Inland advance of supraglacial lakes in north-west Greenland under recent climatic warming

Abstract

ABSTRACT. The inland advance of supraglacial lakes (SGLs) towards the interior regions of the Greenland ice sheet (GrIS) may have implications for the water volumes reaching the subglacial drainage system, and could consequently affect long-term ice-sheet dynamics. Here, we investigate changes to the areas, volumes and elevation distributions of over 8000 manually delineated SGLs using 44 Landsat images of a 6200 km 2 sector of north-west Greenland over three decades . Our resultsshow that SGLs have advanced to higher maximum (+418 m) and mean (+299 m) elevations, and that there has been a near-doubling of total regional SGL areas and volumes over the study period, accelerating after 2000. These changes were primarily caused by an increased SGL area and volume at high (≥1200 m a.s.l.) elevations, where SGL coverage increased by over 2750% during the study period. Many of the observed changes, particularly the post-2000 accelerations, were driven by changes to regional surface-temperature anomalies. This study demonstrates the past and accelerating response of the GrIS's hydrological system due to climatic warming, indicating an urgent need to understand whether the increasingly inland SGLs will be capable of hydrofracture in the future, thus determining their potential implications for ice-sheet dynamics.

Dual-satellite (Sentinel-2 and Landsat 8) remote sensing of supraglacial lakes in Greenland

“…We chose this study location because it is an area of high lake activity, having been the focus of many previous remote-sensing studies with which our results can be compared (e.g. Box and Ski, 2007;Selmes et al, 2011;Miles et al, 2017;Williamson et al, 2017Williamson et al, , 2018.…”

“…The raw digital numbers were converted to top-of-atmosphere (TOA) reflectance using the image metadata and the USGS Landsat 8 equations (available at: https://landsat.usgs.gov/landsat-8-l8-data-users-handbook-section-5). Landsat 8 TOA values adequately 145 represent surface reflectance in Greenland and have been used previously for studying GrIS hydrology Miles et al, 2017;Williamson et al, 2017Williamson et al, , 2018Macdonald et al, in press). Our cloud-masking procedure involved marking pixels as cloudy when their band-6 TOA reflectance value exceeded 0.100 (Fig.…”

“…From the time series, a lake was classified as draining rapidly if two criteria were met: (i) it lost > 80% of its maximum seasonal volume in ≤ 4 days (following Doyle et al, 2014;Miles et al, 2017;Williamson et al, 2017Williamson et al, , 2018;…”

“…Most research to date has used MODIS imagery to identify rapidly draining lakes because the high temporal resolution is required to separate rapidly draining lakes from those draining slowly. Although this 500 MODIS-based research has been helpful for quantifying the characteristics of relatively large lakes (≥ 0.125 km 2 ) and the potential controls on their rapid drainage (Box and Ski, 2007;Morriss et al, 2013;Williamson et al, 2017Williamson et al, , 2018, such work has been unable to study smaller (< 0.125 km 2 ) lakes.…”

“…Second, many lakes affect the dynamic component of the GrIS's mass balance when they drain either "slowly" or "rapidly" in the mid-to late melt season (e.g. Palmer 2013;Liang et al, 2012;Morriss et al, 2013;Everett et al, 2016;Williamson et al, 2017Williamson et al, , 2018. However, this lower spatial resolution means that lakes < 0.125 km 2 cannot be confidently resolved Williamson et al, 2017) and even lakes that exceed this size are often omitted 80 from the satellite record (Leeson et al, 2013;Williamson et al, 2017).…”