Rising Southern Ocean salinity may be causing the terminal decline of Antarctic sea ice

The rising salinity of the Southern Ocean has emerged as a critical factor contributing to the terminal decline of Antarctic sea ice. Recent satellite data indicate that since 2015, there has been a significant increase in salinity levels, coinciding with an unprecedented retreat of sea ice . This phenomenon is alarming because saltier water tends to draw heat from the deeper ocean layers, thereby inhibiting the natural regrowth processes of sea ice. The resulting feedback loop exacerbates ice loss and poses severe implications for global climate patterns.

This finding caught us off guard – melting ice typically makes the ocean fresher. But new satellite data shows the opposite is happening, and that’s a big problem. Saltier water at the ocean surface behaves differently than fresher seawater by drawing up heat from the deep ocean and making it harder for sea ice to regrow.

The loss of Antarctic sea ice has global consequences. Less sea ice means less habitat for penguins and other ice-dwelling species. More of the heat stored in the ocean is released into the atmosphere when ice melts, increasing the number and intensity of storms and accelerating global warming. This brings heatwaves on land and melts even more of the Antarctic ice sheet, which raises sea levels globally.

The findings have been published today (30 June) in the Proceedings of the National Academy of Sciences.

Dr. Alessandro Silvano from the University of Southampton who led the research said, "Saltier surface water allows deep ocean heat to rise more easily, melting sea ice from below. It's a dangerous feedback loop: Less ice leads to more heat, which leads to even less ice.

"The return of the Maud Rise polynya signals just how unusual the current conditions are. If this salty, low-ice state continues, it could permanently reshape the Southern Ocean—and with it, the planet. The effects are already global: stronger storms, warmer oceans, and shrinking habitats for penguins and other iconic Antarctic wildlife."

As Antarctic sea ice diminishes, numerous ecological and climatic ramifications are anticipated. The reduction in sea ice threatens vital habitats for various species, including penguins and seals, while simultaneously increasing storm intensity and contributing to accelerated global warming . Furthermore, this situation highlights potential limitations within current climate models that may not fully account for the complexities arising from changes in oceanic salinity and temperature dynamics . Addressing these intertwined issues is essential for mitigating future impacts on both marine ecosystems and global climate stability.

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Sara H

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