Fig. 4

Vertical ice shelf displacement with water depths and seasonal meltwater budgets for WT and Peanut lake sites. a is for WT and b is for Peanut. 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. The fourth plot for the WT site shows water depth data from a pressure sensor nearest to GPS 1 (Fig. 1b, green open circles). The bottom three plots for each site show the calculated seasonal net meltwater budgets around each GPS station. The black lines (and grey shaded areas) show cumulative volumes of meltwater production (and errors) 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