Impacts of an accumulation hiatus on the physical properties of firn at a low-accumulation polar site

摘要

Recent field investigations of a megadune region of East Antarctica provide evidence that differences in grain size, thermal conductivity, and permeability across a megadune profile are due to spatial accumulation variability in the absence of significant microclimate variations. The megadunes are low-amplitude (2–8 m), long-wavelength (2–5 km) bands with perceptible but low accumulation (less than 40 mm water equivalent (weq) yr~(-1)) and accumulation hiatus within several kilometers proximity, as determined by remote sensing, surface feature classification, and ground-penetrating radar profiling. Our hypothesis that accumulation rate impacts the extent of temperature gradient–driven metamorphic growth in low accumulation rate sites is supported by measurements of various firn physical properties. Relatively small differences in accumulation rate (less than 40 mm weq yr~(-1)) result in large differences in physical properties, including grain size, thermal conductivity, and permeability, which are apparent in satellite-based microwave data from both passive and active sensors. The differences in physical snow structure between low-accumulation areas and accumulation hiatus areas in the near surface are sufficiently distinct that evidence of past accumulation hiatus should be observable in the physical and chemical properties of an ice core record.