Scientists are analysing the sounds of escaping air bubbles from melting glaciers to see if they can provide clues to the speed of the melt. - AFP
SINGAPORE, Jan 15 (The Straits Times/ANN): A colossal chunk of ice breaks from a glacier as it plunges into the ocean, its thunderous splash punctuating the seemingly quiet and frigid landscape of the Arctic.
But at the same time, masses of glacial ice continuously pop, cackle and bubble underwater – almost like the sound of a frying egg – as they lose their weight in meltwater.
This usually occurs in the warm summer months from May to August, and can be difficult to measure since much of the melting occurs underwater, said Dr Mandar Chitre, head of the Acoustic Research Laboratory at the National University of Singapore’s (NUS) Tropical Marine Science Institute.
Warming seas, which trap more heat from greenhouse gases like carbon dioxide, have led to the world losing some 21 per cent of its glaciers over the last two decades.
A recent study has shown through analysis of two decades worth of satellite data that even if the world were to limit temperature rise to 1.5 deg C, it could still lose around half of its glaciers.
This could go up to 68 per cent if global warming continues at its current rate at a temperature increase of 2.7 deg C.
With more glaciers disappearing over the century, its implications on sea level rise could be all the more drastic for low-lying island states like Singapore.
But how quickly is the ice melting and how will this affect the extent of sea level rise?
The terrain surrounding the glaciers in the warmer months tends to be unstable and dangerous, as large chunks of ice often break from the glacier and fall into the water as icebergs. - PHOTO: NYTIMES via The Straits Times
To understand this, Dr Chitre embarked on a mission some five years ago – with researchers from the Institute of Geophysics in Poland and the Scripps Institution of Oceanography in the United States – to the Norwegian archipelago of Svalbard to eavesdrop on the secret language of oceans: the sound of melting glaciers.
“When glaciers were formed thousands of years ago, they had air bubbles trapped inside them. Because of the weight of the snow and ice above it, the air bubbles are under high pressure and stay trapped inside the ice,” he said.
“However, when the glaciers melt and the walls become thinner, the bubbles explode through the glacier wall, as it is no longer able to contain the pressure, thus making the popping noise.”
Dr Chitre and the team are analysing the sounds of these popping bubbles to see if they can provide clues to the speed of glacial melt.
However, the terrain surrounding the glaciers in the warmer months tends to be unstable and dangerous. As these glaciers melt, large chunks of ice often break from the glacier and fall into the water as icebergs, he noted.
Therefore, the team of researchers has deployed underwater microphones, also known as hydrophones, that are placed about half a kilometre away from the glacier to allow researchers to monitor their sounds remotely.
“Traditionally, researchers try to measure glacial melt by looking at satellite photographs to see how much the glacier is receding, but this often doesn’t give you a complete picture since most of the melting actually happens underwater,” he added.
The acoustic methods that are being developed are meant to complement other methods such as measuring the salinity of the water around the glacier, he said. “As the glacier is composed primarily of freshwater, when it melts into seawater, the salinity of the water in the glacier bay would be reduced.”
But the most accurate way of doing this would be to develop a technique to directly measure how much the glacier has melted underwater, which the team is coming close to completing.
They have gone on several expeditions to make sound recordings and other measurements, but at least one more expedition remains – an important one that would enable them to derive a “formula” that equates the popping sounds of bubbles to the speed of ice melting.
This expedition would be the toughest, as they would have to get a lot closer to the glacier than previously to take these sound recordings and other measurements.
Dr Hari Vishnu, a senior research fellow at NUS’ Acoustics Research Laboratory, will be accompanying Dr Chitre on the latest mission.
To prepare for the trip in the summer, Dr Chitre and his colleagues at the lab are creating robots that would go close to the glacier to place the sensors and collect measurements.
“We might end up losing some of these robots or sensors, but these are important measurements to make in order to calibrate our model,” said Dr Chitre, adding that the robots they design would have to be cost-effective.
Once the formula has been created, the team hopes to bring their technology to Greenland, which is known to have a larger mass of glaciers than Svalbard.
But, unlike Svalbard that is largely land mass, Greenland is primarily a mix of ice sheets and glaciers, making the environment more difficult to work with, he said.
Greenland also has a large proportion of ice melange – basically a mixture of ice that can be icebergs, sea ice and snow – covering the surface of water bodies.
“Ice melange makes its own sound, so being able to differentiate between the sounds of glaciers melting and the noise coming from ice melange is an additional problem we have to address in Greenland as well,” said Dr Chitre.
Greenland is surrounded by major ocean bodies like the North Atlantic Ocean, therefore when these ice sheets and glaciers melt, they contribute directly to sea level rise.
A 2019 study found that the giant ice sheets of Antarctica and Greenland contain enough water to raise global sea levels by about 70m if they were to all melt.
With this project, the team hopes to contribute critical information on the rate of glacial ice melt to enable predictions on the rate of sea level rise to be more accurate.
This would allow countries like Singapore to better prepare and come up with measures to adapt and guard against future sea level rise. - The Straits Times/ANN
