Continental shelf pump
Encyclopedia
In ocean
ic biogeochemistry
, the continental shelf pump is proposed to operate in the shallow waters of the continental shelves
, acting as a mechanism to transport carbon
(as either dissolved or particulate material) from surface waters to the interior of the adjacent deep ocean.
and biological
pumps interact with a local hydrography
that feeds dense water from the shelf floor into sub-surface (at least subthermocline
) waters in the neighbouring deep ocean. Tsunogai et al.s (1999) original work focused on the East China Sea
, and the observation that, averaged over the year, its surface waters represented a sink for carbon dioxide
. This observation was combined with others of the distribution of dissolved carbonate
and alkalinity
and explained as follows :
.
One caveat to this calculation is that the original work was concerned with the hydrography of the East China Sea, where cooling plays the dominant role in the formation of dense shelf water, and that this mechanism may not apply in other regions. However, it has been suggested that other processes may drive the pump under different climatic conditions. For instance, in polar regions, the formation of sea-ice
results in the extrusion
of salt that may increase seawater density. Similarly, in tropical regions, evaporation
may increase local salinity and seawater density.
The strong sink of CO2 at temperate latitudes reported by Tsunogai et al. (1999) was later confirmed in the Gulf of Biscay, the Middle Atlantic Bight and the North Sea. On the other hand, in the sub-tropical South Atlantic Bight reported a source of CO2 to the atmosphere.
Recently, work has compiled and scaled available data on CO2 fluxes in coastal environments, and shown that globally marginal seas act as a significant CO2 sink (-1.6 mol C m−2 y−1; -0.45 Gt C y−1) in agreement with previous estimates. However, the global sink of CO2 in marginal seas could be almost fully compensated by the emission of CO2 (+11.1 mol C m−2 y−1; +0.40 Gt C y−1) from the ensemble of near-shore coastal ecosystems, mostly related to the emission of CO2 from estuaries (0.34 Gt C y−1).
An interesting application of this work has been examining the impact of sea level rise over the last de-glacial transition on the global carbon cycle. During the last glacial maximum sea level was some 120 m lower than today. As sea level rose the surface area of the shelf seas grew and in consequence the strength of the shelf sea pump should increase. Rippeth et al (2008) examine the consequences of this sea level rise on the strength of the shelf sea pump.
See also=
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
ic biogeochemistry
Biogeochemistry
Biogeochemistry is the scientific discipline that involves the study of the chemical, physical, geological, and biological processes and reactions that govern the composition of the natural environment...
, the continental shelf pump is proposed to operate in the shallow waters of the continental shelves
Continental shelf
The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...
, acting as a mechanism to transport carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
(as either dissolved or particulate material) from surface waters to the interior of the adjacent deep ocean.
Overview
Originally formulated by Tsunogai et al. (1999), the pump is believed to occur where the solubilitySolubility pump
In oceanic biogeochemistry, the solubility pump is a physico-chemical process that transports carbon from the ocean's surface to its interior.-Overview:...
and biological
Biological pump
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:...
pumps interact with a local hydrography
Hydrography
Hydrography is the measurement of the depths, the tides and currents of a body of water and establishment of the sea, river or lake bed topography and morphology. Normally and historically for the purpose of charting a body of water for the safe navigation of shipping...
that feeds dense water from the shelf floor into sub-surface (at least subthermocline
Thermocline
A thermocline is a thin but distinct layer in a large body of fluid , in which temperature changes more rapidly with depth than it does in the layers above or below...
) waters in the neighbouring deep ocean. Tsunogai et al.s (1999) original work focused on the East China Sea
East China Sea
The East China Sea is a marginal sea east of China. It is a part of the Pacific Ocean and covers an area of 1,249,000 km² or 750,000 square miles.-Geography:...
, and the observation that, averaged over the year, its surface waters represented a sink for carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
. This observation was combined with others of the distribution of dissolved carbonate
Carbonate
In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....
and alkalinity
Alkalinity
Alkalinity or AT measures the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate. The alkalinity is equal to the stoichiometric sum of the bases in solution...
and explained as follows :
- the shallowness of the continental shelf restricts convectionConvectionConvection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
of cooling water - as a consequence, cooling is greater for continental shelf waters than for neighbouring open ocean waters
- this leads to the production of relatively cool and dense water on the shelf
- the cooler waters promote the solubility pumpSolubility pumpIn oceanic biogeochemistry, the solubility pump is a physico-chemical process that transports carbon from the ocean's surface to its interior.-Overview:...
and lead to an increased storage of dissolved inorganic carbon - this extra carbon storage is augmented by the increased biological production characteristic of shelves
- the dense, carbon-rich shelf waters sink to the shelf floor and enter the sub-surface layer of the open ocean via isopycnalIsopycnalAn isopycnal is a surface of constant potential density of water. In the ocean, as the depth increases, so too does the density. Varying degrees of salinity and temperature act to modify the density of water, and the denser water always lies below the less dense water. Because of the action of...
mixing
Significance
Based on their measurements of the CO2 flux over the East China Sea (35 g C m−2 y−1), Tsunogai et al. (1999) estimated that the continental shelf pump could be responsible for an air-to-sea flux of approximately 1 Gt C y−1 over the world's shelf areas. Given that observational and modelling of anthropogenic emissions of CO2 estimates suggest that the ocean is currently responsible for the uptake of approximately 2 Gt C y−1, and that these estimates are poor for the shelf regions, the continental shelf pump may play an important role in the ocean's carbon cycleCarbon cycle
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth...
.
One caveat to this calculation is that the original work was concerned with the hydrography of the East China Sea, where cooling plays the dominant role in the formation of dense shelf water, and that this mechanism may not apply in other regions. However, it has been suggested that other processes may drive the pump under different climatic conditions. For instance, in polar regions, the formation of sea-ice
Sea ice
Sea ice is largely formed from seawater that freezes. Because the oceans consist of saltwater, this occurs below the freezing point of pure water, at about -1.8 °C ....
results in the extrusion
Extrusion
Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed or drawn through a die of the desired cross-section...
of salt that may increase seawater density. Similarly, in tropical regions, evaporation
Evaporation
Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....
may increase local salinity and seawater density.
The strong sink of CO2 at temperate latitudes reported by Tsunogai et al. (1999) was later confirmed in the Gulf of Biscay, the Middle Atlantic Bight and the North Sea. On the other hand, in the sub-tropical South Atlantic Bight reported a source of CO2 to the atmosphere.
Recently, work has compiled and scaled available data on CO2 fluxes in coastal environments, and shown that globally marginal seas act as a significant CO2 sink (-1.6 mol C m−2 y−1; -0.45 Gt C y−1) in agreement with previous estimates. However, the global sink of CO2 in marginal seas could be almost fully compensated by the emission of CO2 (+11.1 mol C m−2 y−1; +0.40 Gt C y−1) from the ensemble of near-shore coastal ecosystems, mostly related to the emission of CO2 from estuaries (0.34 Gt C y−1).
An interesting application of this work has been examining the impact of sea level rise over the last de-glacial transition on the global carbon cycle. During the last glacial maximum sea level was some 120 m lower than today. As sea level rose the surface area of the shelf seas grew and in consequence the strength of the shelf sea pump should increase. Rippeth et al (2008) examine the consequences of this sea level rise on the strength of the shelf sea pump.
See also=
- Biological pumpBiological pumpIn 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:...
- Ocean acidificationOcean acidificationOcean acidification is the name given to the ongoing decrease in the pH and increase in acidity of the Earth's oceans, caused by the uptake of anthropogenic carbon dioxide from the atmosphere....
- Solubility pumpSolubility pumpIn oceanic biogeochemistry, the solubility pump is a physico-chemical process that transports carbon from the ocean's surface to its interior.-Overview:...