First evidence of ocean acidification affecting marine life in the Southern Ocean
The pteropod (marine snail) Limacina helicina antarctica which is abundant member of the Southern Ocean zooplanktonzooplankton Zooplankton form the group of tiny animals such as minuscule jellyfish and rotifers present in the marine environment. They are a major source of food for those higher up the food chain, and their numbers relate directly as a good indicator to the nutrient enrichment of the sea of the area. Note: phytoplankton are microscopic plants, and zooplankton are microscopic animals. community. Specimens mainly inhabit the top 200 m of oceanic waters where they graze on phytoplanktonphytoplankton Microscopic marine plants, usually algae. These microscopic plants are at the base of the food chain, and are the food of zooplankton (microscopic marine animals). Note: phytoplankton are microscopic plants, and zooplankton are microscopic animals. and detritus. Their shells are made of aragonite, a form of calcium carbonate that can dissolve rapidly.
Image provided by Nina Bednarsek
The shells of marine snails – known as pteropods – living in the seas around Antarctica are being dissolved by ocean acidification according to a new study published this week in the journal Nature Geoscience. These tiny animals are a valuable food source for fish and birds and play an important role in the oceanic carbon cycle.
During a science cruise in 2008, researchers from British Antarctic Survey (BAS) and the University of East Anglia (UEA), in collaboration with colleagues from the US Marine Biology Laboratory, Woods Hole and the National Oceanic and Atmospheric Administration (NOAA), discovered severe dissolution of the shells of living pteropods in Southern Ocean waters.
The team examined an area of upwelling, where winds cause cold water to be pushed upwards from the deep to the surface of the ocean. Upwelled water is usually more corrosive to a particular type of calcium carbonate (aragonite) that pteropods use to build their shells. The team found that as a result of the additional influence of ocean acidification, this corrosive water severely dissolved the shells of pteropods.
Ocean acidification is caused by the uptake of carbon dioxide from the atmosphere emitted as a result of fossil fuel burning. 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 websfood web The totality of interacting food chains in an ecological community may be significant.
RRS James Clark Ross in the Bellingshausen Sea, west of the Antarctic Peninsula
Lead author, Dr Nina Bednaršek, formerly of BAS and UEA, and now 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 webfood web The totality of interacting food chains in an ecological community.”
Co-author, Dr Dorothee Bakker from the University of East Anglia, 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 up-welling 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.“
This research was funded by the UK Natural Environment Research Council (NERC) and the European Union Marie Curie Early Stage Training Network.
Source: British Antarctic Survey, 25th November 2012
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