Porewater concentrations of ammonium, nitrite, nitrate, sulfate, hydrogen sulfide, dissolved iron and dissolved manganese at 5 sites along a water depth transect in the Gulf of Mexico (Louisiana continental shelf)

Porewater samples for NH4+, NO3- , and NO2- were analyzed on board with Quattro gas-segmented continuous flow analysers using the indophenolblue method (NH+4), and the sulphanyl-amide method (NOx). Porewater sulfide was determined spectrophotometrically using phenylenediamine and ferric chloride. Porewater samples for SO4 2- were analyzed by ion-chromatography. Dissolved Fe and Mn were analyzed by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES; Spectro Arcos). Porewater concentrations were around or below the detection limit (0.5 and 0.8 μmol L−1, respectively) and are therefore not presented.