Long-term development of a perennial firn aquifer on the Lomonosovfonna ice cap, Svalbard

Abstract. An uncertain factor in assessing future sea level rise is the meltwater runoff buffering capacity of snow and firn on glaciers and ice caps. Field studies have resulted in observations of perennial firn aquifers (PFAs), which are bodies of water present deep in the firn layer and sheltered from cold surface conditions. PFAs can store surface melt, thereby acting as a buffer against sea level rise, and influence the thermodynamics of the firn layer. Furthermore, ice dynamics might be affected by the presence of liquid water through hydrofracturing and water transport to the bed, influencing bed properties and ice flow. In this study, we present results of applying the US Geological Survey (USGS) Modular Hydrological Model MODFLOW 6 to an observed perennial firn aquifer on the Lomonosovfonna ice cap in central Svalbard. The observations span a 3-year period, where a ground-penetrating radar (GPR) was used to measure the water table depth of the aquifer. We calibrate our model against these observations to infer a hydraulic conductivity of firn snow of 6.4×10-4 m s−1 and then use the model to project the aquifer evolution over the period 1957–2019. We find that the aquifer was present in 1957 and that it steadily grew over the modeled period with a relative increase of about 15 % in water table depth. On an annual basis, the aquifer exhibits sharp water table increases during the melt season, followed by slow seepage through the cold season.