Virtually all of the expected sea level rise from climate change will result from the melting of massive ice sheets and glaciers that rest comfortably above sea level – however, the forces that guide this melting process are only coarsely understood, and as a result, large uncertainties persist in estimates of future sea levels. Now, researchers from the Universities of Melbourne and Tasmania are leveraging supercomputing power to understand exactly how these icy masses turn into global sea level changes.
The researchers focused on the processes affecting the Ross Ice Shelf, which stands as the largest in Antarctica at over 180,000 square miles in size and hundreds of meters in height. Using a high-resolution large-eddy simulation, the team recreated the complex ocean conditions beneath the Ross Ice Shelf.
Running that simulation required supercomputing resources – and for those, the researchers turned to Australia’s National Computational Infrastructure (NCI), the largest research supercomputing facility on the continent. NCI Australia is home to the Gadi supercomputer, which boasts 3,024 compute nodes (each with dual Intel Xeon “Cascade Lake” CPUs), 160 GPU nodes (each with four Nvidia V100 GPUs), 567 TB of memory and an aggregate 9.3 Linpack petaflops of supercomputing power, placing it 27th on the most recent Top500 list.
“Supercomputer simulations let us study these remote environments virtually, helping us gain a better understanding of the large-scale physical forces that shape the Earth over time,” said Ben Galton-Fenzi, a glaciologist and senior scientist with the Australian Antarctic Division. And, indeed, the results of the simulation were surprising: it showed that large-scale water currents under the shelf weren’t always the primary driver of the melting process as many researchers had suspected in the past. Instead, the primary culprit was double-diffusive convection, whereby differing rates of heat and salt diffusion in two adjoining water layers begin to actively mix the layers together in complex ways. (To see a visualization of the simulated process, click here.)
“Using supercomputing modelling we can now see that … double-diffusive convection is occurring, due to the unique ocean conditions beneath ice shelves, where cold, fresh water sits above warmer, saltier ocean,” explained Bishakhdatta Gayen, a senior lecturer in the University of Melbourne’s Department of Mechanical Engineering.
“This is actually a very important piece of the puzzle for climate models, because at the end of the day, it helps us to understand the basic forces that drive sea level rise,” Dr Gayen said.
The paper discussing this research, which was written by Galton-Fenzi, Gayen and Madelaine Gamble Rosevear, was published in the February 2021 issue of PNAS.