Assessing ocean alkalinity for carbon sequestration

In the paper

“Dissolution of a mole of Ca 2+ or Mg 2+ sequesters close to 2 moles of C (see section 2).”

In the paper

“In practice the uptake is 1.4 to 1.7 molecules because of the presence of some CO3 2-, (i.e. a reduction of uptake efficiency, η, by 15% -30%), depending on temperature, salinity and pCO2 (equation 23; see supporting information for derivation [Dickson, 1990]).”

What the sources say

• Not checked yetcites Dickson, 1990

In the paper

“Addition of sufficient Ca 2+ to fully compensate for present anthropogenic emission of 10 Gt C a -1 therefore requires addition of 20 Gt Ca 2+ a -1 .”

In the paper

“The increased alkalinity flux in the right hand panels prevents the significant changes in atmosphere CO2 and ocean pH seen in the left-hand figures.”

In the paper

“Even if considering the surface ocean alone this annual addition is less than a 0.3% increase in total Ca 2+ .”

In the paper

“The large volume of the ocean and its high Ca 2+ concentration, however, mean that the oceanic perturbation is very much smaller and only a 0.9 mmoles kg -1 increase in Ca 2+ is required.”

In the paper

“There would be approximately 200 Mt of Si released for every Gt of olivine added to the ocean, so it is not surprising that a significant fertilization effect is observed.”

In the paper

“This is ≈20 times the annual riverine input of Ca 2+ , a very significant perturbation, and obviously a very substantial undertaking in engineering terms.”

In the paper

“However, this work suggests some of the proposals to have a range of energy requirements and financial costs comparable to more widely studied alternatives (e.g., 1-10 GJ tCO2 -1 , $50 -150 tCO2 -1 ).”

In the paper

“On long-timescales (~100-200 ka) the ocean and weathering will reduce atmospheric CO2 to values close to pre-industrial [Lord et al., 2016].”

What the sources say

• Not checked yetcites Lord et al., 2016

In the paper

“It may be possible to sequester hundreds of billions to trillions of tonnes of C without surpassing post-industrial average carbonate saturation states in the surface ocean.”

In the paper

“Sequestration of inorganic C in the ocean is the least represented climate mitigation strategies in the literature [Bellamy et al., 2012].”

What the sources say

• Not checked yetcites Bellamy et al., 2012

In the paper

“This RCP explicitly includes 40 -220 Gt C of negative emissions [Edenhofer, 2014].”

What the sources say

• Not checked yetcites Edenhofer, 2014

In the paper

“With current conventional fossil fuel reserves ~3,000 Gt C [McGlade and Ekins 2015], carbon storage requirements could extend to thousands of Gt.”

What the sources say

• Not checked yetcites McGlade and Ekins 2015

In the paper

“This has led to considerable uncertainty about the potential storage capacity, environmental impact, and cost of this approach [NAS 2015].”

What the sources say

• Not checked yetcites NAS 2015

In the paper

“The feasibility of such approaches is still highly contested given the slower dissolution kinetics at ambient temperatures and pressures, and the solubility limits of naturally occurring minerals.”

In the paper

“It may be possible to store additional carbon in this sink to mitigate climate change at costs that are comparable to conventional mitigation”

In the paper

“Despite this work, AWL research has been largely confined to small-scale experiments.”

In the paper

“So even dissolution of carbonate minerals (e.g., CaCO3) which contain a mole of C leads to some drawdown of CO2.”

In the paper

“Estimates of carbon storage in this reservoir are on the order of 100-1,000 Gt C [Bradshaw et al., 2007]”

What the sources say

• Not checked yetcites Bradshaw et al., 2007

In the paper

“While the kinetics of this process would be rapid, the energy requirements are substantial (section 5).”

In the paper

“The resulting decrease of dissolved CO2 causes uptake of atmospheric CO2 by air-sea gas exchange.”

In the paper

“At the pH of seawater, most of C (≈80-90%) is in the singly-charged HCO3 -form (see Box 1).”

In the paper

“This, coupled to a decrease in calcite solubility with increasing pressure, means that at some depth in the ocean, termed the calcite saturation horizon, water become undersaturated for calcite (Figure 4; [see Zeebe 2012]).”

What the sources say

• Not checked yetcites Zeebe 2012

In the paper

“The products of silicate weathering (e.g., equation 2) therefore have potential to make a larger impact on CO2 removal if they reach the ocean than if they re-precipitate as secondary minerals.”

In the paper

“Weathering of silicates on land can remove CO2 from the atmosphere without involving the ocean if the cations releases are all re-precipitated as secondary minerals (e.g., CaCO3) on land”

In the paper

“At slightly greater depththe lysoclinedissolution rates are sufficiently fast that sediment start to lose an appreciable fraction of the calcite settling from above.”

In the paper

“It is possible to constrain and calculate (at known temperature and salinity) the concentrations of [CO2(aq)] [HCO3 -], [CO3 2-], pH, DIC, Alkalinity, by only knowing two of the parameters.”

What the sources say

• Not checked yetcites Zeebe and Wolf-Gladrow 2001

In the paper

“However, the slightly alkaline pH of ocean water is likely to retard dissolution kinetics so that very small particles are needed [Hangx and Spiers 2009].”

What the sources say

• Not checked yetcites Hangx and Spiers 2009

In the paper

“To a first approximation, the active oceanic cycle of alkalinity is that of Ca 2+ , and particularly the processes of formation and dissolution of CaCO3 (Figure 3 A).”

In the paper

“Where γCa and γCO3 represent the activity coefficients of calcium and carbonate ions respectively, which are difficult to constrain in ionic solutes like seawater [see Mucci 1983]”

What the sources say

• Not checked yetcites Mucci 1983

In the paper

“Upwelling of deep elevated alkalinity waters to the surface, which typically happens at high latitudes in the ocean, leads to surface variation in alkalinity of about 5% (Figure 5).”

In the paper

“By removing alkalinity, biological production of CaCO3 from surface seawater leads to a flux of CO2 from the ocean to the atmosphere [Frankignoulle et al., 1994].”

What the sources say

• Not checked yetcites Frankignoulle et al., 1994

In the paper

“Addition of ions with a divalent charge, such as Ca 2+ , is therefore compensated by formation of two singly-charged ions containing C, and consequently to uptake of two CO2 molecules from the atmosphere.”

In the paper

“It serves to partially neutralize the acidity generated by remineralization of organic matter; a process termed carbonate compensation [Ridgwell and Zeebe, 2005].”

What the sources say

• Not checked yetcites Ridgwell and Zeebe, 2005

In the paper

“The divalent cations present in carbonate minerals (e.g., CaCO3) mean that even weathering of carbonates can lead to removal of CO2 from the atmosphere.”

In the paper

“This deep-ocean dissolution of CaCO3 leads to an increases in alkalinity of up to 10% relative to surface waters.”

In the paper

“This is in contrast to the biological production of organic C (i.e.soft tissue), which causes subsequent ocean uptake of CO2.”

In the paper

“By increasing saturation state, alkalinity addition could keep the ocean at a saturation state conducive to continued coral reef health.”

In the paper

“It is likely that alkalinity addition could not be the sole mechanism used for any substantial negative emissions approach, but would be part of a portfolio of measures.”

In the paper

“This effect is therefore a long-term negative feedback.”

In the paper

“Ilyina et al., [2013], for instance, used the Hamburg Ocean Carbon Cycle Model to simulate the response to the addition of sufficient alkalinity to counteract all anthropogenic emissions from the 'business as usual' A1B baseline scenario (≈1,400 Gt C by 2100).”

What the sources say

• Not checked yetcites Ilyina et al., [2013]

In the paper

“Through transport, mixing, and export, elevated alkalinity at the surface will also eventually have an impact on conditions in the interior ocean.”

In the paper

“Elevated alkalinity in the water column will increase the carbon compensation depth (CCD; the depth in the oceans at which calcite dissolves quicker than it is supplied; [Ridgwell 2007]).”

What the sources say

• Not checked yetcites Ridgwell 2007

In the paper

“Keller et al., [2014] (using the UVic model) also imposed a uniform alkalinity addition, but limited the amount of addition to that which could be delivered by modern ship fleets (≈6 Gt Ca 2+ a -1 as Ca(OH)2 added by uniformly increasing total alkalinity).”

What the sources say

• Not checked yetcites Keller et al., [2014]

In the paper

“This level of addition created only modest uptake of CO2 from the atmosphere (166 Gt C by 2100; ~8% of the A1B/RCP8.5emissions scenario).”

What the sources say

• Not checked yetcites Keller et al., [2014]

In the paper

“If CO2 is removed from the atmosphere, terrestrial carbon sinks would release CO2 [e.g., Vichi et al., 2013].”

What the sources say

• Not checked yetcites Vichi et al., 2013

In the paper

“Natural silica flux into the ocean is approximately 170 Mt of Si a -1 (e.g., from riverine input) [Tréguer et al., 1995].”

What the sources say

• Not checked yetcites Tréguer et al., 1995

In the paper

“However some of this alkalinity will eventually be returned to the surface through upwelling.”

In the paper

“This partially undoes the effect of adding alkalinity.”

In the paper

“However, this may decrease if alkalinity is reduced by increased formation and export of carbonate minerals from the surface ocean.”

In the paper

“[2016] used a fully integrated Earth System Model and added sufficient alkalinity to compensate emissions from RCP8.5 to a level congruent with RCP4.5.”

What the sources say

• Not checked yetcites Ferrer-Gonzalez and Ilyina [2016]

In the paper

“This 'rebound' together with emissions from material extraction, processing and transport would also diminish the net sequestration potential of this and other alkalinity addition approaches”

In the paper

“In that study, sufficient alkalinity was added to exactly compensate for pH changes imposed by fossil fuel addition, which was possible even in their largest emission scenario (compensating for 5,000 Gt C over 500 years) by adding up to 15 Gt Ca 2+ a -1 ).”

What the sources say

• Not checked yetcites Paquay and Zeebe [2013]

In the paper

“However, Hermoso [2015] demonstrated a parabolic relationship between pH (and Ω) and growth rate for the same species.”

What the sources say

• Not checked yetcites Hermoso [2015]

In the paper

“There have been extensive laboratory studies investigating carbonate precipitation in seawater for 'seeded' experiments (i.e.there is nuclei mineral surface in contact with the solution, Figure 12), in which the rate is proportional to the saturation state through equation 24 [see Inskeep and Bloom 1985].”

What the sources say

• Not checked yetcites Inskeep and Bloom 1985

In the paper

“Providing the ratio of POC to PIC is > 1, the organic carbon export would offset the CO2 emission associated with the counter carbonate pump.”

In the paper

“By regulating the concentration of Ca 2+ , CO2 and pH they can express a high degree of control on the internal saturation state of carbonate minerals.”

In the paper

“There is considerable variation in the mechanisms of calcification [Müller, 2011] which result in species/genus variability to environmental stimuli.”

What the sources say

• Not checked yetcites Müller, 2011

In the paper

“This suggests that the calcification rate of O. universa would increase around 12% for a future ocean with Ωcalcite = 7.”

In the paper

“As such, this approach only provides a limited constraint on the impact of elevated alkalinity on calcification rate.”

In the paper

“As such, increased export of inorganic carbon due to increased biological calcification, may also result in increased organic carbon export.”

In the paper

“As ocean acidification is concerned largely with [CO2 (aq)] and the resulting decrease in [CO3 2-], it is difficult to interpret ocean acidification results for ocean alkalinity carbon storage, which would promote a different relationship between [CO2 (aq)] and [CO3 2-].”

In the paper

“Both species showed a reduction in calcification at elevated calcite saturation, possibly in response to lower concentrations of aqueous CO2.”

What the sources say

• Not checked yetcites Langer et al., [2006]

In the paper

“Given the relatively low specific gravity of organic molecules (often <1), their aggregation with inorganic carbon is the mechanism by which they sink out of the surface ocean (often referred to as 'ballasting', [Alldredge and Silver 1988;Klaas and Archer 2002]).”

What the sources say

• Not checked yetcites Alldredge and Silver 1988
• Not checked yetcites Klaas and Archer 2002

In the paper

“For instance, Barker and Elderfield [2002] derive a relationship between [CO3 2-] of seawater to the shell mass of Orbulina universa (a planktonic foraminifera) picked from sediment.”

What the sources say

• Not checked yetcites Barker and Elderfield [2002]

In the paper

“For instance, it is possible to modify dissolved inorganic carbon (DIC) while maintaining constant pH to create conditions in which pCO2 and Ωcalcite are simultaneously elevated [Rickaby et al., 2010].”

What the sources say

• Not checked yetcites Rickaby et al., 2010

In the paper

“Due to other environmental factors influencing shell mass during growth, there is weak significance in most of the shell mass-[CO3 2-] experimental relationships.”

In the paper

“If precipitation occurs on re-suspended sediment, the availability of a carbonate surface area for nucleation is an important control for carbonate precipitation from seawater.”

In the paper

“Generally, species that are more efficient at maintaining pH in the internal environment in which they calcify are less affected by changes in carbonate chemistry of the ambient environment.[Bach et al., 2011;Broecker et al., 2001;Comeau et al., 2009;Gattuso et al., 1998;Hermoso 2015;Hoppe et al., 2011;Iglesias-Rodriguez et al., 2008;Langdon et al., 2000;Langdon and Atkinson 2005;Langer et al., 2”

What the sources say

• Not checked yetcites Bach et al., 2011
• Not checked yetcites Broecker et al., 2001
• Not checked yetcites Comeau et al., 2009

In the paper

“They produce carbonate minerals in controlled microenvironments within the cell [Marsh 2003].”

What the sources say

• Not checked yetcites Marsh 2003

In the paper

“This approach yields various sensitives from experimental studies on a range of organisms (increases from 12 to 79%) [Aldridge et al., 2012;Beer et al., 2010;Marshall et al., 2013].”

What the sources say

• Not checked yetcites Aldridge et al., 2012
• Not checked yetcites Beer et al., 2010
• Not checked yetcites Marshall et al., 2013

In the paper

“However, if this change was directly translated into elevated PIC export (with no impact on carbon returned to the surface through upwelling) then a future increase of ocean alkalinity [e.g., Ferrer-González and Ilyina 2016] would result in a net flux of ~0.5-4 Gt C out of the surface ocean.”

What the sources say

• Not checked yetcites Ferrer-González and Ilyina 2016

In the paper

“Figure 12 suggests that a precipitation rate of around 10 -5 moles m -2 h -1 would be expected for seawater (Ωcalcite = 3-4) seeded with carbonate minerals.”

In the paper

“Spontaneous ('unseeded') nucleation of carbonate minerals is thought to contribute little to carbonate production and export from the surface ocean [Pytkowicz 1965].”

What the sources say

• Not checked yetcites Pytkowicz 1965

In the paper

“This inhibition is not apparent for aragonite, in which there is an order of magnitude less Mg 2+ adsorption onto the precipitating surface [Berner 1975;Mucci and Morse 1983].”

What the sources say

• Not checked yetcites Berner 1975
• Not checked yetcites Mucci and Morse 1983

In the paper

“Similar to phosphate, the presence of sulfate ions (SO4 2-) in solution has been shown to inhibit the precipitation of calcite [Bots et al., 2011;Busenberg and Plummer 1985;Fernández-Díaz et al., 2010;Tang et al., 2012].”

What the sources say

• Not checked yetcites Bots et al., 2011
• Not checked yetcites Busenberg and Plummer 1985
• Not checked yetcites Fernández-Díaz et al., 2010

In the paper

“The presence of phosphate ions (PO4 3-) in seawater has been shown to inhibit calcite precipitation [Burton and Walter 1990;Mucci 1986] through adsorption onto the calcite surface (equation 26).”

What the sources say

• Not checked yetcites Burton and Walter 1990
• Not checked yetcites Mucci 1986

In the paper

“Ground olivine could be fed into a (single-stage) mineral carbonation reactor (at elevated pCO2).This produces magnesite and silica (equation 28).”

What the sources say

• Not checked yetcites Renforth and Kruger [2013]

In the paper

“Both studies investigated elevated initial phosphate concentrations (up to 100's of µmoles of P kg -1 ) with respect to typical surface ocean concentrations (<1 µmole kg -1 ).”

What the sources say

• Not checked yetcites Burton and Walter 1990
• Not checked yetcites Mucci 1986

In the paper

“The concentration is larger in coastal areas (2.5-3.7 μg C l -1 ) compared to the open ocean (0.7 -2.8 μg C l -1 ).”

What the sources say

• Not checked yetcites Balch et al., [2005]

In the paper

“However, given the elevated saturation state of aragonite in seawater (Table S1 in the supporting information [Ball and Nordstrom 1991;Parkhurst et al., 1980;Parkhurst and Appelo 1999;Pilson 1998; U.S. Environmental Protection Agency 1998]), some form of inhibition must be occurring.”

What the sources say

• Not checked yetcites Ball and Nordstrom 1991
• Not checked yetcites Parkhurst et al., 1980
• Not checked yetcites Parkhurst and Appelo 1999

In the paper

“The availability of carbonate mineral surface area in the ocean is therefore critical in upscaling the laboratory derived precipitation rates.”

In the paper

“However, based on these measurements, the volumetric surface area of carbonate minerals in the mixed layer could be between 10 -6.3 and 10 -3.2 m 2 l -1 .”

In the paper

“Accounting for carbon and energy balances across the whole life cycle, the technoeconomics of this approach was assessed by Renforth et al., [2013], for calcite and dolomite feedstocks.”

What the sources say

• Not checked yetcites Renforth et al., [2013]

In the paper

“Using satellite derived Moderate-Resolution Imaging Spectroradiometer data, Balch et al., [2005] present surface particulate inorganic carbon concentrations for a number of oceanic regions.”

What the sources say

• Not checked yetcites Balch et al., [2005]

In the paper

“This surface area is notionally provided by resuspended sediment in whiting events on continental shelves [Morse et al., 2003].”

What the sources say

• Not checked yetcites Morse et al., 2003

In the paper

“Clearly, the larger value is inconsistent with measurements of carbonate production in the ocean carbon cycle (2 Gt C y -1 ).”

In the paper

“Therefore, a magnesium to calcium concentration ratio of 5.1 (typical of the surface ocean) would reduce the ion activity product by 45% compared to a magnesium free solution.”

In the paper

“However applying a range of efficiency scenarios and energy emission intensities, House et al., [2007] suggest that an optimistic scenario (70% efficiency for electrolysis and fuel cell generation, on a 10 moles kg -1 NaCl solution) would require between 3 and 18 GJ per t CO2.”

What the sources say

• Not checked yetcites House et al., [2007]

In the paper

“Therefore, between 1 and 3.5 tons of raw material will need to be extracted for every ton of CO2 captured.”

In the paper

“Increasing the liquid-gas ratio increases the capture efficiency until a maximum is reached, after which the efficiency starts to decrease as CO2 in the gas is used to suppress the natural buffering of seawater rather than promoting carbonate dissolution.”

In the paper

“Therefore, a coal fired power station producing 500 MW and 0.5 t CO2 s -1 will require around 900 m 3 s -1 of seawater”

In the paper

“Seawater brought into equilibrium with 15% CO2 and calcite will be able to sequester 0.53 t CO2 per kt of seawater [Caldeira and Rau 2000].”

What the sources say

• Not checked yetcites Caldeira and Rau 2000

In the paper

“A similar energy expenditure (7.6 GJe per t CO2) was calculated if silicate minerals rather than carbonates were dissolved at the anode in seawater [Rau et al., 2013].”

What the sources say

• Not checked yetcites Rau et al., 2013

In the paper

“However, due to the energy penalty from water evaporation in the kiln, and the additional energy required to grind the olivine, the energy savings over CaCO3 calcination appear to be minimal.”

What the sources say

• Not checked yetcites Renforth and Kruger [2013]

In the paper

“More pessimistic efficiencies are unlikely to be carbon negative when exploiting anything but a decarbonized energy sector.”

In the paper

“However, such a scheme reduces the constraints on plant location (rather than being next to the emission point source it could be located to exploit unused renewable energy)”

In the paper

“To overcome the CO2 geological sequestration burden of ocean liming, House et al., [2007] proposed a method to increase aqueous NaOH through direct electrolysis of seawater (Figure 17).”

What the sources say

• Not checked yetcites House et al., [2007]

In the paper

“A number of multi-step mineral carbonation processes promote the creation of Mg(OH)2 as part of the overall reaction to capture carbon dioxide from point sources as MgCO3 [Fagerlund et al., 2012;Madeddu et al., 2014;Nduagu et al., 2012].”

What the sources say

• Not checked yetcites Fagerlund et al., 2012
• Not checked yetcites Madeddu et al., 2014
• Not checked yetcites Nduagu et al., 2012

In the paper

“Given the water requirements, the AWL reactor must be located adjacent to the coast.”

In the paper

“Future CO2 emissions will decrease the pH further.”

In the paper

“Increasing ocean alkalinity will proportionally decrease the RF by around 0.15 to 0.19 (for every % change in alkalinity there will be a 0.15% to 0.19% decrease in RF, Figure 21).”

In the paper

“Figure 20 shows that addition rates would have to be several orders of magnitude larger than suggested in Renforth et al., [2013] before a significant and extended impact on pH was observed”

What the sources say

• Not checked yetcites Renforth et al., [2013]

In the paper

“The cumulative effect of regional alkalinity addition over decades may produce conditions with the potential significant ecosystem impact [e.g., Ilyina et al., 2013].”

What the sources say

• Not checked yetcites Ilyina et al., 2013

In the paper

“The consequences for organisms that precipitate extracellular carbonate (e.g., corals) is somewhat starker [Hoegh-Guldberg et al., 2007].”

What the sources say

• Not checked yetcites Hoegh-Guldberg et al., 2007

In the paper

“Compared to the distributed global impact, the localized impact of increased alkalinity appears to be more substantial.”

In the paper

“However, these effects would be highly transient in the open ocean.”

In the paper

“Moosdorf et al., [2014] demonstrated that large distances can be covered with minimal impact on the CO2 budget of enhanced weathering proposals.”

What the sources say

• Not checked yetcites Moosdorf et al., [2014]

In the paper

“Even if sufficient alkalinity were introduced to the ocean mitigate all of anthropogenic CO2 emissions for the next 100 years, it is not anticipated to greatly exceed 4 mEq kg -1 .”

In the paper

“The addition of silicate minerals to the ocean could have a substantial fertilization effect from the dissolution of iron and silica in the material [Köhler et al., 2013].”

What the sources say

• Not checked yetcites Köhler et al., 2013

In the paper

“Compared to an existing fleet of 50,000, this represents a small expansion.”

In the paper

“However, sustaining this growth rate for an additional 20 years would create 10 Gt of capacity.”

In the paper

“The proportion of Fe or Si dissolved and liberated is likely to be a fraction of the total added in the olivine, although it is difficult to predict [Hauck et al., 2016].”

What the sources say

• Not checked yetcites Hauck et al., 2016

In the paper

“Transport over land incurs substantially more cost (energy and financial) than over the ocean (see supporting information Table S4, [CEFIC 2011;Davis et al., 2011]).”

What the sources say

• Not checked yetcites CEFIC 2011
• Not checked yetcites Davis et al., 2011

In the paper

“A growth rate of 12% would need to be sustained for 45 to 60 years to create 1 Gt worth of production capacity (based on an initial capacity of 1 -5 Mt a -1 ).”

In the paper

“However, it may be several years before this signal is detectable above the background seasonal variability (0 -0.08 mEq kg -1 ).”

In the paper

“However, the effects may be more significant in poorly mixed waters, waters with existing hypoxia, and sediments and soils.”

In the paper

“A rock with a fayalite to forsterite mass ratio of 1:9 (FeO 7%) would consume approximately 12 g O2 for every kg dissolved.”

In the paper

“Scott et al., [2005] found reduced sodium uptake and ammonia excretion in Perca fluviatilis (Perch) exposed to a pH 9.5 (through potassium hydroxide addition).”

What the sources say

• Not checked yetcites Scott et al., [2005]

In the paper

“This demonstrates the relative sensitivity of species to large transient doses of Ca(OH)2.”

In the paper

“However, at one of the treatment sites they report a considerable reduction in the survival rate the stock (although pH remained at ambient levels).”

What the sources say

• Not checked yetcites Switzer et al., [2011]

In the paper

“Further to biological oxygen removal, fayalite (Fe2SiO4), the iron end member of olivine is composed of Fe 2+ which oxidizes to Fe 3+ during dissolution in the presence of oxygen ( [Schott and Berner 1985]; equation 34).”

What the sources say

• Not checked yetcites Schott and Berner 1985

In the paper

“However, in the case of ocean fertilization the Parties to the London Convention and the London Protocol determined in 2008 that the scope of the London Convention and Protocol includes ocean fertilization activities' due to significant risk that such placement would be contrary”

What the sources say

• Not checked yetcites IMO 2003

In the paper

“This suggests that an addition of 0.005 -0.015 mEq kg -1 a -1 could be detected.”

In the paper

“However, the application rate of alkalinity would need to be large to have the desired effect.”

In the paper

“An ophiolite may contain between 0 and 20% FeO [Miyashiro 1975].”

What the sources say

• Not checked yetcites Miyashiro 1975

In the paper

“All autotrophic organisms have evolved strategies to concentrate carbon during photosynthesis.This is to compensate CO2 undersaturation in the modern atmosphere (and thus ocean) for Rubisco (the enzyme which catalyzes photosynthesis; Henderson et al., 2008).”

What the sources say

• Not checked yetcites Henderson et al., 2008

In the paper

“A key limitation will likely be the ability to collect the appropriate amount of samples/data in a short enough time period to accurately quantify alkalinity changes across the whole ocean.”

In the paper

“Although in a modest lime addition scenario (Keller et al., [2014]; equating to cumulative draw down of around 160 Gt C by 2100) no change in dissolved O2 was demonstrated.”

What the sources say

• Not checked yetcites Keller et al., [2014]

In the paper

“A column of water in the mixed layer (1 m 2 by 60 m deep) could contain on the order of 10 moles of O2 (~200 moles kg -1 , [Stramma et al., 2008]).”

What the sources say

• Not checked yetcites Stramma et al., 2008

In the paper

“It is possible to achieve precision of less than 0.005 mEq kg -1 (0.02%) in routine measurements of seawater alkalinity [Dickson et al., 2007].”

What the sources say

• Not checked yetcites Dickson et al., 2007

In the paper

“For instance, reduced rates of carbon and nitrogen fixation have been demonstrated in cyanobacterium Trichodesmium (an important primary producer) at low pCO2 [Hutchins et al., 2007;Ramos et al., 2007].”

What the sources say

• Not checked yetcites Hutchins et al., 2007
• Not checked yetcites Ramos et al., 2007

In the paper

“It would therefore take around 25 kg m -2 of rapidly dissolving rock to completely remove O2 as it sank through the water column.”

In the paper

“The remainder is re-mineralized into dissolved aqueous species (into CO2, HCO3 -and CO3 2-).”

In the paper

“However, all require the extraction, processing, and reaction of rocks.”

In the paper

“and may be able to store trillions of tons of CO2 with limited changes in bulk chemistry.”