Most gases are retained tightly in the air bubbles in glacial ice, preserving samples of the ancient atmosphere that can be measured in ice cores.  For example, carbon dioxide concentrations in the past are known this way.  However, some gases such as helium, neon, and oxygen, have molecular diameters that are smaller than the natural openings in the ice crystal's cagelike structure.  So these gases can easily hop through the openings in the ice lattice, and therefore leak out of the air bubbles in ice quite easily.  We call these "fugitive gases", because they "flee" from the ice sample quickly after the ice core is brought up to the surface and depressurized.  For helium sampling of the ancient atmosphere, the problem is particularly acute.  Ice samples for helium analysis must be taken within 30 minutes of the ice core depressurization, or else so much helium is lost that the sample is no longer trustworthy. 

This award studied fugitive gases in the WAIS Divide ice core, to learn about the history of atmospheric helium and to test an hypothesis about how helium is lost to space from the atmosphere.  It has long been known that the flux of helium from the solid earth, to the atmosphere, far exceeds the known loss processes of helium to space.  The implication is that our understanding is incomplete in some important respect, and there is some process that we are unaware of.  This so-called "helium problem" has been with us for some four decades without resolution.  Helium is an important strategic resource for the United States and a non-renewable resource, so understanding helium's fate in the atmosphere is more than just an academic curiosity. 

One hypothesis to explain the "helium problem" is that the solar wind impinges on the Earth's atmosphere during times when the geomagnetic field collapses, and causes massive loss of helium from the upper reaches of the atmosphere (in the so-called thermosphere, where hydrogen and helium are the dominant gases).  According to this hypothesis, we are now in a period in which atmospheric helium is building up, and only during magnetic collapse events does helium get lost in large quantities. 

The WAIS Divide ice core happened to provide a rare, one-time opportunity to critically test this hypothesis, because the most recent such collapse of the magnetic field occurred just within the time period covered by the WAIS Divide core (the Laschamp Event, 41,000 years ago, falls within the 67,000 year long WAIS Divide ice core record).  The WAIS Divide ice core is an extraordinary ice core because it is far-and-away the highest accumulation-rate ice core ever drilled through this time period.  For example, accumulation rates were fully 15 cm per year during the Laschamp Event at WAIS Divide, whereas they were only 5 cm per year in Greenland.  This high accumulation rate preserves fugitive gases much better than low-accumulation ice cores, where gases have plenty of time to leak out of the bubbles before they are sufficiently buried to stop the leakage.  Furthermore, the WAIS Divide ice core is extremely long, the longest core ever drilled by the US at 3405 m.  This great length helps to preserve helium signals because of the great thickness of the ice surrounding the Laschamp Event, minimizing the effect of helium diffusion that spreads and smoothes any signal from that time. 

In 2011-2013, samples were taken from the core in the field shortly after core recovery and enclosed in gas-tight, evacuated chambers.  We analysed these samples back home for a variety of gases including helium and its rare isotope, helium-3.  If the solar wind had impinged upon the atmosphere, it might have left an imprint of excess helium-3 (due to the fact that the solar wind is enriched in helium-3 by a factor of 300 ...

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