Figure S7. Correlations between calculated subglacial storage proxies and ice motion: (a) GPS-derived storage proxy S (surface elevation), (b) GPS-derived change in storage, ΔS (surface elevation derivative) (c) meltwater-derived storage proxy S (cumulative input- output), and (d) meltwater-derived change in storage, ΔS (6h input-output). These correlations use a cross-correlation value of 0 (e.g. no time offset correction to ice velocity). Linear correlations (r ) and p -values indicating statistical significance (p ) are shown in the bottom right corner of each plot. Discharge-difference ΔS shows strongest overall correlation with ice speed (r =0.79, panel d).