Ocean acidification

Mean-seawater-ph

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Spatial distribution of global surface ocean pH

Carbon cycle

File:Impacts of ocean acidification (NOAA EVL).webm

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Ocean acidification is a decrease in the pH of the Earth's oceans, caused by the uptake of carbon dioxide (CO2) from the atmosphere. Seawater is slightly basic (meaning pH > 7), and ocean acidification involves a shift towards pH-neutral conditions rather than a transition to acidic conditions (pH < 7). The main cause of ocean acidification is the burning of fossil fuels, which releases large amounts of CO2 into the atmosphere. A significant portion of this CO2 is absorbed by the oceans, leading to a chemical reaction that reduces the pH of seawater.

Causes

The primary cause of ocean acidification is the increase in atmospheric CO2 due to activities such as the burning of fossil fuels, deforestation, and cement production. When CO2 is absorbed by seawater, it reacts with water to form carbonic acid, which then dissociates to bicarbonate, hydrogen ions, and carbonate ions. The increase in hydrogen ions lowers the ocean's pH, leading to acidification. This process also reduces the availability of carbonate ions, which are crucial for the calcification process of many marine organisms.

Effects

Ocean acidification has a wide range of effects on marine ecosystems. It particularly affects organisms with calcareous shells or skeletons, such as corals, mollusks, and some plankton species, by reducing the availability of carbonate ions needed to form their shells and skeletons. This can lead to weaker structures and increased vulnerability to predation and disease. Additionally, acidification can affect the behavior and physiology of fish and other marine organisms, potentially altering food webs and biodiversity.

Coral Reefs

Coral reefs are among the ecosystems most threatened by ocean acidification. Corals use carbonate ions to build their calcium carbonate skeletons. Acidification not only makes it more difficult for corals to construct their skeletons but can also lead to the dissolution of existing structures, weakening the reefs and reducing their biodiversity.

Plankton

Plankton, particularly those species that build calcium carbonate shells, are also affected by ocean acidification. These organisms are at the base of the marine food web, and changes in their abundance and health can have cascading effects on the entire ocean ecosystem.

Mitigation and Adaptation

Mitigating ocean acidification involves reducing CO2 emissions to the atmosphere. This can be achieved through the transition to renewable energy sources, improving energy efficiency, and developing carbon capture and storage technologies. Adaptation strategies for marine ecosystems are more challenging but can include protecting areas that are less affected by acidification, reducing other stressors such as pollution and overfishing, and supporting research into species that are more resilient to acidification.

Research and Monitoring

Ongoing research and monitoring are crucial for understanding the full impact of ocean acidification and for developing effective mitigation and adaptation strategies. This includes studying the basic chemical processes of acidification, its effects on marine life, and the socio-economic impacts on communities dependent on marine resources.