UCLA UCLA Electronic Theses and Dissertations Title Hydrologic dynamics of the Greenland Ice Sheet from remote sensing and field measurements Permalink https://escholarship.org/uc/item/4fs5m1qf Author Chu, Vena Publication Date 2015 Peer reviewed|Thesis/dissertation eScholarship.org Powered by the California Digital Library University of California UNIVERSITY OF CALIFORNIA Los Angeles Hydrologic dynamics of the Greenland Ice Sheet from remote sensing and field measurements A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Geography by Vena Chu 2015 © Copyright by Vena Chu 2015 ABSTRACT OF THE DISSERTATION Hydrologic dynamics of the Greenland Ice Sheet from remote sensing and field measurements by Vena Chu Doctor of Philosophy in Geography University of California, Los Angeles, 2015 Professor Laurence Smith, Chair The current need for forecasting Greenland Ice Sheet contributions to global sea level rise is complicated by the lack of understanding of ice sheet hydrology. The proportion of meltwater contributing to sea level rise, as well as the pathways transporting meltwater on, through, and out of the ice sheet, are not well understood. Remote sensing of hydrologic dynamics in combination with small-scale fieldwork allows examination of broad spatial and temporal trends in the Greenland hydrologic system responding to a changing climate. This dissertation reviews the current state of knowledge on Greenland Ice Sheet hydrology, and examines three components of the Greenland hydrologic system: (1) fjord sediment plumes as an indicator of meltwater output, (2) supraglacial streamflow as an indicator of meltwater input to the ice sheet, and (3) moulin distribution and formation as a mechanism diverting meltwater from the surface of the ice sheet to the bed. Buoyant sediment plumes that develop in fjords downstream of outlet glaciers are controlled by numerous factors, including meltwater runoff. MODIS retrievals of sediment ii plume concentration show a strong regional and seasonal response to meltwater production on the ice sheet surface, despite limitations in fjords with rapidly calving glaciers, providing a tool for tracking meltwater release to the ocean. Summertime field observations and high-resolution satellite imagery reveal extensive supraglacial river networks across the southwestern ablation zone transporting large volumes of meltwater to moulins, yet these features remain poorly mapped and their discharges unquantified. A GIS modeling framework is developed to spatially adapt Manning’s equation for use with high-resolution WorldView-2 imagery to map supraglacial river discharge. Moulins represent connections between surface meltwater on the Greenland ice sheet and subglacial drainage networks, where increased meltwater can enhance ice sliding dynamics. A new high-resolution moulin dataset in western Greenland created from WorldView-1/2 imagery in the 2012 record melt year is used to assess moulin distribution and formation. Moulin locations show a significantly different distribution compared to geospatial variables in the entire study area, with moulins forming in areas of thinner ice, higher velocity and extensional strain rate, as well as lower surface elevation and slope, and higher bed elevation and slope. iii The dissertation of Vena Chu is approved. Gregory S. Okin Yongwei Sheng Steven A. Margulis Laurence Smith, Committee Chair University of California, Los Angeles 2015 iv This dissertation is dedicated to my mom and my brother. v TABLE OF CONTENTS LIST OF FIGURES ................................................................................................................. vi LIST OF TABLES ................................................................................................................. viii ACKNOWLEDGMENTS ....................................................................................................... ix VITA ..........................................................................................................................................x CHAPTER 1: Greenland Ice Sheet Hydrology: A Review 1.1 Abstract ................................................................................................................................1 1.2 Introduction ..........................................................................................................................2 1.3 Ice sheet surface meltwater production ................................................................................9 1.4 Supraglacial storage and drainage .....................................................................................13 1.4.1 Supraglacial lakes ...............................................................................................14 1.4.2 Supraglacial streams ...........................................................................................16 1.4.3 Crevasses and moulins ........................................................................................20 1.5 Englacial and subglacial drainage ......................................................................................23 1.6 Ice dynamics ......................................................................................................................27 1.6.1 Outlet glacier velocity changes and peripheral thinning.....................................28 1.6.2 Response of ice dynamics to inputs of supraglacial meltwater ..........................29 1.7 Proglacial environments.....................................................................................................31 1.7.1 Jökulhlaups .........................................................................................................32 1.7.2 River discharge ...................................................................................................33 1.8 Ocean interactions ..............................................................................................................35 1.8.1 Direct meltwater input into fjords .......................................................................35 1.8.2 Ocean warming effect on tidewater glaciers .......................................................37 1.9 Conclusion .........................................................................................................................39 i 1.10 Figures..............................................................................................................................44 1.11 References ........................................................................................................................52 CHAPTER 2: Hydrologic Controls on Coastal Suspended Sediment Plumes around the Greenland Ice Sheet 2.1 Abstract ..............................................................................................................................70 2.2 Introduction ........................................................................................................................71 2.3 Data and methods ...............................................................................................................75 2.3.1 Ice sheet surface melt ..........................................................................................75 2.3.2 Remote sensing of sediment plumes ...................................................................76 2.3.2.1 MODIS 500 m satellite imagery and quality .......................................77 2.3.2.2 Classification and validation of ‘open water’ ......................................78 2.3.2.3 MODIS spatial sampling and aggregation ...........................................80 2.3.2.4 Calibration/validation of SSC ..............................................................81 2.3.3 Outlet glacier environment .................................................................................82 2.4 Results ................................................................................................................................83 2.4.1 Regional characteristics: mean SSC, mean PDD, data availability, and outlet glacier environment .....................................................................................................85 2.4.2 Hydrologic controls on fjord SSC: spatial, interannual, seasonal, and high frequency......................................................................................................................88 2.4.2.1 Spatial variability .................................................................................88 2.4.2.2 Interannual variability ..........................................................................89 2.4.2.3 Seasonal variability ..............................................................................89 2.4.2.4 High frequency variability ...................................................................90 2.4.2.5 Marine-terminating and land-terminating glacier outlets ....................91 ii 2.4.3 Other factors........................................................................................................91 2.5 Discussion ..........................................................................................................................92 2.6 Conclusion .........................................................................................................................97 2.7 Figures................................................................................................................................98 2.8 Tables ...............................................................................................................................107