Oceans nutrient deficiences

Oceans, despite their much larger surface area, contribute much less than half of the global NPP. The reason is related to highly nutrient deficiency in surface waters, which limits the photosynthesis process. Oceanic production is mainly concentrated... 

Enhanced nutrient loading from land also appears to be increasing the areal extent, duration, and intensity of hypoxia and anoxia in the coastal zone and marginal seas. While the perennial open-ocean systems occupy a fer larger volume of seawater than the seasonal coastal systems, O2 deficiencies are more intense in the latter, often leading to anoxia. Thus, considerable attention is currently fiacused on reducing nutrient loading to nearshore waters. 

In temperate lakes phytoplanktonic blooms occur in response to the seasonal availability of nutrients, which is controlled by stratification of the water column (see Section 3.2.2b). The situation is, therefore, similar to seasonal thermocline development and decline in temperate oceans. During summer stratification nutrients in the epilimnion become depleted. During the spring and autumn overturns, nutrient-rich (and oxygen-deficient) waters of the hypolimnion mix with the epilimnion and fuel phytoplanktonic blooms, primarily in the spring. 

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