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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.

We examine the relationships between ocean ventilation, primary production, water column anoxia, and benthic regeneration of phosphorus using a mass balance model of the coupled marine biogeochemical cycles of carbon (C) and phosphorus (P). The elemental cycles are coupled via the Redfield C/P ratio of marine phytoplankton and the C/P ratio of organic matter preserved in marine sediments. The model assumes that on geologic timescales, net primary production in the oceans is limited by the upwelling of dissolved phosphorus to the photic zone. The model incorporates the dependence on bottom water oxygenation of the regeneration of nutrient phosphorus from particulate matter deposited at the water‐sediment interface. Evidence from marine and lacustrine settings, modern and ancient, demonstrates that sedimentary burial of phosphorus associated with organic matter and ferric oxyhydroxides decreases when bottom water anoxia‐dysoxia expands. Steady state simulations show that a reduction in the rate of thermohaline circulation, or a decrease of the oxygen content of downwelling water masses, intensifies water column anoxia‐dysoxia and at the same time increases surface water productivity. The first effect reflects the declining supply of oxygen to the deeper parts of the ocean. The second effect is caused by the enhanced benthic regeneration of phosphorus from organic matter and ferric oxyhydroxides. Sedimentary burial of organic carbon and authigenic calcium phosphate mineral (francolite), on the other hand, is promoted by reduced ocean ventilation. According to the model, global‐scale anoxia‐dysoxia leads to a more efficient recycling of reactive phosphorus within the ocean system. Consequently, higher rates of primary production and organic carbon burial can be achieved, even when the continental supply of reactive phosphorus to the oceans remains unchanged.

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The in situ or authigenic formation of calcium phosphate minerals in marine sediments is a major sink for the vital nutrient phosphorus. However, because typical sediment chemistry is not kinetically conducive to the precipitation of these minerals, the mechanism behind their formation has remained a fundamental mystery. Here, we present evidence from high-sensitivity x-ray and electrodialysis techniques to describe a mechanism by which abundant diatom-derived polyphosphates play a critical role in the formation of calcium phosphate minerals in marine sediments. This mechanism can explain the puzzlingly dispersed distribution of calcium phosphate minerals observed in marine sediments worldwide.