Ocean
Nutrients

A few elements such as nitrogen, phosphorus, iron, and potassium essential for life, are major components of biological material, and are commonly known as " nutrients ". Nitrate and phosphate have ocean residence times of 10,000 and 69,000 years, respectively, while potassium is a much more abundant ion in the ocean with a residence time of 12 million years. The biological cycling of these elements means that this represents a continuous removal process from the ocean's water column as degrading organic material sinks to the ocean floor as sediment.

Phosphate from intensive agriculture and untreated sewage is transported via runoff to rivers and coastal zones to the ocean where it is metabolized. Eventually, it sinks to the ocean floor and is no longer available to humans as a commercial resource. Production of rock phosphate, an essential ingredient in inorganic fertilizer, is a slow geological process that occurs in some of the world's ocean sediments, rendering mineable sedimentary apatite (phosphate) a non-renewable resource (see peak phosphorus). This continual net deposition loss of non-renewable phosphate from human activities, may become a resource issue for fertilizer production and food security in future.
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