Ocean Acidification Threatens Antarctic Marine Wildlife
November 26, 2012

Marine Life In The Southern Ocean Under Threat From Acidification

redOrbit Staff & Wire Reports - Your Universe Online

An international team of researchers has uncovered the first evidence that marine creatures living in the Antarctic region are being affected by ocean acidification.

That evidence was discovered in 2008, when researchers from the British Antarctic Survey (BAS), the University of East Anglia (UEA), the Woods Hole Oceanographic Institution (WHOI) and the National Oceanic and Atmospheric Administration (NOAA) observed that the shells of pteropods living in the Southern Ocean were dissolving as a result of the decreasing pH balance in those waters.

The research team studied an area of upwelling -- that is an area where winds force cold, deep water to be pushed to the surface of the ocean -- because upwelled water tends to be more corrosive to a specific type of calcium carbonate required by marine snails in order to build their shells. As it turns out, the effect of ocean acidification strengthened that affect, leading to the creature's shells to become severely dissolved by the upwelled water, BAS officials said in a statement.

"Ocean acidification is caused by the uptake of carbon dioxide from the atmosphere emitted as a result of fossil fuel burning," they added. "A number of laboratory experiments have demonstrated the potential effect of ocean acidification on marine organisms. However, to date, there has been little evidence of such impacts occurring to live specimens in their natural environment. The finding supports predictions that the impact of ocean acidification on marine ecosystems and food webs may be significant."

The findings, which have been published in the journal Nature Geoscience, could be vital in helping to predict the impact that ocean acidification will have on marine life in the future, according to BBC Nature. That's partially because pteropods are a key link in the aquatic food chain -- consuming some phytoplankton and being prey of fish, seabirds, and whales, according to study co-author and BAS chief of ocean ecosystems Dr. Geraint Terling -- and partially because the marine snails are "a good indicator of ecosystem health," the British news outlet added.

According to the NOAA's Dr. Nina Bednaršek, lead author of the study, the seawater typically becomes more corrosive to the snail's calcium carbonate or aragonite shells at approximately 1,000 meters deep, which is known as the "saturation horizon". However, at one of the researchers sampling sites, they discovered that the saturation point occurred at just 200 meters, where the pteropods typically live. Bednaršek believes that "ocean acidification, resulting from the addition of human-induced carbon dioxide, contributed to this dissolution."

“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," added study co-author Dr. Dorothee Bakker of the University of East Anglia.

Image 2 (below): The pteropod (marine snail) Limacina helicina antarctica which is an abundant member of the Southern Ocean zooplankton community. Specimens mainly inhabit the top 200 m of oceanic waters where they graze on phytoplankton and detritus. Their shells are made of aragonite, a form of calcium carbonate that can dissolve rapidly. Image provided by Nina Bednarsek