Ocean productivity: Nutrients ride the waves

Over vast areas of oceans, primary productivity is limited by the paucity of new nutrients. Major sources of these nutrients are coastal upwelling and wind-driven mixing, both bringing nutrient-rich deep waters to the ocean surface. But these mechanisms alone are insufficient to account for the observed productivity. Now, the combination of data from satellite altimeters and ocean colour scanners has revealed another way to bring nutrients to the surface. Rossby waves, which travel from east to west around the oceans, displace water to the north and south. Uz et al. show that the passage of these waves are associated with increased productivity, as shown by the surface water chlorophyll concentration. Similar processes have been observed at a regional scale, within large eddies (about 100 km), but this sort of 'nutrient pumping' is now shown to be important for ocean productivity on global scales as well.

Pumping of nutrients to ocean surface waters by the action of propagating planetary waves
B. METE UZ, JAMES A. YODER, VLADIMIR OSYCHNY
Nature 409, 597-600 (1 February 2001)
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Oceanography: The Rossby rototiller
DAVID A. SIEGEL
Planetary waves, also known as Rossby waves, propagate throughout the world's oceans on very large scales. They influence the ocean--climate system and also, it seems, the delivery of nutrients to the ocean surface.
Nature 409, 576-577 (1 February 2001)
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Sea Food
Microscopic ocean-borne plants produce about half of the world's oxygen. But in addition to CO₂ and sunlight they require nutrients, and the only source of fresh nutrients are deeper waters. But what powers the mixing necessary to bring new nutrients to the surface? Part of the answer, claim Uz et al. in this issue, are planetary waves - slow moving west-bound oscillations with thousand-kilometre wavelengths. (1 February 2001)

earth: Giant green waves seen from space
Waves thousands of kilometres across bring deep-ocean nutrients to surface plankton. (1 February 2001)

1 February 2001 table of contents