May Harm Ocean Life
By Christopher Doering
16 June, 2004
The world's oceans have absorbed nearly half of the carbon dioxide emitted
by humans during the last 200 years, creating potential long-term challenges
for corals and free-swimming algae, according to two studies released
team of scientists found that oceans have taken in about 118 billion
metric tons of carbon dioxide from human activities between 1800 and
1994, accounting for nearly a third of their long-term carrying capacity.
These findings could pose a long-term risk for marine organisms, such
as corals, which have greater difficulty in forming their outer shells
as carbon dioxide levels increase, researchers found.
"There is a
price to pay in this process, and that is with living organisms,"
said Richard Feely, a marine chemist with the National Oceanic and Atmospheric
Administration, the lead author on one of the studies.
The research was
published in the July issue of "Science."
Oceans, which cover
about 75 percent of the Earth's surface, have seen the amount of carbon
dioxide they absorb fall to 30 percent as trees and plants soak up more
of the gas before it reaches the water. Currently, 20 percent is taken
in by foliage, with the remaining 50 percent staying in the atmosphere.
The 15-year study,
conducted and analyzed with the help of several researchers around the
world, looked at nearly 72,000 samples taken in the Atlantic, Pacific
and Indian oceans.
Analysis of carbon
dioxide since the industrial age has shown that concentration levels
in the atmosphere have increased to about 380 parts per million (ppm)
from 280 ppm two centuries ago. Without ocean absorption, carbon dioxide
levels in the atmosphere would be about 55 ppm higher.
The data found that
even though the oceans continue to absorb more carbon dioxide, they
are far from being saturated. Currents stir the ocean very slowly by
pulling deep ocean water to the surface, where it is able to absorb
more carbon dioxide.
have a capacity to continue to take in CO2 for thousands of years with
the slow mixing time," said Christopher Sabine, NOAA oceanographer
and lead author of the other study.
The greatest threat
to increasing levels of carbon dioxide is to species that live in the
upper 10 percent of the ocean.
As ocean surfaces
capture and store carbon, the slow circulation of water keeps the gas
more highly concentrated where these creatures live.
The change in ocean
chemistry reduces the level of carbonate ions needed by corals and other
organisms to generate their shells. In areas where the ion level has
fallen too low, calcium carbonate shells can begin to dissolve.
that while the long-term impact on these creatures and other species
that depend on them for food is uncertain, they will closely monitor
how carbon dioxide absorption is affecting the food chain.
"We might see
the structure of the food web change ... and see shifts in species competition"
in the ocean ecosystem, said Victoria Fabry, a biologist at California
State University who worked on the research.