L20

Question 1

What is permafrost?

Answer 1

• Ground frozen for at least two consecutive years
  
  • 24% of land in northern hemisphere
  • Mostly high latitudes but some alpine areas too
  • Permafrost stores carbon as peat and soil organic matter & methane
  • 1300 Gt of carbon stored in permafrost, more than twice as much C than the atmosphere
  • Permafrost is thawing - there are carbon release issues with this
  • Permafrost zones (continuous, discontinuous and sporadic)
  • Permafrost thaws but never melts - eg includes rocks

Question 2

How much of land in the Northern hemisphere is permafrost?

Answer 2

24%

Question 3

How much carbon is stored in permafrost?

Answer 3

1300 Gt - more than twice as much C than the atmosphere

Question 4

The active layer

Answer 4

• Surface that thaws each summer (re-freezes in winter)
  -Permafrost thaw from climate warming
  -Active layer gets progressively deeper
  = active layer thickening/ deepening
  
  • Permafrost is below the active layer
  • Permafrost is thawing due to warmer temperatures, more permafrost is becoming part of the active layer
  • Exposes more carbon to decay previously preserved in the permafrost
• Positive feedback to climate (not good)

Question 5

5 Ecosystem controls of active layer thickness

Answer 5

1. Evergreen trees (vs deciduous)
2. Moss cover (winter vs summer heat transfer)
3. Shrub/ understorey cover (shields irradiance)
4. Organic (peaty) soils
5. Dry soil

Question 6

Evergreen trees (vs deciduous)

Answer 6

• Winter canopy snow trapping
• Stopping snow insulation and help to keep the ground cool

Question 7

Moss promotion

Answer 7

• Protects permafrost
  
  • Moss is dry in summer so insulates and keeps summer heat away
  • It is wet in winter so conducts heat and transfers heat out of the ground to the atmosphere

Question 8

Dry soil

Answer 8

• Drainage
• Precipitation vs transpiration

Question 9

Large scale ecological relationships

Answer 9

• Walker et al 2003

-Transect through northern alaska

-Thaw depth does not get deeper
-North- south changes ecosystem characteristics that affects permafrost
-Larger and leafier southern plants shades and keeps ground dry, so protects permafrost and counters the warmer temperature

-No relationship between active layer depth and temperature

-Demonstrates ecosystem characteristics importance as they counter the warmer climate to protect the permafrost

Question 10

Ecosystem controls on ALT

Answer 10

-Tree canopy leaf area
-Understorey leaf area
-Understorey height
-Moss depth
-Soil organic layer depth
-Soil moisture at surface
-Soil moisture at depth
-% cover of plant species

Question 11

Birch ALT

Answer 11

• Large

Question 12

Large spruce ALT

Answer 12

• Small

Question 13

What increases ALT?

Answer 13

Burning - this is bad for permafrost

Question 14

Why is burning bad for permafrost?

Answer 14

-Heat of fire is little effect, main effect is canopy and moss loss so no protection

Question 15

A thicker moss layer result in…?

Answer 15

A shallower ALT

Question 16

A thicker organic layer results in…?

Answer 16

A shallower ALT

Question 17

Which is more important for ALT, moss thickness or organic matter thickness?

Answer 17

Moss

Question 18

Tree canopy LAI

Answer 18

• Of some importance
• Only surface moisture increases with fire

Question 19

Interaction of ecosystem characteristics

Answer 19

-Steep sites have least influence of organic thickness
- shallower sites organic thickness is more important
- Good drainage on steeper slopes probably lessens importance of insulating organic layer
- Tree canopy leaf area has a much lesser influence in drier soils
-Shading of irradiance less important when you have dry soils that insulate well

Question 20

Methane flux and permafrost thaw

Answer 20

• Subsidence of the ground when ice thaws
  
  • This can then be filled with water and create a wetland

Thermokarst Wetlands produce high methane, little of this comes from old C formerly locked in permafrost

Methane emissions is thought to be ¼ of permafrost associated global warming

Methane emissions increase with biological activity
-Similar amounts of methane emitted from centre of wetland vs outer of wetland (new)
- Long term capacity to keep emitting methane
- Consistent emissions

Question 21

Methane emissions account for what % of permafrost global warming?

Answer 21

1/4

Question 22

Methane dating experiment

Answer 22

-Deepest methane is thousands of years old
- Methane has been made from permafrost carbon
- Permafrost melting must supply carbon

Question 23

Surface methane

Answer 23

• Isn’t dominated by old carbon
  
  • Only 8% of carbon in surface methane is from old deep stores in permafrost
  • Wetlands do not release large amounts of carbon than then contribute to methane emissions
• Methane arises from recent carbon not long term carbon stores