Modelling the long-term mass balance and firn evolution of glaciers around Kongsfjorden, Svalbard

Abstract

We analyse the long-term (1961-2012) distributed surface mass balance and firn evolution of the Kongsvegen and Holtedahlfonna glacier systems in northwestern Svalbard. We couple a surface energy-balance model to a firn model, with forcing provided from regional climate model output. In situ observational data are used to calibrate model parameters and validate the output. The simulated area-averaged surface mass balance for 1961-2012 is slightly positive (0.08mw.e. a- 1), which only fractionally compensates for mass loss by calving. Refreezing of percolating water in spring/summer (0.13mw.e. a- 1) and stored water in fall/winter (0.18mw.e. a- 1) provides a buffer for runoff. Internal accumulation, i.e. refreezing below the previous year's summer surface in the accumulation zone, peaks up to 0.22mw.e. a- 1, and is unaccounted for by stake observations. Superimposed ice formation in the lower accumulation zone ranges as high as 0.25mw.e. a- 1. A comparison of the periods 1961-99 and 2000-12 reveals 21% higher annual melt rates since 2000 and a 31% increase in runoff, which can only in part be ascribed to recent warmer and drier conditions. In response to firn line retreat, both albedo lowering (snow/ice-albedo feedback) and lower refreezing rates (refreezing feedback) further amplified runoff.