Inverse estimation of snow accumulation along a radar transect on Nordenskiöldbreen, Svalbard

Abstract

We present an inverse modeling approach to reconstruct annual accumulation patterns from ground-penetrating radar (GPR) data. A coupled surface energy balance-snow model simulates surface melt and the evolution of subsurface density, temperature, and water content. The inverse problem consists of iteratively calibrating accumulation, serving as input for the model, by finding a match between modeled and observed radar travel times. The inverse method is applied to a 16 km GPR transect on Nordenskiöldbreen, Svalbard, yielding annual accumulation patterns for [2007][2008][2009][2010][2011][2012]. Accumulation patterns with a mean of 0.75 meter water equivalent (mwe) a −1 contain substantial spatial variability, with a mean annual standard deviation of 0.17 mwe a −1 , and show only partial consistency from year to year. In contrast to traditional methods, accounting for melt water percolation, refreezing, and runoff facilitates accurate accumulation reconstruction in areas with substantial melt. Additionally, accounting for horizontal density variability along the transect is shown to reduce spatial variability in reconstructed accumulation, whereas incorporating irreducible water storage lowers accumulation estimates. Correlating accumulation to terrain characteristics in the dominant wind direction indicates a strong preference of snow deposition on leeward slopes, whereas weaker correlations are found with terrain curvature. Sensitivity experiments reveal a nonlinear response of the mass balance to accumulation changes. The related negative impact of small-scale accumulation variability on the mean net mass balance is quantified, yielding a negligible impact in the accumulation zone and a negative impact of −0.09 mwe a −1 in the ablation area.

A plot-scale study of firn stratigraphy at Lomonosovfonna, Svalbard, using ice cores, borehole video and GPR surveys in 2012–14

“…In line with earlier studies (Dunse and others, 2008;Brown and others, 2011;Van Pelt and others, 2014;Sold and others, 2015) we suggest that most of the prominent maxima in the composite data from our radar and video surveys originate at the firn horizons exposed to melt at the end of ablation seasons (summer surfaces). The rate and pattern of water infiltration through snow and firn is highly dependent on the structure of the media (Campbell and others, 2006).…”

“…In 2012 the summer surfaces found by Van Pelt and others (2014) (coloured labels at 4.0, 5.6, 7.5, 8.9 and 9.9 m in Fig. 7a, also see Fig.…”

“…7a) fall between the summer surfaces from Van Pelt and others (2014). They are also noticeable on the 500 MHz radargrams (Van Pelt and others, 2014) but were not regarded as buried summer surfaces based on the lack of lateral consistency on the kilometre scale.…”

“…Recent field and modelling results in the area showed that at the elevation of the study site the average accumulation rate during 2007-12 is ≈0.75 m w.e. a −1 (Van Pelt and others, 2014) and the melt rate during 1989-2010 was on average ≈0.34 m w.e. a −1 (Van Pelt and others, 2012).…”

“…To test if the maxima in our grid-averaged GPR and also video data likewise originate at the buried summer surfaces, we compare their depths with positions of the summer surfaces 2011-2007 detected by Van Pelt and others (2014) in a 15 km long 500 MHz GPR profile done at Lomonosovfonna and Nordenskiöldbreen in April 2012. The uppermost point of this profile was within 10 m from our plot and is used here for comparison.…”