by Julie Brigham-Grette Thursday, January 5, 2012
Although our final results won’t begin to be published until early next year, our team met in May to review all the data we had collected so far.
We had drilled several types of cores. Our initial pilot cores, taken in 1998 and 2003, provided proof of concept, demonstrating the importance of these cores as a climate record, as they contain climate data that extend back in time 300,000 years — roughly three times longer back in time than the oldest portions of the Greenland ice core records.
Our main cores, drilled from November 2008 to May 2009, took the concept even further, extending the record back in time more than 30 times longer than that drilled in Greenland. The temporal length and geologic significance of this climate record are therefore unprecedented in the entire Arctic region.
We recovered sediment and rock from three holes drilled in the center of the lake. While the sediment cores provide information about the climate record over the last 3.6 million years, the rocks beneath the sediment — impact formations such as breccias and suevites — tell us about the impact itself.
From these three holes, at a depth of 130 meters, we recovered sediments that cover roughly the last 2.6 million years. We also collected sediment cores from 100 to 315 meters below the lake floor to the time of impact at 3.6 million years ago, albeit with lower recovery due to surprising sequences of coarse sand and gravel interbedded with lake mud. These coarser units suggest unexpected glacial sources for these materials. Beneath the lake sediments we also collected various impact breccias and suevites (breccia with melted rock) over a depth interval of 207 meters.
Equally exciting is that we recovered roughly 40 meters of the earliest history of the lake in the warm middle Pliocene with nearly 100 percent recovery. This interval is especially fascinating as a possible analogue for future climate due to carbon dioxide forcing.
A weekly diary of all drilling operations is available here.
Interestingly, in the cores covering the last 2.6 million years, we see warm and cold cycles like those we saw in the much younger pilot cores. Furthermore, we confirmed the age of the impact using the initial paleomagnetic reversal stratigraphy of the Earth’s magnetic field recorded in the sediments.
Overall, the record so far suggests that the cores will produce new and exciting information on the style and onset of Northern Hemisphere glacial cycles seen for the first time with such clarity in an Arctic terrestrial setting.
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