Our world is an intricate network, influenced by the intimate connection of all life on Earth – from building blocks unseen to the naked eye to the land-shaking tremor of an earthquake. Now add upside-down "rivers" of warm ocean water to this exquisite complexity.
Warm ocean water is cutting into floating Antarctic ice shelves from below and eroding their fractured edges, “attacking” their most vulnerable points, say authors of a new study published in Science Advances.
"Our findings show that there are more basal channels than we thought forming beneath the edges of fast-flowing ice shelves. Those edges, called 'shear margins,' are the weakest parts of the ice shelves," said Karen Alley of The College of Wooster to IFLScience.
Warm, fresh water is more buoyant than cold, salty water so it rises to high spots in floating ice, forming a river underneath that sometimes extends for kilometers. The warm water flows to the thin spots along the ice shelf base, further eroding it and making the ice shelves vulnerable to collapse.
To observe this happening, the team turned to hundreds of satellite images and studied the ice flow in areas where basal channels are found. They then took note of the shape and size of the basal channels and shear margins using the Reference Elevation Model of Antarctica as a map for surface elevations in the region.
"Ice shelves are really vulnerable parts of the ice sheet, because climate change hits them from above and below,” said NSIDC scientist and study co-author Ted Scambos in 2016. “They are really important in braking the ice flow to the ocean."
Ice shelves are sheets of ice attached to the land. When an ice sheet crumbles, it becomes swept into the ocean, and contributes to sea level rise. Most of Earth’s ice shelves hug Antartica’s coast, with three-quarters of the continent surrounded by ice shelves. This ice can persist for thousands of years but these "upside-down rivers" threaten the stability of the frozen structures.
Antarctica’s ice shelves are losing mass at an accelerating rate. By understanding the systems of melting and collapse, it could help scientists produce better models and forecasts.
"In the big picture, this means that our models that predict future ice flow under warming conditions are probably underestimating the amount and rapidity of sea-level rise we're likely to get in a warming world, because they don't include this weakening mechanism," said Alley. "We haven't yet figured out whether this is a big effect or a little effect, but we know these basal channels impact some of the most important ice shelves in Antarctica, so it's an effect we need to investigate in more detail."