Abstract
ABSTRACTHigh-latitude atmospheric warming is impacting freshwater cycling, requiring techniques for monitoring the hydrology of sparsely-gauged regions. The submarine runoff of tidewater glaciers presents a particular challenge. We evaluate the utility of Moderate Resolution Imaging Spectroradiometer (MODIS) imagery for monitoring turbid meltwater plume variability in the glacier lagoon Jökulsárlón, Iceland, for a short interval before the onset of the main melt season. Total Suspended Solids concentrations (TSS) of surface waters are related to remotely-sensed reflectance via empirical calibration between in-situ-sampled TSS and reflectance in a MODIS band 1-equivalent wavelength window. This study differs from previous ones in its application to an overturning tidewater glacier plume, rather than one derived from river runoff. The linear calibration improves on previous studies by facilitating a wider range of plume metrics than areal extent, notably pixel-by-pixel TSS values. Increasing values of minimum plume TSS over the study interval credibly represent rising overall turbidity in the lagoon as melting accumulates. Plume extent responds principally to consistently-strong offshore winds. Further work is required to determine the temporal persistence of the calibration, but remote plume observation holds promise for monitoring hydrological outputs from ungauged or ungaugeable systems.
Highlights
One of the most important ways in which Arctic hydrology is responding to rapid atmospheric warming is by changing the timing and magnitude of freshwater runoff to the marine environment, with potentially profound implications for coastal circulation, fluxes of sediment and nutrients to nearshore ecosystems and zooplankton productivity (Statham and others, 2008; Arendt and others, 2011)
The corresponding reflectance varies with wavelength, there is a consistent response in a window that corresponds to Moderate Resolution Imaging Spectroradiometer (MODIS) band 1 (B1, 620–670 nm; Fig. 2a)
Total Suspended Solids concentrations (TSS) 1⁄4 4:7004ref (R2 = 0.74, p = 0.00) where ref is reflectance in B1 or the 620–670 nm wavelength window (Fig. 2c; Chen and others, 2015). This simple calibration has the benefit of being linear for the range of TSS sampled in April 2012, with no indication of the reflectance saturation observed in some comparable studies, for example, Chu and others (2009), who measured higher reflectances for a given TSS
Summary
One of the most important ways in which Arctic hydrology is responding to rapid atmospheric warming is by changing the timing and magnitude of freshwater runoff to the marine environment, with potentially profound implications for coastal circulation, fluxes of sediment and nutrients to nearshore ecosystems and zooplankton productivity (Statham and others, 2008; Arendt and others, 2011). Fundamental problem is that runoff from tidewater glaciers emerges in an inaccessible, submarine location and cannot be measured or monitored directly (Straneo and others, 2013). This runoff is fresh, buoyant and often turbid; it frequently forms observable, overturning plumes (Chu, 2013). These plumes are typically much wider than many river channels, and so more amenable to observation with remotely-sensed imagery Their characteristics can be measured and their variations tracked, which is of benefit for the study of both the large-scale hydrology of remote, ungauged (and ungaugeable) regions, and the stability and dynamics of large glaciers draining ice sheets
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