Recent research has uncovered a feedback loop that may be accelerating the melting of the floating portions of the West Antarctic Ice Sheet, thereby pushing up global sea levels. The study, titled “Antarctic Slope Undercurrent and onshore heat transport driven by ice shelf melting” and published in Science Advances, sheds new light on the mechanisms driving the melting of ice shelves beneath the surface of the ocean, which have been unclear until now.
The West Antarctic Ice Sheet has been losing mass in recent decades, contributing to global sea level rise. If it were to melt entirely, global sea levels would rise by around five meters. Circumpolar Deep Water (CDW), a water mass that is above local freezing temperatures, is flowing beneath the ice shelves in West Antarctica and melting them from below. Due to the West Antarctic Ice Sheet lying below sea level, it is particularly vulnerable to warm water intrusion and may further retreat in the future.
Previous observations and models have revealed that eastward undercurrents are transporting warm water to cavities under the ice shelves, but the mechanism driving this undercurrent has remained elusive. Professor Alberto Naveira Garabato, from the University of Southampton, highlighted that the melting of ice shelves leads to the production of more freshwater. This increased freshwater production strengthens the undercurrent, resulting in more heat being transported towards the ice shelves. This feedback loop could potentially speed up the melting of ice shelves, making 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 emphasized that the deep current conveying warm waters toward the ice shelves is driven by the very same ice shelf melting that such warm waters cause. Their models suggest that when warm CDW interacts with the ice shelf, it melts the ice and mixes with the lighter, melted freshwater, leading to a rise through the layers of water above it.
As the water rises, it spreads out and stretches the layer of CDW vertically, creating a swirling motion. If a trough is present near the coast, this swirling motion is carried away from the ice shelf cavity toward the shelf’s edge by the movement of pressure within the water. This movement helps drive a current along the seafloor slope, directing more warm water toward the ice shelf. The underwater current forms farther away from the ice shelf, so as more ice melts, the current becomes stronger, carrying even more warm water toward the ice shelf.
Dr. Silvano pointed out that scientific models that do not account for the cavities under ice shelves may be overlooking this positive feedback loop. This new understanding of the mechanisms driving the melting of ice shelves in West Antarctica provides crucial insights into the potential acceleration of the ice melt and its implications for global sea level rise. As the climate continues to warm, it is essential to consider the feedback loops that may exacerbate the impact of melting ice sheets on sea levels and the environment as a whole.
The feedback loop discovered in this study underscores the urgency of addressing climate change and its consequences. The accelerating melting of the West Antarctic Ice Sheet highlights the interconnectedness of natural systems and the importance of taking decisive action to mitigate the effects of global warming.
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