Concerning the Deposition and Diagenesis of Strata in Polar Firn

• Published in: Journal of Glaciology
• Main Author: Alley, Richard B.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1988
• Subjects: Journal of Glaciology
• Online Access: http://dx.doi.org/10.1017/s0022143000007024; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000007024

Abstract Depth hoar in polar firn 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 firn. 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 firn, 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. Depositional depth-hoar layers may develop at any season, are relatively thin, and have irregular bases. In low-accumulation regions, visual stratification may preserve only an annual signal, but in high-accumulation regions individual storms or other features may be recognizable.