Ocean geoengineering may prove lethal
Tuesday, 16 March 2010 Jessica
Marshall
Discovery News
One type of phytoplankton that
thrives under such circumstances makes domoic acid, a potent neurotoxin (Source:
New Jersey Department of Environmental Protection)
Although phytoplankton may prove an
unlikely ally in the effort to reduce the impact of climate change, enlisting
these microorganisms to sequester carbon could have deadly consequences.
One proposed method to combat
climate change is to dump iron in regions of the ocean where the growth of
marine phytoplankton - tiny organisms that grow via CO2-absorbing
photosynthesis - is limited by the amount of iron available.
Adding iron is intended to cause a
bloom of phytoplankton growth, sucking up CO2 in the process.
But new findings, published today in
the Proceedings of the National Academy of Science, show that one type of phytoplankton that
thrives under such circumstances makes domoic acid, a potent neurotoxin.
This neurotoxin can move up the food
chain as other animals eat the phytoplankton, harming sea life. It can kill or
weaken birds, fish, sea mammals or even humans who eat seafood that contains
the toxin.
In coastal waters, blooms of Pseudonitzschia,
the organism that produces the toxin, have occasionally closed coastal
shellfish harvests. In a few instances, people have died from consuming
contaminated seafood.
Coastal waters typically contain
much more iron, which encourages Pseudonitzschia's growth, says Professor
Charles Trick of the University of Western Ontario, who led the new study.
The researchers gathered samples of
seawater from the eastern Pacific during an expedition designed to test the
effect of adding iron to the ocean to stimulate plankton growth. They added
extra iron to the seawater samples on board their ship and measured the amount
of neurotoxin that was produced and what kind of phytoplankton grew.
"If we added the normal amount
of iron that one would add for these fertilization experiments, the level of
toxins in each of the cells goes higher," says Trick. "It allows (Pseudonitzschia)
to grow faster. And as they grow, they stop the other species from growing.
They become dominant."
"The surprising part was not
just that it made toxin," says Trick, "but that it made lots of
toxin, and it stopped the other species from getting the nutrients."
Growing
concerns
Proposals to use large-scale iron
fertilisation to combat climate change have been met with concern about the
unintended consequences they could bring.
One company that had hoped to sell
carbon offsets by seeding the ocean with plankton, Planktos, has put its
efforts on hold. But other companies are still pursuing the possibility, says
Kenneth Coale of the Moss Landing Marine Laboratory in California.
"We too have measured domoic
acid production in our enrichment experiments, but find a much larger response
than those reported by Trick et al.," says Coale.
"Together these results suggest
a wrinkle in the notion that iron fertilisation could simply draw down
atmospheric carbon dioxide. Nature is always more complex, and the curve she
has thrown us needs to be carefully considered before iron fertilisation should
be seriously considered as a carbon sequestration option."
Trick agrees. "Now we've dealt
with one of the uncertainties, and we recognise that we don't know as much as
we think," he says. "Modifications of nature at this big scale are
kind of a fickle process. We'd like to think that we're smart enough to
understand exactly what's going to happen. But in reality, the possibility that
something unsuspected like this could happen is large, and we might not want to
take that risk."
Weapons
of last resort?
"That's one of the concerns
with all of these geoengineering schemes," says Mak Saito of the Woods Hole Oceanographic
Institution in Massachusetts.
"If we're going to actively
change the planet's chemistry or biology to actively reverse global warming,
what are the unintended consequences? Here he's already documented one of the
concerns. What are the ones we don't even know about?"
"None of these strategies will
really be effective without conservation and reduction of carbon dioxide
emissions," says Saito. "I kind of see them as weapons of last
resort. To what extent are we on a trajectory that is so bad that we have to
use these, and at what point do we say we have to accept these
consequences?"
Source: http://news.discovery.com/earth/geoengineering-carbon-sequestration-phytoplankton.html