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

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 FredstonDoug FeslerDoug 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 FredstonDoug FeslerDoug 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-

tsunamis3.Fjord water surface conditions4.Ice quakes5.Ice-shelf melt rate6.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-

tsunamis3.Fjord water surface conditions4.Ice quakes5.Ice-shelf melt rate6.More?

Sound travels extremely well in the ocean

Ambient Sound in Glacial Fjord - They are noisy!


Overview and Key PointsOverview and Key Points

Ambient Sound in Glacier Fjords


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Earthquakes/Explosions

Heavy Precip

Wind

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Earthquakes/Explosions

Heavy Precip

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Two month average Sound Pressure Level For Icy Bay, AK

Two month average Sound Pressure Level For Icy Bay, AK

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Ambient Sound in Glacier FjordsAmbient 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)

“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)


Manasseh and others, 2000

Icy Bay Bubble


Manasseh and others, 2000

Icy Bay Bubble

1mm bubble ~3kHz3mm bubble ~1kHz


Icy BayIcy Bay

YakutatYakutat

AnchorageAnchorage

Ambient Sound in Glacier FjordsAmbient Sound in Glacier FjordsTwo Week Time Series100 Hz

500 Hz

40000 Hz

Ambient Sound in Glacier FjordsAmbient Sound in Glacier FjordsTwo Week Time Series

Ice Free Surface? Ice Free Surface?

100 Hz

500 Hz

40000 Hz

Acoustic Evolution of a Calving EventAcoustic Evolution of a Calving Event

Model from Doug MacAyealModel from Doug MacAyeal

Meares Glacier

Columbia Glacier

Valdez

Prince William Sound


30 Hz

670 Hz

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Post Calving Event Wave Action


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SummarySummary

•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?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 ComplementsSeismic andOceanographic Observations

Underwater Acoustics ComplementsSeismic andOceanographic 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


Timelapse images from Pfeffer and O’Neel


Sound Travel in the OceanSound Travel in the OceanEffect on Sound Speed

Effect on Attenuation

Salt Increases speed

Specific salts (e.g. MgS increase attenuation

Temperature Increases speed

Through affecting viscosity

Stratification

Refraction (Sound Channels)

Decreases attenuation because of sound channels)

Bubbles Slows speed (simlar to porous medium)

Scattering Losses

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

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