Meltwater and sediment dynamics of the Greenland Ice Sheet
MA: University of Colorado Boulder, .
The Greenland Ice Sheet (GrIS) is an important part of the Earth system, impacting climate, Earth’s surface, and the ocean. Its melt delivers freshwater to fjords and the coastal ocean, influencing sea level, ocean circulation, and sea ice formation. Its sediment decreases fjord light availability and delivers nutrients to the ocean. Sediment also fills fjord basins, builds Greenland’s continental shelf, and serves as an archive of the Earth’s past.
GrIS baseline meltwater and sediment dynamics are poorly characterized. Only one river out of approximately 300 in Greenland has a discharge record > 5 years and sediment dynamics have been studied at limited locations. Even less well understood is how ‘downstream’ systems respond to GrIS mass loss, the rate of which has quadrupled since the 1990s. This work used field and satellite techniques to better characterize understudied meltwater and sediment dynamics of the GrIS.
First, I assessed Greenland river plume dynamics between 2000 and 2012 using NASA MODIS (Moderate Resolution Imaging Spectroradiometer) imagery. Sediment plumes did not respond uniformly to increased melt. Plume size grew for only 50% of study rivers due to highly variable sediment export from the GrIS. Concurrently with this work, I developed a novel cloud mask.
I then explored the dynamics of an unprecedented 160 rivers using Landsat7 imagery and the Google Earth Engine cloud-computing platform. Certain outlets are hotspots of sediment export and erosion. Further, the island as a whole is a hotspot of global sediment production: from 1 % of the Earth’s land surface, it generates 5% to 12% the total sediment exported to the ocean. This sediment is a significant, bioavailable source of iron in the ocean.
Finally, I developed two space-based discharge-estimation techniques. This work gauged two unstudied rivers and unified techniques using river inundation and sediment plumes. Together, these approaches allowed discharge reconstructions that often doubled record lengths. This work also allowed comparisons to modeled GrIS runoff, finding that additional processes need to be incorporated into numerical models.