Fig. 1

Study site on the McMurdo Ice Sheet in the vicinity of McMurdo Station and Scott Base. The background of both a and b is a WorldView-2 image (©2016, DigitalGlobe) dated 2 December 2016. In a, the green star in the top-left inset indicates the location of the McMIS, and the black arrow indicates the local ice flow direction and speed (∼335° True at ∼28 m a⁻¹), based on our own GPS velocity data from the 2016/2017 austral summer. The red box indicates the location of our study site, shown in b, in which the four lake sites are labelled. At each lake site, the locations of three GPS stations are marked with red stars (labelled 1 to 3, where 1 is closest to the lake centre and 3 is furthest away). Green open circles mark the locations of pressure sensors; data from three of these are shown in Figs. 3 and 4. A yellow star marks the location of the automatic weather station (AWS), and a blue circle marks the location of a time-lapse camera (used to produce Supplementary Movie 1 and Supplementary Fig. 1). The dashed-white circles of r = 250 m, centred on each of the 12 GPSs, show the areas where seasonal meltwater budgets were calculated. (N.B. Rift Tip lake was originally named in a previous (2015/2016) fieldwork season, when it was at the end of a rift. Although this rift has since propagated westwards by ~3 km (ref. ²¹), we have kept the original name)