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Onboard听a ship off the icy coast of Greenland, Anne Jennings and the crew have been paying close attention to Fred, a massive, jagged iceberg, for the past two weeks.

鈥淚t鈥檚 really beautiful and peaceful, but we don鈥檛 want it to get too close to our ship,鈥� said听Jennings,听during a Zoom call from the ship last week. Jennings, a senior research associate at the Institute of Arctic and Alpine Research (INSTAAR) at CU Boulder, is the co-chief scientist of an ocean-core drilling expedition in Baffin Bay, off the island鈥檚 northwest shore.听

Fred, as she and the crew call it, is the 41st听iceberg they鈥檝e been tracking since they embarked two months ago. Some drifted too close, forcing the team to abandon their drilling sites and sail away. But despite a few adventures, the trip has been remarkably productive.

鈥淚t鈥檚 been an incredible journey,鈥� Jennings said.听

She and the 116-person crew boarded the JOIDES Resolution (JR), a 470-foot-long research ship on August 13 for the International Ocean Discovery Program鈥檚 (IODP) Expedition 400: Northwest Greenland Glaciated Margin. They set off to recover sediments tens of millions of years old from 0.6 miles below the sea floor to gain insights into how the Greenland ice sheet鈥攐ne of two remaining ice sheets on Earth and the only one in the Northern Hemisphere鈥攈as changed through the planet鈥檚 various warming and cooling cycles.听

鈥淲e are coring back into interglacial periods that were much warmer and had much higher atmospheric CO2 than today. And we're also coring into time periods when atmospheric CO2 level was similar to today鈥檚,鈥� Jennings said. By reconstructing the ice sheet conditions back then, Jennings and other paleoclimate scientists can make better predictions of what scenarios humans may face in the future.

A threat to global sea level听

Over hundreds of thousands of years, ice sheets, essentially very large glaciers, repeatedly covered large areas of Asia, Europe and North America, and melted away.

91制片厂 11,500 years ago, gradual changes in Earth鈥檚 orbit allowed more sunlight to hit the Northern Hemisphere. As a result, Earth warmed up, marking the end of the last ice age and the beginning of what is known as the Holocene, the interglacial period Earth is currently in.

鈥淚t鈥檚 of interest that all these other ice sheets in the Northern Hemisphere are gone, but the Greenland ice sheet is still here,鈥� said Jennings, who studies ancient climate and ocean conditions.听

As human-caused climate change drives up Earth鈥檚 temperature, scientists have observed that the听, and the melting area is growing larger, affecting even high elevations. That鈥檚 concerning because it holds a large amount of fresh water. If the entire ice sheet melted, the global sea level听could .听听

Jennings wants to know if similar melting occurred during the past interglacial periods when Earth was warm, and if the Greenland ice sheet had ever entirely melted. This could offer important clues in predicting its melting patterns in the current warming world.听

Coring the ocean bed

To answer these questions, Jennings and two dozen scientists use a long drill that can pierce the ocean floor and retrieve sediments from over a half-mile beneath the ocean floor. The recovered cores contain rocks, sediments and fossils that have been there for millions of years, revealing a plethora of information that will help scientists understand ancient climates and ice sheet conditions.听听听

While the ice sheet may appear static, it is constantly moving, flowing downhill and outward toward the ocean, she explains. These icy rivers carve up the land, breaking and trapping rocks and sand within. The edge of these large glaciers sometimes breaks off into icebergs like Fred, which drift in the ocean and drop the trapped deposits to the seafloor as they melt.听

Jennings and her team are looking for these deposits, which are telltale signs of ice in the ocean. By locating them in different layers of the sediments formed during different periods, the team can reconstruct how the ice sheet has changed over time. Frequently, paleontologists also find fossils of small plants and animals buried in the sediments, which offer important information on what past environments were like too.听

So far, the team has extracted more than 400 cores at various sites throughout their two-month voyage. The drill pulls up a 32-foot-long core each time and returns to the same hole to drill deeper.听

The oldest and deepest sediments they were able to retrieve during this expedition may be听as much as 20 to 25 million years old, Jennings said.

The JR is heading back to Iceland this week, from where Jennings will fly back home to Boulder.听

All the cores from Expedition 400 will be stored in a repository in Bremen, Germany. Scientists who plan further study on the cores, including Jennings, will convene next spring for a 鈥渟ample party鈥� to take small samples from the repository to their labs all over the world.

After nearly four decades of scientific ocean drilling during over 200 scientific research expeditions, the JR, funded by the U.S. National Science Foundation, will complete its听 in 2024.听

鈥淗opefully there will be support for a new generation of scientific ocean drilling research that will allow us to continue exploration and build on the extraordinary scientific legacy of the JR and IODP,鈥� Jennings said.听