VOLCANIC ERUPTION LINKED TO GREEN TIDES
A huge plankton bloom in the North Pacific is traced to a volcanic eruption and offers a test in iron fertilization.
A large and very unusual plankton bloom in the North Pacific has been tracked, whodunnit style, to the eruption of a remote volcano in the Aleutian Islands. The volcano-plankton connection is the iron-rich volcanic ash that was launched out of the Kasatochi volcano and then rained down into the ocean.
"People have hypothesized about it in the past," said researcher Roberta Hamme of the University of Victoria, regarding the possibility that volcanoes can have such an effect on iron-poor seas. "This the first time we have observed it."
Hamme is the lead author on a paper in Geophysical Research Letters which shows how data from two spacecraft, two research ships, buoys and a robotic ocean glider all came together serendipitously to implicate the volcano well after the event had occurred in the summer of 2008.
She and a diverse group other researchers had found signs of the unprecedented bloom, but it wasn't until they all started talking to one another at a meeting that they discovered they had encountered something in common affecting one to two million square kilometers of ocean.
That's what got Hamme looking at the satellite images of volcanic ash Aleutian eruptions. The Kasatochi volcano stood out because it was timed right and had a wide plume of ash which covered the vast area of the plankton bloom.
"I hadn't put any credence in it until we eliminated the other possibilities," Hamme told Discovery News.
The same sort of plume was not seen in the North Atlantic from the recent Icelandic volcanics, says Hamme, because those waters are not iron deficient. In the north Pacific, just about everything is present for plankton to thrive except iron. So all it takes is a jolt of iron to start a plankton explosion.
The discovery also provides scientists with data on the largest case of ocean iron fertilization ever measured. According to the field measurements, the bloom sucked up 0.01 petagrams of carbon (10 million metric tons). That's just half of one percent of how much carbon the oceans take up all year and an even smaller fraction of the 6.5 petagrams or so of carbon humans release into the atmosphere by burning fossil fuels.
Hamme and her colleagues compared the carbon uptake to that of a deliberate iron fertilization experiment done in the same part of the ocean called in 2002. The Subarctic Ecosystem Response to Iron Enrichment Study (SERIES) managed to get plankton revved up over 1,000 square kilometers of ocean.
"Certainly the take home message is that the purposeful experiment had never been able to get greater than 1,000 square kilometers," said Philip Boyd of the National Institute of Water and Atmospheric Research, University of Otago in Dunedin, New Zealand. Boyd was a key scientist in the SERIES experiment.
"It's a pretty big kahuna," said Boyd regarding the accidental experiment created by the volcanic eruptions. Yet the amount of carbon update, as in the smaller deliberate experiments, is not impressive. "It's a pretty valuable study and certainly I'll be talking about it," said Boyd.
Despite this, there are some geoengineering people who will likely ignore the study, said Boyd, and continue trying to sell iron fertilization as a way to sequester atmospheric carbon.
"If I were a geoengineer and had a couple of venture capital people on the line I'd direct them elsewhere," Boyd said.