This study from the University of East Anglia (UEA) is the result of a somewhat improbable stroke of luck. In December 2022, the Seaglider Marlin was launched into Antarctica’s Ross Sea to collect data on ocean currents. But things didn’t go as planned: instead of rising to open water, Marlin was carried south by a current and found himself stuck under the ice shelf for four days. This unforeseen incident allowed its sensors to dive up to 200 meters deep and measure water temperature, including under the ice.
Surface waters that appear under the ice
The results are surprising. Indeed, scientists discovered a 50-meter layer of “relatively” warm water, with temperatures oscillating between -1.9°C and -1.7°C. Yes, these temperatures remain largely negative, but in the polar ocean, they are enough to eat away at the ice.
Peter Sheehan, who led the study, points out that a small rise in temperature – even four thousandths of a degree per year – can lead to up to 80 cm of additional ice melt each year. For nearly 45 years, data has shown that this “infiltration” of heat has gradually increased in intensity, probably because of global warming.
Another interesting point of this study is the role of Ekman currents, these surface water flows generated by the wind. They transport heat from surface waters directly under the ice shelf, without passing through the deeper layers. With this mechanism, the heat from the ocean arrives more quickly and more directly under the ice, accentuating its melting. Karen Heywood, co-author of the study, explains that this phenomenon is increasing: “ With global warming, the heat carried by these currents and the melting it causes can be expected to continue to increase. »
This phenomenon clearly shows that even minimal changes on the surface can have significant repercussions under the ice. Indeed, the more the ocean warms, the more these Ekman currents, heat “elevators”, play their role under the ice.
Although the melting of floating ice itself does not raise sea levels, it still plays a crucial role. Ice shelves, like that of Ross, act as natural “brakes”, slowing down the flow of terrestrial glaciers towards the ocean. Their melting and weakening could, however, precipitate this flow, accelerating the rise in water levels worldwide.
This study, which draws on decades of data, provides unprecedented insight into the situation beneath the ice shelf. Previously, research on these “intrusive” waters relied mainly on data collected on the surface by ships or seals equipped with sensors. Today, this new information highlights the importance of integrating these processes into climate models to better predict the future of Antarctica in the face of global warming.
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