The role of air-sea exchange in the marine nitrogen cycle

This contribution to the Spot-On volume considers the magnitude and composition of atmospheric nitrogen inputs to the oceans and then goes on to consider the impacts of these inputs. Effects in open ocean and coastal areas are probably different. Offshore atmospheric inputs may produce a small enhancement of overall ocean productivity and hence CO2 drawdown. In coastal waters atmospheric inputs contribute significantly to overall eutrophication pressure, but evidence that they trigger algal blooms is limited. Management of atmospheric inputs to coastal waters to mitigate eutrophication pressures requires that emissions be managed over a wide area reflecting the efficient long range transport of atmospheric nitrogen. Strategies for management of oxidised and reduced nitrogen deposition will be different reflecting their different rates of deposition.