Like their tropical counterparts, cold water corals provide habitat for countless marine life. These hotspots of deep-sea biodiversity only became known to us in the last decade. Cold-water coral reefs stretch along the eastern edge of the Atlantic Ocean for 5,000 kilometers, from northern Norway to the African coast. As we fly over coral reefs admiring their silent beauty, it's hard to imagine that these pristine ecosystems could soon disappear from our planet. Yet, if human carbon dioxide emissions continue to increase at the current rate, corals in vast expanses of ocean will soon be living in the seawater that eats away at their limestone skeletons. The watchword of this process is the acidification of the oceans: the pH value of seawater is constantly decreasing. Like osteoporosis in humans, the calcareous skeletons of corals dissolve faster than they can rebuild.
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Human Impacts
But how can such emissions endanger life in the ocean? The underlying process that leads to ocean acidification is very simple, much simpler than the CO2-induced changes in our climate system. Its origin lies in the absorption of huge amounts of artificial CO2 by the ocean surface. Nearly half of the amount of gas released from fossil fuels by human activities since the start of the industrial revolution - over 500 billion tonnes - has been absorbed by the ocean, as our planet's largest habitat serves larger sink for greenhouse gases: in the long term, it is expected to absorb 90% of all CO2 from fossil fuels released into the atmosphere. It can be described as a blessing for our climate system as it alleviates CO2 induced greenhouse warming, but it will prove to be a curse for marine life.
Did you know?
Freshwater makes up only 2 per cent of all water. |
When carbon dioxide dissolves in seawater, it forms carbonic acid. Some of it is neutralized by the carbonate buffer, a chemical reaction that consumes carbonate ions, the building material used by calcifying organisms to make their shells and skeletons. The remaining acid causes the pH of the seawater to decrease. The lower the pH value, the higher the concentration of hydrogen ions and therefore the more acidic the water. The absorption of carbon dioxide by fossil fuels from the ocean has already caused the pH to drop by 0.1 units, which corresponds to a 30% increase in hydrogen ions. If current trends in CO2 emissions continue, the pH of seawater will decrease by about 0.45 units from pre-industrial times by 2100. That would be lower - and the rate of change more. fast - than it has been for at least the last 400,000, and probably 20 million years.
This will not only affect cold water corals, but calcifying organisms in general. As the concentration of carbonate ions decreases, the production of calcareous structures will become increasingly difficult. All calcifying species tested so far in laboratory simulations show decreased calcification in response to ocean acidification.Calcification is a widespread phenomenon among many marine organisms, ranging from corals to mussels, snails , starfish and sea urchins. plants at the base of the marine food web. Fish also precipitate calcium carbonate to build some of their internal structures, such as calcareous platelets in their vestibular apparatus. Judging from the current experimental results, there is a high risk that many calcifying groups will lose their competitive ability to prevail in an ocean of increasing acidity. The consequences this could have on the marine food web are currently unknown. Looking back on Earth's history, we can learn a lesson from the fossil record. When a comet hit the Yucatan Peninsula in northern Mexico 65 million years ago, huge amounts of calcium sulfate were released into the atmosphere. There it reacts with oxygen and water to form sulfuric acid.The amounts of sulfuric acid were sufficient to make the surface ocean corrosive to the calcareous shells and skeletons of surface organisms. It probably only took a few years to mix with the deep ocean waters to neutralize the surface acidification, but long enough to cause the extinction of nearly all planktonic calcifiers. Two million years passed before corals reappeared in the fossil record. It took another 20 million years for the species diversity of the calcifying groups to return to pre-extinction levels. Research into the effects of current ocean acidification is still in its infancy. No one knows how the negative responses observed experimentally on individual organisms will translate into communities and ecosystems. How will these responses be affected by other stressors such as temperature changes or nutrient availability? Determining the ability of sensitive organisms to adapt to ocean acidification is also a daunting challenge. Despite many uncertainties, it is probably safe to say that continued ocean acidification will result in the loss of marine biodiversity, with currently unpredictable consequences for marine ecosystems and food webs. In its 1995 report, the Intergovernmental Panel on Climate Change (IPCC) published a series of CO2 emissions scenarios predicted for the 21st century.Its worst-case scenario was deemed critical at the time as too pessimistic. But records from the past 10 years indicate that the current trend in global CO2 emissions is higher than in this scenario. Despite growing awareness of the problems associated with increasing levels of CO2 in the atmosphere, our efforts to reverse this process are still long overdue. Ocean acidification and the risks associated with marine life provide an additional incentive to act quickly and decisively to reduce global carbon dioxide emissions.
This will not only affect cold water corals, but calcifying organisms in general. As the concentration of carbonate ions decreases, the production of calcareous structures will become increasingly difficult. All calcifying species tested so far in laboratory simulations show decreased calcification in response to ocean acidification.Calcification is a widespread phenomenon among many marine organisms, ranging from corals to mussels, snails , starfish and sea urchins. plants at the base of the marine food web. Fish also precipitate calcium carbonate to build some of their internal structures, such as calcareous platelets in their vestibular apparatus. Judging from the current experimental results, there is a high risk that many calcifying groups will lose their competitive ability to prevail in an ocean of increasing acidity. The consequences this could have on the marine food web are currently unknown. Looking back on Earth's history, we can learn a lesson from the fossil record. When a comet hit the Yucatan Peninsula in northern Mexico 65 million years ago, huge amounts of calcium sulfate were released into the atmosphere. There it reacts with oxygen and water to form sulfuric acid.The amounts of sulfuric acid were sufficient to make the surface ocean corrosive to the calcareous shells and skeletons of surface organisms. It probably only took a few years to mix with the deep ocean waters to neutralize the surface acidification, but long enough to cause the extinction of nearly all planktonic calcifiers. Two million years passed before corals reappeared in the fossil record. It took another 20 million years for the species diversity of the calcifying groups to return to pre-extinction levels. Research into the effects of current ocean acidification is still in its infancy. No one knows how the negative responses observed experimentally on individual organisms will translate into communities and ecosystems. How will these responses be affected by other stressors such as temperature changes or nutrient availability? Determining the ability of sensitive organisms to adapt to ocean acidification is also a daunting challenge. Despite many uncertainties, it is probably safe to say that continued ocean acidification will result in the loss of marine biodiversity, with currently unpredictable consequences for marine ecosystems and food webs. In its 1995 report, the Intergovernmental Panel on Climate Change (IPCC) published a series of CO2 emissions scenarios predicted for the 21st century.Its worst-case scenario was deemed critical at the time as too pessimistic. But records from the past 10 years indicate that the current trend in global CO2 emissions is higher than in this scenario. Despite growing awareness of the problems associated with increasing levels of CO2 in the atmosphere, our efforts to reverse this process are still long overdue. Ocean acidification and the risks associated with marine life provide an additional incentive to act quickly and decisively to reduce global carbon dioxide emissions.
