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) Liz Moyer (University of Chicago) Jill Fredston Doug Fesler Doug Quinn (DQ Media) 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

What can we learn from underwater acoustics? It is unexplored territory… 1.Discharge of subglacial water (outburst floods) 2.Calving (submarine versus subaerial) and mini-tsunamis 3.Fjord water surface conditions 4.Ice quakes 5.Ice-shelf melt rate 6.More? Sound travels extremely well in the ocean Ambient Sound in Glacial Fjord - They are noisy! Acoustic Evolution of a Calving Event What can we learn from underwater acoustics? It is unexplored territory… 1.Discharge of subglacial water (outburst floods) 2.Calving (submarine versus subaerial) and mini-tsunamis 3.Fjord water surface conditions 4.Ice quakes 5.Ice-shelf melt rate 6.More? Sound travels extremely well in the ocean Ambient Sound in Glacial Fjord - They are noisy! Acoustic Evolution of a Calving Event Overview and Key Points

Ambient Sound in Glacier Fjords Ambient Sound in Glacier Fjords Earthquakes/Explosions Heavy Precip Wind Hz Sound Pressure Level (dB rel 1  Pa)

Ambient Sound in Glacier Fjords Ambient Sound in Glacier Fjords Earthquakes/Explosions Heavy Precip Wind Two month average Sound Pressure Level For Icy Bay, AK Two month average Sound Pressure Level For Icy Bay, AK Hz Sound Pressure Level (dB rel 1  Pa)

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

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

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

Ambient Sound in Glacier Fjords Icy Bay Yakutat Anchorage

Ambient Sound in Glacier Fjords

Two Week Time Series 100 Hz 500 Hz Hz

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

Acoustic Evolution of a Calving Event Model from Doug MacAyeal

Meares Glacier Columbia Glacier Valdez Prince William Sound

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

Acoustic Evolution of a Calving Event Acoustic Evolution of a Calving Event

Post Calving Event Wave Action

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

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

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?) 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?)

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? 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 Underwater Acoustics Complements Seismic and Oceanographic Observations

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

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

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

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

Sound Travel in the Ocean Effect on Sound Speed Effect on Attenuation SaltIncreases speedSpecific salts (e.g. MgS increase attenuation TemperatureIncreases speedThrough affecting viscosity StratificationRefraction (Sound Channels) Decreases attenuation because of sound channels) BubblesSlows speed (simlar to porous medium) Scattering Losses