Alaskan Tundra

Where is the Alaskan tundra located from its southern to northern limits?

From the northern edge of the boreal coniferous forest to the Arctic Ocean

What is the significance of the 10°C July isotherm?

It marks the climatic limit of the tree line

What is the mean annual temperature of the Alaskan tundra?

Around −12°C

For how many months does the tundra have a negative heat balance?

Around 8–9 months

Which part of the ground is not permanently frozen during the Arctic summer?

The active layer (top metre of soil)

Are there times in winter with no sunlight for 24 hours a day?

True

How low can winter temperatures fall in the Alaskan tundra?

Below −30°C

Are daylight hours short in summer in the Alaskan tundra?

False

What is the annual precipitation in most of the Alaskan tundra?

Less than 100 mm

What is the most common form of precipitation?

Snow

Is absolute humidity high or low in the tundra?

Low

What is the length of the growing season in the Alaskan tundra?

Around 3 months

What is much of the Sun’s energy used for at the ground surface?

Melting snow, using up latent heat

Is there significant convection in summer in the Alaskan tundra?

False

Why is there limited groundwater and soil moisture storage?

Permafrost acts as a barrier, preventing infiltration, percolation, soil moisture recharge, and groundwater flow

Why does river discharge increase sharply in spring?

Snow and lake ice melt and the active layer of permafrost thaws

What is the minimum and maximum discharge of the Yukon River?

Minimum about 340 cumecs in winter and maximum about 24,600 cumecs in summer

Why is permeability low in the Alaskan tundra?

Extensive permafrost and impermeable Precambrian igneous and metamorphic rocks

How many lakes are there in Alaska?

Over 3 million

Where are wetlands found in the Alaskan tundra?

In the Yukon River valley, river deltas, and along the Bering Sea coast

Why are there extensive wetlands, ponds, and lakes in summer?

Permafrost impedes drainage, flat relief slows flow, ancient eroded rock creates gentle relief, and glacial deposits block drainage

How does the size of the tundra soil carbon store compare to above-ground biomass?

About five times larger

Why is above-ground biomass small in the Alaskan tundra?

Low NPP (<200 g/m²/year), very short growing season, and limited liquid water

Why is the tundra soil carbon store so large?

Low temperatures slow decomposition, frozen soil prevents decomposition, and organic matter accumulates faster than it breaks down

When is plant litter added to the carbon store?

During the summer growing season

For how long has most carbon been stored in tundra permafrost?

Around 500,000 years

Why does the rate of photosynthesis vary seasonally?

Longer daylight hours and higher temperatures in summer

Why does summer decomposition produce methane?

Waterlogged conditions in the active layer cause anaerobic decomposition

What remains frozen in permafrost during winter?

Dead organic matter

What allows some decomposition to occur even in winter?

Insulating snow cover

How much CO₂ and methane are released annually from melting permafrost in North Slope Alaska?

7–40 million tonnes of CO₂ and 0.024–0.11 million tonnes of methane per year