The calcium cycle is a biogeochemical cycle relating to the transport of calcium through the biosphere, lithosphere, and hydrosphere. The cycling of calcium is an important factor in geology, agriculture, and even nutrition. [1]
Structure
editCreation of bioavailable calcium
editCalcium is found almost entirely on Earth in inorganic form, stored in rocks and minerals usually as calcium carbonate (CaCO3). Limestone is an example of rock formed almost entirely from calcium carbonate. In order to become available to organic processes, these rocks must be broken down via either mechanical weathering or the action of soil microbes. These actions convert the calcium in calcium carbonate and other rocks into its ion form, Ca2+
Use of bioavailable calcium
editThese available Ca2+ ions are taken up by by plants and microorganisms and become part of their cation exchange complex. Plants use calcium to keep cell walls rigid, promote cell division at the meristems, and in photosynthesis. Animals use calcium as a signalling molecule and to maintain skeletal structure.[2] This calcium returns to the inorganic portion of the cycle when organism remains decompose and release the ions back into the environment.
Return to inorganic calcium
editAs free ions, calcium can also react with dissolved inorganic carbon according to the reaction
- Ca2+
+ 2HCO−
3 → CaCO
3 + CO
2 + H
2O
This reaction occurs naturally in the oceans but is also catalyzed by the actions of plankton such as coccolithophores. When it forms, it can take the form of either calcite or aragonite. Both of these forms sink in the ocean and thus result in a net transport of calcium to the deep ocean, where it can form sediments and be buried for many years, until it returns to the surface via uplift and is weathered again. [3]
Importance in global climate
editThe process by which calcium is returned to inorganic form is an important process in global climate. As the calcium reacts chemically with bicarbonate in the ocean, more carbon dioxide is removed from the atmosphere, so the calcium cycle acts as a sink for global carbon emissions. This negative feedback loop is a key component in the mitigation of the greenhouse effect. One theoretical solution to ocean acidification and global climate change is to dump 300 billion cubic feet of limestone into the ocean to raise the pH, a real-world application of the calcium cycle. [4]