6.2 Biological processes sequester carbon on land and in the oceans on shorter timescales

Question 1

Climate

Answer 1

This dictates the rates of plant growth and decomposition; both increase with temperature and rainfall

Question 2

sequestering

Answer 2

The natural storage of carbon by physical or biological processes such as photosynthesis
The oceans are the Earth’s second largest carbon store.
The oceanic store of carbon is 50 times greater than that of the atmosphere.
Most of the oceanic crust is stored in marine algae and coral.
The rest occurs in dissolved form.

Question 3

There are three types of oceanic carbon pump: (circulates and stores carbon)

Answer 3

Biological pumps
Physical pumps
Carbonate pumps

Question 4

Biological pumps

Answer 4

This is the organic sequestration of CO₂ to oceans by phytoplankton.
These microscopic, usually single- celled, marine plants float near the ocean surface to access sunlight to photosynthesise.
They are the base of the marine food web.
Carbon is then passed up the food chain by consumer fish and zooplankton,
which in turn release CO2 back into the water and atmosphere.
Most is recycled in surface waters.
Only 0.1% reaches the sea floor after the dead phytoplankton sink where they either decompose or are turned into sediment.

Question 5

Physical pumps

Answer 5

This is based on the oceanic circulation of water including upwelling, downwelling and the thermohaline current
Downwelling occurs in parts of the ocean where cold, denser water sinks.
The colder the water, the more potential for CO₂ to be absorbed. (polar oceans)
Warm tropical waters release CO₂ to the atmosphere,
whereas colder high-latitude oceans take in CO₂ from the atmosphere.
More than twice as much CO2 can dissolve into cold polar waters than in warm equatorial waters.
As major ocean currents such as the North Atlantic Drift (Gulf Stream) move waters from the tropics to the poles, the water cools and can absorb more atmospheric CO2.

Question 6

carbon pumps

Answer 6

This relies on inorganic carbon sedimentation.
Marine organisms may use calcium carbonate to make hard outer shells and inner skeletons,
such as some plankton species and coral
When organisms die and sink, many shells dissolve before reaching the sea floor sediments.
This carbon becomes part of deep ocean currents.
Shells that do not dissolve build up slowly on the sea floor,
forming limestone sediments such as those in the ‘White Cliffs’ of Dover

Question 7

thermohaline circulation

Answer 7

Thermohaline circulation is an ocean current that produces both vertical and horizontal circulation of cold and warm water around the world’s oceans.
It can be seen as a giant conveyor belt, which plays a vital part in the carbon cycle.
Warm surface waters are depleted of nutrients and CO2,
but they are enriched again as they travel through the conveyor belt as deep or bottom layers.
The rate of circulation is slow; it takes around 1000 years for any cubic metre of water to travel around the entire system.

Question 8

Terrestrial Sequestering

Answer 8

Plants (primary producers in an ecosystem) sequester carbon from the atmosphere during photosynthesis.
In this way, carbon enters the food chains
Respiration returns some of the carbon back to the atmosphere.
Waste from animals/ dead animals is eaten by microorganisms (bacteria and fungi) and detritus feeders (e.g. worms).
Releasing carbon into the soil
Decomposition is faster in tropical climates with high rainfall, temperatures and oxygen levels
Slow if cold/ dry/ oxygen shortage
Combustion may occur when fossil fuels/ organic matter (trees) are burnt to produce energy → the release of carbon emissions that was previously locked inside of them

Question 9

Carbon fluxes within ecosystems vary on two timescales:

Answer 9

Diurnally and Seasonally

Question 10

Diurnally

Answer 10

Diurnally:
day time: positive fluxes - from atmosphere to the ecosystem - photosynthesis (terrestrial sequestering)
night: negative fluxes - from ecosystem to the atmosphere - respiration

Question 11

seasonally

Answer 11

during winter, CO2 concentrations increase because of the low levels of plant growth.
So, as soon as spring arrives and plants grow, these concentrations begin to decrease until the onset of autumn.
In Arctic biomes, ecosystems are locked down by extreme cold for substantial time periods

Question 12

on land carbon sequestering

Answer 12

On land, soils are the largest carbon stores sequestering 30% of global carbon
They sequester about twice as much as the atmosphere
but due to anthropogenic influences they can be source and the level of which depends on the amount of external (human) influences)
Biological carbon is stored in the form of dead organic matter for decades before being decomposed
and then either taken up by plants or released into the atmosphere.
Organic through photosynthesis and subsequent decomposition both above and below ground
All parts of plant (falling leaves/ branches/ roots) are made of carbon so any loss to the ground means a flux from the plant to the soil

Question 13

soil health

Answer 13

Soil health is an important aspect of ecosystems and a key element in the normal functioning of the carbon cycle.
Soil health depends on the amount of organic carbon stored in the soil.
The storage amount is determined by the balance between the soil’s inputs (plant and animals remains, nutrients)
and its outputs (decomposition, erosion and uptake by plant and animal growth.)
A healthy soil has a large surface reservoir of available nutrients which allows for productive ecosystems.
All this explains why even a small amount of surface soil erosion can have an impact on soil health and fertility

Question 14

The actual amount of carbon stored in some soil depends on:

Answer 14

Climate
vegetation cover:
soil type:
land use;

Question 15

Vegetation cover:

Answer 15

This affects the supply of dead organic matter, heaviest in tropical rainforests and least in tundra.

Question 16

soil type:

Answer 16

clay protects carbon from decomposition, so clay-rich soils have a higher carbon content

Question 17

land use;

Answer 17

cultivation (growing plants) and other forms of soil disturbance increase the rate of carbon loss to the atmosphere