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

Abstract

Abstract. Since the start of the industrial revolution, human activities have caused a rapid increase in atmospheric carbon dioxide (CO2) concentrations, which have, in turn, had an impact on climate leading to global warming and ocean acidification. Various approaches have been proposed to reduce atmospheric CO2. The Martin (or iron) hypothesis suggests that ocean iron fertilization (OIF) could be an effective method for stimulating oceanic carbon 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 HNLC regions. These aOIF field experiments have demonstrated that primary production (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 of iron-induced carbon export flux below the winter mixed layer depth, MLD) has been detected. These results, including possible side effects, have been debated amongst those who support and oppose aOIF experimentation, and many questions concerning the effectiveness of scientific aOIF, environmental side effects, and international aOIF law frameworks remain. In the context of increasing global and political concerns associated with climate change, it is valuable to examine the validity and usefulness of the aOIF experiments. Furthermore, it is logical to carry out such experiments because they allow one to study how plankton-based ecosystems work by providing insight into mechanisms operating in real time and under in situ conditions. To maximize the effectiveness of aOIF experiments under international aOIF regulations in the future, we therefore suggest a design that incorporates several components. (1) Experiments conducted in the center of an eddy structure when grazing pressure is low and silicate levels are high (e.g., in the SO south of the polar front during early summer). (2) Shipboard observations extending over a minimum of ∼40 days, with multiple iron injections (at least 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 the water-column-derived thorium-234 (234Th) method at two depths (i.e., just below 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/ocean ecosystems, including production of climate-relevant gases (e.g., nitrous oxide, N2O; dimethyl sulfide, DMS; and halogenated volatile organic compounds, HVOCs), decline in oxygen inventory, and development of toxic algae blooms, with optical-sensor-equipped autonomous moored profilers and/or autonomous benthic vehicles. Lastly, we introduce the scientific aOIF experimental design guidelines for a future Korean Iron Fertilization Experiment in the Southern Ocean (KIFES).

Biogenic Iron Dust: A Novel Approach to Ocean Iron Fertilization as a Means of Large Scale Removal of Carbon Dioxide From the Atmosphere

“…With regard to OIF, the London Protocol was amended in 2013 to regulate marine geoengineering activities with the aim of controlling, and, in effect banning, unregulated commercial activities aimed at marine geoengineering. The amendment was done largely in response to the establishment of commercial ventures that intended to exploit OIF to obtain carbon credits, see Yoon et al (2018) and Scott (2019) for a more detailed discussion of these issues. The amendment does not prohibit research on OIF or other geoengineering approaches; however, it's guidelines are either restrictive, or ambiguous enough, that experimentation on OIF has effectively stopped (Yoon et al, 2018;Scott, 2019).…”

“…The amendment was done largely in response to the establishment of commercial ventures that intended to exploit OIF to obtain carbon credits, see Yoon et al (2018) and Scott (2019) for a more detailed discussion of these issues. The amendment does not prohibit research on OIF or other geoengineering approaches; however, it's guidelines are either restrictive, or ambiguous enough, that experimentation on OIF has effectively stopped (Yoon et al, 2018;Scott, 2019). Given the fact that GHG emissions to the atmosphere continue to increase, despite global action to mitigate emissions (Le Quéré et al, 2018), there is debate about revisiting legal frameworks for NET applications in the marine realm (Brent et al, 2018).…”

“…In all cases, iron fertilization led to phytoplankton blooms confirming the potency of iron as a limiting micro-nutrient. The outcome of net export of C to the depths was more ambiguous with at least one study showing significant export (Smetacek et al, 2012), but others yielding more varied results (Boyd et al, 2007;Yoon et al, 2018). The timing of fertilization efforts, the duration of the experiments both in terms of iron addition and monitoring efforts, as well as the ultimate fate of the iron, are among the factors that likely effected the net export outcomes of these experiments.…”

“…The timing of fertilization efforts, the duration of the experiments both in terms of iron addition and monitoring efforts, as well as the ultimate fate of the iron, are among the factors that likely effected the net export outcomes of these experiments. For a comprehensive analysis of previous OIF efforts, see Yoon et al (2018). Unintended consequences of these experiments include alteration of the population structure of the phytoplankton community, including the production of toxinproducing phytoplankton (Trick et al, 2010).…”

Predictive Connection for 2100 between Atmospheric Carbon, Global Warming and Ocean Height Based on Climate History

“…To replenish the ten percent reduction will require between three and five billion tons of the atmospheric carbon dioxide, says David Kubiak, Director of Planktos. This news has created a stir among the environmentalists who have high uncertainty on the probable problems that may arise due to the huge geo-engineering proposal [84] also questions as to whether the iron fertilization will significantly reduce the carbon dioxide or if the technique can qualify as the viable offsets. Tests to settle the environmental debate are ongoing [85].…”