The other CO2 problem

Image: Wikimedia Commons

Marine life is threatened by the actions of humankind; overfishing is killing off some aquatic species to the point of endangerment; fertiliser run-off is polluting water courses leading to algal blooms and eutrophication; vast swathes of mangrove forests have been cleared to make way for shrimp farming. To make matters worse, a recent key report suggests that another problem exacerbated by humans is affecting the majority of ocean life.

Due to increasing levels of carbon dioxide (CO2 ) emissions, ocean acidification is becoming yet another terminal menace that is threatening marine life. This claim is supported by a study published through the research network BIOACID in collaboration with the German Federal Ministry of Education and Research. The report took eight years to produce and benefitted from over 250 scientists across 20 research institutes, representing a broad range of marine science disciplines. It is to be given to UN climate negotiators at their annual summit occurring in Bonn, Germany this month.

Ocean acidification, sometimes referred to as “the other carbon dioxide problem” or “the evil twin of global warming”, is the process whereby atmospheric CO2 dissolves into the ocean. Once dissolved, the aqueous CO2 forms carbonic acid (H2 CO3 ) by reacting with water. This process is completely normal and has occurred forever. However, since the presence of CO2 in the atmosphere has increased, more and more CO2 is dissolving into the ocean every year. Acting as a massive carbon sink, the ocean has absorbed, it is estimated, as much as one third of the CO2 released due to human activity. Ocean acidification could possibly amplify the effects of global warming, creating a potentially detrimental feedback loop.

Surface seawater’s pH has dropped from 8.2 to 8.1 since the beginning of the Industrial Revolution. While this may seem like a minuscule change, this drop corresponds to a 26 per cent increase in ocean acidity. While attempts at halting further acidification are being made through mitigation measures, this will only be achieved by actively removing carbon already in the atmosphere.

When ocean conditions become more acidic the presence of hydrogen ions increases meaning more valuable carbonate ions (CO3 2-) than normal can be protonated forming bicarbonate (HCO3 – ). The more carbonate there is, the less there will be available for calcifying organisms such as mussels, corals, or certain plankton to build their shells and skeletons.

While ocean acidification has negative impacts on much of oceanic life, it seems to particularly harm the young. Researchers discovered that increased acidification could potentially double the mortality rate of newly hatched cod larvae and that the population of Atlantic cod in the Baltic and Barents seas could fall to a quarter of the size of current populations as a result, another nail in the coffin for a fish that has been subject to massive over-fishing in the past years.

The report’s lead author, Prof essor Ulf Riebesell of the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany has said: “Acidification affects marine life across all groups, although to different degrees. Warm water corals are generally more sensitive than coldwater corals. Clams and snails are more sensitive than crustaceans, and we found that early life stages are generally more affected than adult organisms. But even if an organism isn’t directly harmed by acidification it may be affected indirectly through changes in its habitat or changes in the food web. At the end of the day, these changes will affect the many services the ocean provides to us.”

The report also found that while many organisms have managed to become resistant to the effects of ocean acidification, they could lose these abilities if exposed to other man made problems such as sea warming, excess nutrients, loss of oxygen, reduced salinity, and pollution. Since acidification is now occurring at a faster rate when compared to natural processes, organisms are simply unable to adapt quickly enough.

We have already begun to see this with coral bleaching – a process where increased oceanic acidity and temperature stress microorganisms living within coral, leading to the death of both. This leads to the loss of the colours and the photosynthetic abilities of coral. Sadly, this damage cannot be reversed, and our coral reefs are at risk. Around half of the world’s coral reefs can be preserved if global warming is kept below +1.2°C (1.5°C being the target agreed at the 2015 Paris Accords), however rising water temperatures and acidification is causing intense coral bleaching to the point where some experts claim the Great Barrier Reef is “no longer salvageable”.

Crucially, ocean acidification is yet another result of increased greenhouse gas emissions intensified by harmful human activities. As we move into the Anthropocene, the ever-increasing atmospheric concentration of CO2 will only continue to acidify our oceans. Only a sincere global effort to reduce emissions can prevent detrimental levels of ocean acidification.

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