Northwest Greenland was ice-free 400,000 years ago

2023-07-20 20:00:23

In it paleoclima of the Earth there were warm periods (the interglacials) and other very cold ones. We know this from the natural environmental records that scientists have been finding in ice cores, corals, tree wood and other fossils, or pollen and sediments (environmental dust sheets, lava, ashes or others), especially in regions near the poles.

However, ice-free sedimentary records during interglacial periods are scarce or difficult to obtain due to the current ice cover.

One of the areas that gives good clues to remote climate and its transitions is Greenlandan immense frozen island whose ice surface melts at an unusual rate and leaves traces of different eras half-discovered. On this island located between the Atlantic Ocean and the Arctic Ocean, a secret US base was built during the Cold War, in the form of a tunnel under the ice, called Camp Century. And when it was no longer used for warfare, glaciologists used old samples of ice and drilling mud to study them.

The sediments were examined with cosmogenic nuclide and luminescence dating techniques and found to be deposited by water flowing on ice-free tundra during the MIS 11 interglacial period.

Now, those sediments recovered from the base of the Camp Century ice core show that northwestern Greenland was ice-free during a period in history known to have had the lowest ice volumes on record: the so-called Marine Isotopic Interglacial Period (MIS) 11, which occurred about 400,000 years ago. This is a specific period in which the medium temperature of the atmosphere was similar to what we will experience soon, given the current warming of the Earth, according to a study led by a scientific team from the University of Vermont (USA), published in Science .

The work indicates that the absence of ice in that region, at some point in the Pleistocene, would mean that this melting could have contributed to raising more than 1,4 metros he global sea level during the interglacial, which was already between 6 and 13 meters higher than the current one.

To reach this conclusion, Andrew Christ —a glacial geomorphologist at the University of Vermont—and colleagues analyzed the sediments using cosmogenic nuclide and luminescence dating techniques, and found that they were deposited by flowing water in an ice-free tundra environment during the MIS 11 interglacial period.

“If moderate warming over the roughly 29,000 years of MIS 11 caused major ice loss in Greenland, then rapid and prolonged anthropogenic warming of the Arctic could raise sea levels and trigger feedbacks for centuries to come,” Christ explains.

Ice sheets that slide towards the sea

The climatic conditions of past interglacials, periods of the planet’s climate history characterized by warmer temperatures and less ice cover, give us the opportunity to better understand how the climate will respond. cryosphere to climate warming and how the phenomenon will contribute to the rise in the level of the oceans.

Temperatures during MIS 11 were probably a degree Celsius or perhaps 1.5C higher than today.

Paul Bierman, principal investigator

The cryosphere —which includes snow, sea ice, lake and river ice, icebergs, glaciers and ice caps, ice sheets and shelves, or permafrost— is an inescapable part of the climate. Earth’s climate system. Hence the value of finding out precisely how the deglaciation of Greenland occurred and what could have happened when those ice sheets melted and drained towards the sea, during the MIS 11 interglacial period.

Speaking to SINC, the geologist Paul R. Bierman, one of the main authors of the study, explains that to make the calculations of these equivalences, the volume of the Greenland ice sheet was taken as a base, which “is well known.” With the modeling of that layer, they studied “how climate changes cause melting and the amount of water” it releases.

For each model output, Benjamin Keisling —from the University of Texas at Austin and Columbia University’s Lamont Doherty Observatory—estimated “the volume of water that left Greenland and flowed into the global ocean,” Bierman describes. In order for the Camp Century area not to be frozen, ice equivalent to “at least 1.4 meters of sea level rise” must have melted, he adds.