Controls on West Greenland Outlet Glacier Sensitivity to Climate Forcing
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Controls on West Greenland Outlet Glacier Sensitivity to Climate Forcing Thesis Presented in Partial Fulfillment of the Requirements for the Degree of Master of Science in the Graduate School of The Ohio State University By Ellyn Mary McFadden, B.S. Graduate Program in Geological Science The Ohio State University 2010 Thesis Committee: Dr. Ian M. Howat, Advisor Dr. W. Berry Lyons Dr. Lonnie Thompson Copyright by Ellyn Mary McFadden 2010 Abstract Significant changes in the dynamics of Greenland’s marine-terminating outlet glaciers within the past few years indicate a rapid and complex response of these systems to recent climatic forcing. Widespread and substantial accelerations in flow-speed of outlet glaciers in southeast Greenland have been linked to destabilization and retreat of glacier fronts triggered by thinning to flotation induced by warmer ocean temperatures. There is concern that ongoing coastal thinning in western Greenland will trigger a similar response, further threatening the stability of the ice sheet. Despite regional ice thinning and retreat, the glaciers of Greenland’s northwest coast have not yet undergone substantial acceleration. This suggests a lessened dynamic sensitivity of these glaciers to changes at the ice front than southeastern glaciers, likely due to differences in glacier geometry. To investigate the potential controls behind this contrasting behavior, we derive time series’ of front position, surface elevation, and surface thinning for 59 marine-terminating outlet glaciers in west Greenland from 2000-2009. Surface speeds are derived for several glaciers to determine sensitivity to large front retreats in this region. Using these data, we look for patterns in the relationships between retreat, thinning, acceleration, and geometric variables, such as surface slope, to determine the first-order controls on glacier sensitivity. ii Data are compared to regional changes in air and ocean temperatures to assess similarities in climate forcing conditions along Greenland’s west coast. We conclude there is no direct relationship between front retreat and measured geometric parameters applicable to the entire study region. The relative importance of surface slope as a control of glacier behavior is highly variable and must be coupled to bathymetric data in order to understand and accurately model outlet glacier response to climate forcing. iii Acknowledgements I’d like to thank my advisor, Dr. Ian Howat, for his guidance and support with my Masters research as well as his extensive mentoring in Glaciology, of which I knew little prior to my research. I’d like to thank Dr. Berry Lyons and Dr. Lonnie Thompson for providing helpful suggestions while serving on my thesis committee. I’d also like to thank Dr. Yushin Ahn (Byrd Polar Research Center) for providing velocity data, Dr. Wieslaw Maslowski (Naval Postgraduate School) for providing ocean temperature reanalysis data, and Dr. Ian Joughin (University of Washington) for providing complete RADARSAT mosaics for Greenland. Without their help and support, this paper would not have been possible. iv Vita January 2008 ..................................................B.S. Environmental Science, Lehigh University September 2008 .............................................University Fellowship, The Ohio State University December 2008 ..............................................“Controls on Greenland outlet glacier sensitivity to climate forcing: A comparative approach”, AGU Annual Meeting September 2009 ............................................Rick Toracinta Graduate Scholarship, Byrd Polar Research Center December 2009 .............................................“West Greenland outlet glacier sensitivity (2000-2009)”, AGU Annual Meeting Fields of Study Major Field: Geological Science v Table of Contents Abstract ...............................................................................................................................ii Acknowledgements ............................................................................................................iv Vita ......................................................................................................................................v List of Tables ...................................................................................................................viii List of Figures ....................................................................................................................ix 1. Introduction .....................................................................................................................1 2. Methods ...........................................................................................................................9 2.1 Data and Sources ...................................................................................................9 2.2 Front Positions .....................................................................................................15 2.3 Surface Elevations and Surface Slopes ................................................................16 2.4 Surface Speed ......................................................................................................17 2.5 Additional Observed Parameters .........................................................................18 3. Results .......................................................................................................................... 20 3.1 Overview of Changes in Front Position ................................................................20 3.2 Overview of Changes in Surface Elevation and Slope .........................................21 3.3 Case Studies of Glacier Change ............................................................................23 4. Discussion .....................................................................................................................43 4.1 Climate Forcing Conditions .................................................................................43 4.2 Front Retreat, Thinning, and Surface Slope .........................................................45 vi 4.3 Comparison of Grounded and Floating Termini ..................................................51 4.4 Focus on Smaller Spatial Scales ...........................................................................53 5. Conclusions ...................................................................................................................63 6. References .....................................................................................................................66 vii List of Tables Table 1: Glacier Slopes ....................................................................................................32 viii List of Figures Figure 1: Location map ....................................................................................................19 Figure 2: Front position change (2000-2009) ...................................................................29 Figure 3: Surface elevation profiles .................................................................................30 Figure 4: Front positions (A) and surface elevation profiles (B) for Edvard Glacier (76°18'24.26''N, 61°58'28.31''W) ......................................................................................34 Figure 5: Front positions (A) and surface elevation profiles (B) for Rink South Glacier (76°14'13.71''N, 60°57'46.79''W) ......................................................................................35 Figure 6: Front positions (A), surface elevation profiles (B), and surface speeds (C) for Alison Glacier (74°37'21.31''N, 56°13'4.99''W) ...............................................................36 Figure 7: Front positions (A) and surface elevation profiles (B) for Upernavik North Glacier (73°0'2.33''N, 54°26'32.14''W) .............................................................................38 Figure 8: Front positions (A), surface elevation profiles (B), and surface speeds (C) for Umiamako Glacier (71°44'3.32''N, 52°24'53.34''W) ........................................................39 ix Figure 9: Front positions (A), surface elevation profiles (B), and surface speeds (C) for Jakobshavn Isbræ (69°10'59.33''N, 49°37'27.44''W) ........................................................41 Figure 10: Air Temperatures..............................................................................................57 Figure 11: SSTs for the northern (A), central (B), and southern (C) regions ...................58 Figure 12: Heat flux data for the northern (A), central (B), and southern (C) gates ........60 Figure 13: Surface elevation profiles for glaciers with stable fronts from 2000-2009......62 x 1. Introduction Recent studies have revealed retreat, thinning, and acceleration of Greenland’s marine-terminating outlet glaciers (e.g. Joughin et al. 2004, Moon and Joughin 2008, Howat et al. 2005, 2007, 2008, Luckman et al. 2006, Rignot and Kanagaratnam 2006). Although the frontal retreats of glaciers along the southeast coast of Greenland have been well documented (Howat 2005, 2007, 2008), the stabilization and slight advance of previously retreating fronts following 2005 (Howat et al. 2008, Moon and Joughin 2008) lead to questions regarding external controls on front positions and speed of Greenland’s outlet glaciers. Focus on Greenland glaciers has been primarily concentrated on large outlet glaciers in southeast Greenland, and Jakobshavn