Intense biological phosphate uptake onto particles in subeuphotic continental margin waters

Abstract

Elucidating the processes that affect particulate phosphorus (P) export from the euphotic zone and burial in sediments is important for models of global phosphorus, nitrogen, and carbon cycling. We investigated dissolved inorganic Pi incorporation into particles (>0.2 µm) in the subeuphotic zone and benthic boundary layer of high‐productivity Mauritanian and Namibian shelf waters, using 33PO43− tracer experiments combined with a sequential chemical extraction analysis. Pi uptake (5.4 to 19.9 nmol P L−1 d−1) by particulate matter was biologically mediated (~50% into the organic fraction) and similar to estimated rates of heterotrophic growth. Thus, a substantial fraction of Pi must be recycled through a particle‐associated microbial pool. Rapid adsorption of 33P in the anoxic waters of Namibia indicated the additional existence of a large pool of surface exchangeable P. Particle‐associated Pi recycling and adsorption may influence the export flux and ultimate fate of particle bound P in continental shelf waters.

Global Nitrogen Cycle: Critical Enzymes, Organisms, and Processes for Nitrogen Budgets and Dynamics

“…Below, we refer solely to N*, which was first defined as [NO 3 – ] – 16 ­[PO 4 3– ] + 2.9 μmol/kg, where the terms in the brackets are the nitrate and phosphate concentrations in the seawater sample, respectively, and the intercept of 2.9 μmol/kg yields a global mean N* of zero. ,, Key assumptions are that (1) phytoplankton uptake and organic matter remineralization consume and release N and P with the Redfield ratio of 16 and (2) N 2 fixation and denitrification (plus anammox and similar metabolisms) are the only processes that cause the nitrate-to-phosphate concentration of ocean water to substantially deviate from the Redfield ratio. These assumptions assume the negligibility of a range of processes that may affect ocean N:P in a non-Redfield manner, such as organic P degradation by microbial phosphatases, phosphonate degradation by C–P lyase enzymes, phosphate adsorption on particles, , and non-Redfieldian nutrient uptake by phytoplankton (see below). With these caveats, higher N*, such as that observed in the thermoclines of subtropical gyres (especially of the North Atlantic, Figure ), indicates that nitrate that has been added by N 2 fixation and subsequent remineralization of the resulting organic N to nitrate.…”

Carbon recycling efficiency and phosphate turnover by marine nitrifying archaea

“…1). This flux contributes to the P packaging onto particles known to be mediated by heterotrophic bacteria, having important consequences for the reactivity of organic P in the bathypelagic ocean and eventual burial in marine sediments (36). The proportional release of DOC by N. maritimus NAOA6 (5 ± 2%; tables S2 and S3) was similar to that reported for microbial photoautotrophs [i.e., cyanobacteria; (37)] and suggests that thaumarchaea release 20 to 90 Tg C as DOC into the deep ocean each year (Table 3).…”

“…1). This flux contributes to the P packaging onto particles known to be mediated by heterotrophic bacteria, having important consequences for the reactivity of organic P in the bathypelagic ocean and eventual burial in marine sediments (36).…”