Deglaciation of northwestern Greenland during Marine Isotope Stage 11

Quote:

Understanding the history of the Greenland Ice Sheet (GrIS) is critical for determining its sensitivity to warming and contribution to sea level; however, that history is poorly known before the last interglacial. Most knowledge comes from interpretation of marine sediment, an indirect record of past ice-sheet extent and behavior. Subglacial sediment and rock, retrieved at the base of ice cores, provide terrestrial evidence for GrIS behavior during the Pleistocene. Here, we use multiple methods to determine GrIS history from subglacial sediment at the base of the Camp Century ice core collected in 1966. This material contains a stratigraphic record of glaciation and vegetation in northwestern Greenland spanning the Pleistocene. Enriched stable isotopes of pore-ice suggest precipitation at lower elevations implying ice-sheet absence. Plant macrofossils and biomarkers in the sediment indicate that paleo-ecosystems from previous interglacial periods are preserved beneath the GrIS. Cosmogenic 26Al/10Be and luminescence data bracket the burial of the lower-most sediment between <3.2 ± 0.4 Ma and >0.7 to 1.4 Ma. In the upper-most sediment, cosmogenic 26Al/10Be data require exposure within the last 1.0 ± 0.1 My. The unique subglacial sedimentary record from Camp Century documents at least two episodes of ice-free, vegetated conditions, each followed by glaciation. The lower sediment derives from an Early Pleistocene GrIS advance. 26Al/10Be ratios in the upper-most sediment match those in subglacial bedrock from central Greenland, suggesting similar ice-cover histories across the GrIS. We conclude that the GrIS persisted through much of the Pleistocene but melted and reformed at least once since 1.1 Ma. ... The Camp Century subglacial sediment includes two distinct units of frozen diamicton separated by an intermediate layer of debris-rich ice (Fig. 2A and SI Appendix, Supplementary Information Text). Permafrost features such as subhorizontal ice lenses are present only in the lower and intermediate unit. The contact between the intermediate ice layer and the upper diamicton is nonconformable and angular. The two samples we analyzed are from the upper (1059-4) and lower (1063-7) diamicton units (Fig. 2 B and C). Both diamictons contain a variety of lithologies, but the mineralogy is primarily quartz with few feldspars and mafic minerals. The lower sample contains a greater percentage of fine sediment (<125 µm) (Fig. 2A and SI Appendix, Fig. S1; SI Appendix includes full description). Pore-ice major ion chemistry and SEM-EDS analysis of grain coatings indicate greater chemical weathering in the lower sample than the upper sample (Fig. 2 D and E and SI Appendix, Fig, S1 and Table S1).

https://www.pnas.org/doi/full/10.1073/pnas.2021442118

And all this when CO2 was 286ppm, less than now. But it is CO2 wot dunnit.

https://i0.wp.com/wattsupwiththat.com/wp-content/uploads/2023/07/image-125.png

Fascinating.

https://edition.cnn.com/2023/07/20/world/greenland-ice-sheet-melt-sea-level-rise-climate/index.html



Long-lost Greenland ice core suggests potential for disastrous sea level rise

By Laura Paddison, CNN
Updated 2:59 PM EDT, Thu July 20, 2023



CNN  —

A recently discovered ice core taken from beneath Greenland’s ice sheet decades ago has revealed that a large part of the country was ice-free around 400,000 years ago, when temperatures were similar to those the world is approaching now, according to a new report – an alarming finding that could have disastrous implications for sea level rise.

The study overturns previous assumptions that most of Greenland’s ice sheet has been frozen for millions of years, the authors said. Instead, moderate, natural warming led to large-scale melting and sea level rise of more than 1.4 meters (4.6 feet), according to the report published Thursday in the journal Science.

“When you look at what nature did in the past, as geoscientists, that’s our best clue to the future,” said Paul Bierman, a scientist at the University of Vermont and a lead author of the study.

What it indicates is “frightening,” he told CNN.
A view of the Greenland Ice Sheet.

Greenland and Antarctic ice sheets are melting rapidly and driving sea level rise, new satellite data finds

Levels of carbon dioxide in the atmosphere are 1.5 times higher now than they were 400,000 years ago, and global temperatures keep climbing.

If Greenland’s ice sheet saw rapid melting during a period of moderate warming, it “may be more sensitive to human-caused climate change than previously understood – and will be vulnerable to irreversible, rapid melting in coming centuries,” the study authors said in a statement.

This would have significant impacts on sea level rise.
If Greenland’s ice sheet were to melt completely,
sea levels would rise by about 7 meters (23 feet)
causing devastation to the billions who live along the world’s coasts.

To complete the research, Bierman and a team of international scientists spent years analyzing frozen sediment from an ice core collected in 1966 at Camp Century, a US army base in northwest Greenland. Scientists had drilled through more than 4,500 feet of ice to pull up a 12-foot-long soil and rock sample from beneath the ice sheet.

At the time, there wasn’t the technology to understand the sediment very well and so it was lost in a freezer for decades, Bierman said. Then, in 2017, it was rediscovered in Denmark.

Bierman went to Copenhagen and brought two samples back to the University of Vermont to test. As the scientists started to sieve it to separate out the sediment, they were surprised to see twigs, mosses, leaves and seeds.

“We have a fossilized frozen ecosystem here,” said Bierman, “And what that meant, of course, is the ice sheet had gone away because you can’t grow plants under a mile of ice.”

According to some axial precession existed 400,000 years ago which led to Greenland melting. But the earth's axial precession is not then. It occurs approximately 25,722 years.

lee wrote on Jul 23^rd, 2023 at 2:46pm:

According to some axial precession existed 400,000 years ago which led to Greenland melting. But the earth's axial precession is not then. It occurs approximately every 25,722 years.

I doubt we'll see Greenland or anywhere else melt completely in our lifetimes
or even in the next 1,000 years.