Dynamic Observations of the Evolution of Firn

Dartmouth College, Hanover NH

Investigators

Abstract

Using modern spectroscopy techniques, the PI will determine the mechanisms of ice core densification and microstructure evolution as a function of depth. An 80 meter firn core will be drilled at Summit, Greenland, and transported to Dartmouth. For the shallow part of the core, where the firn is subjected to seasonal and diurnal temperature gradients, the PI will impose Greenlandic in situ temperature gradients at the core boundaries. Continuous ìCT will be used to monitor densification and microstructure evolution. For the deep part of the core, where a Greenlandic in situ temperature gradient does not exist over the length of the core. However, it does experience stresses from the weight of the overburden. The PI will therefore conduct Greenlandic in situ loading experiments on the deep core. Continuous ìCT will be used to monitor densification and microstructure evolution. After the completion of the ìCT experiments, the firn will be sectioned and examined in a cold-stage-equipped scanning electron microscope. Electron backscattering and energy dispersive X-ray spectroscopy will be used to determine ice crystal orientations and local microchemistry. The panel thought that the path presented for the professional development of students, which include attending the Future Faculty Teaching series and the 10-week "Communicating Science" course, was well conceived. The Greenland ice sheet is rapidly melting due to extraordinary Arctic warming. All told, the ice sheet stores enough water to raise sea level by 6 meters. How fast the ice sheet will melt is still an open question. One important factor controlling the ice sheet melt is its physical properties. In this work, the investigators will extract an 80 meter core from the Summit Station, Greenland. Working in a cold room at Dartmouth the investigators will impose the natural temperature conditions on the two ends of the near surface part of the core and compression tests on the deeper part of the core. A suite of spectroscopy techniques will be used to monitor the 3-dimensional real-time densification of the core and the evolution of the crystal orientation. These experiments will provide the values of the numerous physical parameters required for simulation modeling, which will be used to determine the melt rates over the coming decades.