22 - Arctic Tundra Case Study: Carbon Cycle

Question 1

What is the impact of Vegetation and organic matter in soils on stores in the carbon cycle?

Answer 1

• Plant growth in the Arctic Tundra is limited to the short summer months due to a lack of insolation throughout most of the year, which results in a low net primary productivity and overall biomass store.
• Despite the limited growth, the tundra stores a significant amount of carbon, with the majority being stored in the frozen permafrost as partly decomposed plant remains. Some of this carbon has been frozen in the permafrost for over 500,000 years, making the permafrost a crucial long-term carbon sink.
• However, with rising temperatures, the permafrost is at risk of thawing, which could release this stored carbon into the atmosphere, contributing to climate change.

Question 2

What is the impact of Vegetation and organic matter in soils on flows in the carbon cycle?

Answer 2

• The fluxes of photosynthesis and transpiration are limited in the Arctic Tundra due to waterlogged soils, low nutrient availability, and a short growing season.
• Decomposition in the waterlogged environment of the tundra is dominated by anaerobic bacteria, which release methane (CH4) instead of carbon dioxide (CO2).
• Methane is a potent greenhouse gas and has a warming effect more than 25 times greater than carbon dioxide over a 20-year timescale. This makes the release of methane from the tundra an important contributor to climate change.

Question 3

What is the impact of temperature on stores in the carbon cycle?

Answer 3

• The tundra is a critical carbon store, with 1,500 billion tons of organic carbon stored in the permafrost. Throughout most of the year the soil in the tundra stores carbon as permafrost, as cold temperatures limit vegetation cover, leading to little carbon stored in the biomass
• However, in summer, plants take up this carbon. Rising temperatures may cause the tundra to become a source of carbon instead of a sink.
• Since 1970, there has been a 14% increase in plant productivity in the tundra due to a 2.3°C rise in temperature.

Question 4

What is the impact of temperature on flows in the carbon cycle?

Answer 4

• The decomposition rates are generally low in the Arctic Tundra due to limited heat and humidity for bacterial decomposers, but the process occurs more rapidly in the summer when permafrost melts.
• While photosynthesis is typically low, the summer months provide some warmth, causing permafrost to melt and exposing plants to sunlight for photosynthesis. Respiration follows a similar trend.

Question 5

What is the impact of the Mineral composition of rocks on flows/stores in the carbon cycle?

Answer 5

• The mineral composition of rocks impacts the flows and stores in the carbon cycle. The majority of the tundra is composed of intrusive and extrusive igneous rock, which typically have low amounts of carbonates, resulting in minimal carbon storage or emissions.