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Ocean Iron Fertilization Experiments – Past, Present, and Future Looking to a Future Korean Iron Fertilization Experiment in the Southern Ocean (KIFES) Project

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Ocean Iron Fertilization Experiments – Past, Present, and Future Looking to a Future Korean Iron Fertilization Experiment in the Southern Ocean (KIFES) Project Biogeosciences, 15, 5847–5889, 2018 https://doi.org/10.5194/bg-15-5847-2018 © Author(s) 2018. This work is distributed under the Creative Commons Attribution 3.0 License. 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 Joo-Eun Yoon1, Kyu-Cheul Yoo2, Alison M. Macdonald3, Ho-Il Yoon2, Ki-Tae Park2, Eun Jin Yang2, Hyun-Cheol Kim2, Jae Il Lee2, Min Kyung Lee2, Jinyoung Jung2, Jisoo Park2, Jiyoung Lee1, Soyeon Kim1, Seong-Su Kim1, Kitae Kim2, and Il-Nam Kim1 1Department of Marine Science, Incheon National University, Incheon 22012, Republic of Korea 2Korea Polar Research Institute, Incheon 21990, Republic of Korea 3Woods Hole Oceanographic Institution, MS 21, 266 Woods Hold Rd., Woods Hole, MA 02543, USA Correspondence: Il-Nam Kim ([email protected]) Received: 2 November 2016 – Discussion started: 15 November 2016 Revised: 16 August 2018 – Accepted: 18 August 2018 – Published: 5 October 2018 Abstract. Since the start of the industrial revolution, hu- providing insight into mechanisms operating in real time and man activities have caused a rapid increase in atmospheric under in situ conditions. To maximize the effectiveness of carbon dioxide (CO2) concentrations, which have, in turn, aOIF experiments under international aOIF regulations in the had an impact on climate leading to global warming and future, we therefore suggest a design that incorporates sev- ocean acidification. Various approaches have been proposed eral components. (1) Experiments conducted in the center of to reduce atmospheric CO2. The Martin (or iron) hypothesis an eddy structure when grazing pressure is low and silicate suggests that ocean iron fertilization (OIF) could be an ef- levels are high (e.g., in the SO south of the polar front during fective method for stimulating oceanic carbon sequestration early summer). (2) Shipboard observations extending over through the biological pump in iron-limited, high-nutrient, a minimum of ∼ 40 days, with multiple iron injections (at low-chlorophyll (HNLC) regions. To test the Martin hypoth- least two or three iron infusions of ∼ 2000 kg with an inter- esis, 13 artificial OIF (aOIF) experiments have been per- val of ∼ 10–15 days to fertilize a patch of 300 km2 and obtain formed since 1990 in HNLC regions. These aOIF field exper- a ∼ 2 nM concentration). (3) Tracing of the iron-fertilized iments have demonstrated that primary production (PP) can patch using both physical (e.g., a drifting buoy) and biogeo- be significantly enhanced by the artificial addition of iron. chemical (e.g., sulfur hexafluoride, photosynthetic quantum However, except in the Southern Ocean (SO) European Iron efficiency, and partial pressure of CO2) tracers. (4) Employ- Fertilization Experiment (EIFEX), no significant change in ment of neutrally buoyant sediment traps (NBST) and ap- the effectiveness of aOIF (i.e., the amount of iron-induced plication of the water-column-derived thorium-234 (234Th) carbon export flux below the winter mixed layer depth, method at two depths (i.e., just below the in situ MLD and at MLD) has been detected. These results, including possible the winter MLD), with autonomous profilers equipped with side effects, have been debated amongst those who support an underwater video profiler (UVP) and a transmissometer. and oppose aOIF experimentation, and many questions con- (5) Monitoring of side effects on marine/ocean ecosystems, cerning the effectiveness of scientific aOIF, environmental including production of climate-relevant gases (e.g., nitrous side effects, and international aOIF law frameworks remain. oxide, N2O; dimethyl sulfide, DMS; and halogenated volatile In the context of increasing global and political concerns as- organic compounds, HVOCs), decline in oxygen inventory, sociated with climate change, it is valuable to examine the and development of toxic algae blooms, with optical-sensor- validity and usefulness of the aOIF experiments. Further- equipped autonomous moored profilers and/or autonomous more, it is logical to carry out such experiments because they benthic vehicles. Lastly, we introduce the scientific aOIF ex- allow one to study how plankton-based ecosystems work by Published by Copernicus Publications on behalf of the European Geosciences Union. 5848 J.-E. Yoon et al.: Ocean iron fertilization experiments – past, present, and future Figure 1. Diagram showing the monthly atmospheric CO2 con- centrations (ppm) (blue) measured at the Mauna Loa Observa- Figure 2. Schematic representation of several proposed climate- tory, Hawaii (http://www.esrl.noaa.gov/gmd/ccgg/trends/data.html, engineering methods (modified from Matthews, 1996). last access: 6 September 2018); global monthly land-surface air and sea surface temperature anomalies (◦C) (red) (http://data.giss. nasa.gov/gistemp/, last access: 6 September 2018); and pH (green) among the proposed approaches is ocean fertilization (https: measured at station ALOHA in the central North Pacific (http:// //web.whoi.edu/ocb-fert/, last access: 6 September 2018), hahana.soest.hawaii.edu/hot/products/HOT_surface_CO2.txt). The which targets the drawdown of atmospheric CO by nutri- data values represent moving average values for 12 months and 2 ent addition (e.g., iron, nitrogen, or phosphorus compounds) shading indicates the standard deviation for 12 months. to stimulate phytoplankton growth and, subsequently, carbon export to the deep ocean or sediments via the ocean biologi- perimental design guidelines for a future Korean Iron Fertil- cal pump (ACE CRC, 2015). ization Experiment in the Southern Ocean (KIFES). The ocean biological pump is frequently depicted as a single combined process, whereby organic matter produced by phytoplankton during photosynthesis in surface waters is quickly transported to intermediate and/or deep waters 1 Introduction (Fig. 3a) (Volk and Hoffert, 1985; De La Rocha, 2007). Al- though the effectiveness of the biological pump is primar- Since the start of the industrial revolution, human activ- ily controlled by the supply of macronutrients (i.e., nitrate, ities have caused a rapid increase in atmospheric carbon phosphate, and silicate) from the deep ocean into the mixed dioxide (CO2, a major greenhouse gas) from ∼ 280 ppm layer (ML), leading to new production (Sarmiento and Gru- (pre-industrial revolution) to ∼ 400 ppm (present day) (http: ber, 2006), iron acts as an essential micronutrient to stimu- //www.esrl.noaa.gov/, last access: 6 September 2018), which late the uptake of macronutrients for phytoplankton growth has, in turn, led to global warming and ocean acidifica- (Fig. 3b) (Martin and Fitzwater, 1988; Martin, 1990; Morel tion, indicating that there is an urgent need to reduce global and Price, 2003). In the subarctic North Pacific (NP), equa- greenhouse gas emissions (IPCC, 2013) (Fig. 1). As the An- torial Pacific (EP), and Southern Ocean (SO), which are well thropocene climate system has rapidly become more unpre- known as high-nutrient and low-chlorophyll (HNLC) regions dictable, the scientific consensus is that the negative out- (Fig. 4a and b), phytoplankton cannot completely utilize the comes are a globally urgent issue that should be resolved available macronutrients (particularly nitrate) for photosyn- in a timely manner for the sake of all life on Earth (IPCC, thesis due to a lack of iron. As a consequence, primary pro- 1990, 1992, 1995, 2001, 2007, 2013). The various ideas and duction (PP) in these HNLC regions is relatively low, despite approaches that have been proposed to relieve and resolve the high availability of macronutrients (in particular nitrate the problem of global warming (Matthews, 1996; Lenton and and phosphate) (Fig. 4a and b). Vaughan, 2009; Vaughan and Lenton, 2011; IPCC, 2014; Le- Analyses of trapped air bubbles in Arctic–Antarctic ice ung et al., 2014; Ming et al., 2014) largely fall into two cat- cores have revealed that atmospheric CO2 (∼ 180 ppm) dur- egories: (1) reduction of atmospheric CO2 by the enhance- ing the Last Glacial Maximum (LGM; ∼ 20000 years ago) ment of biological CO2 uptake (including ocean fertiliza- was much lower than during preindustrial times (∼ 280 ppm) tion) and/or the direct capture or storage of atmospheric CO2 (Neftel et al., 1982; Barnola et al., 1987; Petit et al., 1999). through chemically engineered processes, and (2) control of Over the last 25 years, several hypotheses have been pro- solar radiation by artificial aerosol injection into the atmo- posed to explain the lowered atmospheric CO2 level during sphere to augment cloud formation and cloud brightening to the LGM (Broecker, 1982; McElroy, 1983; Falkowski, 1997; elevate albedo (Fig. 2). One of the most attractive methods Broecker and Henderson, 1998; Sigman and Boyle, 2000). Biogeosciences, 15, 5847–5889, 2018 www.biogeosciences.net/15/5847/2018/ J.-E. Yoon et al.: Ocean iron fertilization experiments – past, present, and future 5849 Figure 3. The iron hypothesis, as suggested by Martin (1990). (a) Effectiveness of the biological pump under normal conditions. (b) Ef- fectiveness of the biological pump following iron enrichment (modified from Sarmiento and Gruber, 2006). (c) Schematic diagram of the decrease in the downward flux of organic carbon as a function of depth in the water column (modified from Lampitt et al., 2008). OM is organic matter and DIC is dissolved inorganic carbon. Dust inputs are generally regarded as a major natural iron no significant increase in carbon exports has been
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