THE ARCTIC TUNDRA
Background
Arctic tundra occupies some 8 million km2 in northern Canada
It extands from the northern edge of the borel coniferous forest to the Arctic Oean
Its southern limit approximates 10 degree July isotherm (i.e. climatic limit of the tree line)
Climatic Conditions
Severe
Become more extreme with lattitude
For 8-9 months of the year the tundra has a negative heat balance with average monthly temperatures below freezing
Ground is therefore permanently frozen with only the top metre thawing during the Arctic summer
Water Cycle
During winter, Sun remains below the horizon for several weeks; temps. -40
Long hours of daylight in summer provide compensation for brevity of the growing season
Low mean annual precipitation
Biodiversity
Few animals have adapted to this extreme environment
Low BD
Mostly treeless apart from some dwarf species
Conditions are less severe in the Low Arctic and vegetation provides continuous ground cover
In the High Arctic, plant cover is discontinuous with extensive areas of bare ground
Main Features
Low precipitation (50-350mm) with most precipitation falling as snow
Small stores of moisture in the atmosphere owing to low temperatures which reduce absolute humidity
Limited transpiration bc of sparseness of vegetation cover and short growing season
Low rates of evaporation
Much of sun's energy is used to melt snow so that ground temperature remain low and inhibit convection
Surface and soil waters are frozen most of the year
Limited groundwater and soil moisture stores
Accumulation of snow and river/lake ice during the winter months
Permafrost is is a barrier to infiltration, percolation, recharge and groundwater flow
Melting of snow and river ice, and the uppermost active layer of other permafrost in spring/summer = sharp increase in river flow
Extensive wetlands, ponds and lakes on the tundra during the summer
This temporary store of liquid water is due to permafrost which impedes drainage
Carbon Cycle
C Sink
Permafrost is a vast C sink
Globally it is estimated to contain 16000 GT of C
The accumulation of C is due to low temps. which slow decompostion of organic matter
Overall, amount of tundra in soils is *5 greater than in the above-ground biomass
Biomass
C flux Is concentrated in summer months when the active layer thaws
Processes
Plant Activity
NPP is 200 grams/m2/year
Tundra biomass is v. small - ranges between 4 - 29 tonnes/ha depending on density of vegetation cover
Plants grow rapidly in short summer
During growing season, tundra plants input C-rich litter into soil
Activity of microorgs. increases in growing season, releasing Co2 to atmosphere thru respiration
Long hours of daylight allow them to flower and fruit within just a few weeks
Permafrost melting
In winter, pockets of unfrozen soil and water in the permafrost act as sources of CO2 and methane
Snow cover may insulate microbial organisms and allow some decomposition despite the low temperatres
Concerns that permafrost is becoming a C source
Outputs of C from permafrost have increased in recent decades; higher temps. have stimulated plant growth in the tundra and greater uptake of CO2
In turn this has increased the amount of plant litter entering store
So perhaps the C budget in the tundra remains in balance today despite carbon warming
Oil + Gas Production, Alaska
Factors of Flows and Stores
Temperature
Avg. temps. are below freezing for most of the year
So water is stored as ice in the permafrsot layer
During summer the active layer (top metre) thaws and liquid water flows on the surface
Poor draiange
Meltwater forms millions of pools and shallow lakes
Water cannot infiltrate the soil bc of the permafrost at depth
Prevents evapotransp. at winter
Some evapotransp. during summer from standing water, saturated soils and vegetation
Humidity is low year-round and precip. is sparse
Rock Permeability
Permeability is low owing to the permafrost and crystalline rocks that dominate the tundra and sub-Arctic Canada
Relief
Ancient rock surface which underlines the tundra has been reduced to a gradually undulating plan
Hundreds of million of years of erosion and weathering
Minimal relief and chaotic deposits impede drainage = waterlogging during summer
Background
North Slope between Brooks Range (in south) and Arctic Ocean (in north) is a vast wilderness of Arctic tundra
Oil and gas discovered at Prudhoe Bay in 1968
Major challenges to oil and gas exploration from the start:
Harsh climate - extreme cold + long hours of darkness in winter
Permafrost and melting of active layer in summer
Remoteness + poor accessibility
Fragile wilderness of great ecological value
Factors of Stores and Flows
C is mainly stored as partly decomposed plant remains frozen in permafrsot
Most of this C has been locked away for the past 500,000 years
Plant growth is limited
Low temps.
Unavailability of liquid water for most of the year
Parent rocks with few nutrients
So total C store of the biomass is relatively small
Low NPP and photosynthesis
Low temperatures and waterlogging
Impermeable permafrost, impermeable rock, porososity + mineral composition of rocks
Long hours of daylight in summer = short growing season
Slows decomposition and respiration and the flow of CO2 to the atmosphere
Exerts little influence on water + C cycles
Reason for + continuation of production:
High global energy prices
US gov. policy to reduce dependence on oil imports
Massive fixed investments in infrastructure, power stations and gravel quarries in the early 70s and 80s
By the early 90s the North Slope accounted for nearly 1/4 of USA's domestic oil production
Today, the North Slope accounts for 6% of oil production in USA but Alaska still remains an important oil + gas province
Decline in recent years reflects 2 things:
High production costs on the N Slope
Massive growth of the oil shale industry in the USA
Impacts
Carbon Cycle
Permafrost
Major C store in the tundra
High sensitive to change sin the thermal balance
Thermal balance has been disrupted in many areas by activities of oil and has companies
= localised melting of permafrost
Melting of permafrost is associated with:
Construction adn operation of oil + gas installations, settlements and infrastructure diffusing heat directly to the environment
Dust deposition along roadsifes = darkened snow surfaces = increased light absorption
Removal of vegetation cover than insulates the permfrost
Release CO2 + ch4
7-40 million tonnes/ year of CO2 lost on N Slope; 24,000-114,000 tonnes of CH4
Gas flaring + oil spillages release CO2 into atmosphere
Industrial development
Destruction/degradation of tundra vegetation reduces photosyn. + uptake of CO2 from atmosphere
Thawing of soil increase microbial activity, decomposition + CO2 emissions
Slow-growing nature of tundra vegetation means the regeneration adn recovery from damage takes decades
Water Cycle
Melting of permafrost + snow cover increases run-off + river discharge = flooding
More extensive wetlands, ponds + lakes in summer = increased evap.
Strip-mining of aggregates for construction = artificial lake
Disrupt drainage
Expose permafrost to additional melting
Road construction and seismic explosions for oil + gas exploration
Disrupts driange entworks
Water abstracted from creeks + rivers for industrial use and for the building of ice roads in winter reduc elocalised runoff
Management Strategies
Protection of permafrost
Development on NB Slope had often involved deliberate destruction of permafrost
To minimise disruption to water + C cycles + wildlife
Purpose of strategies is pragmatic:
Melting permafrost = widespread damage to roads + buildings + increased maintenance costs for pipelines + other infrastructure
Strategies
Insulated ice + gravel pads
Roads + other infrastructural features can be constructed on insulating ice/gravel pads - thus protecting the permafrost from melting
Buildings + pipelines elevated on pads
Allows cold air to circulate beneath these structures
Provides insulation against heat-generating buildings, pipework etc. which would otherwise melt the permafrost
More powerful computers to detect oil-and-gas-bearing geological structures remotely
Fewer exploration wells nedded, thus reducing environmental impact
Refrigerated supports
Are used on the Trans-Alaska Pipeline to stabalise the temp. of the permafrost
Similar supports used widely to conserve the permafrost beneath buildings + other infrastructure