A swift moving glacier in Antarctica may further contribute to sea-level rise in the coming years as the ice shelf responsible for holding it back continues to crumble.
(CN) — The massive Pine Island Glacier is responsible for most of the sea level rise attributed to Antarctica — and it’s gaining speed at an alarming rate as the floating ice shelf that holds it back continues to fracture and float away.
Around 25% of Antarctica’s total ice loss can be traced to the Pine Island Glacier, one of the continent’s fastest moving hunks of ice. As the grounding line of the ice shelf that retains it melted away from underneath in recent decades due to ever-warming waters, the glacier itself has been left unchallenged in its march to the sea.
The ice shelf retaining the Pine Island Glacier lost one-fifth of its total area between 2017 and 2020, which mostly occurred in three large breaks. Researchers from the University of Washington and British Antarctic Survey documented the glacier’s progression in a new study published Friday in the journal Science Advances.
“In this study we used satellite observations to show that the ice shelf has lost large icebergs at a rate and in places that go well beyond what had been observed at any other time over the past 50 years,” said study co-author Pierre Dutrieux, an ocean and ice scientist with British Antarctic Survey, in an email. “When we remove these pieces of ice shelf in our numerical model of the ice flow, the model reproduces the observed acceleration extremely well.
“We also show from moored observations that ocean temperatures have not dramatically increased over the last few years, so increased melt-induced thinning is not expected to be an important driver of change during the 2017-2020 time period. All of these lines of evidence indicate that the loss of buttressing imparted by the sudden loss of ice is responsible for the recent acceleration.”
Dutrieux said his team expected the acceleration would resume as melt induced thinning continued and the glacier grounding line proceeded to retreat, but the rapid pace of the acceleration and the process driving it were surprising to see.
The glacier’s speed remained relatively stable from 2009 through 2017, according to data from the European Space Agency’s Copernicus Sentinel 1A/B satellites, before speeding up more than 12% since 2017. During that same period, the ice shelf responsible for retaining the glacier retreated 11 miles, reducing support for the glacier it held back, much like demolishing the retaining wall of a house. According to the study, if the ice shelf continues to retreat at this pace, it could further destabilize the glacier sooner than expected.
“For decades, the Pine Island ice shelf that helped to hold back one of the fastest-moving glaciers in Antarctica has gradually thinned, melted from beneath by relatively warm ocean waters,” Dutrieux explained. “After accelerating from ~2.3km/yr [1.4mi/yr] in 1973 to 4km/yr [2.4mi/yr], the velocity at the terminus of the glacier had remained relatively stable since 2009. But following a series of seasonal and anomalous breakups starting in Boreal Summer 2017, its speed increased to close to 4.6 km/year [2.8mi/yr] or about 12.6m/day [41.3ft/day] by 2020, a 12% increase in velocity in only 3 years.”
The authors attributed that speedup to the loss of 20% of the retaining ice shelf between 2017 and 2020. According to their simulations, grounding-line retreat has recently stabilized but due to the numerous factors involved that trend may or may not continue. Other factors such as the slope of the land below the glacier’s receding edge will also have a role to play, but the loss of ice shelf mass in recent years has shifted the timeline for when it may disappear entirely, which could now occur in as little as a decade — or not for decades to come.
Pine Island Glacier is enormous, holding around 180 trillion tons of ice — enough to raise global sea levels 1.6 feet on its own. Along with the neighboring Thwaites Glacier, the pair were once called the “weak underbelly of the West Antarctic Ice Sheet” for good reason. As it stands, Pine Island Glacier is responsible for two-thirds of an inch in global sea level rise per century, a not-insignificant amount for a single chunk of ice, and a number that could continue to rise unless interventions are put in place.
“It may be a long shot, but it’s entirely possible that the rest of the shelf could break up in the next decade or two now that the process as started,” Dutrieux said. “On the other hand, the shelf could stabilize, and the glacier would continue to lose mass at its present rate, with further speedup at some point over the next few decades. Understanding whether the shelf will break up again involves fracture mechanics, which, like earthquakes, are notoriously difficult to predict.”