— Atmospheric carbon dioxide is being pushed deeper into the oceans than previously thought, according to researchers.
The findings mean the oceans may continue to absorb human emissions of the greenhouse gas more rapidly and for longer, they say, reducing their impact on global warming. But the research is bad news for the marine organisms that are already suffering from ocean acidification.
Higher levels of CO2 in the atmosphere, caused largely by industrial activities, push the greenhouse gas into ocean waters. Although this process is fairly well understood, scientists have only estimates of the depth at which CO2 from human activities is stored in the oceans.
"Previous estimates, based on educated assumptions about what the pre-industrial oceans looked like, suggested that in the high latitudes of the North Atlantic, anthropogenic CO2 was not found below 2500 metres," says Douglas Wallace of the University of Kiel, Germany.
Wallace and colleagues have now published the first measurements showing the location of CO2 from human activities in the North Atlantic. They used data collected during a research cruise in 1981 as a baseline, and then returned to exactly the same sampling locations in 2004.
"This revealed quite large changes in the CO2 in very deep water, between 3000 m and 5000 m," Wallace told New Scientist.
If their findings are replicated in the much bigger southern oceans, it could mean that the oceans' capacity to take up CO2 is greater than previously thought.
While this may soak up some of the CO2 that would otherwise warm the atmosphere, the flipside is that the new findings give further evidence that human activities are rapidly changing the chemistry of the deep oceans.
"There is a depth in the ocean above which calcium carbonate shells don't dissolve, and below which they do," says Wallace. The findings suggest that the CO2 pumped into the oceans has pushed up this boundary by 400 m, compared to its level before the industrial age. And the researchers predict that it will be 700 m shallower by 2050 if CO2 emissions continue their fast growth.
Wallace says that whether the findings are replicated in the southern oceans remains to be seen, and he is encouraging colleagues to replicate his study there. There may be differences. For example, much of the southern ocean's water sinks to the bottom off the coast of Antarctica. There, sea ice may prevent CO2 entering the water from the atmosphere to the same extent as in the north.
The scientist who first coined the phrase ocean acidification, Ken Caldeira, at the Carnegie Institution, California, US, says the extent to which the rising boundary will affect deep-sea corals and shelled organisms remains uncertain. But when human activities start impacting remote parts of planet, it's a wake-up call that we are interfering in our planets functioning on a very large scale, he says.
Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0606574104)
Climate Change - Want to know more about global warming the science, impacts and political debate? Visit our continually updated special report.
Mysteries of the Deep Sea -The deep sea is one of the harshest habitats on Earth, but is home to many remarkable creatures. Learn more in our comprehensive special report.
More Science News from New Scientist
Ocean acidification: the other CO2 problem