🧠 Explainer: Ocean Acidification

Willow Beck
Quinn Emmett
January 26, 2023
Audio version

🧠 Explainer: Ocean Acidification

Willow Beck
Quinn Emmett
January 26, 2023
Full name
Job title, Company name

What is ocean acidification?

Ocean acidification is the decrease in the ocean's pH over time due to excess carbon dioxide in the atmosphere.

To understand ocean acidification, first, we must understand what pH means. So, if it’s not too (understandably) traumatic for you, journey back with me to seventh-grade chemistry class.

Basically (pun absolutely intended), pH is a measurement from 0 to 14 of the concentration of hydrogen ions in an aqueous solution (let’s say, water) on a logarithmic scale. Since pH is the inverse of hydrogen ion concentration, the more hydrogen ions in a solution, the higher the acidity and the lower the pH. A pH of 7 is neutral, greater than 7 is basic or alkaline, and less than 7 is acidic.

Ok, back to the ocean and why this matters.


History of ocean acidification

We know atmospheric carbon dioxide concentrations have increased since the Industrial Revolution due to human activities such as burning fossil fuels, mass deforestation, and industrialized agriculture. We also know that this is linked to climate change, causing a whole mess of issues that you can read about weekly in our newsletter! Lucky you.

In addition to increasing Earth’s average temperature, the increase in atmospheric carbon has also caused the pH of surface ocean water to have fallen by 0.1 pH units. This sounds like a small number, but remember that pH is logarithmic and so this change is actually a 30 percent increase in acidity!

The ocean is basic - chemically, not in the PSL way - historically having a pH of 8.2, which has dropped to 8.1.

Current models indicate that if nothing is done about the increased carbon dioxide in the atmosphere, the ocean's pH could drop to 7.8 by the end of the century. Therefore, the ocean is becoming MORE acidic - but still does not classify as an acid.

The ocean being basic (…in 2015? It was a simpler time). *Disclaimer: There is no shame in being basic. Ugg boots are comfortable and pumpkin spice lattes are delicious. The world is on fire, enjoy life’s pleasures (ideally in a reusable cup) where you can.

Ocean acidification chemistry

The ocean absorbs 30 percent of the carbon dioxide in the atmosphere. When carbon dioxide naturally dissolves in seawater, it combines with water (H2O) to carbonic acid:

CO2(aq) + H2O ↔ H2CO3 (1)

Carbonic acid is a weak acid that breaks into hydrogen ions and bicarbonate ions:

H2CO3 ↔ HCO3- + H+ (2)

Bicarbonate ions can further break into carbonate ions:

HCO3- ↔ CO32- + H+ (3)

All of these chemical reactions result in an increase in hydrogen ions (H+), and therefore an increase in acidity.

Why is ocean acidification a problem?

Ocean acidification: coral reefs

Coral reefs, already suffering from warming water causing coral bleaching, are vulnerable to ocean acidification. Corals make their skeletons by combining carbonate and calcium in seawater. Excess hydrogen ions bond with carbonate ions, making it less available for corals to build their skeletons. This results in weaker reefs that are more vulnerable to erosion and the slower growth of new reefs.

By 2080, ocean acidity may be so great that corals will erode more quickly than they can rebuild.

Some coral species are less vulnerable, having the ability to build their skeletons using bicarbonate ions instead of carbonate ions, and others are resilient enough to survive without a skeleton and return to normal once the pH is more comfortable. This has resulted in some reefs being overtaken by boulder colonies of corals in places like Papua New Guinea, which threatens biodiversity as many organisms have adapted to live on specific coral species.

Effects of ocean acidification on other marine life

Like corals, other hard-shell animals such as oysters, make their shells from calcium and carbonate and face similar struggles building their shells in lower pH environments to the extent that oyster larvae cannot even begin growing their shell. The threads that mussels use to hold onto rocks aren’t as strong in more acidic conditions, clownfish have a decreased ability to detect predators, and major types of zooplankton struggle to build their shells as well. All of these animals - especially zooplankton - form the ocean’s food web’s foundation. Zooplankton are also very important to the carbon cycle, storing a lot of carbon when they die and sink to the bottom of the ocean.

One animal that thrives in warmer and more acidic conditions are jellyfish, which compete with other predators for food, and may soon dominate ocean ecosystems.

Ocean acidification effects on humans

Our position at the top of the food chain is precarious. If animals at the bottom disappear, that will have a cascading effect throughout the food web that will directly impact our access to seafood, which many coastal economies are dependent on. Some estimates predict that the US shellfish industry could lose $400 million annually by 2100 if ocean acidification continues.

If you live on the coast and want to see how ocean acidification will impact your community, use this interactive map from the NRDC.

Ocean acidification solutions

Ok, enough doom and gloom. There’s still an opportunity to avoid packing our children’s lunches with jellyfish salad sandwiches instead of tuna, and lots of smart people are working on a myriad of solutions to ocean acidification (other than putting an end to burning fossil fuels and transitioning to clean energy, which yes, obviously that).

Have you ever needed to take an antacid in the morning after eating a large poutine too close to bedtime? The family-sized box of Tums on my bedside table is a drop in the ocean compared to the number of antacids the ocean needs, but some young scientists are working on how to increase the alkalinity of the ocean at scale.

Other scientists have found that growing and farming seaweed may slow acidification because seaweed uses carbon dioxide for photosynthesis.

Governments can take the 30x30 pledge to set aside 30 percent of lands and waters for conservation. The EPA can and should address ocean acidification using the Clean Water Act.

Learn more about our oceans

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