alaskan tundra

Question 1

location

Answer 1

occupied 8 million km2 in northern Canada, Alaska, Siberia
- extends from northern edge of boreal coniferous forest to the Arctic Ocean + its southern limit approximates 10•C July isotherm (climatic limit of tree line)
- Climatic conditions in Alaskan tundra are severe with mean temperatures below -15•C

Question 2

what type of heat balance does the tundra have

Answer 2

for 8 or 9 months a year, has negative heat balance with average monthly temperatures below freezing
- as result, ground permanently frozen with only top metre so thawing during Arctic summer

Question 3

what underlies much of Alaskan tundra + is important feature

Answer 3

permafrost

Question 4

In winter, when for several weeks Sun remains below horizon, temperatures can plunge below

Answer 4

-40•C

Question 5

‘…’ in summer provide some compensation for shortness of growing season.

Answer 5

long hours of daylight

• there is also low mean annual precipitation

Question 6

few plants + animals have adapted to this extreme environment

Answer 6

• low biodiversity
• ecosystem is treeless (apart from few dwarf species)
• in southern areas, low Arctic - conditions less severe + vegetation provides continuous ground cover
• further north in High Arctic, plant cover is discontinuous with extensive areas of bare ground

Question 7

main features of water cycle in Alaskan Tundra

Answer 7

• low annual precipitation (less then 100mm in most places) with most precipitation falling as snow
• small stores of moisture in atmosphere due to low temperatures which reduce absolute humidity
• limited transpiration as sparseness of vegetation cover + short growing season of only abt 3 months
• low rates of evaporation (much of Sun’s energy in summer is expended melting snow so that ground temperatures remain low + inhibit convection
• also, surface + soil water are frozen for most of year
• limited groundwater + soil moisture stores (permafrost is barrier to infiltration, percolation, recharge + groundwater flow)
• accumulation of snow + river/lake ice during winter months (melting of snow, river + lake ice + uppermost active layer of permafrost in spring + early summer, results in sharp increase in river flow)
• extensive wetlands, ponds + lakes on tundra during summer (this temporary store of liquid water is due to permafrost which impedes drainage)

Question 8

How many lakes does Alaska have

Answer 8

3 million
- extensive wetlands lie in valleys (e.g Yukon River), in deltas + along coast (especially of Bering Sea)

Question 9

carbon cycle in tundra

Answer 9

permafrost is vast carbon sink
- accumulation of carbon due to low temperatures which slow decomposition of dead plant material
- overall amount of carbon in Alaskan tundra soils is 5x greater than in above-ground biomass
- flux of carbon is concentrated in summer months when active layer thaws

Question 10

plants in carbon cycle

Answer 10

grow rapidly in short summer (e.g sedges, crow berry + moss)
- long hours of daylight allow them to flower + fruit within few weeks
- Alaskan tundra biomass is small, ranging between 4 + 29 tonnes/ha depending on density of vegetation cover
- during growing season, tundra plants input carbon-rich litter to soil
- activity of microorganisms increases, releasing CO2 to atmosphere through respiration
- but CO2 + CH4 emissions are not just confined to summer
- even in winter, pockets of unfrozen soil + water in permafrost act as sources of CO2 + CH4
- snow cover may insulate microbial organisms + allow some decomposition despite low temperatures

Question 11

-in past, permafrost functioned as carbon sink, but today…

Answer 11

global warming has raised concerns in Alaska that is becoming carbon source
- at moment, evidence is unclear
- while outputs of carbon from permafrost have increased in recent decades, higher temperatures stimulated plant growth in tundra + greater uptake of CO2
- this in turn has increased amount of plant litter entering store
- so it’s possible that despite warming Alaskan climate, carbon budget in tundra today remains close to balance

Question 12

physical factors, seasonal changes + stores + flows of water

Answer 12

flows + stores of water in Alaskan tundra are influenced by temperature , relief , rock permeability
- average temperatures are below freezing for most of year so water stored as ground ice in permafrost layer
- during short summer, shallow active layer (top metre)
thaws + liquid water flows on surface
- meltwater forms millions of pools + shallow lakes which scatter tundra landscape
- poor drainage: water cannot infiltrate soil bc of permafrost at depth
- in winter, sub-zero temperatures prevent evapotranspiration
- in summer, some evapotranspiration occurs from standing water, saturated soils + vegetation
- humidity is low all year round +precipitation sparse
- low permeability due to permafrost + Precambrian igneous + metamorphic rocks which dominate geology of tundra in Alaska
- ancient rock surface which underlies tundra has been reduced to gently undulating plain by hundreds of millions of years of erosion + weathering
- minimal reliefs + chaotic glacial deposits impede drainage + contribute to waterlogging during summer months

Question 13

physical factors, seasonal changes + stores + flows of carbon

Answer 13

• carbon mainly stored as partly decomposed plant remains frozen in permafrost
• most of this carbon has been locked away for at least past 500,000 years
• low temperatures, unavailability of liquid water for most of year + parent rocks containing few nutrients, limit plant growth
• thus total carbon store of biomass is relatively small
• averaged over year, photosynthesis + NPP are low, with growing season lasting barely 3 months
• but there is some compensation for short growing season in long hours of daylight in summer
• low temperatures + waterlogging slow decomposition + respiration + flow of CO2 to atmosphere
• owing to impermeabiliry of permafrost, rock permeability, porosity + mineral composition of rocks exert little influence on cycles

Question 14

oil + gas production + carbon + water cycles in Alaska

Answer 14

North Slope of Alaska, between Brooks Range in South + Arctic Ocean in North, is vast wilderness of Arctic tundra

Question 15

oil + gas were discovered here at Prudhoe Bay in

Answer 15

1968

Question 16

from start, development of oil + gas industries on North Slope presented major challenges:

Answer 16

harsh climate with extreme cold + long periods of darkness in winter

permafrost, + melting of active layer in summer;
remoteness + poor accessibility; + fragile wilderness of great ecological value.

Question 17

despite challenges, production went ahead, driven by

Answer 17

high global energy prices + US government’s policy to reduce dependence on oil imports
- Massive fixed investments in pipelines, roads, oil production plants, gas processing facilities, power lines, power generators + gravel quarries were completed in 1970s + 1980s.
- By early 1990s, North Slope accounted for nearly 1/4 of USAs domestic oil production.
- Today proportion less than 4 %though Alaska remains important oil + gas province

Question 18

Decline in oil production in recent years reflects 2 things:

Answer 18

high production costs on North Slope + massive growth of the oil shale industry in USA

Question 19

Oil and gas exploitation on Alaska’s North Slope has had significant impacts on permafrost + on local water and carbon cycles.

Answer 19

permafrost highly sensitive to changes in thermal balance
- In many areas, this balance has been disrupted by activities of oil + gas companies which have caused localised melting of permafrost.

Question 20

melting associated with:

Answer 20

• construction + operation of oil + gas installations, settlements + infrastructure diffusing heat directly to environment
• dust deposition along roadsides creating darkened snow surfaces, thus increasing absorption of sunlight
• removal of vegetation cover which insulates permafrost.

Question 21

Permafrost melting releases

Answer 21

CO2 + methane (CH4)

Question 22

On North Slope, estimated CO, losses from
permafrost vary from

Answer 22

7 to 40 million/tonnes/year

Question 23

on North Slope, CH4 losses range from

Answer 23

24,000 to 114,000 tonnes/year

Question 24

what also inputs CO2 to atmosphere

Answer 24

gas flaring + oil spillages

Question 25

Other changes to local carbon cycle are linked to industrial development. E.g

Answer 25

destruction or degrading of tundra vegetation reduces photosynthesis and the uptake of CO2 from atmosphere; + thawing of soil increases microbial activity, decomposition + emissions of CO2

Question 26

CO2 emissions from North Slope permafrost are estimated to have increased by

Answer 26

73 % since 1975.

Question 27

slow-growing nature of tundra vegetation means that

Answer 27

regeneration + recovery from damage takes decades

Question 28

Melting of permafrost + snow cover increases…

Answer 28

run-off + river discharge, making flooding more likely.
- means that in summer, wetlands, ponds + lakes have become more extensive, increasing evaporation.

Question 29

Strip mining of aggregates (sand + gravel) for construction creates…

Answer 29

artificial lakes which disrupt drainage + also expose the permafrost to further melting.
Artificial lakes at Goldstream, near Fairbanks, have experienced 15 m of permafrost thaw in the last 60 years.
In addition, drainage networks are disrupted by road construction + by seismic explosions used to prospect for oil + gas.

Question 30

water abstracted from creeks + rivers for industrial use and for the building of ice roads in winter, such as one between Fairbanks + Prudhoe Bay, reduce…

Answer 30

localised run-off.
BP extracts most of the water it needs from Kuparuk River + Big Lake.

Question 31

Management strategies to moderate the impact on the water and carbon cycles. (intro)

Answer 31

Development on the North Slope has often involved the deliberate destruction of the permafrost. Today the emphasis is on protecting permafrost (Table 4.11), thus minimising disruption to the water and carbon cycles and wildlife. However, the purpose of these strategies is also pragmatic: melting permafrost causes widespread damage to buildings and roads as well as increased maintenance costs for pipelines and other infrastructure

Question 32

list strategies to reduce impact of development on water + carbon cycles

Answer 32

• insulated ice + gravel pads
• buildings + pipelines elevated on piles
• drilling laterally beyond drilling platforms
• more powerful computers - can detect oil + gas-bearing geological structures remotely
• refrigerated supports

Question 33

insulated ice + gravel pads

Answer 33

roads + other infrastructural features can be constructed on insulating ice or gravel pads, thus protecting permafrost from melting.
The Spine Road at Prudhoe Bay lies on a 2m deep pad.

Question 34

buildings + pipelines elevated on piles

Answer 34

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, pipework, etc. which would otherwise melt the permafrost.

Question 35

drilling laterally beyond drilling platforms

Answer 35

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 wide area from a single drilling site. With fewer sites needed for drilling rigs, impact on vegetation + permafrost due to construction (access roads, pipelines, production facilities, etc.) is greatly reduced.

Question 36

refrigerated supports

Answer 36

Refrigerated supports are used on the Trans-Alaska Pipeline to stabilise temperature of permafrost.
Similar supports are widely used to conserve permafrost beneath buildings + other infrastructure.

Question 37

more powerful computers - can detect oil + gas-bearing geological structures remotely

Answer 37

Fewer exploration wells are needed thus reducing impact on environment. About 10% of all ‘supercomputers’ have been delivered to oil industry. Its 2 big computational tasks: seismic data processing (to deduce underground geological structures), and reservoir modelling (to simulate the flows within a producing field, in order to optimise amount of oil that can be recovered).