Marine organic phosphorus cycling: Novel insights from nuclear magnetic resonance

In vast regions of the ocean, a significant fraction of the vital nutrient phosphorus (P) in surface waters is associated with dissolved organic matte r (DOM). Oceanic biological productivity in these regions is potentially de pendent on the regeneration of bioavailable forms of P from DOM. Using tang ential-how ultrafiltration, high molecular weight (HMW) DOM samples were co llected for chemical analysis and P-31 Nuclear Magnetic Resonance (NMR) stu dies. In a profile of HMW DOP from the Pacific, depth related changes in di ssolved organic P (DOP) concentration and C/N/P ratios indicate that DOP is preferentially regenerated from HMW DOM relative to dissolved organic car bon and dissolved organic nitrogen. NMR studies of these samples show that P esters (75 percent) and phosphonates (25 percent) were the major compound classes present in HMW DOP. HMW DOP appears to be highly enriched in phosp honates relative to marine organisms, where phosphonates comprise a very sm all fraction of total P. The origin of phosphonates in the marine environme nt is largely unknown, and the biogeochemical dynamics by which phosphonate s become a major fraction of HMW DOP are not well understood. To explore po ssible sources of phosphonates in the marine environment, HMW DOM and parti culate organic matter (POM) from cultures of four marine primary producers, as well as particulates from heterotrophic bacterial cultures, were examin ed by P-31 NMR. P esters were observed in all cultures, and phosphonates we re detected in only two of the heterotrophic bacterial cultures. Several pr ocesses may be acting to produce the observed abundance of phosphonate-P in marine HMW DOP, including (1) selective preservation of phosphonates, and (2) production by an unrecognized source of phosphonates.