ONE-DIMENSIONAL MODELING OF NITROGEN AND SULFUR CYCLES IN THE APHOTICZONES OF THE BLACK AND ARABIAN SEAS

A coupled one-dimensional model of the nitrogen and sulfur cycles in s uboxic and anoxic conditions is developed and applied to the Black Sea redox zone and the oxygen-deficient layer of the Arabian Sea. The ver tical distributions of nitrogen compounds (total organic nitrogen, amm onium, nitrate, nitrite) and inorganic reduced sulfur compounds (hydro gen sulfide, elemental sulfur, thiosulfate, sulfate) as well as dissol ved oxygen agree reasonably well with the observations. The model take s into account the processes of turbulent diffusion, sedimentation, an d biogeochemical transformation of compounds. Rates of biochemical pro cesses mediated by bacteria are described by first-order equations usi ng semiempirical functions of O-2 concentration. The free nitrogen pro duction in the model due to denitrification is estimated to be 34 Tg N yr(-1) in the Arabian Sea and 1 Tg N yr(-1) in the Black Sea; H2S oxi dation and sulfate reduction in the Black Sea water column are in a ba lance of 1.6 mol m(-2) yr(-1).