Antarctica’s ice shelves support the glaciers and slow the flow of ice into the sea. But climate change is endangering these protective shields: between 1997 and 2021, almost 44 percent of the ice shelves have shrunk, a study shows. The losses mainly affect the western side of Antarctica. On the eastern side, the volume of most ice shelves remained the same or increased – but not enough to compensate for the losses. Overall, the study records a net loss of 7.5 trillion tons of ice shelf. The impacts may affect not only the Antarctic ice system, but also global ocean currents.
Ice shelves up to a kilometer thick surround the Antarctic continent. They float on water, but are firmly connected to the mainland and are fed by glaciers. In doing so, they slow down the flow of ice into the ocean and thus stabilize the glaciers. While it has long been known that the Greenland ice sheet in the Arctic is melting as a result of man-made climate change, a differentiated picture emerges in the Antarctic. While the ice shelf is shrinking in some regions, in other regions it is increasing or at least increasing in area as more meltwater flows from the glaciers towards the sea.
A team led by Benjamin Davison from the University of Leeds has now examined the development of the Antarctic ice shelf over the 25 years from 1997 to 2021. For their study, the researchers analyzed more than 100,000 satellite images. They relied primarily on images from the Cryosat-2 and Sentinel-1 satellites of the European Space Agency (ESA) and the EU Earth observation program Copernicus. These work with radar instruments so that they can monitor the ice sheets even under cloudy skies and in the darkness of polar nights. Using radar height measurement, it is also possible to calculate the change in volume of the ice.
More losses than gains
The results show that Antarctica’s ice shelves are also massively affected by climate change: “Of the 162 ice shelves, 71 lost mass, 29 gained mass and 62 did not change their mass significantly,” reports the team. “48 ice shelves lost more than 30 percent of their original mass.” According to the data, almost 67 trillion tons of ice melted over the 25 years studied, most of which was due to the ice sheets becoming thinner from below. In contrast, calving, i.e. the breaking off of icebergs from the edges of the ice shelf, played a smaller role.
The western side of Antarctica was particularly affected by the losses. On the eastern side, however, the volume of most ice shelves remained the same or increased. Around 59 trillion tonnes of ice shelf have been added there since 1997. “This has to do with the sea temperature and the ocean currents around Antarctica,” explains Davison. “The western half of Antarctica is exposed to warm water that can rapidly erode the ice shelf from below, while much of East Antarctica is currently protected from warm water nearby by a band of cold water on the coast.” Overall, that adds up There was a net loss from the Antarctic ice shelves of around 7.5 trillion tonnes of ice, which reached the ocean as meltwater.
Regional and global impacts
Because the meltwater is fresh water, increased thawing could affect ocean circulation. This is created, among other things, by the fact that salt water has a higher density and therefore sinks downwards from the surface. This drives ocean currents that transport important nutrients and heat across the oceans. When the surface salt water is diluted by fresh water, it becomes lighter and sinks more slowly. This weakens the circulation. Studies have already found evidence that this process is already underway.
The impact on the Antarctic ice system is also serious. As the ice shelves recede and become thinner, they are less able to stabilize the glaciers. Ice loss from glaciers is increasing and can contribute significantly to sea level rise. “We expected most ice shelves to undergo a rapid but short-term cycle of shrinkage and then slowly grow again,” says Davison. “Instead, we see that almost half of them are shrinking, with no signs of recovery.” His colleague Anna Hogg adds: “This is further evidence that Antarctica is changing as the climate warms. The study provides a baseline from which we can see further changes that could occur as the climate warms.”
Source: Benjamin Davison (University of Leeds, UK) et al., Science Advances, doi: 10.1126/sciadv.adi0186