Scientists monitoring the Ross Ice Shelf in West Antarctica captured the acoustic oddity. Using a series of ultra sensitive seismic sensors, they produced a soundscape that would fit in perfectly at a Halloween haunted house or as the soundtrack to a 1950s B-movie about aliens arriving on Earth. But beyond being spooky, the sounds reveal how numerous processes from winds to warming are changing Antarctica’s ice.
Julien Chaput, an ambient noise monitoring expert at Colorado State University and new faculty at University of Texas, El Paso told Earther the records were a “happy accident.” In 2014 researchers were deploying seismic equipment on the Ross Ice Shelf, the largest hunk of floating ice in Antarctica, to study the crust and mantle underneath it. Chaput hopped on board hoping to tease out seasonal changes to the ice shelf’s mass, “and instead found strange spectral anomalies that escaped easy explanations, suggesting high frequency trapped seismic waves in the top couple of meters of snow.”
In essence, disturbances on the surface get trapped as seismic waves that ripple through the ice shelf. The team documented those wild waves in a Geophysical Research Letters paper released on Tuesday. They also released some of the sounds they captured over the course of more than two years of continuous recording (sped up below for your convenience).
Those top couple meters of loose snow and ice are called firn, and they’re very vulnerable to what’s going on above the surface, from changes in wind to changes in temperature. And with the sensitive seismic equipment buried below the surface, Chaput was able to intimately document much more than just seasonal shifts.
The frequency of the tune changed after storms blew through, which in itself is interesting. But what really stood out is a January 2016 warm spell when temperatures cracked freezing. The pitch of the tune dropped during that stretch, indicating that the snow and bits of ice melted, slowing down the propagation of seismic waves through the firn. More importantly, the pitch drop didn’t reverse itself after temperatures cooled back down, indicating permanent or semi-permanent changes in the firn layer.
“Melting of the firn is broadly considered one of the most important factors in the destabilization of an ice shelf, which then accelerates the streaming of ice into the ocean from abutting ice sheets,” Chaput said.
The Ross Ice Shelf is located in West Antarctica, parts of which could face an unstoppable meltdown owing to the shape of the bedrock beneath the ice that allows warm ocean currents to undercut the floating ice shelves. The melting of this unstable region could raise sea levels by roughly 3.05m. Surface warming could add another layer of stress that scientists will need to monitor closely.
Chaput pointed to seismic monitoring as a way to keep tabs on one of the most remote locales in the world and also help researcher answer questions about how resilient firn could be to rising temperatures. And of course this type of monitoring could provide more horror movie soundtrack fodder, though if we’re being real, what’s happening in Antarctica is frightening enough on its own.