The cracks lead to further weakening of the ice shelves and could thus be a major contributor to the feared instability of the Antarctic ice sheet.
Of Pine Island Glaciers Antarctica has undergone rapid transformation in recent years. Large cracks in the glacier tongue have repeatedly resulted in the release of large icebergs in recent decades. This has changed the end of the glacier resting on the ice forever. And also located in Antarctica Thwaites Glacier has undergone a tremendous transformation in recent decades; the glacier – which can single-handedly cause sea level rise by tens of centimeters – is rapidly thinning.
It has now been established that the rapid changes can be traced back to global warming. But it is unclear exactly which processes – and to what extent – lead to the changes that are currently taking place at a rapid pace before our eyes. Reason enough for researchers from, among others, TU Delft to take a closer look at one of the processes that seem to play a role in the transformation undergoing the mighty Thwaites and Pine Island glaciers. This concerns the cracks that we increasingly see in the so-called ‘shear zone’ of both glaciers.
The research shows that the crack formation initiates a feedback process, which further promotes crack formation and weakening of the shear zones. And that is very worrying. “The shear zones are the zones that separate the fast-flowing ice from the slow-flowing ice,” explains researcher Stef Lhermitte Scientias.nl from. “As a result, those shear zones slow down the fast ice a bit (like a slow car in a traffic jam). However, if the shear zones fall apart (as we can see now), that brake is partially removed. ” The result is that the fast ice flows even faster and the glaciers lose mass more quickly.
But not only that; the cracks in themselves also lead to more cracks and thus a further weakening of the shear zones. To understand how that feedback process starts, we must first look at how the cracks develop. It all starts with the weakening of the glacier tongue or ice shelf resting on the water. “This is mainly weakened by more melt at the bottom, due to warm ocean water.” The ice shelf becomes thinner and is less able to counterbalance the ice behind it. “This melting speeds up the fast ice, but not the slow ice. This creates greater forces in the shear zones which, in combination with thinner ice, result in cracks and tears. Once the cracks are there, the shear zone is structurally weakened and loses some of the inhibitory effect. This accelerates the fast ice further and creates even more cracks. These cracks weaken the ice shelves, because they make the ice shelves less solid and make them more susceptible to erosion (breaking off large chunks of ice, ed.). ” And with that the circle is complete again: the weakened ice shelf that caused the cracks to form, is further weakened because the cracks lead to more crack formation and thus weakening.
The glaciers are so clearly in a vicious circle, the consequences of which are already visible. For example, the ice shelf of the Pine Island Glacier has shrunk by thirty percent (!) Due to cracks and erosion in the past six years.
The cracks are a fact and we see with our own eyes how these cracks lead to further weakening of the ice shelves and the faster flow of the glaciers. It begs the question of whether anything can be done at this stage to turn the tide. “That is very difficult and perhaps the most worrying. To restore those shear zones, you have to replace the ice shelves, as it were, with the supply of thick and slower ice, which seems unlikely with warmer ocean water and faster glacier tongues. It still remains a great uncertainty how much and how quickly this glacier will melt in the future. The cracks in the shear zone can play an important role in this, but how much and how fast still remains a great uncertainty in the projections. ”
The Antarctic Ice Sheet – and in particular the West Antarctic part, which also includes the Pine Island and Thwaites Glacier – has been a concern for researchers. The ice sheet – which lies largely on a bed below sea level and is therefore largely in contact with increasingly warmer ocean water – has been losing mass at an accelerated rate in recent years, thus contributing to sea-level rise. It is feared that this contribution will only increase in the coming years because the earth is warming up further and feedback processes, such as crack formation, which in turn will lead to mass loss, have been initiated. The greatest fear is that the ice cap will become unstable and the melting of large parts of the ice mass can no longer be prevented. That could lead to major problems worldwide; West Antarctica alone is home to enough ice to raise sea levels by a few meters. No wonder researchers are eager to find out how this rapidly changing portion of the ice sheet will respond to future warming. To get a picture of this, it is very important that the processes that cause the ice sheet to lose mass are mapped. “It is important to include all processes that play a role so that we can reduce that uncertainty on the projections, because Antarctica is currently the largest uncertain factor for sea level rise (globally and very specific to the Netherlands),” says Lhermitte.
The research by Lhermitte and colleagues shows that cracking and the subsequent feedback process (of more cracks and weakening) has a significant influence on the stability of the ice sheet and therefore also sea level rise. The researchers therefore argue in favor of giving this process a place in the climate models that are now used to obtain a picture of how the ice sheet will change under the influence of further warming.
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