A recent reversal in the response of the West Greenland ice caps to climate change

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, University of Washington, Pennsylvania State University, Desert Research Institute and University of Bergen), published today 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 from 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.

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-20th century, coastal ice core studies remain extremely limited, and these new findings offer a new perspective on the change. climatic compared to what scientists previously understood using ice cores from the inner parts of the Greenland ice sheet only.

“Glaciers and ice caps are unique high-resolution repositories of Earth’s climatic 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 cap. growth and decline, ”said Sarah Das, associate scientist in geology and geophysics at OMSI. “Examining the differences in climate change recorded in several ice core recordings allows us to compare and contrast the climatic history and ice response in different regions of the Arctic.” However, during 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 continued 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 have yet to explore how these ice caps have changed in the past due to the changes. climate, “said Matthew Osman, postdoctoral researcher. associated with the University of Arizona and graduated in 2019 from the joint MIT-WHOI program. “The results of this study were a surprise because 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 small degrees of warming, they actually tended to grow larger. “

According to Das and Osman, this phenomenon occurs due to 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 collect. They then took the meter-long carrots to the National Science Foundation’s ice core facility in Denver, Colo., 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 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. method provides a new way to understand past changes in the ice sheet and how this occurs. correlated with climate, “Das said.” Because we are collecting a climatic record of the coast, we are able to document for the first time that there have been these large changes in temperature, snowfall and melt in the past 2,000 years, showing much more variability than what is observed in records. from 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.