Phosphate uptake in sub-euphotic continental margin waters

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 33PO4^3- 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.