Characterizing Meltwater Within a Firn Aquifer on the Greenland Ice Sheet using Active Source Seismology
Abstract
The Greenland ice sheet is melting due to increasing global average temperatures. Radar surveys conducted along the southeast margin of Greenland ice sheet identified a shallow reflector within the firn. Recent cores extracted from the area of reflectors indicate that a layer of liquid water, i.e a firn-aquifer, is responsible. The subsequent radar surveys int eh area find that the amount of water in the aquifer increased, expanding the aquifer up slope at a rate of 1-2 km/year. The date of the water within the firn aquifer is uncertain; it may remain stored in the pore space of the firn, or flow down hill until it encounters pathways into the englacial system and ultimately the ocean, contributing to sea level rise.
Here we show results from an active-source seismology survey of the firn aquifer located 30 km upstream of the terminus of the Helheim glacier in southeastern Greenland. We gathered data using a line of 24 vertical component 40-Hz geophones that were deployed over a 12 km long profile, used an 8-kg sledgehammer and stacked multiple hammer strikes to increase signal-to-noise. Our previous analysis of P-wave velocities and radar sounding found the aquifer to lie at a depth of 27.7 2.9 m under the surface, with an average thickness of 11.5 5.5 m. Calculations of water indicate the Helheim firn aquifer contains 4.7 3.1 gigatons of water.Here we expand this study to incorporate information from S-waves, surface waves, attenuation, and P-waves, all used as joint constraints for an inversion for the water stored of the aquifer. Preliminary results indicate that our joint dataset provides depth constraints on bulk and shear moduli within the aquifer, as well as Vp/Vs ratios and layering in attenuation. These features are all sensitive to liquid water content and will be used to constrain the properties of the Helheim aquifer with higher certainty than P-waves alone.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMNS43B0841G
- Keywords:
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- 0702 Permafrost;
- CRYOSPHEREDE: 0738 Ice;
- CRYOSPHEREDE: 0758 Remote sensing;
- CRYOSPHEREDE: 0794 Instruments and techniques;
- CRYOSPHERE