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One of the important variables in this chemical balance is carbon dioxide CO2. As CO2 dissolves in water, the water becomes mildly acidic (clean rain water has a pH=5.6 to 6; in the diagram 5.7), enough in fact to dissolve calcium from soils and to create dripstone formations inside caves while it evaporates. Intuitively one may think that a doubling in CO2 would result in a doubling of acidity but this is not the case as this graph shows. Without CO2, pure rain water would have a neutral pH of 7.0, and that is where the graph begins on  left. Initially CO2 is very willing to dissolve, thereby rapidly acidifying the otherwise pure water, but eventually this slows down. The red dot is placed at the current situation with CO2 around 350ppm at average temperature and pressure. From here a doubling in CO2 will contribute to a much reduced acidification of only 0.15 pH units or an increase in acidity of around 30%. Note that this is not just a theoretical curve but has been measured by titration. This behaviour of CO2 also applies to sea water, but here the situation is much more complicated due to the buffering effect of limestone.

CO2 'binds' with water like:  CO2 + H2O <=> H2CO3 <=> H⁺  +  HCO3^-  <=> H⁺ + H⁺ + CO3^2-

In this equilibrium equation the double arrow <=> means 'in balance' (equilibrium) or that the chemical reaction can move both ways. The symbols H, O and C stand for hydrogen, oxygen and carbon and their numbers are given by the digit following. The superscripted + and - and 2- symbol denotes their ionised states with loose electrons. In the right hand side are more H⁺ ions, which are measured by a pH meter as 'more acidic'. Of the four 'states' that CO2 can assume, carbondioxide CO2 is a mere 1%, bicarbonate HCO3 is 93% and carbonate CO3 8% . But the total amount of carbon dissolved in the oceans is just short of 40,000Gt (Pg) compared with less than 700Gt in the atmosphere. The sea is a massive carbon dioxide reservoir, in balance with an even more massive limestone reservoir of 40,000,000Gt carbon in marine sediments .
 

Note that the above equations depend somewhat on pressure and also on temperature. The graph shows how CO2 dissolves according to temperature in an atmosphere of pure CO2, but degassing can be assumed to behave similarly for lesser concentrations (60/2000= 3% per degree C; some say 4%). Applied to an ocean of 38,000 Gt CO2, would equate to 1140Gt/ºC or 12/44 x 1140 = 311GtC/ºC. Note that gigaton Gt, one billion metric tonnes, is the same measure as petagram Pg, but we'll use Gt in this chapter and that the atmospher now holds about 700Gt carbon. [To convert from CO2 to C, multiply by 12/44.] Note also that these measurements hold for pure water and 100% CO2 and are not necessarily valid for sea water and low concentrations of CO2. Note also that human emissions are about 7GtC per year.

This equation is a gross simplification of the seawater system because seawater has many more elements that are likely to play a role. One of these is Calcium (Ca²⁺) which 'binds' with CO3 like: Ca²⁺  +  CO3^2- <=> CaCO3  to form limestone as in corals and shells. There exist several forms of limestone, but this is only a finer point (aragonite, calcite, magnesium calcite, ...). The production of limestone by organisms is called calcification. De-calcification on the other hand can be done either by organisms who calcify (echinoderms for instance) or those who dissolve limestone (boring sponges, worms, molluscs, many bacteria) and it can also happen chemically without organisms (coral sand dissolving back into sea water).

It is thought that the carbondioxide in the sea exists in equilibrium with that of exposed rock and bottom sediment containing limestone CaCO3 (or sea shells for that matter). In other words, that the element calcium exists in equilibrium with CO3. But the concentration of Ca (411ppm) is 10.4 mmol/l and that of all CO2 species (90ppm) 2.05 mmol/l, of which CO3 is about 6%, thus 0.12 mmol/l. Thus the sea has a vast oversupply of calcium. It is difficult therefore to accept that decalcification could be a problem as CO3 increases. To the contrary, it should be of benefit to calcifying organisms. Thus the more CO2, the more limestone is deposited. This has also been borne out by measurements (Budyko 1977).

The bit missing at the beginning is that CO2 (atmosphere) <=> CO2 (sea water) or in other words, that the carbondioxide in the air is in balance with that in the surface water, which has not been proved. Note in this respect that rising water temperatures will expel CO2  from this huge reservoir and in doing so, also raise acidity.

It is reasoned that if the amount of CO2 in the atmosphere rises, then more of it will dissolve in the water, working all the way through the chemical reactions, to an increase in acidity and an increase in carbonate CO3. Scientists believe that the sea in pre-industrial times was 'saturated' relative to dissolved limestone, and that recent increases in CO2 have 'desaturated' the sea (beginning in the antarctic sea), with possible dire consequences for sea life. But we have observed that calcium skeletons dissolve back into what scientists call 'saturated' CO3.
 

0704123: the shell of a shield limpet (Scutus antipodes) is normally enclosed within its body, but once exposed to sea water, it begins to dissolve. Here its growth rings have been etched out by nothing more than clean salt water. Boring worms have also been at work. The limpet is a calcifier and the seawater a decalcifier.

f019010: the pink knobbly mass is a crustose coralline alga, spread like a single stony leaf over the underlying rock. Coralline algae are the most important reef builders in the world, also in coral reefs. Here the limestone has been drilled into by a yellow boring sponge Clione celata. The pink alga is a calcifier and the yellow sponge a decalcifier.

f991224: shelly beaches disappearing everywhere in the world because their resupply from live shells is disappearing as shellfish beds and coral reefs are dying. Rainwater and seawater dissolve the shells, broken shells and coral sand.

f046431: closeup of a coral wall at an exposed site (Niue) shows an even matrix of coralline algae, drilled into by molluscs (piddocks). No hard corals here. The holes are expanded by little sea urchins who come out by night to graze the green algae that grow on the coralline 'paint'.

f046532: Porites massive corals form layer upon layer with nothing inbetween. They are the main coral reef builders amongst the corals. The reef is filled in by coralline algae. Notice how the coral polyps are designed to catch sunlight rather than zooplankton. Note also that no part of the skeleton is directly exposed to seawater.

f221523: ancient coral rock has been carved out by salt water and rain, showing the original corals that lived there over 300,000 years ago (Niue). The softer matrix of coralline algae has been decalcified by very clean water. The detail shown in these excavated corals is indeed amazing.

My personal experience with acidity in the ocean stems from many pH measurements that led to the discovery of half a dozen elementary ecological laws that, if confirmed, would turn the whole acid ocean debate on its head. It would in fact send most publications on this subject to the dustbin. That was in 2005, and mainstream scientists have not reacted since. So let's review what these discoveries are about (read the DDA chapter):

• The most important ecological factor in the sea has been overlooked: the guild of decomposing bacteria. They are very active and cause disease and infection. The health of sea water depends on their numbers as all marine organisms live in a delicate balance between the food that plankton brings (soup) and the chance of dying from decomposing bacteria (sewage). Each sea organism thus lives in a precarious balance between the good life (thick soup) and a long life (thin sewage), which are in conflict with one another. This is what I named the plankton balance.
• Alkalinity in the ocean depends substantially on the plankton balance in which the pH results from autotrophs (plants) using hydrogen ions and driving the pH up, while decomposers return hydrogen ions, thus driving the pH down. The daily rhythm can amount to 0.4pH units (250%), and the difference between estuaries and the open sea as much as 1-2 units (1000-10,000%). It is important to keep this in mind, as one can find healthy calcification in shells in these conditions. When seas become eutrophied (overnourished), they also become more acidic due to high levels of decomposing bacteria and their work. Particularly coastal seas show this.
• The most important limiting factor in aquatic ecosystem is the dearth of hydrogen ions (H⁺), which has also been overlooked. The more acidic the water, the higher biological productivity becomes, and the denser the amount of life. In the sea this is borne out by the observed fact that highly productive upwelling areas are more acidic [note 1 below]. In other words, acidic seas are a good thing.
• A serious scientific mistake was not recognising that decomposition cannot completely break organic matter down into inorganic salts. There are conversion losses and the second law of thermodynamics forbids this. So there is an intermediate organic molecule that is neither a nutrient for plants (dissolved salts), nor food for bacteria. My measurements showed that the sea is awash in this mysterious substance that I named slush (like partly molten snow). In fact the biomass in slush is far larger than all life on Earth combined. Reader please note that this is a very serious omission by mainstream science, and cannot be disproved! The other 5 laws tie in closely with this.
• Life on this planet would never have been possible, if slush could not be decomposed further. The only way for this to happen is when plants team up with decomposing bacteria in the act of symbiotic decomposition, where the missing energy is supplied by the plant to allow decomposers to complete the last step in decomposition. This explains how corals can grow where nutrients are severely limited, and it explains why seaweeds are more productive with symbiotic decomposition than without.
• The most important benefit obtained from symbiotic decomposition is firstly hydrogen ions, since these are in shortest supply, and secondly nutrients, and finally CO2 in a form ready to use. The hydrogen ions lower pH on the skins of marine plants (and some phytoplankton), as well as on the skins of coral polyps. In this cocoon of reduced pH, these organisms can be more productive than without.

Since it was first published, a tsunami of me-too publications have seen print, but objective analysis from a wide angle of perspective, is still missing. Most scientific articles are not free, as if scientists have so much to hide. But fortunately the two most important ones are still free, Impacts of ocean acidification .. report of a workshop by NSF, NOAA, USGS (PDF) by J A Kleypas et al. and a clumsy report from the Royal Society UK: Ocean acidification due to increasing atmospheric carbon dioxide (PDF) but which has high educational value. Much has been done with computer models, but these are only as valid as their underlying assumptions, and can neither be proved right nor wrong.

Note1: In upwelling areas, cool deep water reaches the photic (light-) zone. This water is more acidic and it also contains nutrients. Those nutrients were produced from sinking biomatter that became decomposed by bacteria, in darkness underneath the photic zone. As the nutrients became available as soluble salts, also the water became more acidic (less alkaline). In the process, also more CO2 dissolved into the water. When the deep water reaches the surface, the nutrients start plankton blooms which also make the water more alkaline, which in turn limits productivity. However, it is observed that upwelling areas remain relatively acidic, thereby promoting productivity. It could also be that a high turnover of nutrients, possible by active planktonic decomposition, lowers pH in upwelling areas.

It is an important message that I want you to take home and keep in the back of your mind whenever you read about marine science or planetary science. It is a message for scientists too.
 

Dead planet thinking: most oceanographers, physicists, chemists treat the planet as a dead planet, where every force, every process can be described and captured in an equation, and then simulated by a computer. But life frustrates every attempt, as it corrupts equations, while also adapting to changing circumstances. Of all these, the sea is the worst with its unimaginable scale, complexity and influence. We may never be able to unravel the secrets of the sea.

Opening with these thoughts, the (bio)chemistry of the sea is so complicated and unknown that the scare for acidic oceans is entirely unjustified. It is true that humans should act from a position of humility and prudence, adjusting to nature while never exploiting more than 30% of the environment but we have gone far over that limit. Today nature is adjusting to us and we cannot change that without a much smaller human population and much less waste (CO2 is part of human waste). Well, that is not going to happen. So we have to accept that nature is now changing. An important part of that is an increase of the life-bringing gas carbondioxide. With higher CO2 levels, plants will produce more. Hopefully the world will become warmer too, and all this is welcome to the starving billions. As oceans become more acidic, they will become more productive too, adjusting to the new scenario. There will be no 'tipping points' but there could be some unexpected and unforeseen surprises. The world has been changing and adapting to major changes since it came out of the last ice age, and the changes caused by fossil fuel will be relatively small.

As far as the science of ocean acidification goes, there are some major errors and conflicts, and the amount of missing knowledge is much larger than what we know. Scientists have uncritically accepted the findings of the IPCC with critically low 'pre-industrial' levels of CO2, but has anyone tried to grow plants and seedlings at 180ppmv CO2?

Kleypas et al (2006) state "It is certain that net production of CaCO3 will decrease in the future", and then place at highest priority for future research "Determine the calcification response to elevated CO2 in . . [just about every marine organism with a shell]", and ".. in many cases even the sign of the biochemical response, let alone the magnitude, is uncertain". Clearly this is an unscientific and contradictory statement in the light of present ignorance (not knowledge). Their advice is to do more studies in elevated CO2, but will they also look at reduced levels of 180ppm (the hypothetical pre-industrial level)? It is not in their list of recommendations.
Will they also evaluate my own discoveries of slush and symbiotic decomposition by which organisms live inside a 'cocoon' of lower pH for higher productivity? Not likely - they have ignored it completely since 2005.

What annoys me is that an entirely hypothetical threat is blown up out of all proportions, while at the same time the foremost threat to our seas, that of degradation (eutrophication), remains insufficiently acknowledged and investigated. In the world's degrading coastal seas, many questions can be studied that also relate to ocean acidification, for acidification is also a symptom of degradation. What is the main threat to the world's coral reefs - hypothetical decalcification or actual degradation?
 
 

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anthropogenic: (Gk: anthropos= human being; genere=to create) man-made, in the case of carbon dioxide, by burning fossil fuels, burning forests, degrading soils, making cement, etc.
aragonite: (from Aragon, a place in Spain) a needle-like (orthorhombic) crystal structure of limestone CaCO3 with some variations, as produced by most molluscs and corals. Aragonite dissolves more easily than calcite.
aragonite horizon: aragonite is the kind of limestone that shells are made of. It dissolves into seawater if the concentration of carbonate ions CO3 is too low. The boundary concentration is called the aragonite 'horizon', which becomes more pronounced with depth. Note that this entirely a hypothetical concept, the relevance of which to calcifying organisms, has not been demonstrated.
calcification: turning calcium and carbonate ions into hard calcium carbonate (calcite) or similar hard limestone (aragonite)
calcite: another word for calcium carbonate, laid down by organisms like coralline algae, some sponges, some plankton organisms, and many others. It may occur as fibrous, granular, lamellar, or compact. Marble is a form of calcite.
calcite horizon: calcite is a hardy form of calcium carbonate (see above). It dissolves when the concentration of carbonate ions becomes less than the calcite horizon. The calcite horizon has a lower concentration of carbonate ions than the aragonite horizon because calcite does not dissolve as readily. Note that this is an entirely hypothetical concept.
DIC: Dissolved Inorganic Carbon: all inorganic carbon molecules and ions like CO2, HCO3, CaCO3. It also contains slush and dissolved polysaccharides and any biomatter that passes through filtration paper (e.g. small bacteria and viruses).
equilibrium: many chemical reactions can go both ways, resulting in an equilibrium that can be disturbed.
magnesium calcite: a soft limestone that includes magnesium ions Mg in the place of calcium Ca.
nacre: the mother-of -pearl limestone inside shells. Nacre does not decalcify (dissolve) as readily as calcite and aragonite.
polysaccharides: a collective name for sugar-like molecules including storage polysaccharides such as starch and glycogen and structural polysaccharides such as cellulose and chitin. In the sea the protective slime of organisms is often made of polysaccharides. Many kinds of polysaccharide exist.
RDOC: Recalcitrant or Resistant Dissolved Organic Carbon, a collection of biomolecules and other particles that resist being decomposed by natural bacteria, equivalent to the substance named slush by us (see below)
sequestration: (L: sequestrare= to commit for safekeeping) the process by which substances are taken out of circulation, as in the carbon cycles.
slush: (slush as in partly molten snow, named by Floor Anthoni) a collection of short biomolecules that remain as a result of incomplete decomposition. For some reason these molecules are difficult to decompose into nutrients without an additional source of energy. The most simple of these is perhaps dimethylsulfide CH3.S.CH3. Dimethylsulfide (DMS) is a cloud forming molecule that plays a decisive role in the Earth's temperature regulation. Note that scientists discovered Recalcitrant Dissolved Organic Carbon (RDOC) about a decade ago. It is probably identical to our slush. (see publications supporting or refuting Anthoni's findings)

Budyko, M I (1977): Climatic changes. Am Geophys Union, p 128.

Budyko, M I: Global Ecology.1980

Caldeira, K and M Wickett (2003): Anthropogenic carbon and ocean pH. Nature 425: 365. (not free) but available from http://www.thew2o.net/images/folder/PDF%20Ocean%20Observers/Ocean%20Acidification%20November.pdf. Computer simulations based on assumptions. No experiments. http://pangea.stanford.edu/research/Oceans/GES205/Caldeira_Science_Anthropogenic%20Carbon%20and%20ocean%20pH.pdf

Doney, Scott C (2006): The dangers of ocean acidification. SciAm March 2006. (not free) A grossly exaggerated account.

Freely, R A et al. (2004): The impact of anthropogenic CO2 on the CaCO3 system in the oceans. Science, 305, 362-366. (not free)

Henderson, C (2006): Paradise lost. New Scientist 5 August 2006 :29-33. (not free)

Idso, Craig D (2009): CO2, global warming and coral reefs: prospects for the future. http://scienceandpublicpolicy.org/originals/co2_coral_warming.html  free PDF (81 pages). An excellent review of published science confirming that corals adapt well to warmer seas, rising seas and acid oceans. In fact, they love it! Must-read!

Jacobson, Mark Z (2005): Studying ocean acidification with conservative, stable numerical schemes for nonequilibrium air-ocean exchange and ocean equilibrium chemistry J. Geophys. Res. Atm., 110, D07302, April 2, 2005. Extensive equilibrium calculations based on known equilibrium constants, assuming that the ocean is in equilibrium with the atmosphere. Scenarios for 275, 375, 750ppmv CO2 and 0-25ºC. Computer model for future pH.

Kleypas J A et al. (2006): Impacts of ocean acidification on coral reefs and other marine calcifiers. Free from www.isse.ucar.edu/florida/www.ucar.edu/communications/Final_acidification.pdf  (10MB, free) An honest account, including uncertainties and missing knowledge. A must-read. Unfortunately focuses on calcification rather than ecosystem functioning. Also gives an historic timeline and chronicles all organisations involved.

Orr, James C., Victoria J. Fabry, Olivier Aumont, et al. (2005): Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature, 437, 681-686. (not free) Computer simulations based on assumptions. No experiments. http://www.ipsl.jussieu.fr/~jomce/acidification/paper/Orr_OnlineNature04095.pdf

Robinson Arthur B , Noah E Robinson, and Willie Soon (2007): Environmental effects of increased atmospheric carbon dioxide. J Am Phys & Surg (2007) 12, 79-90. An objective account showing strong correlation of temperature and solar activity, both recent and in past centuries. Also shows effect of CO2 outgassing from the oceans. http://www.oism.org/pproject/s33p36.htm Oregon Institute of Science & Medicine (free HTM & PDF)

Royal Society UK, Raven, J A et al.  (2005): Ocean acidification due to increasing atmospheric carbon dioxide. The Royal Society Policy Document 12/05; 55pp; available free at http://www.royalsoc.ac.uk/displaypagedoc.asp?id=13539  Educational but a dishonest account, failing to mention uncertainties and missing science. Lacking experimental facts. "Ocean acidification is a powerful reason, in addition to that of climate change, for reducing global emissions of CO2 to the atmosphere to avoid the risk of irreversible damage to the oceans. We recommend that all possible approaches be considered to prevent CO2 reaching the atmosphere. - excellence in science -" [sigh]

Sabine, C L et al. (2004): The ocean sink for anthropogenic CO2. Science, 305, 367-370. (not free) a novel tracer method for tracing anthropogenic carbon dioxide in the oceans. Makes far-reaching conclusions.

Sarma, V, T Ono, T Saino (1971): Increase of total alkalinity due to shoaling of aragonite saturation horizon in the Pacific and Indian Oceans: influence of anthropogenic carbon inputs. Geophys Res Lett 29, 1971.

Wikipedia article 'ocean acidification' http://en.wikipedia.org/wiki/Ocean_acidification Written by the scaremongers without balance. Provides many links to suppportive science and many media articles and even an upcoming scare movie. A link to the Seafriends balanced article is consistently removed. No doubting or uncertainties allowed!

Acid Test: the global challenge of ocean acidification (movie) - a new propaganda film by the National Resources Defense Council, fails the acid test of real world data. By Dr Craig D Idso, Jan 2010. http://scienceandpublicpolicy.org/images/stories/papers/originals/acid_test.pdf (free)