“People always thought the circulation [in Greenland’s fjords] would be simple: warm waters coming into the fjords at depth, melting the glaciers. Then the mixture of warm water and meltwater rises because it is lighter, and comes out at the top. Nice and neat,” says Woods Hole Oceanographic Institution physical oceanographer Fiamma Straneo, who has now led two survey trips to Sermilik Fjord at the base of Helheim Glacier, Greenland.
“We knew that these warm waters were reaching the fjords, but we did not know if they were reaching the glaciers or how the melting was occurring,” she said.
Straneo, along with colleague Kjetil Våge of University of Bergen, Norway,used a tiny boat and a helicopter to launch probes closer to Helheim Glacier than ever before, approximately 2.5 miles away from the glacier’s edge, in March of 2010. Together with data gathered in August of 09, details began to emerge that the interaction between glacier ice, freshwater runoff and warm, salty ocean waters was much more complicated than previously imagined.
While the fjords contain cold, fresh Arctic water on top, and warm, salty waters transported from the Gulf Stream at the bottom, the melted waters do not behave as previously assumed. They do rise, a little, but not all the way to the top because, according to Straneo, “it’s too dense. It actually comes out at the interface where the Arctic water and warm water meet.”
Straneo adds that this distinction is important, because it prevents the heat contained in the deeper waters that arrived by way of the Atlantic Ocean’s Gulf Stream from melting the upper third of the glacier.
In addition, the researchers found that the vigorous currents within the fjord driven by winds and tides also play a substantial role in the melting and flow speed of the glacier. “The currents in the fjord are like waves in a bath tub,” Straneo says. “This oscillation and mixing contribute to heat transport to the glaciers.”
“One surprise we found was that the warm waters in the fjord are actually 1 degree Celsius warmer in winter, which by Greenland standards is a lot,” Straneo said. “It raises the possibility that winter melt rates might be larger than those in the summer.
“Current climate models do not take these factors into account,” Straneo added. “We’re just beginning to understand all of the pieces. We need to know more about how the ocean changes at the glaciers edge. It’s critical to improving predictions of future ice sheet variability and sea level rise.”
Greenland’s ice sheet has lost mass at an accelerated rate over the last decade, dumping more ice and fresh water into the ocean. Between 2001 and 2005, Helheim Glacier, a large glacier on Greenland’s southeast coast, retreated 5 miles (8 kilometers) and its flow speed nearly doubled.