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What is Ocean Acidification?

The concept of climate change is a sensitive topic in economic, political, and moral circles.  The climate is changing, and whether this is due to human activity or not remains the subject of public debate.  However, it is widely agreed upon that as a global population our emissions of carbon dioxide (CO₂) have increased steadily ever since the Industrial Revolution.  While this phenomenon has been applied to the effects of air quality and global climate (mainly temperature), the effects of increased atmospheric carbon dioxide levels on the world’s oceans are only recently being realized.

The oceans absorb anywhere from 33-50% of all global CO₂ emissions – this amounts to up to 525 BILLION tons of CO₂ over the past 200 years! Because of modern scientific equipment, researchers are able to detect the subtle but significant effects felt by marine ecosystems due to the CO₂.  The chemical reactions that take place due to the ocean absorbing carbon dioxide are what cause ocean acidification.

How Does It Happen?

Step 1: Atmospheric carbon dioxide is absorbed by the ocean.
Step 2: Carbon dioxide reacts with water to form carbonic acid.
Step 3: Carbonic acid dissociates into hydrogen ions and bicarbonate.
Step 4: Bicarbonate dissociates into more hydrogen ions and carbonate.

pH is the scale used to measure the acidity or basicity of a liquid and it is based on the concentration of hydrogen ions in a certain substance.  The more hydrogen ions, the more acidic the liquid is.  As you can see in the schematic above, the absorption of carbon dioxide into the ocean triggers multiple reactions, ultimately resulting in the formation of hydrogen ions and lowering the pH of seawater.  The shocking part is that scientists have found that the average pH of the oceans has fallen 0.1 units since the Industrial Revolution, and is projected to fall another 0.4 units by 2100.

0.1 Units?  So What?

This figure is deceiving for a number of reasons.  While the change of 0.1 units may seem like nothing to be concerned about, the latest research shows that this rate of pH change is 100 times more rapid than any change in the last 650,000 years!

Another reason why this number is deceptive is that the way the pH scale works.  It measures hydrogen ion concentrations in a liquid – the more hydrogen ions, the more acidic the liquid is.  The scale goes from 0 to 14, with 7 being neutral.  Above 7, you have a base; below 7 you have an acid.  However, the pH scale is logarithmic – meaning a change of 1 unit means a 10-fold increase in hydrogen ions.  In other words, the 0.1 unit drop translates to a 26% increase in the concentration of hydrogen ions in the oceans.

What's Affected?

So the question becomes: now that we know the pH of the oceans is decreasing at an unprecedented rate, how does it affect the marine ecosystem?

When carbon dioxide is absorbed by seawater, the cascade of chemical reactions does two things – increases the amount of hydrogen ions (which lowers pH), and decreases the concentration gradient of carbonate ions.  This is deceiving, because in the earlier diagram you see that carbonate ions (CO₃^2-) are produced in the chemical reaction cascade.  However, additional reactions with carbonate, water, and carbon dioxide happen continuously to turn carbonate back into bicarbonate, thus decreasing the availability of carbonate ions.  Chemistry is often impossibly complicated; for further reading, check out this FAQ page from the European Project on Ocean Acidification.

Organisms that will be heavily affected are those that produce calcified structures.  Calcified structures include internal and external hard parts/shells.  As you are most likely aware, many marine animals produce hard or shell-like structures.  In all organisms, acidified oceans decrease the ability to produce calcium carbonate (some animals experience up to 40% reduced production).  Examples of calcifying animals include: bivalves (clams, mussels, oysters), snails, corals, echinoderms (sea stars, urchins), and many varieties of phytoplankton.  While threats to these groups (outside of corals) may not concern you, one common factor unites them: they are all low in the food web.  This means that any changes in their levels will be reflected in all levels above them.  Researchers agree that the effects of ocean acidification will be surprisingly far-reaching.

Research on ocean acidification regarding non-calcifying animals is not fully understood, but new research has shown that subtle effects are evident.  In acidified water, clownfish have been shown to lose their sensory capabilities making them more vulnerable to predation.  Humboldt squid have been shown to have decreased metabolic rates.  As research continues, more adverse effects are sure to be found.

It is difficult to say how ocean acidification will affect each plant and animal species in the long run.  Despite this, researchers and policy makers from all over the world agree that many groups of animals and communities stand to suffer from increased carbon dioxide emissions.

Fact vs. Fiction

The oceans are acidic – FICTION – While one term for the process of decreasing pH is “acidification”, seawater itself is not acidic.  The current average pH is around 8.15, but it is falling – hence the “acidification”.  It takes a pH less than 7 for a liquid to be deemed an acid.  Projections have the pH to be around 7.8 by the year 2100.

Scientists only guess at what the pH of the oceans was millions of years ago, and therefore we cannot truly tell if current rates of acidification are unnatural – FICTION – Scientists can use many different tools to study past geologic climates such as glacial air bubbles and isotope ratios of fossilized sea life.  Scientists can calculate rather accurately the pH from these measurements.

Because ocean pH has changed before, eons and eons ago, the ocean acidification we are experiencing is natural – FICTION – The rate at which carbon is being released into the atmosphere, and therefore the amount taken up by the oceans, has never been experienced by our planet.  It is happening much too fast for plant and animal life to adapt to it.  In the past, these changes have occurred over thousands, perhaps hundreds of thousands of years.  Right now, they are happening on the scale of decades.

The animals in the ocean are the only organisms who are affected by changing ocean chemistry – FICTION – The oceans play a large part in global processes vital to humans such as carbon, nitrogen, and oxygen cycles as well as processes like cloud formation.  Changes in ocean chemistry are likely to produce abnormal or unusual conditions that will certainly affect terrestrial animals as well as humans.

Ocean acidification will kill all ocean life – FICTION – The main effect of ocean acidification will be a shift in ecosystem balance.  Some organisms will be in a position to suffer with increased acidification, while some may not be affected.  However, pH levels will not reach levels that will kill off all life in the oceans.

We have the ability to decrease the effects of ocean acidification – FACT – The sharp declines in pH felt by the oceans are due to carbon emissions to the atmosphere.  Ocean acidification can be mitigated by working to reduce fossil fuel usage on an individual, regional, and national scale.  For more tips on how to reduce greenhouse gas emissions, look at these tips from the U.S. Environmental Protection Agency.

What To Do

Ocean acidification is often dubbed “the other CO₂ problem”.  While it is true that most resources and attention regarding carbon dioxide emissions is given to atmospheric and climate concerns, we must begin to incorporate ocean conditions with these other areas of concern.  The world is a complex machine, chugging along and advancing rapidly – and carbon emissions are higher than ever.  But there are strategies you can take to help mitigate the problem of ocean acidification.

• One of the most important things that you can do is to be aware.  Reading more material about the issue or telling your friends and family will encourage the spread of information.
• Practice energy efficiency.  Consumer trends are changing as the “green” movement becomes more popular.  Because of this, it is becoming easier than ever to buy efficient light bulbs, cars, appliances, etc.  Reducing the carbon footprint of your home, business, or lifestyle goes a long way.
• Support various organizations that conduct research or provide outreach regarding ocean acidification.  The goal of many of these organizations is to bring this problem to public light.  Everyone in our country has heard of global warming and greenhouse gases – not everyone knows about ocean acidification.

The oceans are a highly complex system.  There are multiple geologic control mechanisms that can mitigate carbon emissions, but they are simply being overwhelmed.  By supporting the overall health of the oceans, they will be more resilient to the extreme conditions they are currently subjected to.  Establishing marine reserves, reducing litter/pollution, and ending overfishing can all help protect the oceans from further negative change, including acidification.