Large Antarctic Ice Shelf Could Disintegrate Faster | Polarjournal
The Pine Island Glacier and the ice shelf in front of it have been under scientific study for years. If the ice shelf disappears, the ice masses behind it will flow unchecked into the Southern Ocean. This is likely to raise sea levels by up to half a meter. Photo: NASA

At first glance, Antarctica’s ice sheets still appear to be very stable. But a closer look (and measurements) reveal huge cracks in the facade. One of the fastest changing regions is the Pine Island ice shelf, which holds back the eponymous glacier like a cork. For a long time, research teams have feared that the ice shelf could slowly disintegrate. Now a study shows that this could happen faster than previously thought.

The combination of increased melting and calving (iceberg formation) are responsible for the decline of the ice shelf over the past decade, that much was already clear to science. But a study by British researchers led by Dr. Alex Bradley of the British Antarctic Survey shows that these two factors together could have a much greater impact and accelerate the collapse of the ice shelf. “The study shows the interplay between calving and melting can promote disintegration of the Pine Island Ice Shelf, which we already thought was vulnerable to collapse.,” Dr. Bradley says of the study’s findings. This was published in the Journal of Geophysical Research: Oceans.

ESA’s video shows how huge cracks had formed on the 2019 shelf front within a short time. These were the result of melting beneath the ice, driven by warmer deep waters rising up beneath the shelf. This accelerates the formation of icebergs and the disintegration of the shelf. Video: ESA

It had been clear for several years that slightly warmer water masses from the north and west were being pushed up from under the Pine Island ice shelf. The only slightly higher temperatures of these water masses are already sufficient to melt the ice from below and thus weaken the ice shelf. The result is break-offs (calving) and the formation of tabular icebergs. What Bradley and his colleagues have now discovered is that these calving events in turn have an impact on melt rates by further thinning the ice shelf.

The underwater area beneath the ice shelf is over 1,000 meters deep (blue colorations). But in the back, a ridge (dashed line) with an opening that acts like a funnel and through which warmer deep water flows backward, abuts the shelf support zone. Here, the melting has different effects and leads to calving further ahead, which in turn weakens the shelf and accelerates the melting. Graph: Bradley et al (2022) J Geophys Res

The reason, according to the research team, is a submarine ridge that separates the back of the ice shelf from the edge underwater, forming a sort of pocket or cavity that extends to the support zone, the part of the shelf that rests on the seafloor. Because the ridge has a depression, this acts as a funnel through which warmer deep water can flow backward and negatively affect the shelf at its base. This leads to massive calving in the front. Model calculations by Bradley and his team now show that these calvings in turn lead to higher melt rates. The researchers suspect a feedback loop that was previously unknown. As a result, the ice shelf is likely to reach the point of collapse much faster than previously thought. The consequence of this would be an unimpeded outflow of the Pine Island Glacier, which holds about 25 percent of the West Antarctic Ice Sheet. If this mass of ice reaches the sea, global sea levels will rise by half a meter, a devastating scenario for low-lying coastal regions.

The walls of the Pine Island ice shelf still rise up to 60 meters above the water. But in many places, openings in the ice wall are showing. In such places, the ice is vulnerable to further calving. Image: Thomas Ronge, AWI

The new results of the study by Dr. Bradley’s research team could also explain why the front of the Pine Island ice shelf had retreated so rapidly over the past 10 years. Since 2009, the ice shelf has lost an area equivalent to Greater London. According to the results of the study, this process is likely to accelerate further. “Our simulations suggest that the melt rate will have an approximately linear dependence on the distance that the ice front retreats in further calving events.,” the authors write in their paper. This means that the more the ice shelf loses surface area due to ice breakup, the faster the melting process from below.

Dr Michael Wenger, PolarJournal

Link to study: Bradley et al (2022) J Geophys Res Oceans 127 The Influence of Pine Island Ice Shelf Calving on Basal Melting;

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