Hydroxylamine (NH₂OH) in the Baltic Sea

Abstract. The vertical distribution of dissolved hydroxylamine (NH₂OH) was measured for the first time at 10 stations in the western, southern and central Baltic Sea during a cruise in February 2004. The distribution of dissolved NH₂OH was complex due to the interplay of in-situ production in the shallow western and southern Baltic Sea and the hydrographical setting in the central Baltic Sea caused by the major North Sea water inflow event in January 2003. We conclude that nitrification might be the major source of NH₂OH, whereas anaerobic ammonium oxidation (anammox) appeared to be negligible. We suggest that a "fresh" nitrifying system, in which the NH⁺₄-oxidation rates exceeded the NO⁻₂-oxidation rates, favoured the build-up of NH₂OH.