Impact of enhanced vertical mixing on marine biogeochemistry: lessons for geo-engineering and natural variability

Sébastien Dutreuil (1, 2) , L Bopp (2) , A Tagliabue (3)

1 LGENS - Laboratoire de géologie de l'ENS
2 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
3 Department of Earth Ocean and Ecological Sciences [Liverpool]

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 CO 2 sink. We use an ocean general circulation and biogeo-chemistry model (OGCBM) to examine the impact of arti-ficially enhanced vertical mixing on biological productivity and atmospheric CO 2 , as well as the climatically significant gases nitrous oxide (N 2 O) and dimethyl sulphide (DMS) dur-ing 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 CO 2 concentrations by 2020. We quantified the individual effect of changes in dissolved inorganic carbon (DIC), alka-linity and biological production on the change in pCO 2 at characteristic sites and found the increased vertical supply of carbon rich subsurface water to be primarily responsible for the enhanced CO 2 outgassing, although increased alkalinity and, to a lesser degree, biological production can compensate in some regions. While ocean-atmosphere fluxes of DMS do increase slightly, which might reduce radiative forcing, the oceanic N 2 O source also expands. Our study has impli-cations for understanding how natural variability in vertical mixing in different ocean regions (such as that observed re-cently in the Southern Ocean) can impact the ocean CO 2 sink via changes in DIC, alkalinity and carbon export.

Mots clés: geoengineering; ocean pipes

Domaines: Ingénierie de l'environnement; Océan, Atmosphère

Sébastien Dutreuil, L Bopp, A Tagliabue. Impact of enhanced vertical mixing on marine biogeochemistry: lessons for geo-engineering and natural variability. Biogeosciences, 2009, 6, pp.901 - 912. ⟨10.5194/bg-6-901-2009⟩. ⟨hal-01109181⟩