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Open Eveland Msthesis.Pdf The Pennsylvania State University The Graduate School College of Engineering SNOW DYNAMICS IN A POLAR DESERT, MCMURDO DRY VALLEYS, ANTARCTICA A Thesis in Civil Engineering by Jeffery W. Eveland © 2012 Jeffery W. Eveland Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science May 2012 ii The thesis of Jeffery Eveland was reviewed and approved* by the following: Michael N. Gooseff Associate Professor of Civil Engineering Thesis Advisor Derrick J. Lampkin Assistant Professor of Geography Christopher J. Duffy Professor of Civil Engineering William D. Burgos Professor of Environmental Engineering Graduate Officer of the Department of Civil and Environmental Engineering *Signatures are on file in the Graduate School. iii ABSTRACT Snow in the McMurdo Dry Valleys is rare source of moisture for subnivian soils (beneath snow) in a cold desert ecosystem. While sublimation dominates the ablation process, measurable increases in soil moisture are expected to provide more favorable conditions for subnivian soil communities. In addition, snow cover insulates the underlying soil from temperature extremes. Quantifying the spatial distribution and ablation patterns of seasonal snow is necessary to understand these dynamics. Annual snowfall varies spatially ranging from 3 to 50 mm of snow water equivalent, with greater amounts occurring at the coast. Despite receiving very little precipitation, significant amounts of snow can accumulate (via aeolian redistribution) in topographic lees at the valley bottoms, forming thousands of discontinuous patches (typically 1- 100 m2 in area). These patches have the potential to act as fertility islands, controlling the landscape distribution of microbial communities, and biogeochemical cycling. High resolution imagery acquired during the 2009-2010 and 2010-2011 austral summers was used to quantify the distribution of snow across Taylor and Wright Valleys. An object- based classification was used to extract snow-covered area from the imagery. Coupled with topographic parameters, unique distribution patterns were characterized for 5 regions within the neighboring valleys. Time lapses of snow distribution during each season in each region provide insight into spatially characterizing the aerial ablation rates (change in area of landscape covered by snow) across the valleys. The distribution of snow-covered area during the 2009-2010 austral summer is used as a baseline for seasonal comparison. The surrounding regions of Lake Fryxell, Lake Hoare, Lake Bonney, Lake Brownworth, and Lake Vanda exhibited losses of snow-covered area of 9.61 km2 (-93%), 1.63 km2 (-72%), 1.07 km2 (-97%), 2.60 km2 (-82%), and 0.25 km2 (- 96%) respectively, as measured from peak accumulation in October to mid-January during the iv 2009-2010 season. Differences in aerial ablation rates within and across local regions suggest that both topographic variation and regional microclimates influence the ablation of seasonal snow cover. Elevation has shown to be the strongest control over aerial ablation. Fifteen 1 km2 plots (3 in each region) were selected to assess the prevalence of snow cover at smaller scales. Results confirm that snow patches form in the same locations each year with some minor deviations observed. Stable isotopes from snow patches also provide insights into temporal and spatial processes associated with ablation. At the snow patch scale, neighboring patches often exhibit considerable differences in aerial ablation rates, presumably controlled by snow depth. This highlights the importance of both the landscape and snow patch scales in assessing the effects of snow cover on biogeochemical cycling and microbial communities. v TABLE OF CONTENTS LIST OF FIGURES ................................................................................................................... vii LIST OF TABLES ..................................................................................................................... x ACKNOWLEDGEMENTS ....................................................................................................... xi Chapter 1 Introduction ...............................................................................................................1 Chapter 2 Spatial and Temporal Patterns of Snow Accumulation and Aerial Ablation ............ 4 2.1 Introduction ............................................................................................................. 4 2.2 Methods for Quantifying Snow-Covered Area ....................................................... 5 2.3 Snow Accumulation Patterns .................................................................................. 12 2.4 Aerial Ablation Patterns .......................................................................................... 17 2.5 Implications of Snow Distribution Analysis ........................................................... 24 2.6 Conclusions ............................................................................................................. 28 Chapter 3 Seasonal Controls on Aerial Ablation and the Influence of Scale ............................ 30 3.1 Introduction ............................................................................................................. 30 3.2 Seasonal Comparison of Accumulation Patterns .................................................... 31 3.2 Seasonal Controls on Snow Accumulation and Aerial Ablation ............................ 40 3.3 Snow Ablation Rates and Modeled Snow Water Equivalent ................................. 46 3.4 Coupling of Landscape and Snow-Patch Processes................................................ 52 3.5 Conclusions ............................................................................................................. 55 Chapter 4 Stable Isotopic Analysis of Snow.............................................................................. 57 vi 4.1 Introduction ............................................................................................................. 57 4.2 Description of Sampling Scheme and Sample Analysis ......................................... 59 4.3 Results and Discussion of Stable Isotopic Analysis ............................................... 64 4.4 Conclusions ............................................................................................................. 82 Chapter 5 Conclusions ............................................................................................................... 84 4.1 Snow Accumulation Patterns .................................................................................. 84 4.2 Aerial Ablation of Seasonal Snow .......................................................................... 85 4.3 Snow-Patch Dynamics ............................................................................................ 86 REFERENCES .......................................................................................................................... 87 Appendix A UEB Model Parameters ......................................................................................... 93 Appendix B Snow Patch Outlines.............................................................................................. 95 Appendix C Depth Profile Measurements ................................................................................. 102 Appendix D Linear Regression Analysis ................................................................................... 106 vii LIST OF FIGURES Figure 2.2-1: Study Regions for Snow Distribution Analysis. ................................................. 6 Figure 2.2-2: Example of Extracted Snow-Covered Area from WorldView-1 Image Using ENVI EX Feature Extraction Algorithm .......................................................................... 10 Figure 2.2-3: Algorithm for Superimposing Topographic Parameters onto Extracted Snow- Covered Area .......................................................................................................... 12 Figure 2.3-1: Contrast of Early and Late Season Snow-Covered Area in Taylor Valley ......... 13 Figure 2.3-2: Distributions of Snow-Covered Area as Functions of Topography at Peak Accumulation ......................................................................................................... 16 Figure 2.4-1: Bulk Rates of Changes in Snow-Covered Area for each Study Region ............. 18 Figure 2.4-2: Snow-Covered Area as Functions of Topography for each Study Region ......... 20 Figure 2.4-3: Relative Proportions of Snow-Covered Area within each Topographic Interval throughout the Summer Season for each Study Region ......................................... 22 Figure 2.4-4: Seasonal Change in Snow-Covered Area in Taylor Valley and the Relationship to Elevation ................................................................................................................. 24 Figure 3.2-1: Locations of Selected Plots for Seasonal Accumulation Comparison ................ 33 Figure 3.2-2: Example of Seasonal Overlap Methodology ...................................................... 34 viii Figure 3.2-3: Exceedance Probabilities for Defined Levels of Seasonal Snow Patch Overlap 36 Figure 3.2-4: Seasonal Peak Accumulation Distributions of Snow-Covered Area .................. 38 Figure 3.3-1: Seasonal Distributions of Snow-Covered Area as Functions of Along-Valley Distance .................................................................................................................
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