Despite the overwhelming evidence that humans are the primary, heck in a realistic sense, the only major contributor to the recent warming experienced by the global climate in the past 3 decades, very little outside of Europe has been done to curb emissions. The United States Senate has sat on a poor, but something climate bill for over a year. China ‘claims’ they will reduce climate intensity, but still continue to build coal plants at a rate of at least 1 per week and with plenty of growth still remaining for its economy a reduction in climate intensity basically does nothing to significantly reduce total emissions. Australia once in line to be the first major emitter outside of the EU to pass major climate legislation has failed considerably. Other ‘developing’ nations like South Africa, Brazil and Russia seem lackadaisical at best in tackling the human emission problem offering small piecemeal actions like ‘maybe we’ll try to stop some people from cutting down more rainforest.’ Clearly barring a 180 change in policy or another global recession/depression it will be decades before global emissions begin to fall at a consistent pace. Unfortunately such a reality creates a significant environmental feedback problem, especially with relation to the loss of Arctic sea ice.
The rate of Arctic ice loss has already considerably outpaced every single prediction made by every single climate model attempting to predict changes in global temperature based on a wide variety of different emission scenarios. The sad, but not surprising, reality is that each year the Arctic loses more and more ice either at its surface or internally (thickness). Although the more highly publicized consequence of ice melt is a significant increase in sea level, which could threaten to flood coastal cities all over the world, the more important issue is the change in Arctic Ocean albedo. White ice reflects a majority of the sunlight that strikes it, but the darker ocean water absorbs more of the sunlight resulting in a faster increasing ocean temperature. An increasing ocean temperature reduces the total gas permeability of the ocean, which reduces its overall effectiveness as a carbon sink. With ocean absorption accounting for about 65-70% (depending on what exact numbers are used) of total natural carbon sink absorption ensuring a maximum absorption rate of a time is an important consideration. With the best solution to save the Arctic, a dramatic reduction in human-derived greenhouse gas emissions, not being probable in the near-future, much to chagrin of most environmentalists, technology must come to the rescue. In short mankind must develop a technological method(s) to hinder, if not reverse the loss of ice trend. Basically it is time to enter the idea phase and below is one to get the ball rolling.
The use of unmanned robots has gained a new sense of familiarity through their role in helping BP seal the breach in the oil well at Deepwater Horizon. What if these robots could be used, after slight modification, to help lessen the loss of Arctic ice? The modification would proceed as follows: a special rectangular compartment would be attached to the dorsal side of the unit. The box would consist of three insulated regions (the bottom, left and right sides) and one highly conductive region (the top). Inside the box would be a supply of liquid nitrogen that would encompass 75-90% of the total area of the box.
The overall idea is that the liquid nitrogen would conductively cool the water in contact with the top portion of the box where hopefully the Leidenfrost effect would be marginalized due to the top portion of the box acting as the cooling element instead of the liquid nitrogen directly. The insulated portions of the box should eliminate any significant conduction in a non-upward direction, basically making the system a one-dimensional conduction in the y-direction. Although such a method may be initially scoffed at due to the sheer volume difference between the robot and the amount of water that would need to be frozen, one must recall that the point of this device is more to ward off further ice melt over actually rebuilding ice mass.
Although action to reduce emissions is still the primary and a mandatory objective, time is moving away from the point where a reduction in emissions will be the only action required to maintain a comfortable living environment. While the suggested device or some similar may not seem practical, the age of practicality is quickly coming to a close when it comes to the environment. Of course such a device must be tested for safety reasons, part of the reason liquid nitrogen is suggested over something like Freon, for any strategy that causes more damage than benefit is clearly not advisable. Some environmentalist are making a big deal about President Obama convening the Interagency Ocean Policy Task Force to study and create policy for oceans, but if such a group is going to act like the NOAA, just ‘studying’ and tracking the increasing levels of acidity and ice melt while putting out solutions that amount to reducing emissions then such a group will not be effective. In short this new group, the NOAA, Scripps, or just some group needs to start developing potential technological solutions to the address the problems that are happening in the ocean beyond the mindset that all that can be done is to reduce emissions and hope.
Showing posts with label ocean acidity. Show all posts
Showing posts with label ocean acidity. Show all posts
Friday, July 23, 2010
Friday, November 13, 2009
A Method to Reduce Ocean Acidity
Background or part 1 for this post can be viewed here:
http://bastionofreason.blogspot.com/2009/09/ocean-acidity-danger-and-remediation.html
The current infeasibility of available oceanic remediation mechanisms is troubling because as previously discussed it does not appear that global CO2 neutrality will be achieved at any point in the near future. This lack of neutrality will lead to further ocean acidity raising the probability of catastrophic loss of ocean biodiversity. Therefore, new strategies need to be proposed in effort to alleviate the problem of ocean acidity. Note that this proposal is theoretical and has not been tested in any way, shape or form.
As the situation currently stands it appears that the most viable economic route to CO2 removal would be to design a piece of technology that could somehow remove the unassociated CO2 from the ocean by facilitating a chemical reaction to bind it and then dissociate from the CO2 at a later time, making the material reusable. This strategy eliminates various problems with the catalytic option used in iron fertilization by anchoring any catalyzing agent to a device and even if needed sequestering it away from any detrimental elements. It also redirects the limiting factor of CO2 turnover to the material that is absorbing the CO2, which is more controllable and can be manipulated more easily than biological organisms or limestone deposits. In addition if the material can be manufactured at reasonable cost, the material being the limiting factor in CO2 absorbed would only be a minor inconvenience. Although such a strategy seems daunting, there is reason to be optimistic. Below is a description of the type of device that may accomplish the desired reduction in acidity.
Considering the solubility factors and the role of the natural carbon cycle, it appears that withdrawing CO2 closer to the surface is preferable. Therefore, it would be useful for the device to behave in similar fashion to a buoy in that the absorption portion of the device would be submerged below the surface, but most of the device remains above the surface. The main reason for this strategy is the fact that permanently submerging the entire unit may be counter-productive as the non-submerged portion could be used to support a solar panel system to power any autonomous actions for the device or some other non-aquatic advantage. Also salvaging the system after reaching maximum CO2 storage would be made more complicated if it were fully submerged.
Due to the sheer size of the ocean, reducing total average acidity without significant removal of atmospheric CO2 is rather farfetched. The principle idea behind the device presented here is not to reduce the acidity of the entire ocean, but instead focus on small critical portions to delay or even prevent the erosion of oceanic biodiversity and food chains. For example it would be difficult to argue that some portion of the Pacific Ocean in the middle of nowhere is of equal importance to oceanic biodiversity to that of the Great Barrier Reef. Granted that it is highly likely that due to the mixing differential of the ocean a point location reduction of acidity would not be straightforward, but by applying continuous acidic reduction pressure at a particular point, there is a high probability that acidity levels at that point will fall faster than will be recouped by mixing. In fact there is a small probability that if significant points of action are established total average ocean acidity throughout the system will be reduced. However, such reduction would not be anything of significance beyond the point locations.
There are a number of different materials that are known to interact with and bind CO2 either as a catalyst or in a chemical reaction (NaOH, different resins, amines, aqueous ammonia, ionic liquids, membranes, etc). Most of these elements have been explored or are currently being used in the design of carbon capture mechanisms for coal power plants. Unfortunately very few of these options, for obvious reasons due to the focus on source capture in power plants, have been tested in aquatic conditions. Another problem is that most of these processes are scaled-up to function over a much larger area than that which would be economically feasible for an ocean CO2 absorbing device. However, metal organic frameworks (MOF), a hybrid material constructed from metal oxide clusters with organic linkers1,2 appear to be a possibility. The reason MOFs are an attractive option is they do not appear to require as much supporting infrastructure as other CO2 absorption materials. Also MOFs have a fairly unique selectivity for CO2, which may increase the efficiency of ‘filtering’ CO2 from other molecules in the ocean while also reducing the probability of contamination and fouling.1
The selectivity of MOF for CO2 is derived from its ability to interact with the large quadrupole moment possessed by CO2.1,3 At certain times CO2 oscillates into a state where its electrons are not evenly distributed (the quadrupole moment). At this point in time based on the molecular arrangement of the particular species of MOF the CO2 binds to the MOF. Technically the quadrupole moment for CO2 is thought to be –4.1 to –4.4 x 10^26 e.s.u. cm^-24,5 Another useful attribute for MOF is the fact that although selective, the bond with CO2 is still rather weak; therefore, less heat and pressure is required to remove the CO2 from the MOF vs. other processes (most notable amine CO2 binding).3 However, it must be noted that similar to the methods listed above, MOF has yet to be tested in an aqueous environment, so there could definitely be some future concerns.
While there are a wide variety of MOFs to choose from, the best option appears to be MOF-177 because so far in empirical studies it has the greatest surface area of all MOF and MOF-similar compounds and has the highest CO2 capacity between all of these compounds.6 MOF-177 has a BET surface area of 4,508-4,750 m^2/g, a bulk density of 0.43 g/cm^3 and absorbs CO2 at a capacity of 1,470 mg/g.6 Note that if covalent organic frameworks (COF) 102 and 103 are much cheaper to produce, they may become viable alternatives to MOF-177.6
Due to the presence of the target CO2 in ocean water, water would need to make contact with the material (probably MOF) doing the binding with CO2, for any attempt to collect out-gassed CO2 would be a rather inefficient means of reducing ocean acidity. There are two primary ways to accomplish this interaction, passive or active. Passive interaction would rely on the natural movement of the water to initiate contact with the material. Active interaction would work to create some form of pressure difference that would draw the water over the material, thus the material would be in contact with the water at certain periods of time instead of random periods of time. For the sole purpose of driving the reaction between the CO2 and the material there does not appear to be a significant difference between passive and active interaction, with the exception that active interaction would require additional energy and/or complexity to power the pump or other drawing mechanism.
Similar to CO2 absorption through technological means via either point source capture or air capture, ocean CO2 absorption has the important lingering question of where to transport the CO2 after absorption. It makes little economic sense to keep the CO2 bound to the material in question; therefore, the CO2 needs to be relocated to an environment where it will not easily re-enter either the atmosphere or the ocean. This question has always been somewhat problematic because there are few options for the collected CO2. As previously discussed in the air capture/sequestration post there are some that would like to utilize capture CO2 in industrial applications like making carbon-neutral fuel, enhancing oil retrieval or augmenting greenhouse-based crop growth; however, none of these options are viable long-term to utilize the amount of CO2 that would be collected and it is difficult to view anything, but enhancing oil retrieval as viable in the short-term. Due to the lack of a viable long-term industrial application and the sheer amount of CO2 that needs to be sequestered, most view storage in natural sinks as the best option.
Based on the specific location of the acidity reduction, storage in sinks could be useful for implementation of such a device. However, if the device is floating on the surface transport to an appropriate storage site could require either a long transfer line or increasing the depth of operation. A short transfer line would not be a significant problem, but when considering that the device will be at a depth of 5-20 ft when on the surface and the typical storage region will have a depth ranging from 5,000-10,000+ ft one could understand how such a long transfer line/pipe would be cumbersome. Therefore, it seems reasonable that the device would have to change depth.
Unfortunately storage in this manner from the device itself is highly unlikely because oceanic sequestration requires that the CO2 be in liquid form, which involves the application of a significant amount of heat and pressure, to be applied within the device, which would probably be largely isolated to a specific compartment. This phase change would provide increased complexity in design because not only would there need to be a separate storage area for the CO2 in gaseous form, but a storage area would be required for CO2 in liquid form as well as the means to generate the necessary levels of heat and pressure. These additional pieces will increase the total weight of the device reducing the maximum capacity of CO2 acquisition and things that could go wrong with the device in general. However, as will be seen, the idea involving a depth changing cycle is still viable.
If direct from the device oceanic sequestration is not rational, then the CO2 collected from the device will need to be manually retrieved and taken to a processing plant to be prepared for sequestration. If this is the case then it is important that the device have as high a maximum capacity for CO2 absorption as possible. It is unlikely that such a capacity can be achieved if passive interaction is used because too little of the material would be in contact with water at a given time. Therefore, it would be wise to create isolated compartments where a large percentage of the environment could contain the material and react with CO2 from water that is moved using active interaction through these areas. However, in order to make the attempt to maximize CO2 capacity mass and density shifts will be expected in the device creating depth changes.
So how will the change in depth be achieved in a device that has the primary function of floating on the surface of the water while trying to maximize CO2 capacity? To best illustrate the process first begin with the question of how a ship floats on water. Basically a ship floats on water because the bulk density of the ship is less than the bulk density of the liquid supporting it (i.e. the water). For reference recall that density is defined as the mass of an object divided by its volume. A ship will no longer float when its density becomes greater than the density of water; most notably this change occurs when the ship’s hull is breached and water begins to flow into the ship increasing its mass. In normal function a ship will sink to an overall depth relative to its density vs. the density of the water (the closer its density is to water the more it will sink). Note that overall object buoyancy is more complex than a simple relationship between densities, (weight related liquid displacement relative to exotically shaped objects and their buoyancy) but for general practice, restricting the discussion to density is fine for non-exotically shaped objects.
Clearly it would be a mistake to breach any portion of the device to induce sinking; however, there is something to be learned from adding water to change the density of the device to initiate sinking. A controlled rate of water acquisition would require compartmentalization and a form of active transport, which is exactly what was proposed to increase CO2 absorption capacity and efficiency. The water would be driven into an alternative compartment(s) in the device via a pump. This alternative compartment would also contain the absorption material. As water continues to flow into these compartments, the device should begin to sink. Once the compartments fill and enough time is allotted for binding reactions, the device can then eject the stored water from the compartments both lowering its density and creating a concentrated jet propulsion stream to hasten its ascent to the surface.
Upon returning to the surface the material should have absorbed a significant amount of CO2 from the water. Regardless of the material, to release the CO2 a considerable amount of heat (temperature increase) will need to be applied. This temperature increase can be achieved through activation of heating units placed on the wall opposite the material. Once released the CO2 will be drawn into a gaseous CO2 storage compartment, which is normally restricted via a valve or some other obstruction. Then the process begins anew with the device changing depth and sinking again.
For this device to function in such a capacity it needs to have a significant level of autonomy. Various sensors and valves (for restricting access) in addition to a centralized computer system would be required. Although difficult to accomplish, autonomous action can also facilitate a form of repeating action or multiple passing, which will increase the probability of reaching the maximum level of CO2 extraction before collecting the CO2 for sequestration. Fortunately the autonomous action elements of the device are not developed for use in a blind environment. Information can be acquired regarding the maximum depth, submergence time, device surface area and volume, etc. which can generate versatile designs for a given region reducing the work required to attain autonomy. For example it is reasonable to know deployment depth, thus timing mechanisms can be utilized to start and end certain processes such as pump action, heating and valve opening and closing.
In some respects think of this device as a significantly more complicated APEX type float. The pump would have to be of greater horsepower and the communication systems more advanced, but the general descent and ascent properties would operate in a similar capacity. The biggest difference is instead of using the pump to transfer fluid to and from a hydraulic bladder, the pump transfers ocean water to and from the MOF absorption regions.
With all that has been said, an example description of how such a device would operate is given below:
The device consists of four units, one main unit and three wing units. The main unit is a sealed rectangle constructed out of titanium or some other non-corrosive metal, which is airtight and houses all of the electronics that issue the commands to facilitate autonomy. The electronics in the main unit are powered by either a lithium-ion battery or a series of solar cells that are positioned on the top of the main unit.
The wing units are attached to the main unit in a way that forms a tripod base structure to aid stability and uniformity of shape when on the surface and sinking and are connected to the main unit through ascending sealed pipes/tubes. The volume of each wing unit is approximately 30%-90% the size of the main unit, the size is dependent on how much space in the main unit is required for the necessary electronics, with a spherical bottom and rectangular top and a centralized ascending pipe sealed by mechanical valves ascending from the spherical bottom. Spherical bottoms are used because the conical shape further aids stability and buoyancy. Behind the valves are grated sieves covering the pipes, which allow for the influx of water, but not elements of significant size like various forms of marine life.
A wing unit has a secondary compartment containing the absorption material that can be sealed off from the main portion of the wing unit. The material, which is MOF-177 in this example, is lined on all of the sidewalls of the rectangular portion of the wing unit. As the water fills the wing unit it will come into contact with the MOF-177. Test results demonstrate that MOF-177 interacts better with CO2 as pressure increases to about 30-40 bars.1,6 However, if such a pressure increase proves to be too complicated or too detrimental within the device (there is a sufficient probability that it may) MOF-177 can still recover CO2 at atmospheric pressure although at a very significant efficiency loss. The external pressure during submersion could aid in the reaction process, but the extent of that aid is unclear if even significant.
Fortunately, the repetitive action of the device should compensate for this efficiency loss. Heating units are sandwiched between the inner wall of the wing unit and an outer wall, which shields the units from the outer environment. These heating units increase the temperature of the inner wall up to at least 70 C to facilitate separation of the CO2 from the MOF. The heating units will automatically shutoff after a preset time determined through empirical study.
The newly freed gaseous CO2 will then be moved to a storage unit attached to the top of each wing unit. These storage units will have a sensor reporting to a base station when the unit is full and will also be detachable so that recovery crews can remove the collected CO2 and transfer it to a storage unit on the recovery ship. The storage unit will then be reattached to the device and the device can be reinitialized. If such a design proves too cumbersome, there is the possibility of storing the CO2 in the main unit with the electrical equipment, but a minor concern of long-term corrosive damage would need to be addressed.
A summary of the lifecycle of the device:
- The device is placed in the water at a point of interest for ocean acidity reduction where it floats/bobs like a buoy on the surface
- after an initial acclimation time the valves in at the bottom of the wing units open and the corresponding pumps activate increasing the uptake of water and the mass of the device causing it to sink - during the uptake of water and the descent of the device the pressure of the water within each wing unit increases to increase the efficiency of the interaction rate between the material and the CO2
- once the carrying capacity of the wing units is reached (identified by a sensor), the pumps reverse action and push the water out of the wing units resulting in the device ascending back to the surface
- once on the surface heating units opposite the material activate separating the CO2 from the material
- after a pre-determined time the heating units turn off, triggering activation of vacuums transferring the free gaseous CO2 from the wing units to the storage units
- the storage units are sealed and the process begins anew.
==
1. Walton, Krista, et, Al. “Understanding Inflections and Steps in Carbon Dioxide Adsorption Isotherms in Metal-Organic Frameworks.” Journal of American Chemical Society. 2008. 130: 406-407.
2. Long, Jeffrey, and Yaghi, Omar. “The pervasive chemistry of metal–organic frameworks.” Chemical Society Reviews. 2009. 38: 1213-1214.
3. Voosen, Paul. “New Material Could Vastly Improve Carbon Capture.” Scientific American Online. June 30, 2009. http://www.scientificamerican.com/article.cfm?id=metal-organic-frameworks-carbon-capture
4. Buckingham, A, and Disch, R. “The Quadrupole Moment of the Carbon Dioxide Molecule.” Proceedings of the Royal Society of London. Mathematical and Physical Sciences. 273(1353): 275-289.
5. Xu, Ruren, Chen, Jiesheng, Gao, Zi, and Yan, Wenfu. From Zeolites to Porous MOF Materials. The 40th Anniversary of International Zeolite Conference. Vol. 170. 2009.
6. Furukawa, Hiroyasu, and Yaghi, Omar. “Storage of Hydrogen, Methane, and Carbon Dioxide in Highly Porous Covalent Organic Frameworks for Clean Energy Applications.” Journal of American Chemical Society. 2009. 131: 8875-8883.
Monday, September 21, 2009
Ocean Acidity: The Danger and the Remediation
One of the more immediate problems with the rapid increase in atmospheric CO2 concentration due to human activities is the sudden shift in ocean acidity. The natural dynamic equilibrium exchange of carbon between the atmosphere and the ocean has existed for eons. For a vast majority of that time, there was little disruption in that exchange for although pH levels have oscillated between 7.3 and 8.2 such oscillation occurred over millions of years at a slow and steady pace.1 However, the excess CO2 that is being released into the atmosphere in the last 200 years, largely due to burning fossil fuels and deforestation, has accelerated oceanic uptake of atmospheric CO2 in effort to maintain the carbon concentration equilibriums. This additional uptake over a much shorter time frame than that of the past has created a concern regarding the adaptation and survival ability of oceanic flora and fauna.
Recall that when CO2 dissolves in water it forms carbonic acid eventually leading to the reactionary increase in ocean acidity (additional hydrogen atoms are contributed from the breakdown of carbonic acid). In fact CO2 absorption has reduced surface pH (increased acidity) by approximately 0.1 in the last decade after over 100 million years of steady decrease in acidity.1,2,3 Calcium carbonate becomes thermodynamically less stable as oceanic acidity increases, due to reducing concentrations of carbonate, a result tied to the increase in CO2 concentration, increasing the metabolic cost to organisms when constructing calcium carbonate-based infrastructure (shells and skeletons).
In fact the Southern Ocean near Antarctica is already experiencing significant acidification far beyond anywhere else in the world and this increase is having a negative influence on the ability of G. bulloides to build their shells.4 Similar results in calcification rates have also been seen in the Arabian Sea for other similar calcium carbonate shell builders.5 This negative influence limits the ability of the ocean to expand CO2 uptake from the atmosphere without increasing acidity due to reduction in sedimentation burial. In addition this infrastructure instability disrupts a variety of different and important food chains.
There are some that believe nature will be able to adapt to these acidity changes because the Arctic and Southern Ocean regions have life that is more used to higher acidity conditions, but this mindset comes off as rather naïve optimism. The most popular example relating to this belief is the analogy that a 5 degree average temperature increase in Phoenix will not faze its residence as much as a 5 degree average temperature increase in Siberia (or some other cold region). However, such an example irrationally seems to mitigate the fact that pH exists on a log scale, thus even small changes are significant to a given life form, hence why most life, without special ‘millions of years in the making’ adaptation, can only exist within a very small range of pH. It does not matter whether one lives in Phoenix or Siberia, dealing with consistent 120 degree temperatures that arise suddenly is a burden that will have significant influence on livelihood. In fact over 65 million years ago ocean acidification was linked to mass extinctions of calcareous marine organisms,6 it would be foolish to assume that a more rapid acidity increase would fail to replicate this extinction in due time.
Another influencing factor when considering ocean acidity is ocean temperature. It is common chemistry that gas solubility in a liquid decreases as temperature increases because increasing temperature increases available kinetic energy which increases molecule movement. Greater molecule movement increases the probability of bond breaking which reduces the ability of the gas to remain in solution. There is no argument that global temperatures both on land and in the ocean are increasing; therefore, as these temperatures go up it is likely that the overall capacity of the ocean to absorb excess CO2 from the atmosphere will decrease and cause the ocean to release CO2 into the atmosphere.
Releasing CO2 into the atmosphere until a new equilibrium is achieved may slightly increase ocean pH (lower ocean acidity), but the problem is that the magnitude or timing of such a reaction is completely unknown. The ocean cannot be viewed so simply as a giant beaker of water sitting on a bench in a laboratory, so applying any simplistic CO2 solubility curve to determine when any switch from sink to source for the ocean may occur is naïve. Regardless of when the ocean begins to naturally decrease in acidity due to decreased CO2 solubility, it is reasonable to believe that ocean acidity levels will not naturally drop below their present level. Therefore, despite the potential for CO2 release at some point in the future, the issue of ocean acidity still needs to be addressed in the near future.
The rate of calcium carbonate precipitation is an important element in determining the sink capacity of the ocean and the total expected acidity change because calcium carbonate has a tendency to be removed through gravitational settling.1 Considering this removal due to calcium carbonate precipitation is important because despite the total sum of dissolved carbon species (DIC) decreasing, the remaining carbon shifts its balance in favor of pure CO2 (aq) increasing the higher partial pressure of CO2 in the ocean.1 The reason for the shift is the loss of CO3 which drives the aqueous carbonate equilibrium reaction [CO2 (aq) + CO32- + H2O ↔ 2HCO3] to the left to compensate.1
However, dissolution of calcium carbonate, frees more carbonate ions, resulting in an opposite shift reducing oceanic concentration of CO2 enhancing atmospheric CO2 acquisition. Basically precipitation of carbonate reduces CO2 uptake from the atmosphere whereas dissolution of carbonate increases CO2 uptake from the atmosphere. Remember that because both the carbonic acid and the calcium carbonate are in equilibrium, loss of reactionary species typically CO32-, will be influenced by Le Chatlier’s principal.
However, a second factor in this process of CO2 exchange must be considered, the interaction and association between particulate organic carbon and calcium carbonate concentration shifts.7,8 A decrease in calcium carbonate reduces the rate and effectiveness of moving particulate organic carbon to deeper waters, thus weakening the biological pump portion of oceanic CO2 absorption method.1 This result reduces the total CO2 sink capacity of biological denizens of the ocean like phytoplankton.9,10 So an impasse exists in that does decreasing the concentration of calcium carbonate increase oceanic sink capacity or decrease oceanic sink capacity? Currently there is no good answer to that question.
Regardless of the correct answer it cannot be debated that the ocean is becoming more acidic due to an increased rate in uptake of atmospheric CO2, the only thing up for debate is the rate of acidity change. Also it is important to note that any geo-engineering strategy to ward of atmospheric global warming that does not result in the removal of CO2 from the atmosphere will have no ability to reduce the rate of acidification. In fact such geo-engineering methods may actually increase ocean acidity by delaying any CO2 release from the ocean due to temperature increases.
Unfortunately the atmospheric-oceanic exchange is the not the only contribution to increased ocean acidity. Increasing surface temperatures have destabilized methane hydrate stored in sediments beneath the seabed throughout various portions of the ocean. Due to the accelerated warming in the Arctic, most of the new methane hydrate destabilizations are originating in the Arctic and Southern Oceans and areas along the continental shelf.11 The good news/bad news aspect of this destabilization is that most of the methane is absorbed/dissolved in an upper layer of the ocean before it is able to fully escape into the atmosphere, thus only a small percentage of this released methane will immediately influence global warming. Unfortunately it does not stay as methane for long in the ocean as methanotrophs interact with this methane converting it into CO2 not only further increasing ocean acidity, but also increasing the concentration of CO2 in the ocean which will eventually cause the ocean to become a source of atmospheric CO2 instead of a sink for atmospheric CO2. However, unlike the solubility change due to temperature increase scenario, the acidity will not go down because for all of the CO2 released more methane will be converted to CO2 to take the place of the released CO2. The final side detriment to this methane hydrate release is that in the process of converting the methane to CO2 the methanotrophs use oxygen which creates the high probability for hypoxic or anoxic conditions within the localized region of ocean.
With the continuing increase in acidity and the negative influence it seems to be having on oceanic fauna, a remediation strategy is needed before permanent damage occurs. Unfortunately the best option, significantly reducing the concentration of CO2 released into the atmosphere from human based sources, which would eventually reverse the process of ocean CO2 absorption, is decades away, if it happens at all; therefore an alternative stabilizing strategy needs to be considered.
The most straightforward means to reduce ocean acidity would be to speed the removal of unassociated (free) CO2 from the ocean. Reducing free CO2 would in turn reduce the probability of carbonic acid formation and the resultant equilibrium shifts. One of the first ideas that comes to mind would be iron fertilization, but unfortunately iron fertilization does not appear to be as useful as advertised,12,13 especially where it counts in the Southern and Arctic Oceans.
Another idea that has gained some backing in recent years is thermally decomposing limestone into CO2 and calcium oxide and then depositing the calcium oxide into the ocean to facilitate a chemical reaction to sequester CO2. When dumped into the ocean the calcium oxide reacts with water forming calcium hydroxide. Finally the calcium hydroxide reacts with free dissolved CO2 in the ocean creating calcium bicarbonate. The three primary chemical reactions governing this strategy are shown below.
Unfortunately there are some concerns that significantly reduce the viability of this option. First, the reaction rate between calcium hydroxide and CO2 is contingent on many factors, similar to most chemical reactions most notably pH, pressure and temperature. Also CO2 within the ocean is still rather dilute, which further lowers the probability of reaction. Realistically it is logical to anticipate some inefficiency or non-reaction from the total amount of calcium hydroxide. Therefore, an estimate of 1.6 to 1.8 moles of CO2 reacted per 1 mole of calcium hydroxide in the ocean seems more realistic.
Although some of the benefit was lost, so far so good as the process still removes more CO2 than it generates, right? Not necessarily, second most of the proponents of this strategy play-down that the limestone needs to be processed and that requires significant amounts of heat energy (800-900 C). It takes approximately 2.67 GJ (741.67 kw-h) to calcinate 1 ton of limestone.
Looking at general power sources that could provide that energy, coal typically produces 1 ton of CO2 per 1000 kw-h of electricity, which would put the process on the edge of being carbon positive/negative unless calcium hydroxide reaction efficiency was higher than anticipated, so coal is out. Oil cannot be used because of a continuing dwindling supply and the emission profile is not much better as although it remains carbon negative (approximately 1300 kw-h per 1 ton of CO2) the ratio drops to about 0.1-0.3 tons of CO2 per ton of calcium hydroxide). Natural gas is a bit better, depending on the total efficiency of the combustion, 2,000 to 2,500 kw-h of electricity per 1 ton of CO2 emitted; however, using natural gas would still require the generation of 0.297 to 0.371 tons of CO2, which would take a bite out of the overall CO2 absorption. Overall it does not seem to matter whether the source of the energy provider is stranded or not because the resultant CO2 emission would put unacceptable economic burden on the overall removal ability of the process. Therefore, it appears that a zero carbon emission energy source will have to be used to generate the calcium oxide from limestone to ensure appropriate economical action.
The additional CO2 produced aside, another problem is the shear cost of the electricity to run the process. For example in the United States using an average of 11 cents per kW-h conversion of 1 ton of limestone would cost $81.58. Taking that cost and expanding it to calculate the cost of removing 1 net ton of CO2 from the ocean assuming a zero carbon emission source is used to generate the power, zero transportation emissions (highly unlikely) and a high efficiency reaction of 1.8 moles of CO2 from the ocean and it would currently cost approximately $102 to remove 1 net ton of CO2 from the ocean with this process, just for the energy required for the limestone conversion alone. Assuming that 100% of all of the CO2 produced from the limestone conversion reaction were sequestered the cost would drop to $45.32 per net ton of CO2, but that cost is not absolute because of the cost uncertainty associated with the capture and sequestration processes. Finally in order to generate a reasonably pure CO2 product stream during the limestone reaction either co-firing with limestone, fuel/electricity source and oxygen or separation of the heating/calcine reactions will have to take place increasing the probability of greater cost.
Overall the initial calculations project the limestone strategy to not be economically attractive. However, clearly it is worth paying a price to avoid severe and detrimental climate change, which would cost much more in the long run. Unfortunately the cost may not be the only problem with the limestone strategy. Currently there has been very little practical application of the limestone strategy through discussion of exactly how the calcium oxide would be distributed throughout the ocean. This lack of discussion is a problem because it is very unrealistic to expect a widespread distribution strategy to be successful largely because first the ocean is rather huge. Second, the transport emissions associated with widespread distribution would almost certainly switch the process from slightly carbon negative to definitely carbon positive, and that does not include the associated transportation costs. Remember there are no viable zero emission planes, zero emission ships would probably be too inefficient in transport time and the cost to create infrastructure for new zero emission trains would be backbreaking.
Based on these two problems it appears that the best option is a localized release. Initially this result may seem beneficial because of the large limestone deposits located at Nullarbor Plain, Australia. However, localized distribution also has a significant problem, rate of deposit. If too much calcium oxide is depsoited into the ocean over too short a timeframe and/or area then it is highly possible that a pH shift in the opposite direction would occur in that localized region significantly reducing the biodiversity of the deposit region. If too little calcium oxide is deposited into the ocean then the overall CO2 removal process would be far too slow to make any real difference in averting climate change or reducing ocean acidity and the entire process itself could be viewed as a waste of time and money. Therefore, a proper despoit rate over a given localized area would need to be determined, a determination that appears to be difficult to do in the lab. Also even if a proper balance was determined, another lingering problem is that although the ocean does mix, calcium oxide interaction over a small localized region would probably induce faster reaction over ocean mixing and atmospheric uptake which would further reduce the efficiency of the reaction and the prospect of it being carbon negative. Overall it appears that the total amount of limestone, energy and cost required for the above strategy provide too great of obstacles to make this an effective strategy for remediation of atmospheric or oceanic CO2 at the current time.
With more natural methods lacking efficiency perhaps a more technological strategy to facilitate CO2 removal is necessary. One advantage with the deployment of such a solution is that it does not need to be scaled-up to reduce the acidity of the entire ocean. Due to the non-uniformity of oceanic flora and fauna, technologies can be designed and applied to higher density and biologically and/or commercially important regions to reduce localized levels of acidity to increase survivability. Note that it is important that any technology eliminate the acidity at the localized region not simply divert it elsewhere further increasing the acidity levels at non-targeted regions of the ocean because due to ocean mixing such a strategy would not achieve the desired goal, even in the short-term. At a later time such a device will be proposed here at the Bastion of Reason that will hopefully provide a means to reduce ocean acidity.
--
1. Ridgwell, Andy, and Zeebe, Richard. “The role of the global carbonate cycle in the regulation and evolution of the Earth system.” Earth and Planetary Science Letters. 2005. 234: 299– 315.
2. Caldeira, K, and Wickett, M. “Anthropogenic carbon and ocean pH.” Nature. 2003. 425: 365.
3. Keeling, C, and Whorf, T. “Atmospheric CO2 records from sites in the SIO air sampling network, Trends: A Compendium of Data on Global Change.” Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., USA, 2004. (http://cdiac.esd.ornl.gov/trends/co2/sio-mlo.htm).
4. Moy, Andrew, et, Al. “Reduced calcification in modern Southern Ocean planktonic foraminifera.” Nature Geoscience. 2009. 2: 276 – 280.
5. del Moel, H, et, Al. “Planktic foraminiferal shell thinning in the Arabian Sea due to anthropogenic ocean acidification?” Biogeosciences Discussions. 2009. 6(1): pp.1811-1835.
6. Hood, Maria, et, Al. “Ocean Acidification: A Summary for Policymakers from the Second Symposium on the Ocean in a High-CO2 World.” Intergovernmental Oceanographic Commission of UNESCO.
7. Armstrong, R, et, Al. “A new, mechanistic model for organic carbon fluxes in the ocean: based on the quantitative association of POC with ballast minerals.” Deep-Sea Res. 2002. Part II 49: 219–236.
8. Klaas, C, Archer, D. “Association of sinking organic matter with various types of mineral ballast in the deep sea: implications for the rain ratio.” Glob. Biogeochem Cycles. 2002. 16(4): 1116.
9. Ridgwell, Andy. “An end to the ‘rain ratio’ reign?” Geochem. Geophys. Geosyst. 2003. 4(6): 1051.
10. Barker, S, et, Al. “The Future of the Carbon Cycle: Review, Calcification response, Ballast and Feedback on Atmospheric CO2.” Philos. Trans. R. Soc. A. 2003. 361: 1977.
11. Natural Environmental Research Council. http://www.noc.soton.ac.uk/nocs/news.php?action=display_news&idx=628
12. “Lohafex project provides new insights on plankton ecology: Only small amounts of atmospheric carbon dioxide fixed.” International Polar Year. March 23, 2009.
13. Black, Richard. “Setback for climate technical fix.” BBC News. March 23, 2009.
Recall that when CO2 dissolves in water it forms carbonic acid eventually leading to the reactionary increase in ocean acidity (additional hydrogen atoms are contributed from the breakdown of carbonic acid). In fact CO2 absorption has reduced surface pH (increased acidity) by approximately 0.1 in the last decade after over 100 million years of steady decrease in acidity.1,2,3 Calcium carbonate becomes thermodynamically less stable as oceanic acidity increases, due to reducing concentrations of carbonate, a result tied to the increase in CO2 concentration, increasing the metabolic cost to organisms when constructing calcium carbonate-based infrastructure (shells and skeletons).
In fact the Southern Ocean near Antarctica is already experiencing significant acidification far beyond anywhere else in the world and this increase is having a negative influence on the ability of G. bulloides to build their shells.4 Similar results in calcification rates have also been seen in the Arabian Sea for other similar calcium carbonate shell builders.5 This negative influence limits the ability of the ocean to expand CO2 uptake from the atmosphere without increasing acidity due to reduction in sedimentation burial. In addition this infrastructure instability disrupts a variety of different and important food chains.
There are some that believe nature will be able to adapt to these acidity changes because the Arctic and Southern Ocean regions have life that is more used to higher acidity conditions, but this mindset comes off as rather naïve optimism. The most popular example relating to this belief is the analogy that a 5 degree average temperature increase in Phoenix will not faze its residence as much as a 5 degree average temperature increase in Siberia (or some other cold region). However, such an example irrationally seems to mitigate the fact that pH exists on a log scale, thus even small changes are significant to a given life form, hence why most life, without special ‘millions of years in the making’ adaptation, can only exist within a very small range of pH. It does not matter whether one lives in Phoenix or Siberia, dealing with consistent 120 degree temperatures that arise suddenly is a burden that will have significant influence on livelihood. In fact over 65 million years ago ocean acidification was linked to mass extinctions of calcareous marine organisms,6 it would be foolish to assume that a more rapid acidity increase would fail to replicate this extinction in due time.
Another influencing factor when considering ocean acidity is ocean temperature. It is common chemistry that gas solubility in a liquid decreases as temperature increases because increasing temperature increases available kinetic energy which increases molecule movement. Greater molecule movement increases the probability of bond breaking which reduces the ability of the gas to remain in solution. There is no argument that global temperatures both on land and in the ocean are increasing; therefore, as these temperatures go up it is likely that the overall capacity of the ocean to absorb excess CO2 from the atmosphere will decrease and cause the ocean to release CO2 into the atmosphere.
Releasing CO2 into the atmosphere until a new equilibrium is achieved may slightly increase ocean pH (lower ocean acidity), but the problem is that the magnitude or timing of such a reaction is completely unknown. The ocean cannot be viewed so simply as a giant beaker of water sitting on a bench in a laboratory, so applying any simplistic CO2 solubility curve to determine when any switch from sink to source for the ocean may occur is naïve. Regardless of when the ocean begins to naturally decrease in acidity due to decreased CO2 solubility, it is reasonable to believe that ocean acidity levels will not naturally drop below their present level. Therefore, despite the potential for CO2 release at some point in the future, the issue of ocean acidity still needs to be addressed in the near future.
The rate of calcium carbonate precipitation is an important element in determining the sink capacity of the ocean and the total expected acidity change because calcium carbonate has a tendency to be removed through gravitational settling.1 Considering this removal due to calcium carbonate precipitation is important because despite the total sum of dissolved carbon species (DIC) decreasing, the remaining carbon shifts its balance in favor of pure CO2 (aq) increasing the higher partial pressure of CO2 in the ocean.1 The reason for the shift is the loss of CO3 which drives the aqueous carbonate equilibrium reaction [CO2 (aq) + CO32- + H2O ↔ 2HCO3] to the left to compensate.1
However, dissolution of calcium carbonate, frees more carbonate ions, resulting in an opposite shift reducing oceanic concentration of CO2 enhancing atmospheric CO2 acquisition. Basically precipitation of carbonate reduces CO2 uptake from the atmosphere whereas dissolution of carbonate increases CO2 uptake from the atmosphere. Remember that because both the carbonic acid and the calcium carbonate are in equilibrium, loss of reactionary species typically CO32-, will be influenced by Le Chatlier’s principal.
However, a second factor in this process of CO2 exchange must be considered, the interaction and association between particulate organic carbon and calcium carbonate concentration shifts.7,8 A decrease in calcium carbonate reduces the rate and effectiveness of moving particulate organic carbon to deeper waters, thus weakening the biological pump portion of oceanic CO2 absorption method.1 This result reduces the total CO2 sink capacity of biological denizens of the ocean like phytoplankton.9,10 So an impasse exists in that does decreasing the concentration of calcium carbonate increase oceanic sink capacity or decrease oceanic sink capacity? Currently there is no good answer to that question.
Regardless of the correct answer it cannot be debated that the ocean is becoming more acidic due to an increased rate in uptake of atmospheric CO2, the only thing up for debate is the rate of acidity change. Also it is important to note that any geo-engineering strategy to ward of atmospheric global warming that does not result in the removal of CO2 from the atmosphere will have no ability to reduce the rate of acidification. In fact such geo-engineering methods may actually increase ocean acidity by delaying any CO2 release from the ocean due to temperature increases.
Unfortunately the atmospheric-oceanic exchange is the not the only contribution to increased ocean acidity. Increasing surface temperatures have destabilized methane hydrate stored in sediments beneath the seabed throughout various portions of the ocean. Due to the accelerated warming in the Arctic, most of the new methane hydrate destabilizations are originating in the Arctic and Southern Oceans and areas along the continental shelf.11 The good news/bad news aspect of this destabilization is that most of the methane is absorbed/dissolved in an upper layer of the ocean before it is able to fully escape into the atmosphere, thus only a small percentage of this released methane will immediately influence global warming. Unfortunately it does not stay as methane for long in the ocean as methanotrophs interact with this methane converting it into CO2 not only further increasing ocean acidity, but also increasing the concentration of CO2 in the ocean which will eventually cause the ocean to become a source of atmospheric CO2 instead of a sink for atmospheric CO2. However, unlike the solubility change due to temperature increase scenario, the acidity will not go down because for all of the CO2 released more methane will be converted to CO2 to take the place of the released CO2. The final side detriment to this methane hydrate release is that in the process of converting the methane to CO2 the methanotrophs use oxygen which creates the high probability for hypoxic or anoxic conditions within the localized region of ocean.
With the continuing increase in acidity and the negative influence it seems to be having on oceanic fauna, a remediation strategy is needed before permanent damage occurs. Unfortunately the best option, significantly reducing the concentration of CO2 released into the atmosphere from human based sources, which would eventually reverse the process of ocean CO2 absorption, is decades away, if it happens at all; therefore an alternative stabilizing strategy needs to be considered.
The most straightforward means to reduce ocean acidity would be to speed the removal of unassociated (free) CO2 from the ocean. Reducing free CO2 would in turn reduce the probability of carbonic acid formation and the resultant equilibrium shifts. One of the first ideas that comes to mind would be iron fertilization, but unfortunately iron fertilization does not appear to be as useful as advertised,12,13 especially where it counts in the Southern and Arctic Oceans.
Another idea that has gained some backing in recent years is thermally decomposing limestone into CO2 and calcium oxide and then depositing the calcium oxide into the ocean to facilitate a chemical reaction to sequester CO2. When dumped into the ocean the calcium oxide reacts with water forming calcium hydroxide. Finally the calcium hydroxide reacts with free dissolved CO2 in the ocean creating calcium bicarbonate. The three primary chemical reactions governing this strategy are shown below.
Unfortunately there are some concerns that significantly reduce the viability of this option. First, the reaction rate between calcium hydroxide and CO2 is contingent on many factors, similar to most chemical reactions most notably pH, pressure and temperature. Also CO2 within the ocean is still rather dilute, which further lowers the probability of reaction. Realistically it is logical to anticipate some inefficiency or non-reaction from the total amount of calcium hydroxide. Therefore, an estimate of 1.6 to 1.8 moles of CO2 reacted per 1 mole of calcium hydroxide in the ocean seems more realistic.
Although some of the benefit was lost, so far so good as the process still removes more CO2 than it generates, right? Not necessarily, second most of the proponents of this strategy play-down that the limestone needs to be processed and that requires significant amounts of heat energy (800-900 C). It takes approximately 2.67 GJ (741.67 kw-h) to calcinate 1 ton of limestone.
Looking at general power sources that could provide that energy, coal typically produces 1 ton of CO2 per 1000 kw-h of electricity, which would put the process on the edge of being carbon positive/negative unless calcium hydroxide reaction efficiency was higher than anticipated, so coal is out. Oil cannot be used because of a continuing dwindling supply and the emission profile is not much better as although it remains carbon negative (approximately 1300 kw-h per 1 ton of CO2) the ratio drops to about 0.1-0.3 tons of CO2 per ton of calcium hydroxide). Natural gas is a bit better, depending on the total efficiency of the combustion, 2,000 to 2,500 kw-h of electricity per 1 ton of CO2 emitted; however, using natural gas would still require the generation of 0.297 to 0.371 tons of CO2, which would take a bite out of the overall CO2 absorption. Overall it does not seem to matter whether the source of the energy provider is stranded or not because the resultant CO2 emission would put unacceptable economic burden on the overall removal ability of the process. Therefore, it appears that a zero carbon emission energy source will have to be used to generate the calcium oxide from limestone to ensure appropriate economical action.
The additional CO2 produced aside, another problem is the shear cost of the electricity to run the process. For example in the United States using an average of 11 cents per kW-h conversion of 1 ton of limestone would cost $81.58. Taking that cost and expanding it to calculate the cost of removing 1 net ton of CO2 from the ocean assuming a zero carbon emission source is used to generate the power, zero transportation emissions (highly unlikely) and a high efficiency reaction of 1.8 moles of CO2 from the ocean and it would currently cost approximately $102 to remove 1 net ton of CO2 from the ocean with this process, just for the energy required for the limestone conversion alone. Assuming that 100% of all of the CO2 produced from the limestone conversion reaction were sequestered the cost would drop to $45.32 per net ton of CO2, but that cost is not absolute because of the cost uncertainty associated with the capture and sequestration processes. Finally in order to generate a reasonably pure CO2 product stream during the limestone reaction either co-firing with limestone, fuel/electricity source and oxygen or separation of the heating/calcine reactions will have to take place increasing the probability of greater cost.
Overall the initial calculations project the limestone strategy to not be economically attractive. However, clearly it is worth paying a price to avoid severe and detrimental climate change, which would cost much more in the long run. Unfortunately the cost may not be the only problem with the limestone strategy. Currently there has been very little practical application of the limestone strategy through discussion of exactly how the calcium oxide would be distributed throughout the ocean. This lack of discussion is a problem because it is very unrealistic to expect a widespread distribution strategy to be successful largely because first the ocean is rather huge. Second, the transport emissions associated with widespread distribution would almost certainly switch the process from slightly carbon negative to definitely carbon positive, and that does not include the associated transportation costs. Remember there are no viable zero emission planes, zero emission ships would probably be too inefficient in transport time and the cost to create infrastructure for new zero emission trains would be backbreaking.
Based on these two problems it appears that the best option is a localized release. Initially this result may seem beneficial because of the large limestone deposits located at Nullarbor Plain, Australia. However, localized distribution also has a significant problem, rate of deposit. If too much calcium oxide is depsoited into the ocean over too short a timeframe and/or area then it is highly possible that a pH shift in the opposite direction would occur in that localized region significantly reducing the biodiversity of the deposit region. If too little calcium oxide is deposited into the ocean then the overall CO2 removal process would be far too slow to make any real difference in averting climate change or reducing ocean acidity and the entire process itself could be viewed as a waste of time and money. Therefore, a proper despoit rate over a given localized area would need to be determined, a determination that appears to be difficult to do in the lab. Also even if a proper balance was determined, another lingering problem is that although the ocean does mix, calcium oxide interaction over a small localized region would probably induce faster reaction over ocean mixing and atmospheric uptake which would further reduce the efficiency of the reaction and the prospect of it being carbon negative. Overall it appears that the total amount of limestone, energy and cost required for the above strategy provide too great of obstacles to make this an effective strategy for remediation of atmospheric or oceanic CO2 at the current time.
With more natural methods lacking efficiency perhaps a more technological strategy to facilitate CO2 removal is necessary. One advantage with the deployment of such a solution is that it does not need to be scaled-up to reduce the acidity of the entire ocean. Due to the non-uniformity of oceanic flora and fauna, technologies can be designed and applied to higher density and biologically and/or commercially important regions to reduce localized levels of acidity to increase survivability. Note that it is important that any technology eliminate the acidity at the localized region not simply divert it elsewhere further increasing the acidity levels at non-targeted regions of the ocean because due to ocean mixing such a strategy would not achieve the desired goal, even in the short-term. At a later time such a device will be proposed here at the Bastion of Reason that will hopefully provide a means to reduce ocean acidity.
--
1. Ridgwell, Andy, and Zeebe, Richard. “The role of the global carbonate cycle in the regulation and evolution of the Earth system.” Earth and Planetary Science Letters. 2005. 234: 299– 315.
2. Caldeira, K, and Wickett, M. “Anthropogenic carbon and ocean pH.” Nature. 2003. 425: 365.
3. Keeling, C, and Whorf, T. “Atmospheric CO2 records from sites in the SIO air sampling network, Trends: A Compendium of Data on Global Change.” Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., USA, 2004. (http://cdiac.esd.ornl.gov/trends/co2/sio-mlo.htm).
4. Moy, Andrew, et, Al. “Reduced calcification in modern Southern Ocean planktonic foraminifera.” Nature Geoscience. 2009. 2: 276 – 280.
5. del Moel, H, et, Al. “Planktic foraminiferal shell thinning in the Arabian Sea due to anthropogenic ocean acidification?” Biogeosciences Discussions. 2009. 6(1): pp.1811-1835.
6. Hood, Maria, et, Al. “Ocean Acidification: A Summary for Policymakers from the Second Symposium on the Ocean in a High-CO2 World.” Intergovernmental Oceanographic Commission of UNESCO.
7. Armstrong, R, et, Al. “A new, mechanistic model for organic carbon fluxes in the ocean: based on the quantitative association of POC with ballast minerals.” Deep-Sea Res. 2002. Part II 49: 219–236.
8. Klaas, C, Archer, D. “Association of sinking organic matter with various types of mineral ballast in the deep sea: implications for the rain ratio.” Glob. Biogeochem Cycles. 2002. 16(4): 1116.
9. Ridgwell, Andy. “An end to the ‘rain ratio’ reign?” Geochem. Geophys. Geosyst. 2003. 4(6): 1051.
10. Barker, S, et, Al. “The Future of the Carbon Cycle: Review, Calcification response, Ballast and Feedback on Atmospheric CO2.” Philos. Trans. R. Soc. A. 2003. 361: 1977.
11. Natural Environmental Research Council. http://www.noc.soton.ac.uk/nocs/news.php?action=display_news&idx=628
12. “Lohafex project provides new insights on plankton ecology: Only small amounts of atmospheric carbon dioxide fixed.” International Polar Year. March 23, 2009.
13. Black, Richard. “Setback for climate technical fix.” BBC News. March 23, 2009.
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