Ocean Acidification

Cliff Ollier
Honorary Research Fellow, The University of Western Australia

Email: cliff.ollier@uwa.edu.au


Climate alarmists believe the world is warming, and that this is caused exclusively by man-made carbon dioxide. ‘Global Warming” is now stretched to Climate Change”, but it must be stressed that carbon dioxide can only produce warming: the deceptive change of name does not change the alleged process.

To demonise carbon dioxide further it is supposed to cause ‘acidification’ of the oceans. They claim that anthropogenic carbon dioxide causes the ocean to become more ‘acid’, which dissolves carbonate. This despite the fact that the oceans are alkaline, and have never been acid throughout their existence on Earth. We are implored to reduce the production of anthropogenic carbon dioxide to ‘protect’ the ocean. In this article I show that such claims are baseless, and indeed that carbon dioxide is beneficial to the ocean.



‘Acid’ is an emotive word to the general public, which is why it is seized upon by the alarmists in their search for yet another scare. In reality increasing CO2 makes the ocean become ‘less alkaline’, but never ‘acid’.

Acidity and alkalinity are measured on a pH scale which goes from 0 to 14. pH is a measurement of the amount of hydrogen ion concentration in a solution, the log of the hydrogen ion concentration with the sign changed. The pH needs to be less than 7 to be ‘acid’ and above 7 is alkaline. Because it is a log scale it is very hard to move a pH of 8.2 to 7.0, which is neutral. Claims of ‘increasing acidity’ in the oceans are misleading wordplay, because the ocean would not even start to be acid until the pH was below 7. It is like saying a block of ice is becoming more liquid if the temperature changes from -30oC to -20oC when it cannot become liquid until it reaches 0oC. The ocean has never been acid throughout Earth history.

The pH of sea water can be very variable. Ocean pH varies regionally by 0.3, and seasonally in a particular location by 0,3. Rhodes Fairbridge told me that he found the day-night variation in a coral pool was 9.4 to 7.5. David Barnes reports that on the Great Barrier Reef water is pushed onto the front of reefs at around pH 8.1-8.2. It then flows across the shallow reef flat and into the lagoon or back-reef area. The pH of water leaving the reef flat in the daytime is around 8.4-8.5. The pH of water leaving the reef flat at night is around 7.9-8.0. This shift is entirely due to removal of CO2 during the day because of photosynthesis by reef organisms, notably corals, coralline algae and ubiquitous, all-pervasive filamentous green algae (note that most of the significant calcifiers on reefs are photosynthetic; examples are green algae, foraminifera and giant clams). During the day photosynthesis considerably exceeds respiration. During the night there is only respiration. Hence, at night, addition of CO2 to the water mass by respiration of benthic organisms decreases the pH.


Chemical equilibrium is a bit too complex to describe here, but some of the Alarmists make use of it to create scares. Gattuso and Hanson (2011) edited a book called Ocean Acidification, which has many papers with the usual alarms. Strangely there is a very level-headed Foreword by Wallace Broecker, who wrote: “Surface waters are supersaturated for calcite (fixed by oysters and coccoliths amongst others) and aragonite (corals, clams and others), so what is the problem?” Perhaps the problem is that despite the seawaters being supersaturated, bubbling carbon dioxide still causes increased biological activity as described below.


Many marine organisms need CO2 to make their coral skeletons, carbonate shells and so on. Corals also have symbiotic plants within their flesh that use CO2 in photosynthesis.

Marine life flourishes where CO2 is abundant. Professor Walter Stark (2010) described the relationship between organisms and pH at two carbon dioxide ‘vents’, the Bubble Bath’ and Esa’Ala, near Dobu Island, Papua New Guinea. Here CO2 of volcanic origin is bubbling visibly through the water so that the water is saturated with CO2. Life flourishes in abundance to make the vents spectacular favourite sites for scuba divers. He reported many accurate measurements of pH in the area and concluded “It seems that coral reefs are thriving at pH levels well below the most alarming projections.”

At Esa’Alaa sample taken immediately adjacent to a Porites coral and about 10 cm from a small bubble stream had a pH value of 7.96. A sample from next to a Porites coral at the “Bubble Bath” measured 7.74. This was about 10 cm from a large bubble stream and about 12 m from the main gas vent. A sample next to the main vent measured 6.54.

Other such sites are known around the world, such as the Champagne Reef, a premier diving site in Dominica, which is reported to be ‘full of life’. It is probable that the oceanic carbonate fixers are suffering CO2 starvation. Just as terrestrial plants grow better under elevated CO2 levels, marine life does better with more CO2.

As the modern investigation into the potential impacts of increasing carbon dioxide in sea water on marine life continues, one narrative is beginning to emerge across the scientific literature, which is that rising atmospheric CO2 concentrations will likely benefit the growth of primary producers. For example Pardew et al. (2018) studies the growth responses of seven phytoplankton species from four major taxons to elevated levels of seawater pCO2. Each of the species was grown under controlled-environment conditions under either ambient (~500 µatm) or elevated (~1,000 µatm) pCO2 in either a high-nitrogen or low-nitrogen culture medium.

They say the growth rates of all species “increased with high CO2 independent of culture regime, where on average an increase of 0.12 ± 0.07 per day was observed in phytoplankton exposed to high CO2 compared to ambient conditions” (p < 0.001). The picture painted by this study is quite different from that sold to the public by climate alarmists, who consistently claim that so-called ocean acidification is detrimental to marine life.

In a comprehensive analysis of experimental studies that explored the effects of rising atmospheric CO2 concentrations on marine biota, Hendriks et al. (2010) assembled a database of 372 experimentally-evaluated responses of 44 different marine species to ocean acidification that was induced by equilibrating seawater with CO2-enriched air. This they did because, as they describe it, “warnings that ocean acidification is a major threat to marine biodiversity are largely based on the analysis of predicted changes in ocean chemical fields,” which are derived from theoretical models that do not account for numerous biological phenomena and have only “limited experimental support.”

They note that “calcification is an active process where biota can regulate intracellular calcium concentrations,” so that “marine organisms, like calcifying coccolithophores (Brownlee and Taylor, 2004), actively expel Ca2+ through the ATPase pump to maintain low intracellular calcium concentrations.” They suggest “there is evidence that calcification could even increase in acidified seawater, contradicting the traditional belief that calcification is a critical process impacted by ocean acidification.”

In brief Hendriks et al. conclude that the world’s marine biota are “more resistant to ocean acidification than suggested by pessimistic predictions identifying ocean acidification as a major threat to marine biodiversity.” Biological processes can provide homeostasis against changes in pH of surrounding water.

For further details of coral adaption see Sully et al. 2019, and Steele, 2019. These authors suggest that corals can successfully adapt to stressful environments.

One of the factors affecting ocean pH is photosynthesis by plants. Experimental results show that plants grow better if CO2 is increased, and greenhouse managers commonly increase the CO2 artificially to increase crops, often by 30% or more. There is every reason to suppose that marine plants also thrive if CO2 is increased. There is also experimental evidence that carbonate secreting animals thrive in higher CO2. Herfort and colleagues (2008) concluded that the likely result of human emissions of CO2 would be an increase in oceanic CO2 that could stimulate photosynthesis and calcification in a wide variety of corals.

Marine life, including that part that fixes CO2 as the carbonate in limestones such as coral reefs, evolved on an Earth with CO2 levels many times higher than those of today, as reported by Berner and Kothaval (2001). It may be true to say that today’s marine life is getting by in a CO2-deprived environment. A sample from next to a Porites coral at the “Bubble Bath” measured 7.74.


In a book about the coast of South Australia Bourman et al. (2016) provided the concept of ‘carbonate factories’. The coasts are dominated by carbonate sands in the form of beaches and dunes. The source of the sediment was a subtidal carbonate factory with the prolific growth of calcareous marine invertebrates such as molluscs, bryozoans, coralline algae, echinoids, and foraminifers. Attrition of their remains leads to the formation of sand-sized sedimentary particles of calcium carbonate.

In Gulf St Vincent seagrasses thrive with extremely productive calcareous algae, foraminifers and molluscs manufacturing vast amounts of calcareous sediment. In Spencer Gulf the dominant processes of coastal development are related to the massive production and accumulation of biogenic skeletal carbonate fragments derived from coralline algae, foraminifers, molluscs and bryozoans. The site is a major carbonate factory sequestering much CO2.

“The coastline of South Australia is part of the world’s largest aeolianite (dune limestone) temperate sedimentary carbonate province, which extends from western Victoria to north of Shark Bay, Western Australia. The aeolianite deposits attest to the high calcium carbonate bioproductivity of the surrounding continental shelf environments”.


Whether the Earth started as a hot or cold body, any primordial gas would have escaped. Volcanic eruptions produced the gases, including water which formed the oceans, and carbon dioxide which formed 98% of the original atmosphere. The evolution of life changed that. When photosynthesis started, more and more oxygen was introduced into the atmosphere (which changed the course of rock weathering), and when carbonate secretion arrived in the late Precambrian, limestone deposition started to sequester CO2.

Most modern reef coral genera have fossil histories going back from 5-10 million years to over 100 million years. They have survived both ice ages and very warm periods, and times when CO2 was at 5-10 times current levels.

Contrary to popular belief, at 400 parts per million (0.04 per cent), CO2 is lower now in the atmosphere than it has been during most of the 550 million years since modern life forms emerged during the Cambrian period. CO2 was about 10 times higher than it is today. Corals and shellfish evolved early and have obviously managed to survive through eras of much higher CO2 than present levels. Finally, it is a fact that people who have saltwater aquariums sometimes add CO2 to the water in order to increase coral growth and to increase plant growth.

The truth is CO2 is the most important food for all life on Earth, including marine life. It is the main food for photosynthetic plankton (algae), which in turn is the food for the entire food chain in the sea. On top of this some marine organisms use CO2 to produce their skeletons of calcium carbonate. This has led to the ever-increasing amount of limestone amongst the sedimentary rocks, sequestering vast amounts of carbon dioxide.



There is a completely fake argument used by Alarmists including NASA implying that coral bleaching is caused by carbon dioxide. Bleached coral is perfectly normal, and recovers in a few years by recolonization. It occurs when wave driven mixing ceases during periods of extended calm associated with unusual warming of the surface 1-2 m.


The iconic Great Barrier Reef is one of the best-known features of Australia, and we are constantly told it is in danger. The Australian Government’s Great Barrier Marine Park Authority writes (2018): “In the long-term, ocean acidification is likely to be the most significant impact of a changing climate on the Great Barrier Reef ecosystem”.

Another example is provided by Albright et al. (2016) who claim their research shows, the reduction in seawater pH – caused by carbon dioxide from human activities such as burning fossil fuels – is making it more difficult for corals to build and maintain their skeletons. Possibly the greatest danger to the GBR is the huge amount of money, tens of millions of dollars, made available for research on the reef. This has led to a feeding-frenzy of people wanting to use the money, who maintain that the reef is in danger, to keep the money flowing.

David Barnes has spent many hours measuring the pH in all parts of the reef. He tells me “On the GBR water is pushed onto the front of reefs at around pH 8.1-8.2. It them flows across the shallow reef flat and into the lagoon or back-reef area. The pH of water leaving the reef flat in the daytime is around 8.4-8.5. The pH of water leaving the reef flat at night is around 7.9-8.0. This shift is entirely due to removal of CO2 during the day because of photosynthesis by reef organisms, notably corals, coralline algae and ubiquitous, all-pervasive filamentous green algae (note that most of the significant calcifiers on reefs are photosynthetic; examples are green algae, foraminiferans and giant clams). During the day photosynthesis considerably exceeds respiration. During the night there is only respiration. Hence, at night, addition of CO2 to the water mass by respiration of benthic organisms decreases the pH.

Notice that the organisms at the back of a reef flat are experiencing daily a shift in pH that our alarmist friends would have us believe will bring destruction to coral reefs if it had taken place in the water flowing onto a reef. Coral growth is usually at its most luxurious at the back of a reef flat.”

The Great Barrier Reef has been able to re-establish itself repeatedly during high sea level episodes associated with major environmental fluctuations in sea level, temperature and CO2 over the past several hundred thousand years. The GBR complex goes back about two million years, but the reef as we know it is only about 10,000 years old. Before that there were huge changes in climate and sea level. Where the GBR reef complex is from tens to over a hundred Km in width today, it was reduced to a narrow fringing reef along the edge of a vast coastal plain during the last glacial period. It was not great and was not a barrier reef. It also experienced earlier glacial periods, with sea level falls. The GBR has survived many wide changes in environmental conditions, yet still ocean acidification is singled out by alarmists as the great threat to the reef.


Marine life depends on CO2, and some plants and animals fix it as limestone, which is not generally re-dissolved. Over geological time enormous amount of CO2 have been sequestered by living things, so that today there is far more CO2 in limestones than in the atmosphere or ocean. This sequestration of CO2 by living things is far more important than trivial additions to the atmosphere caused by human activity.

The ‘carbonate factories’ described here show that carbon dioxide is vital for the production of carbonate sands and ultimately limestone. Trying to reduce the carbon dioxide content of the ocean by reducing emissions by human activities is not only futile, but if it could be done it would have harmful consequences on all the carbonate fixing animals and plants in the ocean. The continued existence of the Great Barrier Reef, like coral reefs all over the world, depends on corals and other plants and animals fixing carbon dioxide as part of their skeletons, as part of the carbon cycle. Carbon dioxide in sea water does not dissolve coral reefs, but is essential to their survival.


Albright, R., Caldeira, L. et al. 2016. Reversal of ocean acidification enhances net coral reef calcification. Nature, 531, pages362-365.

Bourman, R.P., Murray-Wallace, C.V. and Harvey, N. 2016. Coastal Landscapes of South Australia. University of Adelaide Press, Adelaide. 420pp. Paperback $A 132. Ebook free from University of Adelaide Press. DOI: http://dx.doi.org/10.20851/coast-sa

Berner., R.A. and Kothavala, Z. 2001. A revised model of atmospheric CO2 over Phanerozoic time. American Journal of Science, 301, 182-204.

Herfort, L, Thake, B. and Taubner, I. 2008. Bicarbonate stimulation of calcification and photosynthesis in two hermatypic corals. Journal of Phycology, 44, 91-8.

Gattuso, J-P. and Hanson, L. (eds) 2011. Ocean Acidification. Oxford University Press.

Hendriks, I.E., Duarte, C.M. and Alvarez, M. 2010. Vulnerability of marine biodiversity to ocean acidification: A meta-analysis. Estuarine, Coastal and Shelf Science 86: 157-164.

Marine Park Authority. 2018. http://www.gbrmpa.gov.au/managing-the-reef/threats-to-the-reef/climate-change/how-climate-change-can-affect-the-reef/ocean-acidification

Pardew, J., Pimentel, M.B. and Low-Decarie, E. 2018. Predictable ecological response to rising CO2 of a community of marine phytoplankton. Ecology and Evolution 8: 4292-4302.

Starck, W. 2010. Observations on Growth of Reef Corals and Sea Grass Around Shallow Water Geothermal Vents in Papua New Guinea. Quadrant Online, 15 March 2010.

Steele, J. 2019. More Evidence for Rapid Coral Adaptation. https://wattsupwiththat.com/2019/04/02/more-evidence-for-rapid-coral-adaptation/

Sully, S., Burkepile, D.E., Donovan, M.K., Hodgson, G. and van Woesik, R. 2019. A global analysis of coral bleaching over the past two decades. Nature Communications, 10, Article number: 1264. https://www.nature.com/articles/s41467-019-09238-2

For a Data Base on Ocean Acidification see http://www.co2science.org/data/acidification/acidification.php

See also: https://carbon-sense.com/2012/05/13/acid-ocean-bogeyman/

3 thoughts on “Ocean Acidification”

  1. In comparison to carbon dioxide, sulphur dioxide is much more acidic. The release of sulphur dioxide through submarine volcanism is potentially a natural cause of ocean acidification impacting marine life including corals. This is an underestimated natural cause of ocean acidification.

  2. As well the amount of carbon dioxide dissolved in seawater remains constant at a set temperature and pressure.
    The seawater is said to be saturated and in equilibrium with the atmosphere.
    Increase the temperature and more carbon dioxide escapes from the water and the pH increases so that the water is more alkaline / less acidic.
    Increase the concentration of carbon dioxide in the atmosphere and the partial pressure of carbon dioxide increases with more resultant solution and increased neutralisation of the water.
    However as mentioned in the article each change results in more carbonate ions being available to organisms making shells and increased photosynthesis. So new equilibriums are reached through the process of homeostasis. Then you have the continual raining of dead organisms to the seafloor taking carbonate with them – resulting in an overall and steady decrease in the available carbon.
    It is not as simple as the climate alarmists make out.

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