Why carbon dioxide in the oceans is a problem
Is there CO2 in the oceans?
Carbon dioxide (CO2) is a greenhouse gas (GHG) that has been implicated in causing climate change. We generally know this but what is less known is that increasing CO2 in the oceans is a big a problem as climate change. Perhaps not many people realize that oceans absorb atmospheric CO2. Even less realize that increasing CO2 in the oceans is actually a big problem.
Oceans and the carbon cycle
When CO2 is released into the atmosphere (whether it is a natural emission or human-induced emission) some of it stays there but some of it is cycled to other areas of the globe. Organisms, especially plants, uptake some of this CO2. Forests, for example, are carbon sinks where they can absorbed more carbon than they emit. Soils also act as a carbon sinks leading to some governments undertaking programs for farmers to take up carbon in their soil for carbon credits. This is also known as carbon farming.
But the oceans actually absorbed a very significant proportion. Approximately one third, or 30%, of the CO2 that is emitted into the atmosphere is absorbed by oceans. Therefore, with increasing amount of CO2 in the atmosphere, there is also an increasing amount of CO2 in the oceans.
The process of ocean acidification
Ocean acidification is explained in detail elsewhere. Briefly, CO2 entering the ocean becomes dissolved and changes the water chemistry. When CO2 reacts with water it forms carbonic acid which then dissociates into hydrogen ions and bicarbonate ions. When hydrogen ions increase in a solution, the pH decreases or becomes more acidic. So increasing CO2 in the ocean is decreasing the pH and leading to ocean acidification.
More precisely, increasing CO2 is leading the oceans to become less alkaline. In pre-industrial times, the pH of the ocean was 8.2. Today, the pH of the oceans is approximately 8.1. By the year 2100 it is predicted to be approximately 7.8. Therefore, the oceans are not becoming a sea of acid, rather a sea of less alkalinity.
Ocean acidification explained in 2 minutes
Small changes, big problems
Oceans with less alkalinity doesn’t sound as scary as ocean acidification. Additionally, a change in pH from 8.2 to 7.8 seems rather trivial. But scientific evidence shows that even this small shift in ocean pH can lead to big problems.
Ocean acidification is leading to a decrease in carbonic ions in the oceans. This ion is critical for many marine organisms to form their hard shells and skeletons. Developing a strong body for organisms such as corals, molluscs and crustaceans will become a problem. If these organisms cannot survive, then it could lead to wider ecological and ecosystem issues. For example, thousands of species, including humans, depend on corals. If corals should collapse, then this will lead to significant environmental problems.
Research shows ocean acidification is already a problem
Scientists have been performing many experiments on how future changes in ocean acidification will impact on marine organisms, although some caution has been expressed over the validity of experimental parameters in certain experiments. For example, in near-shore ocean environments, particularly where there is extensive seagrass vegetation, pH can vary quite widely.
Recently, the journal Nature published research showing that current levels of ocean pH is already having a significant impact on coral reefs. The unique experiment was conducted on a naturally occurring coral reef on the Great Barrier Reef off the coast of eastern Australia. As most ocean acidification experiments in the laboratory decrease pH, in this instance the scientists actually increased pH (that is, they made the oceans more alkaline). The motivation to increase the alkalinity of the ocean was to return the pH to levels that were observed prior to the industrial revolution.
The scientists found that the marine organisms in the pre-industrial ocean grew better skeletons and were more robust than the marine organisms in the modern ocean. The experiment demonstrated that changes in the oceans caused by an increase in atmospheric CO2 is not something that will occur in the future. Rather, the process of ocean acidification is occurring now.
Coral reefs and climate change
Reef building corals are the most vulnerable
Ocean acidification will affect many different types of species. However, emphasis has been given to reef building corals and their vulnerability to changes in ocean pH. As already described, a decrease in the ocean's pH will make it harder for corals to form skeletons. But other changes, occurring along with ocean acidification, are increasing the possibility of reef building coral extinction.
Temperature is another big environmental change in the oceans that will affect corals. Increasing temperature leads to organism stress and events such as coral bleaching. Direct human impacts, such as dredging for coal mines, as well as the impacts of invasive species, such as the crown of thorns star fish, are also making coral reefs vulnerable.
Coral bleaching - before and after
CO2 is not only a problem for climate change, but it is also a problem for the earth's oceans. Increasing CO2 is leading to ocean acidification which, in turn, is causing a range of ecological and environmental problems for marine life.