Near‐Surface Environmentally Forced Changes in the Ross Ice Shelf Observed With Ambient Seismic Noise

Abstract

Continuous seismic observations across the Ross Ice Shelf reveal ubiquitous ambient resonances at frequencies >5 Hz. These firn-trapped surface wave signals arise through wind and snow bedform interactions coupled with very low velocity structures. Progressive and long-term spectral changes are associated with surface snow redistribution by wind and with a January 2016 regional melt event.Modeling demonstrates high spectral sensitivity to near-surface (top several meters) elastic parameters. We propose that spectral peak changes arise from surface snow redistribution in wind events and to velocity drops reflecting snow lattice weakening near 0 ∘ C for the melt event. Percolation-related refrozen layers and layer thinning may also contribute to long-term spectral changes after the melt event. Single-station observations are inverted for elastic structure for multiple stations across the ice shelf. High-frequency ambient noise seismology presents opportunities for continuous assessment of near-surface ice shelf or other firn environments.Plain Language Summary Ice shelves are the floating buttresses of large glaciers that extend over the oceans and play a key role in restraining inland glaciers as they flow to the sea. Deploying sensitive seismographs across Earth's largest ice shelf (the Ross Ice Shelf ) for 2 years, we discovered that the shelf nearly continuously sings at frequencies of five or more cycles per second, excited by local and regional winds blowing across its snow dune-like topography. We find that the frequencies and other features of this singing change, both as storms alter the snow dunes and during a (January 2016) warming event that resulted in melting in the ice shelf's near surface. These observations demonstrate that seismological monitoring can be used to continually monitor the near-surface conditions of an ice shelf and other icy bodies to depths of several meters.

Diurnal seismicity cycle linked to subsurface melting on an ice shelf

“…The present study joins a few other recent cryoseismological efforts (e.g. Chaput and others, 2018; MacAyeal, 2018; Podolskiy and Others, 2018) in attempting to characterize surface conditions such as melting, freezing and changing temperature using seismological methods and data.…”

Annual cycle in flow of Ross Ice Shelf, Antarctica: contribution of variable basal melting

“…Nicolas and others (2017) described an extraordinary 14 days of stronger RIS surface melting, between the 10 th and the 21 st of January, due to persistent air temperatures higher than −2°C over a region covering the western part of RIS that included the DRRIS GPS network. These temperature anomalies were identified at several seismic stations of the network, co-located with GPS, that detected spectral resonance evolution patterns consistent with melting/freezing sequences (Chaput and others, 2018). Surface heat fluxes over the ocean during this unusually widespread melt event in January 2016 may have been substantially different than those used to drive the ocean model that provided the basal melt rates used to force the ice-flow model.…”

The influence of environmental microseismicity on detection and interpretation of small-magnitude events in a polar glacier setting

“…This activity, referred to as seismicity, comprises a superposition of discrete, transient seismic events over a background of persistent, low-amplitude microseismic energy that evolves with time. The variability of such seismicity tends to match the variability of environmental processes that include summertime melting and runoff at the glacier surface (Hart and others, 2019); englacial and subglacial water flow (Röösli and others, 2014); snow redistribution (Allstadt and Malone, 2014;Chaput and others, 2018); fluctuations in air temperature (Podolskiy and others, 2018); and thermal bending and fracture of ice during melt/freeze cycles on supraglacial ponds (MacAyeal and others, 2018), sea ice (Bažant, 1992) and lake ice (Ghofrani and Atkinson, 2018;Kavanaugh and others, 2019). In this paper, we use the term 'environmental microseismicity' to refer to the background component of periglacial and glacial seismicity (i.e.…”