English: Anthropogenic activities and their effects on the marine N cycling. Bioavailable N (Nb) is introduced into the marine ecosystems by runoff or atmospheric deposition, causing eutrophication, the formation of dead zones and the expansion of the ocean minimum zones (OMZs). The release of N oxides (N2O, NO) from anthropogenic activities and oxygen-depleted zones causes stratospheric ozone depletion leading to higher UVB exposition, which produces the damage of marine life, acid rain and ocean warming. Ocean warming causes water stratification, deoxygenation, and the formation of dead zones. Dead zones and OMZs are hotspots for anammox and denitrification, causing N loss (N2 and N2O). Elevated atmospheric CO2 acidifies seawater, decreasing pH-dependent N-cycling processes such as nitrification, and enhancing N2 fixation.