Ocean Fertilization

The impasse in international efforts to curb greenhouse gas emissions has led to increased interest in the study and development of carbon dioxide removal (CDR) methods to enhance atmospheric carbon drawdown and sequestration. Ocean iron fertilization (OIF) is arguably one of the best studied ocean-based CDR approaches. However, OIF is not featured in most CDR research agendas and initiatives, being perceived as inefficient and with potential large negative impact on ecosystems. Since the early 90s, when OIF in the Southern Ocean was first proposed as an ocean-based CDR approach, seven OIF experiments and two studies of natural iron fertilization (downstream of islands) were carried out in the Southern Ocean. While in all cases iron fertilization has resulted in significant increases in plankton biomass and productivity, the impacts of iron fertilization on plankton assemblage composition, food webs, carbon export and carbon export efficiency are still poorly known and understood. The potential and uncertainties of this approach both as a tool for basic research and ocean-based CDR approach will be highlighted, based on results from 3 OIFs (EisenEx, EIFEX and LOHAFEX) carried out in closed eddy cores ensuring horizontal containment and vertical coherence from the surface down to 3000 m depth