Climate Science

Waters of Life

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Science  19 Sep 2008:
Vol. 321, Issue 5896, pp. 1606-1607
DOI: 10.1126/science.321.5896.1606c

River discharge transports nutrients such as nitrate to the sea, fueling the primary production that removes carbon dioxide from the atmosphere and thereby helps to regulate climate. Some of the atmospheric carbon dioxide fixed by this production is effectively diverted from the active carbon cycle and buried in sediments on the sea floor in a process referred to as the “biological pump.” It has been shown that river discharge causes significant carbon sequestration in the shelf areas near the mouths of rivers, yet it remains unclear whether its influence extends much further from the coast.

Subramaniam et al. report that the Amazon River plume stimulates a great deal of carbon fixation in the open ocean far off the coast, largely by stimulating diazotrophy (fixation of atmospheric nitrogen by bacteria) in surface waters. They estimate that the amount of organic carbon produced through this pathway is nearly three times as much as that resulting from the near-shore production that is supported by nitrate, and they speculate that this could be an important effect of rivers worldwide. Because river runoff is influenced by climate, this aspect of the biological pump could be affected by anthropogenic climate change as well. — HJS

Proc. Natl. Acad. Sci. U.S.A. 105, 10460 (2008).

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