By Alexandra Witze, Science News
DENVER—It took the better part of a decade, $10 million, and help from the guys who build ice roads for Canadian truckers. But scientists now have the most continuous record of ancient climate ever extracted from the terrestrial Arctic.
What's more, the record—cored through sediment layers at the bottom of a lake in northeastern Siberia— also illuminates what happened when a big meteorite smashed into the spot 3.6 million years ago, when the ground was warmer and forested as opposed to the barren tundra it is today. Water filled the resulting crater and formed Lake El'gygytgyn (pronounced EL-gih-git-gin).
"We're really pleased that we have a complete record of that entire time period," said Julie Brigham-Grette, a geologist at the University of Massachusetts at Amherst and one of the project's leaders. She described the findings in Denver on October 31 at the annual meeting of the Geological Society of America.
Analysis of the lake cores is revealing details of how the Arctic landscape warmed and cooled over the past several million years, she said. Comparing similar data from the Arctic Ocean and Antarctica can show how the two polar regions—which are more sensitive to climate change than temperate or tropical latitudes—react differently to changing temperatures.
"The sheer logistics prevented anyone from doing this before," said Brigham-Grette.
Lake El'gygytgyn lies 100 kilometers north of the Arctic Circle and 360 kilometers from the nearest inhabited town: Pevek, Russia. The 12-kilometer-wide lake is too windy and rough to be drilled from a floating rig in the summer, so the researchers decided to drill in the winter from an ice platform.
To get there, the team had to ship camp materials and a drill rig to Pevek, then use helicopters or trucks running on an ice road that ended 90 kilometers short of the lake. For the final 90 kilometers equipment had to be hauled with bulldozers through the snow.
After all that, the team had to artificially thicken the lake ice by drilling a small hole and pumping water to the top to freeze again, to get the ice to the 2 meters of thickness that could support the weight of the drill rig.
The lake is deep enough to not freeze all the way to the bottom in winter, meaning it is a sediment trap whose layers of mud contain pollen and other indicators of what the environment was like at the time the material settled. Other lakes in the far north have frozen solid many times and thus don't contain such a detailed record.
This unique record along with the lake's high latitude make the work important scientifically, says Yarrow Axford, a paleoclimate expert at Northwestern University in Evanston, Ill., who is not involved in the project.
At the time the kilometer-wide meteorite hit, temperatures were probably 10 to 14 degrees Celsius warmer than today, Brigham-Grette said. The impact vaporized much of the silica-rich rock, turning it into a jumble known as breccia with fractured quartz grains and other particles melted by the impact's heat, said team member Christian Koeberl of the University of Vienna.
The core holds no tiny fossils or pollen in the 15 meters just above the layer that marks the meteorite impact, Brigham-Grette reported at the conference—possibly because the searing heat zapped anything that would otherwise have been preserved. At least ten different layers of volcanic debris, scattered throughout the core, reflect eruptions of volcanoes on the Kamchatka peninsula to the south, she said.
Brigham-Grette hopes to compare the cores to others from the same time period, like those drilled in Lake Baikal—also in Siberia but at 54 degrees north rather than 67 degrees—and others taken from the underwater Lomonosov Ridge in the Arctic Ocean.