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. Since the start of the industrial revolution, human activities have caused arapid increase in atmospheric carbon dioxide ( CO2 ) concentrations, which have, inturn, had an impact on climate leading to global warming and oceanacidification. Various approaches have been proposed to reduce atmospheric CO2 . The Martin (or iron) hypothesis suggests that ocean ironfertilization (OIF) could be an effective method for stimulating oceaniccarbon sequestration through the biological pump in iron-limited,high-nutrient, low-chlorophyll (HNLC) regions. To test the Martin hypothesis,13 artificial OIF (aOIF) experiments have been performed since 1990 in HNLCregions. These aOIF field experiments have demonstrated that primaryproduction (PP) can be significantly enhanced by the artificial addition of iron.However, except in the Southern Ocean (SO) European Iron Fertilization Experiment (EIFEX),no significant change in the effectiveness of aOIF (i.e., the amount ofiron-induced carbon export flux below the winter mixed layer depth,MLD) has been detected. These results, including possible side effects, have been debatedamongst those who support and oppose aOIF experimentation, and many questionsconcerning the effectiveness of scientific aOIF, environmental side effects, andinternational aOIF law frameworks remain. In the context of increasing globaland political concerns associated with climate change, it is valuable toexamine the validity and usefulness of the aOIF experiments. Furthermore, itis logical to carry out such experiments because they allow one to study howplankton-based ecosystems work by providing insight into mechanisms operatingin real time and under in situ conditions. To maximize theeffectiveness of aOIF experiments under international aOIF regulations in thefuture, we therefore suggest a design that incorporates several components. (1) Experimentsconducted in the center of an eddy structure when grazingpressure is low and silicate levels are high (e.g., in the SO south of the polar front during early summer). (2) Shipboard observationsextending over a minimum of ∼40  days, with multiple iron injections (atleast two or three iron infusions of ∼2000 kg with an interval of ∼10 –15 days to fertilize a patch of 300  km2 and obtain a ∼2 nM concentration). (3) Tracing of the iron-fertilized patch using both physical(e.g., a drifting buoy) and biogeochemical (e.g., sulfur hexafluoride,photosynthetic quantum efficiency, and partial pressure of CO2 ) tracers.(4) Employment of neutrally buoyant sediment traps (NBST) and application of thewater-column-derived thorium-234 ( 234Th ) method at two depths (i.e., justbelow the in situ MLD and at the winter MLD), with autonomous profilers equipped with an underwater video profiler(UVP) and a transmissometer. (5) Monitoring of side effects on marine/oceanecosystems, including production of climate-relevant gases (e.g.,nitrous oxide, N2O ; dimethyl sulfide, DMS; and halogenated volatile organic compounds, HVOCs), decline inoxygen inventory, and development of toxic algae blooms, withoptical-sensor-equipped autonomous moored profilers and/or autonomous benthic vehicles.Lastly, we introduce the scientific aOIF experimental design guidelines for afuture Korean Iron Fertilization Experiment in the Southern Ocean (KIFES).

biogeosciences

Reviews and syntheses: Ocean iron fertilization experiments – past, present, and future looking to a future Korean Iron Fertilization Experiment in the Southern Ocean (KIFES) project