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Continental Shelf Pump
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OVERVIEW

Originally formulated by Tsunogai ''et al.'' (1999), the pump is believed to occur where the Solubility 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 :

  • 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

  • the dense, carbon-rich shelf waters sink to the shelf floor and enter the sub-surface layer of the open ocean via Isopycnal mixing


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 (Takahashi ''et al.'', 2002) and modelling (Orr ''et al.'', 2001) 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 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 (''e.g.'' Yool & Fasham, 2001) 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.


REFERENCES

  • 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.

  • 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). Global sea-air CO2 flux based on climatological surface ocean ''p''CO2, and seasonal biological and temperature effects. ''Deep-Sea Res. Pt. II'' 49, 1601-1622.

  • Tsunogai, S., S. Watanabe and T. Sato (1999). Is there a "continental shelf pump" for the absorption of atmospheric CO2. ''Tellus, Ser. B'' 51, 701-712.

  • 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.



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