Date of Award

Spring 1-1-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geological Sciences

First Advisor

James P.M. Syvitski

Second Advisor

Irina Overeem

Third Advisor

Gregory E. Tucker

Fourth Advisor

Noah P. Molotch

Fifth Advisor

W. Tad Pfeffer

Abstract

The Greenland Ice Sheet (GrIS) is an important part of the Earth system, impacting climate, the land it occupies, and the ocean it borders. Its meltwater delivers fresh water 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 longer than 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 dissertation employs both field and satellite techniques to better characterize understudied meltwater and sediment dynamics of the GrIS.

In Chapter 2, 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, likely due to highly variable sediment export from the GrIS. Concurrently with this work, I developed a novel cloud mask (Chapter 3). I then explored water and sediment 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 export to the ocean. This sediment is a significant, bioavailable source of iron in the ocean (Chapter 4).

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 (Chapter 5).

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