The interplay between land ice, sea ice, oceans and the atmosphere plays a big role in determining the weather of coming seasons, and the climate of coming decades. The melting of ice sheets impacts sea level rise and ocean circulation, which impacts global climate. Understanding how ice shelves melt means we can get a better sense of sea-level rise, of ocean circulation, and of global weather.
When a sheet of ice slides off the Antarctic continent and into the ocean, it experiences a new environment for the first time. Where underneath it there was only rock, sea water now comes into contact with the ice shelf. Sea water brings with it heat, currents, salt and melting.
Measurements of the melting, taking place beneath hundreds of metres of ice, are difficult to obtain. Instead, high-resolution simulations run on the national supercomputer Gadi can show us what happens beneath the surface. Research from a group of Australian scientists including Dr Madelaine Rosevear from the University of Tasmania, Dr. Bishakhdatta Gayen from the University of Melbourne and Dr. Ben Galton Fenzi from the Australian Antarctic Division, has shown that as the ice melts, it drives a unique type of flow in the ocean beneath it. This flow transports heat to the ice, driving significant melting. Previously, researchers believed that large-scale currents bringing warmer water to the ice was the main driver of ice-shelf melting.
Lead researcher Dr Madelaine Rosevear says, “The double-diffusive convection mechanism that our simulations found shows that even without currents, there can be significant melting of the ice-sheet caused by the local temperature differences. It is important to understand the melting of Antarctic ice because it has a major effect on both global sea level rise and global weather.”
By integrating this finding into larger scale ocean models, the researchers can now learn about how this change in melting behaviour affects our predictions for climate and oceans in the future.
The Gadi supercomputer at NCI plays a key role in ocean and ice modelling of this sort. Dozens of processors work at the same time on calculating the interaction between ice and water at the boundary between the ice and the ocean. Simulating resolutions down to less than 1 millimetre, the research team breaks down their area of interest into separate horizontal slices and distributes those calculations to the different processors.
The findings from this cutting-edge, turbulent resolving simulation can now be incorporated into the bigger ocean and atmosphere models that cover the entire Antarctic continent and Southern Ocean. In particular, the ice-ocean boundary layer is an area of interest for scientists trying to improve the accuracy of some of the biggest climate models in the world. Improving the way that phenomena like ice shelf melting are dealt with helps these models continue to get better over time.
You can read the whole paper detailing these findings here.