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

Abstract

Abstract. We present an improved method for estimating accumulation and compaction rates of dry snow in Antarctica with ground penetrating radar (GPR). Using an estimate of the emitted waveform from direct measurements, we apply deterministic deconvolution via the Fourier domain to GPR data with a nominal frequency of 500 MHz. This reveals unambiguous reflection horizons which can be observed in repeat measurements made one year apart. At two measurement sites near Scott Base, Antarctica, we extrapolate point measurements of average accumulation from snow pits and firn cores to a larger area by identifying a dateable dust layer horizon in the radargrams. Over an 800 m × 800 m area on the McMurdo Ice Shelf (77 • 45 S, 167 • 17 E) the average accumulation is found to be 269 ± 9 kg m −2 a −1 . The accumulation over an area of 400 m× 400 m on Ross Island (77 • 40 S, 167 • 11 E, 350 m a.s.l.) is found to be higher (404 ± 22 kg m −2 a −1 ) and shows increased variability related to undulating terrain. Compaction of snow between 2 m and 13 m depth is estimated at both sites by tracking several internal reflection horizons along the radar profiles and calculating the average change in separation of horizon pairs from one year to the next. The derived compaction rates range from 7 cm m −1 at a depth of 2 m, down to no measurable compaction at 13 m depth, and are similar to published values from point measurements.

Sea ice freeboard in McMurdo Sound, Antarctica, derived by surface-validated ICESat laser altimeter data

“…Linear extrapolation of the MY trend for M‐1 gives a mean freeboard of 0.20 m in 2001 suggesting that FY sea ice was present over most of McMurdo Sound at this time and MY sea ice developed thereafter. Assuming an upper estimate of annual snow accumulation of 300 mm yr −1 water equivalent as indicated by in situ and satellite measurements [ Kruetzmann et al ., ; Arthern et al ., ] suggests that only half of the observed increase in freeboard can be attributed to snowfall. The remainder of the observed growth in MY sea ice can be attributed to two separate processes.…”

Methodological approaches to infer end-of-winter snow distribution on alpine glaciers

“…Since the 1960s this has been used for ground-based or airborne detection of ice thickness (Robin and others, 1969; Bauder and others, 2003; Damm, 2004; Lalumiere and Prinsenberg, 2009) or internal layers within snow and firn (Kohler and others, 1997; Kanagaratnam and others, 2004; Dunse and others, 2009; Heilig and others, 2010). Radar-based surveys of snow accumulation distribution have focused on ice sheets (Helm and others, 2007; Dunse and others, 2008; Eisen and others, 2008; Kruetzmann and others, 2011) and snow on the ground (Marchand and others, 2003; Yankielun and others, 2004; Marshall and Koh, 2008). For mapping snow accumulation on alpine glaciers, however, the airborne application of GPR has only been addressed by Machguth and others (2006b), although results show that it can be a highly effective tool, especially in remote and inaccessible areas.…”

Antarctic firn compaction rates from repeat-track airborne radar data: I. Methods

“…t 2 – t 1 ) yields the firn compaction rate (m a −1 ). Both ground and airborne radar systems image the internal stratigraphy in the firn column; however, few studies have used these natural markers to determine firn compaction rates (Kruetzmann and others, 2011; Simonsen and others, 2013). Recent work by Medley and others (2013) highlighted the potential of imaging the internal stratigraphy of the firn column from airborne radar data for determination of the spatio-temporal variability in SMB and produced a dataset with which to test various SMB model outputs at the basin scale.…”