Response of supraglacial rivers and lakes to ice flow and surface melt on the northeast Greenland ice sheet during the 2017 melt season

Abstract

Fast ice flow and substantial surface runoff form distinct and extensive supraglacial rivers and lakes on the northeast Greenland Ice Sheet (GrIS). These supraglacial rivers and lakes play an important role in controlling surface meltwater routing and storage. However, the hydromorphology of these complex supraglacial features remains poorly quantified. In this study, we mapped the multi-temporal supraglacial rivers and lakes on the northeast GrIS (area ~ 3 × 104 km2) using sixty-five 10 m Sentinel-2 multispectral satellite images acquired during the 2017 summer, and quantified their primary hydromorphology, including meltwater area fraction, meltwater volume, supraglacial river length, river sinuosity, river depth, supraglacial lake area, lake shape, and lake depth. The quantified hydromorphology was compared with variable ice flow regimes and regional climate model (RCM) runoff. The results indicate that widespread supraglacial rivers and lakes maximally cover 5.3% of the northeast GrIS, which is more than double the previous estimates and only slightly lower than that for the strongly melting southwest GrIS (~7.0%). As the surface runoff increases and the snowline retreats, supraglacial rivers and lakes migrate from the ice sheet margin (~400 m) to high elevations (~1400 m). The satellite-mapped surface meltwater area fraction for the entire study area is positively correlated with the RCM surface runoff before the timing of peak melt (August 1), but decreases relatively slowly (by 32–45%) compared to the rapidly decreasing runoff (by 84–96%) in August. Large elevational variations were found for the peak magnitude and timing of the meltwater extent and volume. High (800–1400 m) elevation bands achieve peak values over two weeks later than low (400–800 m) elevation bands, and the 800–1000 m elevation band yields maximum peak values due to the wide distribution of supraglacial rivers. Furthermore, the supraglacial drainage patterns vary with different ice flow regimes. There are long rivers and few lakes in areas where ice deformation controls the ice flow velocity while there are short rivers and large, narrow lakes in areas where basal sliding is a major component of the ice flow. Meanwhile, long, sinuous rivers and small lakes form on the floating ice. In general, this study conducts a preliminary investigation of supraglacial rivers and lakes on the poorly-studied northeast GrIS and reveals that surface melt and ice flow control the hydromorphology of supraglacial rivers and lakes.