A New View from Within: Borehole Pressure Sensors and the Measurement of Glacier Mass Balance

High-sensitivity borehole pressure sensors provide a novel means of monitoring the surface mass balance (SMB) of Earth’s great ice sheets. When properly coupled to the ice, these instruments are expected to detect millimeter-scale changes in ice thickness corresponding to variations in snow accumulation. The Boussinesq solution guarantees that a pressure sensor buried at a depth of 1000 m will represent a spatially weighted average of surface mass load variations with an approximate radius of 1000 m at the surface. The sensing system itself consists of a pressure sensor connected to a pressure coupling element such as a sack filled with antifreeze. Once freeze-in related transients have passed, the internal fluid pressure in the sack reflects the full overburden stress exerted by the overlying ice column. Long term drift of the sensors requires special engineering attention and may be corrected for using some combination of pre-deployment pressurization, in situ calibration, and/or the use of multiple in situ sensors. We discuss deployment considerations using the IceDiver thermal melt probe for a potential deployment at Greenland Summit Station. The borehole SMB observatory described here supports altimetry-based inference of glacier mass change, provides a critical dataset for validating firn densification models, and establishes a fundamentally new approach to measuring glacier mass balance.