Variability of subglacial discharge recorded with thermal infrared timelapse of a tidewater glacier, West Greenland

Abstract:

Subglacial hydrology and the dynamics therein are important modulators of ice flow in the Greenland Ice Sheet. At tidewater outlet glaciers the characteristics of proglacial discharge affect fjord circulation, sediment deposition, submarine melt rates, and iceberg calving. Information about the spatio-temporal variability of discharge is limited by the challenges of in situ data collection at tidewater glaciers. Here, we present summertime measurements of subglacial discharge variability using a thermal infrared (7.5μm to 13μm) camera and intervalometer at Kangerlussuup Sermia (KS), a ~4km wide outlet glacier in the Uummannaq Bay region of West Greenland (71.46 N, 51.43 W). KS has an advantageous geometry for this investigation because of its shallow grounding zone and well-entrenched subglacial hydrologic system. In tandem, these characteristics promote buoyant freshwater to rise to the fjord surface from discrete outlets at the glacier's base. We investigate the timing of plume activity at these outlets and discuss potential controls on outlet switching.

Raw camera measurements cannot be accurately converted to surface temperature without correcting for environmental variables and scene geometry, both of which are time-evolving during data acquisition. Our processing methodology relies on a variety of existing techniques -- image segmentation, ray casting, atmospheric radiative transfer modeling, Monte Carlo simulations -- and a variety of ancillary data products -- satellite imagery, atmospheric reanalysis, meteorologic and hydrologic measurements -- to produce the final results. What is gained is an unprecedented view into interactions between the cryosphere, hydrosphere, and atmosphere that control the dynamic and sensitive terminus region of a tidewater outlet glacier.