Biological pump
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In oceanic biogeochemistry, the biological pump is the sum of a suite of biologically-mediated processes that transport carbon from the surface euphotic zone to the ocean's interior.
The carbon is transported primarily by sinking particulate material, for example dead organisms (including algal mats) or faecal pellets. However, some carbon reaches the deep ocean as dissolved organic carbon (DOC) by physical transport processes such as downwelling rather than sinking.
Carbon reaching the deep ocean by these means is either organic carbon or particulate inorganic carbon such as calcium carbonate. The former is a component of all organisms, the latter only of calcifying organisms, for example coccolithophorids or foraminiferans. In reference to the different use of these materials in organisms, the organic carbon portion of this transport is known as the soft tissues pump, while the inorganic carbon portion is known as the hard tissues pump.
In the case of organic material, remineralisation processes such as bacterial respiration, return the organic carbon to dissolved carbon dioxide. Calcium carbonate dissolves at a rate dependent upon local carbonate chemistry. As these processes are generally slower than synthesis processes, and because the particulate material is sinking, the biological pump transports material from the surface of the ocean to its depths. For an overview, see Raven & Falkowski (1999).
The biological pump has a physico-chemical counterpart known as the solubility pump. See also the continental shelf pump.
References
- Raven, J. A. and P. G. Falkowski (1999). Oceanic sinks for atmospheric CO2. Plant Cell Environ. 22, 741-755.