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Two New Studies Detail Impact and Acceleration of Ocean Acidification in Different Regions

The potential for coral growth—represented by aragonite concentration—in the Caribbean region is dramatically changing due to ocean acidification. Click to view an animation of changes from 1988 to 2007. Credit: NOAA

Two recently published studies highlight the growing impact of ocean acidification—the lowering of the pH of seawater due to the increasing absorption of large amounts of carbon dioxide—in the Caribbean and the Southern Ocean.

A paper by scientists from NOAA (National Oceanic and Atmospheric Administration and the University of Miami’s Rosenstiel School of Marine and Atmospheric Science confirms significant ocean acidification across much of the Caribbean and Gulf of Mexico. The paper, published in the 31 October issue of the Journal of Geophysical Research—Oceans, reports strong natural variations in ocean chemistry in some parts of the Caribbean that could affect the way reefs respond to future ocean acidification.

Such short-term variability has often been underappreciated and may prove an important consideration when predicting the long-term impacts of ocean acidification to coral reefs, according to the authors.

A second paper, by scientists from the University of New South Wales (Australia) and the Centre for Australian Weather and Climate Research and Antarctic Climate & Ecosystems Cooperative Research Centre, concludes that the Southern Ocean will acidify past a critical tipping point when atmospheric CO2 levels pass 450 ppm, projected to occur within 30 years at most.

At this point of aragonite undersaturation, the shells of sea creatures will start to dissolve. Previous estimates found that this dissolution point for shells in the Southern Ocean would occur after atmospheric carbon dioxide concentrations reached 550 ppm, which is projected to occur in the latter part of the century. This paper is published in the journal Proceedings of National Academy of Sciences.

Since the beginning of the industrial era, the oceans have absorbed about a third of all anthropogenic carbon dioxide emissions released into the air—this has served as a carbon sink, and retarded some of the warming that otherwise would have occurred.

Atmospheric CO2 reacts with seawater to form carbonic acid (H2CO3). Increasing the amount of CO2 dissolved in the ocean lowers the pH, decreases the availability of carbonate (CO32-) ions, and lowers the saturation state of the major shell-forming carbonate minerals such as aragonite. Carbonate ions are building blocks for the calcium carbonate (e.g., aragonite, calcite) that many marine organisms use to grow their skeletons and create coral reef structures.

With increasing carbon dioxide in seawater, shellfish and corals cannot absorb enough calcium carbonate to build strong skeletons and shells. The greater acidity slows the growth and even dissolves ocean plant and animal shells.

Ocean acidification has been called the ‘silent climate change issue’ because it gets far less press than global warming, sea level rise and rainfall changes. Yet for marine systems, it could end up being the most important consequence of industrial pollution of all because it risks dissolving coral reefs and undermining the food chain upon which the world’s fisheries and marine mammals depend.

—Professor Barry Brook, Sir Hubert Wilkins Chair of Climate Change and Director of the Research Institute for Climate Change and Sustainability at Adelaide University.

The Caribbean. A number of recent studies demonstrate that ocean acidification is likely to harm coral reefs by slowing coral growth and making reefs more vulnerable to erosion and storms.

In the new study, Dwight Gledhill, Rik Wanninkhof, Frank Millero and Mark Eakin used four years of ocean chemistry measurements taken aboard the Royal Caribbean Cruise Line ship Explorer of the Seas together with daily satellite observations to estimate changes in ocean chemistry over the past two decades in the Caribbean region.

(The resulting new ocean acidification tracking products are available online along with animations of the changes since 1988.)

The study supports other findings that ocean acidification is likely to reduce coral reef growth to critical levels before the end of this century unless humans significantly reduce carbon dioxide emissions. While ocean chemistry across the region is currently deemed adequate to support coral reefs, it is rapidly changing as atmospheric carbon dioxide levels rise.

The study demonstrates a strong natural seasonal variability in ocean chemistry in waters around the Florida Keys that could have important consequences for how these reefs respond to future ocean acidification.

—NOAA’s Dwight Gledhill, lead author

The Southern Ocean. By using a new technique that better quantifies natural variations of carbon dioxide in the Southern Ocean, Ben McNeil and Richard Matear found that natural seasonal variations in carbonate ion concentrations could either hasten or dampen the future onset of the dissolution point.

Their large-scale observational analysis of the Southern Ocean shows an intense wintertime minimum in CO32- south of the Antarctic Polar Front. When combined with anthropogenic CO2 uptake, it “is likely to induce aragonite undersaturation when atmospheric CO2 levels reach ˜450 ppm.

Under the IPCC IS92a scenario, Southern Ocean wintertime aragonite undersaturation is projected to occur by the year 2030 and no later than 2038.

—McNeil and Matear 2008

Oceanic acidification is a direct consequence of increasing atmospheric carbon dioxide concentrations. Our new results point to irreversible and detrimental impacts to Southern Ocean marine calcifying organisms if atmospheric CO2 exceeds 450 ppm. It provides additional and direct scientific evidence for the world to do everything in its power to limit CO2 concentrations to 450 ppm in order to avoid the irreversible consequences associated with ocean acidification.

—Dr. McNeil

In July, a team of researchers led by Richard Zeebe of the University of Hawai’i at Manoa published a paper in the journal Science warning that the ecological and economic consequences of ocean acidification are difficult to predict but possibly calamitous, and that halting the changes already underway will likely require even steeper cuts in carbon emissions than those currently proposed to curb climate change. (Earlier post.)


  • Dwight K. Gledhill, Rik Wanninkhof, Frank J. Millero, Mark Eakin (2008) Ocean acidification of the Greater Caribbean Region 1996–2006. J. Geophys. Res., 113, C10031, doi: 10.1029/2007JC004629

  • Ben I. McNeil and Richard J. Matear (2008) Southern Ocean acidification: A tipping point at 450-ppm atmospheric CO2. PNAS doi: 10.1073/pnas.0806318105


Kit P

How very very deceptive!

“is dramatically changing due to ocean acidification”

The animated maps of annual mean aragonite saturation state do not show a dramatic change. Selecting a dramatic color change in the 'optimal' range of 'Coral Reef Growth Potential' makes a dramatic animation.

The ocean and other bodies of water like the Great Salt Lake in Utah are alkaline and the unit of measurement is Total Alkalinity (μmol/kg). NOAA provide a graphic of that measurement without the deceptive color scheme. Total CO2 (μmol/kg) and pCO2,sw (μatm) are also provided.

If you go back a few years scientist used the term alkalinity to describe the ocean and if OO2 increased the water would become less alkaline but then 'ocean acidification' was substituted to the AGW fear mongers.

Wait for it!!!


OK then what are we supposed to call this process? Ocean de-alkalination? Ocean acidification is a perfectly appropriate name for this process.

As with the previous story on global warming, I have to agree that these stories are moving beyond the theme of GCC. If you want to open up all these other cans of worms and delve into the science of the impacts of rising GHG levels (rather than their **sources**, from vehicles), then a much larger and more thorough effort is warranted in order to address these topics seriously and fairly -- in which case the original purpose of GCC will be diminished.


I, for one, don't consider these too outside the perview of GCC and appreciate their inclusion. It is, after all, our current transportation systems that are responsible for a large amount of increased CO2 concentrations.

As for "acidification" being propagated by "AGW fearmongers",...ah, nevermind. If that's what you think, go with that.


B-O-R-I-N-G. And over.

richard schumacher

Keep it coming! Part of the value of GCC is in being reminded of the consequences of driving non-Green Cars. Geeking out on technology removed from the context of the human and natural worlds is sterile and a mere hobby.


GCC can and does maintain a comprehensive interest in the related subjects including fuels, climate and developments in the realities and concepts as such is a one stop shop.
Thats a big part of the attraction.
Broaden your mind.

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