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Of Bubbles and Bergs: Passive Underwater Acoustics at the Ice/Ocean Boundary

Of Bubbles and Bergs: Passive Underwater Acoustics at the Ice/Ocean Boundary. Erin Pettit University of Alaska Fairbanks and… Shad O’Neel (USGS) Jeff Nystuen (University of Washington) Doug MacAyeal (University of Chicago) Jim Miller (University of Rhode Island)

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Of Bubbles and Bergs: Passive Underwater Acoustics at the Ice/Ocean Boundary

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  1. Of Bubbles and Bergs: Passive Underwater Acoustics at the Ice/Ocean Boundary Erin Pettit University of Alaska Fairbanks and… Shad O’Neel(USGS) Jeff Nystuen (University of Washington) Doug MacAyeal (University of Chicago) Jim Miller (University of Rhode Island) Liz Moyer (University of Chicago) Jill Fredston Doug Fesler Doug Quinn (DQ Media) Near Jakobshavn Isbrae, Photo T. Nylen

  2. Overview and Key Points • What can we learn from underwater acoustics? • It is unexplored territory… • Discharge of subglacial water (outburst floods) • Calving (submarine versus subaerial) and mini-tsunamis • Fjord water surface conditions • Ice quakes • Ice-shelf melt rate • More? • Sound travels extremely well in the ocean • Ambient Sound in Glacial Fjord -They are noisy! • Acoustic Evolution of a Calving Event

  3. 120 Earthquakes/Explosions Heavy Precip 80 Wind 40 2 0 5 3 4 1 10 10 10 10 10 10 Ambient Sound in Glacier Fjords Sound Pressure Level (dB rel 1Pa) Hz

  4. 120 Earthquakes/Explosions Heavy Precip 80 Wind 40 0 2 1 4 5 3 10 10 10 10 10 10 Ambient Sound in Glacier Fjords Two month average Sound Pressure Level For Icy Bay, AK Sound Pressure Level (dB rel 1Pa) Hz

  5. Ambient Sound in Glacier Fjords “The sound of the screaming, infant microbubblelasts for many milliseconds and generally radiates much more energy than the impact [of the rain drop]” Medwin and Clay (1998)

  6. Ambient Sound in Glacier Fjords Icy Bay Bubble Manasseh and others, 2000

  7. Ambient Sound in Glacier Fjords Icy Bay Bubble 1mm bubble ~3kHz 3mm bubble ~1kHz Manasseh and others, 2000

  8. Ambient Sound in Glacier Fjords Anchorage Icy Bay Yakutat

  9. Ambient Sound in Glacier Fjords

  10. Ambient Sound in Glacier Fjords Two Week Time Series 100 Hz 500 Hz 40000 Hz

  11. Ambient Sound in Glacier Fjords Two Week Time Series 100 Hz 500 Hz 40000 Hz Ice Free Surface?

  12. Acoustic Evolution of a Calving Event Model from Doug MacAyeal

  13. Columbia Glacier Meares Glacier Valdez Prince William Sound

  14. Acoustic Evolution of a Calving Event 30 Hz 670 Hz Difference in SPL from quiescent period (dB) 11 kHz 35 kHz

  15. Acoustic Evolution of a Calving Event

  16. Post Calving Event Wave Action

  17. Acoustic Evolution of a Calving Event 30 Hz 670 Hz Difference in SPL from quiescent period (dB) 11 kHz 35 kHz

  18. Acoustic Evolution of a Calving Event 30 Hz 670 Hz Difference in SPL from quiescent period (dB) 11 kHz 35 kHz

  19. Summary • Fjords are noisy places • (what does this mean for marine ecosystem?) • Pressurized bubbles in glacier ice create loud high frequency (1-5kHz) signal in water column during melt (distinctively different than sea ice) • Calving Event: • Low Freq Rumble pre calving(ice fracture?) • All Freqs Bang(berg hits water?) • High Freq wave action post calving(seiche?)

  20. What is possible around WAIS? • Monitoring for subglacial outburst floods? • (depends on how turbulent/bubbly the discharge event is) • Measuring sub ice-shelf melt rate? • Observe wave/ice interactions? • Variability in ice surface conditions? • Rifting events? • Other ideas? Underwater Acoustics Complements Seismic and Oceanographic Observations

  21. What happens to this water when it exits the glacier? Freshwater is less dense than salt water – it is buoyant, rises turbulently to the surface. Sediment also comes out with the water

  22. Outburst flood upwelling from Columbia Glacier, AK Freshwater upwelling Images from Pfeffer and O’Neel

  23. Outburst flood upwelling from Columbia Glacier, AK Images from Pfeffer and O’Neel

  24. Outburst flood upwelling from Columbia Glacier, AK Timelapse images from Pfeffer and O’Neel

  25. Sound Travel in the Ocean

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