9:45 AM - 10:00 AM
[ACC25-04] Study of the formation of stratified firn on the snow surface near Dome Fuji, Antarctica, by multiple physicochemical analyses
Keywords:Firn, Densification, Surface snow, Dome Fuji
The physicochemical properties of ice cores characterized on the surface of the ice sheet not only record past climate signals but also affect the densification and bubble formation processes of firn. For example, the impurity concentrations and microstructure such as developed vertical bonds of snow grains change the densification rate for each layer, controlling the degree of density variability. The density variability in deep firn changes the range of the bubble close-off zone, which would, in turn, affects the chronology and the degree of fractionation of gas components; e.g., when the bubble close-off zone is narrow, the age distribution at a depth is also narrowed and the amount of gas fractionation is reduced. Therefore, to better interpret paleoclimatic signals in ice cores, it is important to understand the physicochemical properties and their layering formation on the ice sheet surface.
To investigate and select a site for the third Dome Fuji deep core drilling, one of the base camp was placed at about 54 km south of the Dome Fuji station (tentatively named as NDF , 77°47’18S, 39°3’15E, 3763 m a.s.l.), where a 152-m firn core was collected in December 2017. In this area, the accumulation rate is extremely low, and the surface snow is affected by sublimation and condensation for a long period. We performed multiple high-resolution (2.5-20 mm depth increment) continuous measurements of physical and chemical properties on this core. The properties include (1) density measured by a gamma-ray absorption method, (2) microwave permittivity ε as a proxy for density, (3) dielectric anisotropy Δε as a proxy for vertical elongation of ice and pore spaces, (4) reflectance R for near-infrared light as a proxy for specific surface area, and (5) water stable isotope ratios δ18O, δD, (6) concentration of major elements (Na, Mg, Al, S, K, Ca, Fe) measured by a continuous flow analysis system. Here, we mainly focus on the surface roughly down to a depth of 10 m.
We found significant positive correlations between ρ, ε, Δε, R, δ18O, and δD, calculated within 1-m segments, near the surface. We also found significant negative correlations between these properties and the concentration of all the major elements, although impurities in the precipitation must show different seasonal fluctuations. Hoshina et al. (2016) suggested that the negative correlations between impurity concentrations and δ18O at low-accumulation site can be formed by long-term sublimation and condensation within snow and between snow and atmosphere, which alter the original signal. However, the detailed process has not been clarified. In the JpGU presentation, we will discuss the snow deposition and sublimation-condensation process that alter the impurity concentrations and water stable isotope ratios, considering the development of density and microstructure of firn.
To investigate and select a site for the third Dome Fuji deep core drilling, one of the base camp was placed at about 54 km south of the Dome Fuji station (tentatively named as NDF , 77°47’18S, 39°3’15E, 3763 m a.s.l.), where a 152-m firn core was collected in December 2017. In this area, the accumulation rate is extremely low, and the surface snow is affected by sublimation and condensation for a long period. We performed multiple high-resolution (2.5-20 mm depth increment) continuous measurements of physical and chemical properties on this core. The properties include (1) density measured by a gamma-ray absorption method, (2) microwave permittivity ε as a proxy for density, (3) dielectric anisotropy Δε as a proxy for vertical elongation of ice and pore spaces, (4) reflectance R for near-infrared light as a proxy for specific surface area, and (5) water stable isotope ratios δ18O, δD, (6) concentration of major elements (Na, Mg, Al, S, K, Ca, Fe) measured by a continuous flow analysis system. Here, we mainly focus on the surface roughly down to a depth of 10 m.
We found significant positive correlations between ρ, ε, Δε, R, δ18O, and δD, calculated within 1-m segments, near the surface. We also found significant negative correlations between these properties and the concentration of all the major elements, although impurities in the precipitation must show different seasonal fluctuations. Hoshina et al. (2016) suggested that the negative correlations between impurity concentrations and δ18O at low-accumulation site can be formed by long-term sublimation and condensation within snow and between snow and atmosphere, which alter the original signal. However, the detailed process has not been clarified. In the JpGU presentation, we will discuss the snow deposition and sublimation-condensation process that alter the impurity concentrations and water stable isotope ratios, considering the development of density and microstructure of firn.