Everything about Biological Pump totally explained
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.
Overview
The organic carbon that forms the biological pump 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 (CaCO
3). The former is a component of all organisms, the latter only of calcifying organisms, for example
coccolithophores,
foraminiferans or
pteropods. 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 (or
decomposition) 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.
As the biological pump plays an important role in the Earth's carbon cycle, significant effort is spent quantifying its strength. However, because they occur as a result of poorly-constrained ecological interactions usually at depth, the processes that form the biological pump are difficult to measure. A common method is to estimate primary production fuelled by
nitrate and
ammonium as these nutrients have different sources that are related to the remineralisation of sinking material. From these it's possible to derive the so-called
f-ratio, a proxy for the local strength of the biological pump. Applying the results of local studies to the global scale are complicated by the role the ocean's circulation plays in different ocean regions.
The biological pump has a physico-chemical counterpart known as the
solubility pump. For an overview of both pumps, see Raven & Falkowski (1999).
Anthropogenic changes
Land-use changes, the
combustion of
fossil fuels, and the production of
cement have led to a flux of CO
2 to the atmosphere. Presently, about one third (approximately 2 Gt C y
-1) of anthropogenic emissions of CO
2 are believed to be entering the ocean. However, the biological pump isn't believed to play a role in this flux. This is because the biological pump is primarily limited by the availability of light and nutrients, and not by carbon. This is in contrast to the situation on land, where elevated atmospheric concentrations of CO
2 may increase
primary production because land
plants are able to improve their water-use efficiency (= decrease
transpiration) when CO
2 is easier to obtain. However, there are still considerable uncertainties in the marine carbon cycle, and some research suggests that a link between elevated CO
2 and marine primary production exists.
However,
climate change may affect the biological pump in the future by warming and
stratifying the surface ocean. It is believed that this could decrease the supply of nutrients to the euphotic zone, reducing primary production there. Also, changes in the ecological success of calcifying organisms caused by
ocean acidification may affect the biological pump by altering the strength of the hard tissues pump. This may then have a "knock-on" effect on the soft tissues pump because calcium carbonate acts to ballast sinking organic material.
Further Information
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