When a Greenland glacier melted in the unusually hot summer of 2012, it pushed so much water through that it warped the Earth's crust and caused a massive wave of ice and water to push its way seaward.
That wave is a newly identified phenomenon for climate researchers and represents a troubling new trend in the understanding of how current sea-level rise estimates may be underestimated, according to a new study published yesterday in Geophysical Research Letters. The wave caused the amount of ice typically lost from the Rink Glacier to increase by more than 50 percent, said Eric Ivins, a scientist at NASA's Jet Propulsion Laboratory and a co-author of the study.
“We didn't know we would discover that phenomenon, and it proves the point that when the ice goes down to the bottom of the ice sheet, it doesn't just refreeze,” he said. “It does something to the whole system to make it move faster.”
The Rink Glacier is one of the primary glaciers on Greenland dumping ice into the ocean. It drained 11 billion tons of ice into the ocean in the early 2000s. That's about the weight of 30,000 Empire State Buildings. But in the warm summers of 2012, because of the wave, it drained an additional 6.7 billion tons of ice and water.
That increased volume of ice and water was troubling to scientists because it could mean global warming could push more intense ice loss in the future. The melting of land-based glaciers in Greenland is a primary cause of sea-level rise.
“The real concern here is to understand how this melt event, if this kept repeating more and more into the future, how will they impact an ice sheet which is already primed to react?” said Eric Larour, a co-author of the paper and a researcher at JPL.
The Arctic is already a profoundly different place than it was a decade or two ago because of the warming, according to Walt Meier, a research scientist at NASA's Goddard Space Flight Center who was not involved in the study. In a recent report card on the region, researchers from the National Oceanic and Atmospheric Administration determined that 2016 was the warmest year on record for the region and that record-low sea ice levels had been measured.
Because the summers of 2010 and 2012 were so warm in Greenland, more than 95 percent of the surface ice was melting. There was also a buildup of snow and ice in the basin at the center of Greenland, behind the Rink Glacier. Greenland loses an annual average of more than 250 billion tons of ice a year, but 2012 saw an increase.
Researchers found that the wave moved at a speed of roughly 2.5 miles per month in June, the beginning of the melting season. By September, however, the wave speed had increased to 7.5 miles a month. Typically, the glacier itself moves at the speed of about 1 or 2 miles a year, researchers found.
The mass of ice in the wave moved quickly because the melted water lubricated the base of the glacier and softened the areas along the side where it was attached to rocks or other glaciers, researchers found. It moved 15 miles in about four months.
The relatively quickly moving wave troubles scientists because it shows warming causing a major increase in ice loss from land-based glaciers, the kind that contribute to sea-level rise. They are concerned that more warming in the future, as scientists predict, could lead to an accelerated ice loss not previously considered in sea-level-rise conditions.
“You're essentially losing the grounded ice, meaning the ice that is on land that is dumping into the ocean, so it does have implications for sea-level rise,” said NASA scientist Surendra Adhikari, the study's lead author.
Adhikari said scientists are sure that the wave was triggered by the surface melting of snow and ice, but cautioned that they don't fully understand the process that caused it to generate. While the phenomenon of solitary waves have been observed in rivers, he said this was the first time researchers had found it in a glacier. It would not have been have been visible to the naked eye but was measured by a series of GPS sensors.
He said they also don't yet understand the future implications of the wave.
“What we don't know at this point in time is how much effect this kind of seasonal wave of substantial loss has on long-term ice loss from the Greenland melting glaciers,” he said.