As climate scientists attempt to forecast how increases in atmospheric temperatures expedite the melting of polar ice sheets, a team of paleoclimatologists is searching back in time for important clues on the effects of previous climate disruptions. Specifically, the team, led by Dr. Jason Briner (State University of New York, Buffalo), is studying Greenland's Jakobshavn Isbrae to understand how climate changes during the Little Ice Age and Holocene thermal maximum—a time span of roughly 10,000 to 100 years ago—impacted the glacier's behavior. Given that the most comprehensive data on the glacier span only about two to three decades, reconstructing the Jakobshavn's response to climate change over a period of thousands of years will yield insights into the relationship between warming temperatures and glacial trends, said Briner.
"The intent of paleoclimatology is to see what the earth systems are capable of doing in longer time periods and in different climate regimes," said Briner. "By looking in the past, we have the ability to know what happened when it was 5 to 10 degrees colder or warmer. We are trying to make our research relevant in the context of modern climate changes so we might better understand what might happen in the future."
Working on the Jakobshavn also provides a unique opportunity to do paleo work on an existing glacier, said Briner.
Jakobshavn Isbrae: The World's Fastest Moving Glacier
Jakobshavn Isbrae is considered the world's fastest moving glacier. According to a recent article in the Financial Times, the Jakobshavn Isbrae is perhaps the fastest moving glacier in the world. It drains roughly 6.5 percent of the Greenland ice sheet, and has been documented to be moving at 13 km per year and pouring about 40 km3 per yearof ice into the fjord.
In the past two years, Briner and his team conducted a National Science Foundation-supported pilot study to demonstrate the utility of analyzing the glacier's past. Concentrating on the Holocene period, which began about 12,000 years ago, when average temperatures were about 3 degrees Celsius warmer than they are today, they attempted to identify more precise temperature ranges as well as to understand the glacier's activity. They also collected information from the Little Ice Age, which followed the middle Holocene warm period and marked a cooling of the earth's climate from about 600 to 100 years ago.
Their data came from isotope analysis and radiocarbon dating of lake sediment, as well from three-dimensional maps created using historical photos and an assessment of the insect remains within their lake sediment samples. Although the team's research focuses on the glacier itself, their detective work took place on the surrounding rocks and in the many lakes on the glacial moraine.
"We work where the ice was, not where it is," said Briner. "Our geologic record comes from the landscape."
Lakes Rich With History
These lakes serve as conservatories of glacial debris, which drained into them when the Jakobshavn melted and retreated over time. Briner and his team study sediment cores from the lakes to date the contacts, which is how they confirmed the glacier advanced during the Little Ice Age.
"Until the Little Ice Age, the lakes had no glacial meltwater input," said Briner. "The ice margin advanced during the Little Ice Age close to pre-existing lakes, but not over them. In fact, it advanced just barely close enough that it spilled its melt water into the lake basin and ultimately the silt particles in the ice sheet melt water were deposited in the lake, which, prior to that, just had the organic sediments. When the glacier retreated, its margin receded back out of the lake's drainage basin."
Putting the Puzzle Together
The team aims to reconstruct the climate and establish a more specific temperature record that spans the Holocene period. Currently scientists have a broad understanding of the average temperatures during the Holocene, but those temperatures varied significantly depending on altitude and location, said Briner.
"We are trying to get a record from our site and quantify the changes in ecology to get a local temperature record to see if it syncs with what the glacier was doing," he said
The research at Jakobshavn is similar to research Briner and fellow scientists recently completed at the Sam Ford Fjord in Canada's Baffin Island. Similar climate reconstruction efforts found that 9,500 years ago, the fjord's kilometer-thick glacier melted in a "geologic instant" during a climate-warming period. Like the glacier in Sam Ford, Jakobshavn is sitting in a similarly deep fjord. Briner said the Baffin Island work revealed the significance of glaciers that lie in very deep water.
"When glaciers that calve retreat into deeper water, that promotes further retreat," he said. "And that amplifies the retreat rate."
The Jakobshavn is one of these glaciers; the calving front is in only 800 meters of water, but people who have done radar surveys discovered that most of Jakobshavn resides in a trough that is 1,400 meters below sea level. Once the Jakobshavn starts to retreat, it likely will continue retreating quickly, much like the glacier in Sam Ford did almost 10,000 years ago.
"With the Sam Ford, the glacier retreat was triggered by a warming climate," said Briner. "This mechanism having to do with water depth was superimposed on the warming and made the response drastic. We reconstructed the relative instant disappearance of the glacier."
That raises questions about the Jakobshavn. Specifically, when did it retreat in the past, what were the retreat rates, and were those associated with climate warming, said Briner. Preliminary conclusions are that the Jakobshavn Isbrae is tightly linked to climate change. The glacier's fastest retreat rates occurred in the middle Holocene, at the height of the warmest temperatures. Then, when the Little Ice Age occurred, there was a rapid response and glacial growth—the glacier advanced about 35 kilometers—followed by significant retreat of 30 kilometers since the modern, 20th century warming began, said Briner.
"This tells us that when there is a climate perturbation, Jakobshavn has a really monstrous response," he said.
Improving Climate Change Models
This information could help improve the accuracy of climate models. Currently the Intergovernmental Panel on Climate Change (IPCC) is hampered by a lack of models that can accurately predict complex ice flow. By incorporating long-term, historic data and reconstructed climates, modelers will have a critical baseline by which to measure what the ice sheet did then and simulate potential actions it may take now, Briner said.
And though this specific research project on the Jakobshavn was only a two-year pilot study on the feasibility, Briner is confident much more research remains.
"Our initial project is limited in scope and we've had great success in doing what we said we were going to," Briner said. "The possibilities for what's next are big."
In fact, one of Jason Briner's next projects is huge: he leads the U Buffalo component of a 10-institute collaborative funded by NSF and led by Darrell Kaufman (U Northern Arizona). The investigators will collect lake sediments all over the Arctic for very detailed climate history information going back about 8000 years. Read our recent conversation with Darrell Kaufman here.