Carbon Cycling

The lecture aims to:

Discuss the history of atmospheric carbon dioxide (CO2) on Earth
Explore sources and sinks of CO2
Analyse rising atmospheric CO2 concentrations
Describe the carbon cycle with an emphasis on biological turnover
Examine key systems for carbon sequestration, such as tropical rainforests, the Arctic, and marine systems
Address human activities related to CO2 emissions

From an ancient star carbon atoms were part of the earth’s early formation.
Volcanoes first introduced carbon into the earth’s atmosphere as CO₂
CO₂ reacted chemically with rock to create limestone which lay at the bottom of the sea for millions of years.
This was then released back into the atmosphere as CO₂but ultimately became rock again
3.5 billion years ago, the cycle of carbon accelerated with new biological contributors (E.g. plants).
Photosynthetic microorganisms started converting CO2 into organic compounds, with respiration processes returning CO2 to the atmosphere, a cycle that continues currently.

Charles Keeling began monitoring atmospheric CO2 in 1958, providing crucial data on carbon trends.
Data shows a rise in CO2 concentration
Infra red gas analysis
Seasonal variations occur, with lower CO2 concentrations in summer compared to winter.
- lower photosynthesis
- Mammals are more active = fossil fuels

CO2 levels vary due to several factors:

Geological Inputs: Volcanic activity and mid-ocean ridges contribute to CO2 emissions.
Biological Inputs: Respiration processes naturally release CO2.
Human Inputs: Activities like deforestation and fossil fuel combustion significantly raise CO2 levels.
- Disturbing of land to create agriculture
- Burning of fossil fuels

Geological Removal: CO2 interacts chemically with weathered rocks.
- may release or absorb CO2
Biological Removal: Photosynthesis actively removes CO2 and is essential for short-term carbon cycling.

Green Carbon: Stored in terrestrial vegetation and soil.
- deforesting removes this carbon
Blue Carbon: Found in marine habitats and sediment.
Brown Carbon: Refers to greenhouse gases emitted.
Black Carbon: Emissions from incomplete combustion, such as soot.

Isotope analysis indicates significant alterations in carbon cycling correlated with industrialization.
Atmospheric CO2 rise aligns with increased fossil fuel usage during the industrial period.

The atmospheric carbon holds roughly 750 billion tonnes.
Various exchanges occur within terrestrial and marine systems, illustrating the dynamic interactions and transfers of carbon.

Volcanism and oxidation of ancient organic matter introduce CO2 into the atmosphere.
Weathering processes effectively remove CO2, with a minimal amount transforming into both coal and oil.

Photosynthesis is a critical process alongside respiration, promoting carbon cycling.
Decomposition: The breakdown of organic material is fundamental for nutrient recycling.

Food webs elucidate the flow of carbon through ecosystems, illustrating interactions from primary producers through secondary consumers and decomposers.

Soil nurtures plant roots and serves as a major carbon storage layer
Arctic soils alone containing a third of the planet's soil carbon.
- tundra = deep rooted planets
- Atmosphere is cold and dry = less decomposition
Tropical rains forests have shallow soil
- Deforestation causes draught due to less water vapour being released into atmosphere

Marine autotrophs capture more than 50% of the global CO2, playing a vital role in managing atmospheric carbon levels.
- Phytoplankton and Macrophytes

With the global human population nearing 8 billion, the implications for carbon cycling and emissions become more complex and urgent.

The lecture outlined: