Fig. 3

Vertical ice shelf displacement with water depths and seasonal meltwater budgets for Ring and Rift Tip lake sites. a is for Ring, and b is for Rift Tip. For each site, the top three plots show the vertical ice-shelf displacement (relative to arbitrary elevation) from three GPS stations (Fig. 1b, red stars). The first red dot above each time series shows when GPS 1 reaches its highest elevation, before reaching its lowest elevation, shown by a second red dot. The third red dot indicates when GPS 1 reaches its highest elevation during the whole time period. Numbers next to red arrows (which depict the direction of movement) are the total vertical deflections, and deflection rates, measured by each GPS over the two respective time periods between the first and second red dots, and the second and third red dots. Some of the elevation data for Rift Tip GPS 1 are missing so are linearly interpolated (dashed-red line). The fourth plot for each lake site shows water depth data from the pressure sensor nearest to each GPS 1 (Fig. 1b, green open circles). Water depths relative to lake bottom were estimated from sensors fixed at constant heights (see Methods). The bottom three plots at each site show the calculated seasonal meltwater budgets around each GPS station. The black lines (and grey shading) show cumulative volumes (and errors) of meltwater production calculated by a PDD model; light blue dots show the measured volumes of meltwater ponding from 9 cloud-free Landsat 8 images (see Supplementary Table 2 for image dates), and the dashed-light blue lines show these data linearly interpolated between the image dates; purple dots (and whiskers) show the net meltwater budget (and errors) on each image date, and the dashed-purple lines show these data linearly interpolated between the dates. Purple numbers next to the net meltwater budget plots refer to the seasonal net meltwater budgets, each defined as the maximum minus minimum net meltwater budget during the melt season, which are all negative. See Methods for details of GPS and water-depth data processing, and meltwater budget and error calculations