Assistant geosciences professor Dylan Mikesell has been awarded a two-year, $353,000 grant from the National Science Foundation to monitor Antarctic ice melt using seismic techniques normally employed for monitoring earthquakes.
Rising global sea-level poses a significant long-term risk for both human populations and our infrastructure and to mitigate the potential damage done by the changing level, scientists need to be able to accurately predict future sea level rise and fall. However, using current methods it is difficult to estimate the amount of ice that melts from polar ice sheets, especially from the West Antarctica ice sheet, and where that melt goes.
Mikesell explained that Earth’s crust is porous, like a sponge. When we press on the top of the crust (i.e. put a huge glacier on top of it), we squeeze out the fluid in the cracks and pores. If we go in the other direction (i.e. melt all the ice away), the cracks and pores open back up. These changes in open or closed cracks and pores change the elastic parameters of Earth’s crust. Mikesell and his team will use seismology to measure these very small changes in the elastic parameters of the crust.
“Once we measure the changes in the elastic parameters, we can relate the amount of change to the amount of ice mass removed or added to the ice sheet sitting on the crust,” he said.
This method is a departure from the two current methods scientists use to estimate how ice sheets fluctuate. The first method involves using airplanes and repeated flybys to monitor changes to ice sheet topography and estimate the gain or loss of ice. The second method utilizes satellite measurements to track gravity fluctuations that correlate with changes in ice sheet volume.
Mikesell’s project uses a passive seismic monitoring method to estimate the change in weight of the ice pressing on Earth’s crust. One advantage of this seismic method is that data are recorded continuously; therefore, it is possible to monitor the changes of the ice sheet with better temporal resolution. The sensitivity of the seismic waves also provides a picture of the structure of the interface between the ice and the rocks beneath the ice, where most of the dynamics and changes of the ice sheet take place.
“How well we predict sea-level change depends on how well we can characterize certain inputs to our predictive models. One of these inputs is ice melt. We have a few methods that measure surface-ice melt (e.g. satellite or airborne altimetry), but that does not actually tell us where the melt goes,” Mikesell explained. “Does the melt simply trickle down through the snow a few feet and refreeze, thus increasing the snow density? Does the melt make it all the way to the ocean, where it can actually have an impact on sea level? These are questions that we are hoping to better answer with the seismic method proposed in this new study.”
The award is being distributed by NSF’s Office of Polar Programs. Mikesell is the principal investigator for the project; he and Zongbo Xu, a graduate student in the geosciences department, will be working in collaboration with a team from the Massachusetts Institute of Technology (MIT).