Mass Balance

Abstract

Michiel van den Broeke and Rianne Giesen 7.1 Introduction In this chapter we discuss the methods used to assess temporal mass changes of different ice masses-valley glaciers, ice caps and ice sheets. We provide definitions of the key terminology in Sect. 7.2 and discuss the main methods to observe and model glacier mass balance in Sect. 7.3. Next, we present the specific application of these methods to valley glaciers and ice caps in Sect. 7.4 and to the two large ice sheets of Antarctica (Sect. 7.5) and Greenland (Sect. 7.6). The reason for this subdivision is that the ice sheets are large enough to allow for direct observation of mass changes by satellite remote sensing and dynamical downscaling of surface processes (using for example regional climate models), while valley glaciers and ice caps are usually so small that they require statistical downscaling of satellite observations or global/regional atmospheric model output. 7.2 Definitions To be specific, let us consider an ice sheet or glacier which terminates in the ocean, so that it has a grounding line where it goes afloat. Glacier mass balance (MB, denoted as B, kg y −1) represents the temporal change of glacier mass M i , which, if we neglect basal melting of grounded ice and assume that the grounding line position is stationary, is governed by the difference between surface mass balance (SMB, denoted S) and ice discharge across the grounding line (D): M. van den Broeke (B) · R. Giesen