Ocean Science

Down from the Shelves

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Science  26 Oct 2007:
Vol. 318, Issue 5850, pp. 535
DOI: 10.1126/science.318.5850.535c

Biological productivity in the ocean—which helps control climate on glacial time scales through its effect on the global carbon cycle—is regulated by the availability of nutrients such as phosphorus. The marine phosphorus cycle has in turn been thought to depend greatly on the variations in sea level caused by the growth and decay of continental ice sheets during the glacial cycle, which alternately expose and submerge continental shelves, but data relating to this hypothesis are scarce. Filippelli et al. combine measurements of the phosphorus concentration in deep sea sediments from the Atlantic and the Pacific with recent advances in the understanding of phosphorus geochemistry to show that the phosphorus inventory of those sediments increased during glacial periods and decreased during interglacials over the past 400,000 years. This finding supports the Shelf-Nutrient Hypothesis, which postulates that phosphorus should be transferred from shallow continental margins to the deep sea when continental shelves become exposed during glacial sea-level lowstands. These results should help to define the role that productivity plays in the regulation of atmospheric carbon dioxide over glacial/interglacial transitions, as well as the respective roles of external processes such as dust deposition, and internal processes such as upwelling, in the regulation and distribution of ocean nutrients. — HJS

Deep-Sea Res. II 10.1016/j.dsr2.2007.07.021 (2007).

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