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The 5 W's of Ocean Acidification

Image is courtesy of DHI Blog.

What is ocean acidification?

As the name suggests, ocean acidification is an ocean becoming more acidic or, in other words, the ongoing decrease in the pH of the world’s ocean over an extended period of time. Aqueous solutions (liquids where the solvent is water) can be ranked on the pH scale (from 1-14, 1 being the most acidic, 14 is the most basic, and seven is neutral) where the solution is specified how acidic or basic it is. When the pH level of an aqueous solution decreases, it becomes more acidic. The pH level of seawater is generally around 8 (neutral and a bit basic), but this number has been decreasing. Ocean acidification has become a more prevalent environmental issue due to an increase in anthropogenic activities. The decrease in pH is a problem as the pH of water determines the solubility and biological availability (the amount that can be utilized by aquatic life) of chemicals like nutrients (phosphorus, nitrogen, and carbon) and heavy metals (lead, copper, etc.). The pH level can also affect how much and what form phosphorus is in and which aquatic life can use it (note that phosphorus is an essential nutrient for plant growth).

Where is ocean acidification taking place?

Ocean acidification is happening in oceans all over the world, including coastal estuaries and waterways. Some specific areas are more sensitive to ocean acidification, as the polar oceans in the Arctic and Antarctic. In contrast, other regions like waters off of California are acidifying twice as rapidly as elsewhere on Earth, according to a study published in 2019, which suggests that climate change is likely hastening and worsening chemical changes in the ocean that could threaten seafood and fisheries. The heating of global waters is another effect of climate change where research has indicated that human-induced climate warming will trigger the temperature to increase, even more, causing problems within the ecosystem of the Indian Ocean (the warmest ocean basin in the world).

Who is responsible and affected by ocean acidification?

Ocean acidification is an effect of climate change that is caused by human activities. Thus humans are responsible for ocean acidification. A human activity that has led to climate change is the increased use of fossil fuels like coal, oil, and gas to generate electricity, run cars and other forms of transport, and power manufacturing and industry. Mass deforestation has also contributed to climate change as living trees absorb and store carbon dioxide. They are more causes of climate change, primarily due to human activity increasing CO2 emissions in the atmosphere and ultimately the amount of CO2 dissolved in the sea. Ocean acidification affects everyone directly or indirectly; a direct impact is that when these fishing populations begin to dwindle because of the decreased pH, the fishing industry will suffer as they have less to fish from and sell. Unfortunately, many jobs and economies worldwide depend on the fish and shellfish that live in the ocean. Some indirect effects are: the safety of the seafood (i.e., whether the fish are safe to eat coming from such an acidic environment), not enough food as billions of people worldwide rely on food from the ocean as their primary source of protein, and the increased temperature from the heating of the ocean. At night, the land cools quickly without the heat of the Sun. However, water heats and cools much more slowly than land, and consequently, the air over the ocean becomes warmer than the air over land. When the sea warms up, the cooling ability of the water during the day decreases, and the cooling capacity of the land decreases at night.

Marine organisms are also affected; Dr. Peter Land, an expert in satellite earth observation at the Plymouth Marine Laboratory, said, “Ocean acidification is expected to have a direct effect on calcifying organisms such as corals, making it harder for them to grow, with knock-on effects on organisms that depend on them … As with temperature, each organism has its preferred range of pH, just like plants in a garden. When the whole ocean becomes more acidic, this can leave some organisms with nowhere to hide.”

Why is ocean acidification happening?

Climate change has been one of the biggest concerns in the 20th century. Human development has been progressing exponentially, resulting in high rates of carbon dioxide emissions into the atmosphere. Large amounts of carbon emissions released into the atmosphere result in an imbalance within the carbon system. Ocean acidification, the decrease in the ocean’s pH level, results from the increase of carbon dioxide concentration in the atmosphere. One of the most significant contributors of CO2 is the excess burning of fossil fuels and land-use change (ex. urbanization). The oceans absorb about 30% of the CO2 in the atmosphere and as a result of the atmospheric CO2 increasing, CO2 levels in the ocean increase. Aqueous solutions become more acidic with the increase of hydrogen ions. Thus the ocean becomes more acidic when CO2 is absorbed in seawater as a series of chemical reactions increase the concentration of hydrogen ions. This increase causes the seawater to become more acidic and causes carbonate ions to be relatively less.

When did ocean acidification become a larger issue?

Ocean acidification became more amplified 200 years ago when the industrial revolution began; the industrial revolution shifted the manufacturing of goods from small businesses to large factories. Since the beginning of the industrial era, the ocean has absorbed some 525 billion tons of CO2 from the atmosphere, presently around 22 million tons per day. In the manufacturing process, there was an increase in CO2 emissions due to the dramatic expansion of human activity, including but not limited to burning fossil fuels, deforestation, and increase in the use of automobiles. During this time, the pH of surface ocean waters fell by 0.11 pH, which corresponds to approximately a 30% increase in the hydrogen ion concentration. This might not sound like much, but the pH scale is logarithmic, so this change represents roughly a 30 percent increase in acidity. Many organisms are sensitive to the ocean’s pH level changes even if they are minimal; the change in pH can have direct or indirect effects on marine organisms. Fundamental physiological processes like respiration, calcification (shell/skeleton building due to decrease in carbonate ions), photosynthesis, and reproduction have been shown to have a negative reaction to changes in CO2 concentrations in seawater and the changes in pH and carbonate ion concentrations. This issue is expected to continue if CO2 emissions are not drastically reduced.

Besides the pH levels of ocean water decreasing, there has been an increase in average sea temperature due to a rise in CO2 in the atmosphere and the greenhouse effect. According to the International Union for Conservation of Nature, the ocean absorbs most of the excess heat from greenhouse gas emissions, mainly from human consumption of fossil fuels. A report published by the Intergovernmental Panel on Climate Change in 2013 revealed that the ocean had absorbed more than 93% of the excess heat from greenhouse gas emissions since 1970. From this data, “IPCC predicted that there is likely to be a 1 - 4 degree (Celcius) increase by 2100 in global ocean temperatures”; the top part of the ocean is warming up about 24% faster than it did a few decades ago. The temperature of oceans is rising everywhere, technically there is only one global ocean, but there are several water basins with different temperatures and aquatic plant life depending on its location (i.e., is it near the equator). The warming of the oceans has affected the efficiency of habitats and how some organisms function.

How can you help?

There are two main goals here: 1) Use and create energy more efficiently so there is less CO2 being put into the atmosphere. 2) Protect marine habitats and wildlife so that the ocean is more resilient and can bounce back from the damage that has already been caused.

The Climate Interpreter explains that there is more we can do than we think. Although mega-corporations are the more significant contributors to ocean acidification than the day-to-day person, it's always best to reduce our carbon footprint anyway!

Article Author: Kelley Liang

Article Editor: Maria Giroux