Topic 6: EQ1

Question 1

What stores is carbon present in?

Answer 1

-The atmosphere, as CO2 and in compounds like methane.
-The Hydrosphere, as dissolved CO2.
-The lithosphere, as carbonates in limestone and fossil fuels such as coal,oil and gas.
-The biosphere, in living and dead organisms.

Question 2

What is the carbon cycle?

Answer 2

This is the biogeochemical cycle by which carbon moves from one sphere to another. It acts as a closed system made up of linked subsystems that have inputs, throughputs and outputs. Carbon stores functions as sources (adding carbon to the atmosphere) and sinks (removing carbon from the atmosphere).

Question 3

What happens when there is complete decomposition of organic matter?

Answer 3

This results in carbon returning to inorganic forms such as CO2 and carbonates contained in rock and seawater.

Question 4

What are fluxes?

Answer 4

These are movements of organic compounds through an ecosystem.

Question 5

What are examples of processes which drive flows and fluxes?

Answer 5

-Photosynthesis
-Diffusion
-Respiration
-Chemical Weathering
-Volcanic Outgassing

Question 6

What is system feedback?

Answer 6

Earth system’s normally operate by negative (stabilising) feedbacks, maintaining a stable state by preventing the system from moving beyond certain thresholds. Any change is cancelled out, maintaining equilibrium. Positive (amplifying) feedback loops occur when a small change in one component causes changes in another component. This shifts the system away from its previous state and towards a new one.

Question 7

Who are the intergovernmental Panel on Climate Change?

Answer 7

They are the leading international organisation for the scientific assessment of climate change.

Question 8

What does anthropogenic mean?

Answer 8

This means the processes and actions associated with human activity.

Question 9

What is a petagram (pg)?

Answer 9

Also known as a gigatonne (gt), is the unit used to measure carbon.

Question 10

What is reservoir turnover?

Answer 10

This is the rate at which carbon enters and leaves a store, which is measured by the mass of carbon in any store divided by the exchange flux.

Question 11

What are the two main components of the carbon cycle?

Answer 11

-The geological carbon cycle
-The biological carbon cycle

Question 12

What is the geological carbon cycle?

Answer 12

This is centred around carbon stores in rocks and sediments, with reservoir turnover rates of at least 100,000 years. This is because organic matter that is protected from decay as it is buried deep in sediment takes millions of years to turn into fossil fuels.

Carbon is exchanged in the fast component through the volcanic emissions of CO2, chemical weathering, erosion and sediment formation on the sea floor.

Question 13

What is the biogeochemical carbon cycle?

Answer 13

This fast component of the carbon cycle has relatively large exchange fluxes and rapid reservoir turnovers of a few years up to millennia. Carbon is sequestered in, and flows between, the atmosphere, oceans, ocean sediments and on land in vegetation, soils and freshwater.

Question 14

How is carbon stored crustal/terrestrial stores geologically?

Answer 14

In sedimentary rocks, with very slow cycling over millennia. PgC is 100,000,000. Fossil fuels store an extra 4,000.

Question 15

How is carbon stored deep in the ocean?

Answer 15

Most carbon is dissolved inorganic carbon stored at great depths, very slowly cycled. PgC is about 38,000.

Question 16

How is carbon stored in terrestrial soil?

Answer 16

From biomass, microorganisms break most organic matter down to CO2 in a process that can take days in hot,humid climates to decades in colder climates. PgC around 1,500.

Question 17

How is carbon stored in the surface layer of the ocean?

Answer 17

Exchanges are rapid with the atmosphere through physical processes (CO2 dissolving into the water), and biological processes (plankton). Some sinks to the deeper ocean store. PgC average 1,000.

Question 18

How is carbon stored atmospherically?

Answer 18

CO2 and CH4 store carbon as greenhouse gases with a lifetime of up to 100 years. PgC average 560.

Question 19

How is carbon stored in terrestrial ecosystems?

Answer 19

CO2 is taken from the atmosphere by plant photosynthesis; carbon is stored organic, especially in trees; rapid interchange with atmosphere over seconds/minutes.

Question 20

What are carbon fluxes measured in?

Answer 20

On a global scale they’re expressed as Pg per year (PgC/yr).

Question 21

What is sequestering?

Answer 21

This is the natural storage of carbon by physical or biological processes such as photosynthesis.

Question 22

What does the majority of the earth’s carbon form from?

Answer 22

As the majority is geological, it results from the formation of sedimentary carbonate rocks (limestone) in the ocean, as well as biologically derived carbon in rocks like shale and coal.

Slow geological processes then release carbon into the atmosphere through chemical weathering of rocks, and volcanic outgassing at ocean ridges/subduction zones.

Question 23

What are processes?

Answer 23

These are the physical mechanisms that drive the flux of material between stores.

Question 24

Why are geological fluxes essential?

Answer 24

Despite being small on an annual basis, without them the carbon stored in rocks would remain there forever, eventually depleting the sources of CO2 that are vital to life forms.

Question 25

What are the 5 key processes in the geological carbon cycle?

Answer 25

1) mechanical, chemical and biological weathering of rocks on land in Situ.
2) Decomposition
3)Transportation
4) Sedimentation
5) Metamorphosis

Question 26

What is the result of the weathering processes in the geological carbon cycle?

Answer 26

-Mechanical weathering causes the breakup of rocks by frost; shattering and exfoliation produces small, easy-to-transport particles.
-Chemical weathering causes the breakdown of rocks by carbonic acid in rain, which dissolves carbonate-based rocks.
-Biological weathering by the burrowing animals and the roots of plants can break rocks up.

Question 27

What is the result of decomposition in the geological carbon cycle?

Answer 27

Plant and animal particles that result from decomposition after death and surface erosion store carbon.

Question 28

What is the result of transportation in the geological carbon cycle?

Answer 28

Rivers carry particles (ions) to the ocean, where they are deposited.

Question 29

What is the result of sedimentation in the geological carbon cycle?

Answer 29

Over millennia these sediments accumulate, burying older sediments below, such as shale and limestone.

Question 30

What is the result of metamorphosis on the geological carbon cycle?

Answer 30

The layering and burial of sediment causes pressure to build, which eventually becomes so great that deeper sediments are changed into rock: shale becomes slate and limestone becomes marble.

Question 31

How is carbon stored in limestone and shale?

Answer 31

In the oceans today, 80% of carbon-containing rock is from shell-building organisms and plankton. These are precipitated on to the ocean floor, form layers, are cemented together and lithified into limestone. The remaining 20% of rocks contain organic carbon from organisms that have been embedded in layers of mud. Over millions of years heat and pressure compress the mud and carbon, forming sedimentary rock such as shale.

Question 32

What are carbon fossil fuels?

Answer 32

They were made up to 300 million years ago from the remains of organic material. Organisms, once dead, sank to the bottom of rivers and seas, were covered in silt and mud, and then started to decay anaerobically. This occurs over millennia. The deeper the deposits, the more heat and pressure which build up on the deposits. When the organic matter builds faster than it can decay, layers of organic carbon become oil, coal or natural gas instead of shale.

Question 33

How is oil and natural gas formed?

Answer 33

-This is formed from the remains of tiny aquatic animals and plants. Gas and oil occur in ‘pockets’ in rocks, migrating up through the crusts until meeting caprocks.
-Natural gas, such as methane, is made up of the fractions of oil molecules, so small they are in gas form not liquid, and usually found with crude oil.
-Other hydrocarbon deposits include oil shales, tar sands and gas hydrates.

Question 34

How is coal formed?

Answer 34

Carbon fossil fuels (e.g. coal) were made up to 300 million years ago from the remains of dead organic material. Organisms once dead, sank to the bottom of rivers and seas, were covered in silt and mud, and then started to decay anaerobically. This process operates over millennia. When organic matter builds up faster than it can decay, layers of organic carbon become fossil fuels instead of shale.

Question 35

How long does it take for carbon to move between the rock, soil, ocean and atmosphere?

Answer 35

Between 100-200 million years. On average 10-100million tonnes of carbon moves through this slow carbon cycle annually.

Question 36

How much carbon moves through the ecosystem and anthropogenic carbon cycles annually?

Answer 36

This is faster than the geological processes. At 10^16 g for the ecosystem cycle and 10^15 grams annually for the anthropogenic cycle.

Question 37

How does chemical weathering play a role in the geological carbon cycle?

Answer 37

1) water reacts with atmospheric CO2 and carbonic acid forms. When this weak acid reaches the surface, it reacts with some surface minerals, slowly dissolving them into their component ions,
2) Transportation of calcium ions by rivers from the land into oceans. These combine with bicarbonate ions to form calcium carbonate and precipitate out as minerals such as calcite (CaCO3).
3) Deposition and burial turns calcite sediment into limestone.
4)Subduction of the sea floor under continental margins by tectonic spreading.
5) Some of the carbon rises back up to the surface within heated magma and returns to the atmosphere as CO2. Diamonds have also been discovered to form 700km below the surface, proving carbon is cycled between Earth’s Surface and the lower mantle.

Question 38

How does the processes of volcanic outgassing play a role in the geological carbon cycle?

Answer 38

Outgassing occurs at: active or passive volcanic zones associated with tectonic plate boundaries (including subduction zones), places with no current volcanic activity (e.g hot springs in Yellowstone National Park USA), and direct emissions from fractures in the earth’s crust.

Volcanoes currently emit 0.15-0.26 Gt CO2 annually, compared to the 35 Gt humans emit, this makes volcanic degassing fairly insignificant.

Question 39

How many surface volcanoes are currently active?

Answer 39

About 70 surface volcanoes are currently active. An example of major degassing as a pulse is the 1991 eruption of Mt Pinatubo in the Philippines, part of an island arc created by a subduction zone, such eruptions not only return CO2 to the atmosphere, but the fresh silicate rock erupted starts the carbon cycle again.

Question 40

What is the negative feedback cycle which regulates the geological carbon cycle?

Answer 40

Increase in volcanic activity -> Rise in CO2 emissions and loss of carbon from rocks -> Temperature rises -> More uplift of air, condensation and rain -> More chemical weathering and erosion of rocks -> More ions deposited on ocean floors -> More carbon stored in rocks.

Question 41

What is oceanic sequestration?

Answer 41

The oceans are the Earth’s largest carbon store, being 50x greater than that of the atmosphere; 93% of CO2 is stored in undersea algae, plants and coral, with the remainder being in a dissolved form. Small changes oceanic carbonic cycling can have significant global impacts.

The CO2 gas exchanged flux between ocean and atmosphere operates on a timescale of several hundred years. There is also a significant input of both organic carbon and carbonate ions from continental river run-off. Only a small proportion of this carbon is eventually buried in ocean sediments, but these are important long-term carbon stores with fluxes operating over millennia.

Question 42

What are carbon cycle pumps?

Answer 42

When looking at the carbon cycle pump: the biological pump, and the actions of the linked carbonate pump involving thermohaline circulation. This circulation is part of a third important process called the physical pump. These pumps flux surface ocean CO2 to the deep ocean.

The definition of the carbon cycle pumps is the processes operating in oceans to circulate and store carbon.

Question 43

What is the thermohaline circulation?

Answer 43

The global system of surface and deep water ocean currents is driven by temperature (thermo) and salinity (haline) differences between areas of oceans.

Question 44

What is the biological pump?

Answer 44

-The organic sequestration of CO2 to oceans by phytoplankton. These marine plants float near the ocean surface to access sunlight to photosynthesise. Despite being the base of the marine food web, their huge numbers make up half of the planets biomass.
-Phytoplankton have rapid growth rates, called net primary productivity. This is especially in the shallow waters of continental shelves, where rivers carry nutrients far our to sea. Arctic and southern oceans are very productive.
-Carbon is then passed up the food chain by consumer fish and zooplankton, releasing CO2 back into the water and atmosphere.

Question 45

How much CO2 does phytoplankton sequester to the deep ocean annually?

Answer 45

2 billion metric tonnes annually.

Question 46

What is the carbonate pump?

Answer 46

This relies on inorganic carbon sedimentation. Marine organisms make hard outer shells and inner skeletons from calcium carbonate. These include coral, oysters and lobsters.
When organisms die and sink, many shells dissolve before reaching the sea floor sediments. This carbon becomes part of deep ocean currents. Shells which don’t dissolve build up on the sea floor slowly, forming limestone sediments, e.g the white cliffs of Dover.

Question 47

What is the Physical Pump?

Answer 47

-Based on the oceanic circulation of water including upwelling, downwelling and the thermohaline current.
-CO2 in the oceans is mixed much more slowly than in the atmosphere, so there are large spatial differences in CO2 concentrations.
-CO2 can be absorbed more in colder waters. Concentration is 10% higher in the deep ocean than at the surface. Polar oceans store more than tropical oceans.
-Warm tropical waters release CO2 to atmosphere, but high-latitude oceans take it in. More than 2x the CO2 can dissolve in cold polar waters than equatorial waters.
-As ocean currents carry the water towards the poles, it cools and absorbs more CO2. This increases its density, causing the water to sink which takes accumulated CO2 downwards.

Question 48

Why is the THC important?

Answer 48

It is a vital component of the global ocean nutrient and carbon dioxide cycles. The ocean currents circulate carbon, with water flows equivalent to over 100x the Amazon river. In the 1000 year process for a cubic metre of water to travel the whole system, the water is depleted of CO2 and nutrients in warm surface zones, and then enriched in the colder deeper layers.

The planets food chain system relies on the cool, nutrient rich waters which support algae and seaweed growth. The circulation also helps shift carbon in the carbonate pump cycle from.upper to deeper waters.

Question 49

How has the balance of carbon uptake from the oceans changed?

Answer 49

The carbon uptake (92PgC) and carbon loss (90PgC) from the oceans is dependent on organic and inorganic processes acting at both surface and deep ocean locations. Until the 20th century began, oceans were able to sequester increased CO2 emissions, but evidence now suggests a slowing of this storage. Increased oceanic acidification, due to increased CO2, reduces the capacity for extra CO2 storage.

Question 50

What is the terrestrial sequestration process?

Answer 50

-Primary producers - plants - take carbon out of the atmosphere through photosynthesis and release CO2 back into the atmosphere through respiration.
-When consumer animals eat plants, carbon from the plant becomes part of its fats and proteins.
-Microorganisms and detritus feeders such as beetles feed on waste material from animals, and this becomes part of these micro-organisms.
-After this plant and animal death, tissues such as leaves decay faster than more resistant structures, such as wood. Decomposition is fastest in tropical climates with high rainfall, temperatures and oxygen levels; it is very slow in cold, dry conditions or where there is a shortage of oxygen. In arctic biomes, ecosystems are locked down by extreme cold for substantial periods of time.

Question 51

Which biomes are the most productive globally?

Answer 51

Tropical forests, the savannah and grasslands, which together account for half of global net primary productivity (NPP). Storage is mainly in plants and soils, with smaller amounts in animals and microorganisms such as bacteria and fungi. The largest store is in trees, which can live tens, hundreds and even thousands of years.

Question 52

How can carbon fluxes vary?

Answer 52

Diurnally - during the day the fluxes are positive, from the atmosphere to the ecosystem; at night the flux is negative, with loss from the ecosystem to the atmosphere.

Seasonally - in the northern hemisphere winter, when few land plants are growing and many are decaying, atmospheric CO2 concentrations rise; during the spring, when plants begun growing again, concentrations drop.

Question 53

What are tropical rainforests?

Answer 53

These are one of the largest organic stores of carbon on Earth. The Amazon rainforest alone, which covers 5.3million sq km, sequesters 17% of all terrestrial carbon, more than any other land-based biome. Some species, such as Brazil nut trees, dominate this process. 1% of the Amazons 16,000 tree species store 50% of its carbon, removing CO2 from the atmosphere for centuries.

Question 54

What are wetlands and peat lands?

Answer 54

Wetlands that contain peat, an organic sediment, are important carbon stores. Many peat lands formed during the Holocene have been a store for thousands of years; with climate change and overuse, however, they are becoming net carbon sources.

Question 55

How is biological carbon stored?

Answer 55

Soils store 20-30% of global carbon, sequestering about 2x the quantity of carbon as the atmosphere and 3x that of terrestrial vegetation. However, whether it sequesters or actually emits CO2 depends on the local conditions.

Question 56

What are the two sources of carbon in soil?

Answer 56

Arid and semi-arid soils, and those developed on limestone, contain inorganic carbon. But the most important store is from organic sources through plant photosynthesis and subsequent decomposition both above and below ground, living organisms represent about 5% of the total soil organic matter. They have seasonal as well as daily patterns, and not all are active at the same time.

Question 57

How is carbon transferred from plants to soil?

Answer 57

As all plants are made of carbon, any loss to the ground means a transfer or flux from the plant to the soil. Litterfall and branch litter includes whole plants, leaves and branches shed during any year. Roots may also be shed. Carbon is stored as dead organic matter in soils for years, decades or even centuries in colder climates or wetland environments, before being broken down by soil microbes and released back to the atmosphere.

Question 58

What is humus?

Answer 58

The formation of humus is the most long-term process in the soil decomposition process. Humus is seen easily in soils as it has a dark, rich colour. Humus soils are 60% carbon and are important for sequestration as well as for water storage.

Question 59

What layer of soil is carbon cycling most active?

Answer 59

Carbon cycling and formation is most active in topsoil horizons. Stabilised carbon, with longer turnover times, is located in deeper soil layers. In permafrost regions, over 61% of carbon is stored deeper than 30cm. An additional long-term carbon store in many soils is pyrogenic carbonaceous matter, formed from biomass burned and carbonised during wildfires. This resists microbial decomposition and can remain in soils for long periods.

Question 60

What factors determine the capacity of soil to store organic carbon?

Answer 60

-Climate: this dictates plant growth and microbial and detritivore activity. Decomposition is rapid at high temps or in waterlogged soils. High rainfall increases potential carbon storage. Arid soils also only store 30 tonnes per hectare compared to 800tonnes per hectare in cold regions.
-Soil type: clay-rich soils have a higher carbon content than sandy soils. Clay protects carbon from decomposition.
-Management and use of soils: Since 1850, soils globally have lost 40-90Gt of carbon through cultivation and disturbance. Current rates of carbon loss due to land-use change are 1.6 +- 0.8 Gt of carbon/year.

Question 61

How does rising atmospheric CO2 have indirect effects on carbon dynamics and stability of soils?

Answer 61

It does this by affecting vegetation and little stores and flows. For example, the Arctic biome contains 1/3 of the earth’s soil but with a rapidly warming climate and rising CO2, so its net storage function may have already ‘flipped’ from a store to a source.

Question 62

What is a carbon balance?

Answer 62

The carbon stores of the atmosphere, ecosystems and soils are in constant exchange. The carbon balance in soils is regulated by plant productivity, microbial activity, geology, erosion, climate and the amount of upwards and downwards (leaching) water movement in soil.

Question 63

What is a balanced carbon cycle crucial for?

Answer 63

Sustaining other global systems. The carbon cycle plays a key role when regulating the Earth’s global temperature and climate by controlling the amount of CO2 in the atmosphere, which then affects the hydrological cycle. Ecosystem development and agriculture depends on the carbon cycle. Carbon stores and fluxes involve natural processes which have helped to regulate the carbon cycle and atmospheric CO2 levels for millions of years.

Question 64

What is the natural greenhouse effect?

Answer 64

The sun is the natural driver of almost all of the earth’s atmospheric energy. Short-wave solar radiation comes from the sun and then dark surfaces on the earth absorb this and radiate it back as heat. One of the most vital roles in the carbon cycle is the release of CO2, and other gases such as methane (CH4) into the atmosphere. Some of the long-wave length radiation emitted from the earth is absorbed and reflected by the greenhouse gases back towards earth, and some passes back out into space.

Retaining this heat causes the earth’s temps to be 16°C warmer than it would be otherwise, allowing life to be sustained.

Question 65

What are the most common greenhouse gases?

Answer 65

-CO2 - makes up 89% of greenhouse gas produced. 30% increase since 1850.
-Methane (CH4) - makes up 7% of greenhouse gases produced and is 21x more powerful than CO2. 250% increase since 1850.
-Nitrous oxide (N2O). Makes up 3% of greenhouse gases produced. From jet engines and car pollution. 250x more powerful than CO2. 16% increase since 1850.
-Hydrocarbons. 1% greenhouse gases produced. Used in industry. 3000x more powerful than CO2.

Question 66

What is the enhanced greenhouse effect?

Answer 66

The concentration of several greenhouse gases in the atmosphere have increased by 25% since 1750, when industrialisation began in the UK. Since the 1980s, 75% of CO2 emissions have come from burning fossil fuels. Most researchers believe this is the cause of increased global temps.

Human activity, such as burning fossil fuels and deforestation, release natural stores of carbon and nitrogen, which combine with oxygen in the air to form greenhouse gases. Global temps also increase the amount of water Vapor in the atmosphere, leading to greater condensation and cloud cover, trapping heat in the atmosphere.

Question 67

How does the earth absorb incoming short-wave solar radiation from the sun?

Answer 67

-Approx 31% reflected by clouds, aerosols and gases in the atmosphere and by the land surface.
-The other 69% is absorbed at the earth’s surface, especially by oceans.
-69% of what is absorbed at the surface is re-radiated to space as longwave radiation. Some of this is re-reflected back towards the earth’s surface by clouds and greenhouse gases, ‘trapping’ the radiation.

Question 68

How does temperature vary globally?

Answer 68

-Different latitudes experience different concentrations of solar radiation, which in turn influences temperature. Solar insulation is most concentrated at the equator, but more dispersed at the Poles, causing the cooler pole temps.
-Earth surface characteristics also have implications, e.g snow reflects a lot of sunlight and dark forests will absorb it.
-Air movement, ocean currents and atmospheric circulation also distributes heat around the world.

Question 69

How does precipitation vary globally?

Answer 69

-Solar radiation (insolation) is most intense over the Equator, convection and low-pressure systems dominate meaning rainfall is high all year.
- At 30° N/S precipitation decreases and high pressure conditions means clouds rarely form.
-Different air masses meet at the mid latitudes, and the low pressure systems bring rainfall.
-Closer to the poles, precipitation falls as the air cools further and is dense and dry - creating polar deserts.

Question 70

How do regional and seasonal variations occur in precipitation?

Answer 70

The effects of topography and migration of global pressure and wind systems (such as the movement of the ITCZ N and S of the equator) can cause regional variation.

Question 71

How does photosynthesis play a crucial role in regulating the composition of the atmosphere?

Answer 71

-Phytoplankton sequesters CO2 through photosynthesis, transferring it from the atmosphere to the ocean stores. Known as the biological pump. This transfers 5-15 Gt of carbon from atmosphere to ocean each year.
-Terrestrial photosynthesis allows for 100-120 Gt of carbon to be sequestered each year. Respiration and decomposition then releases this back into the atmosphere.

Question 72

How do climatic changes affect how different ecosystems absorb CO2?

Answer 72

-Anything which affects the level of phytoplankton in the world’s oceans, or area of land covered by forest will have an impact on carbon sequestration, which in turn affects composition of the atmosphere.
-Tropical rainforests climates are ideal for plant growth, and this promotes photosynthesis.
-In oceans, warm tropical shallow waters are the ideal homes from coral reefs and mangroves, the marine equivalents of rainforests in terms of plant growth.
-Deserts have sparse vegetation and offer little in terms of CO2 sequestration.
-Melting arctic sea ice means that greater expanses of ocean are exposed to direct sunlight, and seasonal thaws now last longer. Increasing photosynthesis by phytoplankton now results in algal blooms in Arctic waters, so more CO2 is now being stored there.

Question 73

How does carbon impact soil health?

Answer 73

Soil health depends on the amount of organic carbon which is stored in the soil. This depends on its inputs and outputs (decomposition, erosion and use in plant and animal productivity).

Carbon is the main component of soil organic matter and helps to give soil its water-retention capacity, its structure and fertility. This is the opposite to ‘active’ soil carbon found in topsoil. Organic carbon is concentrated in the surface soil layer as easily eroded small particles, which is why soil erosion is a major threat to carbon storage and soil health.

Question 74

How has carbon storage in plants changed from early to mid 20th century?

Answer 74

Changes from a carbon source to a carbon sink. The deforestation, resource destruction and soil erosion which was occurring globally still occurs, but afforestation and reforestation efforts in North America, Europe and China as well as improvements in agricultural practice is helping to reform plant stores as carbon sinks.

2015 onwards could see warmer temps trigger faster decomposition and recycling of carbon in dead plants and soils, possibly causing them to become a carbon source again.

Question 75

What is ecosystem productivity?

Answer 75

About 1% of solar insolation reaching earth is captured by photosynthesis and used by plants to produce organic material or biomass. The rate at which plants produce biomass is called primary productivity. Net primary productivity (amount of biomass produced by plants minus energy lost through respiration) is high in tropical rainforests with warm and humid conditions, and a year-round growing season. Tundra ecosystems, with a cool and dry climate, grow much more slowly and have a much lower level of productivity.

Question 76

What ecosystems have the highest and lowest net productivity?

Answer 76

Highest:
-Tropical rainforest (≈2200g/m2/yr)
-Temperate deciduous forest
-Savanna
-Taiga
-Temperate grassland
-Tundra
-Desert and scrubs (≈100 g/m^2/yr)

Question 77

How has fossil fuel consumption increased?

Answer 77

Since the Industrial Revolution in Europe, coal, oil and natural gas have been taken from the ground and used by industries, power stations and machinery. Compared to the natural carbon cycle, this happened very quickly, and atmospheric CO2 is the highest it has been in the past 800 000 years (over 400ppm).

Question 78

What are the implications of fossil fuel consumption on the climate?

Answer 78

-Temperate and tropical areas may have stronger storms because atmospheric heat and moisture has increased.
-Fewer extreme cold events but more extreme warm events due to average temps increasing.
-Biggest increase in average temps will be in the Arctic due to more heat being transferred from the tropics.
-Precipitation patterns will change, higher near poles and lower near subtropics as warmer air can hold more soil moisture.

Question 79

What are the implications of fossil fuel consumption on the ecosystem?

Answer 79

-10% of land species face extinction because of a lack of a ability to adapt to rising temperatures. Especially in polar areas.
-80% of coral reefs could be bleached by warm seawater and suffer chemical erosion due to oceans becoming more acidic.
-Warmer winters will allow the season for pests and disease to thrive to increase.
-Biodiversity will change and habitats move further north to cooler regions, which will change food webs.

Question 80

Why is carbon stored as organic matter in soil important?

Answer 80

Organic matter helps retain soil moisture and nutrients, which in turn improves the productivity of an ecosystem by providing water and dissolved nutrients for plants to absorb through their roots to grow (increasing biomass).

Question 81

What are the implications of fossil fuel combustion on the hydrological cycle?

Answer 81

-The shift of subtropical high pressure areas towards poles will increase drought conditions in Mediterranean climate zones.
-Permafrost will melt, adding more water to Arctic rivers and streams.
-River discharges will decrease in areas with lower precipitation and lower effective precipitation (where evaporation rates increase).
-Cryosphere stores will decrease as glaciers retreat or surface ablation increases, this will increase river discharges in the short-run but decrease them in the long-run.

Question 82

Why do mangroves and wetlands store so much carbon?

Answer 82

As carbon can be stored in soils as dead organic matter, in some regions this will be a process which takes thousands of years.

Mangroves have thick layers of organic litter, humus and peat, all containing high levels of carbon. And as twice a day these soils are submerged below water by high tide, the soils are anaerobic and thus means decomposition is slow as microbes and bacteria cannot survive, so carbon is stored for thousands of years.

Question 83

What is potentially reversing mangroves and wetlands role as significant store of soil carbon?

Answer 83

Their drainage and clearing, which causes their once anaerobic conditions preventing the biota needed for decomposition to be removed. This will cause significant amounts of carbon to be released into the atmosphere.

Question 84

What are the 3 different ways volcanic outgassing can occur?

Answer 84

-Subduction zones, where carbon sources are oxidised and and vented back into the atmosphere or ocean.
-Divergent plate boundaries, where rising magma releases CO2.
-Hotspots (e.g Yellowstone), where non-erupting volcanoes passively diffuse CO2 into the atmosphere.