A fresh look at sediment recovered decades ago from almost a mile below the icy surface suggests that Greenland supported thriving vegetation and ecosystems within the last 1.1 million years.

An international group of researchers, including scientists from Lawrence Livermore National Laboratory (LLNL), recently analyzed subglacial sediment and rock at the base of the Camp Century ice core collected in 1966.

The sediment, frozen beneath nearly 1.4 kilometers (.9 miles) of ice, contains fossil plants and biomolecules from at least two ice-free warm periods in the past few million years.

“The history of the Greenland Ice Sheet and the ecosystems that occupied Greenland during ice-free intervals are poorly known,” said LLNL scientist Alan Hidy, a co-author of the study, which appeared in the Proceedings of the National Academy of Sciences.

“This fragmentary knowledge of Greenland’s climate history limits our understanding of ice-sheet and ecosystem sensitivity to climate warming,” Hidy said.

The Camp Century ice core, collected from the ice sheet in northwestern Greenland, recovered 3.44 meters of frozen sediment from beneath the ice -- the thickest subglacial sediment ever recovered from a Greenland ice core.

However, the sample was never studied beyond initial reports of microfossils, including abundant freshwater diatoms, algae, pollen, and scarce marine fossils, and remained in frozen storage for decades until it was rediscovered in 2017.

In the new research, scientists were able to decipher the glacial and ecological history of northwestern Greenland using analytical techniques that were unavailable when the sediment was retrieved more than 50 years ago. Researchers analyzed samples from the upper- and lower-most sections of the subglacial sediment.

“We found that the Camp Century subglacial sediment preserves a unique, multi-million-year-old record of glaciation and vegetation,” Hidy said. “These data are consistent with persistent ice cover interrupted by at least two periods of ice-sheet loss and regrowth, once in the Early Pleistocene and another in the past 1.1 million years.”

Studying the history of the Greenland Ice Sheet is considered critical in understanding the potential impact of global warming. If the Greenland ice sheet should melt completely, scientists predict that sea level would rise by as much as 20 feet.

The research was funded by the Gund Institute for Environment, the National Science Foundation, NASA, and the Belgian National Fund for Scientific Research.

In addition to LLNL, the team of researchers came the University of Vermont, Columbia University, University of Manitoba, the Goddard Institute for Space Studies, University of Buffalo, University of Washington, Utah State University, Free University of Brussels, University of Lorraine, Williams College, Purdue University, and University of California, Irvine.