Arctic Tundra

• The Arctic tundra is a major biome that covers 8 million kilometers squared and can be found in Northern Canada, Alaska and Siberia
• Arctic tundra

  • Temperatures are incredibly low, with an average of -15 °C and can reach as low as -40 °C in winter
  • Has a negative heat balance for 8 - 9 months of the year, with more heat lost to the atmosphere than gained from solar radiation
• The Arctic tundra has an extremely severe climate, with most of the year (8-9 months) being below 0 °C and very little precipitation (50 - 350 mm per year on average, about 10% of the Amazon)
• Permafrost

  • A layer of permanently frozen soil and ice below the surface that acts as a barrier to water infiltration and deeper percolation
• Seasonal changes in the Arctic tundra

  1. In winter, most water is stored as permafrost or snow on the surface

  2. In summer, the top layer of soil (active layer) thaws, allowing some liquid water to form pools and lakes on the surface
• The geology of the Arctic tundra, dominated by Precambrian igneous and metamorphic rocks, is very impermeable and prevents water from infiltrating or percolating deeper
• The Arctic tundra has very flat, uniform relief, which also contributes to water staying on the surface in pools and lakes rather than draining away or infiltrating
• Climate change and increasing temperatures

  May lead to more vegetation growth and "greening" of the Arctic, which could affect the water and carbon cycles
• The water cycle in the Arctic tundra is characterised by very limited precipitation (less than 100mm in most areas), low atmospheric moisture content, and restricted infiltration, percolation and groundwater storage due to permafrost and impermeable geology
• Winter - water stored as ground ice in permafrost / snow on surface. Limited evapotranspiration.

  Summer - Liquid water on surface (melted active layer) with some evapotranspiration from standing water and now exposed plants
• Arctic tundra

  • Very low temperatures
  • Not much liquid water for most of the year
• Most of the tundra is on large crystalline igneous rock (the Canadian Shield) which has very few nutrients
• Photosynthesis and plant growth

  Very limited due to poor conditions
• The carbon cycle in the Arctic is quite slow, with limited transfers between stores
• Growing season

  Short period of about 3 months above the negative heat balance with lots of sunlight
• Net primary productivity is still very low at 200 grams per square meter per year
• Biomass in the biosphere is between 4 to 29 tons per hectare, much lower than the Amazon
• Seasonal changes in the Arctic

  1. Plants drop leaf litter which decomposes and releases CO2

  2. Decomposers are more active due to warmer temperatures

  3. Waterlogged conditions limit decomposition and respiration
• Permafrost

  A large carbon sink containing over 1600 gigatons of carbon in the form of dead organic matter
• Permafrost starts to thaw due to global temperature rise

  Decomposers can attack the organic matter, releasing CO2 and methane - a feedback loop that worsens climate change
• Methane released from thawing permafrost is 4 times more damaging for climate change than CO2
• As permafrost melts and temperatures rise

  There may be increased photosynthesis and plant growth, which could offset some of the carbon released, but likely not enough to prevent the Arctic becoming a net carbon source
• The carbon cycle in the Arctic is generally very slow due to the severe physical conditions
• Biodiversity is low and the ecosystem is treeless
• Water cycle in the Alaskan Tundra

  • Low annual precipitation (less than 100mm)
  • Most precipitation falls as slow snow
  • Limited transpiration due to sparse vegetation and short growing season
  • Low evaporation rates
  • Permafrost is a barrier to infiltration, percolation, recharge and groundwater flow
  • Accumulation of snow, river and lake ice in winter
  • Sharp increase in river flow in spring and early summer
  • Extensive wetlands, ponds and lakes in summer
• Carbon cycle in the Alaskan Tundra

  • Permafrost is a vast carbon sink, containing 1600 gigatons of carbon
  • Carbon accumulation due to low temperatures slowing decomposition
  • Net primary productivity is less than 200g/m2/year
  • Tundra biomass is small (4-29 tons/hectare)
  • CO2 and CH4 emissions occur even in winter from unfrozen soil and water pockets
  • Unclear if tundra is currently a carbon source or sink
• Physical factors, seasonal changes, and stores and flows of water and carbon influence the Alaskan Tundra
• Water cycle in the Alaskan Tundra

  • Temperatures well below freezing for most of the year, storing water as ground ice in permafrost
  • Short summer thaw of the active layer allows liquid water to flow on the surface
  • Drainage is poor due to permafrost, leading to formation of pools, lakes and wetlands
  • Transpiration is limited, and evaporation is low due to low humidity
  • Permeability is low due to permafrost and ancient igneous/metamorphic rocks
• Carbon cycle in the Alaskan Tundra

  • Most carbon stored as decomposed plant remains in permafrost
  • Low temperatures, water availability and nutrient-poor rocks limit plant growth and productivity
  • Slow decomposition and respiration due to low temperatures and water-logging
• Rock permeability, porosity and mineral composition have little influence on the water and carbon cycles
• Oil and gas production in the Alaskan Tundra

  • Harsh climate with extreme cold, long winter darkness, permafrost
  • Remoteness and poor accessibility
  • Fragile wilderness of great ecological value
  • Massive fixed investments in infrastructure in 1970s-1980s
  • North Slope accounted for nearly 25% of US oil production by early 1990s, now less than 4%
• Oil and gas exploitation in the Alaskan Tundra

  • Disrupts the thermal balance of the permafrost, causing localized melting
  • Releases CO2 and CH4 from the permafrost, estimated at 77-400 million tons CO2/year and 24,000-114,000 tons CH4/year
  • Destroys or degrades tundra vegetation, reducing CO2 uptake and increasing decomposition emissions
  • Increases runoff and river discharge, making flooding more likely
  • Disrupts drainage networks and creates artificial lakes
• Strategies to moderate impact on water and carbon cycles

  • Constructing insulated ice and gravel pads to protect permafrost
  • Elevating buildings, pipelines and infrastructure on piles to allow cold air circulation
  • Using directional drilling techniques to reduce surface footprint
  • Applying advanced computer modelling to optimize oil/gas extraction with less environmental impact
• Refrigerated supports are used to stabilize permafrost under infrastructure