Woods Hole Oceanographic Institution

New insights on the chemical forms and cycling of phosphorous in oligotrophic environments

Wednesday, May 20, 2015
Pacific Forum—11:00 a.m.

Phosphorus is an essential element for life, and in the ocean it exists predominantly in the oxidation state of +5. It is in this state that phosphorus forms phosphoester bonds in essential biochemicals in plankton such as phospholipids, nucleic acids, and nucleotides. In addition, polyphosphate has recently been identified as an additional important biochemical pool of phosphorus. In a survey of the western North Atlantic Ocean, we found that polyphosphate is relatively more abundant in oligotrophic waters than in nutrient-rich temperate waters, contradicting the canonical oceanographic view of polyphosphate as a luxury phosphorus storage molecule. An enigmatic pool of dissolved phosphonate molecules, with phosphorus in the +3 oxidation state, is also abundant in oligotrophic waters; however, cycling of phosphorus between oxidation states has remained poorly constrained. Using simple incubation and chromatography approaches, we measured the rate of the chemical reduction of phosphate to P +3 compounds in the western tropical North Atlantic Ocean. Colonial nitrogen-fixing cyanobacteria in surface waters played a critical role in phosphate reduction, but other classes of plankton, including potentially deep-water archaea, were also involved. These data are consistent with marine geochemical evidence and microbial genomic information, which together suggest the existence of a vast oceanic phosphorus redox cycle.

Next: June 1—Sherri W. Goodman