The deep ice at Camp Century in northwestern Greenland entirely melted at least once within the last million years and was covered with vegetation, including moss and perhaps trees, according to a paper published in the Proceedings of the National Academy of Sciences.
Understanding the history of the Greenland Ice Sheet is critical for predicting its response to future climate warming and contribution to sea-level rise. Image credit: Rolf Johansson.
“Ice sheets typically pulverize and destroy everything in their path, but what we discovered was delicate plant structures — perfectly preserved,” said Dr. Andrew Christ, a researcher in the Department of Geology and the Gund Institute for Environment at the University of Vermont.
“They’re fossils, but they look like they died yesterday. It’s a time capsule of what used to live on Greenland that we wouldn’t be able to find anywhere else.”
Dr. Christ and colleagues analyzed sediment at the bottom of the Camp Century ice core, collected 120 km (75 miles) from the coast in northwestern Greenland.
“The subglacial sediment from the Camp Century ice core was collected in 1966,” they explained.
“The sediment was stored frozen, initially at University at Buffalo from 1966, until it was transferred to Niels Bohr Institute in 1994 and 1996.”
The sediment, frozen under nearly 1.4 km (0.9. miles) of ice, contained well-preserved fossil plants and biomolecules sourced from at least two ice-free warm periods in the past few million years.
Micrographs of fossils (A-J); leaf wax concentrations of n-alkanoic acids and alkanes (K), multiple columns correspond to replicate analyses. Image credit: Christ et al., doi: 10.1073/pnas.2021442118.
“We used a series of advanced analytical techniques — none of which were available to researchers fifty years ago — to probe the sediment, fossils, and the waxy coating of leaves found at the bottom of the Camp Century ice core,” the scientists said.
“For example, we measured ratios of rare isotopes of both aluminum and the element beryllium that form in quartz only when the ground is exposed to the sky and can be hit by cosmic rays.”
“Another test used rare forms of oxygen, found in the ice within the sediment, to reveal that precipitation must have fallen at much lower elevations than the height of the current ice sheet, demonstrating ice sheet absence.”
The authors concluded that the Greenland Ice Sheet persisted through much of the Pleistocene but melted and reformed at least once since 1.1 million years ago.
“Our study shows that Greenland is much more sensitive to natural climate warming than we used to think — and we already know that humanity’s out-of-control warming of the planet hugely exceeds the natural rate,” Dr. Christ said.
“Greenland may seem far away, but it can quickly melt, pouring enough into the oceans that New York, Miami, Dhaka — pick your city — will go underwater,” added Dr. Paul Bierman, a researcher in the Department of Geology, the Gund Institute for Environment, and the Rubenstein School of the Environment and Natural Resources at the University of Vermont.
Andrew J. Christ et al. 2021. A multimillion-year-old record of Greenland vegetation and glacial history preserved in sediment beneath 1.4 km of ice at Camp Century. PNAS 118 (13): e2021442118; doi: 10.1073/pnas.2021442118