Carbon is exchanged between the hydrosphere (oceans, lakes, rivers, etc.) and the biosphere (living organisms) primarily through photosynthesis, respiration, and decomposition, playing a vital role in sustaining life.
Here's a breakdown of the key processes:
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Photosynthesis: Aquatic plants, algae, and phytoplankton in the hydrosphere absorb dissolved carbon dioxide (CO2) from the water during photosynthesis. This process uses sunlight to convert CO2 and water into glucose (sugar) and oxygen. This incorporation of inorganic carbon into organic compounds forms the base of many aquatic food webs.
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Respiration: All living organisms in both the hydrosphere and biosphere, including plants, animals, and microorganisms, respire. Respiration is the process where organisms break down glucose to release energy, producing carbon dioxide as a byproduct. Aquatic organisms release CO2 back into the water, and terrestrial organisms release it into the atmosphere; the CO2 in the atmosphere can then dissolve into the hydrosphere.
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Decomposition: When aquatic organisms die, their bodies decompose. Decomposition is carried out by bacteria and fungi, which break down the organic matter, releasing carbon compounds (including CO2) back into the water. Some of this organic carbon also gets buried in sediments and can eventually form fossil fuels.
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Diffusion: While not a biological process, diffusion is a key mechanism for carbon exchange. CO2 readily dissolves in water. There is a constant exchange of CO2 between the atmosphere and the hydrosphere, driven by differences in concentration. The ocean acts as a large carbon sink, absorbing significant amounts of atmospheric CO2. However, the rate of absorption is affected by factors such as temperature and salinity.
In summary, the exchange of carbon between the hydrosphere and biosphere involves the uptake of dissolved carbon dioxide by photosynthetic organisms, its incorporation into organic matter, and its subsequent release back into the hydrosphere through respiration and decomposition. This continuous cycle is essential for regulating the Earth's climate and supporting life in both aquatic and terrestrial environments.
