ARCTIC TUNDRA CASE STUDY (2b)

Arctic tundra overview

- The Arctic tundra occupies 8 million km squared in Northern Canada, Alaska, and Siberia.

- It has severe climate conditions, mean temperature is -15°C, and for 9 months of the year the temperature is sub-zero.

- The ground is permanently frozen (permafrost) with only the top thawing in the summer months.

- Mean annual precipitation is low.

- Permafrost is an important feature of the water cycle.

- Biodiversity is low due to the extreme environment.

Physical factors, seasonal changes, and stores + flows of the carbon cycle

- Low temperatures and water logged soils lead to slow decomposition and respiration, leading to less carbon dioxide flowing from biomass to the atmosphere.

- Carbon stored as partly decomposed plants remain in permafrost, locked away for 500,000 years.

- Low temperatures and lack of liquid water limit plant growth - low biomass carbon store.

- Photosynthesis and net primary productivity are low, short growing season but fast growth in the summer.

- Rock composition has little influence due to permeability of permafrost, rock, and minerals.

Physical factors, seasonal changes, and stores + flows of the water cycle

- Relief, erosion, and weathering result in a gently undulating plain. This, combined with glacial deposits, reduce drainage and contribute to water logging in the summer.

- Temperatures average below 0 so water is stored in permafrost.

- Active layer thaws in summer and flows on the surface, forming pools and lakes - poor infiltration = poor drainage.

- Rock permeability is low due to permafrost and metamorphic rocks.

Water stores and flows

- Low annual precipitation (<100mm which is mostly snow).

- Small stores in atmosphere due to low temperatures and low humidity.

- Limited transpiration due to little vegetation cover and short growing season (around 3 months).

- Low evaporation rates as the sun's energy in summer is used to melt snow/frozen soil.

- Limited ground and surface water stores as permafrost is a barrier to infiltration, percolation, recharge, and groundwater flow.

- Accumulation of snow and river/lake in the winter, melting of this active layer increases river flow in the spring.

- Extensive temporary stores in wetlands, ponds, and lakes in summer due to permafrost, limiting drainage (e.g. 3 million lakes in Alaska).

Carbon stores and flows

- Permafrost is a vast carbon sink, globally 1,600 GT of carbon.

- Carbon accumulates due to low temperatures which slow decomposition of dead plants.

- Carbon in soils is 5x more than biomass.

- Carbon flux is concentrated in the summer when the active layer thaws.

- Net primary productivity is low (200g/m squared annually), small tundra biomass (4-29 tonnes/ha).

- Growing season: plants input carbon rich litter into the soil. Increased micro-organism activity (respiration) releases carbon dioxide into the atmosphere.

- Carbon dioxide and methane are released from unfrozen soil and permafrost water in the winter.

- Snow cover insulates microbial organisms in low temperatures, aiding decomposition.

- Global warming reduced permafrost function as a carbon store and becomes a carbon source.

- Warmer temperatures increase plant growth, increasing stores, which increases plant litter entering the permafrost store.

Oil and gas

- North slope of Alaska is a vast wilderness of tundra, oil and gas discovered at Prudhoe Bay 1968.

- Challenges of extraction: harsh climate, extreme cold, long dark periods, permafrost, melting active layer, poor accessibility.

- Production driven by high global energy prices and US policy to reduce imports.

- Early 1990s: North slope gave US 25% of its domestic oil production. Today it is 4% due to high production cost and growth of industry.

Impacts on carbon and water cycles: localised melting of permafrost

- Construction of settlements and infrastructure. Dust deposition along roads darken snow and reduce albedo.

- Removal of vegetation cover insulates permafrost. Releases carbon dioxide and methane, carbon dioxide loss from permafrost vary from 7-40 million tonnes annually.

- Gas flaring and oil spillages input carbon dioxide into the atmosphere.

Impacts on carbon and water cycles: industrial development

- Destruction of vegetation reduces photosynthesis and uptake of carbon dioxide from the atmosphere.

- Thawing of soil increase microbial activity, decomposition, and carbon dioxide emissions.

- North slope emissions increased by 73% since 1975.

Impacts on carbon and water cycles: water abstraction

- From creeks/rivers for industrial use, reduces localised runoff.

- Strip mining of aggregates: mining for sand/gravel creates artificial lakes, disrupting drainage, and melting permafrost.

Impacts on carbon and water cycles: melting of permafrost/ice cover

- Increased runoff and river discharge leads to flooding.

- Wetlands/ponds/lakes are more common, increasing evaporation in the summer.

Strategies to moderate the impacts

- Insulated ice and gravel pads: roads can be constructed on insulated ice/gravel pads, protecting permafrost underneath from melting.

- Buildings and pipelines elevated on piles: constructing on piles allows cold air to circulate under structures, provides insulation against heat-generating buildings.

- Refrigerated supports: used on the Trans-Alaskan pipeline to stabilise temperature of permafrost, also used to conserve permafrost under buildings.

Strategies to moderate the impacts cont.

- More powerful computers to detect oil + gas bearing geological structures remotely: fewer exploration wells needed, reducing environmental impact. 10% of all super computers belong to the oil industry.

- Drilling laterally beyond drilling platforms: new drilling techniques mean oil/gas can be extracted kms from drilling sites. Fewer sites needed, so reduced vegetation loss and permafrost impact.