Ocean acidification

Many people know that the atmosphere has a higher concentration of CO2 today than at any point in the past 800,000 years. 


There are theories that these carbon emissions are changing the oceans too. The air and the water constantly exchange gases, so a portion of anything emitted into the atmosphere eventually ends up in the sea. Winds quickly mix it into the top few hundred feet, and over centuries currents spread it through the ocean depths. In the 1990s an international team of scientists undertook a massive research project that involved collecting and analyzing more than 77,000 seawater samples from different depths and locations around the world. The work took 15 years. It showed that the oceans have absorbed 30 percent of the CO2 released by humans over the past two centuries. They continue to absorb roughly a million tons every hour.

 The head of the National Oceanic and Atmospheric Administration, Jane Lubchenco, a marine ecologist, has called ocean acidification global warming’s “equally evil twin.” 

The pH scale, which measures acidity in terms of the concentration of hydrogen ions, runs from zero to 14. At the low end of the scale are strong acids, such as hydrochloric acid, that release hydrogen readily. … At the high end are strong bases such as lye. Pure, distilled water has a pH of 7, which is neutral. Seawater should be slightly basic, with a pH around 8.2 near the sea surface. It is said that so far CO2 emissions have reduced the pH there by about 0.1. Like the Richter scale, the pH scale is logarithmic, so even small numerical changes represent large effects. A pH drop of 0.1 means the water has become 30 percent more acidic. If present trends continue, surface pH will drop to around 7.8 by 2100. At that point the water will be 150 percent more acidic than it was in 1800. [1]

Although it is unlikely that the ocean will ever become actual acid (fall below a pH of 7.0), the term acidification refers to the process of the oceans becoming more acidic. [2]

Some scientists say that as carbon dioxide (CO2) is absorbed from the atmosphere it bonds with sea water forming carbonic acid. This acid then releases a bicarbonate ion and a hydrogen ion. The hydrogen ion bonds with free carbonate ions in the water forming another bicarbonate ion. 


The more dissolved carbon dioxide in the ocean, the less free carbonate ions available for making calcium carbonate. [3]

Calcium carbonate minerals are the building blocks for the skeletons and shells of many marine organisms. In areas where most life now congregates in the ocean, the seawater is supersaturated with respect to calcium carbonate minerals. This means there are abundant building blocks for calcifying organisms to build their skeletons and shells. However, continued ‘ocean acidification’ may causing many parts of the ocean to become undersaturated with these minerals, which is likely to affect the ability of some organisms to produce and maintain their shells.

Ocean acidification is expected to impact ocean species to varying degrees. Photosynthetic algae and seagrasses may benefit from higher CO2 conditions in the ocean, as they require CO2 to live just like plants on land. On the other hand, studies have shown that a more acidic environment has a dramatic effect on some calcifying species, including oysters, clams, sea urchins, shallow water corals, deep sea corals, and calcareous plankton. When shelled organisms are at risk, the entire food web may also be at risk. Today, more than a billion people worldwide rely on food from the ocean as their primary source of protein. [4]

Although the chemistry of ocean acidification is simple, its effect on marine life is much less well-known as the process has only been recognised for less than a decade. Even relatively small increases in ocean acidity may decrease the capacity of corals to build skeletons, which in turn decreases their capacity to create habitat for the Reef’s marine life. [3]

Coral Reefs provide habitat for at least a quarter of all marine species. Many of these face extinction if reefs disappear. reef

If atmospheric CO2 can be stabilised at 450 ppm, (one possible target that has been discussed by politicians) it is feared only 8% of existing tropical and subtropical coral reefs will still be in waters of the right pH level to support their growth. [5]

In the long-term, ocean acidification could be the most significant impact of a changing climate on the Great Barrier Reef ecosystem. [3]

Left unchecked, Ocean Acidification could possibly destroy all our coral reefs by as early as 2050. It also has the potential to disrupt other ocean ecosystems, fisheries, habitats, and even entire oceanic food chains. [6]

Yet this theory is quite young and some scientists believe that ocean pH varies by 0.3 naturally and that it has been assumed, without any empirical evidence, that the pre-industrial pH was 8.25. So the claimed drop in pH may not be valid.

Furthermore carbon dioxide levels have varied enormously in earth’s past, at times reaching concentrations far exceeding those at present and those projected over the next 100 years. Yet during these times of differing carbon dioxide concentrations, calciferous sea organisms continued to thrive.

Consistent with these historical observations are the reported experimental studies that show that calciferous marine organisms are much more immune to the effects of ocean acidification than is usually supposed. [7]

However acidification may impact on a broad range of other physiological and ecological processes, such as fish respiration [8] (fish, squid, and other gilled marine animals may find it harder to “breathe”, as the dissolved oxygen essential for their life becomes difficult to extract) [9] larval development and changes in the solubility of both nutrients and toxins. Scientists are working on an initial assessment of the possible impacts of ocean acidification on microbial components of the marine ecosystem. [8]

The second video – titled ‘Acid Ocean’ – on the page listed immediately below runs for nearly an hour and investigates the consequences of ocean acidification on coral reefs.


References:                                                               1. http://ngm.nationalgeographic.com/2011/04/ocean-acidification/kolbert-text (April, 2011)

2. http://usa.oceana.org/what-ocean-acidification (& image)

3. http://www.gbrmpa.gov.au/managing-the-reef/threats-to-the-reef/climate-change/how-climate-change-can-affect-the-reef/ocean-acidification (?2011)

4. http://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F

5. http://hardenup.org/climate-change/climate-change-impacts/ocean-acidification.aspx

6. http://www.oceanarkalliance.org.au/downloads/Ocean-Acidification-Factsheet-OAA.pdf

7. http://joannenova.com.au/2011/11/the-chemistry-of-ocean-ph-and-acidification/ (November 14, 2011)

8. http://www.acecrc.org.au/Research/Ocean%20Acidification

9. http://wwf.panda.org/about_our_earth/blue_planet/problems/climate_change/



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