Coral reefs support 25 per cent of marine life and where they exist in our world support one billion people directly and indirectly involved in the tourist trade. – Photo from PxHere
NEWTON, in his book ‘Philosophiae Naturalis Principiae Mathematica’, which was published in 1687, stated the above quote as his Third Law of Motion. This mechanics theory can also be applied to the chemistry of our oceans for currently 30 per cent of our anthropogenic carbon dioxide is absorbed by our oceans.
This is the so-called ‘evil twin of global warming’ and the ocean’s chemical composition is being changed by this carbon sink with quite dramatic effects.
Changes in chemistry
Normally our alkaline ocean waters have a pH of above 7 but gradually our sea waters are getting more acidic. The carbon dioxide (CO2) absorbed by the water changes to a dilute form of carbonic acid, thus decreasing the sea’s salinity. At present our oceans are absorbing CO2 at a daily rate of 22 million tonnes and in total over the last 30 years at about 525 billion tonnes.
Our seawater has a normal average pH of 8.2 and this is the result of alkaline ions brought in through solution by streams and rivers flowing over weathered and eroded land-based rocks. Since the start of the Industrial Revolution (1786), the average pH has fallen to 8.1 today.
As the pH scale is logarithmic, a change of 1 single pH unit means a tenfold change in hydrogen ion concentration. Thus, a change in point 1 pH is equivalent to a tenfold change in acidity. This equates to a 26 per cent increase in acidity over the last two and a half centuries. This fall to pH 8.1 was first discovered exactly 30 years ago when research scientists first coined the term ‘ocean acidification’.
Taken in the context of geological time, the rate of acidification of our oceans is nearing that of the great mass extinction of animals and plants that occurred about 56 million years ago.
Pre-industrial pH levels and predicted pH levels for 2100. – Image from Unesco
Ocean acidification in historical context
The last surge in increased ocean acidification through the build-up of atmospheric carbon dioxide was during the so-called ‘Palaeocene-Eocene Thermal Maximum (PETM) which occurred, as stated earlier, about 55.5 million years before the present. A massive release of CO2 into the atmosphere has been estimated to have lasted 20,000 to 50,000 years during which the average global temperatures increased by 5 to 8 degrees Centigrade.
The increase in CO2 in the air was thought to be occasioned by an increase in volcanic activity associated with plate movements. During this time our planet was ice-free unlike today where our glaciers act as massive carbon sinks.
The increased acidification of the seawater caused the extinction of many species of marine life and, indeed, animals and it took very many thousands of years for our planet to recover. Recently, it has now been verified that the rate of carbon release then was much slower than the human induced carbon emissions of today.
Impact on today’s marine life
Coral reefs, composed of calcium carbonate, and home to fish and many other marine organisms have had the severest setbacks as acidification has limited coral reef growth owing to the corrosion of their pre-existing skeletons as well as slowing new growth. Thus, they are unable to rebuild themselves at a faster rate than the acid ocean is dissolving them. Increased acidity also affects corals at their larval stage in life as it does prevent them from finding a suitable place to settle and reach adulthood.
The progressive deoxygenation of seawater has led to fish working harder thereby burning extra energy to remove the fall in pH levels from their gills, kidneys, and intestines. This has led to increased lethargy which now finds it more difficult for them to escape their predators, reproduce, and even digest their food.
Fish embryos are extremely vulnerable to increases in acidity and this has been seen in the case of the Atlantic eel. This fish spends most of its life in river estuaries and then migrates on the long trans-Atlantic journey back to the Sargasso Sea for spawning after which it dies. It is now classified by the International Union for Conservation of Nature (IUCN) as a ‘critically endangered’ species.
Clams, crabs, sea urchins, and starfish are suffering corrosion to their shells through the increased acidity, and with weakened shells, are more vulnerable to predators. Massive ‘die offs’ of these creatures have been recorded as their shells are dissolved faster than they can grow them.
Marine algae and plants on the other hand have been boosted by an increase in CO2 as they survive by combining CO2 with sunlight thereby promoting photosynthesis. Some seaweed species such as seagrass have been observed to be growing taller with deeper roots. Phytoplankton also thrives with increased CO2 levels and develops into huge blooms with the side effects of deoxidising the seawater.
The increase in CO2 has led to some seaweed species such as seagrass growing taller with deeper roots. – Photo from PxHere
Impacts upon humans
Coral reefs support 25 per cent of marine life and where they exist in our world support one billion people directly and indirectly involved in the tourist trade. With the deceleration of calcification in the acid oceans, the rate of growth of these reefs has slowed down leading to a decrease in fish stocks.
In turn this means a decrease in catch for local fishermen. Inshore crab and lobster fisheries have been similarly affected. Seafood restaurants in coastal tourist hotspots, once famed for the quality of their dishes, have seen a decline in local fish catches and thus have resorted to smaller choices of menu.
What is the answer to the acidification of our seas?
Undoubtedly, the artificial alkalisation of seawater by adding lime to the already acidic water is a quick fix solution. This process has earned the name of ‘ocean liming’. Studies in the enclosed Mediterranean Sea of the routes of the global commercial fleets of bulk carriers and container ships used as the distributors of lime as they ply their journeys may well prove literally to be the solution. How this may be applied to our open oceans is not very clear but suffice to say that research projects are currently working on this.
Our oceans and their ecosystems play such an important part in our daily lives so much so that we cannot afford to allow anthropogenic emissions of CO2 to continue. It is only by ceasing the burning of fossil fuels that this can be achieved. We forget that in the mid-1960s there was a massive outcry about the acidification of our forests through acid rainwater, caused by coal burning power stations, pouring down on our trees. This outcry has, today, been replaced with the buzzword ‘oceanic acidification’. The fate of our oceans now lies in our hands and those of the political leaders of our nations.