Sediment plume response to surface melting and supraglacial lake drainages on the Greenland ice sheet

Abstract

ABSTRACT. Increased mass losses from the Greenland ice sheet and inferred contributions to sea-level rise have heightened the need for hydrologic observations of meltwater exiting the ice sheet. We explore whether temporal variations in ice-sheet surface hydrology can be linked to the development of a downstream sediment plume in Kangerlussuaq Fjord by comparing: (1) plume area and suspended sediment concentration from Moderate Resolution Imaging Spectroradiometer (MODIS) imagery and field data; (2) ice-sheet melt extent from Special Sensor Microwave/Imager (SSM/I) passive microwave data; and (3) supraglacial lake drainage events from MODIS. Results confirm that the origin of the sediment plume is meltwater release from the ice sheet. Interannual variations in plume area reflect interannual variations in surface melting. Plumes appear almost immediately with seasonal surface-melt onset, provided the estuary is free of landfast sea ice. A seasonal hysteresis between melt extent and plume area suggests late-season exhaustion in sediment supply. Analysis of plume sensitivity to supraglacial events is less conclusive, with 69% of melt pulses and 38% of lake drainage events triggering an increase in plume area. We conclude that remote sensing of sediment plume behavior offers a novel tool for detecting the presence, timing and interannual variability of meltwater release from the ice sheet.

Quantifying suspended sediment concentration in subglacial sediment plumes discharging from two Svalbard tidewater glaciers using Landsat-8 and in situ measurements

“…As turbidity increases and sediment concentrations reach values >80 mg l the surface reflectance saturates (e.g. Chu et al 2009), and the accuracy of determining SSC from surface reflectance decreases. Doxaran et al (2002) showed reflectance in the 700-900 nm (NIR) range was approximately zero for SSC values less than 50 mg l −1 but increased as SSC grew; therefore, the use of the NIR band is ideal in extremely turbid waters with high sediment concentrations.…”

“…This study focuses on the suspended sediment concentration (SSC) of subglacial meltwater plumes; we therefore chose wavelengths optimal for detecting minerals. In less turbid waters, the wavelength can be restricted to visible bands (Binding, Bowers, and Mitchelson-Jacob 2005) as early studies were successful using the MODIS (Moderate Resolution Imaging Spectroradiometer) red band (620-670 nm, 250 m) to calculate SSC (Miller and McKee 2004;Chu et al 2009;McGrath et al 2010;Chu et al 2012;Tedstone and Arnold 2012). As turbidity increases and sediment concentrations reach values >80 mg l the surface reflectance saturates (e.g.…”

“…However, sediment plumes remain an indicator of subglacially transported meltwater and capture meltwater discharge, thereby integrating poorly constrained processes of meltwater refreezing and water storage (McGrath et al 2010). Sediment plumes have been used as a proxy for meltwater run-off at land-terminating glaciers (Gurnell and Warburton 1990;Chu et al 2009;McGrath et al 2010) and can be used at tidewater glaciers if a new metric can be established to quantify sediment in plumes at tidewater margins.…”

“…Therefore, using remote sensing to observe meltwater discharge is optimal in these numerous inaccessible locations. Previous studies have used a combination of remote-sensing and in situ measurements to relate measured meltwater run-off with the behaviour of sediment plumes at both landterminating (Dowdeswell and Cromack 1991;Chu et al 2009) and tidewater glaciers (Chu et al 2012;Hudson et al 2014). Sediment plumes originate from subglacially transported meltwater that has collected glacially eroded fine-grained sediment along the way (Hallet, Hunter, and Bogen 1996;Hubbard and Nienow 1997).…”

“…The sediment plume is visible on the ocean surface if (1) there is sufficient sediment to transport, (2) there is enough water to transport the sediment, and (3) the meltwater plume doesn't equilibrate before the surface (at tidewater glaciers). Previous work has used satellite and in situ surface reflectance to delineate plume boundaries, and measure plume shape and size to compare against meltwater discharge (Chu et al 2009;Tedstone and Arnold 2012;Hudson et al 2014). …”