9,000 Years of History from the Køge Bugt

The Køge Bugt glacier system contains three of the largest glaciers of the Greenland Ice Sheet (Source: Laurence Dyke).

The glaciers of southeast Greenland are not easy to research. You ride in on a small fishing boat, searching among the icebergs for the best place to stick a glorified straw into the mud. Which is just what a team of researchers did in 2011 to retrieve a sediment core that describes 9,000 years of history from the Køge Bugt glacier system. In September, the team released a paper in Nature’s Scientific Reports describing the results.

The Køge Bugt glacier system contains three of the largest glaciers of the Greenland Ice Sheet, all of which have contributed to recent ice loss. Because of the lack of previous research in the area, investigating this system promised worthwhile results. The team collected a nearly two-meter-long sediment core from the center of Køge Bugt, the body of water that also gives the glacier system its name. This area receives sediment input from the three glaciers in the system, and while the core cannot provide inference about the individual glaciers, it gives information about the system’s collective behavior, according to the report.  

“We expected it to be a record that would, if we were lucky, be just a few thousand years and possibly even much less than that, so it was really quite a surprise when we got our first radiocarbon dates back,” lead researcher Laurence Dyke told Glacier Hub. A record this old, especially for a glacier system like Køge Bugt, with little previous historical research, can now provide baseline data to contrast with the changes in the system over the last two decades.

Compared to the more well-studied Jakobshavn Glacier in Western Greenland, the levels of retreat exhibited by Køge Bugt over the past 9,000 years appear minimal, the team notes. There is evidence of Jakobshavn retreating in the order of 30 to 50 kilometers further inland than its current location during the Holocene. Køge Bugt seems to have only retreated five or six kilometers. Due to the difficulty of studying this area, it is hard to say how anomalous these results are without further investigation.

The researchers attribute this minimal retreat of Køge Bugt glaciers to their sub-ice topography. Most studied glaciers on Greenland sit in a deep fjord system several hundreds of kilometers long– essentially a long trough that runs onto the continental shelf and inland beneath the glacier. However, the glaciers in the Køge Bugt system are different. These glaciers sit on a steep bedrock slope, more like a bowl than a trough. This helped to stabilize the glacier throughout the Holocene.

While the researchers are not sure of what caused this configuration, Dyke says it’s certainly what is controlling the glaciers’ behavior. “If you want to predict the whole of Greenland,” says Dyke, “then you really need to have very good geometry of both the sub-ice and the sub-ocean.” Dyke and his team hope that their research into Køge Bugt will be used by climate modelers to further inform how models reflect glacier geometry and to interpret the Køge Bugt system’s current and future behavior.

Køge Bugt faces challenges posed by climate change (Source: Laurence Dyke).

The paper’s findings would not be so striking if not for recent activity in the system. Based on the historical record, it is surprising that these glaciers have changed so much in recent years. The loss of ice between 2003 and 2012 is about one-third of the maximum ice that could have been lost in the Holocene before these glaciers would have retreated out of tidewater, according to Dyke. “However, it is important that we can’t be sure that the glaciers didn’t change as much as they currently are at other periods during our record,” he said. “What we can say with certainty is that if the glaciers continue to retreat just a few more kilometers, and retreat onto land, this will be unprecedented within at least the last 9,000 years, and in all likelihood, the last 130,000 years.”

Rising temperatures in the ocean and atmosphere affect glaciers around the globe, and despite its unique setting, Køge Bugt is no exception. “There’s some pretty good predictions now of what will happen to Greenland in the long run,” Dyke said.“Greenland is going to get a lot smaller. These glaciers will retreat out of the water, and how quickly that happens really depends on how warm the atmosphere and the oceans get. And that’s something that ultimately we have control over.”