April 22 () –
A feedback loop may be accelerating the melting of floating portions of the West Antarctic Ice Sheet, raising global sea level.
The discovery, published in Science Advancessheds new light on the mechanisms driving the melting of ice shelves beneath the ocean surface, which until now were unclear.
The West Antarctic ice sheet has been losing mass in recent decades, contributing to global sea level rise. If it were to melt completely, global sea levels would rise by about five metres.
Circumpolar deep water (CDW), a mass of water up to 4°C above local freezing temperatures, is known to flow beneath ice shelves in West Antarctica and melt them. from below. Since much of the West Antarctic ice sheet lies below sea level, is particularly vulnerable to this warm water intrusion and may recede further in the future.
Previous observations and models have revealed that eastward underground currents are transporting this warm water to cavities beneath the ice shelves. Despite its importance, The mechanism driving this undercurrent remains elusive.
Professor Alberto Naveira Garabato, from the University of Southampton, co-author of the paper, says: “Our findings suggest a positive feedback loop: as the ice shelf melts more rapidly, more fresh water is produced, leading to a stronger undercurrent and more heat being transported towards the ice shelves.”
“This cycle could accelerate the melting of ice shelves, which could make the West Antarctic Ice Sheet less stable in the future.”
Researchers from the University of California, Los Angeles, MIT, and the University of Southampton used high-resolution simulations to investigate the dynamics of the undercurrent.
Dr Alessandro Silvano from the University of Southampton, co-author of the study, said: “These simulations reveal that this deep current that transports warm waters towards the ice shelves “It's driven by the same melting of the ice shelf that causes those warm waters.”
Their models suggest that when warm CDW interacts with the ice shelf, it melts it and mixes with the lighter fresh melt water.
This water then rises through the layers of water above it. Doing so spreads and stretches the CDW layer vertically. This stretch creates a spinning motion in the water.
If there is a depression (a type of underwater valley) near the coast, this rotating movement is moved away from the cavity of the ice shelf towards the edge of the shelf by the movement of pressure within the water. This movement helps drive a current along the slope of the seafloor, directing more warm water toward the ice shelf.
The underwater current forms a little further from the ice shelf, so as more ice melts, the current becomes stronger, bringing even more warm water to the ice shelf.
Dr Silvano added: “Scientific models that do not include cavities under ice shelves are probably overlooking this positive feedback loop. Our results suggest it is an important factor that could affect how quickly the ice shelves melt. ice shelves and the stability of the West Antarctic ice sheet over time.”
The Antarctic slope. Groundwater currents and heat transport on land driven by ice shelf melt are published in Science Advances.
