Consequences of man-made Nitrogen input into the world's oceans

Frank Dentener, a scientist working in the climate change team has co-authored a study published in Science Magazine (Science 16 May 2008: Vol. 320 no. 5878, p. 893) on the consequences of man-made nitrogen input into the world's oceans.

A large amount of nitrogen compounds are emitted into the atmosphere by humans, through the burning of fossil fuels and the use of fertilizers. This enters the globe's oceans, where it acts as a fertilizer and increases the production of marine plant life, including algae. That increase draws down carbon dioxide (CO2) from the atmosphere, leading to the removal of up to 10 % of the CO2 emitted by human activities, and reducing its greenhouse warming potential. However, bacterial processing of this nitrogen in the oceans may also lead to additional emissions of the potent greenhouse gas nitrous oxide (N2O), cancelling out about two-thirds of the apparent gains from the CO2 removal. A vital part of this study was the modelled nitrogen deposition, retrieved from recent international multi-model studies organised and analysed by JRC scientists.

The work continues in a project endorsed by the United Nations Economic Commission for Europe (UN-ECE). It studies the impacts of transport of air pollution in the northern hemisphere of the planet, with a long-standing organisational and scientific input from the JRC.

Figure: Global deposition of reactive nitrogen [mg N/m2/year] in the year 2000. This study focussed on the effect on the deposition on the coastal shelves and open ocean (adopted from F. Dentener et al., Global Biogeochem. Cycles, 20, 4003, 2006).