A recent study of the Thwaites Glacier (Doomsday Glacier),namely, Unsettling Currents: Warm Water Flowing beneath the ‘Doomsday Glacier’, by scientists in the University of Gothenburg,Sweden, was published in the journal Science Daily on April 9, 2021. The study has found that the supply of warm water to the glacier is larger than previously thought, triggering concerns of faster melting and accelerating ice flow. The researchers have obtained data from underneath the glacier. Besides, the researchers have made a number of new discoveries with the help of the uncrewed submarine Ran that made its way under the glacier front. This data will help researchers better calculate ice melting in the future to improve the models and reduce the great uncertainty that now prevails around global sea level variations. The Thwaites Glacier has long been a cause of concern because of its high potential of speeding up the global sea level rise due to climate change, which has nearly doubled the amount of ice melt over the past 30 years.
About the Thwaites Glacier
The Thwaites glacier is popularly known as the ‘Doomsday Glacier’ due to the imminent risk to it, caused by global warming but also with respect to the risk it poses to the world once it melts. It is 120 km wide at its broadest with a size of 1.9 lakh square kilometres. It contains enough water to raise the world sea level by more than half a metre. Its melting already contributes 4 per cent to global sea level rise each year. As an estimate, it would collapse into the sea in 200–900 years. It is important for Antarctica as it slows the ice behind it from freely flowing into the ocean.
Impact on Global Sea Level
The West Antarctic Ice Sheet accounts for about ten percent of the current rate of sea level rise. It also most potentially increases the rate due to the fastest changes worldwide in the Thwaites Glacier, which is particularly sensitive to warm and salty ocean currents underneath it due to its location and shape.This process can result in an increased melting taking place at the bottom of the glacier and inland movement of the so-called grounding zone—the area where the ice transitions from resting on the seabed to floating in the ocean. There has been a great shortage of in situ measurements from the grounding zone because of its inaccessible location, which is usually blocked by thick sea ice and many icebergs, leading to big knowledge gaps for the ice-ocean boundary processes.
Key Highlights of the Study
Some of the key highlights of the study are as follows:
- The researchers have presented the results,the first ever, from the uncrewed submarine, Ran, that measured strength, temperature, salinity, and oxygen content of the ocean currents that go under the glacier.
- The researchers used these results to map the ocean currents underneath the floating part of the glacier, anddiscovered that there is a deep connection to the east through which deep water flows from Pine Island Bay. This connection was previously thought to be blocked by an underwater ridge.
- The scientists measured the heat transport in one of the three channels that were unknown to them. These channels lead warm water towards the glacier from the north. Thereare distinct paths that water takes in and out of the ice shelf cavity, influenced by the geometry of the ocean floor.
- The value 0.8 TW, measured there, corresponds to a net melting of 75 km3 of ice per year, which is almost as large as the total basal melt in the entire ice shelf.
- The heat transport has a large effect locally and may indicate that the glacier is not stable over time in spite ofthe amount of less melting of ice compared to other global freshwater sources.
- Large amounts of meltwater flowed north, away from the front of the glacier.
- Variations in salinity, temperature, and oxygen content indicate that the area under the glacier is a previously unknown active area where different water masses meet and mix with each other, which is important for understanding the melting processes at the base of the ice.
Cause of Worry
The study has shown that warm water is approaching the pinning points of the glacier from all sides, impacting these locations where the ice is connected to the seabed and where the ice sheet finds stability. Therefore, it may pose potential threat to the glacier whose ice shelf is already retreating. However, the good news is that the scientists are, for the first time, collecting data that is necessary to model the dynamics of the glacier. This data will help scientists better calculate ice melting in the future, and improve the models and reduce the great uncertainty that now prevails around global sea level variations.
Experts’ Views
According to Professor Karen Heywood, University of East Anglia, this was Ran’s first venture to polar regions and her exploration of the waters under the ice shelf was much more successful than they had dared to hope. Therefore, further missions would be carried out in the following years, based on those exciting findings, such as measurement of the strength, temperature, salinity, and oxygen content of the ocean currents that go under the glacier.
As per Anna Wahlin, Professor of Oceanography at the University of Gothenburg and lead author of the new study, published in the journal Science Advances, global sea level is affected by how much ice there is on land, and the biggest uncertainty in the forecasts is the future evolution of the West Antarctic Ice Sheet.
According to Dr Rob Larter of the British Antarctic Survey, “This work highlights that how and where warm water impacts Thwaites Glacier is influenced by the shape of the sea floor and the ice-shelf base as well as the properties of the water itself. The successful integration of new sea-floor survey data and observations of water properties from the Ran missions shows the benefits of the multidisciplinary ethos within the International Thwaites Glacier Collaboration.”
In 2019, a study had discovered a fast-growing cavity in the glacier, sized roughly two-thirds the area of Manhattan. Thereafter, researchers from New York University detected warm water at a vital point below the glacier in 2020. The NYU study reported water at just two degrees above freezing point at the glacier’s ‘grounding zone’ or ‘grounding line,’ which is the place below a glacier at which the ice transitions between resting fully on bedrock and floating on the ocean as an ice shelf. The line points to the rate of retreat of a glacier.In the NYU study, the researchers had dug a 600-mdeep and 35-cmwide access hole, and deployed an ocean-sensing device, known as, Icefin to measure the waters moving below the glacier’s surface.
© Spectrum Books Pvt Ltd.