Climate engineering by mimicking the natural dust climate control : 1 the Iron Salt Aerosols method

This PDF files contains on pages 1 and 2 the point-to-point response to the reviewers and 1 the list of all relevant changes made in the manuscript, inclusive the revised figures, the 2 expanded table 1 and the new tables 2 and 3. Then starting page 3 till the end on page 86, 3 the revised manuscript with yellow marked paragraphs for every relevant changes made. 4 5 6 Point-to-point response to the reviewers and list of all relevant 7 changes made in the manuscript: “Climate engineering by mimicking the natural 8

weakness of our recent THC may worsen. Any THC collapse would not only result in severe 145 damages to ecosystems, food chains, and food resources of the oceans, but would also lead 146 to an acceleration of the increase of atmospheric CO 2 concentration, resulting in a faster 147 climate warming than forecasted.

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The best way to prevent such disturbing situations and consequences is to stop GW.

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The dust concentration in the troposphere increased during every cold period in ice ages and 155 reached a multiple of today's levels [35]. Dust deposition in the Southern Ocean during 156 glacial periods was 3 to 10 times greater than during interglacial periods, and its major

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Aerosols have a climate impact through aerosol-cloud interactions and aerosol-radiation 328 interactions [100]. By reflecting sunlight radiation back to space, some types of aerosols 329 increase the local albedo (which is the fraction of solar energy that is reflected back to 330 space), producing a cooling effect [101]. If the top of clouds reflect back a part of the incident 331 solar radiation received, the base of clouds receive the longwave radiation emitted from the 332 Earth surface and reemit downward a part of it. Usually, the higher a cloud is, in the 333 atmosphere, the greater its effect on enhancing atmospheric greenhouse warming, and 334 therefore the overall effect of high altitude clouds, such as cirrus, is a positive forcing.

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Meanwhile, the net effect of low altitude clouds (stratocumulus) is to cool the surface, as they 336 are thicker and prevent more sunlight from reaching the surface. The overall effect of other 337 types of clouds such as cumulonimbus is neutral: neither cooling nor warming.

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More outgoing long-wave radiation is possible when the cirrus cover is reduced. Efficient ice 339 nuclei (such as bismuth tri-iodide) seeding of cirrus cloud might artificially reduce their cover 340 [102,103].

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In order to enhance the cooling effects of low altitude clouds, marine cloud brightening has 342 been proposed [104], for instance by injecting sea salt aerosols over the oceans. The effect 343 depends on both particle size and injection amount, but a warming effect is possible [105].

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Aerosol effects on climate are complex because aerosols both reflect solar radiation to space 345 and absorb solar radiation. In addition, atmospheric aerosols alter cloud properties and cloud 346 cover depending on cloud type and geographical region [106]. The overall effect of aerosols 347 on solar radiation and clouds is negative (a cooling effect), which masks some of the GHGs-

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Currently, methane (CH 4 ) in the troposphere is destroyed mainly by the hydroxyl radical °OH.

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Otherwise the aerosol lifetime would be too short to bridge any intercontinental distance or 441 arrive in polar regions. That reduces the possible Clexchange by particle contact. But 442 absorption of gaseous HCl by reactive iron oxide aerosols resulting in Fe(III) chloride 443 formation at the particle surfaces is possible [127]. Gaseous HCl and further gaseous chloro-444 compounds are available in the troposphere: HCl (300 pptv above the oceans and 100 pptv 445 above the continents) [118], ClNO 2 (up to 1500 pptv near flue gas emitters) [

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As we learn from Henry's law constants in Table 1

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The Fenton reaction mechanism is dependent on pH and on the kinds of ligands bound to 611 the Fenton metal. The reaction mechanism with oxidants of SO 4 2-, NO 3 -, Cland 1,2-612 dihydroxy benzene ligands had been studied [194].

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In

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The contact of arctic snow layers with iron oxides is confirmed by Kim [252]. Dorfman [254] 834 found recent loess dust sedimentation rates in the Alaskan Arctic Burial Lake of 0.15 mm/a.

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It has been discussed that the alkalinity loss by phytoplankton calcification and CaCO 3 loss 886 with phytoplankton debris from the ocean surface is said to produce calcium and alkalinity

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But if the organic debris is re-oxidized during its journey downwards, some acidification could 893 and changed to organic debris. Sedimentation of organic debris and CaCO 3 , increase both,

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according to the ISA-induced phytoplankton productivity.

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The increasing amount of CaCO 3 sedimentation within iron fertilized ocean regions had been 897 discussed by Salter [262]. In a sufficient mixed ocean, alkalinity loss at the surface is more

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The THC activation by the ISA method is described in the chapters 4.1 -4.3.

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Sudden ISA-induced phytoplankton growth generates increased calcite-shell production. This  930 by assimilation of HCO 3 anions) produces alkalinity as further compensation of the alkalinity loss by calcification. NaHCO 3 reduction/formation to organic carbon generates Na alkalinity.

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The cation previously bound to HCO 3 loses its anion and produces alkalinity. reduced. To reach this goal, we suggest farming fixed filter feeders such as mussels and 943 oysters within the ISA precipitation region.

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Mussels and oysters produce faeces and so called "Pseudo-faeces" in the shape of rather

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To further optimize the CO 2 -C conversion to sediment-bound C the biomass of oysters and 953 mussels including their shells and fixing systems might be periodically dumped into the 954 sediment.

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Additional floating supports such as coral habitats, sponges, sea lilies and sea anemones 956 between the mussel supports might complete and again optimize the ISA precipitation areas.

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The oceanic water deserts can be changed into productive ecosystems and protein sources 958 for an increasing population by these measures, among others, for an optimized CO 2 fixation 959 induced by ISA.

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A further proposal in order to maximize the CO 2 fixation induced by ISA is our suggestion to 961 integrate a solution to the plastic waste problem on the ocean surfaces into the ISA method.

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About 5 to 13 million metric tons of solid plastic waste per year are entering the oceans [275].

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Over the last years the plastic waste drifting on the ocean has developed into a huge

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Through the ISA induced cooling, the oxygen and CO 2 flux into the deep ocean basins will be 1020 restored due to the input of the cold dense oxygen and CO 2 enriched polar surface water:

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Reduced melt water production of the Greenlandic and Antarctic ice shields by falling surface 1022 layer temperatures will restore and intensify the thermohaline circulation within the northern

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Silicon is mobilized too, from the dissolution of silicates and SiO 2 at methanogenic conditions 1074 by complexation with reduced humic acid (HA) [286,291]

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The deep ocean currents take up the pore water percolates out of the sediment, and

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There is no doubt that the efficiency of the pH dependent CO 2 absorption and carbonic acid

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THC is the main transport medium of carbon from the atmosphere into the deep on Earth.

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This makes THC the most prominent climate stabilization element.

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The realization of the significance of THC as stabilization element of our recent climate

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Just that we now have to fear this combination, of both the CO 2 -dependent temperature rise-1285 generated precipitation increase, plus the melt water increase from glacier melt. Mankind has 1286 to find now the appropriate tool to win or to fail this challenge.

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A melt increase might drive the destabilization of THC. And at first the top layers of the ocean 1288 basins will suffer from acidification and the deep layers will become alkaline and anoxic.

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By starting the ISA process, the induced climate cooling will decrease the Greenland glacier

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The oxygen-dependent life will become problematic, due to its decreasing oxygen content

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The glacial age proved that in spite of the multiplicity of the cooling processes induced, they 1473 caused little disturbance to the ecosystems. This predestines ISA as a steering tool to 1474 prevent climate fluctuations such as the recent climate warming mankind is suffering from.

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The present study aims to describe in chapter 5 the technical means to realize this climate 1476 engineering project by the ISA method.

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Iron is the 4 th most abundant element of the earth's crust (4.2%) and thus iron is seldom 1503 deficient, as despite its high abundance in soil, iron solubility is extremely low and its 1504 availability depends of the whole soil system and chemistry.

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Although foliar Fe fertilization seems to be potentially effective, the scientific background for 1531 this practice is still scarce and we did not found evidence that soluble iron contained in 1532 atmospheric dust aerosols has already been proved to be able to play this role.

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The fertilizing role of African dust in the Amazon rainforest is well known

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anticipates that benefits are substantial as timely treatment can restore personal health and 1611 raise national productivity levels by as much as 20%.

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The biofortification of bioavailable iron in staple plants provides a sustainable and 1613 economical tool to use, in order to rescue iron deficiency in target populations globally [420].

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In contrast with fruit trees, where foliar iron fertilization is generally used in chlorotic leaves,

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Amos et al. [432] found support for the hypothesis that Fe(III) mediates CH 4 oxidation in 1644 crude contaminated aquifer.

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Although some iron oxides such as magnetite and hematite have different properties and

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show that upon addition of acetate, production increase of CH 4 is much greater (67 times) 1653 than that of Fe 2+ (2 times), indicating that the two process were acetate limited and

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This Cl generation is four times higher than the reference which corresponds to a significant

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Analogue to CCN behavior in cloud processing [113] most of the small-sized ISA particles 1750 are protected by their small sizes from coagulation or coalescence with sea-salt aerosol 1751 particles. This effect prevents ISA from leaving the optimum active atomic chlorine emission 1752 conditions: low pH and low particle diameter range.

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The residence time difference of more than one order of magnitude in comparison to sea-salt 1754 aerosol further reduces the Fe demand for ISA production from 18 Tg yr -1 to less than 1755 troposphere lower than one day according to its coarse particle diameters without any 1770 possible bridging of intercontinental distances.

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In reality the chloride transfer between sea-salt aerosol particles and ISA particles may take 1772 place without any touch or coagulation, because the troposphere is an acidic environment.

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Troposphere is a source of organic and inorganic acids which are in permanent contact with

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In order to take care not to overstep the cooling effect too far, a reasonable goal might be to Preceding calculation evidenced that the ISA method has the potential to cut back the rise of 1826 CH 4 and CO 2 and, vice versa, the small decline of atmospheric oxygen content [457,458]

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The most important actor in the process of CO 2 C transfer from atmosphere into the Earth 1964 interior is the carbonate C precipitation in the crust rocks and sediments below the ocean.

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The ocean crust acts like a conveyor belt between crust evolution at MOR and its subduction

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That might be efficient enough to deliver the artificial iron aerosol needed over the boundary 2023 widely distributed [485].

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According to Luo [79], deposition of soluble iron from combustion already contributes from 20 2026 to 100% of the soluble iron deposition over many ocean regions.

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As an example we calculated the possible production and emission of the ISA precursor

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One alternative delivery method that seems promising and can easily be adapted to ISA

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Deeper insight into this debate is given by Boyd and Bressac [67].

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The iron fertilization procedure tests done so far had been restricted to relatively small ocean

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The ISA method allows the use of the same atom of iron several times by catalytic and 2084 photocatalytic processes into the atmosphere, with different cooling effects (such as albedo 2085 modification and enhancement of the methane destruction) and then reaches the oceans,

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with further cooling effects such as the enhancement of CO 2 carbon fixation.

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The organic C / carbonate C burial ratio in sediments and bedrock increase after ISA method 2098 start, until a maximum. Then this ratio begins to decrease as soon as the vertical current 2099 components in the ocean basin begin to act. Then the ratio arrives to a very low permanent 2100 level, while the total of buried C arrives at a permanent maximum level when the maximum 2101 vertical mixing conditions have been obtained by the ISA method.

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Why does ISA appear to be more effective than ocean iron fertilization? For ocean iron

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Any stratification event disturbs this cycling and interrupts the CO 2 transport. Climate 2118 warming can induce stratification events by producing huge amounts of melt water. Recent 2119 research found signs of at least regional development of a beginning stratification.

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The numerous climate cooling effects of natural dust show in this review, according to its

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In order to explicitly handle the interaction of climate and biogeochemistry, the complex

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Using mineral dust as a natural analogue tool, this article proposes to enhance the natural 2188 ISA in order to raise and heighten the cooling impacts of at least two of the dozen natural 2189 effects found: i.e. CH 4 removal by tropospheric °Cl and CO 2 removal by soluble-Fe ocean 2190 fertilization.

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The ISA method proposed is feasible, probably with few to no-environmental side-effects, as