CCI glaciologist: Meltwater can influence ocean circulation, climate

A University of Maine glaciologist discovered icebergs likely contribute more meltwater to Greenland’s fjords than glaciers do, which can slow the melting rate of glaciers and potentially influence ocean circulation and climate.

Greenland, the world’s largest island, is almost entirely covered by a permanent ice sheet that has been shrinking due to warming temperatures in the region.

UMaine research assistant professor Ellyn Enderlin found more than half of all meltwater entering Greenland’s glacial fjords — narrow inlets where glaciers meet the sea — comes from dense packs of icebergs that break free of glaciers.

Enderlin, lead author of the study published in the American Geophysical Union’s journal Geophysical Research Letters, says ocean circulation patterns could be disrupted as the less dense freshwater meets denser saltwater in the fjords.

“We should now be able to better measure the freshwater fluxes that are coming off of Greenland. That could be really important when we’re thinking about how Greenland melts, how that influences ocean circulation and climate,” says Enderlin. “The results of this study should lead to more accurate modeling of ocean circulation change and a more complete understanding of interactions between the atmosphere, glaciers and oceans.”

Ocean circulation is a major driver of heat movement from the tropics to the poles, and disruptions to it could cause chaotic and unpredictable changes to weather and climate, says Enderlin, who is affiliated with the UMaine Climate Change Institute and the School of Earth and Climate Sciences.

“To the average person, glacier and iceberg melting may seem like something that’s not terribly important because most people have never even seen a glacier and they have only been told that glacier melting is causing sea level to rise by some tiny amount per year,” she says.

“However, it’s important that people realize that not only the amount of meltwater that enters the ocean is important, but also where that water enters the ocean. If we look at records of climate going back thousands of years, we see there are times when glaciers in Greenland and Canada pumped out tremendous volumes of ice into the North Atlantic.

“These armadas of icebergs caused huge changes in the weather patterns in North America and Europe. To understand whether the modern increase in glacier and iceberg melting will detrimentally influence our climate, we need to know where the meltwater enters the ocean and how that influences ocean circulation.”

Jason Amundson, a University of Alaska Southeast geophysicist not involved with the study, says the cold freshwater from melting icebergs can create a buffer, insulating glaciers from warmer saltwater and slowing their melting rate. And he says Enderlin’s research may help scientists better understand what happens at the ice-ocean interface where glaciers meet the water.

“The reason that’s interesting is that there’s been quite a few studies in the past 20 years that have shown that the stability of … glaciers depends on what happens at the ice-ocean interface,” he says.

The Greenland Ice Sheet annually releases more than 240 cubic miles (1,000 cubic kilometers) of meltwater. Previous research found half of the meltwater came from icebergs and half came from glaciers, but the amount that icebergs melted in fjords before they reached the ocean had been a mystery.

Until now.

Enderlin and her colleagues used satellite images of two Greenland fjords to calculate the total volume of icebergs within them. They tracked the icebergs over days, weeks and months to calculate how much volume they lost through melting before they reached the ocean. The team found between 10 to 50 percent of iceberg melting occurs in the fjords, rather than in the open ocean as assumed by other scientific studies.

Enderlin determined the dense packs of icebergs melted at a peak rate of about 260,000 gallons per second, (1,000 cubic meters per second), the equivalent of filling an Olympic-sized swimming pool every 2.5 seconds.

From October through April, little to no melting occurs on the surface of the glaciers — only the part of the glacier that is underwater melts. During these months, submarine melting of the glacier and icebergs probably occurs at similar rates. Although the icebergs are tiny in size compared to the glaciers, their melt is the dominant source of fresh water to fjords in winter, and accounts for up to half of the fresh water in fjords in summer, because their large surface area allows them to melt more quickly, says Enderlin.

“If you took an ice cube and put it in your drink, one solid ice cube would melt pretty slowly, but if you took it out, hit it with a hammer and put it back in, it would melt a lot faster,” she says.

The team also used satellite images to estimate the iceberg distribution in the two fjords, which they used to calculate the icebergs’ total underwater surface area.

“What I see now is that iceberg melting is huge, and so if you don’t take that into account you’re going to come up with some crazy high estimates for glacier melting that might not be representative,” says Enderlin, who grew up adjacent to the Appalachian Trail in Pennsylvania.

“I spent a lot of time playing outside as a kid. I was always really interested in nature and weather, and I have a lot of great memories of playing in the snow with my brother and sister,” she says. “As I got older I realized that I would really like to study the Earth and the natural environment for my career and I decided to pursue my bachelor’s degree in environmental science at Lehigh University.

Before attending college, Enderlin hadn’t ventured outside the U.S. But the summer after her first year at Lehigh, she was invited to go to Peru with her undergraduate adviser to map glacial landforms.

“It was during that trip when I realized that I really wanted to focus on understanding the links between climate and glacier change,” she says.

Enderlin calls Greenland a spectacular place and says it’s similar to Maine in that some people rely on the environment for their livelihood.

“The climate is much more harsh than in Maine, however, with temperatures only reaching the 50s in the summer and well below minus 30 in the winter in many places,” she says.

Because the ground is often snow-covered from September until May, vegetation primarily consists of bushes and hearty low-lying plants. And Enderlin says animals — musk-oxen, reindeer, Arctic hares and polar bears — are hearty, too.

“Overall it’s a really peaceful place. When it’s calm — and it can be very windy for much of the year — you can hear the noise of blocks of ice falling from the glaciers and icebergs into the fjords,” she says.

Enderlin intends to expand her studies on iceberg meltwater flux to other areas, including Antarctica. It’s work she started with Gordon Hamilton, co-author of the study and former UMaine glaciologist who died in October while conducting research in Antarctica.

“I would say that really this was sort of our joint brainchild,” Enderlin says. “I bounced lots of ideas off of him…He was really instrumental to [the research] and it was sad that he couldn’t finally see it get published.”

Enderlin met Hamilton when she was a Ph.D. student in Earth Sciences at The Ohio State University and attended a workshop on a research boat in Svalbard, Norway.

“While at the workshop, I had lots of opportunities to informally chat with Gordon Hamilton about the work I had been doing for my Ph.D. and his research here at UMaine,” she says.

“Gordon was such a fun-loving person and did such fascinating work that I mustered up the courage to ask him if he would like me to come to UMaine to work as his postdoc after I finished my degree. Gordon was enthusiastic, as always, and secured funding for me to begin work with him the following summer.”

Contact: Beth Staples, 207.581.3777