How a volcanic super-eruption launched algae army into the sky
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Slimy brown algae not only survived a wild ride into the stratosphere via a volcanic ash cloud, they landed on distant islands looking flawless, a new study finds.
"There's a crazy contrast between these delicate, glass-shelled organisms and one of the most powerful eruptions in Earth's history," said lead study author Alexa Van Eaton, a postdoctoral scholar at both the Cascades Volcano Observatory in Washington and Arizona State University.
The diatoms were launched by the Taupo super-eruption on New Zealand's North Island 25,000 years ago. More than 600 million cubic meters (20 billion cubic feet) of diatoms from a lake flew into the air, Van Eaton reported Sept. 6 in the journal Geology. Lumped together, the microscopic cells speckled throughout Taupo's ash layers would make a pile as big as Hawaii's famed Diamond Head volcanic cone.
Some diatoms drifted as far as the Chatham Islands, 525 miles (850 kilometers) east of New Zealand. "They just hitched a ride," Van Eaton said. The pristine shells in the Chatham Island ash suggest diatoms could infect new niches by coasting on atmospheric currents.
"If they made it there alive, this is one way microorganisms can travel and meet each other," Van Eaton told LiveScience's OurAmazingPlanet. "We know that ash from smaller events easily travels around the world." [5 Colossal Cones: Biggest Volcanoes on Earth]
World domination, cell by cell
Diatoms, a golden brown algae, rule Earth's waterways. From Antarctica's glacial lakes to acidic hot springs to unkempt home aquariums, diatoms are everywhere. It's a good thing. The tiny creatures pump out up to 50 percent of the planet's oxygen, said Edward Theriot, a diatom expert and evolutionary biologist at the University of Texas at Austin, who was not involved in the study.
The algae look like little petri dishes or footballs, depending on the species, and spend most of their lives drifting on currents. How diatoms manage to colonize new homes remains a mystery: They can't swim.
Yet diatoms get around. When Wyoming's Yellowstone Lake emerged from its mile-thick ice cover 14,000 years ago, diatoms quickly arrived, Theriot said. "They had to be blown in by some mechanism or carried in by water birds," he added.
Diatoms particularly love volcanic lakes, because they are the only creatures that build shells of glass. (Glass sponges, for instance, produce a skeleton of glass spicules — tiny spike-like structures — but not a hard shell.) Silica-rich magma often causes the volcanic explosions that leave behind lake-filled craters, and silica is the key ingredient in diatom shells. Yellowstone Lake, which sits in a caldera created by a super-eruption, contains so many diatoms that the lake sediments are mostly shells (85 percent by weight), Theriot said.
Now scientists know what happens to diatoms when a massive volcano such as Yellowstone blasts through a big lake.
The Taupo Volcano super-eruption slammed through a deep lake that filled a rift valley, similar to the elongated lakes in East Africa. The combination of water and ash created a hellish dirty thunderstorm, with towering clouds and roaring winds. The detonation flung ash and algae upward at more than 250 mph (400 km/h), Van Eaton said. Volcanic hail (called accretionary lapilli) pelted the landscape for miles.
Van Eaton discovered the diatoms while examining the volcanic hail with a scanning electron microscope.
"The first time I ever saw them I was looking at these volcanic ash aggregates and, bam, these gorgeous little symmetrical shells were there," she said. "Their shells are immaculately preserved."
Van Eaton soon determined that one of the three diatom species entombed in the ash lives only on the North Island of New Zealand. This meant she could track the 25,000-year-old ash layers around the South Pacific with a unique biologic marker. The unique North Island diatoms turned up in a few inches of ash on the Chatham Islands. The diatoms' trip to the Chatham Islands took longer than it looks on a map. The prevailing winds blew west at the time, so the shells circled the Southern Hemisphere before landing on the islands, Van Eaton and her colleagues think.
Some of the diatoms even kept their color, both in ash close to the volcano and at the Chatham Islands. The color suggests they weren't cooked to extreme temperatures in the volcanic eruption, Van Eaton said.
Spores infect the sky
But even though the Taupo diatom shells are pristine, Theriot is doubtful any diatoms lived through the eruptions. Instead, he suspects diatom resting spores could travel the atmospheric currents, dropping out and colonizing new ecosystems. Diatoms fashion spores to ride out inhospitable changes in their environment. Two years ago, Danish researchers revived 100-year-old resting spores from muck in a local fjord. Resting spores have been found in clouds. The eruption could have launched spores from the lake bottom into the atmosphere, Theriot said.
"I and many others have joked about Yellowstone blowing up again and dispersing the diatomite that is being created at the bottom of Yellowstone Lake," Theriot said. "This is the most thoroughly studied and best documented example of this phenomenon, and so it really says maybe we can add volcanoes to the list of possibilities (of how diatoms spread). And volcanoes would be particularly effective." [Infographic: The Geology of Yellowstone]
Van Eaton hopes the discovery will prompt other scientists to search for microscopic life in "wet eruptions," where magma hit water.
"This is potentially another tool to pinpoint where ash deposits come from," Van Eaton said. "If the work is done to characterize the kinds of microbes that are unique to an area, then it could give you a biogenic fingerprint for your eruption deposits. This has likely been going on in modern eruptions, but no one has taken the time to look for them."
Ash travels hundreds of miles, but once it's far from its source, linking a few inches of glass back to a single volcano becomes difficult, particularly in regions like the South Pacific, where volcanoes pop off all the time.
But Theriot is skeptical that diatoms will prove to be a useful tool for tracking volcanic ash. Diatoms are so global that endemic species — known only to one place — are hard to find, he said. "If you found diatoms in ash deposits in a bog in Ohio, you would have no idea if it was from Yellowstone or from that bog," Theriot said. "It would take a really extraordinary set of circumstances, like this New Zealand (diatom) that is clearly out of place, to be convincing that the diatoms had blown in with the ash."