Carbon Cycle

The carbon cycle is the movement of carbon between the different reservoirs on the earth. It is important for planetary health as the balance of the carbon cycle can affect the climate.

In 2015, the first legally binding global climate deal was adopted by 195 countries in the Paris Climate Conference (COP21).

The slow cycle takes between 100 million years and 200 million years for carbon to move between the rocks, soil, ocean and atmosphere. The fast carbon cycle is the flow of carbon through life forms.

Examples of movement in a fast carbon cycle can be seen in terrestrial or marine ecosystems. In terrestrial ecosystems, the movement of carbon is through the living organisms into the atmosphere from respiration with carbon dioxide and methane released from the decomposition of plants and animals. Also, when the animal and plant matter decay, the carbon stored gets converted into another carbon store by going into the soil. In marine ecosystems, carbon is stored in the ocean as dissolved CO2 in the water and also in carbon compounds in marine organisms. The input to the ocean store is through absorption via gas exchange with the atmosphere. Carbon can leave the atmosphere mixing with water vapour. When precipitation happens this falls as carbonic acid, commonly known as acid rain.

Chemical weathering is the wearing away of rock by chemical reactions, causing material to dissolve through solution, hydrolysis and oxidation. Carbon dioxide in the atmosphere reacts with the moisture to form weak carbonic acid, which then falls as acidic rain. When acidic rain hits carbon-rich rocks (e.g. limestone), it can dissolve material and form calcium carbonate. These dissolved materials are transported down rivers and deposited into the sea, forming into sedimentary rock.

Volcanic out-gassing.

Carbon stores are important to maintain the balance of carbon within the carbon cycle which can influence the climate of the Earth.

Gigaton of carbon (GtC) is used as a measure.

Carbon is stored in the atmosphere as gasses such as carbon dioxide.

(1) as organic molecules in living and dead organisms found in the biosphere; (2) as the gas carbon dioxide in the atmosphere; (3) as organic matter in soils; (4) in the lithosphere as fossil fuels and sedimentary rock deposits such as limestone, dolomite and chalk; (5) in the oceans as dissolved atmospheric carbon dioxide and as calcium carbonate shells in marine organisms; and (6) as frozen ground in arctic regions containing plant material.

The lithosphere contains 99.9% of all of the Earth’s carbon.

Terrestrial plants.

(1) Fossil fuel deposit is depleting due to being exploited by humans for power and energy. (2) Soil organic matter is affected through deforestation, agriculture and land use. (3) Atmosphere is affected through the combustion of fossil fuels creating CO2 levels to rise. (4)Terrestrial plants are affected by deforestation and climate change.

Limestone forms from marine organisms that have carbon-based shells made from calcium carbonate.

The formation of crude oil begins with the settling of fine-grained sediments and biologically degraded materials. There needs to be at least 2% organic carbon. A series of anaerobic reactions happen that turns most organic carbon into a liquid, crude oil.

Biological carbon sequestration is the storage of carbon dioxide in soils, the ocean, and vegetation (such as grasslands or forests).

On land, carbon is sequestered by plants through photosynthesis and is then returned to the atmosphere through the respiration of consumers.

Terrestrial primary producers are land plants that are the first organisms in the food chain.

Consumers are organisms that eat the other organisms below them in the food chain. Primary consumers are the first organisms to eat plants. They return the carbon (that the primary producer sequestered) to the atmosphere through the process of respiration.

Decomposers consume dead organic matter and return the carbon to the atmosphere through respiration.

The whole process of carbon entering and moving around the ocean is referred to as the carbon pump. Phytoplankton sequester atmospheric carbon during photosynthesis in ocean waters. This carbon transforms into terrestrial carbon or biological carbon before returning to the atmosphere.

Phytoplankton sequester carbon dioxide from the atmosphere through the process of photosynthesis.

Phytoplankton sequester carbon dioxide from the atmosphere through the process of photosynthesis. As this happens, they build their shells from calcium carbonate. The carbon in the atmosphere is transformed into biological carbon.

The carbonate shell sink exists at the bottom of the ocean. It is created by dead aquatic organisms when they sink and accumulate as sediment. This then turns into sedimentary rock.

Thermohaline circulation is the global movement of water.

The flow of water is determined by thermohaline circulation and therefore affects oceanic sequestering.

Because warm Caribbean water passes the UK as it moves northward towards the poles, the UK is relatively warmer compared to other locations at the same latitude.

Mangroves found at tropical coastlines sequester 1.5 metric tonnes of carbon per hectare every year.

Soils found in mangrove forests consist of layers of litter, humus and peat, which contain over 10% carbon.

Tundra regions of the world have permanently low temperatures, so there is ancient carbon permanently frozen in the soil because there is no microbe activity to decay the material. Tundra is therefore a massive carbon store, holding carbon for hundreds of thousands of years.

Solar radiation enters the earth's atmosphere and passes through the greenhouse gases layer. The Earth’s surface absorbs the solar radiation, and some is reflected. Some reflected radiation passes back into space. The greenhouse gas layer acts like a blanket and warms the earth to be a high enough temperature to support life on Earth.

Human activity, such as burning fossil fuels through vehicles, has caused an increase in greenhouse gases in the atmosphere. These gases create a thicker blanket causing more of the reflected radiation to be retained by the Earth's atmosphere than usual, leading to a rise in temperature.

The concentration of atmospheric carbon strongly influences the natural greenhouse effect, which in turn determines the distribution of temperature and precipitation.

Gases such as methane (CH4) and carbon dioxide (CO2) are naturally emitted through respiration and out-gassing.

The greenhouse effect impacts temperature/heat distribution and precipitation on the Earth.

This movement of air is called atmospheric circulation.

Ocean circulation redistributes thermal energy across the surface of the Earth.

The heating of the Earth's surface leads to warm air rising, cooling and condensing to create clouds. The intense radiation on the equator leads to warm air rising causing high levels of rainfall all year. At 30 degrees north and 30 degrees south the air cools and sinks again resulting in high surface pressure where rainfall is rare. At 60 degrees north and 60 degrees south different air masses meet, resulting in frontal rainfall. The poles are cold resulting in air sinking, causing little rainfall.

The albedo effect is the reflectivity of the surface of the Earth and how much it absorbs the sun's radiation.

Photosynthesis help balance the composition of the atmosphere.

Global atmospheric carbon is higher in the winter than in the summer because there is less sunlight for plants to use for photosynthesis. 

Slash-and-burn

Phytoplankton!

Blue carbon

False! The greenhouse effect is a natural process. However, human activity has amplified it. 

Since the beginning of the Industrial Revolution in the mid-eighteenth century, fossil fuels have been burnt to provide power and energy.

The carbon reservoirs can be both a source (adding carbon to the atmosphere) and sink (removes carbon from the atmosphere). When the sources and sinks are balanced it is said the carbon cycle is in equilibrium.

Human activities such as burning fossil fuels have increased the concentration of atmospheric carbon dioxide CO2 without any increase in carbon sinks.This has been linked to the rise in global temperatures due to the carbon dioxide CO2 enhancing the greenhouse effect.

The carbon cycle is usually balanced by the sinks and sources of carbon. However as the fossil fuels are being burnt, there is more carbon released into the atmosphere than sequestered and puts the carbon cycle out of balance.

Due to the rising global temperature, the annual average land temperatures are projected to increase by more than the global average. It is predicted that Northern and Eastern Europe to have warmer winters whilst Southern Europe to have warmer summers.