Arctic tundra landscape in summer.
Photo: Nicolas Valiente.
He global change is causing changes in climate patterns at regional, continental and hemispheric scales. One of the regions most vulnerable to climate change is the Arcticwhich has warmed almost four times faster than the rest of the planet in recent decades.
The Arctic regions are home to the world’s largest reserves of organic carbon y nitrogen from the ground, linked to areas with permafrost.
What is permafrost?
Permafrost is the layer beneath the Earth’s surface that remains at a temperature equal to or below 0 ºC for at least two consecutive years. It can be found on land or under the ocean floor.
The ‘active layer’ of permafrost refers to the surface layer that thaws in summer and refreezes in autumn, and whose thickness depends on the region where it is located. In the northern hemisphere it covers about 23 million km² (more than twice the surface area of Europe) and owes its origin to the glaciations that occurred during the Pleistocene. They were trapped in the permafrost Dead plant remains and humus before its decomposition began and, therefore, also organic carbon and nitrogen.
When the ground melts
Climate models estimate that due to global warming, the global surface area of subsoil permafrost will have decreased by 93% for 2100 in the worst possible scenario.
The effects of this decline are already visible in the northern hemisphere as a result of the increase in soil temperature.
Permafrost losses occur both from the deepening of the active layer and from the development of thermokarst processes.
Evolution of the area occupied by permafrost between 2003 and 2017. ESA.
When permafrost has a low ice content, a gradual melting process occurs from the top down during the summer period. However, melting of ice-rich permafrost results in thermokarst processess, which occur abruptly and lead to the alteration of the hydrological conditions of the terrain.
Due to the loss of volume when frozen ground turns to water, the ground sinks and collapses. Although thermokarst formation is a localized alteration of the soil’s thermal regime, its widespread occurrence affects large areas, reaching 40% of the northern permafrost region.
Thermokarst processes have impacts on the landscape such as erosion along the coast or the formation of numerous lakes in inland areas. These lakes are dynamicvarying with each annual freeze-thaw cycle.
Permafrost core of about 40 cm. An upper part can be seen, in contact with the active layer, rich in frozen organic matter, and a lower part where the presence of ice wedges predominates. Photo: Nicolás Valiente.
Consequences for communities and climate
The melting of permafrost, and especially that linked to the formation of thermokarst, has significant impacts on local communities of these regions, causing serious damage to their infrastructure.
In addition, this merger has global consequences for the climateAs if it were a huge refrigerator, the fusion caused by the increase in temperature accelerates the decomposition of organic matter stored for thousands of years.
As existing microorganisms become active and break down organic matter, release greenhouse gases such as carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O).
The release of these gases increases global warming, which in turn induces further melting of permafrost. This feedback loop is one of those identified as climate tipping pointsthe overcoming of which compromises the viability of our planet.
Positive carbon feedback
Permafrost contains about twice as much carbon as is found in currently in the atmosphere. In the northern hemisphere alone, it is home to approximately 1.7 trillion tons of carbon.
As permafrost melts, water saturation conditions determine which microbial processes transform the available organic carbon. In well-drained soils, oxic (oxygen-rich) conditions favor the decomposition of organic matter, giving rise to CO₂. In wetlands and waterlogged areas, conditions are mostly anoxic, which favors the release not only of CO₂ but also of methane, which has a global warming potential. almost 30 times higher than CO₂.
Thus, recent studies show the role of microbial processes in the supersaturation of both gases in thermokarst lakesHowever, it is not all “bad news”. It is believed that up to 60% of the CH₄ produced in these systems is metabolized by methanotrophic organisms, reducing its potential impact on the atmosphere.
What happens to nitrogen?
Compared to the carbon cycle, little is known about the oxygen cycle. nitrogen in soils affected by permafrost.
Polar regions are deficient in nitrogen due to the low rates of mineralization and biological fixation that occur there. Nitrogen availability determines the primary productivity of ecosystems.
Microorganisms can use nitrogen either to produce biomass or to obtain energy through metabolic processes. Some, such as nitrification and denitrification, produce nitrous oxide as a byproduct. N₂O is an important greenhouse gas, with a potential 273 times greater than that of CO₂.
As global warming degrades permafrost deposits, some of the nitrogen stored could be released, affecting the productivity of terrestrial, aquatic and marine ecosystems. This could lead to additional N₂O emissions, but could also mitigate the climate feedbacks by promoting greater carbon sequestration by existing vegetation and microbial communities.
As permafrost melting is projected to increase significantly over the coming decades, further efforts are needed to improve understanding of the microbial processes controlling carbon and nitrogen cycles in these regions, especially those associated with greenhouse gas emissions.
Nicolas Valiente Parraprofessor of Biotechnology and researcher in Microbial Ecology, University of Castilla-La Mancha
This article was originally published in The Conversation. Read the original.
