Recent reversal discovered in Greenland ice caps response to climate change

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Ice-covered and snow-capped mountains on the west coast of Greenland. (April 2015). Credit: Matthew Osman © Woods Hole Oceanographic Institution

Greenland is perhaps best known for its enormous continental-scale ice sheet that rises up to 3,000 meters above sea level, of which the rapid melting is one of the major contributors to the global sea level rise. But around this huge ice cap, which covers 79% of the world’s largest island, lies the rugged coastline of Greenland dotted with mountain peaks covered in ice. These peripheral glaciers and ice caps are now also undergoing significant melting due to anthropogenic (man-made) warming. However, global warming and the loss of these ice caps may not have always gone hand in hand.

New collaborative research from the Woods Hole Oceanographic Institution and five partner institutions (University of Arizona, Washington University, Pennsylvania State University, Desert Research Institute and University of Bergen), published on September 9, 2021 in Geosciences of nature, reveals that in past periods, the glaciers and ice caps of the west coast of Greenland have experienced very different climatic conditions than those of the interior of Greenland. Over the past 2,000 years, these ice caps have undergone periods of warming in which they have enlarged rather than shrunk.

Matthew Osman and Mike Waszkiewicz

Matthew Osman, Postdoctoral Research Associate at the University of Arizona, and Mike Waszkiewicz, US Ice Drilling Program Specialist, set up a barrel of ice cores in West Greenland as part of their work aimed at studying the response of ice caps to climate change. Credit: Sarah Das © Woods Hole Oceanographic Institution

This new study breaks down the climatic story displayed in a core taken from an ice cap off the west coast of Greenland. According to study researchers, while ice core drilling has been underway in Greenland since the mid-20e century, studies of coastal ice cores remain extremely limited, and these new findings offer a new perspective on climate change compared to what scientists previously understood using only ice cores from the interior parts of the ice cap. from Greenland.

“Glaciers and ice caps are unique high-resolution repositories of Earth’s climate history, and analysis of ice cores allows scientists to examine how environmental changes – such as changes in precipitation and global warming – affect the rates of snowfall, melt and in turn influence the ice sheet. growth and decline, ”said Sarah Das, associate scientist in geology and geophysics at OMSI. “Examining the differences in climate change recorded on multiple ice core recordings allows us to compare and contrast the climate history and ice response in different regions of the Arctic. However, in the course of this study it also became evident that many of these coastal ice caps are now melting so dramatically that this incredible record is in great danger of disappearing forever.

Due to the difficult nature of the study and the access to these ice caps, this team was the first to carry out such work, centering their study, which began in 2015, around a core taken from the Nuussuaq peninsula in Greenland. This unique core offers insight into how coastal climatic conditions and ice sheet changes have covariated over the past 2,000 years, due to the tracked changes in its chemical composition and the amount of snow archived year after year in the core. Through their analysis, investigators discovered that during periods of past warming, the ice caps were expanding rather than melting, contradicting what we see today.

“Currently, we know that Greenland’s ice caps are melting due to warming, further contributing to sea level rise. But we still have to explore how these ice caps have changed in the past due to climate change,” said Matthew Osman, postdoctoral research associate at the University of Arizona and the 2019 graduate of the MIT– OMSI joint program. “The results of this study were a surprise as we see that there is a change underway in the fundamental response of these ice caps to climate: today they are disappearing, but in the past with low degrees of warming, they actually tended to grow larger. “

According to Das and Osman, this phenomenon occurs because of a “tug of war” between what causes an ice sheet to grow (increased precipitation) or shrink (increased melt) during periods of warming. . Today, scientists are observing rates of melt that exceed the rate of annual snowfall at the top of the ice caps. However, over the past centuries, these ice caps have grown larger due to increased precipitation brought on by warmer temperatures. The difference between the past and the present is the severity of modern anthropogenic warming.

The team collected this data by drilling through an ice cap atop one of the highest peaks on the Nuussuaq Peninsula. The whole core, about 140 meters long, took about a week to recover. They then brought the meter-long carrots to the National Science Foundation Ice Core Facility in Denver, Colorado, and stored them at -20 degrees. Celsius. The core pieces were then analyzed by their layers for melting characteristics and trace chemistry at the Desert Research Institute in Reno, Nevada. By examining different properties of the core’s chemical content, such as parts per billion of lead and sulfur, investigators were able to accurately date the core by combining these measurements with a past ice flow model.

“These model estimates of the ice sheet flow, coupled with the actual ages we got from this high precision chemistry, help us describe changes in ice sheet growth over time. This method offers a new way to understand past changes in the ice sheet and their correlation with climate, ”said Das. “Because we are collecting a climatic record of the coast, we are able to document for the first time that there have been these great changes in temperature, snowfall and melt in the past 2,000 years, showing much more variability than what is observed in the recordings. of the interior of Greenland, ”added Das.

“Our results should prompt researchers to look back on these remaining ice caps and collect new climate records while they still exist,” Osman added.

Reference: “Abrupt Common Era hydroclimate shifts drive west Greenland ice cap change” by Matthew B. Osman, Benjamin E. Smith, Luke D. Trusel, Sarah B. Das, Joseph R. McConnell, Nathan Chellman, Monica Arienzo and Harald Sodemann, September 9, 2021, Geosciences of nature.
DOI: 10.1038 / s41561-021-00818-w

Additional collaborators and institutions:

  • Benjamin Smith, University of Washington
  • Luke Trusel, Pennsylvania State University
  • Joseph McConnell, Desert Research Institute
  • Nathan Chellman, Desert Research Institute
  • Monica Arienzo, Desert Research Institute
  • Harald Sodemann, University of Bergen and Bjerknes Center for Climate Research, Norway

This research is funded by the National Science Foundation (NSF), with additional support from the United States Department of Defense Science and Engineering Graduate Scholarship; and an Ocean Outlook grant to the Bjerknes Center for Climate Research; the national infrastructure for high performance computing and data storage in Norway; Norwegian Research Council; and Air Greenland.

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