Using tangential-flow ultrafiltration and solid-state 31 P 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-m size fraction) samples from the Pacific Ocean and the North Sea were also analyzed using 31 P 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.

Total particulate phosphorus (TPP), particulate inorganic P (PIP), and particulate organic P (POP) concentrations were measured in a year-long series of sediment trap samples collected throughout the oxic-anoxic water column (275 m, 455 m, 930 m, and 1,255 (PON). The lack of a relationship between POC and PIP fluxes and the large fraction of TPP associated with the PIP pool in both oxic and anoxic traps suggests that future analyses must separate PIP and POP when evaluating biological relationships between C, N, and P. The strong relationships between POC, PON, and POP also suggest that POP is not preferentially remineralized relative to PON and POC with increasing depth in this anoxic environment. P composition was also determined using solid state 31 P nuclear magnetic resonance (NMR), and it was found that phosphonates, chemically and thermally inert compounds, are a significant fraction of the TPP pool. Furthermore, these compounds were preferentially removed relative to more bioavailable P esters during a low flux event. Their selective removal suggests that these compounds may be an unrecognized source of bioavailable P under anoxic conditions.

Sediment geochemistry, as well as benthic exchange of nutrients, was investigated in Effingham Inlet, a fjord located on the west coast of Vancouver Island in Barkley Sound. The effect of bottom-water oxygenation on sediment carbon, nitrogen and phosphorus cycling was compared at sites overlain by oxic and anoxic bottom waters. The sites, separated by only 3 kilometers, were similar in terms of key diagenetic parameters including mass accumulation rate and bulk sediment organic carbon content, thus allowing a focus on diagenetic effects attributable to depositional oxygen availability. Benthic flux chamber incubations, sulfate reduction rate measurements, measurements of solid-phase and pore water chemical profiles were compared for the sites. These comparisons reveal that diagenetic processes in the site overlain by oxic waters act to retain more phosphorus in the sediment relative to the anoxic site. Differences in phosphorus benthic fluxes and burial between the two sites most likely result from differences in organic matter cycling under aerobic versus anaerobic conditions and are not strongly influenced by cycling of P associated with metal oxide phases.

[1] Rock weathering is the ultimate source of phosphorus (P) to the oceans, where P can be a limiting nutrient for biological production. In this paper, P weathering is examined in soil chronosequences formed in weathering profiles on the organic-rich Woodford Shale, New Albany Shale and Green River Shale. At all sites, organic P and inorganic P concentrations reveal that P weathering is far from complete, prior to erosion. Carbon (C)/P ratios decrease significantly from unweathered shale to the weathered shale at all sites, which is driven by loss of total organic C with weathering. Here we characterize organic phosphorus across a weathering profile from the Woodford Shale using solid-state CPMAS 31 P NMR spectroscopy techniques, revealing that P esters are the dominant forms of P during all stages of weathering. Certain P esters appear to be resistant to chemical weathering during the millions of years between deposition, uplift and erosion, possibly representing a significant long-term global sink for P. INDEX

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