Fig. 3: Schematic of core stratigraphy, drilling technology sequence and estimated temperature profile (not to scale).
From: Rare ice-base temperature measurements in Antarctica reveal a cold base in contrast with predictions
a The stratigraphy is typical for the dry-snow accumulation zone. The boundaries between snow, firn, and bubbly ice are defined by core density47 and are conventionally drawn at densities of about 550 kg m-3 and 830 kg m-3. b The borehole construction consisted of the following steps: (1) dry core drilling of the upper permeable snow–firn layer with an auger drill; (2) fluid core drilling of glacial ice using bottom fluid reverse circulation; (3) drilling through debris-rich ice with a PDC drill bit; and (4) bedrock core drilling. c The measured borehole temperature (red dots) and estimated temperature profile with a zone with a negative geothermal gradient down to a depth of ∼135 m. Further down, the temperature profile increases with depth with an approximate mean gradient of 3.5 °C / 100 m.
