Continental shelf pump
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{{ocean fisheries topics}}
In [[ocean|oceanic]] [[biogeochemistry]], the '''continental shelf pump''' is proposed to operate in the shallow waters of the [[continental shelf|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<ref name=tsun99>Tsunogai, S., S. Watanabe and T. Sato (1999). Is there a "continental shelf pump" for the absorption of atmospheric CO<sub>2</sub>. ''Tellus, Ser. B'' '''51''', 701-712.</ref>.
==Overview==
Originally formulated by Tsunogai ''et al.'' (1999)<ref name=tsun99/>, the pump is believed to occur where the [[solubility pump|solubility]] and [[biological pump|biological]] pumps interact with a local [[hydrography]] that feeds dense water from the shelf floor into sub-surface (at least [[thermocline|subthermocline]]) waters in the neighbouring deep ocean. Tsunogai ''et al.'''s (1999)<ref name=tsun99/> 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 :
* the shallowness of the continental shelf restricts [[convection]] 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 pump]] and lead to an increased storage of dissolved inorganic carbon
* this extra carbon storage is augmented by the increased biological production characteristic of shelves<ref name=woll98>Wollast, R. (1998). Evaluation and comparison of the global carbon cycle in the coastal zone and in the open ocean, p. 213-252. In K. H. Brink and A. R. Robinson (eds.), ''The Global Coastal Ocean''. John Wiley & Sons.</ref>
* the dense, carbon-rich shelf waters sink to the shelf floor and enter the sub-surface layer of the open ocean via [[isopycnal]] mixing
==Significance==
Based on their measurements of the CO<sub>2</sub> flux over the East China Sea (35 g C m<sup>-2</sup> y<sup>-1</sup>), Tsunogai ''et al.'' (1999)<ref name=tsun99/> estimated that the continental shelf pump could be responsible for an air-to-sea flux of approximately 1 Gt C y<sup>-1</sup> over the world's shelf areas. Given that observational<ref name=tak02>Takahashi, T., S. C. Sutherland, C. Sweeney, A. Poisson, N. Metzl, B. Tilbrook, N. Bates, R. Wanninkhof, R. A. Feely, C. Sabine, J. Olafsson and Y. C. Nojiri (2002) [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VGC-452W7KK-2&_user=10&_coverDate=12%2F31%2F2002&_rdoc=2&_fmt=summary&_orig=browse&_srch=doc-info(%23toc%236035%232002%23999509990%231%23FLA%23display%23Volume)&_cdi=6035&_sort=d&_docanchor=&view=c&_ct=19&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=1eb682d5552c8d58911ddf6e2012da02 Global sea-air CO<sub>2</sub> flux based on climatological surface ocean ''p''CO<sub>2</sub>, and seasonal biological and temperature effects.] ''Deep-Sea Res. Pt. II'' '''49''', 1601-1622.</ref> and modelling<ref name=orr01>Orr, J. C., E. Maier-Reimer, U. Mikolajewicz, P. Monfray, J. L. Sarmiento, J. R. Toggweiler, N. K. Taylor, J. Palmer, N. Gruber, C. L. Sabine, C. Le Quéré, R. M. Key and J. Boutin (2001). Estimates of anthropogenic carbon uptake from four three-dimensional global ocean models. ''Global Biogeochem. Cycles'' '''15''', 43-60.</ref> of anthropogenic emissions of CO<sub>2</sub> estimates suggest that the ocean is currently responsible for the uptake of approximately 2 Gt C y<sup>-1</sup>, and that these estimates are poor for the shelf regions, the continental shelf pump may play an important role in the ocean's [[carbon cycle]].
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<ref name=yool01>Yool, A. and M. J. R. Fasham (2001). An examination of the "continental shelf pump" in an open ocean general circulation model. ''Global Biogeochem. Cycles'' '''15''', 831-844.</ref> that other processes may drive the pump under different climatic conditions. For instance, in polar regions, the formation of [[sea ice|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 CO<sub>2</sub> at temperate latitudes reported by Tsunogai ''et al.'' (1999)<ref name=tsun99/> was later confirmed in the Gulf of Biscay<ref name=frank01>Frankignoulle, M. and A. V. Borges (2001). European continental shelf as a significant sink for atmospheric carbon dioxide. ''Global Biogeochemical Cycles'' '''15''', 569-576.</ref>, the Middle Atlantic Bight<ref name=degran02>DeGrandpre, M. D., G. J. Olbu, C. M. Beatty, and T. R. Hammar (2002). Air-sea CO<sub>2</sub> fluxes on the US Middle Atlantic Bight. ''Deep-Sea Research Part II'' '''49''', 4355-4367.</ref> and the North Sea<ref name=thom04>Thomas, H., Y. Bozec, K. Elkalay, and H. J. W. De Baar (2004). Enhanced open ocean storage of CO<sub>2</sub> from shelf sea pumping. ''Science'' '''304''', 1005-1008.</ref>. On the other hand, in the sub-tropical South Atlantic Bight reported a source of CO<sub>2</sub> to the atmosphere<ref name=cai03>Cai, W.-J., Z. H. A. Wang, and Y. C. Wang. (2003). The role of marsh-dominated heterotrophic continental margins in transport of CO<sub>2</sub> between the atmosphere, the land-sea interface and the ocean. ''Geophysical Research Letters'' '''30''', 1849-doi:10.1029/2003GL017633.</ref>.
Recently, work<ref name=borges05a>Borges A. V. (2005). Do we have enough pieces of the jigsaw to integrate CO<sub>2</sub> fluxes in the Coastal Ocean? ''Estuaries'' '''28''', 3-27.</ref><ref name=borges05b>Borges A. V., B. Delille and M. Frankignoulle (2005). Budgeting sinks and sources of CO<sub>2</sub> in the coastal ocean: Diversity of ecosystems counts, ''Geophysical Research Letters'' '''32''', L14601, doi:10.1029/2005GL023053.</ref> has compiled and scaled available data on CO<sub>2</sub> fluxes in coastal environments, and shown that globally marginal seas act as a significant CO<sub>2</sub> sink (-1.6 mol C m<sup>-2</sup> y<sup>-1</sup>; -0.45 Gt C y<sup>-1</sup>) in agreement with previous estimates. However, the global sink of CO<sub>2</sub> in marginal seas could be almost fully compensated by the emission of CO<sub>2</sub> (+11.1 mol C m<sup>-2</sup> y<sup>-1</sup>; +0.40 Gt C y<sup>-1</sup>) from the ensemble of near-shore coastal ecosystems, mostly related to the emission of CO<sub>2</sub> from estuaries (0.34 Gt C y<sup>-1</sup>).
==References==
{{reflist}}
==See also==
* [[Biological pump]]
* [[Ocean acidification]]
* [[Solubility pump]]
[[Category:Aquatic ecology]]
[[Category:Biological oceanography]]
[[Category:Carbon]]
[[Category:Chemical oceanography]]
[[Category:Fisheries]]
[[Category:Geochemistry]]
[[Category:Oceanography]]