Composition and cycling of marine organic phosphorus

Using tangential-flow ultrafiltration and solid-state P-31 nuclear magnetic resonance (NMR) spectroscopy, the dominant compound classes of marine high-molecular weight (1-100-nm size fraction) dissolved organic phosphorus (DOP) have been characterized in 16 samples from the Pacific Ocean, the Atlantic Ocean, and the North Sea. NMR spectra of ultrafiltered dissolved organic matter (UDOM) from all sites and depths reveal that P esters (75%) and phosphonates (25%) are the major components of ultrafiltered DOP (UDOP). P esters and phosphonates are present in unchanging proportions throughout the ocean. The homogeneity of UDOP from different oceanic regions suggests that processes leading to this chemical composition are ubiquitous. Ultrafiltered particulate organic matter (UPOM; 0.1-60-mum size fraction) samples from the Pacific Ocean and the North Sea were also analyzed using P-31 NMR. In these samples, P esters are the only P compound class measured. Differences in the observed chemical compound classes of UDOM versus UPOM may result from (1) less-reactive phosphonates accumulating relative to P esters as particulate organic matter (POM) decomposes to DOM or (2) phosphonates originating from another source. C:N:P ratios of UDOM are significantly higher than Redfield ratios for POM. In general, C:P and N:P ratios of UDOM double between surface waters and the deep ocean. Increasing C:P and N:P ratios suggest that P is preferentially remineralized from UDOM relative to C and N throughout the water column.