by Agence France-Presse
WASHINGTON—Adding iron to the world’s oceans to capture
carbon and fight global warming could do more harm than good, as the mineral appears
to boost the growth of a plankton that produces a deadly neurotoxin, a study
published on Monday shows.
Researchers led
by Charles Trick of the University of Western Ontario in Canada found that
fertilizing the ocean with iron can boost the growth of Pseudo-nitzschia, a
phytoplankton that produces a component of the neurotoxin domoic acid.
Humans who eat
shellfish or crab that have ingested Pseudo-nitzschia could get amnesic
shellfish poisoning, severe cases of which can cause neurological symptoms,
including permanent, short-term memory loss, which gives the intoxication its
name. Amnesic shellfish poisoning can also be fatal.
For the study,
which was published in the Proceedings of the National Academy of Sciences, the
researchers examined water samples taken from open-ocean tracts in the
sub-Arctic North Pacific Ocean where iron-fertilization experiments were
conducted.
They found that
the population of Pseudo-nitzschia had doubled compared to controls, that
adding iron to the water appeared to increase the amount of domoic acid
produced by individual phytoplankton, and that the natural release of the toxin
boosted further growth of the potentially harmful plankton.
Previous
iron-enrichment experiments have focused on studying how adding iron to the sea
affects carbon cycling, but have overlooked the potential ecological impacts of
geoengineering-designed fertilizations, the study found.
Earlier studies
by other teams have shown that iron fertilization produced no measurable
quantities of domoic acid, and that some coastal Pseudo-nitzschia produced only
low concentrations of the toxin.
Iron
fertilization is still mainly in the experimental phases, with about “12 experiment-sized iron fertilizations”
already undertaken, mainly in the Pacific Ocean, Trick told AFP.
The findings of
the study he led raise “serious concern over the net benefit and
sustainability of large-scale iron fertilizations.”
Scientists in
the 1990s began fortifying small areas of the ocean where the sea water is rich
in nutrients but low in plankton, to see if adding iron to the water would
stimulate the growth of phytoplankton and boost carbon capture.
Adding iron resulted
in rapid growth of the phytoplankton, which, in the process of photosynthesis,
uses energy from sunlight to fix inorganic carbon in surrounding surface waters
to produce organic carbon.
Some of the
organic carbon ends up deep in the ocean, effectively removing carbon from the
surface waters, while surface-water carbon is replenished by taking carbon
dioxide from the atmosphere.
Iron
fertilization, like other forms is geoengineering, is “purposely changing
the system and may have unintended consequences,” said Scott Doney, a
senior scientist at Woods Hole Oceanographic Institution in Massachusetts,
commenting to AFP on the findings.
“You have to weigh how the changes affect higher animals, how it
affects fish and mammals,” said Doney, who did not take part in the study.
“You have to know what are the trade-offs between how much carbon you
actually store and how big an effect you have on the environment.”
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