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

Abstract

We investigate causes of the stratigraphic variation revealed in a 177 km, 400 MHz shortpulse radar profile of firn from West Antarctica. The profile covers 56 m depth, and its direction was close to those of the ice flow and mean wind. The average, near-surface accumulation rates calculated from the time delays of one radar horizon consistently show minima on leeward slopes and maxima on windward slopes, confirming an earlier study based on stake observations. The stratigraphic variation includes up to 30 m depth variation in individual horizons over tens of km, fold limbs that become progressively steeper with depth, and fold-hinge loci that change direction or propagate down-ice with depth over distances far less than predicted by the ice speeds. We use an accumulation rate model to show how local rate anomalies and the effect of ice speed upon a periodic variation in accumulation rate cause these phenomena, and we reproduce two key features seen in the stratigraphic variations. We conclude that the model provides an explanation of changes in spatial stratigraphy and local measures of accumulation history given the constraints of surface topography, ice and wind velocities, and a general accumulation rate for an area.

Snow accumulation variability derived from radar and firn core data along a 600 km transect in Adelie Land, East Antarctic plateau

“…7 is a wellknown feature caused by spatial variations in accumulation rates (see e.g. Arcone et al, 2005b). To conclude, the undulations we observe would be the result of accumulation variations caused by interactions between katabatic wind and local topography.…”

“…To conclude, the undulations we observe would be the result of accumulation variations caused by interactions between katabatic wind and local topography. These processes are described in Arcone et al (2005b).…”

“…Several authors have investigated the origin of reflections in firn (e.g. Hempel et al, 2000;Eisen et al, 2003a,b;Kohler et al, 2003;Arcone et al, 2005b), but it is still unclear how continuous reflecting horizons are produced in firn and ice. In particular, "there remains some uncertainty about how the material properties in firn combine to form the continuous reflecting horizons" (Eisen et al, 2008).…”

Non-climatic signal in ice core records: lessons from Antarctic megadunes

“…As pointed by Arcone et al (2005), the apparent dune drift velocity observed in the GPR images is a combination of the real dune velocity and the ice movement, and the real dune velocity is higher than the observed one. According to (Richter et al, 2013), ice flow velocities in this region do not exceed 2 m yr −1 , so the real dune drift velocity could be up to 6.6 m yr −1 .…”

Snow accumulation and compaction derived from GPR data near Ross Island, Antarctica

“…Reflections seen in radar recordings can sometimes be associated with distinct accumulation or melt events, or depth hoar layers (Eisen et al, 2004;Arcone et al, 2005;Helm et al, 2007;Dunse et al, 2008). Analysis of internal layers in ice and snow with commercial GPR systems for estimating accumulation has been demonstrated by Arcone et al (2004), Dunse et al (2008), and Heilig et al (2010), amongst others.…”