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Figure 2. Ocean color measured by satellite. In the tropical open ocean, productivity is comparatively low due to permanent thermal stratification of surface waters that limits the supply of nutrients from deeper waters. The resulting flux of biogenic material to the deep sea is also low. In contrast, in the more productive regions of the ocean, abundant phytoplankton sustain much larger sinking fluxes of biogenic material. These regions are most prominent at the eastern margins of the oceans and at the equator, where divergence of wind-driven surface currents brings nutrient-rich water from intermediate depths to the surface. Seasonally high productivity can also be found at higher latitudes due to the seasonal breakdown of upper water stratification in winter and to deep convective mixing.[back]
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