Modelling the effects of iron fertilisation on the ocean
Research has shown that the ocean's ability to sequester carbon from the atmosphere may, in some regions, be limited by the availability of iron in the surface waters. This has prompted proposals for iron fertilisation of the world's oceans in an attempt to remove carbon from the atmosphere. This would result in a corresponding reduction in the atmospheric concentration of carbon dioxide and potentially global warming. Before proceeding with such a grand undertaking, one must be sure the desired result will be achieved. This is where ocean modelling can help. The Max Planck Institute for Meteorology (MPI-M), in Hamburg, Germany applied the Biogeochemical Ocean General Circulation Model (BOGCM) HAMOCC5 to this problem. Difficulties in paramaterising iron transport led to an overestimation of the iron concentration near the ocean's surface by HAMOCC5 in comparison with measurement data. MPI-M was able to overcome this difficulty by tweaking the iron scavenging rate constant. This adjustment also improved HAMOCC5's ability to model global carbon fluxes, particularly in the Southern Ocean. The next step was to fertilise the modelled ocean with iron and observe. Uptake of atmospheric carbon dioxide increased considerably over the Southern Ocean, but little elsewhere. Even more surprising was that the enhanced uptake died down rapidly, within two model decades. In the end, the net gain in carbon uptake was minimal. These results suggest caution regarding the potential of iron fertilisation as a possible answer to combating rising carbon dioxide concentrations and subsequent global warming.