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Klima 4-2011

CO2 from Arctic soil

When temperatures rise, enormous amounts of organic material in the soil can break down and release CO2. Studies show that peat soils in the Arctic contains especially large amounts of degradable organic material.

Av Daniel Rasse, Christophe Moni, Annelene Pengerud, Line Tau Strand, Katrin Knoth De Zarruk og Arne Grønlund

Vast expanses of Arctic land areas are covered by permafrost, permanently frozen ground that only thaws on the surface in the summer.
 
The amount of carbon in permafrost has previously been estimated at about 400 gigatonnes down to a depth of three metres, but more recent research suggests that this amount may be as much as 1,000 gigatonnes. This shows that enormous amounts of organic material may be available for biological degradation if temperatures rise.
 
The Arctic is vulnerable 
The Arctic region is believed to be the part of the world that is most vulnerable to climate change as well as the region that can expect the greatest increase in temperatures. Some Arctic land formations shaped by permafrost are already on the verge of disappearing due to thawing. One example of this is the palsa mires in Finnmark County in northern Norway. As temperatures continue to rise, more and deeper soil will thaw and be exposed to free-flowing water and temperatures over the freezing point after having been frozen for several thousands of years.
 
In Earth system models developed to predict feedback mechanisms for greenhouse gases in the climate system, the uncertainty of the response of organic material to global warming is greater than the uncertainty related to ocean circulation. There are no other areas where the amount of carbon in the soil and the uncertainty of the response to climate change are as great as in the Arctic.
 
Mineralization leads to CO2
Increasing temperatures have a major impact on the rate of conversion of organic matter to CO2. This process is called mineralization because it converts organic carbon to mineral form. When the temperature is below zero, almost no mineralization occurs. This is the main reason for the large stores of carbon in Arctic soil. A key factor in predicting future climate change is the rate of organic matter mineralization as the permafrost thaws and temperatures rise. Many studies have been conducted on the sensitivity of soil organic matter mineralization to increasing temperature in more temperate soils, but it is unknown whether Arctic soils have a similar temperature response. The main reason for this uncertainty is that the degradation of organic matter and the temperature response appear to depend on the quality and the chemical composition of the organic material. As a result, knowledge about the amount and quality of the organic material is crucial for gaining insight into the future carbon balance.
 
In the past three years we have studied how Arctic soil with and without permafrost responds to increasing temperatures, and we have looked at this in relation to the chemical composition of the organic material.
 
Large variation
We have collected soil samples from Svalbard, Finnmark County and Northwest Russia, conducted numerous chemical characterizations of the organic matter, and determined the rate of CO2 production as a function of increasing temperature. So far we have found a large variation in the chemical composition of organic material, but we have not found qualitative differences that can be attributed directly to permafrost. The response to a temperature increase is high for Arctic soil both with and without permafrost, with more than a doubling of the rate of CO2 production for a 10-degree increase in temperature (Figure 1). CO2 production appears to respond to a temperature increase in the same way as that reported for soil from more temperate areas. However, we have observed that peat soil with permafrost is more sensitive than mineral soil. The peat soil we studied presented at depth larger amounts of easily degradable organic material with a great capacity for producing CO2 when warming occurs. When we know in addition that peat soil in permafrost areas has large carbon stores, this emphasizes the need to closely monitor greenhouse gas emissions from bog areas with permafrost as temperatures rise.
 
PEAT SOIL: Palsa mire in Neiden in Finnmark County, Norway, is a special type of landscape on the outskirts of the permafrost area, which consists of mire with peat mounds – palsas – with permafrost. The mounds can be up to several metres high and cover several hundred square metres. Between the mounds is mire without permafrost.

Sist oppdatert: 11.10.2011

Facts: CO2 from mineralized carbon in soil

The project entitled “Organic Matter in Permafrost: Molecular Composition and Associated Response to Increasing Temperature” (PERMASOM) is being carried out in the period from 2008 to 2011. The project manager is Daniel Rasse of Bioforsk.

Figure 1: CO2 production in soil as response to increasing temperature

CO2 production (µg per g organic carbon per day)
Mineral soil
Peat soil
Temperature, °C

Figure 1: CO2 production in soil as response to increasing temperature

CO2 production (µg per g organic carbon per day)
Mineral soil
Peat soil
Temperature, °C
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