2.b. The Arctic Tundra - Physical Factors Affecting the Carbon and Water Cycles
How much carbon is permafrost estimated to contain?
1,600 GT
What is isolated permafrost?
Covers 0-10% of land surface
When is the flux of carbon and why?
In the Summer, when the active layer thaws and plants grow rapidly due to long daylight hours
How is CO2 and CH4 released in Winter?
Through pockets of unfrozen soil and water
What is the NPP of the Tundra?
Under 200g/m^2/year
How low can temperatures reach during the Winter?
-40 degrees C
How do low temperatures affect the stores and flows of the water cycle?
-Atmosphere: little evapotranspiration and reduced absolute humidity (less moisture stored) -Surface water: lots in the summer months due to melting of active layer of permafrost, but little that isn't ice by winter -Ground water: very limited, but mostly permafrost
How does evapotranspiration vary seasonally?
-In winter, sub-zero temperatures prevent evapotranspiration -In summer, some occurs from saturated soils and vegetation
Why are the rates of evapotranspiration low?
-Much of the Sun's energy in Summer is spent melting snow; temperatures remain low and water is frozen most of the year -Sparse vegetation cover and short growing season
Why do rivers flowing over continuous permafrost respond more to changes in temperature and rainfall, and what is the consequence of this?
-The ground is impermeable, which increases surface runoff and reduces throughflow -More extreme regime and more likely to flood on summer/tend to have a higher peak discharge
What is balancing the carbon output from permafrost?
-The plant growth and subsequent CO2 intake stimulated by warmer weather; this has also increased the plant litter entering the store -Possible that the carbon budget may remain balanced in this way (despite global warming)
How do low temperatures affect the stores and flows of the carbon cycle?
-Vegetation: no trees, but some smaller adapted plants -Biodiversity: limited, due to extreme climate -Ground: limited decomposition, due to temperature -Atmosphere: limited photosynthesis and respiration
By how much is the carbon store in soils greater than the above ground biomass store?
5 x
What is the annual precipitation of the Tundra?
50-350mm (low)
For how long each year does the Tundra have a negative heat balance and what does this mean?
8-9 months: temperatures are below 0 degrees C
What percentage of the basin in Southern Alaska is underlain with continuous permafrost?
3% (mostly discontinuous permafrost)
What does Tundra biomass range from?
4-29 tonnes/ha
What is permafrost?
Any ground remaining at or below freezing point for at least 2 years. This varies due to air temperature variation, affected by: latitude, altitude, aspect and vegetation cover
What is talik?
Any unfrozen material within the permafrost zone
What does periglacial mean?
Around the edge of a glacier
Why is NPP low?
Because of the short growing season
Why is there limited transpiration?
Because of the sparseness of vegetation cover and the short growing season
Why is absolute humidity low?
Due to low temperatures, which means that little moisture is stored in the atmosphere
Why is permeability low in the Tundra?
Due to permafrost and crystalline rocks, which dominate the geology of the tundra
What has been causing permafrost to become a carbon source, as opposed to a carbon sink?
Global warming (although current evidence unclear)
What water stores are limited?
Groundwater and soil moisture stores
What is permafrost a barrier to?
Infiltration, percolation, recharge and groundwater flow
Where is the Tundra situated?
It occupied 8m km^2 in nothern Canada, Alaska and Siberia and extends from the northern edge of the boreal coniferous forest to the Arctic Ocean
Describe the global distribution of tundra environments:
Located in the northern hemisphere, found at the edges of the glacial environments, e.g. northern Siberia, Canada, Alaska and Scandinavia
What allows for rapid photosynthesis in the Summer?
Long daylight hours
What is continuous permafrost?
Mean annual air temperatures of below -5 all year and as low as -50. Little surface melting of the ground. It has been estimated to reach up to a depth of 1500 metres and covers 90-100% of land surface
What is sporadic permafrost?
Mean annual temperature is just below 0 and summer temperatures reach several degrees above but isolated pockets of permanently frozen ground remain below the surface. Covers 10-50% of land surface
What is discontinuous permafrost?
Mean annual temperatures between -1 and -5. Islands of permanently frozen ground separated by small pockets of unfrozen ground. Slightly warmer zones close to surface water (lakes, rivers, the sea). Covers 50-90% of land surface
What leads to a sharp increase in river flow during the Summer?
Melting of snow and ice and the active layer of the permafrost
What contributes to water-logging during summer months?
Minimal relief and chaotic glacial deposits impede drainage
What percentage of the basin in Northern Alaska is underlain with continuous permafrost?
Over 50%
What happens during the growing season?
Plants input rich carbon litter to the soil and decomposition increases (releasing CO2, via respiration)
What appears during the summer months?
Several wetlands, ponds and lakes, due to poor drainage (permafrost)
What happens to water during the Winter?
Snow and river/lake ice accumulates
How does slow decomposition occur in the Winter?
Snow cover can insulate microbes
What is the difference between the Low Arctic and the High Arctic?
The Low Arctic is warmer and has a continuous ground cover of vegetation, unlike the High Arctic where vegetation is discontinuous
Why are there two peaks in river flow in the Tundra?
The first peak is due to snow and ice melt and permafrost thawing out. The permafrost underneath remains and the snowmelt results in runoff. The second peak is due to precipitation, as a result of the increase in temperature allowing plants to grow and increasing the humidity in the atmosphere
Why does permafrost contain so much carbon?
The low temperatures slow decomposition of dead plant material
What is the active layer?
The top metre or so of permafrost that thaws during the Summer