CASE STUDY - Arctic tundra

Where is the Artic Tundra typically found on Earth?

They are high latitude landmasses just below the ice caps of the Arctic, North of the Artic circle (66’N).

Artic Tundra covers 8 million km² of land.

It comprises of Alaska (USA), Canada, Russia, Greenland, Iceland, Norway, Sweden and Finland.

What are the key climatic characteristics of Arctic Tundra?

Temperatures are frequently cold but it can get slightly warmer in the summers.

In certain areas, temperatures can reach -40’C.

• Mean annual temperatures are below -15’C.

• Long cold winters with average temperatures of around -30’C. They are below 0’C for 6 to 10 months of the year.

• Maximum temperature of 16’C, with short summer seasons lasting 6 to 10 weeks - restricts vegetation growth & evapotranspiration rates

• Low annual precipitation of 150-250mm

• Low temperatures causes evaporation of water to be slow

• Atmospheric stores of water are low due to low rates of evapotranspiration

What is permafrost?

Permafrost is permanently frozen ground consisting of soil, gravel and sand usually bound together by ice, that remains at 0’C or colder for at least 2 consecutive years.

CARBON - Why is permafrost an important part of the carbon cycle?

Permafrost stores 1700 Gt of carbon, representing 1/3 of total global soil carbon.

It is a long term store, locking carbon away for 500,000 years.

Near the surface, permafrost soils contain large quantities of organic carbon, a material left over from dead plants that couldn’t decompose.

The layer of soil on top of permafrost is called the active layer and does not stay frozen all year. In colder regions, the active layer is very thin of 10-15 cm. In warmer regions, the active layer can be several metres thick.

What type of vegetation is found in the Arctic Tundra and why?

Small shrubs, grasses, mosses and lichens.

Most water is stored in ice sheets and permafrost with limited groundwater and soil moisture stores due to low ground permeability and permafrost restricting infiltration/ percolation.

This limits vegetation and plant growth.

This with cold and dry climate means that the tundra is a treeless environment with patchy, low-to-ground vegetation.

WATER - List 4 features of the Arctic water cyle.

• Low annual precipitation - less than 100mm in most places

• Limited transpiration - due to spareness of vegetation and start growing seasons

• Limited groundwater and soil moisture stores - permafrost is a barrier to infiltration, percolation, recharge and groundwater flow

• Accumulation of snow & river/lake ice - during the winter months. [melting of snow, river and lake ice as well as active layer in spring and early summer, results in a sharp increase in river flow.] E.g. the Yukon river has a minimum discharge of 340 cumecs in winter and a maximum of 25,000 cumecs in summer

WATER - How does temperature influence precipitation patterns? - FLOWS

Flows:

• Low average temperatures of between 0’C and -30’C from Oct to May, 0’C to 10’C from jun to sept, which means there is little chance for convectional rainfall and results in low annual average precipitation (<100 mm/year) mainly falling as snow

• Low rates of evapotranspiration because the sun’s energy is spent melting the snow or most water just remains frozen.

• High rates of freezing especially sep-oct as the temperatures start to fall

• Ablation and sublimation especially may-jun as temperatures rise above 0’C

• Higher rates of channel flow in summer months as rivers are flowing

WATER - How does temperature influence precipitation patterns? - STORES

Stores:

• Low humidity and small atmospheric stores of moisture

• Melting of snow, river, lake ice and active layer of permafrost in spring and early summer result in water stored in liquid stores (rivers and lakes)

WATER - How does temperature influence infiltration?

Low rates of infiltration due to permafrost acting as a barrier.

Low temperatures result in large stores of water in glaciers and permafrost, both of which are a barrier to infiltration so limited groundwater and soil moisture stores.

WATER - Why are there low levels of groundwater storage?

Low levels of groundwater storage as a result of the low permeability of the igneous and metamorphic rocks.

Most rocks are Precambrian igneous and metamorphic rocks which have low levels of permeability, reducing percolation from the soil into the bedrock.

WATER - Why does water collect in pools rather than drain away during summer months?

Because much of the Arctic tundra is gently undulating plains caused by millions of years of erosion and weathering.

CARBON - How much carbon is stored in Arctic tundra globally?

1,700 Gt of carbon, much in long-term store for 500,000 years

CARBON - What is the NPP of Arctic tundra?

very low, 200 g/m²/year

CARBON - When does most carbon flux between atmosphere and biosphere, and why?

Most concentrated in the summer months when active layer thaws.

Plants like sedges, crowberry and moss grow rapidly during the summer. Longer hours of daylight allow them to flower and fruit within just a few weeks.

CARBON - What does Arctic biomass range between?

Between 4 - 29 tonnes/ha depending in density of vegetation cover.

CARBON - How does temperature influence the rate of decomposition?

During summer months, microorganisms increase rate of decomposition and release CO2 into the atmosphere through respiration.

Even during winter months, snow cover can act as an insulator, allowing decomposition under snow despite low air temperatures.

Low temperatures = slow accumulation of carbon → slows down decomposition of dead plant material

Low temperatures form permafrost which stores 1700 Gt of carbon

WATER - How does seasonal changes influence water cycle flows or stores of the Arctic tundra?

During winter:

• temperatures are permanently below 0’C to -20’C, meaning flows like percolation and stores like rivers freeze, slowing or stopping the water cycle

• frozen ground becomes more impermeable but surface runoff does not increase because surface water is also frozen

During summer:

• active layer of permafrost thaws, creating through flow, surface runoff, infiltration, percolation, recharge and groundwater flow

• when soil thaws, infiltration but only into the active layer

CARBON - How does seasonal changes influence carbon cycle flows or stores of the Arctic tundra?

• short growing season in summer months means rates of photosynthesis and respiration will increase only slightly

• decomposition and respiration rates remain low all-year, only slightly higher in summer months (explains why NPP is so low)

• little mechanical (freeze thaw) weathering during transitional moths between summer and winter (may/ sep)

HUMAN IMPACTS - Introduce the North slope of Alaska and ANWR.

The North Slope of Alaska is a significant area of the Arctic tundra, spanning approximately 25,000 km².

the Arctic National Wildlife Refuge encompasses 80,000 km² in remote northeastern Alaska. it is a protected area with extensive oil and gas reserves.

HUMAN IMPACTS - How many barrels of oil per day does Prudhoe Bay produce?

280,000 barrels of oil per day

HUMAN IMPACTS - How long is the Trans-Alaska Pipeline?

1,200 km

HUMAN IMPACTS - What temperature does the oil in the pipeline travel at and why is it a problem?

60’C, the pipes buried into or sat on top of permafrost could melt it and also crosses earthquake zones.

500 oil spills annually, e.g Fort Geely in 2010, damages during earthquakes

HUMAN IMPACTS - Outline the ways in which the issues of the Trans-Alaska pipeline has been reduced through management strategies.

• Pipes are built on stilts instead

• Construction of ‘thermosyphons’ which remove heat from permafrost in order to reduce thawing and further damage to the pipeline.

HUMAN IMPACTS - Outline ways in which damages to the water and/or carbon cycles have been reduced through management strategies.

• Buildings and pipelines elevated on piles - constructing buildings, oil/gas pipelines and other infrastructure on piles allows cold air to circulate beneath these structures. This provides insulation against heat-generating buildings, pipe works, etc. which would otherwise melt the permafrost.

• Drilling laterally beyond drilling platforms - new drilling techniques allow oil and gas to be accessed several kilometres from the drilling site. Shell has developed the ‘snake drill’ which allows directional drilling across a wide area from a single drilling site. With fewer sites needed from drilling rigs, the impact on vegetation and the permafrost due to construction (access roads, pipelines, production facilities) is greatly reduced.

WATER - Outline ways in which the water cycle has been impacted by the development of the oil and gas industry.

• Melting of permafrost and snow cover increases runoff anf river discharge, making flooding more likely. E.g. in summers, wetlands, ponds and lakes become more extensive, increasing evaporation

• strip mining of aggregates (sand and gravel) for construction create artificial lakes which disrupt drainage and expose permafrost to further melting.

• drainage networks are disrupted by road construction and by seismic explosions used to prospect for oil and gas

CARBON - Outline ways in which the carbon cycle has been impacted by the development of the oil and gas industry.

• permafrost melting releases CO2 and methane. On the North slope, estimated Co2 losses from the permafrost can be up to 40 mil/tonnes/year

• gas flannels and oil spillages input up to 114,000 tonnes of CO2 to the atmosphere every year

• destruction or degrading of tundra vegetation reduces photosynthesis and uptake of atmospheric carbon.

• thawing of soil increases microbial activity, decomposition and therefore, emissions of CO2

How did the construction of the Dalton Highway impact the water or carbon cycle?

Water - increased overland water flows due to impermeable urban surfaces

Carbon - asphalt production releases atmospheric carbon and reduction in biosphere carbon storage

How has the Deadhorse Oil Refinery impacted the water stores?

Each year, approximately 20 billion barrels of water are extracted and used to refine oil, depleting groundwater and river water stores.