The world’s second largest ice body is the Greenland Ice Sheet. It has the possibility of considerably adding to the rise in global sea level in a warming global climate.
Overlooking the iceberg-covered fjord from where the margins of Akullersuup Sermia (left) and Kangiata Nunaata Sermia (right) were located in the 1920s (10 km from the current ice margin). While the Norse were in Greenland, these glaciers merged and ultimately advanced another 13 km beyond this point. Image Credit: James Lea.
Comprehending the long-term record of the Greenland Ice Sheet, including the records of glacial advance as well as retreat, is essential in corroborating methods that model future ice-sheet situations. However, this recreation can be very tough.
Published recently in the journal Geology, a new study recreated the movement of one of the largest tidewater glaciers in Greenland to offer more insight into long-term glacial dynamics.
In the news, we’re very used to hearing about glacial retreat, and that’s because in a warming climate scenario—which is what we’re in at the moment—we generally document ice masses retreating. However, we also want to understand how glaciers react if there is a climate cooling and subsequent advance. To do this, we need to reconstruct glacier geometry from the past.
Danni Pearce, Study Co-Lead, Norwegian University of Life Sciences
An interdisciplinary group of scientists analyzed the movement of Kangiata Nunaata Sermia (KNS) — the biggest tidewater glacier in southwest Greenland — during a cooling period when the Norse had inhabited Greenland. In contrast to glaciers that are firmly on land, tidewater glaciers spread and drift all the way to a sea or the ocean, where they calve and disintegrate into icebergs.
Rebuilding the progress of glaciers can be extremely tough because the glacier usually breaks up or reworks everything in its route as it moves forward. The researchers embarked on several field seasons in Greenland, walking to remote locations—a number of which had not been inspected since the 1930s—to attempt and expose the record of KNS progress.
When we went out into the field, we had absolutely no idea whether the evidence would be there or not, so I was incredibly nervous. Though we did a huge amount of planning beforehand, until you go out into the field you don’t know what you’re going to find.
James Lea, Study Co-Lead, University of Liverpool
Walking allowed the scientists to more carefully analyze and explore locations that otherwise may have been overlooked if they had flown by helicopter. The team’s planning was fruitful, and the sedimentary sequences they examined and sampled contained the clues they were seeking to date and follow the glacier’s advance.
The researchers found that during the 12th and 13th centuries CE, KNS progressed no less than 15 km, at a rate of ~115 m/year. This rate of advance is similar to modern rates of glacial retreat witnessed throughout the past ~200 years, signifying that when the climate is cooler, glaciers can move just as rapidly as they are currently retreating.
The glacier attained its highest extent by 1761 CE during the Little Ice Age, finishing in a total advance of ~20 km. Since then, KNS has retreated ~23 km to its current spot.
The era when the glacier was moving overlapped with when the Norse inhabited Greenland. Before its maximum extent during the Little Ice Age, the scientists learned that KNS moved to a location within just 5 km of a Norse farmstead.
Even though KNS was rapidly coming down the fjord, it did not seem to affect the Norse, which we found really unusual. So the team started to think about the surrounding environment and the amount of iceberg production in the fjord during that time. At the moment, the fjord is completely filled with icebergs, making boat access challenging, and we know from historical record that it has been like this for the last 200 years while the glacier has been retreating.
Danni Pearce, Study Co-Lead, Norwegian University of Life Sciences
“However, for KNS to advance at 115 m/yr, it needed to hang onto its ice and could not have been producing a lot of icebergs. So we actually think that the fjord would have looked very different with few icebergs, which allowed the Norse far more easy access to this site for farming, hunting, and fishing,” Pearce continued.
Archaeologists, who went to the location in the 1930s, theorized that the surroundings in the fjord must have been diverse from today in order for the Norse to have lived there, and this present study offers data to back these long-believed ideas.
“So we have this counterintuitive notion that climate cooling and glacier advance might have actually helped the Norse in this specific circumstance and allowed them to navigate more of the fjord more easily,” said Lea.
In the fifteenth century CE, the Norse left Greenland, and these results are consistent with the concept that a cooling climate was probably not the reason for their migration; rather, a mixture of economic factors possibly caused the Norse to leave Greenland.
The outcomes from this study recreating rapid glacial movement are also proven to be constant with the way ice sheet models function, which delivers reliability to the projections from these models. Having precise projections and models is important in comprehending and preparing for future circumstances of continued retreat of the Greenland Ice Sheet and related sea-level rise.
Melt from Greenland not only impacts sea-level change but also the ecology around the ice sheets, fisheries, the biological productivity of the oceans—how much algae is growing. And also because the types of glaciers we’re looking at produce icebergs these can cause hazards to shipping and trade, especially if the Northwest Passage opens up as it is expected to.
James Lea, Study Co-Lead, University of Liverpool
Pearce added, “Our research shows that climate cooling can change iceberg calving behavior and drive glacier advance at rates just as rapid as current retreat. It also shows how resilient the Greenlandic Norse were to the changing environmental conditions. Such adaptation can give us hope for the changes we may face over the coming century.”
Journal Reference:
Pearce, D. M., et al. (2022) Greenland tidewater glacier advanced rapidly during era of Norse settlement. Geology. doi.org/10.1130/G49644.1.