxygen limitation on the oxic
decomposition Oxygen limitation, no methane Methanogenesis and
methanotrophy included
Step forcing and soil response
Biomass decomposition and methanotrophy
➔ …are accompanied by heat release to the soil
➔ …occur without heat release
Surface forcing: 1000 + 125 + 1000
Soil carbon consumption
Model sensitivity analysis
Carbon (kgC m-2)
releasead since
the 2 CO2 warming
Accumulated surface
methane flux over
the same time
Sensitivity to respiration heat
Threshold between 35 and 40 MJ kgC-1
Very small changes in consumed C elsewhere
Methane fraction grows very slightly
Sensitivity analysis résumé
Control soil respirationand heat transfer
Control methanogenesis,methanotrophy
Simulations for the Yedoma Ice region
About 2 GtC areconsumed in the first100 yrs, 4 GtC in 200 yrs
Conclusions
The model reasonably simulates methane fluxes on seasonal timescales
The carbon consumption time scale is about a few centuries in response to 2xCO2 forcing
Decomposition heat release can be essential for the positive feedback between the global warming and frozen soil response
Availability of oxygen, methanogenesis, and local climate conditions determine its existence and parameters
Model sensitivity is the largest with respect to the parameters determining soil heating, freezing/thawing, and respiration
About 4 GtC are released in the atmosphere as CO2 in the first 200 years after the rapid 2xCO2 warming