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 (DO P) have been characterized in 16 samples from the Pacific Ocean, the Atlant ic Ocean, and the North Sea. NMR spectra of ultrafiltered dissolved organic matter (UDOM) from all sites and depths reveal that P esters (75%) and pho sphonates (25%) are the major components of ultrafiltered DOP (UDOP). P est ers and phosphonates are present in unchanging proportions throughout the o cean. The homogeneity of UDOP from different oceanic regions suggests that processes leading to this chemical composition are ubiquitous. Ultrafiltere d 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 t hese samples, P esters are the only P compound class measured. Differences in the observed chemical compound classes of UDOM versus UPOM may result fr om (1) less-reactive phosphonates accumulating relative to P eaters as part iculate organic matter (POM) decomposes to DOM or (2) phosphonates originat ing 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 bet ween surface waters and the deep ocean. Increasing C:P and N:P ratios sugge st that P is preferentially remineralized from UDOM relative to C and N thr oughout the water column.