Water loss from Antarctica’s ice shelves due to increased heating almost enough to fill Grand Canyon: Report
Floating ice shelves in Antarctica have experienced a loss of nearly 4,000 gigatons since 1994, producing an amount of meltwater that can nearly fill the Grand Canyon, according to scientists. They explain that the loss is a result of melting from increased heat in the ocean under the ice shelves and that the ice is melting faster than it is being replenished.
The team, led by researchers at Scripps Institution of Oceanography at UC San Diego, created a detailed history of mass loss from Antarctica’s floating ice shelves. They used 25 years' data from four separate European Space Agency (ESA) satellite missions, NASA ice velocity data and outputs from NASA computer models.
The experts found that there is a lot of variation around Antarctica in the rate at which the ocean is melting the ice shelves, but overall, there is more loss than gain of ice shelf mass. Ice shelf loss itself does not directly contribute to sea-level rise because ice shelves are already floating. However, ice shelves act as a buffer to help slow the slide of ice sheets from land into the ocean, and when they become smaller this effect is weakened, explains the team. If the West Antarctic Ice Sheet were to completely melt into the ocean, for example, it would raise sea levels worldwide by around 3 meters or 10 feet. While that amount of melt is unlikely in the coming decades, even four inches of sea-level rise can double the frequency of flooding on the US West Coast, say researchers.
“This is the most convincing evidence so far that long-term changes in the Southern Ocean are the reason for ongoing Antarctic ice loss. It’s incredible that we are able to use satellites that orbit around 500 miles above the earth to see changes in regions of the ocean where even ships can’t go,” writes lead author and Scripps Oceanography graduate student Susheel Adusumilli in the NASA-funded study which has been published in Nature Geoscience.
Obtaining detailed information on Antarctic ice shelves is challenging because of their vast size and the difficulty for scientists to physically reach them. But satellites allow for year-round monitoring and are the only practical way to routinely collect information on Antarctic ice loss, say authors. Accordingly, for their study, the scientists used data from ESA radar satellites which send radio waves to the ground up to 20,000 times a second and measure the travel time of those waves as they bounce back to the satellite. Researchers can use that information to determine the precise height of land or ice, they explain.
An assessment of radar signals shows changes in the melt of all Antarctic ice shelves which collectively cover an area of 1.5 million square kilometers (580,000 square miles) – more than three times larger than California.
“We have produced two new datasets of basal melt rates for nearly all of Antarctica’s ice shelves. One dataset provides melt rates at high spatial resolution (500m grid) for most ice-shelf areas, averaged over the period 2010-2018. The second dataset allows for the evaluation of annual estimates of basal melt rates at lower spatial resolution (greater than 10km) for the 1994-2018 period. Together, these datasets reveal large variability in total meltwater fluxes from individual Antarctic ice shelves, with distinct, regionally variable, signatures of temporal variability for different modes of ocean-driven melting,” write authors.
The report also identified the depths in the ocean at which melting is occurring. According to the research team, this is important because the increased melting of ice shelves has major environmental consequences beyond the global sea-level rise. Melting ice produces water that is colder and fresher than the surrounding ocean. Depending on where this water ends up in the ocean, it can have a large effect on ocean circulation and climate around the globe.
The findings could help improve the accuracy of climate models and projections of sea-level rise. “We now have a continuous and detailed record of how all the ice shelves have changed since the mid-1990s, and where the meltwater has entered the ocean. This will allow us to decipher the atmospheric and ocean forces responsible for the changes, and how the meltwater affects the ocean, allowing us to improve models that predict future sea-level rise,” says co-author of the study, Helen Amanda Fricker, a Scripps Oceanography glaciologist.