Fig. 1. Phosphorus cycle in the ocean. Phosphorus is required by all living organisms to make DNA, RNA, ATP (energy molecules), and other essential organic compounds. The most abundant phosphorus exists in the form of phosphate (PO43-) ions. In the ocean, phytoplankton utilize phosphate for growth under high phosphate conditions. After assimilation, a fraction of the phosphorus is released back to the ocean pool as dissolved organic phosphorus, which is in turn converted back to phosphate by bacteria. However, under low phosphate conditions, phytoplankton and other marine organisms will utilize dissolved organic phosphorus and/or scavenge for phosphate by releasing phosphate from organic molecules using alkaline phosphatase.
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