Phosphorus behaviors in Sedimentary Pore water: Evidence of Phosphorite Formation in the South Korea Plateau, East Sea

Abstract

In order to estimate the fluxes of nutrients in sedimentary pore water and the formation mechanism of phosphorite, we analyzed dissolved nutrients (ammonium, nitrite, nitrate, silicate and phosphate), dissolved trace metals (manganese, vanadium and phosphorus), solid phase organic matter and sediment characteristics (porosity, dry bulk density) in 4 box core samples along the slope of the South Korea Plateau, East Sea. Dissolved phosphate concentration in bottom water and pore water at phosphorite collected site was 2-3 times higher than the other sites. The flux of ammonium from sediment to bottom water was estimated to be 15.6-54.2 mmol/m2/yr; nitrite and nitrate, 22.7-73.2 mmol/m2/yr; phosphate, 9.5-25.9 mmol/m2/yr and silicate, 16.8-30.1 mmol/m2/yr. Especially, phosphate ion is enriched in the bottom water and near surface sediments at the site which is located beneath Oxygen Minimum Zone (OMZ). The vertical profiles of redox sensitive ions (nitrate, phosphate, dissolved manganese and vanadium) suggest that redox boundaries are located at 5-15 cm below the surface sediments. Based on the correlation between phosphorite-bound ions, phosphate reduction or re-oxydation at the redox boundary appears to facilitate the diagenetic processes of phosphorite formation in the topmost sedimentary layer.