D3 Surveying and Drilling Methods

Topic

Probing and drilling methods allow us to understand conditions within ice masses and the frozen subsurface while disturbing the interior as little as possible—or not at all. These methods range from techniques that explore the ice's interior without physical contact to those that extract material directly from within for analysis.

Ground-penetrating radar emits high-frequency radio pulses into the ice; these pulses reflect whenever they encounter an interface between two different materials—such as snow and ice, ice and liquid water, or ice and the underlying bedrock. The way these reflected pulses return to the radar unit reveals the ice thickness, the internal stratigraphy formed by successive layers of accumulated ice, and the architecture of the terrain beneath the glacier.

Seismic reflection and refraction surveys send elastic waves into the ice and the underlying subsurface; the manner in which these waves reflect and refract as they pass through different materials makes it possible to determine both the geometry of the glacier's bed and the structure of the frozen subsurface extending beyond it.

An ice core obtained through drilling serves as a high-resolution climate archive: air bubbles trapped within the ice as the snow compacted preserve the composition of the past atmosphere—including levels of carbon dioxide and methane—while the ratio of heavy oxygen and hydrogen isotopes within the ice itself records the air temperature at the time the ancient snow condensed. By calibrating the relationship between the heavy-isotope ratio and temperature against modern measurements, an ice core allows for the reconstruction of past temperatures with annual resolution during periods of rapid snow accumulation.

In contrast, a permafrost borehole measures the vertical temperature profile of the permafrost itself at various depths; the shape of this profile makes it possible to infer how surface temperatures have evolved over recent decades or even centuries.

The expected outcome for all these probing and drilling methods is that their records will be mutually consistent: that different boreholes in the same region will yield the same climate history, and that this history will align with findings from other independent indicators of past climate—thereby confirming the ability of these methods to reconstruct conditions within ice masses and frozen subsoil with the minimal disturbance mentioned earlier.

ID:2660