Ocean Acidification and its Consequences

The oceans cover ⅔ of our planet - they are so huge that they seem invulnerable. But through our daily work we know that they are struggling with many problems, such as pollution, overfishing, warming or overfertilization. But there is another issue: ocean acidification. We explain what this is and what it means for the oceans in this article!

cause of ocean acidification

The ocean has absorbed about ⅓ of anthropogenic carbon dioxide over the last six decades. This has increased by 40% compared to pre-industrial times, which is why the amount of daily absorption is now about 24 million tons of CO ₂ “That’s great!” we could say. Without the oceans, climate change would progress even faster. But as pleasing as this service may be for the climate, for the oceans it is worrying .

The Chemistry Behind Acidification

Since CO ₂ is soluble in water (H ₂ O), a chemical reaction occurs when it is absorbed. The CO ₂ from the atmosphere reacts with the H ₂ O to form carbonic acid, which is converted into hydrogen carbonate (HCO ₃ ^– ) and (Attention, important:) hydrogen ions ( H ⁺ ) splits. You can follow the exact progression in Figure 1.

Figure 1: Chemical process CO2 uptake

In this case, we only need to remember that the absorption of CO ₂ leads to an increase in hydrogen ions. But what does this have to do with a acidification to do?

To find out whether an aqueous solution is acidic or basic, the pH value is measured. pH means “Power of Hydrogen” and, as the name suggests, depends on hydrogen ions in the solution. Since CO ₂ triggers a chemical process that releases many hydrogen ions, the pH value in the water changes – the oceans are becoming more acidic .

course of ocean acidification

Compared to pre-industrial times, the pH value of seawater at the surface has fallen by 0.1 units - from 8.2 to 8.1. This may not sound dramatic at first, but it is already associated with an increase in acidity of about 30%. As can be seen in Figure 2, scientists expect a further increase of 0.3 to 0.4 units by the end of this century. The expected increase in acidity by the year 2100 is therefore 170% .

Figure 2: pH scale from 1 (very acidic) to 14 (very alkaline/basic)

Source: Heinrich Böll Foundation

Figure 3 shows the fluctuations in the ocean pH over the last 25 million years. So it is not unusual for pH to fluctuate. The problem is that these fluctuations normally take place over millions of years and are now occurring at a much more rapid rate due to the enormous emissions of carbon dioxide.

Figure 3: Ocean pH fluctuations over millions of years; Turley et al. (2006): 67 – Turley, C., JC Blackford, S. Widdicombe, D. Lowe, PD Nightingale, AP Rees (2006): Reviewing the Impact of Increased Atmospheric CO2 on Oceanic pH and the Marine Ecosystem, in: Avoiding dangerous climate change 8: 65-70. Cambridge University Press, New York.

Effects of ocean acidification on the underwater world

Ocean acidification has far-reaching Effects for the waters and their creatures. Some are already in full swing. As you know by now, the amount of free hydrogen ions (H ⁺ ) in the sea is decreasing due to the absorption of CO ₂ to – which is why the pH value increases. If you look at the first picture again, you will see that the free hydrogen ions (H ⁺ ) in the reaction with carbonate can form hydrogen carbonate (HCO ₃ ^– ).

Organisms such as mussels, crustaceans and corals use calcium carbonate to build and maintain their shells and skeletons. The basic requirements for the formation of calcium carbonate are calcium (Ca ²⁺ ) and carbonate (CO ₃ ^2- ). The latter is bound to hydrogen ions (H ⁺ ) through the increased release of these to form hydrogen carbonate (HCO ₃ ^– ), which means that less is available to bind with calcium ions. In the worst case, the shells and skeletons dissolve due to the undersaturation of carbonate ions.

In summary:

1. An increase in CO ₂ = increase in free H ⁺ ions

   → Binding of many free H ⁺ ions with carbonate (CO ₃ ^2- ) to form hydrogen carbonate (HCO ₃ ^– ).

2. Increase in free H ⁺ ions = decrease in carbonate

   → Organisms such as mussels, crustaceans or corals need carbonate to build and maintain their shells or skeletons (together with calcium).

3. Decrease of carbonate = decrease of mussels, shellfish and corals

Figure 4: Dissolution of a pteropod shell; Source: NOAA, PMEL Carbon Program

Figure 4 shows the shell of a pteropod (also called a sea butterfly) exposed to seawater that was adjusted to the predicted temperature and saturation levels of the year 2100. It took only 45 days for it to almost completely dissolve.

Further episodes

Mussels, crustaceans and corals are not only affected by carbonate deficiency when they are fully grown. Their development is particularly disrupted in the larval stage, their growth is restricted and population sizes become smaller. Overall, there is a lower survival rate. This also means that fish have less prey available. While adult animals are generally very tolerant of the decreasing pH value, the larvae of the animals are particularly sensitive here. In young clownfish, for example, the acidification affects the sense of smell, making it more difficult for them to detect enemies early on. In addition, the animals are losing their natural habitat due to the decline in coral reefs. Since biodiversity is maintained in particular by corals, which will hardly exist by the end of the century due to acidification, it is very likely that there will be major changes. Their loss will not only greatly change the habitat of many other marine animals, but will also be felt by coastal protection, the tourism sector and fisheries. What the exact developments will look like is currently unclear. However, since there are organisms such as algae or sea grasses that benefit from the CO ₂ surplus due to their photosynthesis, they could dominate the underwater world in the future. How this or the change in the food chain will affect the lives of individual fish species or marine mammals is not yet known. Ultimately , the change in pH also influences the acoustic properties of the oceans. Whales, which can communicate over several kilometers through their song, are already affected by this (read more in our blog post about Underwater noise ). The exact relationships are very complex and not yet fully explored .

Impacts of Ocean Acidification on Humanity

Ocean acidification will not only be felt in the seas themselves. Since the ocean provides several functions for humans, humanity will also Follow feel it.

• The ocean as a source of food
  Fisheries will have to expect fewer catches due to the decline in many populations. This will not only bring changes for people who are involved in fishing itself. It will affect everyone who works with fish, such as in the production and supply chain, restaurants or in the fishing equipment sector. In addition, poorer countries or isolated islands that depend on fish as their main source of food or protein will suffer in particular.
  
  
• The Ocean as Climate Regulator
  The ocean plays a major role in regulating the climate as a CO ₂ sink. But the more CO ₂ the ocean absorbs and the more acidic the ocean becomes, the lower its absorption capacity becomes. When the CO ₂ If emissions continue to rise as expected, the oceans’ ability to absorb them will stagnate around 2050, but no later than 2075. As a result, climate change would progress even faster and measures aimed at reducing CO ₂ would have to be increased significantly.
  
  
• The ocean as a vacation spot
  Ultimately, the ocean provides cultural services by offering us space to relax our bodies and souls. However, the rise in temperature and increasing acidification mean that cyanobacteria, also known as blue-green algae, can multiply very well. Because they contain toxins and spread like a carpet on the water surface when they bloom, swimming is prohibited when they appear. In the long term, this will have fatal consequences for tourism.

solutions

Since research has so far focused more on the effects of ocean acidification and less on possible solutions, there is a very clear selection of literature on this topic. In total, three solution strategies are known, some of which go hand in hand: reduce, repair, protect. Reducing refers to limiting the CO ₂ concentration. This can be achieved either by reducing CO ₂ emissions or by removing CO ₂ emissions from the atmosphere. Other measures against the destruction of coral reefs, such as the use of alkaline agents or the "application of seaweed", can serve to repair them, but are limited to local use. There are also various approaches to protection strategies that are specifically designed to strengthen resilience. This can be in the form of sustainable fishing or reducing waste in coastal areas, for example. You can find out more about these solutions here .

Conclusion

All in all, ocean acidification is not without reason referred to as the “evil twin” of climate change. In both cases, the extent is global and so far-reaching that it will have a major impact on our future lives. Since CO ₂ emissions contribute significantly to the progression of the problem in both cases, an acute and drastic reduction in CO ₂ The good news is that there are theoretically enough ways to reduce emissions. As a study recently published, there is great potential for reducing CO ₂ emissions directly in the fishing industry. When fishing with bottom trawls will be within one year gigatonne of carbon released, which does not reduce CO ₂ emissions than by Air travel . About fewer nets in the seas and less CO ₂ in the air, not only nature and animals would be very happy, but also we! If you want to know more, please read up on the topic yourself. Scanning our QR code will take you to our sources:

Written by Neele from Team Bracenet
Cover photo by yang wewe on Unsplash