Case study: Alaskan Tundra

How much land does the Arctic tundra cover?

8 million km2 in Northern Canada, Alaska and Siberia

What are the climate conditions in the Alaskan tundra?

Severe with temps of below -15 degrees

What is the average heat balance?

Negative heat balance with average temps below freezing

What is the result of temps being below freezing?

Permafrost is formed

What are the flows and stores of the water cycle like in the tundra?

• Low annual precipitation (less than 100mm) with most precipitation falling as snow

• Small stores of moisture in the atmosphere due to low temps leading to low humidity

• Limited transpiration because of the sparseness of vegetation cover and short 3 month growing period

• Low rates of evaporation as much of the Sun’s energy is summer is focused on melting snow so ground temps remain low.

• Surface and soil water remain frozen for most of the year.

• Limited groundwater and soil moisture stores. Permafrost is a barrier to infiltration, percolation and groundwater flow.

• Extensive wetlands, ponds and lakes are temp stores of liquid water in the summer as permafrost blocks the drainage.

What is the seasonal pattern of the water cycle?

• Accumulation of snow and river ice during the winter months

• Melting of snow, river ice and the active layer in spring and early summer results in a big increase of river flow

What is the Yukon Rivers maximum discharge in the winter and summer?

• Winter: 340 cumecs

• 24,6000 cumecs

How many lakes does Alaska have?

Over 3 million lakes in extensive wetlands, valleys and along the coast

What does permafrost store and how much?

Carbon store - 1600 GT

Why is the accumulation of carbon slow?

Slow decomposition of dead plants

How much more carbon is stored in the tundra’s soil than it biomass?

5x more

When is the flux of carbon most concentrated?

In the summer months when the active layer thaws - Plants such as sedges crowberry and moss grow rapidly in the short summer with long daylight hours.

What is the NPP in the tundra?

Less than 200 grams/m2/year

How does carbon leave the tundra?

During the growing season tundra plants input carbon-rich litter to the soil. Decomposition by microorganisms increases, releasing CO2 emissions through respiration. Even in the winter pockets of unfrozen soil and act acts as sources of CO2.

What is the link of snow cover and decomposition?

Snow cover insulated microbial organisms and allow some decomposition to occur despite low temperatures

What is the impact of global warming and the permafrost store?

• Area may become a carbon source instead of storing it as temps increasing means more melting of the permafrost and the slow release of CO2 into the atmospheric store

• On the other hand, more plant growth and greater CO2 uptake. This increases the amount of plant litter and thus carbon entering the soil store. (may still remain in balance)

What are the physical factors that impact the water cycle?

• Average temps are well below freezing for most of the year so that water is stored as ground ice in the permafrost layer.

  During the short summer the active layer thaws and liquid water flows on the surface.

  Meltwater forms millions of pools across the landscape.

  Poor drainage means water infiltrate the soil because of the permafrost. Sub-zero temps prevent evapotranspiration occurs from standing water, saturated soils and vegetation. Humidity is low all year round.

• Permeability is low owing to the permafrost and the metamorphic igneous rocks that dominate the Tundra.

What are the physical factors that impact the carbon cycle?

• Mainly stored as partly decomposed plant remains frozen in the permafrost (locked away for 500,000 years)

• Low temps, the unavailability of liquid water for most of the year and parent rocks containing few nutrients, limit plant growth and NPP. There is some compensation for the short growing season in the ling hours of sunlight.

• Low temps and waterlogging slow decomposition and respiration and the flow of CO2 to the atmosphere

• Rock permeability, porosity and mineral composition exert little influence on the water and carbon cycle due to the permeability of the permafrost

When was oil and gas discovered in Prudhoe Bay?

1968

How much oil did the Trans-Atlantic pipeline in the 1980-90s produce?

Nearly ¼ of the US’ domestic oil supply

What is the impact of the extraction of oil in Prudhoe Bay on the carbon cycle?

• Permafrost, major carbon store is highly sensitive to changes in the thermal balance. In many areas, the balance has been disrupted by localised melting as the construction of the infrastructure adds heat to the permafrost

• Dust decomposition along roadsides darken snow surfaces which increasing absorption of sunlight; removal of vegetation cover which insulates the permafrost

• The melting releases CO2 (7-10 million tonnes per year) and CH4 (24,000-114,000 tonnes per year)

• Gas flaring and oil spillages also input CO2 into the atmosphere

• The destruction or degradation of vegetation means less photosynthesis and uptake of CO2

How much has CO2 emissions rose in the tundra sine 1975?

73%

Why can’t the tundra recover easily from the degradation?

The lack of vegetation growth means the damage can‘t recover easily

What is the impact of the extraction of oil in Prudhoe Bay on the water cycle?

• Melting has increased snow coverage and run-off and river discharge, making floods more likely. This increases evaporation.

• Drainage networks are disrupted by road construction and by seismic explosion used to prospect for oil and gas.

• Water abstracted from creeks and rivers for industrial use and for building of ice roads reduce localised run-off

How much thawing has occurred in Lake Goldstream in the last 60 years?

• 15m of permafrost thaw

Management strategies to modernise the impact: Insulated ice and gravel pads

• Roads are constructed on top of these to reduce heat transfer and protect it from melting.

• E.g: Spine Road in Prudhoe Bay lies on a 2m deep pad

Management strategies to modernise the impact: Building and pipelines elevated

Cold air can circulate around these structure so heat isn’t directly transferred to the permafrost. Insulation of heat-generate buildings also protects melting.

Management strategies to modernise the impact: Drilling lateral beyond drilling platforms

New drillings techniques allow directional drilling across a wide area. so there would be less drilling sites all together - less clearing of land and permafrost exposed

Management strategies to modernise the impact: more accurate detection of oil

Less wasted wells and exposed permafrost - using seismic data to locate the geological structures making it more efficient

Management strategies to modernise the impact: refrigerated support

Used on the Trans-Atlantic Pipeline to stabilise the temperature of the permafrost