When the Coast Guard research vessel John P. Tully churned across the North Pacific in the summer of 2008, scientists on board discovered an anomaly on a microscopic scale. Tiny ocean plants called phytoplankton were blooming like crazy.
By sheer luck, the ship was sailing through an event that temporarily turned the North Pacific Ocean into a colossal lab experiment. The findings - published Tuesday by a Canada-U.S. team led by University of Victoria oceanographer Roberta Hamme - have dashed a hopeful theory: that sprinkling iron into oceans to stimulate phytoplankton growth might reverse the effects of global warming.
The largest phytoplankton bloom recorded since satellite monitoring began in 1997 was triggered by a series of explosive volcanic eruptions on the remote island of Kasatochi, part of Alaska's Aleutian Islands chain.
In just 25 hours, the volcano spewed as much as a quarter of a cubic kilometre of material, with gas and ash clouds spreading across Canada and the continental United States. The once-lush island, home to hundreds of thousands of seabirds, was buried under debris tens of metres thick.
Then a perfectly timed storm swept volcanic ash out to sea, sprinkling iron-rich particles across a 1,000-kilometre stretch of the Pacific. The phytoplankton literally ate it up - and thrived.
The free-floating, single-celled plants - the foundation of the marine food chain - absorb carbon dioxide (CO2) when they die, effectively creating a carbon sink in the ocean depths. Based on that knowledge, scientists have suggested that seeding key regions of the ocean with iron could offset carbon dioxide in the atmosphere.
But the phytoplankton bloom in 2008 had only a modest impact on CO2 levels, Prof. Hamme concluded.
Earth's oceans naturally absorb about two petagrams of carbon annually - compared to the estimated 6.5 petagrams of carbon released each year by fossil fuel consumption. (A petagram is one of those mind-numbing measurements that has too many zeros to really grasp - 15 in all.) The huge plankton bloom barely nudged the meter - Prof. Hamme estimates it absorbed 0.01 petagrams of carbon.
"It tells us the amount of iron we would have to put into the ocean would just be gigantic, and it disappeared so fast, you'd have to keep putting it in over and over again," she said in an interview.
Prof. Hamme said the unique events of the huge Kasatochi volcano provided a natural test lab that would be almost impossible to reproduce. But it was also a perfect storm of scientific monitoring that helped capture the data. The John P. Tully makes its trek to Station Papa, a spot in the middle of the Pacific, three times each year to gather data. New monitoring equipment also happened to be deployed in the right spots at the right time. In all, her paper published in Geophysical Research Letters cited 20 different data sets.
The connection between the plankton bloom and the volcano wasn't immediately obvious. Prof. Hamme brought her odd readings to a conference at the Institute of Ocean Sciences in Sidney, B.C., in the spring of 2009.
"Each person came to talk about their data set, they all got up and said, 'Here's something different.' We started brainstorming, and someone mentioned volcanoes. I didn't think it was that, I laughed."
It wasn't until months later, when she was researching the Aleutian Islands and came across a video of the Aug. 7-8, 2008, eruption of Kasatochi volcano, that she realized the potential for one substantial disruption to explain the other. "It all came together," she said.Report Typo/Error