Investigating the interior of West Antarctica with light, radar, and electrical conductance

Abstract

Ice sheets play an important role in both the modern climate and in past variations of Earth's history. Our understanding of ice sheets has been limited by few observations until recent advances in technology, notably air planes and satellites, which have allowed increasingly more detailed investigations. Here I focus on using the internal structure of ice sheets to place modern observations in context. This is done with a variety of tools. First, I investigated the ability of borehole camera measurements to recover information about the physical properties of firn. I found that a measurement with a single wavelength of light was not capable of differentiating between brightness variations due to changes in grain size and changes in density. An additional measurement in the near infrared, which is sensitive to grain size variations, was identified as a way to differentiate density variations from grain size variations. I also use the internal structure of the ice sheet imaged using ice penetrating radar to examine the past flow structure of a major outlet glacier of West Antarctica. The flow directions were found to have not changed significantly in the past few hundred years and the analysis also revealed that the satellite-derived velocities had uncertainties larger than reported. The internal structure of an ice sheet can also be investigated by drilling an ice core. By obtaining samples of ancient ice, many detailed measurements are possible to look at past variations in climate and ice sheet behavior. I measured the electrical properties of the WAIS Divide ice core and was able to identify an annual signal to a depth of 2800. I then developed the first annually resolved timescale from the Southern Hemisphere that spanned into the last glacial period, 30 ka. The annual timescale allowed identification of accumulation-rate changes not resolvable in other Antarctic ice cores. The timescale and accumulation-rate history were combined with the water stable isotopes, sea-salt sodium, and climate modeling to show that the onset of deglacial warming in West Antarctica occurred before a trigger from the Northern Hemisphere with a likely cause increasing local insolation. The annual timescale was also used to assess the timescales from other coastal Antarctic ice cores. The timescales of these 3 cores were based on linear interpolation, which causes significant problems: large age uncertainty between tie points, large changes in the duration of climate events at the tie points, and a consistent bias to older ages. Two inverse techniques were developed to improve timescale interpolation.