Acidification Attack


For tens of millions of years, Earth's oceans have maintained a relatively stable acidity level. It is within this steady environment that the rich and varied web of life in today's seas has flourished. However, research shows that this ancient balance is being undone by a recent and rapid drop in surface pH that could have devastating global consequences.

Since the beginning of the industrial revolution in the early 1800s, fossil fuel-powered machines have driven an unprecedented burst of human industry and advancement. The unfortunate consequence, however, has been the emission of billions of tons of carbon dioxide (CO2) and other greenhouse gases into Earth's atmosphere.

About half of this anthropogenic or man-made CO2 has been absorbed by the oceans over time, which has benefited us by slowing the climate change. Nevertheless, the introduction of massive amounts of CO2 into the seas is altering water chemistry and affecting the life cycles of many marine organisms, particularly those at the lower end of the food chain.

When CO2 dissolves in the ocean, carbonic acid is formed, leading to higher acidity, mainly near the surface, which has been proven to inhibit shell growth in marine animals and is suspected as a cause of reproductive disorders in some fish.

On the pH scale, which runs from 0 to 14, solutions with low numbers are considered acidic and those with higher numbers are basic, seven is neutral. Over the past 300 million years, ocean pH has been slightly basic, averaging about 8.2; today, it is around 8.1, a drop of 0.1 pH units, representing a 25% increase in acidity over the past two centuries.

The oceans currently absorb about a third of human-created CO2 emissions, roughly 22 million tons a day. Projections based on these numbers show that by the end of this century, continued emissions could reduce ocean pH by another 0.5 units. Shell-forming animals including corals, oysters, shrimp, lobsters, many planktonic organisms and even some fish species could be gravely affected.

Scientific awareness of ocean acidification is relatively recent, and researchers are just beginning to study its effects on marine ecosystems; however, all signs indicate that, unless humans are able to control and eventually eliminate fossil fuel emissions, ocean organisms will find themselves under increasing pressure to adapt to their habitat's changing chemistry or perish.

The new chemical composition of our oceans is expected to harm a wide range of ocean life, particularly creatures with shells as increased acidity reduces carbonate; the mineral used to form the shells and skeletons of many shellfish and corals. The effect is similar to osteoporosis, slowing growth and making shells weaker. If pH levels drop enough, the shells will literally dissolve; the resulting disruption to the ocean ecosystem could have a widespread ripple effect and further deplete already struggling fisheries worldwide.

Delicate corals may face an even greater risk than shellfish because they require very high levels of carbonate to build their skeletons. Acidity slows reef-building, which could lower the resiliency of corals and lead to their erosion and eventual extinction. The tipping point for coral reefs could happen as soon as 2050.

Coral reefs serve as the home for many other forms of ocean life; their disappearance would be akin to rainforests being wiped out worldwide. Such losses would reverberate throughout the marine environment and have profound social impacts, as well, especially on the fishing and tourism industries. The loss of coral reefs would also reduce the protection that they offer to coastal communities against storms surges and hurricanes, which might become more severe with warmer air and sea surface temperatures due to global warming.

Combating acidification requires reducing CO2 emissions and improving the health of the oceans. Creating marine protected areas and stopping destructive fishing practices would increase the resiliency of marine ecosystems and help them withstand acidification. Evidence suggests that coral reefs in protected ocean reserves are less affected by global threats, such as global warming and ocean acidification, demonstrating the power of ecosystem protection.

Creator: Australian Institute of Marine Science | Credit: LTMP
Copyright: Australian Institute of Marine Science


Ultimately, though, reducing the amount of CO2 absorbed into the oceans may be the only way to halt acidification. The same strategies needed to fight global warming on land can also help in seas. This problem is an international one and although we do not have oceans in the Arab region, it affects our Mediterranean Sea.

The Mediterranean is considered a small-scale ocean with high environmental variability and steep physicochemical gradients within a relatively restricted region. Its circulation is characterized by zonal gradients of physicochemical variables, with salinity, temperature, stratification and alkalinity all increasing towards the East. The generally low-nutrient (from oligotrophic(1) to ultraoligotrophic(2)) waters offshore stand in contrast to many near-shore regions, often containing coral and sea grass ecosystems, which are affected by human-induced eutrophication(3).

Containing only 1% of Earth’s vast ocean water, the Mediterranean hosts 8% of the world’s biodiversity that is currently under threat. Acidification is an additional anthropogenic pressure on Mediterranean ecosystems already suffering from overfishing, increasing sea surface temperatures and alien species invasion.

Creating more marine protected areas in the Mediterranean is a good short-term solution to reduce adverse impacts from fishing, shipping and tourism on its biodiversity hot spots. However, the Mediterranean is already vulnerable because it is a semi-enclosed sea; with all of its sociopolitical complexity, one wonders how the Mediterranean will be able to meet these grand environmental challenges. Scientists can talk all they want; but, the action will actually be carried out by policymakers, governments and the public.

We are harming our Earth in many ways that we are fully aware of; but, when it comes to marine life, we, the general public, are tragically unaware of the hidden and indispensable treasures that our oblivious actions are destroying. The inevitable reality is that ocean acidification is the hidden side of the world’s carbon emission crisis caused and perpetuated by us. We are thus required to reinforce drastic changes on how we fuel our world, and we need to do it quickly.


  1. Oligotrophic: a term used to refer to environments that offer little to sustain life, organisms that survive in such environments, or the adaptations that support survival.
  2. Ultraoligotrophic: a term used to refer to environments that nutrient concentrations in both the water column and lake sediments are extremely low.
  3. Eutrophication: is the ecosystem response to the addition of artificial or natural substances, such as nitrates and phosphates, through fertilizers or sewage, to an aquatic system.

*The original article is published in the PSC Newsletter, Summer 2012 Issue.

References (image).


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