Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 6 5 2009 10.5194/bg-6-901-2009 http://www.biogeosciences.net/6/901/2009/ http://www.biogeosciences.net/6/901/2009/bg-6-901-2009.html http://www.biogeosciences.net/6/901/2009/bg-6-901-2009.pdf 901 912 2009-05-25 Impact of enhanced vertical mixing on marine biogeochemistry: lessons for geo-engineering and natural variability S. Dutreuil L. Bopp laurent.bopp@lsce.ipsl.fr A. Tagliabue Laboratoire des Sciences du Climat et de l'Environnement, IPSL-CEA-CNRS-UVSQ Orme des Merisiers, Bat 712, CEA/Saclay, 91198, Gif sur Yvette, France Ecole Normale Supérieure, 45 rue d'Ulm, 75005 Paris, France Artificially enhanced vertical mixing has been suggested as a means by which to fertilize the biological pump with subsurface nutrients and thus increase the oceanic CO₂ sink. We use an ocean general circulation and biogeochemistry model (OGCBM) to examine the impact of artificially enhanced vertical mixing on biological productivity and atmospheric CO₂, as well as the climatically significant gases nitrous oxide (N₂O) and dimethyl sulphide (DMS) during simulations between 2000 and 2020. Overall, we find a large increase in the amount of organic carbon exported from surface waters, but an overall increase in atmospheric CO₂ concentrations by 2020. We quantified the individual effect of changes in dissolved inorganic carbon (DIC), alkalinity and biological production on the change in <I>p</I>CO₂ at characteristic sites and found the increased vertical supply of carbon rich subsurface water to be primarily responsible for the enhanced CO₂ outgassing, although increased alkalinity and, to a lesser degree, biological production can compensate in some regions. 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