Piecing together phosphonate cycling in the surface oligotrophic ocean

In phosphorus (P) limited oligotrophic regions of the ocean, a large fraction of P assimilated by microbes is recovered from the hydrolysis of organophosphorus compounds. Phosphonates are reduced organophosphorus compounds that constitute between 20-25% of total phosphorus in high molecular weight dissolved organic matter. They are therefore an important source of phosphorus in P limited areas. However, very little is known about phosphonate production and cycling or its relevance in the marine phosphorus cycle. On a recent cruise to the Eastern Mediterranean Sea, we used ³³P to measure phosphonate production rates. We coupled our phosphonate production rates with rate measurements of phosphonate degradation via the C-P lyase pathway using a recently introduced fluorescent assay. Degradation rates were further coupled with measurements of methane, a by-product of methylphosphonate degradation. We also took samples to study phosphonate distribution and used liquid chromatography coupled with two different mass spectrometry techniques (HPLC-ICPMS-ESIMS) to measure phosphonates in the different P pools. With this information we present a framework for understanding the phosphonate cycle.