What is Ocean Acidification? Causes and Impact

Ocean Acidification became a problem after the rise of the Industrial Revolution. Since the industrial revolution began, we’ve seen an alarming increase in the production of carbon emissions. These emissions have nowhere to go because we have destroyed forested ecosystems that could have absorbed them. 

Instead, the ocean steadily absorbs carbon dioxide. This absorption harms various oceans because its decreasing pH leads to acidity, negatively impacting the aquatic ecosystem, animals, and humans. 

This article explores the process and causes of ocean acidification. We will also discuss how to measure ocean acidification and its potential impacts on marine organisms and humans. 

What is ocean acidification? 

Ocean acidification results from a chemical reaction caused by the absorption of carbon dioxide from the atmosphere. Many human activities, such as burning fossil fuels, various land uses, and manufacturing practices, release tons of C02 into the atmosphere. These carbon emissions don’t stay in the atmosphere.

Plants and the oceans absorb carbon dioxide. The world’s oceans absorb 30% of the carbon dioxide in the atmosphere, causing an increase in ocean acidity. An increase in the ocean’s pH directly impacts excess carbon pollution from burning fossil fuels. The ocean absorbs one-third of the carbon released from burning fossil fuels. 

The pH scale is from 0 to 14; anything over 7 is alkaline, and anything below 7 is acidic. More hydrogen ions lead to higher acidity and a lower pH. As seawater absorbs carbon dioxide, it forms carbonic acid (H2CO3). Carbonic acid (H2CO3) is a weak acid that separates into hydrogen ions and bicarbonate ions, increasing its acidity.

Before the industrial revolution began, seawater's pH was 8.2. In the 21st century, it dropped by 0.1 pH units to 8.1. Scientists predict surface ocean waters will become more acidic by 2100², falling to 7.8. 7.8 makes the ocean 150 times more acidic.

Causes of Ocean Acidification  

Human activities that produce carbon dioxide cause ocean acidification. Some examples are deforestation, unsustainable agricultural practices, and burning fossil fuels. 

Deforestation 

Deforestation is one of the significant causes of carbon dioxides in the atmosphere. We cut down trees and clear forest areas to make room for buildings, agricultural land use, construction, and manufacturing purposes, leading to the absence of trees and greenery to soak carbon dioxide in the atmosphere. 

Most of the farmlands on earth used to be part of a great expanse of forests. China lost most of its forested areas in the past 4000 years, while we cut down most of the trees in North America from the 1600s to the 1870s for construction, timber, and agriculture. We are destroying most of the remaining tropical rainforests to construct roads connecting inaccessible regions.

Forests and other green ecosystems play a unique role in preventing the accumulation of CO2 in the atmosphere. They sequester carbon, meaning they are like a sponge, soaking carbon from the air. Trees absorb carbon dioxide through photosynthesis, preventing the environment from overheating. 

Deforestation strips the environment of forests’ sequestering benefits. As we cut and burn down trees, we release the carbon stored in the tree while increasing the carbon dioxide levels in the atmosphere. Deforestation produces 4.8 billion tons of carbon dioxide annually. The increase causes a chain reaction, creating more acidic waters¹.

Fewer trees are in the environment to absorb the carbon dioxide released into the air. So, it accumulates in the air, leading to ocean acidification and increasing its impact on ocean life.   

Fossil fuel burning 

Fossil fuels are nonrenewable energy sources used to generate electricity, heating, and transportation over the past two decades. The extraction and use of fuels such as coal, oil, and natural gas contribute to the carbon dioxide in the air. 

We use these fuels to produce energy in various manufacturing companies, to produce electricity, and to power big engines. We also use them to cook and provide heat when it's cold. We also use them to power transport systems like buses, cars, airplanes, and ships.  

Burning crude oil, coal, and natural gas produces enormous amounts of carbon dioxide in the air, making it the most significant contributor to global warming. In 2022, 81% of the United States' energy comes from coal, natural gas, and crude oil, so you can imagine the amount of carbon dioxide released into the atmosphere daily.

Fossil fuels contribute the most CO2 to the air. In 2023, the fossil fuel industry released 36.8 billion tons of carbon, with the United States being the world’s second carbon emitter after China⁴.

Unsustainable farming practices 

Another reason ocean pH decreases is unsustainable farming practices. These practices contribute to environmental pollution and harm the earth instead of producing a bountiful harvest without damaging the soil and its organisms. 

These harmful practices include monoculture, excessive pesticide and fertilizer use, and improper livestock waste disposal. Improper livestock waste disposal and fertilizer applications produce the second largest nitrogen emission. In contrast, monoculture, land clearance, and improper soil management contribute to agricultural carbon emissions. 

The ocean absorbs up to 30% of carbon emissions yearly, so imagine how high its acidity is now—it is steadily increasing. Excessive use of pesticides and fertilizers reduces the soil’s ability to provide nutrients for trees, plants, and other vegetation, making it challenging to sequester carbon from the air. 

Apart from producing carbon, the other gas emissions produced in agriculture also contribute to climate change. It increases global warming, traps more heat in the air, warms surface waters, and increases the chances of ocean acidification.

How To Measure Ocean Acidification  

Scientists from NOAA’s Ocean Acidification Program track the acidity of seawater through total alkalinity (TA) and pH. Seawater pH shows the number of free-moving hydrogen ions in the water. The more ions are present, the more acidic the water is. Measuring the water’s alkalinity also helps understand the CO2 content in the water. 

Total alkalinity measures the total concentration of calcium carbonate and bicarbonate in seawater because these molecules neutralize ocean pH. An ion-sensitive field-effect transistor (ISFET) is used to calculate seawater pH. 

It is a device that measures the pH from a single drop or larger volume with a silicon chip sensor.  The sensor chip is in a rigid structure, which prevents breakage or damage. It measures the H+ concentration in the water.

Researchers suggest other ways of measuring ocean acidification, like Diffused Inorganic Carbon (DIC). DIC measures how much non-biological carbon is in oceans and other water bodies. They measure the presence of inorganic carbons, such as carbon dioxide, carbonate, and bicarbonate, to determine carbon balance and the potential development of ocean acidification.

They also watch for the partial pressure of CO2 because it shows how much carbon dioxide seawater has absorbed. Learning about the quantity of carbon in seawater helps scientists understand the ocean's carbonate chemistry and biological productivity. A high partial pressure of CO2 indicates high absorption levels of CO2.

Environmental Impacts of Ocean Acidification 

Impacts Of Ocean Acidification On Marine Ecosystems 

Ocean acidification harms marine species in various ecosystems. It harms many marine species that rely on carbonate-based shells and those with high sensitivity to acid. Acidification also affects the complex food webs in the ocean. For instance, other marine species high on the food web feed on the ones with high sensitivity. 

Calcifying organisms are marine animals that use calcium carbonate to build their shells and skeletons. These marine species include coral reefs, plankton, oysters, etc. Ocean acidification breaks existing shells and skeletons and makes creating a new one challenging because of the ocean's limited calcium carbonate. 

Their shells become weak and vulnerable to damage from external factors, which weakens their recovery rates. For example, sea urchins help protect coral reefs from algae. However, they can't in acidic coastal areas because their weak protective shells make them more vulnerable to predators.

It also disrupts the food web because calcifying organisms prey on other animals. Some fish species are vulnerable to ocean acidification. Fish eggs and larvae might find it challenging to grow, develop, and survive in acidic oceans. An example is the clownfish larvae, which showed a reduced sense of smell in acidic marine environments, leading to risky swimming behaviors.

Ocean Acidification Impacts On Human Health 

Besides its harmful impacts on the marine environment, ocean acidification harms humans and their health. The ocean ecosystem is a primary source of many resources vital to our survival. Ocean acidification affects humans in four different ways. 

First, bad air quality causes respiratory problems, which are primarily caused by algae blooms. For instance, the blooms of Florida red tiles (Karenia brevis) produce brevetoxins, which cause upper and lower respiratory issues in Florida. 

Ocean acidification also threatens food security. About 4.5 billion humans get 15% of their protein from fish. Acidification reduces the lifecycle of these animals, creating a scarcity of marine life. Most tropical fish become vulnerable to extinction as ocean acidification destroys corals.

It also disrupts the nutritional qualities of the marine food web, especially lipid and protein content. Eating seafood with low lipid content harms humans because lipids are essential to human health³. They provide fatty acids, fat-soluble vitamins, and anti-inflammatory properties.

Conclusion   

Ocean acidification is a deadly problem for the environment, especially with the increasing rates of climate change. Climate change increases the speed of ocean acidification and worsens its impacts. It disrupts the food source and life cycle of organisms.

We should work together to prevent complete ocean acidification by reducing our contribution to greenhouse gas emissions. Other solutions include planting seagrass to prevent acidification on calcifying organisms and using alkaline rock materials to lower pH.