The world's oceans have soaked up half of the carbon dioxide pumped
into the air by human activities since the beginning of the
industrial age, according to new two studies. The gas is acidifying
the seas and may harm marine life, the authors warn.
shot up from 280 parts per million (ppm) in 1800 to 380 ppm today.
But that figure would be greater than 435 ppm were it not for the
"The oceans are producing this tremendous service to humankind by
reducing the amount of carbon dioxide in the atmosphere, which can
lead to global warming," says Chris Sabine, lead author of one study
and an oceanographer at the US National Oceanic and Atmospheric
Administration (NOAA) in Seattle. "But it's changing the chemistry
of the oceans and may have consequences for marine ecosystems."
Sabine, with other researchers from around the world, spent 10
years criss-crossing the globe in ships. They made nearly 10,000
stops along the way, measuring ocean temperatures and salinity, as
well as levels of nutrients, carbon, oxygen, and chlorofluorocarbons
They used chemical models and data from a similar ocean survey in
the 1970s to subtract natural CO2
levels from their data. They also focused on depths that showed
signs of recent contact with the atmosphere, such as CFCs.
The researchers discovered that the oceans have absorbed 48 per
cent of all CO2
from fossil-fuel burning and cement manufacturing, which is
dissolved in the top 10 per cent of the world's seas.
They also studied the effects of CO2
on sea creatures and plants. When CO2
dissolves in seawater, it forms carbonic acid, which in turn can
dissolve the shells and skeletons of marine life.
The snail species Clio pyramidata, scooped up by the
researchers during one cruise, had lost the ability to grow their
shells, having being exposed to CO2
at levels of 1000 ppm for just 48 hours.
"Although the animals were actively swimming, their shells were
clearly dissolving," team member Victoria Fabry, a biologist at
California State University in San Marcos, told New Scientist.
The animals' survival or reproductive success may be affected, or
they may have to move to waters with lower CO2
concentrations, Fabry says.
"We don't really know what kind of domino effects might occur,"
says colleague Richard Feely, a marine chemist at the NOAA.
The dissolution of the calcium carbonate shells of animals and
plankton also plays a key role in ocean chemistry, he says, those
effects are "critical to understand how the oceans can absorb CO2
from the atmosphere in the future".
Ken Caldeira, a chemical oceanographer at California's Lawrence
Livermore National Laboratory, who was not involved in the research,
says the new studies may help inform a debate about whether to
actively remove CO2
from the air and store it in the ocean.
"It's clear that putting more CO2
into the ocean would help global warming but there would be some
biological cost associated with that," he told New Scientist.
"It's not clear whether or not there would be a net benefit."
Journal references: Science (vol 305, p 362, 367)