Chapter 4- Carbon

Why is the carbon cycle defined as a 'closed system'?

The amount of carbon is constant and finite.

How is carbon stored in the following earth spheres:

• Atmosphere

• Hydrosphere

• Lithosphere

• Biosphere

• Cryosphere

• Atmosphere- carbon dioxide and methane

• Hydrosphere- dissolved CO₂

• Lithosphere- carbonates in limestone and fossil fuels

• Biosphere- living and dead organisms

• Cryosphere- biological carbon stored in permafrost- prevents bacterial decay

Define fluxes

What are they measured in?

The flows which move carbon between stores

Measured in pentagrams or gigatonnes of carbon per year

What is the largest and smallest flux of carbon?

Largest- Earth”s crust

Smallest- Volcanoes or burial of sediment

Define processes + examples

The physical mechanisms which drive the fluxes between stored e.g photosynthesis and diffusion

Define source

A carbon store that adds carbon to the atmosphere

Define sink

A carbon store that removes carbon from the atmosphere

Under what condition is the carbon cycle considered to be in equilibrium?

When the sources equal the sinks.

What is the primary process by which plants (primary producers) remove carbon from the atmosphere?

Photosynthesis.

What are the key geological processes in the carbon cycle?

Weathering of rocks

Decomposition

Transportation

Sedimentation

Metamorphosis

Which biological process releases CO₂ back into the atmosphere from living organisms?

Respiration.

What happens to stored carbon when plants and animals die?

It is released back into the atmosphere through decomposition.

What is the typical reservoir turnover rate for the geological (slow) carbon cycle?

At least 100,000 years.

What is the process of chemical weathering?

CO₂ from the atmosphere reacts with water to form carbonic acid, this acid rain falls to the surface where it reacts with carbonate rocks such as chalk and limestone, dissolving them.

Why does organic matter buried deep in sediments take millions of years to turn into fossil fuels?

It is protected from decay due to a lack of oxygen

What is the typical reservoir turnover rate for the bio-geochemical (fast) carbon cycle?

A few years up to a thousand years.

In the geological carbon cycle, what process results in the mechanical or chemical breakdown of rocks?

Weathering.

How do rivers contribute to the geological carbon cycle?

They transport calcium ions from the dissolved rocks into oceans, this reacts to form minerals such as calcite.

What is the geological process of sediment layers building up and burying older sediments?

Sedimentation.

How long can carbon take to move between rocks, soil, the ocean, and the atmosphere?

Between 100 and 200 million years.

What percentage of carbon-containing rocks in the ocean originates from shell-building organisms and plankton?

80%.

What is the process of ocean sediments being cemented together and turning into limestone?

Lithification.

What sedimentary rock is formed when organic carbon is embedded in mud and compressed over millions of years?

Shale.

Fossil fuels form when organic matter builds up faster than it can _____.

Decay.

How long does it take for coal, oil and gas to form?

Over 300 million years

What is volcanic outgassing?

The release of gas (pockets of CO₂) during volcanic activity that was dissolved, trapped or frozen in rock

How is carbon released from each of the following plate margins/ tectonic locations:

• Convergent

• Divergent

• Hot spots

Convergent- at subsection zone, partial melting of subjected material frees CO_2, rises through the magma, released by volcanoes

Divergent- plates move away from each other, as plates separate, magma rises to the surface, drop in pressure allows CO₂ to escape from mantle

Hot spots- mantle plume rises from within the mantle, contains carbon rich material which is emitted during volcanic eruptions through continuous degassing

Approximately how many gigatonnes of CO₂ are emitted by fossil fuel use annually?

35- 40 Gt

What percentage of CO₂ is stored in the oceans, making them the largest carbon store?

93%.

Define diagenesis

The geological process that forms limestone, sedimentary rock and crude oil

Explain the process of organic carbon sequestration in the sea/ seafloor

Phytoplankton, absorb carbon from the atmosphere for photosynthesis

Phytoplankton die and their remains accumulate on the sea floor

Layers of sediment form, exposed to high pressures and temperatures

Leads to compaction and cementation

Organic limestone is formed.

Explain the process of inorganic carbon sequestration in the sea/ seafloor

Direct precipitation of calcium carbonate from salt of fresh water e.g. river- carried ions from chemical weathering of rock upstream or from evaporation of seawater

Leaved behind calcium carbonate deposits

Rain becomes weak carbonic acid when falls through the air

Dissolves the calcium carbonate

Allows erosional processes to transfer dissolved carbon for deposition on the seabed.

Define carbon sequestration

The removal and storage of carbon from the atmosphere, usually occurs in oceans, forests and soils through photosynthesis

Which global system is responsible for the horizontal movement of carbon within the oceans?

Thermohaline circulation.

What mechanism in the biological pump transports carbon to the deep ocean?

The sinking of dead cells, shells, and organisms.

What is the estimated size of the sea bed sediment carbon store?

1750 Gt

What type of ocean currents take dissolved CO₂ down to deep ocean stores?

Downwelling currents.

Why is more CO₂ absorbed as equatorial waters move toward the poles?

Cold water absorbs more CO₂

How does salinity change as water cools and sinks in the physical pump?

Salinity increases.

What process brings previously stored carbon from deep ocean stores back to the surface?

Upwelling.

Thermohaline circulation is driven by differences in what?

Salinity and temperature

Why are warm surface waters often depleted of CO₂ and nutrients?

Due to evaporation.

Which sequestration process operates on the shortest time scale (seconds to years)?

Terrestrial sequestration.

In what type of climate is decomposition fastest?

Tropical climates (high temperature, rainfall, and oxygen).

Where is carbon mainly stored in productive biomes like rainforests and savannahs?

In vegetation.

Terrestrial carbon fluxes are most active during the day (diurnally) and during which seasons?

Spring and summer.

Why does vegetation and animal matter decay much slower in clay?

Clay can easily get waterlogged, creating anaerobic conditions and therefore a lack of oxygen for decomposers to survive

What are the two primary greenhouse gases that influence the natural greenhouse effect?

Carbon dioxide and methane.

What percentage of incoming shortwave solar radiation is reflected by the atmosphere and land?

31%.

In the greenhouse effect, absorbed solar radiation is re-radiated from the surface as _____ radiation.

Long-wave.

What is NPP

The chemical energy stored in plant biomass after respiratory losses to the environment are subtracted, represents the total energy available to consumers in an ecosystem

Where does the highest Net Primary Productivity (NPP) occur in the oceans?

In shallow ocean waters.

Why is soil erosion a major threat to carbon storage?

Organic carbon is mainly found in the surface soil layer.

What is a major threat to marine ecosystems caused by rising ocean temperatures?

Lower oxygen levels (or ocean acidification).

How does global warming affect the timing of the hydrological cycle's precipitation type?

It leads to earlier snowmelt in the spring.

Limestone is an example of a _____ carbonate rock.

Sedimentary.

During subduction how can carbon can rise back to the surface and be released as CO₂

Within magma, dissolved CO₂ can make its way back to the surface, as pressure decreases, the gas bubbles increase in size until they reach the surface of the magma where they are released into the atmosphere

What organisms are the primary drivers of the ocean's biological pump?

Phytoplankton.

How does increased evaporation due to global warming affect the hydrological cycle?

More moisture circulates through the cycle, water vapour acts as a greenhouse gas, accelerating climate change

If the North Atlantic Drift slows or reverses, what is the likely impact on UK winters?

Temperatures would decrease significantly.

How do coastal ecosystems primarily face risk from the unbalanced carbon cycle?

Through sea level rise.

What is the annual rate of CO₂ emissions from volcanoes compared to human activity?

Volcanoes emit 0.15Gt, while humans emit about 35Gt.

Why is photosynthesis considered the main process for lowering atmospheric CO₂?

It sequesters carbon into long-term biological stores.