Greenland –
Daily tides fueled by warmer water ate a hole taller than the Washington Monument to the bottom of one of Greenland’s biggest glaciers in the last several years, hastening the glacier’s retreat, according to new research.
Scientists are concerned that the occurrence is not isolated to just one glacier, calling into doubt prior estimates of melting rates on the world’s vulnerable ice sheets.
The rapid melt seen in this study occurred on Petermann Glacier in Greenland’s extreme northwest. If this happens throughout the rest of Greenland and the even larger Antarctic ice sheet, global ice loss and sea level rise could accelerate up to twice as quickly as previously estimated, according to a study published in the Proceedings of the National Academy of Sciences on Monday.
“It’s bad news,” said research author and glaciologist Eric Rignot of the University of California, Irvine. “We recognize that the present predictions are overly conservative. We know they will have a difficult time matching the current melt record.
He stated that the newly discovered effect of tidal activity “could potentially double the projections” of global melt.
The study focuses on the critical grounding line area of glaciers on ice sheets. This is the point at which glaciers transition from being on land to floating on the sea. Previous research indicates that it is also a hotspot for rapid ice loss.
The grounding line zone at rural Petermann, where few people have gone and no base camps, is more than six-tenths of a mile (1 kilometer) wide and might be as much as 3.7 miles (6 kilometers) wide, according to the study.
Scientists used to believe that daily tides had little impact on the melt. Rignot claimed the day before leaving for an expedition to Petermann that the snow dumped on top of the glacier compensated for the tides pushing further in.
The rapid melt seen in this study occurred on Petermann Glacier in Greenland’s extreme northwest.
However, in Greenland with a warmer ocean due to climate change, tides have become “a very powerful mechanism,” according to Rignot.
“The seawater goes much farther beneath the grounded ice (than previously thought), kilometers, not hundreds of meters,” Rignot added. “And that water is hot enough to melt the glaciers quickly.” And it’s also the glacier’s most vulnerable area.”
Rignot’s team discovered a 669-foot-tall (204-meter) hollow near the grounding line using satellite altitude readings, where the melt rate had been 50% higher in the previous three years than from 2016 to 2019. Previous models predicted no melting there.
Rignot hypothesized that the melting in Petermann has intensified in recent years, later than in the rest of Greenland, since it is so far north that the water melting it from beneath is from the North Atlantic, and it takes longer for the warmer water to arrive there.
Rignot is investigating Petermann this month to obtain further ground-based data utilizing ultrasonography. He last arrived in 2006, a decade before satellites revealed the alterations. When Rignot visited Petermann before the glacier’s retreat increased, he noted motions that made it appear alive.
“When you are standing on that shelf or sleeping on that shelf, you hear noises all the time, loud noises from deep inside cracks forming,” Rignot explained. “That’s when the idea of a glacier being alive starts to sink in.”
Jason Box of the Geological Survey of Denmark and Greenland, who was not involved in the study, praised Rignot’s technique and stated the work made sense, demonstrating “that ocean heat delivery to tidewater glacier grounding lines represents a potentially destabilizing effect.”
Box calculates 434 billion metric tonnes of ice on Petermann is already committed to melting using a new technique called “zombie ice,” which employs a different technique to quantify how much ice is no longer being fed by glaciers and is bound to melt.
According to Pennsylvania State University glaciologist Richard Alley, who was not involved in the Rignot study, “The study provides strong evidence that models need to include these tidal effects deep inland, and if they don’t, they are underestimating future sea level rise.”
SOURCE – (AP)
