Dive into the slow carbon cycle!
Fluxes include: respiration and photosynthesis (between the biosphere, hydrosphere and atmosphere), sedimentation and metamorphosis (between the biosphere and lithosphere), weathering, erosion, volcanism and combustion of fossil fuels (between the lithosphere and the atmosphere), dissolution and degassing (between the hydrosphere and the atmosphere), and precipitation, melting, evaporation and sublimation (between the cryosphere, the hydrosphere and atmosphere).
When plants photosynthesize, they âinhaleâ CO2 and combine it with the sun to produce sugars and oxygen. 6CO2 + 6H2O -> C6H12O6 + 6O2. (Plankton in the ocean creates calcium carbonate (CaCO3) shells). Photosynthesizers literally build plant matter and tiny shells from atmospheric CO2, storing it in their biomass. Is it cool? Plants, trees and plankton are therefore carbon sinks, i.e. they remove atmospheric CO2 and store it in the form of a woody / leafy / carbonate shell. When plants, trees and plankton die, they degrade and decompose, succumbing to the reverse process and releasing CO2 into the atmosphere.
Think of a carbon sink as a literal sink: the only way to empty the atmospheric tub of CO2 is to open a drain, or to store the carbon somewhere other than the atmosphere. Biogeochemical cycles are the flows to other reservoirs.
If the biomass is buried (undergoes sedimentation) and is subjected to intense heat and pressure (undergoes metamorphosis) instead of breathing in the atmosphere, it can become: a limestone rock which precipitates sediment produced by dead plankton , petroleum or natural gas (plankton metamorphoses under different temperature and pressure regimes and in different geological formations), or coal (buried trees, which have generally undergone anoxic decomposition in ancient swamps). Technically, limestone precipitates biogenic material in seawater, and quick note, marble is metamorphosed limestone.
Metamorphosis occurs deep in the lithosphere, in particular the esthenosphere: the border between the crust and the mantle. The lithosphere is therefore also a carbon sink, because sedimentation, metamorphosis, weathering and erosion are the flows that take place for hundreds of millions of years, but allow the geosphere to store the greater amount of carbon. It is estimated that 65.5 trillion metric tons (one billion in scientific notation is 1 x 10 ^ 9) are stored in the crust and the esthenosphere as sediment and sedimentary and metamorphic rocks (https: //earthobservatory.nasa. gov / features / CarbonCycle).
Weathering and erosion (the mechanical and chemical decomposition of rocks), transports carbon from the atmosphere to the lithosphere via a brief stop in the hydrosphere! Rainwater dissolves CO2, forming weak carbonic acid that erodes the lithosphere over hundreds of millions of years. Geoscientists call this âatmospheric cleaningâ because the more CO2 there is in the atmosphere, the more acidic the rainwater is. And remember, more CO2 -> higher temperatures -> a more active hydrologic cycle -> more cleaning of atmospheric carbon. This is an example of a negative feedback loop, which means that the increase in CO2 leads to an increase in inclement weather, which lessens the effect of warming caused by the initial increase in CO2. Chemical weathering is one of the greatest long-term corrective mechanisms (again, HUNDREDS of MILLION years, an astronomically long time) when the Earth’s atmosphere is left with excess CO2. But unfortunately for humans, it doesn’t work on a timescale that could be beneficial to us and our survival as a species for the next century. In addition, mountain-forming events, such as the collision of the Indian subcontinent and the Eurasian plate causing the Himalayan uplift, are needed to stimulate weathering by providing cool rock surfaces. Plate tectonics is also, you guessed it !, an extraordinarily slow geological process.
Dissolution and degassing are intuitive. Gases can either dissolve in solution (such as water) or be released from a material in which they have been frozen, dissolved, trapped or absorbed. We know the hydrologic cycle fairly well, so we won’t waste any more time here.
The slow carbon cycle (metamorphosis, weathering, erosion, sedimentation) acts as a climate thermostat, keeping the atmospheric quantity of CO2 relatively stable, within a certain range of values. Milankovich’s astronomical cycles cause the growth and decay of polar ice caps and continental ice caps.
We bring it all together. . .
Many thanks to Dr Tom Brandes and Trinity Bob for mentioning Eunice Foote’s work in the 1850s on discovering the heat-trapping properties of carbon dioxide!