Seismic waves resonating within the upper layers of the Ross ice shelf could help scientists monitor the Antarctic melt season and understand factors that could lead to sudden ice shelf collapse
— Antarctica is ringed by ice shelves: vast, glacier-fed slabs of floating ice that can stretch hundreds of kilometers from the coastline into the sea. Because of their exposure to both the air above and the seawater below, ice shelves are considered more susceptible to rising global temperatures than either glaciers or continental ice sheets.
Recent dramatic examples of ice shelf disintegration, including the collapse of 3,250 square kilometers of the Larsen B ice shelf in 2002 and the ensuing accelerated ice loss in nearby glaciers, have highlighted the potential for widespread ice loss from the southernmost continent. Understanding how Antarctic ice shelves respond to warming temperatures is thus crucial for calculating future global sea level rise, which could affect hundreds of millions of people or more.
To investigate how ice shelves respond to atmospheric, oceanic, and other types of forcing, Chaput et al. conducted seismic observations at 34 stations distributed along two Ross ice shelf transects from November 2014 through February 2017. The resulting data revealed an unexpected discovery: a year-round pattern of high-frequency, wind-generated waves—akin to a steady dissonant hum—that are trapped within the upper layers of the shelf’s partially compacted surface.
The team also found meltwater infiltrating and freezing within these layers, which consistently changed the frequency of the wind-generated wave patterns. As the ice shelf approaches melting temperatures, the bonds between snow grains weaken, resulting in this drop in frequency. In other words, a hush falling over the humming ice shelf is an early warning of melt.
Collectively, these findings will help scientists conduct detailed observations of the ice shelves’ near-surface structure during the southern continent’s increasingly elongated melt season. In comparison to satellite observations, which are often limited by orbital cycles, this approach enables direct and continuous detection of melting, observations that also have the potential to shed light on the processes that lead to precipitous ice shelf collapse. (Geophysical Research Letters, https://doi.org/10.1029/2018GL079665, 2018)
by Terri Cook | Eos