The Geological Carbon Cycle
– Carbon regulates the climate, making it warm enough to survive.
– Stores can be terrestrial, oceanic or atmospheric.
– Flux refers to the movement of carbon between stores, creating cycles and feedback.
The geological carbon cycle is a natural cycle that moves carbon between spheres. This movement involves a number of chemical reactions that create new stores, which store carbon for significant time periods. There tends to be a natural balance between carbon production and absorption.
Geological stores
Carbon in limestone and shale
– Carbon in limestone starts off as oceanic sediments rich in calcium carbonate.
– Folded up by mountain building, this carbon is actively weathered, eroded and transported back to the oceans.
– Today, 80% of carbon containing rock is from calcifying organisms and plankton.
– These are precipitated on to the ocean floor, form layers, are cemented together and cemented together and lithified into limestone.
– The remaining 20% of rocks contain organic carbon from organisms that have been embedded in layers of mud and compressed under heat and pressure over millions of years.
Carbon fossil fuels
– Organisms, once dead, sank to the bottom of seas, were covered in silt and mud, and then started to decay anaerobically.
– When organic matter builds up faster than it can decay, layers of organic carbon become oil, coal or natural gas instead of shale.
The bio-geochemical carbon cycle
Key processes in the cycle are:
– Volcanic eruptions – emissions from volcanic eruptions send extra CO2 into the atmosphere, increasing temperatures and leading to higher levels of atmospheric moisture
– Chemical weathering – acid rain weathers rocks and creates biocarbonates that will eventually be deposited on the ocean floor
– Photosynthesis – removing CO2 from the atmosphere to promote plant growth
– Respiration – releasing CO2 into the atmosphere as animals consume plant growth and breathe
– Decomposition – breaking down organic matter and releasing CO2 into soils
– Combustion – burning of biomass and fossil fuels – releasing CO2 and other greenhouse gases into the atmosphere
