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Geophysical evidence for englacial brine associated with Blood Falls, McMurdo Dry Valleys, Antarctica

by Badgeley, Jessica

Abstract

Ground-penetrating radar (GPR) images of Taylor Glacier, in the McMurdo Dry Valleys, Antarctica, reveal an englacial drainage system near this polar glacier’s terminus at Blood Falls. Blood Falls is the surface manifestation of episodic releases of subglacial, iron-rich, hypersaline, microorganism-bearing brine. Locating englacial brine near Blood Falls would allow us to extract unoxidized brine in order to better understand the geochemistry and microorganisms as a proxy for life on other planets. In the current study, we collected a grid of GPR transects immediately upglacier from Blood Falls to locate the path by which brine surfaces and to inform future drilling operations in search of subsurface brine. Additionally, this study explores the extent of the subglacial and englacial brine reservoirs and seeks to refine hypotheses about the mechanisms driving the brine to the surface. In each of the GPR profiles, we found an englacial scattering zone located above a break in the basal-ice reflection. Downwarping of the basal-ice reflection on either side of the break and the break itself indicate that the scattering zone has slowed down the electromagnetic waves and prevented their further propagation into the glacier. We interpret this scattering zone as evidence of water-saturated and/or salty ice. A three-dimensional plot of the scattering zones visible on the profiles reveals a linear trend upglacier from Blood Falls nearly paralleling previously active brine-releasing cracks. Our evidence suggests that the zone is a recently or currently active englacial brine reservoir. In 2014, a team drilled near the area and successfully extracted pressurized brine ~16 m deep and upstream from Blood Falls at -7.1°C within surrounding ice of ~-17 °C. This brine temperature is consistent with the theoretical basal temperature of -7.8 °C that Hubbard et al. (2004) modeled near their hypothesized brine source 3-6 km upglacier from the terminus using geothermal heat flux and friction caused by ice deformation. Further study of the GPR data has allowed us to better understand the extent and movement of subglacial brine to the surface. Our cross-terminus traverse GPR transect shows that the subglacial brine reservoir may, in some form, extend all the way to the terminus and allow continuous brine release into Lake Bonney. As the subglacial brine surfaces, our data and analyses confirm hypotheses that it follows favorable pressure gradients up through surface cracks that penetrate the brine reservoir.

Note

The author has given permission for this work to be deposited in the Digital Archive of Colorado College.

Colorado College Honor Code upheld.

Includes bibliographical references.

Administrative Notes

The author has given permission for this work to be deposited in the Digital Archive of Colorado College.

Colorado College Honor Code upheld.

Copyright
Copyright restrictions apply.
Publisher
Colorado College
PID
coccc:11284
Digital Origin
born digital
Extent
79 pages : illustrations
Thesis
Senior Thesis -- Colorado College
Thesis Advisor
Leonard, Eric
Department/Program
Geology
Degree Name
Bachelor of Arts
Degree Type
bachelor
Degree Grantor
Colorado College
Date Issued
2015-05