Appropriate Location and Deployment Method for Successful Iron Fertilization

“High nutrient, low chlorophyll (HNLC)” regions were created by locking iron into sedimentary iron sulfides with hydrogen sulfide available from volcanic eruptions in surrounding oceans. Appropriate locations and deployment methods for the iron fertilization were far from volcanoes, earthquakes and boundaries of tectonic plates to reduce the chance of iron-locking by volcanic sulfur compounds. The appropriate locations for the large-scale iron fertilization are proposed as Shag Rocks in South Georgia and the Bransfield Strait in Drake Passage in the Southern Ocean due to their high momentum flux causing efficient iron deployment. The iron (Fe) replete compounds, consisting of natural clay, volcanic ash, agar, N 2 -fixing mucilaginous cyanobacteria, carbon black, biodegradable plastic foamed polylactic acid, fine wood chip, and iron-reducing marine bacterium, are deployed in the ocean to stay within a surface depth of 100 m for phytoplankton digestion. The deployment method of Fe-replete composite with a duration of at least several years for the successful iron fertilization, is configured to be on the streamline of the Antarctic Circumpolar Current (ACC). This will result in high momentum flux for its efficient dispersion on the ocean surface where diatom, copepods, krill and humpback whale stay together (~100 m). Humpback whales are proposed as a biomarker for the successful iron fertilization in large-scale since humpback whales feed on krill, which in turn feed on cockpods and diatoms. The successful large-scale iron fertilization may be indicated by the return of the humpback accurate measurement of algal blooms.


Introduction
The sequestering atmospheric CO 2 produced in enormous quantities by fossil fuel combustion, must be within the emission standards set up by the 2005 Kyoto Protocol and the 2016 Paris Agreement within the United Nations Framework Convention on Climate Change. It is well known that the increase of atmospheric CO 2 causes the air temperature to rise, by contributing to climate change.
It is evident that global CO 2 emissions increase continuously over the years (R 2 = 0.9497), as shown in Figure 1.
Furthermore, fossil CO 2 emissions (Mt CO 2 /yr) were proportional to Total Deaths of the coronavirus outbreak with R 2 = 0.7081 in Figure 2, as well described elsewhere [1].
It is therefore important to reduce the atmospheric CO 2 not only for the global temperature decrease but also for the reduction of coronavirus casualties in 2020.
The iron fertilization was initiated by American oceanographer John Martin in 1988 [2]. Minas et al. [3] designated the terms of "high nutrient, low chlorophyll (HNLC)" in 1986. Martin's iron enrichment experiments [4] into the amounts of carbon drawn into the seas by algae formed the basis for 14 mesoscale international efforts during the last 25 years to understand the ocean's role in the Earth's carbon budget, as summarized in Table 1.
However, none has yet proposed economically feasible locations and deployment   methods. Therefore, further modification of such experimental protocols should be developed so that Martin's hypothesis is seen to be true on a large scale. 14 mesoscale iron enrichment experiments have been carried out in southern Africa, Australia, and New Zealand in the Southern Ocean with the Equatorial Pacific and the Subarctic Pacific [5]. As pointed out by Boyd in 2005 [6], the right location for the iron experiment is so important to be successful in the atmospheric CO 2 sequestration. SO 2 concentration in air over the Sierra Negra volcano in the Galapagos Islands during an eruption in October 2005 showed that SO 2 plumes coincide with the surface nitrate, DO and Fe-limited profiles in the Equatorial Pacific Ocean. It is thus evident that SO 2 dispersion from sub-aerial volcanoes in tectonic plate boundaries, is linked to not only high nitrate concentration but also Fe-limitation, which are typical conditions in HNLC regions.
Sulfate reducing bacteria (SRB) produce H 2 S from SO 2− 4 while iron reducing bacteria produce Fe from Fe 2 O 3 /FeOOH [7]. The resultant submarine reaction produces iron sulfides (FeS/FeS 2 ) that are buried in the submarine sediment as pyrite, which may be one of the reasons why 14 iron fertilization experiments of mesoscale enrichment, since IronEx I of 1993 till Haida Gwaii of 2012 in HNLC, have shown or a limited impact on the sequestration of atmospheric CO 2 . It is thus very important to choose the appropriate location and the deployment method of the iron fertilization. Martin's hypothesis of iron fertilization cannot practically be realized unless such an experiment is carried out at a specific location where serial volcanic eruptions have never occurred before at least recently to ensure a minimal presence of sulfur for lack of iron in the form of iron sulfides. The volcanic eruptions are important not only in relation to current eruptions but also to past eruptions in consideration of cumulative fallout of sulfur dioxide (SO 2 )-laden volcanic plumes.
The objective of the present study is to propose the appropriate location and the deployment method for successful iron fertilization in the oceans.

Bench Test of Hydrogen Sulfide with Iron
Hydrogen sulfide (H 2 S) is produced by 4 routes; volcanic gas (0.04% -0.68%), sulfur oxidizing bacteria such as Beggiatoa, sulfate reducing bacteria (SRB) such as Desulfovibrio desulfuricans, and decomposed microorganism. Iron sulfate heptahydrate (FeSO 4 ·7H 2 O) has been widely used in the iron fertilization experiments as the main source of iron due to its high solubility in water. In the present study each of the 25 grams was dissolved in two bottles with 1 liter seawater; one was bubbled with pure H 2 S gas (50 ppm, 2 liter per minute (LPM), 40 minutes) while another was kept as blank without H 2 S bubbling. Figure 3(a) shows the orange color (left) for the control without H 2 S bubbling while the dark black color (right) shows the experiment with H 2 S bubbling. It was evident that H 2 S gas from biogas induced rapid sedimentation of Chlorela vulgaris with clear supernatant in Figure 3(c). Such a clearness could be the result of loss of cell viability caused by either the lack of dissolved iron reacted with H 2 S or the toxicity of H 2 S.
The sedimentary materials were filtered for analysis by X-ray diffractometer

Iron
Iron is an important limiting nutrient for algae to produce chlorophyll and protein. Photosynthesis depends on adequate iron supply, whose concentration in water is quite low because of its low solubility. The primary producers in the ocean that absorb iron from aeolian dust, volcanic ash and upwelling [8] are typically phytoplankton or cyanobacteria, as shown in Figure 4. Iron is then assimilated by consumers when they eat the bacteria or plankton, the latter providing a crucial source of food to many large aquatic organisms such as fish and whales. When animals, fish and plankton die, decomposing bacteria return iron to the soil and the water as part of the nutrient cycle on the Earth, as schematically shown in Figure 5. Hematite (Fe 2 O 3 ) and goethite (FeOOH) in the aeolian dust in Figure 5 tend to be associated with fine (0.3 -1 μm) particles, with long residence times (days) in the atmosphere and thus potentially long transport paths [9]. Under oxic conditions typifying surface waters, Fe exists largely in the oxidized ferric (Fe 3+ ) form as insoluble oxides, hydroxides and carbonates which readily precipitate and deposit in the sediments. Under anoxic conditions, Fe may be released from the sediments as more easily bindable Fe 2+ prior to algal blooms. Since the solubility of N 2 is very low in comparison with those of CO 2 (high), PO 3− 4 (moderate), and SO 2 (very high), the overall algal growth rate is governed by the rate of N assimilation and N 2 fixation, requiring plenty of iron atoms. In HNLC regions extremely low levels of dissolved iron (0.000004 ppm) [10] indicate low algal productivity. However, Synechococcus reached high densities in most HNLC regions. This may be caused by its ability to synthesize siderophores and iron-binding compounds, which facilitated the transport of iron ion into cells within 2 hours [11] during periods of iron deficiency. Iron is an enzyme cofactor in numerous biochemical pathways. Specifically, enzymes involved in photosynthesis, electron transport, energy transfer, N (specifically nitrate and nitrite) assimilation and (in the case of cyanobacteria) N 2 fixation, require iron.

Pathways of Iron and Sulfur
Algae utilize the dissolved iron, Fe 2+ (aq) while the amount of insoluble FeS/FeS 2 is  and LNHC (low-nutrient, high-chlorophyll), as investigated by Kim et al. [5].
Oceans with iron limitation can also be categorized in 4 regions depending upon the relative rates of accumulation of iron and sulfur, , in the following order of largest to smallest: LNLC, HNLC, LNHC and HNHC, as summarized in Table 2.
Iron is available mainly from 3 sources-desert, volcano and upwelling while sulfur is available from 2 sources-volcano and desert, the latter being negligible due to its sulfur wash-out over a long time by rainfall and weathering. It is important to note that the Antarctic is not only has HNLC regions in the Southern Ocean but also has one of 8 major fishing areas of LNHC. This Antarctic duality can be caused by the co-presence of deserts Fe and volcanoes S in the Antarctic. The carriers of the inorganic nutrient pool in Figure 5 are winds and currents, which have seasonal variations. Therefore, 4 cases of HNLC, LNLC, HNHC, and LNHC can have their own variations with seasons.
In HNLC regions, a buffering capacity of H 2 S is much larger than that of non-HNLC regions due to the additional supply of sulfur compounds from volcanic gas (H 2 S, SO 2 , H 2 SO 4 ) and volcanic ash (S, metallic sulfates). This leads to the more abundant product of H 2 S not only from the volcanic gas but also from the enhanced sulfate reducing bacteria (SRB). Figure 6 shows the pathways of iron and sulfur prior to algae assimilation in both non-HNLC (broken line) and HNLC (solid line) regions. This indicates that the enhanced production of H 2 S from volcanic eruptions in HNLC regions is changed from Fe 2+ (aq) to FeS and FeS 2 transformations. Therefore, both iron and sulfide may not easily penetrate into the overlying surface ocean but rather be pulled down into the hypoxic deep sediment (~1100 m) with abundant Fe (~565 μM) and H 2 S (~150 μM) in the    [17]. Figure 6 shows that volcanic S compounds (S, SO 2 , SO 3 , H 2 S, H 2 SO 4 , sulfates) transform bio-available Fe 2+ (aq) into rapid mackinawite (FeS) and slow pyrite (FeS 2 ) sedimentations in HNLC regions [11] without releasing Fe 2+ (aq) to phytoplankton during pyrite (FeS 2 ) formation. Therefore, HNLC regions, compared to non-HNLC and non-Fe limited regions [18], are big reservoirs of S compounds from extensive volcanic eruptions that induce sedimentary FeS and FeS 2 in Fe-limited (4 × 10 −6 ppm) (0.07 nmol•L −1 ) oceans. As seen in Figure 6, H 2 S is produced by 4 routes; 1) directly from volcanic gas with relatively high solubility (0.3 g/100g H 2 O) compared to that of FeS (4.4 × 10 −5 ), 2) from sulfur by sulfur oxidizing bacteria such as Beggitoa, 3) from soluble sulfate by sulfate reducing bacteria (SRB) such as Desulfovibrio desulfuricans, 4) from soluble sulfides by hydrogenation. The more H 2 S available from either the volcanic gas and sulfur oxidation, or soluble sulfates through SRB and soluble sulfides, the more sedimentation occurs in the forms of FeS and FeS 2 .
Therefore, it is apparent that a volcanic eruption enhances the formation of FeS and FeS 2 , which allows less and less Fe to be available to algae causing iron limited conditions for "LC" (low-chlorophyll). On the other hand, nutrients such as nitrate, phosphate and silicate are fairly soluble and can be consumed to be utilized by algae. However, since Fe is limited, the growth of algae is retarded and thus nutrients are less utilized and further enriched, thereby becoming "HN" (high-nutrient). the Subarctic Pacific and at the Galapagos Islands in the Equatorial Pacific) or temperature-driven hydrothermal vents (as is in the Southern Ocean). Regardless of HNLC or non-HNLC regions, the additional driving force of Fe flux (Fe amount per unit area per unit time) is caused by the concentration gradient of dissolved Fe. This occurs between the hypoxic deep ocean, with plenty of decomposed Fe, as the source of Fe and the oxic surface ocean with Fe-starved algae as a sink of Fe. In HNLC, however, the amount of Fe available to algae was far less (0.000004 ppm) than that in non-HNLC regions (0.0034 ppm) due to greater sedimentations of FeS and FeS 2 by the abundant supply of sulfur compounds from the volcanic eruptions in HNLC regions. This is compared to the minor supply of sulfur from the desert dust. In Table 3, flux and gradient with source and sink in HNLC regions were summarized, which implied that momentum (current flow rate), heat (temperature) and mass (Dissolved Oxygen, The hypoxic condition in the deep ocean allowed SRB (Desulfovibrio ~40 μm), surviving only one day in air, to produce H 2 S and Fe 2+ , the latter being partly engulfed by bacteria for their own concentrated growth (10 8 -10 9 cells•mL −1 ). SRB produced H 2 S and metal ions along with Fe 2+ from high sulfates in the hypoxic water, while HNLC regions in extensive volcanic eruptions were enriched with sulfur compounds (S, H 2 S, SO 2 , H 2 SO 4 and sulfates) and FeSO 4 to produce more H 2 S and Fe 2+ . Consequently, H 2 S might lock and hold more Fe 2+ in the forms of FeS and FeS 2 making less Fe 2+ accessible to algae in the surface ocean.
Importantly, the bacterial growth in the hypoxic water was further enhanced by the plentiful supply of Fe 2+ from iron sulfate through their own sulfate-reducing

HNLC Regions
In most regions of the world ocean photosynthetic production is limited by the availability of the nutrients of nitrate and phosphates. wt%) in trace metals [21] from volanic eruptions, the resultant concentration of silicate in HNLC is relatively high, as typically summarized in Table 4.
Diatoms and copepods have Sverdrop critical depths of about 100 m. Copepod numbers are controlled by a combination of competition and predation by krill [22]. Humpback whales reside in the top 100 m layer to feed on krill which are also mainly in the top 100 m layer. Therefore, the depth for the iron fertilization can be in the top 100 m where diatoms, krill, and humpback reside together while copepods live deeper to escape from krill with an inverse relationship between krill and copepod abundances [22]. Although diatoms are intermediates in the food webs cycle followed by copepods, krill or even humpback whales, diatoms feed on photosynthetic cyanobacterium picoplankton and reproduce cell walls. They use a cheap (8%) energy requirement with a genetically adapted system in iron-limited HNLC regions. The successful blooms by diatoms through the iron fertilization are inevitable not only to draw-down the atmospheric CO 2 through their high sinking rate (0.96 m•d −1 ) but also to be fundamentally abundant prey for copepods, krill and, sequentially fish and humpback whale.

Appropriate Location for Iron Fertilization
The In other words, it is preferable that such an iron experiment be carried out somewhere humpback whales feed and breed, since the fertilized iron can be fed on by the phytoplankton and consumed by copepod and krill, and eventually by humpback whales. July is usually the mating season for the Southern Hemisphere humpback whales, with births occurring in June of the subsequent year. A calf is generally strong enough to migrate with its mother at three months old. Since humpback whales feed on krill and small fish in the Antarctic during the winter while they breed at the tropical or subtropical oceans during the summer, it is recommended that the iron fertilization experiment start during the early summer of January when there is a warm coastal temperature (−3˚C -15˚C) and sufficient irradiance. When humpbacks return to the Southern Ocean after a long journey from the Northern Hemisphere tropical or subtropical oceans, the iron stimulated area, somewhere in the Southern Ocean, may have already algal bloomed with a friendly eco-system community of heterotropic bacteria, picoeukaryotes and picoplankton, diatoms, copepods and krill if the intended iron enrichment experiment is successful on a large scale.

Deployment Method for Iron Fertilization
As reviewed by Shaked and Lis [26], small phytoplanktons are favored under Fe limitation. On the basis of relative scale of Fe availability established from phytoplankton uptake rates, picoplankton such as Synechococcus and Synechocystis appear to be grazed by diatoms such as Thalassiosira spp. and Chaetoceros spp., flagellates of Phaecysts spp. and dinoflagellates of Chrysochromulina Ericina.
Such results correlate with other results for four size classes (0.2 -2, 2 -5, 5 -20, and >20 μm) of Fe cycle with the highest Fe uptake rate of picoplankton. It was suggested that copepod numbers can be controlled by a combination of competition and predation by krill, the latter being fed on by humpback whale. It can be thus postulated that the route of Fe availability starts from picoplankton, diatoms, copepods and krill to the final destination of humpback whale. Therefore, in order to make successful algal blooms for feasible atmospheric CO 2 sequestration, the size of Fe source must be smaller than that of picoplankton (<2 μm).
Fe-replete compounds are deployed to stay as long as possible within the 100 m deep surface area of the ocean with aid of Fe-replete eco-friendly composite consisting of natural aeolian dust and/or clay, volcanic ash, mucilaginous cya-T.-J. Kim nobacteria to avoid the chemical conversion of iron to iron sulfide and enhance phytoplankton digestion. Iron input for algal blooms is not provided by bulk scale additions of direct iron or iron sulfate, but by instead deploying natural clays or soils available around nearby islands with a possible content of iron in the range of 3.5 wt% to 6wt%, as observed elsewhere in the Continents [8], along with volcanic ash desulfurized by rainfall and weathering for long time. Such a Fe-replete complex is encapsulated by agar so that phytoplankton can digest easily and slowly prior to its sinking to the deep ocean where iron is changed to iron sulfide (FeS) and eventually pyrites (FeS 2 ). The deployment of Fe-replete composite is configured on the streamline of the ACC (~4 km/h) in order to Since Fe in the aeolian dust was in the size range of 0.3 -1 μm and summer krill were mainly in the top 100 m layer [28] where cyanobacterium picoplankton stays for efficient photosynthesis and N 2 -fixation, it is important to deploy the Fe enriched eco-friendly composite on ocean surfaces. It will be carried in components of Fe-replete fine silt and clay (11% of the west Australian desert dust, compared to 3.5% -6% of the aeolian dust), water-buoyant floating enhancer such as carbon black (~0.1 μm), rice husk ash containing 90% -98% silica for enhancement of diatom growth, biodegradable plastic foamed poly lactic acid, fine wood chip from sawmills (<~1400 μm) and iron-reducing marine bacterium Shewanella algae. This causes the reduction of ferric iron (Fe 3+ ) to ferrous iron (Fe 2+ ) for facilitated assimilation to picoplankton. Since the wood chips are far greater than other components and their density is less than that of water, the wood chips may play a role of floating moiety whose surface is covered with iron oxides (0.05 -0.1 μm) from clay particles and reinforced carbon black (~0.1 μm) and Chewanella algae (~1.5 × 10 7 CFU, colony-forming unit) with 100% survival in cold seawater (2˚C) over a period of 1 to 2 months [29].
The extracellular carbohydrate polymers from five desert soil algae with different cohesion were studied [30] in the stabilization of fine sand grain in the sequence of the great kinematic viscosity of Desmococcus olivaceus (1.1474), Scytonema javanicum (1.0278), Nostoc sp. (1.0149), Phormidium tenue (0.967), and Microcoleus vaginatus (0.9434), which all belong to cyanobacteria except Desmococcus olivaceus. Among them, Scytonema javanicum and Nostoc sp. are N 2 -fixing marine cyanobacteria. To minimize the occurrence of FeS 2 in the ocean, the best strategy is for Fe-replete eco-friendly composite to be floated on the surface of the ocean as long as possible until its finely pulverized Fe component is assimilated by the algae for their growth. Therefore, such two N 2 -fixing desert soil algae can be used not only as the Fe-replete eco-friendly binder but also as a buoyancy promoter due to its copious viscous mucilage. Besides, agar gel for bacterial culture may spherically encapsulate such a Fe-replete composite for buoyancy to be efficiently fed on by phytoplankton in the seawater.
Special precautions may be followed in the preparation of Fe enriched composite, not to violate the United Nations Convention on Biological Diversity (CBD) and the London Convention on the dumping of wastes at sea, as happened near the islands of Haida Gwaii in 2012. For the appropriate iron fertilization, the deployment of Fe replete composite cannot be in the common mode of FeSO 4 bubbled with SF 6 tracer, but in the mode of eco-friendly composite over the surface water of the fast flow rate (~4 km per hour) of the ACC.
The location of a few fertilizing ships must be perpendicular to the ACC streamline for wide even distribution on the surface water, not in patch length scale, but in large scale (  10 km) as suggested by Boyd et al. [31]. Since it took one week for diatom blooms [32] and the flow rate of the ACC is 4 km/h, the distance between the iron deploying ship and blooms monitoring ship can be at most 672 km (=7 days × 24 hrs × 4 km/h) for one week of diatom growth. However, the ACC is analogous to the moving boundary, so the monitoring ship can be behind the iron deploying ship, as close as 10 to 100 km in the case of the Southern Ocean.
The most preferable location is Shag Rocks (42˚W) (200 × 50 km) in South Georgia due to the following reasons; 1) located outside of major tectonic plate and micro plate boundaries [33], 2) located where the high nutrient (22.2 -28.8 μm nitrate) and high chlorophyll (0.46 -0.93 μg•L −1 ) are present [34]  There will be on-line monitoring of the algal removal rates of nitrate, phosphate and silicate by corresponding sensors. The algal production rates of dissolved oxygen (DO) in the ocean and the oxygen in the atmosphere will be measured by DO and O 2 sensors. The algal consumption rates of dissolved carbon dioxide (DCO 2 ) in the ocean or the fugacity of CO 2 in the atmosphere will be recorded by CO 2 sensors and the production rate of chlorophyll will be monitored by a chlorophyll sensor system. All of this can be continuously measured on fertilizing ships to see the effect of the iron fertilization. The light-dependent reaction of photosynthesis requires inorganic phosphate to convert H 2 O to O 2 , which leads to the increase of dissolved oxygen (DO) and thus the uptake rate of the phosphate and iron are also increased during the daytime for ATP production. Therefore, the iron deployment will be made during the daytime. The rate determining step for nitrogen uptake at the Fe-replete condition is the transformation from the nitrite (NO − 2 ) to the ammonium (NH + 4 ) with electron transfer of ferredoxin [11]. Since the nitrate reductase prefers anaerobic conditions, the nitrogen uptake mainly occurs during the nighttime, corresponding with the diel T.-J. Kim variation of Synechococcus spp. of maximal cell concentration at midnight [35]. It is thus expected that Synechococcus grows during the night. However, diatoms are capable of dividing at any point of the diel cycle [36]. Therefore, the monitoring of chlorophyll, nitrate phosphate and silicate concentrations after deploying the Fe-replete complex can be made throughout the day and the night for the accurate prediction of algal blooms.
A successful iron fertilization experiment with a deployment period of at least several years can be expected with increased rates of chlorophyll, DMS, DO, O 2 , pCO 2 , fugacity of atmospheric CO 2 concentrations along with the decreased rates of nitrate, phosphate, silicate concentrations. Dominant plankton feeds in the sequence of picoplankton, diatoms, copepods and krill resulting in the return of humpback whale. Humpback whales live at the surface of the ocean, both in the open ocean and shallow coastline water. In order to be successful in iron fertilization, the appropriate location can be shallow coastline water with abundant numbers of krill and copepods, the latter feeding on ciliates and heterotrophic flagellates eating phytoplankton. Since HNLC regions are rich in nitrate, phosphate and silicate but starved of iron, the iron fertilization is expected to increase the phytoplankton productivity starting from picoplankton, copepods and krill. This may induce, the possible biomarker humpback whales to return to the vicinity of the forgotten whale station of Grytviken in South Georgia. This will prove the success of the iron fertilization, which can be cross-checked by satellite images of nitrate, chlorophyll and DMS (dimethyl sulfide) along with the on-line database established by chlorophyll sensors.
The present method is significantly different from other known methods 1) The present method proposes that sulfur compounds have to be free from iron fertilization, which has never been attempted before.
2) The previous 14 methods of iron fertilizations using FeSO 4 ·7H 2 O as iron additives removed the iron (Fe) in the form of black iron sulfides (FeS/FeS 2 ) ( Figure 3(a)) after chemical reaction with sulfur compounds as illustrated in Figure 6. Therefore, algal growth is retarded for Fe-limited conditions at locations with volcanic eruptions.
3) The present method uses the natural clay or desert dust for iron fertiliza-

Conclusions
The appropriate location for the large-scale sequestration of atmospheric CO 2 can be found if the iron fertilization is carried out not only close to deserts but also as far from volcanoes, earthquakes and the boundaries of tectonic plates. The appropriate locations for the large-scale iron fertilization are proposed as Shag Rocks and Bransfield Strait in the Southern Ocean due to their high momentum fluxes which are suitable for efficient iron deployment.
Fe-replete compounds are deployed in the ocean to stay as long as possible within a surface depth of 100 m with the aid of Fe-replete eco-friendly composite with iron-reducing marine bacterium Shewanella algae, Chewanella, algale to avoid the chemical conversion of iron to iron sulfide and enhance phytoplankton digestion. The iron input for algal blooms is not direct iron or iron sulfate. It is preferable to deploy natural clays or soils available on nearby islands, as observed in the Continents and Tasmanian dust, along with volcanic ash desulfurized by rainfall and weathering for long time. Such a Fe-replete complex is encapsulated by agar so that phytoplankton can digest easily and slowly prior to its sinking to the deep ocean where iron is changed to iron sulfide (FeS) and eventually pyrites (FeS 2 ).
Since Fe in the aeolian dust was in the size range of 0.3 -1 μm and summer krill was mainly in the top 100 m layer, where cyanobacterium picoplankton stays for efficient photosynthesis and N 2 -fixation, it is important to deploy the Fe enriched eco-friendly composite on ocean surfaces. It will be carried in components of Fe-replete fine silt and clay (11% of the west Australian desert dust, compared to 3.5% -6% of the aeolian dust), water-buoyant floating enhancer such as carbon black (~0.1 μm), rice husk ash containing 90% -98% silica for enhancement of diatom growth, biodegradable plastic foamed poly lactic acid and fine wood chip from sawmills (<~1400 μm) and iron-reducing marine bacterium Shewanella algae to reduce ferric iron (Fe 3+ ) to ferrous iron (Fe 2+ ) for facilitated assimilation to picoplankton. Since the wood chips are far lighter and/or more buoyant than other components and their density is less than that of water, the wood chips may play a role of floating moiety whose surface is covered with iron oxides (0.05 -0.1 μm) from clay particles and reinforced carbon black (~0.1 μm) and Chewanella algae (~1.5 × 10 7 CFU, colony-forming unit) with 100% survival in cold seawater (2˚C) over a period of 1 to 2 months. Scytonema javanicum and Nostoc sp. are N 2 -fixing marine cyanobacteria. To minimize the occurrence of FeS 2 in the ocean, the best strategy is for Fe-replete eco-friendly composite to be floated on the surface of the ocean until its finely pulverized Fe component is assimilated by the algae for their growth. Therefore, such two N 2 -fixing desert soil algae can be used not only as the Fe-replete eco-friendly binder but also as a buoyancy promoter due to its copious viscous mucilage. Besides, agar from agar gel for bacterial growth may spherically encapsulate such a Fe-replete composite for buoyancy to be efficiently fed on by phytoplankton in the seawater.
Oceans are categorized by 4 groups such as 2 LC (HNLC, LNLC) and 2 HC (HNHC, LNHC) regions on the basis of the relative degree of accumulation rates for iron from deserts and for sulfur from volcanoes. HNLC regions have a T.-J. Kim stronger lock of sulfur compounds by hydrogen sulfide available from volcanic eruptions without the key of iron sulfides than that of non-HNLC regions. The deployment of Fe-replete composite with a duration of at least several years for successful iron fertilization, is on the streamline of the ACC (~4 km/h) in order to have a high momentum flux for efficient dispersion of Fe-replete composite on the ocean surface where diatom, copepods, krill and humpback whales stay together (~100 m). Humpback whales act as a biomarker for the successful iron fertilization in large-scale since humpback whales which feed on krill, which in turn feed on cockpods and diatoms. The success of the large-scale iron fertilization may be indicated by the return of the humpback whales if there were no humpback whales for a long period before the iron fertilization.
On-line monitoring for the successful iron fertilization is shown by the simultaneous changes of two groups; the increasing concentration group (chlorophyll, O 2 , DO, DMS) and the decreasing concentration group (nitrate, phosphate, silicate, CO 2 , DCO 2 ). On-line monitoring of components is carried out on the fertilizing ships; one ship deploying the Fe-replete composite is located at the upward stream of the ACC while another ship monitoring the response of the iron fertilization by both of satellite (chlorophyll-a, nitrate, dimethyl sulfide) and serial sensors (chlorophyll-a, phosphate, silicate, iron, O 2 , DO, CO 2 , DCO 2 ) are positioned at the downward stream of the ACC. The maximal distance between the two ships can be 672 km (=7 days × 24 hrs × 4 km/h of the ACC flow rate), considering the growth period of 1 week in diatoms. However, the ACC is analogous to the moving boundary, the monitoring ship can be behind the iron deploying ship at a distance of 10 to 100 km. The monitoring of chlorophyll-a, nitrate phosphate, and silicate concentrations after deployment of the Fe-replete complex is made throughout the day and night for the accurate prediction of algal blooms.