Ocean acidification: Causes, Mechanism & Effects

Continuous lowering of the pH of the ocean due to the absorption of carbon dioxide (CO₂) from the atmosphere is known as ocean acidification. The combustion of fossil fuels is the primary cause of modern ocean acidification. The quantity of carbon dioxide absorbed by the ocean increases as atmospheric carbon dioxide levels increase. This results in the occurrence of chemical reactions in the ocean that have an adverse effect on the ocean and aquatic organisms.

However, when carbon dioxide is dissolved in the ocean’s water, carbonic acid (H₂CO₃) is formed by the reaction of water (H₂O) and carbon dioxide (CO₂). The concentration of hydrogen ions (H⁺) in the ocean rises due to the dissociation of certain carbonic acid (H₂CO₃) molecules into bicarbonate and hydrogen ions. It is predicted that between 1751 and 1996, the pH of the ocean surface declined from around 8.25 to 8.14, which means increasing the quantity of H⁺ ions in the ocean by roughly 30%.

The results of ocean acidification are very harmful to aquatic organisms. For example, a reduction in the synthesis of calcium carbonate shells in shellfish and other aquatic life. Under very saturated and acidic conditions, organisms with calcium carbonate shells cannot reproduce easily.

History of ocean acidification

There is historical evidence of ocean acidification. The results were an ecological oceanic collapse that had long-lasting repercussions on the climate and carbon cycle across the world. For instance, the breakdown of carbonate deposits in all ocean basins occurred during the Paleocene-Eocene Thermal Maximum (PETM), roughly 56 million years ago, when enormous quantities of carbon entered the ocean and atmosphere.

The sharp rise in atmospheric carbon dioxide was linked to the oceanic mass extinction events. Maybe this is due to volcanism or thermal dissociation of hydrates in the ocean. Early studies examined how biodiversity might be affected by climate change caused by carbon dioxide (CO₂). However, a potential lethal mechanism for oceanic mass extinction at the end of the Triassic was proposed in 2004 and involved decreasing CaCO₃ saturation.

However, the end-Triassic biotic catastrophe remains the best-documented instance of an ocean mass extinction caused by ocean acidification. This can be due to a precise stratigraphic correlation between ocean extinction, a decrease in carbonate sedimentation, and volcanic activity.

Causes of ocean acidification

These are the major causes of ocean acidification:

The burning of fossil fuels like oil and gas.
Smoke from industries and mechanical engines.
Burning of wood and forests, etc.

A larger amount of carbon dioxide, about 30-40% released by the activities of human beings.

This carbon dioxide enters the atmosphere as a result of human activities, particularly the burning of fossil fuels. In this way, 45% (out of the total amount) of carbon dioxide remains in the atmosphere, and the rest of it is absorbed by the ocean, with some also being absorbed by plants.

Carbon cycle

The movement of carbon dioxide (CO₂) between the earth’s surface, atmosphere, plants, and ocean can be explained by the carbon cycle. There are two types of compounds that are involved in the carbon cycle.

Organic compounds like cellulose, starch, etc.
Inorganic compounds, such as carbon dioxide (CO₂), carbonate ion (CO₃^2-), bicarbonate ion (HCO₃^–), etc.

Therefore, the carbon cycle expresses the abolition of carbon dioxide (CO₂) in the ocean. A balance of ionic and non-ionic chemical species, including aqueous carbon dioxide, carbonic acid (H₂CO₃), bicarbonate (HCO₃), and carbonate (CO²₃), are formed when CO₂ dissolves in water.

However, the ratio of these chemical species is influenced by the salinity, pressure, and temperature of the water in the ocean. The solubility pump or force of an ocean transports these various types of dissolved inorganic carbon from the surface to the interior of the ocean.

Mechanism of ocean acidification

when Carbon dioxide (CO₂) is dissolved in the ocean, the concentration of acid (hydrogen ions H⁺) increases, which results in a decrease of the pH of the ocean.

CO₂ _(aq) + H₂O ⇌ H₂CO₃ ⇌ HCO₃⁻ + H⁺ ⇌ CO₃²⁻ + 2H⁺

Further studies revealed that about one-third of the carbon dioxide released by human activities is dissolved in the ocean. This makes the ocean very acidic. Whereas, from the start of the industrial revolution, there is a 30% increase in the acidification of the ocean surface.

These are the other factor than contribute to ocean acidification:

Photosynthesis
Respiration
Movement of water to the edges of the land.
Ecosystem metabolism in freshwater also enhances acidity.

Effects of ocean acidification

These are the following effects of ocean acidification:

Biological effects
Nonbiological effects
Effects on ocean calcifying organism
Effects on industries
Coral bleaching

Biological effects

Increased level of acid in the ocean leads to changes in the biological activities of the oceanic organisms. For example, Increased acidity has been seen to slow the blue mussel’s immune responses and lower the giant squid’s metabolic rates. Ocean acidification changes the acoustic characteristics of seawater, allowing sound to travel farther and increasing ocean noise. All creatures that use sound for communication or echolocation are affected by this. Similarly, In seawater with a lower pH, Atlantic longfin squid eggs take too much time for hatching and become malformed during the stage of development.

Non-biological effects

Ocean acidification is predicted to eventually result in a significant reduction in the burial of carbonate sediments and the dissolution of existing carbonate sediments. This increases ocean basicity and improves the ocean’s capacity to store carbon dioxide (CO₂), which has an effect on climate change as more carbon dioxide (CO₂) leaves the atmosphere for the ocean.

Effects on ocean calcifying organism

Ocean acidification also affects the organism in the ocean. A high level of acidity inhibits the excess of carbonate ions that are required for the production of the outer covering (exoskeleton) of the organisms. Oceanic calcifying organisms, which include coccolithophores, corals, foraminifera, echinoderms, crabs, and mollusks, complete the food chain from autotrophs to heterotrophs.

Calcite and aragonite are stable in surface waters where carbonate ions are present in higher concentrations. Whereas, as ocean pH lowers, the concentration of carbonate ions becomes lower and calcium carbonate-based structures are susceptible to breakdown.

Effects on industries

There is a larger effect of ocean acidification on the industries like fish industry, etc. For example, commercial fisheries depend on the calcifying organisms that are responsible for making Artic food webs.

For example, pteropods, and brittle stars, which are the base of the Arctic food webs, are severely harmed by acidification. As the environment becomes more acidic, pteropod shells disintegrate, and brittle stars lose muscle mass when developing new limbs.

Coral bleaching

One of the effects of rising ocean acidity is the phenomena of coral bleaching or coral whitening and the decline of coralline reef ecosystems. Coral bleaching is most prevalent in the tropical and sub-tropical environments, which include places like the Caribbean and surrounding areas, tropical Asia (such as Indonesia, Philippines, Thailand, Maldives), and tropical Pacific (such as the Australian Barrier Reef, Pacific Islands, Papua New Guinea). These regions of the world are home to the largest and most extensive coral reef systems.

Concepts Berg

What is ocean acidification?

Ocean acidification is the increase in the acidity of the ocean. This is due to the absorption of carbon dioxide (CO₂) from the atmosphere. The absorbed carbon dioxide and water react with each other and formed acidic components. Like carbonic acid, etc.

What is ocean acidification and why is it a problem?

High levels of acidity in the water of the ocean by absorbing the atmospheric carbon dioxide (CO₂) known as ocean acidification. It is a major problem for the organisms in the ocean water. They cannot survive and reproduce due to ocean acidification.

What are the three effects of ocean acidification?

These are the 3 effects of ocean acidifications:

Coral bleaching
Effect on the lives of organisms
Change the behaviors of the fishes

What is the one-way ocean acidification impact humans?

Ocean acidification has a large impact on the market for fish.

What animals are most affected by ocean acidification?

These are oceanic animals that are affected by ocean acidification:

Jumbo squid
Starfish
Blue mussels

What caused ocean acidification?

The burning of fossil fuels and human activities are the causes of ocean acidification. Because due to human activity, there is about 25-30% of carbon dioxide released into the atmosphere from where it is absorbed by the ocean.

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