An Enhanced Vapor Transport and Sublimation Model using 10+ Years of Field Measurements of Earth's Oldest Ground Ice in Beacon Valley, Antarctica

Ground ice in the Antarctic Dry Valleys is fundamentally important as a reservoir of water, proxy for climatic information, and a major component of the periglacial landscape. It is also one of Earth's closest analog for widespread, near-surface ice found in Martian soils. While the exact antiquity of the ground ice at Beacon Valley is still under discussion, considerable evidence suggests that it is the oldest known ice on Earth. Why this ice can persist for so long is still unclear since models based solely on water vapor fluxes predict drying of the soil to depths of several meters within only a few thousand years; however, ice persists in the ground at depths of only a few decimeters. Other independent data of a profile of cosmogenic isotopes of ¹⁰Be in the ice and quartz grains within the ice indicates that, on time scales of ~10⁵ years or more, ice sublimates much more slowly. The interest in determining the age of relict ice in Beacon Valley, Antarctica, as well as the discrepancy between theoretical modeled and field sample-based ground ice sublimation rates are bringing renewed attention to this ice. Here we present an enhanced model of water vapor diffusion and corresponding sublimation using detailed climate and soil temperature data from 1999 to 2011 in Beacon Valley, where the massive ground ice is found as close as ~0.30 m below the surface. This is the first model to incorporate the effect of snow cover and snow melt on the soil vapor pressure that is based on actual field measurements using a camera and electrical conductivity probes. It suggests that water vapor condenses in the upper dry soil during the winter but is completely lost to the atmosphere during the austral summer. Episodic snowmelt events and snow cover in the summer temporarily reverses the vapor transport and reduces the annual ice loss. These episodic events slow down the sublimation rates by one-third; this effect is likely to be extended due to persistence of water in the top layers of the ground where sensors are not installed. Our enhanced model indicates that ice currently sublimates at 0.12 mm a^-1, which approaches consistency with the ¹⁰Be data. The current modeled rate is larger by over a factor of 2 than the ¹⁰Be-drived rate but this may be explained because current temperatures are warmer than they have been on average over much of the Quaternary.