Uncovering a New Mechanism for Ice Sheet Meltwater Flow and Freezing: A Game-Changer for Sea Level Rise Predictions
The newly discovered mechanism for the flow and freezing of ice sheet meltwater could have significant implications for improving estimates of sea level rise around the globe. Researchers from The University of Texas at Austin, NASA’s Jet Propulsion Laboratory (JPL), and the Geological Survey of Denmark and Greenland (GEUS) have identified a new process that explains how impermeable horizontal ice layers are formed below the surface, a crucial factor in determining the impact of ice sheet meltwater on sea level rise.
The study, led by Mohammad Afzal Shadab, a graduate student at UT’s Oden Institute for Computational Engineering and Sciences, and supervised by Marc Hesse and Cyril Grima at UT’s Jackson School of Geosciences, was recently published in Geophysical Research Letters. The research focused on the Greenland and Antarctica ice sheets, which are covered in porous old snow called firn that has not yet turned into solid ice. When snow melts, it can drain into the firn and refreeze, reducing the amount of meltwater that reaches the sea. However, impermeable ice layers can also form within the firn, diverting meltwater directly to the ocean.
According to Shadab, these ice layers can accelerate the rate of meltwater runoff into the oceans, highlighting the importance of understanding freezing dynamics within the firn layer for estimating sea level rise. Previous studies on firn in mountains suggested that ice layers form when rainwater accumulates on older layers and refreezes, but this mechanism did not seem to apply to ice sheets.
The new research proposes that ice layer formation is a result of a competition between warmer meltwater flowing through the firn and cold ice freezing the water in place. The depth at which heat conduction surpasses heat advection determines where a new ice layer forms. By understanding the physics behind ice layer formation, researchers hope to improve predictions of meltwater retention in firn.
To validate their findings, the researchers compared their models to data collected in Greenland in 2016, which confirmed the accuracy of the new mechanism. An unexpected discovery was that the location of ice layers can act as a record of the thermal conditions when they formed, with deeper layers indicating warmer conditions.
Currently, Greenland contributes more meltwater to the sea than Antarctica, with over 270 billion tons per year compared to Antarctica’s 140 billion tons. Predictions for future sea level rise vary widely, from 5 to 55 centimeters by 2100, underscoring the importance of understanding the role of ice layers in this process.
The researchers believe that their work advances the state of the art in predicting sea level rise and underscores the complexity of the interactions between ice sheets and meltwater. By improving our understanding of these processes, we can better prepare for the potential impacts of climate change on global sea levels.