ELSS Case Study 2: Arctic Tundra

Question 1

Between what latitudes does the Arctic Tundra lie, and what does its southern limit approximate?

Answer 1

Between 60 -75* North and the southern limit approximated the 10*C July Isotherm

Question 2

Describe the seasonal variation in temperature and precipitation in the Arctic Tundra.

Answer 2

There is a great seasonal variation in temperature, varying between -28C in the winter months to around 7C, with a range of 35*C. The precipitation also varies, ranging from around 10mm in the winter months to over 60mm, however the mean annual precipitation is still low.

Question 3

How much average annual precipitation does the arctic tundra get?

Answer 3

Between 50 - 350mm annually on average.

Question 4

Describe evapotranspiration patterns in the arctic tundra.

Answer 4

Low rates of evapotranspiration, with the sun’s energy expended melting snow, leaving ground temperatures low, and the surface and soil water is frozen most of the year, and due to the sparseness of vegetation and the short growing season, tranpiration rates are low.

Question 5

Why is there limited groundwater and soil moisture stores in the arctic tundra?

Answer 5

Because the permafrost acts as an impermeable barrier to infiltration, percolation, recharge and groundwater flow.

Question 6

Why do wetlands occur during the summer months?

Answer 6

The snow and river/lake ice is melted, but the permafrost impedes infiltration and percolation, resulting in excess surface water.

Question 7

How much carbon is the permafrost estimated to contain globally?

Answer 7

1600GT of carbon.

Question 8

Why does it accumulate so much carbon?

Answer 8

The low temperatures slow decomposition of dead plant material, accumulating lots of carbon slowly.

Question 9

What is the ratio of carbon in above ground biomass to the tundra soils.

Answer 9

1:5

Question 10

Why is the flux of carbon concentrated in the summer months?

Answer 10

Due to the regional plant’s rapid growth cycle, allowing them to grow and flower and fruit in just a few weeks. The higher temperatures also facilitate greater microorganism activity, releasing more CO2 as the short cycle plants input carbon rich litter to the soil.

Question 11

What is the average NPP in the arctic tundra?

Answer 11

Less than 200g/m2/yr

Question 12

What is the tundra biomass per ha

Answer 12

Between 4 and 29 tonnes/ha

Question 13

How is the permafrost slowly becoming a carbon source?

Answer 13

Rising global temperatures are causing more permafrost to melt each year, releasing ancient stores of methane and carbon which wouls have remained untouched for millenia.

Question 14

What are some physical factors affecting the water cycle in the arctic tundra?

Answer 14

Average temperatures are below 0 annually, so most of the water is stored in the permafrost layer as ground ice, however during the summer months some of the shallow active layer melts, and liquid flows onto the surface, forming millions of small pools and shallow lakes.
Drainage is poor, due to the deep permafrost.
Sub 0 temps in the winter prevent any evaporation, however some can occur in standing water in the summer.
Humidity and precipitation is low all year round.
Crystalline rocks and permafrost across the tundra result in low permeability.
Millions of years of erosion of the ancient rock surface has resulted in a gently undulating plain, with minimal relief, contributing to waterlogging in the summer months.

Question 15

What are some physical factors affecting the carbon cycle in the arctic tundra?

Answer 15

Stores carbon is mostly part of frozen partially decomposed plant remains, locked away for at least 500,000 years.
Due ot low temps, the unavailability of water for most of the year and parent rocks containing few nutrients, plant growth is limited, resulting in a low total biomass carbon store.
Photosynthesis and NPP averaged throughout the year are low, with a growing season of less than 3 months, however long days in the summer compensate for this somewhat.
Low temps and waterlogging slow decomposition and respiration and thus the flow of CO2 to the atmosphere.
Due to impermeable permafrost, rock permeability, porosity and the mineral composition of rocks has little influence on either the water or carbon cycle.

Question 16

Where is oil and gas produced in Alaska, and for how long?

Answer 16

The North Slope of alaska, between the Brooks range in the south and the Arctic Ocean in the north. Oil was discovered here in 1968, however production only completed in the 1980s.

Question 17

Why was production completed despite incredible challenges from the local climate?

Answer 17

Production was driven by high global energy prices and the US government’s policy to reduce dependence on oil imports.

Question 18

How much of the US’s domestic oil production does Alaska provide, and how has this changed over time and why?

Answer 18

In the early 1990s, it accounted for nearly a quarter of the US’s domestic oil production, however today it is only around 6%, due to high production costs on the North Slope and the massive growth of the oil shale industry in the USA.

Question 19

What impact has the human activity of oil production had on the permafrost in the Alaskan Arctic Tundra?

Answer 19

Permafrost is highly sensitive to changes in thermal balances, and production has caused much localised melting of the permafrost. This melting is associated with:
-Construction and operation of oil and gas installations, settlements and infrastructure diffusing heat to the environment
-Dust deposition along roadsides creating darker surfaces that absorb more heat.
-Removal of limited vegetation cover, exposing permafrost to more sunlight.
Also gas flaring and spillages input CO2 to the atmosphere.
Destruction of tundra vegetation reduced photosynthesis and the uptake of CO2 from the atmosphere.
Thawing of soils increases microbal activity, accelerating decomposition of hundreds of millenia old biomass.

Question 20

How has the human activity in the Alaskan Arctic Tundra affected the carbon cycle?

Answer 20

Gas flaring and spillages input CO2 to the atmosphere.
Destruction of tundra vegetation reduced photosynthesis and the uptake of CO2 from the atmosphere.
Thawing of soils increases microbal activity, accelerating decomposition of hundreds of millenia old biomass.
Estimated CO2 losses vary from 7 to 40 million tonnes/year and CH4 losses vary from 24000 to 114000 tonnes per year.

Question 21

How has the human activity in the Alaskan Arctic Tundra affected the water cycle?

Answer 21

Melting of the permafrost and snow cover has resulted in more surface run-off and river discharge, increasing likelihood of flooding. – More extensive wetlands, ponds and lakes in the summer. - increases evaporation.
Strip mining of aggregates for contruction creates artificial lakes whch disrupt drainage and expose the permafrost to further melting.
Drainage networks disrupted by road construction and seismic explosions used to prospect oil and gas.
Water extracted from local creeks and rivers for industrial use reduces localised run-off.

Question 22

How much more potent is Methane as a greenhouse gas compared to carbon?

Answer 22

28 times as potent.

Question 23

What are some strategies to moderate the impact on water and carbon cycles in the Arctic Tundra?

Answer 23

Insulated ice and gravel pads - Roads and other infrastructural features can be built on these to protect the permafrost from melting
Buildings and pipelines elevated - This allows cold air to circulate beneath these structures, providing insulation against heat generating structures which would otherwise melt permafrost.
Drilling laterally beyond drilling platforms - This allows oil and gas to be accessed several kilometres away from the drilling site, requiring fewer sites to drilling rigs, greatly reducing the impact on vegetation and permafrost.
Better detection of oil an gas bearing geological structures. - Better computers and detection facilitates the need for less exploration wells, reducing the impact on the local environment.
Refrigerated supports - Used on the trans-Alaskan pipeline to stabilise the temperature of the local permafrost. Similarly used beneath buildings and other infrastructure.