Ice oozes across the surface of Antarctica and breaks off into the southern oceans constantly — but not normally in chunks the size of Delaware.
So after a massive iceberg separated from the Antarctic peninsula this week, the burning question among glacial scientists is: Was it influenced by warming seas or air, or was its separation just an abnormally dramatic stage in the natural evolution of Earth's southern ice cap?
Though the divorce was captured by multiple satellites, researchers have little data on what might have caused it or the long list of potential factors behind it, including not just temperatures but the speed and directions of winds, currents and glacial flows.
Pools of water and other signs of thinning have preceded major losses in other parts of the same ice shelf since the 1990s, but not this time.
Scientists said the iceberg's size demands further study as they look to forecast whether it suggests a coming acceleration in sea level rise.
"It's a pretty amazing chunk of the coastline of Antarctica," said Christopher Shuman, a research scientist with the University of Maryland, Baltimore County who is based at the NASA Goddard Space Flight Center in Greenbelt.
The 1-trillion-ton iceberg, which contains twice as much water as Lake Erie, was already floating, so it has no impact on ocean height. But researchers say what happens next could have an influence on vulnerable waterfront communities such as Baltimore and Annapolis.
"We'll be watching to see if there are signs that other rifts are getting activated or if the flow field from glaciers begin to accelerate," Shuman said. "That would begin to tell us that, 'Hey, things are probably going to change more in the future.' "
The iceberg made up 12 percent of an ice shelf known as Larsen C. The formation, itself about the size of West Virginia, extends off the eastern side of a peninsula that stretches toward Chile and Argentina.
It is the product of glacial flows that originate in the middle of the continent, oozing outward like syrup from the middle of a stack of pancakes, and is naturally prone to some fracturing because it is exposed to winds above and currents below.
Project MIDAS, a team of researchers from the United Kingdom investigating the effects climate change on Larsen C, began documenting a fissure in the shelf in 2011. They said the 2,200-square-mile floe likely to be named A68 became one of the largest icebergs ever recorded some time between Monday and Wednesday.
They detected the final breakthrough using NASA's Aqua satellite and confirmed it with another NASA spacecraft, Suomi. Both are managed from the Goddard center. They also used European Space Agency satellites to track the massive crack.
Researchers said they did not have any evidence climate change influenced the breakup, but they are alarmed that the Larsen C shelf is "in a very vulnerable position."
"This is the farthest back that the ice front has been in recorded history," said Martin O'Leary, a glaciologist at Swansea University in Wales on the MIDAS team. "We're going to be watching very carefully for signs that the rest of the shelf is becoming unstable."
Other scientists are similarly interested in watching what happens next, though they said it could take years to reach conclusions on what is shaping the ice shelf.
Kelly Brunt, a glaciologist with the Earth System Science Interdisciplinary Center at the University of Maryland who is also based at Goddard, plans to use data on glaciers' altitude to watch whether the flow toward the Larsen C shelf increases. That would indicate that the iceberg was holding back a flow of ice that could now pour into the ocean, potentially accelerating ice loss and sea level rise.
But she said it's also possible the iceberg broke off as part of a normal process known as calving, in which ice shelves splinter and then recover. That would suggest less of an influence from climate change, and could stand in contrast to the collapses of the nearby Larsen A and B ice shelves in 1995 and 2002.
"Larsen B, we can pin a little more directly to changes globally contributing to the breakdown," Brunt said. "It is hard to do that with Larsen C."
The MIDAS Project scientists suggested "a risk that Larsen C may eventually follow the example of its neighbour, Larsen B." They likened this week's event to one that preceded the collapse of that ice field.
Scientists have little confidence in predicting the influence the iceberg's separation will have on ice cover going forward.
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Anand Gnanadesikan, an earth and planetary sciences professor at the Johns Hopkins University, said it's equally possible the ice loss could lead to an increase or a decrease in sea ice, whether by allowing warmer waters to reach the surface and freeze or by exposing water to more heat from the sun.
"It isn't actually something we seem to understand very well from a fundamental physics point of view," he said. "When something big like this happens, it's just a reminder of that fact."
Alek Petty, another Goddard-based scientist affiliated with the University of Maryland earth science center, said "there's nothing to suggest this is climate change-driven." He speculated that the more suspicious losses of Antarctic ice in recent years "might be adding to the confusion."
"Similar size icebergs have happened before," he said — a larger piece of Larsen C broke away in 1986. "We expect similar sized icebergs to happen in the future."
Brunt said fascination with the iceberg is natural: "Calving events are sort of the earthquakes of our science.