Quantifying the impact of anthropogenic nitrogen deposition on oceanic nitrous oxide

Abstract

Anthropogenically induced increases in nitrogen deposition to the ocean can stimulate marine productivity and oceanic emission of nitrous oxide. We present the first global ocean model assessment of the impact on marine N 2 O of increases in nitrogen deposition from the pre-industrial era to the present. We find significant regional increases in marine N 2 O production downwind of continental outflow, in coastal and inland seas (15-30%), and nitrogen limited regions of the North Atlantic and North Pacific (5-20%). The largest changes occur in the northern Indian Ocean (up to 50%) resulting from a combination of high deposition fluxes and enhanced N 2 O production pathways in local hypoxic zones. Oceanic regions relatively unaffected by anthropogenic nitrogen deposition indicate much smaller changes (<2%). The estimated change in oceanic N 2 O source on a global scale is modest (0.08-0.34 Tg N yr -1, ∼3-4% of the total ocean source), and consistent with the estimated impact on global export production (∼4%). Copyright 2012 by the American Geophysical Union.