The Carbon Cycle

What are the 5 spheres of the earth/how do they store carbon?

> atmosphere (air) - as carbon dioxide and compounds e.g. methane;

> hydrosphere (water) - as dissolved CO2;

> lithosphere (rocks) - as carbonates in limestone and fossil fuels;

> biosphere (life) - living and dead organisms;

> cryosphere (ice) - biological carbon is stored in permafrost, prevents bacterial decay.

how much carbon is stored in these spheres? *in petagrams*

Lithosphere - 100,000 PgC

Hydrosphere - 38,000 PgC

Biosphere - 2,000 PgC

Atmosphere - 750 PgC

Carbon cycle?

closed system - 3 components:

1) stores

2) fluxes (transfers) which moves carbon between stores, measured in petagrams or gigatonnes of carbon per year.

3) processes - physical mechanisms which drive the fluxes between stores e.g. photosynthesis.

carbon stores - equilibrium.?

act as sources and sinks - balanced in equilibrium when sources equal the sinks.

examples of sinks/sources?

> when plants and animals die, carbon released back into atmosphere, cycle continues.

> undisturbed carbon cycle maintains CO2 levels in atmosphere and maintains global temps so Earth can sustain life.

> BUT when huge amounts of CO2 are released into atmosphere in short period of time, cycle becomes unbalanced!

define 'reservoir turnover rates'

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

Explain geological carbon cycle?

> slow part - carbon stores in rocks & sediments with reservoir turnover rates of at least 100,000 years.

> organic matter buried deep in sediments - protected from decay - millions of years to turn into fossil fuels.

> carbon flows through volcanic eruptions, chemical weathering, erosion and sediment formation on the ocean floor.

explain bio-geochemical carbon cycle?

> fast part - large fluxes and rapid reservoir turnovers varying between a few years to thousands.

> carbon sequestered in and flows between the atmosphere, oceans, ocean sediments, vegetation, soils and freshwater.

Geological stores of carbon?

> sedimentary carbonate rocks (limestone) in ocean.

> biologically derived carbon in shale, coal, and other rocks.

geological process (release into atmosphere)? (5)

> weathering of rocks

> decomposition (of plants/animals)

> transportation - rivers carry particles to the ocean + deposit)

> sedimentation - build up, burying older sediments below e.g. shale/limestone.

> metamophosis - pressure builds ot in layers of sediment > deeper sediment changes to rock e.g. shale becomes slate.

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

between 100 to 200 million years.

Carbon in limestone and shale?

> 80% of carbon containing rocks in the ocean is from shell-building organisms and plankton (fall to ocean floor and become lithified).

> remaining 20% of rocks contain organic carbon originating from organisms that have been embedded in layers of mud.

Explain volcanic outgassing?

> release of gas that has been dissolved, trapped, frozen or absorbed in rock.

> happens at: volcanic zones with plate boundaries + direct emissions from fractures in the Earth's crust.

How much carbon do volcanoes (in comp. to human activity) emit?

> emit 0.13 to 0.6 gigatonnes of carbon dioxide annually.

> in comparison, fossil fuel use (human activity) currently emits about 35 Gt annually.

define sequestration?

the movement of carbon into carbon stores, which can lower the amount of CO2 in the atmosphere.

define photosynthesis?

(by land-based plants and phytoplankton) is the main process responsible for sequestering carbon from the atmosphere.

Positive Feedback?

A type of regulation that responds to a change in conditions by initiating responses that will amplify the change e.g. increases global temperatures by global warming.

Negative feedback?

A type of regulation that responds to a change in conditions by initiating responses that will counteract the change, meaning a state of dynamic equilibrium. E.g. increased temps leading to increased plant growth... eventually causing more co2 to be sequestered...

Biological carbon pump?

A transfer of CO2 and nutrients from the surface waters to the deep ocean as a result of photosynthesis in shallow waters, the settling of organic matter, and decomposition in deep waters.

> phytoplankton absorb CO2 and transfers it into the deep ocean carbon store where it is held - either by 'sinking' after death OR via fecal matter through phytoplanton being consumed by other species.

How much carbon (+ specific CO2) does the ocean store?

Approx 38,000 gigatonnes.

> 93% of CO2 stored in undersea algae, plants, coral & dissolved form = ocean is largest carbon store on Earth.

Why is the enhanced greenhouse effect a problem?

Natural carbon emissions within the carbon cycle are in a state of equilibrium (inputs equal outputs) but increased carbon fluxes caused by human activity, e.g. deforestation, cause the system to become unbalanced.

Carbonate pump? (3)

Part of the biological carbon pump - moves inorganic carbon

1) marine organisms use dissolved calcium and carbonate ions to make calcium carbonate shells; 2) die, their CaCO3 shells sink, transferring carbon from surface to deep ocean; 3) shells dissolve in deep water, releasing carbonate ions which can be stored in sediments.

explain the solubility (physical) pump?

CO2 is absorbed by oceans surface via diffusion, then taken to deep ocean stores through downwelling currents (96 Gt of carbon annually) which is then distributed around the planet by thermohaline circulation.

Thermohaline Circulation? (2/3)

An ocean current that produces both vertical and horizontal circulations of warm and cold water around the world's oceans.

> cold water absorbs more CO2 so as equatorial waters move towards the poles, more CO2 is absorbed + salinity also increases

> Water in N Atlantic is v cold + v saline = denser > this water then sinks > this then draws in warmer water from the surface from the tropics...

Why is the decline in thermohaline circulation problematic? (2)

• Weakens the role of the ocean as a carbon sink as slower circulation means less mixing between surface water and deep waters, reducing the uptake of co2 from atmosphere > increases enhanced greenhouse effect (reinforces positive feedback loop).

• Disrupts nutrient cycling from the deep ocean water which limits phytoplankton growth/ health = less biological carbon pump efficiency...

breakdown of biological carbon? (3)

> 20 to 30% of global carbon stored as dead organic matter in soils.

> carbon that isn't stored is returned to atmosphere via biological weathering.

> litter fall = transfer of carbon to the soil.

determining factors of soil health?

amount of organic carbon stored in the soil...

>>> inputs - plant and animal residues and nutrients

>>> outputs - decomposition, erosion, and use in plant and animal productivity.

carbon helps to provide soils with its water retention capacity, its structure and fertility.

3 things which impacts the capacity of the soil to store organic carbon?

1) climate - influences plant growth + rapid decomposition happens at higher temps + high rainfall means increased potential carbon storage.

2) soil type - clay rich soils have higher carbon content than sandy soil as clay protects carbon from decomposition.

3) use and management of soils - globally, soils have lost 40-90 billion tonnes (Gt) of carbon since 1850 through cultivation and disturbance.

What are the UK's current energy make-up stats according to the national grid?

Fossil fuels but only gas (31%), nuclear (8%) plus renewables (45%) - mostly wind but some solar/ hydroelectric.

US 2024 stats for energy mix?

Oil - 36%

Natural Gas - 36%

Nuclear - 9.8%

Rest includes - coal, hydropower, renewables (solar/wind) + biofuels.

list 5 major players in energy

1) TNCs

2) Organisation of the Petroleum Exporting Countries (OPEC)

3) Energy companies

4) consumers

5) Governments.

Explain TNCs as a major player in energy?

> estimated 50% of players in oil and gas (incl. BP) are state owned.

> majority of TNCs are involved in a variety of operations incl. exploring, extracting, transporting, refining, and producing petrochemicals.

Explain OPEC as a major player in energy?

> currently has 13 member countries owning around 2/3 of world's oil reserves between them = OPEC can control amount of gas and oil in global market + prices.

> accused of forcing up the prices by witholding/slowing production.

Define 'energy security'?

Being able to access reliable and affordable sources of energy - may be foreign or domestic...

Define 'energy mix'?

The range and combination of sources required to supply a country with energy.

list factors affecting access to/consumption of energy? (7)

> physical availability

> cost

> technology

> public perception - depending on economic development of a country/standard of living.

> level of economic development - HICs tend to have higher levels of energy consumption...

> climate - extreme temps often require higher levels of energy consumption to make life more comfortable.

> environmental priorities

Example of an energy rich (secure?) country and problems?

Russia - largest exporter of natural gas (47,000 billion m3) + largest supplier to European Union, through nord stream pipe > unreliable/ unsecured, especially due to recent conflict with Ukraine?

Define 'choke points'?

Narrow sea channels where transport can easily be disrupted e.g. Strait of Hormuz - only 39km wide.

> if choke points are threatened/ exploited, can cause rise in energy prices, plus can damage energy security of dependent nations.

What are the three terrestrial stores?

1) producers - carbon fixation through photosynthesis, biomass production, carbon sink...

2) consumers - ingesting/ photosynthesising and respiring OR through decomposition.

3) decomposers - breaking down DOM, releasing co2 back into the atmosphere.

Bio-geochemical carbon cycle

The exchange of carbon between its four main reservoirs—the atmosphere, terrestrial biosphere, oceans, and sediments (rocks).

Radiative forcing effect (RFE)?

the amount that a greenhouse gas affects the balance between the Earth's incoming solar radiation and outgoing long-wave radiation.

Solar insolation?

The angle of the sun's rays makes solar insolation intense/ concentrated at the equator, but dispersed over a wider surface at the poles.

breakdown of the greenhouse effect? (3)

> 31% of shortwave solar radiation is reflected by clouds, aerosols and gases in the atmosphere/land surface.

> remaining 69% is half absorbed at the surface e.g. oceans + half re-radiated back into space as long-wave radiation.

> greenhouses gases deflect long-wave radiation back to earth's surface (natural greenhouse effect which supports life)...

Albedo effect?

Describes the ability of surfaces to reflect the sun's rays back out into space - snow and ice reflects the majority of the sun's rays that are directed at them.

Peatlands as a carbon store?

only 3% of land surface BUT contains 33% of world's soil carbon.

Permafrost as a carbon store?

> an area of ground that has been frozen for years and traps carbon within layers of ice.

> stores approx 1600 gigatons of carbon.

CCS

Carbon Capture and Storage - takes carbon directly out of the atmosphere, pumps it underground and injects it in liquid form into underground water bodies or permeable rocks which then stores the carbon.

> 228 operation CCS plants in the world - 30 of them in USA.