Ocean Acidification Dissolves Shells of Marine Animals

The shells of marine snails, known as pteropods that dwell in the seas around Antarctica are being dissolved by ocean acidification. This was noticed by researchers from British Antarctic Survey (BAS) and the University of East Anglia (UEA) in collaboration with colleagues from the US Woods Hole Oceanographic Institution and the National Oceanic and Atmospheric Administration (NOAA).

This was discovered during a science cruise in 2008. 

Compared to previous years, concentration of CO2 has increased greatly, which in turn is contributing to Global Warming.

Climatic changes are forcing the world's oceans to change. Ocean acidification is taking place due to excessive uptake of carbon dioxide from the atmosphere. It is suggested that the carbon dioxide levels are up due to excessive fossil burning . This rise in the acid level in oceans is killing marine organisms that produce calcium carbonate shells or use calcium carbonate in their skeletal structure.

The team examined an area of upwelling where winds cause cold water to be pushed upward from the deep to the surface of the ocean. The upwelled water is mostly acidic to a particular type of calcium carbonate that is being used by the pteropods to build their shells. 

The team noticed that due to the additional influence of ocean acidification, this corrosive water severely dissolved the shells of pteropods.

There were several experiments conducted that showed the potential effect of ocean acidification on marine organisms.

This new finding supports predictions that the impact of ocean acidification on marine ecosystems and food webs may be significant.

Lead author, Dr. Nina Bednaršek, of the National Oceanic and Atmospheric Administration (NOAA) says: "We know that the seawater becomes more corrosive to aragonite shells below a certain depth -- called the 'saturation horizon' -- which occurs at around 1000m depth. However, at one of our sampling sites, we discovered that this point was reached at 200m depth, through a combination of natural upwelling and ocean acidification. Marine snails -- pteropods -- live in this top layer of the ocean. The corrosive properties of the water caused shells of live animals to be severely dissolved and this demonstrates how vulnerable pteropods are. Ocean acidification, resulting from the addition of human-induced carbon dioxide, contributed to this dissolution. "

Co-author and science cruise leader, Dr. Geraint Tarling from BAS, says: "Although the upwelling sites are natural phenomena that occur throughout the Southern Ocean, instances where they bring the 'saturation horizon' above 200m will become more frequent as ocean acidification intensifies in the coming years. As one of only a few oceanic creatures that build their shells out of aragonite in the Polar Regions, pteropods are an important food source for fish and birds as well as a good indicator of ecosystem health. The tiny snails do not necessarily die as a result of their shells dissolving, however it may increase their vulnerability to predation and infection consequently having an impact to other parts of the food web."

Co-author, Dr. Dorothee Bakker of UEA, says: "Climate models project a continued intensification in Southern Ocean winds throughout the 21st century if atmospheric carbon dioxide continues to increase. In turn, this will increase wind-driven upwelling and potentially make instances of deep water -- which is under-saturated in aragonite -- penetrating into the upper ocean more frequent. Current predictions are for the 'saturation horizon' for aragonite to reach the upper surface layers of the Southern Ocean by 2050 in winter and by 2100 year round. "

The new study was published in the journal Nature Geoscience.