Properties of the Near Surface Firn at NEEM

Physical characteristics of the firn column affect gas transport and ultimately can affect the nature of the pore close-off process. The core from the CO2 firn air sampling site at NEEM was retrieved in July 2009, and the physical properties are being analyzed to improve the understanding of firnification and pore close-off processes. The firn core being studied extends from the surface down to a depth of 81m. Accompanying measurements from a snow pit at the site were made at the time that the core was drilled. The snow pit measurements show that the NEEM snow is highly layered, and in the top two meters the density ranges from 0.203g cm-3 to 0.416g cm-3 and the permeability ranges from 9.63m2 x10-10 to 93.31m2 x10-10. The density and permeability profiles are comparable to the Summit firn core to a depth of 2m. The properties in the top 20m at NEEM are similar to the properties at Summit. Continuing measurements through the deeper firn to pore close-off, and characterizing the firn microstructure, will examine pore close-off processes and will be correlated to the firn air measurements made on site. Understanding the metamorphic processes acting on the firn column to pore close-off at the NEEM site may improve understanding of the temperature and gas record of the NEEM deep ice core.