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Permafrost carbon cycle

Permafrost carbon cycle is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Permafrost carbon cycle rather than just read about it. In short: The permafrost carbon cycle or Arctic carbon cycle is a sub-cycle of the larger global carbon cycle. Permafrost is defined as subsurface material that remains below 0o C (32o F) for at least two consecutive years.

Permafrost carbon cycle — main illustration
Permafrost carbon cycle — illustration

Key takeaways

  • Permafrost carbon cycle belongs to earth science; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Permafrost carbon cycle to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Permafrost carbon cycle from memory before moving on to harder problems.

Reference excerpt

The permafrost carbon cycle or Arctic carbon cycle is a sub-cycle of the larger global carbon cycle. Permafrost is defined as subsurface material that remains below 0o C (32o F) for at least two consecutive years. Because permafrost soils remain frozen for long periods of time, they store large amounts of carbon and other nutrients within their frozen framework during that time. Permafrost represents a large carbon reservoir, one which was often neglected in the initial research determining global terrestrial carbon reservoirs. Since the start of the 2000s, however, far more attention has been paid to the subject, with an enormous growth both in general attention and in the scientific research output. The permafrost carbon cycle deals with the transfer of carbon from permafrost soils to terrestrial vegetation and microbes, to the atmosphere, back to vegetation, and, finally, back to permafrost soils through burial and sedimentation due to cryogenic processes. Some of this carbon is transferred to the ocean and other portions of the globe through the global carbon cycle. The cycle includes the exchange of carbon dioxide and methane between terrestrial components and the atmosphere, as well as the transfer of carbon between land and water as methane, dissolved organic carbon, dissolved inorganic carbon, particulate inorganic carbon, and particulate organic carbon.

Storage Soils, in general, are the largest reservoirs of carbon in terrestrial ecosystems. This is also true for soils in the Arctic that are underlain by permafrost. In 2003, Tarnocai, et al. used the Northern and Mid Latitudes Soil Database to make a determination of carbon stocks in cryosols—soils containing permafrost within two meters of the soil surface. Permafrost affected soils cover nearly 9% of the Earth's land area, yet store between 25 and 50% of the soil organic carbon. These estimates show that permafrost soils are an important carbon pool. These soils not only contain large amounts of carbon, but also sequester carbon through cryoturbation and cryogenic processes.

Processes Carbon is not produced by permafrost. Organic carbon derived from terrestrial vegetation must be incorporated into the soil column and subsequently be incorporated into permafrost to be effectively stored. Because permafrost responds to climate changes slowly, carbon storage removes carbon from the atmosphere for long periods of time. Radiocarbon dating techniques reveal that carbon within permafrost is often thousands of years old. Carbon storage in permafrost is the result of two primary processes.

The first process that captures carbon and stores it is syngenetic permafrost growth. This process is the result of a constant active layer where thickness and energy exchange between permafrost, active layer, biosphere, and atmosphere, resulting in the vertical increase of the soil surface elevation. This aggradation of soil is the result of aeolian or fluvial sedimentation and/or peat formation. Peat accumulation rates are as high as 0.5mm/yr while sedimentation may cause a rise of 0.7mm/yr. Thick silt deposits resulting from abundant loess deposition during the Last Glacial Maximum form thick carbon-rich soils known as yedoma. As this process occurs, the organic and mineral soil that is deposited is incorporated into the permafrost as the permafrost surface rises. The second process responsible for storing carbon is cryoturbation, the mixing of soil due to freeze-thaw cycles. Cryoturbation moves carbon from the surface to depths within the soil profile. Frost heaving is the most common form of cryoturbation. Eventually, carbon that originates at the surface moves deep enough into the active layer to be incorporated into permafrost. When cryoturbation and the deposition of sediments act together carbon storage rates increase.

Current estimates

It is estimated that the total soil organic carbon (SOC) stock in northern circumpolar permafrost region equals around 1,460–1,600 Pg. (1 Pg = 1 Gt = 1015g) With the Tibetan Plateau carbon content included, the total carbon pools in the permafrost of the Northern Hemisphere is likely to be around 1832 Gt. This estimation of the amount of carbon stored in permafrost soils is more than double the amount currently in the atmosphere. Soil column in the permafrost soils is generally broken into three horizons, 0–30 cm, 0–100 cm, and 1–300 cm. The uppermost horizon (0–30 cm) contains approximately 200 Pg of organic carbon. The 0–100 cm horizon contains an estimated 500 Pg of organic carbon, and the 0–300 cm horizon contains an estimated 1024 Pg of organic carbon. These estimates more than doubled the previously known carbon pools in permafrost soils. Additional carbon stocks exist in yedoma (400 Pg), carbon rich loess deposits found throughout Siberia and isolated regions of North America, and deltaic deposits (240 Pg) throughout the Arctic. These deposits are generally deeper than the 3 m investigated in traditional studies. Many concerns arise because of the large amount of carbon stored in permafrost soils. Until recently, the amount of carbon present in permafrost was not taken into account in climate models and global carbon budgets.

… excerpt ends here. Continue reading the full article.

Illustrations

Permafrost carbon cycle: The annual number of scientific research papers published on the subject of permafrost carbon has grown from next to nothing around 1990 to around 400 by 2020.[1]
The annual number of scientific research papers published on the subject of permafrost carbon has grown from next to nothing around 1990 to around 400 by 2020.[1]
Permafrost carbon cycle illustration
Permafrost carbon cycle: Permafrost peatlands under varying extent of global warming, and the resultant emissions as a fraction of anthropogenic emissions needed to cause that extent of warming.[11]
Permafrost peatlands under varying extent of global warming, and the resultant emissions as a fraction of anthropogenic emissions needed to cause that extent of warming.[11]
Permafrost carbon cycle: Greater summer precipitation increases the depth of permafrost layer subject to thaw, in different Arctic permafrost environments.[16]
Greater summer precipitation increases the depth of permafrost layer subject to thaw, in different Arctic permafrost environments.[16]
Permafrost carbon cycle: Recent observations suggest that CO2 absorption had been increasing at a faster rate over the areas with a lot of permafrost and limited tree cover than over the areas with extensive tree cover.[22]
Recent observations suggest that CO2 absorption had been increasing at a faster rate over the areas with a lot of permafrost and limited tree cover than over the areas with extensive tree cover.[22]

Worked examples

Example 1 — a first encounter with Permafrost carbon cycle

Start with the simplest possible case. Write down what Permafrost carbon cycle claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Permafrost carbon cycle before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Permafrost carbon cycle ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Permafrost carbon cycle

In research
Permafrost carbon cycle appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Permafrost carbon cycle in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Permafrost carbon cycle is common in secondary-school and first-year university syllabi. It links to neighbouring topics Carbon cycle, Climate change feedbacks, Permafrost, so understanding it makes those chapters shorter.
In everyday life
Look for Permafrost carbon cycle outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.
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How to study Permafrost carbon cycle in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Permafrost carbon cycle means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Permafrost carbon cycle out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Permafrost carbon cycle in simple terms?

The permafrost carbon cycle or Arctic carbon cycle is a sub-cycle of the larger global carbon cycle. Permafrost is defined as subsurface material that remains below 0o C (32o F) for at least two consecutive years.

Why does Permafrost carbon cycle matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Permafrost carbon cycle?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Permafrost carbon cycle.

Tags

  • Carbon cycle
  • Climate change feedbacks
  • Permafrost

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