USAP-DC

This award supports a project intended to discover, through field observations and numerical simulations, how ocean wave-induced vibrations on ice shelves in general, and the Ross Ice Shelf (RIS), in particular, can be used (1) to infer spatial and temporal variability of ice shelf mechanical properties, (2) to infer bulk elastic properties from signal propagation characteristics, and (3) to determine whether the RIS response to infragravity (IG) wave forcing observed distant from the front propagates as stress waves from the front or is "locally" generated by IG wave energy penetrating the RIS cavity. The intellectual merit of the work is that ocean gravity waves are dynamic elements of the global ocean environment, affected by ocean warming and changes in ocean and atmospheric circulation patterns. Their evolution may thus drive changes in ice-shelf stability by both mechanical interactions, and potentially increased basal melting, which in turn feed back on sea level rise. Gravity wave-induced signal propagation across ice shelves depends on ice shelf and sub-shelf water cavity geometry (e.g. structure, thickness, crevasse density and orientation), as well as ice shelf physical properties. Emphasis will be placed on observation and modeling of the RIS response to IG wave forcing at periods from 75 to 300 s. Because IG waves are not appreciably damped by sea ice, seasonal monitoring will give insights into the year-round RIS response to this oceanographic forcing. The 3-year project will involve a 24-month period of continuous data collection spanning two annual cycles on the RIS. RIS ice-front array coverage overlaps with a synergistic Ross Sea Mantle Structure (RSMS) study, giving an expanded array beneficial for IG wave localization. The ice-shelf deployment will consist of sixteen stations equipped with broadband seismometers and barometers. Three seismic stations near the RIS front will provide reference response/forcing functions, and measure the variability of the response across the front. A linear seismic array orthogonal to the front will consist of three stations in-line with three RSMS stations. Passive seismic array monitoring will be used to determine the spatial and temporal distribution of ocean wave-induced signal sources along the front of the RIS and estimate ice shelf structure, with the high-density array used to monitor and localize fracture (icequake) activity. The broader impacts include providing baseline measurements to enable detection of ice-shelf changes over coming decades which will help scientists and policy-makers respond to the socio-environmental challenges of climate change and sea-level rise. A postdoctoral scholar in interdisciplinary Earth science will be involved throughout the course of the research. Students at Cuyamaca Community College, San Diego County, will develop and manage a web site for the project to be used as a teaching tool for earth science and oceanography classes, with development of an associated web site on waves for middle school students. Understanding and being able to anticipate changes in the glaciological regime of the Ross Ice Shelf (RIS) and West Antarctic Ice Sheet (WAIS) are key to improving sea level rise projections due to ongoing ice mass loss in West Antarctica. The fate of the WAIS is a first-order climate change and global societal issue for this century and beyond that affects coastal communities and coastal infrastructure globally. Ice shelf--ocean interactions include impacts from tsunami, ocean swell (10-30s period), and very long period ocean waves that impact ice shelves and produce vibrations that induce a variety of seismic signals detected by seismometers buried in the ice shelf surface layer, called firn. To study the wave-induced vibrations in the RIS, an extensive seismic array was deployed from Nov. 2014 to Nov. 2016. This unique seismometer array deployment on an ice shelf made continuous observations of the response of the RIS to ocean wave impacts from ocean swell and very long period waves. An extensive description of the project motivation and background (including photos and videos of the deployment operations), and list of published studies of analyses of the seismic data collected by this project, are available at the project website https://iceshelfvibes.ucsd.edu. Two types of seismic signals detected by the seismic array are most prevalent: flexural gravity waves (plate waves) and icequakes (signals analogous to those from earthquakes but from fracturing of the ice). Long period ocean waves flex the ice shelf at the same period as the ocean waves, with wave energy at periods greater than ocean swell more efficient at coupling energy into flexing the ice shelf. Termed flexural gravity waves or plate waves (Chen et al., 2018), their wave-induced vibrations can reach 100’s of km from the ice edge where they are excited, with long period wave energy propagating in the water layer below the shelf coupled with the ice shelf flexure. Flexural gravity waves at very long periods (> 300 s period), such as from tsunami impacts (Bromirski et al., 2017), can readily reach grounding zones and may play a role in long-term grounding zone evolution. Swell-induced icequake activity was found to be most prevalent at the shelf front during the austral summer (January – March) when seasonal sea ice is absent and the associated damping of swell by sea ice is minimal (Chen et al., 2019). In addition to the seismic array, a 14 station GPS (global positioning system) array was installed during seismic data retrieval and station servicing operations in October-November 2015. The GPS stations, co-located with seismic stations, extended from the shelf front southward to about 415 km at interior station RS18. Due to logistical constraints associated with battery weight during installation, only one station (at DR10) operated year-round. The GPS data collected give a detailed record of changes in iceflow velocity that are in close agreement with the increasing velocity estimates approaching the shelf front from satellite observations. Importantly, the year-round data at DR10 show an unprecedented seasonal cycle of changes in iceflow velocity, with a speed-up in northward (seaward) ice flow during Jan.-May and then a velocity decrease from June-Sep. (returning to the long-term mean flow velocity). This annual ice flow velocity change cycle has been attributed in part to seasonal changes in ice shelf mass (thinning, reducing buttressing) due to melting at the RIS basal (bottom) surface from intrusion of warmer ocean water (Klein et al., 2020).

Person	Role
Bromirski, Peter	Investigator and contact
Gerstoft, Peter	Co-Investigator
Stephen, Ralph	Investigator

Antarctic Glaciology	Award # 1246416
Antarctic Glaciology	Award # 1246151

USAP-1246151_1

Deployment	Type
Ross Ice Shelf	field camp

None in the Database

Repository	Title (link)	Format(s)	Status
IRIS	Collaborative Research: Dynamic Response of the Ross Ice Shelf to Wave-Induced Vibrations and Collaborative Research: Mantle Structure and Dynamics of the Ross Sea from a Passive Seismic Deployment on the Ross Ice Shelf. International Federation of Digital Seismograph Networks.	Not Provided	exists
UNAVCO	Dynamic Response of the Ross Ice Shelf to Wave-induced Vibrations 2015/2016, UNAVCO, Inc., GPS/GNSS Observations Dataset	Not Provided	exist

1. Baker, M.G., Aster, R.C., Wiens, D.A., Nyblade, A., Bromirski, P.D., Gerstoft, P., Stephen, R.A. (2020). Teleseismic earthquake wavefields observed on the Ross Ice Shelf, J. Glaciol. (doi:10.1017/jog.2020.83)
2. Klein, E., C. Mosbeux, P.D. Bromirski, L. Padman, Y. Bock, S.R. Springer, and H.A. Fricker (2020). Annual cycle in flow of Ross Ice Shelf, Antarctica: contribution of variable basal melting, J. Glaciol., 1-15 (doi:10.1017/jog.2020.61)
3. Chen, Z., P.D. Bromirski, P. Gerstoft, R.A. Stephen, W.S. Lee, S. Yun, S.D. Olinger, D.A., Wiens, R.C. Aster, and A. Nyblade (2019). Ross Ice Shelf icequakes associated with ocean gravity wave activity, Geophys. Res. Lett, 46 (doi:10.1029/2019GL084123)
4. Baker, M.G., Aster, R.C., Anthony, R., Chaput, J., Wiens, D., Nyblade, A., Bromirski, P.D., Stephen, R., Gerstoft, P. (2019). Seasonal and spatial variations in the ocean-coupled ambient wavefield of the Ross Ice Shelf, Annals of Glaciology (doi:10.1029/2019GL082842)
5. Chaput, J., Aster, R.C., McGrath, D., Baker, M., Anthony, R.E., Gerstoft, P., Bromirski, P.D., Nyblade, A., Stephen, R.A., Wiens, D. (2018). Near-surface wind, temperature, and melt-induced changes on the Ross Ice Shelf observed continuously with seismology, Geophys. Res. Lett. (doi:10.1029/2018GL079665)
6. Chen, Z., P.D. Bromirski, P. Gerstoft, R.A. Stephen, D.A. Wiens, R.C. Aster, and A. Nyblade (2018). Ocean-excited plate waves in the Ross and Pine Island Glacier Ice Shelves, J. Glaciol (doi:10.1017/jog.2018.66)
7. Bromirski, P.D., Z. Chen, R.A. Stephen, P. Gerstoft, D. Arcas, A. Diez, R.C. Aster, D.A. Wiens, and A. Nyblade (2017). Tsunami and infragravity waves impacting Antarctic ice shelves, J. Geophys. Res.-Oceans (doi:10.1002/2017JC012913)
8. Diez, A., P.D. Bromirski, P. Gerstoft, R.A. Stephen, R.E. Anthony, R.C. Aster, C. Cai, A. Nyblade, and D.A. Wiens (2016). Ice shelf structure derived from dispersion curve analysis of ambient seismic noise, Geophys. J. Int., 205, 785-795 (doi:10.1093/gji/ggw036)
9. Bromirski, P.D., A. Diez, P. Gerstoft, R.A. Stephen, T. Bolmer, D.A. Wiens, R.C. Aster, and A. Nyblade (2015). Ross ice shelf vibrations, Geophys. Res. Lett., 42 (doi:10.1002/2015GL065284)
10. White-Gaynor, A., Nyblade, A., Aster, R.C., Wiens, D., Bromirski, P., Gerstoft, P., Stephen, R., Hansen, S., Wilson, T., Dalziel, I. Huerta, A., Winberry, P., Anandakrishnan, S., Heterogeneous upper mantle structure beneath the Ross Sea Embayment and Marie Byrd Land, West Antarctica, revealed by P-wave tomography, EPSL, 513, 40 - 50, 10.1016/j.epsl.2019.02.013, 2019. (doi:10.1016/j.epsl.2019.02.013)
11. Lucas, E. M., Nyblade, A. A., Accardo, N. J., Lloyd, A. J., Wiens, D. A., Aster, R. C., Wilson, T. J., Dalziel, I. W., Stuart, G. W., O’Donnell, J. P., Winberry, J. P., & Huerta, A. D. (2022). Shear Wave Splitting Across Antarctica: Implications for Upper Mantle Seismic Anisotropy. Journal of Geophysical Research: Solid Earth, 127(4). Portico. (doi:10.1029/2021jb023325)
12. Booth, A. D., Emir, E., & Diez, A. (2016). Approximations to seismic AVA responses: Validity and potential in glaciological applications. GEOPHYSICS, 81(1), WA1–WA11. (doi:10.1190/geo2015-0187.1)
13. Chen, Z., Bromirski, P. D., Gerstoft, P., Stephen, R. A., Lee, W. S., Yun, S., … Nyblade, A. A. (2019). Ross Ice Shelf Icequakes Associated With Ocean Gravity Wave Activity. Geophysical Research Letters, 46(15), 8893–8902. (doi:10.1029/2019gl084123)
14. Shen, W., Wiens, D. A., Anandakrishnan, S., Aster, R. C., Gerstoft, P., Bromirski, P. D., … Winberry, J. P. (2018). The Crust and Upper Mantle Structure of Central and West Antarctica From Bayesian Inversion of Rayleigh Wave and Receiver Functions. Journal of Geophysical Research: Solid Earth, 123(9), 7824–7849. (doi:10.1029/2017jb015346)
15. Olinger, S. D., Lipovsky, B. P., Wiens, D. A., Aster, R. C., Bromirski, P. D., Chen, Z., … Stephen, R. A. (2019). Tidal and Thermal Stresses Drive Seismicity Along a Major Ross Ice Shelf Rift. Geophysical Research Letters, 46(12), 6644–6652. (doi:10.1029/2019gl082842)
16. Sergienko, O. V. (2017). Behavior of flexural gravity waves on ice shelves: Application to the Ross Ice Shelf. Journal of Geophysical Research: Oceans, 122(8), 6147–6164. (doi:10.1002/2017jc012947)
17. Lucas, E. M., Soto, D., Nyblade, A. A., Lloyd, A. J., Aster, R. C., Wiens, D. A., … Huerta, A. D. (2020). P- and S-wave velocity structure of central West Antarctica: Implications for the tectonic evolution of the West Antarctic Rift System. Earth and Planetary Science Letters, 546, 116437. (doi:10.1016/j.epsl.2020.116437)
18. Hell, M. C., Cornelle, B. D., Gille, S. T., Miller, A. J., & Bromirski, P. D. (2019). Identifying Ocean Swell Generation Events from Ross Ice Shelf Seismic Data. Journal of Atmospheric and Oceanic Technology, 36(11), 2171–2189. (doi:10.1175/jtech-d-19-0093.1)
19. Bromirski, P. D., Chen, Z., Stephen, R. A., Gerstoft, P., Arcas, D., Diez, A., … Nyblade, A. (2017). Tsunami and infragravity waves impacting A ntarctic ice shelves. Journal of Geophysical Research: Oceans, 122(7), 5786–5801. (doi:10.1002/2017jc012913)
20. Jenkins, W. F., Gerstoft, P., Bianco, M. J., & Bromirski, P. D. (2021). Unsupervised Deep Clustering of Seismic Data: Monitoring the Ross Ice Shelf, Antarctica. Journal of Geophysical Research: Solid Earth, 126(9). (doi:10.1029/2021jb021716)