The study shows how upside-down ‘rivers’ of warm ocean water are eroding the edges of floating Antarctic ice shelves from below. This contributes to the conditions that lead to ice-shelf breakup and sea-level rise.
As these vast ice shelves float out into the ocean they can warp and break along the edges, making them particularly vulnerable to erosion from channels of warm water from below.
“Warm water circulation is attacking the undersides of these ice shelves at their most vulnerable points,” said lead researcher Dr Karen Alley, who earned her PhD at the University of Colorado Boulder. “These effects matter. But exactly how much, we don’t yet know. We need to.”
Cold salt water is not as buoyant as warm, fresh water, therefore these plumes move up into the ice from beneath, forming an ‘upside-down river.’ These rivers can grow miles wide and tens of miles long, eroding and weakening the margins of the ice shelf, making it more unstable and vulnerable to collapse.
“Now we’re seeing a new process, where warm water cuts into the shelf from below,” said co-author Ted Scambos, a scientist of both CIRES and the International Thwaites Glacier Collaboration. “Like scoring a plate of glass, the trough renders the shelf weak, and in a few decades, it’s gone, freeing the ice sheet to ride out faster into the ocean.”
These floating shelves can be hemmed in by canyon-like walls and bumps in the ocean floor. When restrained by bedrock obstructions such as these, ice shelves slow down the flow of ice from the interior of the continent towards the ocean. Dr Alley’s team used satellite imagery to show that, at the ends of shear margins on many of Antarctica’s fastest-changing glaciers, warm water rises to the surface, melting sea ice and forming areas of open water called “polynyas”.
The study states that, as ice shelves float out into the ocean and break apart, land-based ice melt flows more quickly into the ocean, which increases the rates of sea-level rise. Approximately 75% of the Antarctic continent is surrounded by these extensions of the ice sheet, but it’s relatively new information that these warm plumes appearing beneath ice-shelf margins is not that uncommon.
The research team has previously published work focused on the damaging effects of meltwater on the surface of the ice shelves. Scambos, Alley and a team of researchers are heading back to Antarctica this year to continue research on the continent’s ice dynamics.
To read ‘Troughs developed in ice-stream shear margins precondition ice shelves for ocean-driven breakup’, click here.
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