The worlds largest deserts

An extreme climate and permafrost mean that nutrient cycling is limited. The dominant pathway is that between the plant cover and litter the 

Geographically, the chief distinction is the dominance of diatoms in the colder waters of the Southern and Arctic Oceans, especially where upwelling occurs to bring nutrients from the ocean deep, and the abundance 

The phytoplankton are the basis of all marine food chains. Then-primary productivity is constrained mainly by nutrient availability and is thus not uniform throughout the oceans. Moreover, the importance of the grazing pathway of energy transfer varies spatially along with detrital energy transfer (see Section 3.7) estimates of the latter vary from c. less than 10 percent to c. 90 percent. 

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