The shells of some marine snails in the seas around Antarctica are dissolving as the water becomes more acidic, threatening the food chain, a study published in the journal Nature Geoscience said on Sunday.

Seawater becomes more corrosive below a certain depth which occurs at around 1,000 metres

Oceans soak up about a quarter of the carbon dioxide released into the atmosphere each year and as CO2 levels in the atmosphere increase from burning fossil fuels, so do ocean levels, making seas more acidic.

Ocean acidification is one of the effects of climate change and threatens coral reefs, marine ecosystems and wildlife.

The shell of the pteropod sea snail in the Southern Ocean was severely dissolved by more acidic surface water, the re­searchers from the British Antarctic Survey, Royal Netherlands Institute for Sea Research, the US National Oceanic and Atmospheric Administration (NOAA) and other institutions found.

And although the snails did not necessarily die, it increased their vulnerability to predators and infection which could affect other parts of the food chain.

“The corrosive properties of the water caused shells of live animals to be severely dissolved and this demonstrates how vulnerable pteropods are,” said lead author Nina Bednarek, from the NOAA.

“Ocean acidification, resulting from the addition of human-induced carbon dioxide, contributed to this dissolution.”

The sea snails are an important source of food for fish and birds as well as an indicator of marine ecosystem health.

But until now, there has been little evidence of the impact of ocean acidification on such live organisms in their natural environment and the study supports predictions that acidification could have a significant effect on marine ecosystems.

The researchers examined surface water, where wind causes cold water to be pushed up from deeper water, because it is usually more corrosive to a particular type of calcium carbonate which the sea snails use to build and maintain their shells.

“We know that seawater be­comes more corrosive below a certain depth which occurs at around 1,000 metres.

“However, at one of our sampling sites, we discovered that this point was reached at 200m depth. Marine snails – pteropods – live in this top layer of the ocean,” Bednarek said.

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