The short-term carbon cycle describes the swift movement of carbon atoms among the atmosphere, oceans, and all living organisms. This dynamic exchange occurs over relatively brief periods, from days to a few thousand years, unlike the millions of years in the long-term carbon cycle. It is a continuous process where carbon constantly shifts forms and locations.
Carbon’s Short-Term Stores
Carbon is held in several distinct reservoirs within the short-term carbon cycle. The atmosphere stores carbon primarily as carbon dioxide (CO2), a gaseous form that helps regulate Earth’s temperature. Oceans represent the largest active carbon pool near the Earth’s surface, holding about 95% of the total active carbon for durations less than 10,000 years, mainly as dissolved inorganic carbon like bicarbonate and carbonate ions. On land, carbon is stored within the terrestrial biosphere, including all living plants and animals as organic compounds. When these organisms die, their organic matter contributes to carbon stored in soils, known as soil organic matter.
How Carbon Moves
Carbon moves through the short-term cycle via several interconnected processes.
Photosynthesis is a primary mechanism where plants, algae, and phytoplankton absorb atmospheric carbon dioxide, water, and sunlight to create organic compounds. This removes carbon from the atmosphere and incorporates it into living biomass.
Respiration releases carbon dioxide back into the atmosphere. Most living organisms, including plants, animals, and microbes, respire, breaking down organic compounds to release energy and carbon dioxide. This means carbon cycles from plants to animals when consumed, and then back to the atmosphere through breathing.
Decomposition occurs as bacteria and fungi break down dead organic matter. Decomposers respire, releasing carbon dioxide and sometimes methane back into the atmosphere and soil. While some carbon becomes stable soil organic matter, a substantial portion returns to the atmosphere.
Oceans engage in a constant two-way exchange of carbon dioxide with the atmosphere, primarily through surface waters. Carbon dioxide dissolves into the ocean, reacting with water to form carbonic acid, which then dissociates into bicarbonate and carbonate ions. CO2 solubility in water is influenced by temperature, with colder water generally absorbing more.
Wildfires rapidly release carbon by burning biomass, emitting carbon dioxide and other greenhouse gases into the atmosphere. While fires are natural, the landscape’s ability to reabsorb this carbon can be reduced if fires occur too frequently or intensely.
Why the Short-Term Carbon Cycle Matters
The short-term carbon cycle supports life on Earth. Carbon atoms form the basic building blocks of all organic molecules, including proteins, lipids, and DNA. Through photosynthesis, carbon becomes available to plants, forming the base of most food chains and providing energy for nearly all life forms.
This cycle also regulates Earth’s climate. Atmospheric carbon dioxide concentration directly influences global temperatures by trapping heat. A balanced short-term carbon cycle helps maintain atmospheric CO2 levels within a range that supports a stable climate. Disruptions can alter atmospheric carbon, influencing ecosystems and the planet’s environmental balance.