Evolution of Firn Layers at Summit, Greenland

The physical properties of snow determine the processes in the snow responsible for chemical and physical evidence of past climate information. These properties are continuously changing due to the nature of snow, and are important to understand in order to better interpret climate records from ice cores. For the past seven years, the physical properties of snow and firn layers in snow pits dug at Summit Station, Greenland have been examined. Summit Station is a year-long research station located at the summit of the Greenland Ice Sheet, an area that rarely experiences melt. In this region, snow layers persist year after year, are buried by subsequent storms, and undergo firn metamorphism, primarily driven by diurnal temperature gradients in the top two meters. Repeat pits at exact locations have been dug and analyzed for stratigraphy, grain size, air permeability, thermal conductivity and gas diffusivity. The spatial variability of the snow stratigraphy from small to large scale has been examined, as well as the temporal variability of the near surface snow. The evolution of the snow physical properties has been tracked over time. In general, we see an increase in permeability, gas diffusivity, and thermal conductivity as a snow layer ages. These changes in physical properties are linked to changes in the firn microstructure due to temperature gradient metamorphism. This work has helped to further understand firn air models of past atmospheric conditions, as well as help to support photochemistry experiments.