Never Heard of Ocean Acidification?

Many people haven't. But because of human activities, ocean acidification is happening right now, and may change our oceans forever. This page provides an overview of what ocean acidification is and how to stop it.

Carbonated Beverages/Carbonated Oceans

Acids, Bases and pH

Carbonate chemistry

More to explore

Activities

Acids, Bases & pH

Disappearing Shell Egg-speriment

Save Our Planet From Vampires

Carbonated Beverages/Carbonated Oceans

You know about global warming, right? Every time your mom drives you to a soccer game, your car spews carbon dioxide into the atmosphere, which warms our planet. But not all of the carbon dioxide released into the atmosphere stays there. In fact, scientists now believe about a third it ends up in the oceans.

In a way, it’s a good thing that the oceans soak up carbon dioxide, because if they didn’t there would be a lot more in the air, and global warming would speed up. The problem is, the excess carbon dioxide in ocean water changes ocean chemistry, and any change in ocean chemistry is bad news for ocean life.

To understand how carbon dioxide affects ocean chemistry, think about soda pop. When you open a bottle, the gas that bubbles out is carbon dioxide. In the soda, carbon dioxide combines with water to form carbonic acid; that's why it's called a “carbonated beverage”. Carbonic acid gives soda its zing.

If you leave a bottle of soda open for a few hours, the carbon dioxide gas, which was injected under pressure, is released into the air. The bubbles disappear and the soda tastes flat. But even flat soda has some carbon dioxide in it. How much is there depends on several factors, including temperature, atmospheric pressure, and the amount of carbon dioxide in the air.

Which leads us back to the burning of fossil fuels. Like open bottles of soda, oceans are exposed to the air, so the more carbon dioxide we humans release into the air, the more that ends up in the oceans. Because carbon dioxide makes the oceans more acidic, scientists call this process “ocean acidification.”

fish

See for yourself how carbon dioxide acidifies ocean water.

See for yourself how acid dissolves shells

snail

The creatures most likely to be affected by ocean acidification are corals, shellfish, and some types of plankton that have shells or skeletons made of calcium carbonate, because acid is corrosive to calcium carbonate. Even if the pH drops a little bit, it becomes harder for these plants and animals to build shells and skeletons, and those already built tend to dissolve.

Global warming and ocean acidification are scary problems, but we already know how to solve them: we need to reduce our use of fossil fuels. It’s not going to be easy, but if we work together we can do it. So, as you sip your next soda, think about how you can stop ocean acidification, but also think about this: acid is not only corrosive to calcium carbonate, it is also corrosive to calcium phosphate, the primary ingredient in tooth enamel.

If you'd like to dig a bit more into water and carbonate chemistry, read on:

Learn how to vanquish eletricity- sucking vampires and other ways you can save energy.

Acids, Bases & pH

Visit my blog for experiments with acids, bases and pH

As you may know, water has the chemical formula H2O. This means that a water molecule is made up of two hydrogen (H) atoms and one oxygen (O) atom. You can’t see a water molecule, but if you could it would look something like this:

water

Water molecules can break down into hydrogen (H+) and hydroxide (OH-) ions, like so:

water breakdown

At any given time a tiny fraction of water molecules are broken down into H+ and OH-. Each time a water molecule splits, it produces exactly one hydrogen (H+) and one hydroxide (OH-) ion. This means that if the water is completely pure, there is an equal number of each ion. In real life though, water, even fresh out of the tap, is never pure. Metal ions, chorine, fluoride, even air contaminate our drinking water. Luckily, none of these contaminants cause us any harm, but they do change the chemistry of the stuff we’re drinking.

Two special groups of chemicals, called acids and bases, disrupt water’s H+/OH- balance. Acids add excess hydrogen (H+) to water. Bases add excess hydroxide (OH-).

acid

Acids add excess H+ to water

bases

Bases add excess OH- to water

The relative concentration of H+ and OH- ions is a very important concept in water chemistry. It is so important, in fact, that scientists have developed a special scale to measure it: the pH scale. The pH scale, which is logarithmic and ranges in value from 0 to 14, is a measure of the concentration of H+ ions. At 25°Celcius (77° Fahrenheit), pure water has a pH of seven and is considered neutral, meaning that it has an equal number of hydrogen (H+) and hydroxide (OH-) ions.

pH scale:

pH scale

Acidic solutions have a pH less than seven; the lower the pH, the more acidic the solution. Acids, like lemon juice, taste sour. Soda pop is really acidic, with a pH ranging from 2.5 to 4.5. By comparison vinegar has a pH of 2.4, so some types of soda are almost as acidic as vinegar! Basic solutions have a pH greater than seven; the higher the pH the more basic the solution. Bases like soap and baking soda taste bitter.

Ocean water is naturally a little basic, with a pH of about 8.1, but the pH is dropping. Modern human activities are increasing the amount of carbon dioxide in the oceans. The carbon dioxide combines with ocean water to form carbonic acid, and just as carbonic acid acidifies soda pop, so it acidifies ocean water. As a result of human activities, scientists estimate that the average pH of surface ocean water is about 0.1 pH unit lower than it was in the 1800s, prior to the industrial revolution. This may not sound like a lot, but a drop of 0.1 pH unit is equivalent to a twenty-five percent increase in H+ concentration.
The world’s population is growing and becoming more industrialized, and by the end of the century, the rate of fossil fuel consumption could double. If this happens, the surface ocean pH could drop 0.3-0.4 pH units, equivalent to a 100 to 150% increase in acidity!

Carbonate Chemistry

Chemists use formulas to describe chemicals. The formula of carbon dioxide is CO2, the formula of water is H2O, and the formula of carbonic acid is H2CO3. Carbon dioxide reacts with water to form carbonic acid, like so:

Reaction 1: CO2 + H2O = H2CO3
Carbon dioxide water carbonic acid

Carbonic acid can, in turn, can break down into bicarbonate (HCO3-1) and carbonate (CO3-2), thereby releasing hydrogen ions (H+), which makes the solution acidic:

Reaction 2: H2CO3 = H+ + HCO3-1 = 2H+ + CO3-2
Carbonic acid bicarbonate carbonate

Some ocean life uses carbonate (CO3-2), the far right product of Reaction 2, to make calcium carbonate (CaCO3) shells or skeletons. Looking at these reactions, you might think that adding carbon dioxide to the ocean would increase the amount of carbonate present, but in fact it has the opposite affect: the excess carbon dioxide adds H+ to the water, which combine with carbonate to form bicarbonate. Reaction 2 shifts to the left, toward bicarbonate. This is bad news for the corals, planktons and shellfish that make calcium carbonate shells and skeletons, and bad news for the ocean life that relies on these plants and animals for food and shelter.