Concerning the Deposition and Diagenesis of Strata in Polar Firn

Abstract

ABSTRACT. Depth hoar in polar fim forms when large temperature gradients act on low-density firn, but high-density firn does not develop into depth hoar. Low densities in firn may be depositional (burial of surface hoar or still-air snowfall) or diagenetic (mass loss to the freE( atmosphere, typically in autumn); however, diagenesis is sufficiently strong to cause significant mass loss only in the top 50-100 mm of fim. Between about 50-100 mm and 2 m depth, grain growth and densification are accelerated strongly by temperature-gradient effects; from 2 to 5 m, temperature gradients have a small but measurable effect on rates of processes in fim, and below 5 m rates essentially have isothermal values.Diagenetic depth-hoar layers typically develop in the autumn, are relatively thick, and have smooth bases.

Stratigraphic variation within polar firn caused by differential accumulation and ice flow: interpretation of a 400 MHz short-pulse radar profile from West Antarctica

“…Spikes and others (2004) show that these horizons are, indeed, isochrones, as has long been assumed. Arcone and others (2004, in press) argue that the general variation of horizon amplitude with depth, their -25 to -50 dB reflection coefficients and the consistent phase structure of their wavelets are consistent with the stratification processes caused by the post-depositional snow metamorphosis and sublimation that form couplets of hoar and ice (Alley, 1988).…”

Snow megadunes in Antarctica: Sedimentary structure and genesis

“…Glazed surfaces were one of the common features observed in the megadune area and consist of thin (0.1 to 2 mm) films of regelated ice. When the wind capacity for snow transportation exceeds the snow supply the snow surface is scoured clean and flat and suffers neither erosion nor deposition [ Gow , 1965; Alley , 1988]. The regelated ice films form on the surface following the kinetic heating by saltant drift snow under constant katabatic wind flow [ Goodwin , 1990].…”

“…When wind speeds decrease, such dunes sinter rapidly into hard features of positive relief. After sintering, wind erosion of the dune typically produces scoops and hollows with the formation of sastrugi [ Alley , 1988]. Dunes and sastrugi are believed to ablate faster than adjacent flat areas, because microrelief surfaces are more exposed to wind; thus both erosion and deposition tend to smooth the snow surface [ Gow , 1965; Weller , 1969].…”

Firn Stratigraphic Genesis in Early Spring: Evidence From Airborne Radar

“…This false assumption can mask the actual correlation between the radar-detected SILs and other observed or modeled data sets with finer temporal resolutions. The connection between the radar-detected SILs and the presence of depth hoar and ice crust layers is well known [23], [24], with the formation caused by strong internal thermal gradients. Such gradients occur when the snow below the surface is warmed by penetrating sunlight, while the snow surface is still cold.…”

“…Such gradients occur when the snow below the surface is warmed by penetrating sunlight, while the snow surface is still cold. The standard conceptual model of snow deposition/diagenesis [24] postulates that autumn is when most layers should form because that is when the near-surface snow is warmest. However, sunlight also penetrates in the spring and may cause temporary conditions for depth hoar formation [25].…”