Greenland drilling campaign aims for bedrock to trace ice sheet’s last disappearance

Global warming is accelerating the melting of Greenland’s ice sheet, which locks up enough water to raise sea levels by 7 meters. In 2021, U.S. researchers will go to the frozen expanse to pinpoint the last time it disappeared.

The 5-year, $7 million campaign, awarded last month by the National Science Foundation, will mark the first large U.S. ice drilling program in Greenland in more than 25 years. Unlike past projects, the target is not the climate records held in the ice, but the rocks below, which contain radioactive clocks that show when they were last exposed to air.

“The whole bedrock is an archive,” says Joerg Schaefer, a geochemist at Columbia University and co-leader of the project, called GreenDrill. “It’s just a question of getting these freaking samples under the ice.”

Greenland already accounts for 25% of global sea level riseand that share is growing. Scientists have recently identified the island’s north as a hot spot for melting during the next century. The drilling project could not only validate those near-term fears, but also inform climate models that struggle to predict the long-term fate of the ice.

As a bonus, the effort could shed light on the timing of the asteroid or comet impact that gouged the Hiawatha crater, a 31-kilometer scar hidden under the ice, sometime within the past 3 million years. Some scientists think the event was recent and the trigger for a bout of global cooling 13,000 years ago known as the “Younger Dryas.” But so far, no firm dates have been recovered from crater material to support that controversial claim. Although GreenDrill researchers will not drill into the crater itself, one of its four sites is just 20 kilometers to the west. Rocks there could show when the ice last melted away—perhaps in the sudden heat of the impact. And any impact ejecta recovered in the rock could be sifted for minerals, such as zircons, that offer precise dates.

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