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2010-07-08
Physical and chemical properties of ice in a main valley glacier and a tributary glacier, Gornergletscher, Canton Valais, Switzerland
Annika M. Quick Brigham Young University - Provo
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Physical and chemical properties of ice in a main valley
glacier and a tributary glacier, Gornergletscher,
Canton Valais, Switzerland
Annika Marie Quick
A thesis submitted to the faculty of Brigham Young University in partial fulfillment of the requirements for the degree of
Master of Science
Summer B. Rupper, chair John H. McBride Stephen T. Nelson
Department of Geological Sciences
Brigham Young University
August 2010
Copyright © 2010 Annika M. Quick
All Rights Reserved
ABSTRACT
Physical and chemical properties of ice in a main valley
glacier and a tributary glacier, Gornergletscher,
Canton Valais, Switzerland
Annika M. Quick
Department of Geological Sciences
Master of Science
Glacier models often fail to incorporate the geometry and/or physical properties of tributaries included in complex glaciers. Tributary glaciers have different source areas and flow conditions than the adjacent main valley glacier. Ice cores (~3m depth) and surface samples (<0.5m depth) were collected from Grenzgletscher (main valley glacier) and Zwillingsgletscher (tributary glacier) in the Gornergletscher system of the Swiss Alps. Stable water isotopes 18 indicate seasonal variation, showing 1-2 annual layers. The mean δ OVSMOW for Grenzgletscher is ~4.8‰ lower than for Zwillingsgletscher. This difference may be accounted for in part by elevation differences between the accumulation areas (~1.1‰ δ18O), increased avalanching in Grenzgletscher (~1.8 ‰ δ18O), and by varying climatic conditions at the time of precipitation (~0.9-1.4‰ variation in δ18O). Using a kinematic ice flow model, core ages were estimated using effective annual layer thickness (based on seasonal variations), annual accumulation rate and ice thickness. The Grenzgletscher core is ~4 years older than the Zwillingsgletscher core. Based on ages and flow distances, the tributary has a lower flow velocity (63-87 m/yr) compared to Grenzgletscher (61-134 m/yr). To understand thermal properties of the tributary, a 775 m GPR survey (200 MHz) was conducted along a flow line of Zwillingsgletscher. Topographic waves (ogives) observed on the surface are mimicked by the onset of reflectivity 10-20 m below the surface. Reflective regions are interpreted as warmer ice at the pressure melting point, overlain by colder ice. This thermal structure is likely related to acceleration through an ice fall. Since most tributary glaciers include ice falls, thermal properties of tributary glaciers may be different from those of the main valley glacier. The properties and geometry of tributary glaciers are significantly different from main valley glaciers and should therefore be incorporated into glacier models in the future.
Keywords: Gornergletscher, Zwillingsgletscher, Grenzgletscher, ice dynamics, ogives, GPR
ACKNOWLEDGEMENTS
This research was funded by the BYU College of Physical and Mathematical Sciences
High Impact Research Grant and NSF Geomorphology and Landuse Dynamics Grant 0913107.
In addition, many people have contributed in diverse ways to the completion of this work. I would like to express appreciation to my thesis committee members, Dr. John McBride and Dr.
Steve Nelson, for their patience, guidance and constructive reviews; and especially my committee chair, Dr. Summer Rupper, for introducing me to glaciology, helping me understand how I could contribute to the field, and seeing it through to the end. I would like to thank Chris
Burton and Dave Tingey for their tireless assistance in the extensive preparations for field work, and Emily Keller and Jessica Williams for help with laboratory analyses. For enduring ten days of odd hours, cold food, sunburns, snow, rain, and all the complexities of living on ice, I am enormously grateful to the 2009 BYU Glacier Expedition Crew: Summer Rupper, John McBride,
Scott Ritter, Dave Tingey, Adam McKean, and Nathan Jones. Finally, I would like to acknowledge those family members, roommates, and especially fellow graduate students who have offered their much-appreciated support and laughter during the last two years.
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TABLE OF CONTENTS
TITLE…..…………………………………………………………………………....………….…i ABSTRACT ...... ii ACKNOWLEDGEMENTS ...... iii TABLE OF CONTENTS...... iv LIST OF TABLES ...... vi LIST OF FIGURES ...... vii 1. Introduction ...... 1 2. Background ...... 1 2.1 Glaciers as Indicators of Climate Change ...... 1 2.2 Numerical Models of Glaciers...... 2 2.2.1 Models of Basal Sliding and Hydrology ...... 2 2.2.2 Mass Balance Models ...... 3 2.2.3 Models of Internal Ice Dynamics...... 4 2.3 Tributary Glaciers ...... 8 3. Study Area ...... 11 3.1 Gornergletscher System ...... 11 3.2 Ogives ...... 13 4. Methods ...... 14 4.1 Ice Cores ...... 14 4.1.1 Collection procedures ...... 14 4.1.2 Processing procedures ...... 16 4.2 Surface Samples ...... 17 4.2.1 Collection and processing procedures...... 17 4.3 Laboratory Measurements ...... 17 4.4 Ground Penetrating Radar ...... 17 5. Results ...... 18 5.1 Isotopes ...... 18 5.2 Solutes ...... 23 5.3 Temperature, Density ...... 23 5.4 Dust Content ...... 28 v
5.5 Bubble Density ...... 28 5.6 Ground Penetrating Radar ...... 33 6. Discussion ...... 35 6.1 Isotopes ...... 35 6.1.1Elevation of Source Area ...... 35 6.1.2 Microclimate Effects ...... 37 6.2 Age and Flow Rates ...... 43 6.2.1. Age ...... 43 6.2.2. Flow Rates ...... 50 6.2.3. Isotopes and Ages of Ice in Cores...... 51 6.3 Solutes, Dust Content, Bubble Density ...... 54 6.3.1. Solute Concentrations ...... 55 6.3.2 Dust Content ...... 56 6.3.3 Bubble Density ...... 56 6.4 Ground Penetrating Radar ...... 58 7. Conclusion ...... 61 8. References ...... 65 9. Appendix A: Additional Tables...... 70 10. Appendix B: Additional Figures ...... 80
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LIST OF TABLES
Table 1. The influence of physical and chemical properties on glacier strain rate ...... 7 Table 2. Summary of Isotope Results...... 21 18 Table 3. Comparisons of Mean δ OVSMOW , Slopes, and Deuterium Excess Factors ...... 21 Table 4. Summary of Isotopic Effects in the Accumulation Areas ...... 43 Table 5. Shape Factors (F) for shear stress in glacier ice* ...... 70 Table 6. UTM Coordinates (Zone 32T) of Ice Cores and Surface Samples ...... 70 Table 7. Published Elevation Lapse Rates ...... 71 Table 8. Accumulation Zone Elevations (from DEM) ...... 71 Table 9. Comparison of δ18O for ―Winter‖ (lowest ¼) and ―Summer‖ (highest ¼) ...... 71 Table 10. Annual Accumulation Rates for Grenzgletscher Region ...... 72 Table 11. Core Sample Field Measurements ...... 73 Table 12. Core Stable Water Isotopes and Anion Concentrations ...... 76 Table 13. Core Dust Content and Bubble Density ...... 79
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LIST OF FIGURES
Figure 1. A strain-time curve for polycrystalline ice loaded in uniaxial compression...... 5 Figure 2. Modeled changes in glacier length for a linear increase in air temperature ...... 9 Figure 3. Index map of study area...... 11 Figure 4. Gornergletscher System with approximate glacier outlines...... 11 Figure 5. Panorama of Gornergletscher System looking south from Gornergrat...... 12 Figure 6. View of Zwillingsgletscher ogives...... 14 Figure 7. Location of three ice cores...... 15 Figure 8. Close-up of study area...... 15 Figure 9. Stable isotopes in ice cores with depth from surface...... 19 Figure 10. Stable water isotopes and meteoric water line...... 20 Figure 11. Stable water isotopes from surface samples ...... 20 Figure 12. Anion concentrations in μg/L for ice cores ...... 24 Figure 13. Total anion concentrations with depth in μg/L for ice cores...... 25 Figure 14. Anion concentrations in μg/L with depth for ice cores ...... 26 Figure 15. Anion concentrations in μg/L for surface samples ...... 27 Figure 16. Bubble density and dust concentration with depth in cores...... 30 Figure 17. Photographs of core sections (backlit)...... 31 Figure 18. Photographs of thin section of ices cores...... 32 Figure 19. NW end of GPR profile showing unmigrated amplitude ...... 33 Figure 20. GPR profiles (200 MHz) of Zwillingsgletscher ...... 34 Figure 21. Elevations of accumulation areas...... 37 Figure 22. Slope of Zwillingsgletscher and Grenzgletscher accumulation areas ...... 38 Figure 23. Annual solar radiation for the accumulation zones ...... 41 Figure 24. Histograms of δ18O (‰) in surface samples and ice cores...... 46 Figure 25. δ18O (‰) for surface samples plotted against Easting...... 47 Figure 26. Ice thickness (m) in the confluence region...... 49 Figure 27. Estimated ages of ice in core 2 (Zwillingsgletscher) and core 3 (Grenzgletscher). .... 50 Figure 28. Estimated velocity for Zwillingsgletscher and Grenzgletscher...... 51 Figure 29. Long term climate from 5 Swiss weather stations ...... 53 Figure 30. Measurements from core 2 with depth showing possible seasonal correlation ...... 54
Figure 31. Steady state permittivity εs of pure polycrystalline ice and pure water ...... 59 Figure 32. Locations of isotope stations near the study area...... 80 Figure 33. Seasonality in δ18O from three Swiss precipitation stations, 1998-2007...... 80 Figure 34. Histograms of anion concentrations of ~5cm sections of ice cores ...... 81 Figure 35. Histograms of anion concentrations of ~15 cm sections of surface samples ...... 82 Figure 36. Seasonal variation at Grimsel (1950 m) ...... 83 Figure 37. Long term variation at Grimsel (1950 m)...... 84 1
1. INTRODUCTION
The physical and chemical properties of glacier ice, together with a glacier’s geometry, determine how a glacier system responds to changes in climate. In order to more accurately study glacier flow, it is important to understand how physical and chemical properties vary across a glacier system. In this study, a first order test was conducted to determine if there is significant variation in the physical and chemical properties of ice between a main valley glacier and a tributary glacier in the Gornergletscher system in the Swiss Alps. This variation was examined through ice cores and ground penetrating radar surveys. Spatial inhomogeneity in a complex glacier such as the Gornergletscher system would require modifying numerical models of glacier flow to include tributary glaciers. Improved glacier models would be better able to evaluate the response of a complex glacier system to climate. The possible causes of variation between tributary and main valley glaciers are the focus of this study.
2. BACKGROUND
2.1 Glaciers as Indicators of Climate Change
Glaciers are commonly used to understand past, present, and future climate change due to their sensitivity to changes in temperature and precipitation. Low-frequency climate change is reflected in glacier length variations (Lemke et al., 2007). Past glacier advances and retreats have been determined using field measurements, historical documents and photographs, tree ring widths, archaeological data, and radiocarbon dating. The correlation between glacier advance and retreat and meteorological data recorded during historic times indicates the ability of glaciers to respond to changes in temperature, precipitation, and solar radiation (Holzhauser et al., 2005). 2
Global climate change impacts the existence and extent of glaciers. At times in the past, rapidly advancing glaciers have covered arable land and destroyed roads and structures. For the second half of the last century, a decidedly negative mass balance has been calculated for the world’s glaciers (Lemke et al., 2007). Retreating glaciers may negatively impact hydroelectric potential and freshwater reservoirs. Hydroelectric facilities are often located in mountainous, glaciated areas due to the constant source of stream flow and naturally-regulated storage reservoirs (Tangborn, 1984). In Switzerland, for example, hydroelectric power provides 75% of the country’s consumed electricity (Schaefli et al., 2007). Melting of glaciers may be a significant contributor to possible sea level rise. The loss of all glaciers (excluding ice caps,
Greenland, and Antarctica) may result in ~0.1m of global sea level rise (Raper and Braithwaite,
2005). In addition, the frequency of flooding caused by ice-dammed lakes increases as glaciers retreat (Costa and Schuster, 1988). In light of recent and projected changes, it is important to improve models that describe the relationship between glaciers and climate.
2.2 Numerical Models of Glaciers
In order to create more accurate glacier models, it is necessary to understand those properties of glaciers that influence their advance and retreat. These are the physical and chemical properties that will be examined in this study and compared between a tributary and main valley glacier. The three most important factors in glacier advance and retreat are: basal sliding and hydrology, mass balance (both of which will be discussed briefly), and internal ice dynamics (Paterson, 1994) (the main focus of this study).
2.2.1 Models of Basal Sliding and Hydrology
Basal sliding occurs as glaciers move over their beds, aided by meltwater and bed deformation (often granular rock debris). Numerous studies have explored and attempted to 3
quantify sliding movement at the base of glaciers (see chapter 7 of Hooke, 2005 and references therein).
2.2.2 Mass Balance Models
The mass balance of glacier, b, is the change in mass (in water volume equivalent) per unit area of a glacier relative to the previous summer surface (Paterson, 1994). It is defined as the sum of the accumulation (positive) and the ablation (negative), given by:
b = c + a (1) where c is the accumulation or mass gained by the glacier (precipitation, snow drift, avalanching) and a is the ablation or mass lost by the glacier (melting, sublimation, calving, etc.). The net balance, bn, is defined as the mass balance at the end of the balance year. Positive bn results in glacier advance and negative bn in glacier retreat (Hooke, 2005).
In terms of mass balance, glaciers are divided into two zones. In the accumulation zone of a glacier, there is net accumulation during the year. In the ablation zone, there is net ablation.
The two zones of a glacier are separated by the equilibrium line, where b=0. As glacier size and shape adjust to climatological parameters, the equilibrium line shifts to higher or lower elevations. Changes in equilibrium line altitude (ELA) over time may therefore be used as an indicator of the response of glaciers to climate change (Hubbard and Glasser, 2005; Leonard,
2007).
Mass balance models attempt to quantify changes in ELA (e.g., Hostetler and Clark,
1997; Rupper and Roe, 2008) or glacier length (e.g., Huybers and Roe, 2009). Most models quantify accumulation as winter precipitation, interpolating from nearby climate stations for modern day conditions. Quantifying ablation is more complicated due to various modes of mass loss (calving, bottom melting, evaporation, sublimation, and surface melting) and variables 4
within these modes. For mid-latitude and high-latitude glaciers that terminate on land, surface melting is considered dominant (Hooke, 2005; p. 26) and is influenced by temperature, cloudiness, wind, longwave and shortwave radiation, fluxes of sensible and latent heat, and humidity (Huybers and Roe, 2009).
Multiple approaches may be taken to address surface melting, including positive degree day models (e.g., Braithwaite and Zhang, 2000) and more complex ablation models, such as those calculating energy balance (e.g., Shea et al., 2009). Surface energy balance models calculate the amount of energy available for melting snow and ice at the glacier surface.
Variables such as air temperatures, surface temperatures, saturation vapor pressure, and wind speed are included in these calculations (e.g., Rupper and Roe, 2008).
A mass balance model that incorporates glacier geometry is described by Huybers and
Roe (2009). Perturbations in glacier length (L’) are caused by changes in temperature (T’) and precipitation (P’) according to the following equation:
L’ t+∆t = γL’t – αT’t + βP’t (2) in which γ, α, and β are functions of ablation area, glacier height, an empirically determined melt factor, lapse rate, slope angle, area of the ablation zone, total area of the glacier, and the time step.
2.2.3 Models of Internal Ice Dynamics
As shown in the models described above, glacier length changes are calculated as a function of glacier size and mass balance. These models, however, neglect internal ice dynamics. The actual mechanisms of ice flow are determined by multiple rheologic parameters related to crystal structure, stress, and strain. 5
Ice consists of tetrahedra (each vertex formed by an oxygen atoms bonded to two hydrogen atoms) joined into hexagonal rings. The hexagonal rings define a basal plane, within which bonds are stronger than between planes. The c-axis is defined perpendicular to the basal plane (Hooke, 2005; p. 43). Single crystals of ice are therefore anisotropic with respect to the c- axis, and slippage occurs most readily parallel to the basal plane, which requires breaking fewer bonds (Pounder, 1965). Polycrystalline ice (which best approximates glacier ice), however, consists of randomly oriented crystals and exhibits more complex behavior than single crystals
(Paterson, 1994; p. 24).
Figure 1. A strain-time curve for polycrystalline ice loaded in uniaxial compression from (Hooke, 2005; p. 51). This curve indicates that strain rate varies in polycrystalline aggregates due to the creep mechanism.
The deformation of solid ice occurs due to dislocations in the ice structure (irregularities or defects in which the crystal structure is discontinuous or offset in some way, allowing planes of atoms to move more easily). The number of dislocations increases with the application of stress, and in turn, the rate of deformation (i.e., strain rate) in polycrystalline ice depends on how rapidly dislocations can move. During transient or primary creep, dislocations increase until they begin to interfere with one another and cause a pile up that resists further deformation and lowers strain rate. In other words, polycrystalline ice initially becomes ―harder‖ with increasing 6
strain (Figure 1). The later increase in strain rate during tertiary creep is attributed to recrystallization, in which the newly formed grains have their c-axes more favorably aligned for slip along the basal plane (Petrenko and Whitworth, 1999; p. 204).
At the temperatures and pressures typical in glaciers, the most important deformation mechanism is power-law creep, described by the constitutive relation commonly referred to as
Glen’s flow law (Glen, 1958):
ε = Aτ n (3) in which ε is the shear strain rate and τ is the shear stress. The exponent n depends on the creep mechanism and is commonly assigned a value of 3 for glacier ice (Paterson, 1994; p. 85). The variable A is a ―softness‖ parameter that depends on ice temperature, fabric, crystal size, viscosity, water content, and other factors that may be significant, such as pressure, texture, dislocation density, and grain boundary structure. Souchez and Lorrain (1991; p. 8) refer to A as the ―thermally activated ice hardness factor‖, which is defined by the Arrhenius relation
(Paterson, 1994; p. 27).
(4)
A0 is a temperature-independent constant, Q is the activation energy for creep, R is the gas constant, and T is the temperature.
On a given glacier, A will vary with physical and chemical properties of the ice. In particular, A0 depends on crystal size, shape and orientation and the concentrations of air bubbles and impurities in the ice (Paterson, 1994; p. 28). Additional models that further quantify the effects of anisotropic fabrics on strain rate are described by Petit, et al.(2007). The influence of selected physical and chemical properties on glacier strain rate is summarized in Table 1. 7
Table 1. The influence of physical and chemical properties on glacier strain rate
As temperature increases, strain rate increases (see Eq. 4). Temperature Water content increases with temperature, preventing grain-boundary interactions and increasing strain rate (Hooke, 2005; pp. 68, 70).
Dissolved solutes increase strain rate by lowering melting temperatures and increasing Solutes sliding at grain boundaries (Paterson, 1994; p. 29); (Souchez and Lorrain, 1991; p. 83).
Above certain concentrations, particle impurities should inhibit grain growth and dislocation movement, decreasing strain rate (Paterson, 1994; p. 29); (Souchez and Particles Lorrain, 1991; p. 84). In large concentrations, particulate debris possibly causes softening of the ice and increased strain rate (Echelmeyer and Zhongxiang, 1987).
Bubble-rich ice has been found to deform at higher strain rates than bubble-free ice (Hooke, 1973), as cited in Rüegg et al. (2008). At grain boundaries, air bubbles would be expected to inhibit grain growth and Air Bubbles dislocation movement, decreasing strain rate (Paterson, 1994; p. 29). Air bubbles may have no significant effect on recrystallization or grain growth (Kamb, 1972).
Density does not strongly impact ice ―hardness,‖ except possibly as it reflects bubble density (see above) (Souchez and Lorrain, 1991; p. 85); (Hooke, 1973). Density, Density however, is directly proportional to shear stress (Eq. 5), so increasing density increases strain rate.
With increasing grain size above -10°C, the contribution of grain-boundary sliding decreases, so the strain rate decreases (Paterson, 1994; p. 29); (Petrenko and Whitworth, 1999; p. 203). Grain Size Large grains may reflect recrystallization, which also results in greater anisotropy and increased strain rate. The relationship between grain size and strain rate is complicated by the effects of recrystallization.
Fabric (c-axis With increasing anisotropy (aligned c-axes) of the ice crystals, strain rate increases orientation) (Paterson, 1994; p. 29); (Hooke, 2005; p. 69; Pettit et al., 2007).
Any irregularities in grain boundaries will interfere with grain-boundary sliding and Crystal Shape decrease strain rate (Paterson, 1994; p. 29).
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The shear stress, τ, at a point on a glacier is calculated from the ice density (ρ), ice thickness (h), acceleration due to gravity (g), and slope angle (ø):
τ = ρ g h sinø (5)
This equation may be altered to account for variables including atmospheric pressure and glacier shape (see Hooke, 2005; Paterson, 1994; chapters 5 and 6, respectively). With equations for shear stress and strain rate (Eq. 3 and 5), ice flow rates may be calculated. In this manner internal ice dynamics are incorporated into models of glacier advance and retreat. Due to the number and complexity of factors that influence the parameter A, it is typically assumed to be a constant in both space and time. This assumption may be invalid if A varies greatly across a glacier system (i.e. between the tributary and main valley glaciers). The validity of the assumption that physical and chemical properties are constant within a glacier system is examined in this study.
2.3 Tributary Glaciers
Glacier studies, in general, have focused on main valley or trunk glaciers. Many large glaciers, however, are actually part of complex glacier systems that involve ice fields feeding side valley glaciers that converge into the main valley glacier. These interconnected systems often have more complex sensitivities to changes in climate than simple valley glaciers (Larsen et al., 2007; Osmaston, 2005). Tributaries affect the mass balance of the glacier system and may have different strain rates and chemical and physical properties.
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Tributary glaciers contribute mass to the main valley glacier, which influences response time. A glacier’s response time serves as a buffer against large and rapid changes in climate. In other words, smaller glaciers react more quickly to changes in climate than do larger glaciers
(Jóhanneson et al., 1989). Considering tributary glaciers by themselves, their smaller size dictates a shorter response time. These glaciers will therefore advance or retreat more quickly, cutting off mass input to the main valley glacier.
In the above described perturbation model (Eq. 2) of Huybers and Roe (2009), the glacier geometry may be adjusted to include a tributary. Figure 2 shows the results of modeling a temperature increase of 2.5°C over 150 years. The dashed line shows the decrease in glacier length for a simple valley glacier with total area, ablation area, volume, and slope gradient equal to the Gornergletscher, Switzerland (the study area). The solid line represents the same model altered to include three retreating tributary glaciers. The retreat of a tributary cuts off mass input to the main glacier, significantly changing the sensitivity and response time of the main valley glacier in a nonlinear fashion, as shown in Figure 2. Tributary glaciers therefore increase the magnitude and rate of the response of main valley glaciers to climate changes in a nonlinear fashion.
Figure 2. Modeled changes in glacier length for a linear increase in air temperature of 2.5°C over 150 years, using the perturbation model of Huybers and Roe (2009). Dashed line represents a glacier with three tributary glaciers.
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Tributaries alter the cross section of the main valley glacier and may have different cross- sectional shapes throughout their lengths. The cross-sectional shape of a glacier has an effect on the shear stress, as shown by a modified version of Equation 5:
τ = - F ρ g h sinø (6) in which F is a shape factor that depends on the shape of the glacier channel (parabolic, semi- elliptical, or rectangular) and its width to height ratio. Values of F range from 0.445 to 1.000
(Paterson, 1994; p. 103) as shown in Table 5 (Appendix A).
Beyond changing the mass balance and geomorphology of glacier systems, confluencing glaciers also affect the physical and chemical properties of the ice. Ice within a tributary glacier originates from a different temperature and accumulation regime. Accordingly, physical and chemical properties of these glaciers may be significantly different than those of the main valley glacier. Physical ice properties include fabric (c-axis orientation), grain size, and grain shape.
Chemical properties include dust content and solutes.
Based on the equations for strain rate (Eq. 3) and shear stress (Eq. 6), tributary glaciers may have different strain rates due to differences in the channel size and shape, slope, density, and those parameters that are incorporated into the softness parameter A (e.g. c-axis orientation, dust content, chemistry, grain shape and grain size). Together with the influence of mass balance, tributary glaciers will influence both the rate and magnitude of glacier responses to climate change. The purpose of this research is to determine if and how the physical properties of ice in a tributary glacier differ from those of a main valley glacier. Data collection and analysis included (a) obtaining and analyzing ice samples from both a main valley glacier and an adjacent tributary glacier, and (b) conducting surveys of the confluence region using ground penetrating radar (GPR) to determine subsurface ice structure and thermal properties. 11
3. STUDY AREA
3.1 Gornergletscher System
The glacier system chosen for study is the Gornergletscher system in the Swiss Alps
(45.97°N, 7.80°E), shown in Figure 4. The system is the second largest in the Swiss Alps
(Holzhauser et al., 2005) and was chosen for study due to its multiple tributary glaciers, extensive previous study, and relative ease of access.
Figure 3. (left) Index map of study area. The location of the area shown in Figure 4 is indicated by a star, southeast of Zermatt.
Figure 4. (below) Gornergletscher System with approximate glacier outlines (2009), Valais, Switzerland. The dashed line outlines the area shown in Figure 7. The dotted line outlines the area shown in Figure 8.
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The system consists of a main valley (or trunk) glacier, Grenzgletscher, which trends northwestward from its accumulation area on Monte Rosa, and multiple tributaries (Figure 5).
Gornergletscher feeds into the Grenzgletscher from the north, and three smaller tributaries
(Zwillingsgletscher, Schwärzegletscher, and Breithorngletscher) enter the main valley glacier from the south. Upper and Lower Theodulgletschers have retreated beyond the point of confluence with Grenzgletscher in recent years (SwissTopo, 2003). This study focuses on
Grenzgletscher (main valley glacier) and Zwillingsgletscher (tributary glacier). Comparisons were made between the two glaciers, near their confluence and below the ice fall in the tributary.
Figure 5. Panorama of Gornergletscher System looking south from Gornergrat. The study area is located approximately at the arrows pointing to Grenzgletscher and Zwillingsgletscher. Photo by Adam McKean.
The Gornergletscher system is very dynamic and has experienced large changes during historic time. Since its last maximum at the end of the Little Ice Age (1859), at which time it was visible from Zermatt, advancing 10 m/yr and destroying houses and farmland,
Gornergletscher has retreated 2600 m since 1865 (Holzhauser et al., 2005). According to the
World Glacier Monitoring Service, the Gornergletscher system covered an area of approximately
38 km2 in 2003, a dramatic decrease from approximately 68 km2 less than decade earlier, as stated in the report for 1995-2000. The elevation of the toe of the glacier has increased from 13
2150 m to 2240 m within the same time period. The toe of the glacier retreated an average of
~19 m per year from 1996 to 2005. Between 1931 and 2003, the glacier lost an estimated volume of 1.694 km3 (Haeberli et al., 2005; Haeberli et al., 2008).
Research in the Gornergletscher area has been extensive, including early topographic observations (e.g., Fisher, 1962). Ice core drilling began in the 1970s on Colle Gnifetti (part of the accumulation area for Grenzgletscher, Figure 4) and continues today (e.g., Rüegg et al.,
2008). Numerous studies involving ground penetrating radar (e.g., Eisen et al., 2008; Eisen et al., 2009; Eisen et al., 2003; Riesen et al., 2006) have been used to determine basal elevations and temperatures. Ice cores have been analyzed for temperature data (e.g., Haeberli and Funk,
1991; Suter et al., 2001), stable isotopes (e.g., Haeberli et al., 1983; Stichler and Schotterer,
2000), and aerosols and dust (e.g., Dams and Jonge, 1976; Döscher et al., 1995). Recent studies have focused on incorporating data from Gornergletscher into numerical models (e.g., Eichler et al., 2000; Kretz et al., 2007; Lüthi and Funk, 2000, 2001; Lüthi, 2000). These models and ice cores have led to estimations of annual accumulation rates (e.g., Schwerzmann et al., 2006;
Smiraglia et al., 2000). This study contributes to previous work by drilling short ice cores in the ablation areas of both Zwillingsgletscher and Grenzgletscher for side-by-side comparison.
3.2 Ogives
Ogives in the Gornergletscher system have yet to be studied in detail but provide insight into mechanisms of mass transport within the tributary glacier. The ogives are therefore relevant to the flow of the entire glacier system (Waddington, 1986). Wave ogives (swales and troughs) are observed below the Zwillingsgletscher ice fall within the study area on the ice surface
(Figure 6) and in aerial photos. Ogives occur frequently in tributary glaciers below the ice falls created in the confluence regions with larger glaciers (Goodsell et al., 2002). In this study, 14
ground penetrating radar surveys were conducted along Zwillingsgletscher to better understand subsurface ogive structure.
Figure 6. View of Zwillingsgletscher ogives, looking southwest from the moraine between Zwillingsgletscher and Grenzgletscher. Approximately five wave ogives (topographic swales and troughs) may be seen from this view. Photo by Adam McKean.
4. METHODS
In order to compare the physical and chemical properties between a main valley glacier and tributary glacier, ice samples were collected during July 2009 from adjacent glaciers
(Grenzgletscher and Zwillingsgletscher) in the Gornergletscher system. All samples were collected from the ablation zones, ranging in elevation from 2545 to 2584 m a.s.l. (see Table 6,
Appendix A). A ground penetrating radar survey was also conducted in the vicinity of the ice sampling locations to gain insight into subsurface ice properties.
4.1 Ice Cores
4.1.1 Collection procedures
As shown in Figure 7, ice cores were drilled in three locations: (1) up-glacier (i.e. upstream) in Zwillingsgletscher, (2) down-glacier in Zwillingsgletscher, and (3) Grenzgletscher.
Cores were drilled using a custom-built portable solar-powered drill. Cores were 5.6 cm in diameter and extracted in sections 4 to 88 cm long, down to depths of about 3 m. Sections removed from the drill were measured and the temperature was recorded in 10 cm increments 15
along the section using Raytek MiniTemp MT6 infrared thermometers. Sections were then bagged in 6 ml plastic tubing and labeled for processing. Sections were kept in a cooler with dry ice prior to processing in the field.
Figure 7. Location of three ice cores (circles), shown by the dashed line in Figure 4. The heavy black line indicates the location of the GPR transect. The area covered by Figure 8 is outlined by the dotted line.
Figure 8. Close-up of study area (dotted line in Figure 4) showing the location of surface samples (boxes) relative to ice cores (circles). 16
4.1.2 Processing procedures
Each ice core section was placed into a custom light box which allowed the core to be illuminated from the underside. Photographs were taken in order to record features such as fractures and possible foliation. The sections were then cut into ~5 cm segments using a portable band saw. The thickness of each segment was measured using digital calipers. The segment was then weighed using an Ohaus ScoutPro SP2001 portable scale. An estimate of density was later determined using the segments’ weights, lengths, and the core diameter.
Individual segments were broken into smaller pieces and then placed into WhirlPak plastic bags to prevent contamination. The ice in each bag was crushed into small pieces using a rubber mallet over a metal plate. The crushed ice was finally transferred into 20 ml plastic sample bottles with inverted-cone caps. Sample bottles were previously double-rinsed with ultra pure water (18MΩ-cm). The ice was allowed to melt and the sample bottles were transported back to the laboratory at Brigham Young University for analysis of isotopes and solutes.
At approximately 20 cm intervals, ~0.6 cm sections were cut for use in making thin sections, and ~2.5 cm sections were cut and set aside to measure dust content. Thin sections were placed under an Omano OMSZ55LT Stereo Microscope with a linear polarizer and photographed using a mounted Canon Power Shot G10 when the ice thickness was ~0.4 cm.
Sections for measuring dust content were placed in a covered filter apparatus and allowed to melt. The pre-weighed filters (pore size = 0.45 μm) were placed in plastic containers, wrapped in Parafilm, and returned to the lab to be re-weighed on a Mettler AE 50 scale.
Controls were run using water pre-filtered through Nalgene 0.4 μm filters.
17
4.2 Surface Samples
4.2.1 Collection and processing procedures
Surface samples (<50 cm total depth) were collected using the portable drill (core diameter = 5.6 cm) in 30 locations on Zwillingsgletscher and 10 locations on Grenzgletscher as shown in Figure 8. Samples were measured and photographed (backlit when possible). Samples were split into ~15 cm segments using a metal plate and the temperature of each recorded using infrared thermometers. Following the same procedures used for sections of the longer core, samples were saved for analysis of isotopes and solutes.
4.3 Laboratory Measurements
For each of the ice core and surface samples, stable isotope ratios, δDVSMOW and
18 plus δ OVSMOW, were measured using a Finnigan Delta isotope ratio mass spectrometer at Brigham
Young University (BYU) following methods similar to Anderson, et al. (2006a). δDVSMOW and
18 δ OVSMOW values were normalized to VSMOW (Nelson and Dettman, 2001). Uncertainties for
18 the given equipment and procedures are ± 1‰ for δDVSMOW and ± 0.16‰ for δ OVSMOW. Anion analysis detected chloride, nitrate, fluoride, sulfate, and phosphate using a Dionex ICS-90 ion chromatography system.
4.4 Ground Penetrating Radar
To gain a better understanding of the subsurface, a ground penetrating radar survey was conducted along 775 m of Zwillingsgletscher; roughly between ice cores 1 and 2 (see Figure 7).
The survey was approximately parallel to the glacier flow direction and crossed multiple wave ogives. A Geophysical Survey Systems, Inc. (GSSI) 5106 200-MHz bistatic antenna was used in continuous mode with a fixed transmitter-receiver offset. During an up-glacier traverse 18
(northwest to southeast), reflections were recorded with a 50-600 MHz field filter, a sample rate of 2048 samples/scan over 500 ns, and ~39.4 scans/m. To reduce scattering from surface water and to increase the depth of investigation, a second, downward transect (southeast to northwest) covering the same distance was completed using a sample rate of 2048 samples/scan over 1500 ns, ~13.1 scans/m, and a 5-300 MHz field filter that did not record the highest frequencies.
During the upward traverse, geographic positions were measured every 15-30 m using a Sokkia
SET3E Total Station Theodolite. During the downward traverse, GPS positions were recorded every 60-200 m to ensure that the two transects very nearly overlapped.
During acquisition, data were recorded with an exponential trace gain function. Low- frequency ―background‖ noise was removed during processing. Migration and time-to-depth conversion for the two profiles used a nominal value of 0.16 m/ns for the speed of light in freshwater ice, similar to other GPR studies conducted in the region (Eisen et al., 2009; Goodsell et al., 2002). Geographic locations (measured approximately every 20 m) were used to correct the profiles for surface topography.
5. RESULTS
5.1 Isotopes
Stable water isotope ratios were measured in ice cores because isotopic variation may be an indicator of variations in other chemical and physical properties of the ice. Isotopic ratios are reported below for both ice cores (2-3 m depth) and surface samples (<50cm depth). Values of
δ18O and δD are plotted with depth from the surface in each ice core in Figure 9. The isotopic ratios vary with depth with periodicities on the order of 1.5-2 m. Periodicity, which will be related to seasonal cycles below, is most pronounced in cores 2 and 3. An offset between the δ 19
values from Zwillingsgletscher (cores 1 and 2) and from Grenzgletscher is apparent for both deuterium and 18O. This offset is also apparent in the mean δ values reported in Table 2.
18 δDVSMOW (‰) δ OVSMOW (‰) -200.0 -150.0 -100.0 -50.0 0.0 -25.00 -20.00 -15.00 -10.00 -5.00 0.00 0.00 0.00
0.50 0.50
1.00 1.00
Core 1 Core 1 1.50 1.50 Core 2 Core 2 Core 3 Core 3
2.00 2.00
Depth from surface(m) Depthfrom Depth from surface (m) surface from Depth
2.50 2.50
3.00 3.00
3.50 3.50
Figure 9. Stable isotopes in ice cores with depth from surface. Cores 1 and 2 are from Zwillingsgletscher (tributary). Core 3 is from Grenzgletscher (main valley glacier). Core locations are shown in Error! Reference source not found.. Uncertainty is ± 1‰ for δD, ± 0.16‰ for δ18O.
20
0.0 -30.00 -25.00 -20.00 -15.00 -10.00 -5.00 0.00 -20.0
Core 1 -40.0 Core 2 -60.0 Core 3
-80.0 (‰) -100.0
-120.0 VSMOW
δD -140.0
-160.0
-180.0
-200.0
18 δ OVSMOW (‰) Figure 10. Stable water isotopes from Zwillingsgletscher (Cores 1 and 2) and Grenzgletscher (Core 3). Uncertainty is ± 1‰ for δD, ± 0.16‰ for δ18O. The meteoric water line is shown for reference.
0.0 -30.00 -25.00 -20.00 -15.00 -10.00 -5.00 0.00 -20.0
Zwillingsgletscher Surface -40.0
Grenzgletscher Surface -60.0
-80.0 (‰) -100.0
VSMOW -120.0 δD -140.0
-160.0
-180.0
-200.0 18 δ OVSMOW (‰) Figure 11. Stable water isotopes from surface samples of Zwillingsgletscher (tributary glacier) and Grenzgletscher (main valley glacier). Uncertainty is ± 1‰ for δD, ± 0.16‰ for δ18O. The meteoric water line is shown for reference. 21
Table 2. Summary of Isotope Results for Main Glacier (Grenzgletscher) and Tributary (Zwillingsgletscher)
Mean Stable Water Isotope Ratios Meteoric Water Line * Deuterium Excess Location n δD (‰) StDev δ18O (‰) StDev Slope +/- Intercept +/- d (‰) StDev Ice Cores 1 Tributary, down glacier 33 -100.94 6.6 -13.50 2.3 7.9 1.4 13 20 14.1 3 2 Tributary, up glacier 43 -110.19 17.1 -14.71 3.0 8 0.79 12 12 11.1 5.7 3 Main glacier 32 -143.20 11.7 -19.15 1.5 6.66 0.76 -12 15 14.1 5 1 and 2 Tributary, both cores 76 -106.18 14.3 -14.86 1.7 8.19 0.62 15.6 9.3 12.4 5 Surface Samples S1-S30 Tributary 70 -125.50 23.4 -17.03 2.9 8.1 0.54 12.6 9.4 10.9 6.4 S31-S40 Main glacier 35 -128.94 27.4 -18.63 2.3 7.81 0.58 8 11 11.9 3.8
*Plots were constructed using Isoplot (Ludwig, 2003) to account for uncertainty in isotopic measurements (± 0.16‰ for δ18O and ±1.0‰ for δD). For comparison, the meteoric water line for Switzerland is δD= 8 x δ18O +10 (Schürch, et al, 2003).
18 Table 3. Comparisons of Mean δ OVSMOW , Slopes, and Deuterium Excess Factors
18 18 Mean δ OVSMOW Slopes of δ O versus δD Deuterium Excess (d) Statistical Comparisons Statistically Significant Statistically Significant Statistically Significant Diff. (‰) p-value p-value p-value α=0.01 α=0.001 α=0.01 α=0.001 α=0.01 α=0.001 Ice Cores Main glacier and Tributary, up glacier Core 2 vs Core 3 -4.44 4.14E-15 yes yes <<0.001 yes yes 0.0007 yes no Main glacier and Tributary, down glacier Core 1 vs Core 3 -5.65 1.37E-19 yes yes <<0.001 yes yes 0.9570 no no Tributary, up and Tributary, down Core 1 vs Core 2 -1.21 0.0211 no no 0.3427 no no 0.0037 yes no Main glacier and Tributary, both cores Cores 1,2 vs Core 3 -4.80 4.31E-19 yes yes <<0.001 yes yes 0.1166 no no Surface Samples Surfaces of Main glacier and Tributary S1-S30 vs S31-S40 -1.61 0.0026 yes no <<0.001 yes yes 0.3279 no no
* P-values were determined using 2-tail t-tests for 2 samples with unequal variance.
22
18 Plots of δ OVSMOW versus δDVSMOW are shown in Figure 10 (ice cores) and Figure 11
(surface samples). All samples plot near the local meteoric water line: δD= 8 x δ18O +10 (Craig,
1961). In order to take into account analytical uncertainty, generic regression that accounts for errors in both X and Y was conducted using the Isoplot add-in for Microsoft Excel (Ludwig,
2003). Slopes and intercepts are reported in Table 2.
Deuterium excess factors for each data set are also reported in Table 2. The deuterium excess factor reflects non-equilibrium evaporation and is commonly taken as the intercept of the plot of δD versus δ18O, although it is preferable to use the equation
d= δD – 8* δ18O (7) because the slopes of all data sets are not equal to 8 (the slope of the meteoric water line)
(Souchez and Lorrain, 1991). The global average for deuterium excess is +10‰ (Craig, 1961).
In order to address the research question of differences between the tributary and main valley glacier of the system, statistical comparisons of isotopic data are reported in Table 3.
Two-tailed t-tests for two groups with unequal variance were conducted to determine if the sets of data were statistically different. As shown in the table, differences in the mean δ18O and slopes (δ18O versus δD) of the two glaciers are statistically significant at α=0.001 significance level. The difference in the mean δ18O of the surface samples between the two glaciers (~1.6‰) is significant at α=0.01 significance level, but not at α=0.001. The differences in the mean δ18O and slopes (δ18O versus δD) of the two cores from the same glacier (Zwillingsgletscher) are not statistically significant. At α=0.001, none of the differences in deuterium excess are significant.
23
5.2 Solutes
Solute concentrations can directly affect strain rates (Table 1), and were measured in addition to isotopes. Anion concentrations for ice core samples reported in Figure 12 have ranges similar to those reported previously reported for ice from Colle Gnifetti in the
Grenzgletscher accumulation area (Döscher et al., 1995). Data show a large spread of concentrations, especially in cores 1 and 2. Core 1 has high chloride concentrations, while core
2 has high sulfate concentrations. In all three cores, nitrate concentrations were generally lower than chloride and sulfate. Concentrations with depth are shown in Figure 13 (total anions) and
Figure 14 (chloride, nitrate, and sulfate). Some periodicity is apparent in concentrations with depth, particularly in sulfate. Peaks in chloride occur at about 1.25-2.0 m depth, and sulfate peaks are observed around 1.0, 1.75, and 2.5 m depth. Anion concentrations in surface samples are plotted in Figure 15 against UTM easting values (glacier flow is roughly left to right in this figure). In general, the surface samples have lower anion concentrations than the ice cores, with a narrower range of values. Histograms of anion concentrations in both ice cores (Figure 34) and surface samples (Figure 35) are located in Appendix B.
5.3 Temperature, Density
As shown in equations 4 and 5 (also see Table 1), glacier strain rate is related to temperature and density. Although temperatures were recorded for ice cores and surface samples, temperature measurements were imprecise due to thermometer drift or changes in battery charge. Core and surface sample temperatures are therefore not reported here. However, temperatures of all ice samples were between -2 and -5°C.
Density measurements are considered estimates due to the crude method for measuring section dimensions. Densities are reported in Table 11 in Appendix A. The average density 24
across all three cores is 0.907 g/cm3 with a standard deviation of 0.045 g/cm3. All three cores show a rapid increase in density within the first 10 cm. Below this interval, densities are roughly
9.1 g/cm3.
3000
2500
2000
g/L) μ
1500 Anion Concentration ( Concentration Anion
1000
500
0 Cl- NO - SO 2 - NO - 2 - - 2 3 4 Cl 3 SO4 Cl NO3 SO4 - - - Core 1 Core 2 Core 3
Figure 12. Anion concentrations in μg/L for ice cores from Zwillingsgletscher (core 1, n=34 and core 2, n=44) and Grenzgletscher (core 3, n=32). Not all anions were detected in each sample. Fluoride and phosphate concentrations were negligible but are reported in Appendix B. 25
Total Anion Concentration (μg/L) 0 500 1000 1500 2000 2500 3000 3500 0
0.5
1
1.5 Core 1
Core 2
Core 3
2 Depth from surface (m) surface from Depth
2.5
3
3.5
Figure 13. Total anion concentrations with depth in μg/L for ice cores from Zwillingsgletscher (core 1, n=34 and core 2, n=44) and Grenzgletscher (core 3, n=32). Total includes chloride, nitrate, sulfate, and negligible amounts of phosphate and fluoride. Not all anions were detected in each sample. 26
Chloride Nitrate Sulfate
Anion Concentration (μg/L) Anion Concentration (μg/L) Anion Concentration (μg/L)
0 1000 2000 3000 0 500 1000 1500 0 500 1000 1500 2000 2500 0.00 0.00 0.00
0.50 0.50 0.50
1.00 1.00 1.00
1.50 1.50 1.50
2.00 2.00 2.00
Depth from surface (m) surface from Depth (m) surface from Depth (m) surface from Depth 2.50 2.50 2.50
Core 1 Core 1 Core 1
3.00 Core 2 3.00 Core 2 3.00 Core 2
Core 3 Core 3 Core 3
3.50 3.50 3.50
Figure 14. Anion concentrations in μg/L with depth for ice cores from Zwillingsgletscher (core 1, n=34 and core 2, n=44) and Grenzgletscher (core 3, n=32). Not all anions were detected in each sample. Negligible amounts of fluoride and phosphate are reported in Appendix B. 27
2500
Chloride_Zwillingsgletscher Chloride_Grenzgletscher Nitrate_Zwillingsgletscher Nitrate_Grenzgletscher Sulfate_Zwillingsgletscher 2000 Sulfate_Grenzgletscher
1500
g/L) μ
Zwillingsgletscher Grenzgletscher
1000 Anion Concentration ( ConcentrationAnion
500
0 406400 406500 406600 406700 406800 406900 407000 407100 407200 Easting (m)
Figure 15. Anion concentrations in μg/L for surface samples from Zwillingsgletscher (n=71) and Grenzgletscher ( n=35). Not all anions were detected in each sample. Fluoride and phosphate concentrations are reported in Appendix B. Eastings are for UTM Zone 32T. 28
5.4 Dust Content
Dust in ice originates from the wet and dry deposition of dust suspended in the atmosphere and may reflect certain meteorological conditions, such as periods free from precipitation (Haeberli et al., 1983). When reweighing filters through which melt water from core samples was passed, many of the filters unexpectedly weighed less than they did originally.
To compensate for this effect, corrections were applied based on the mass lost by filters through which ultra pure water had been passed. Dust concentrations in mg/cm3 ice reported with depth in Figure 16 lie in the range 0.02-0.06 mg/cm3.
Direct comparison with dust concentrations reported in the literature is difficult. In studies in which dust concentrations are reported, methods for obtaining concentrations differ from the filter weighing method in this study. Reported methods are either unspecified
(e.g.Eisen et al., 2003), estimates from titanium, calcium, or potassium in filtered residue
(Haeberli et al., 1983), or use a turbidity meter (Wagenbach et al., 1996). Background dust levels reported for ice cores from Colle Gnifetti are 0.005mg/cm3 (Eisen et al., 2003) and 0.0068 mg/cm3 (Haeberli et al., 1983), almost two orders of magnitude smaller than the dust concentrations reported for the current study. It is likely that the crude measurement and correction methods prevent comparison of the magnitude of dust concentrations with previous studies. Trends in relative dust concentrations between cores and with depth are significant, however, and may still provide useful information.
5.5 Bubble Density
Bubbles visible within thin section photographs were counted using ArcGIS software with an artificial reference scale appropriate to the size of the microscope field of view. Bubble density was determined by dividing the bubble count within the clearest area of the thin section 29
by the area in square centimeters. Bubble density with depth in each of the three cores is shown in Figure 16. In general, ice taken from the Grenzgletscher core had higher bubble density (~300 bubbles/cm2) compared to the Zwillingsgletscher cores (~200 bubbles/cm2).
Photographs of core sections are shown in Figure 17, and representative thin section photographs are shown in Figure 18. In core 1, many of the bubbles were very elongated, suggesting a foliation at a steep angle to the glacier surface. Some smaller, round bubbles were also present.
Core 2 does not show the same degree of elongation. Thin sections show varying bubbles size and density. Clear bands were also observed in the cores (not shown), possibly indicating fractures filled with water that later refroze. Small perpendicular cracks observed in many sections were possibly the result of drilling and/or sawing.
In core 3 (Grenzgletscher), dust was observed in the top 9-10 cm. Photographs show a very high density of very small bubbles. Most bubbles are round, although some show signs of slight elongation. 30
Bubble Density Dust Concentration (Bubbles per cm2) (mg/cm3 ice) 0 200 400 600 0 0.02 0.04 0.06 0.08 0.00 0.00
0.50 0.50
1.00 1.00
Core 1 Core 1 1.50 1.50 Core 2 Core 2 Core 3 Core 3
2.00 2.00
Depth from surface(m) Depthfrom Depth from surface (m) surface from Depth
2.50 2.50
3.00 3.00
3.50 3.50
Figure 16. Bubble density and dust concentration with depth in cores. Data points for core 1 with gray outlines indicate a possible discrepancy in labeling, and therefore questionable depth locations along the core. 31
Figure 17. Photographs of core sections (backlit). Depth from the surface is indicated below each photograph. Upward orientation is towards the top of each photograph. Note varying bubble size, density, and elongation. (Zwillingsgletscher, cores 1 and 2; Grenzgletscher, core 3.) 32
Figure 18. Photographs of thin section of ices cores (Zwillingsgletscher, cores 1 and 2; Grenzgletscher, core 3). Depth from the surface of each section is indicated.
33
5.6 Ground Penetrating Radar
The location of the GPR transect on Zwillingsgletscher is shown in Figure 7. A close-up of the NW side of the profile with a 50-600 MHz field filter is shown in Figure 19. Both profiles are shown in Figure 20. Both reflection strength and amplitude reveal an undulatory pattern for the onset of reflectivity, below a relatively transparent zone in the upper 10-20 m. In the upper profile in Figure 20, shallow intermittent ―reflectivity‖ is an artifact of surface-generated noise and gain balancing. The antiformal shape of reflectivity onset is partly an artifact of hyperbolic diffraction move-out. As shown in Figure 20, the antiformal shapes of the high reflectivity zones become more closely spaced and the amplitudes of the ―waves‖ decrease down glacier.
Figure 19. NW end of GPR profile showing unmigrated amplitude (50-600 MHz field filter). Corrected for topography. Depth shown is meters below datum (2646 m a.s.l.). 34
Figure 20. GPR profiles (200 MHz) of Zwillingsgletscher. Both profiles show reflection strength, migrated and corrected for topography. Red indicates high reflection strength, blue indicates low reflection strength. Depths are shown in meters below datum (2646 m a.s.l.). Migration and depth conversion use a nominal value of 0.16 m/ns for the speed of light in ice. Glacier flow is from right (SE) to left (NW). Lower frequencies were emphasized with a 5-300 MHz field filter to produce the lower profile. 35
6. DISCUSSION
6.1 Isotopes
Isotopes from the tributary glacier show significant differences from those of the main valley glacier (Table 2), suggesting that there may be significant differences in other physical and chemical properties between the glaciers. These differences are more apparent for the ice cores (down to depths of ~3 m) than for the surface samples (<50 cm depth). This relationship is most clearly seen by examination of Figure 10 and Figure 11. Isotopic differences are most likely smoothed in the surface samples by recent precipitation with the same isotopic composition that occurs across both ablation zones. The precipitation freezes within the uppermost glacier surface and disguises the original isotopic composition of the ice.
18 The mean of the δ OVSMOW for the Grenzgletscher core, -19.66‰, is 4.8‰ lower than
18 the mean δ OVSMOW of both cores from Zwillingsgletscher. For δDVSMOW, the difference is
37.02‰. Possible causes of variation in isotopic composition are discussed below. Because most isotopic literature studies the relationship between meteorological conditions and δ18O, this discussion will focus on δ18O, although similar discussions could be made for δD.
6.1.1Elevation of Source Area
Multiple factors affect the isotopic composition of precipitation. Isotopes of hydrogen and oxygen in water have different masses, allowing fractionation of isotopes when water changes phase. Oxygen isotopic ratios in precipitation are related to mean annual air temperature at the surface (T) by
δ18O = 0.69 T – 13.6‰ (8) 36
(Dansgaard, 1964). Based on GNIP data for the Grimsel station (1950 m a.s.l., see Figure 32 in
Appendix B), the local relationship is
δ18O = 0.45 T – 14.55‰ (9)
(monthly data, 1970-1992) (IAEA, 2008). In mountainous regions, air temperatures change with elevation according to the local lapse rate. Thus, isotopic fractionation with varying elevation of precipitation is mostly a result of air temperature (Li et al., 2006). This effect is termed the altitude effect or elevation lapse rate.
The altitude effect is caused by the progressive depletion of heavier isotopes in vapor during successive precipitation events, and the orographic ascent and cooling of the water vapor
(Siegenthaler and Oeschger, 1980). The elevation lapse rate calculated from Swiss GNIP stations is -0.26‰ δ18O / 100 m, which falls within the range of published estimates (Dray et al.,
1998; Poage and Chamberlain, 2001; Schürch et al., 2003; Siegenthaler and Oeschger, 1980;
Stichler and Schotterer, 2000; Zuppi and Bortolami, 1982).
To determine the magnitude of the elevation effect in the study area, a digital elevation model of the upper portions of the Gornergletscher system was created from a contour map of the Zermatt area (SwissTopo, 2003) using ArcMap 9.3 (Figure 21). Using an equilibrium line altitude of 3250 m (Piccini and Badino, 2001), the accumulation areas of Zwillingsgletscher and
Gornergletscher were outlined. The mean elevations of the Zwillingsgletscher and
Grenzgletscher accumulation areas (3492 m and 3704 m, respectively) differ by about 213 m.
Maximum elevations of the accumulation areas (3774 m and 4209 m) differ by 435 m. Using an elevation lapse rate of -0.26‰ δ18O / 100 m , the elevation difference alone between
Zwillingsgletscher and Grenzgletscher may explain ~1.1‰ difference in the δ18O values from 37
the two glaciers. Using an equation that incorporates latitude with the relationship between δ18O and elevation from Bowen and Wilkinson (2002):
δ18O = -0.0051 (lat2) + 0.1805 (lat) – 0.002 (elev) – 5.247‰ (10) the isotopic difference based on maximum elevations of the accumulation zones is 0.87‰ δ18O.
The measured difference is ~4.8‰, indicating that additional effects must account for the isotopic differences in the ice cores.
Figure 21. Elevations of accumulation areas of Zwillingsgletscher (left) and Grenzgletscher (right).
6.1.2 Microclimate Effects
In addition to elevation, isotopic variation may also be caused by microclimates and changes in the source of the precipitation. In relation to glaciers, microclimate includes the small scale differences in an area that affect the accumulation and ablation. The isotopic compositions of ice cores serve as proxies for accumulation. Accumulation by precipitation could be altered due to rain shadow effects, deposition of atmospheric water vapor (Town et al., 2009), wind 38
direction, and storm paths. Accumulation by avalanching could be enhanced by steeper slopes.
Ablation is enhanced by erosive wind loss from exposed areas (Schürch et al., 2003) and increased solar radiation (due to variations in shading and aspect). Changes in the sources and mechanisms of accumulation and ablation may explain isotopic differences in the ice cores.
6.1.2a. Accumulation: Storms and Avalanching
In this area of the Alps, wind from the south and southwest bring precipitation into the glacier valley (Meteomedia, 2010). The accumulation areas are similarly oriented with respect to these storm tracks (see Figure 21), so the microclimatic effects relative to storm tracks are similar, and there should not be rain shadow effects. The contribution of avalanching to accumulation could be larger for Grenzgletscher due to the large area to the southwest of its accumulation zone with slopes prone to avalanching (Figure 22). Depending on weather and snow conditions, slopes above approximately 30 degrees are prone to avalanching (USFS, 2010).
Figure 22. Slope of Zwillingsgletscher and Grenzgletscher accumulation areas (outlined). 39
Avalanching will contribute precipitation from higher elevations to the accumulation area. The slope to the southwest of the Grenzgletscher accumulation area may introduce precipitation from as high as 4400 m, 700 m above the average elevation of the accumulation zone. Using the same -0.26‰ δ18O / 100 m elevation lapse rate, snow avalanching from the highest slopes above Grenzgletscher may have ~1.8‰ lower δ18O than the mean for the entire accumulation area. Zwillingsgletscher may also receive high elevation snow due to avalanching from the slope east of its accumulation area, but the avalanche-prone area is much smaller.
When considering the influence of avalanching, it is important to note that steep slopes will accumulate less snow. The contribution of isotopically light snow to the accumulation zone depends on the location and amount of snow avalanching. Ice originating at the edges of the accumulation zone will be more likely influenced by avalanching. If the ice sampled in core 3 on Grenzgletscher was influenced by avalanching in the accumulation zone, avalanching could explain up to 1.8‰ lower δ18O than in cores without an avalanche influence.
6.1.2b. Accumulation: Precipitation Source
Another microclimate effect is the source of the precipitation, which may be reflected by the deuterium excess (Chamberlain and Poage, 2000). The deuterium excess parameter reflects the evaporation effect (rate and source) of isotope fractionation in precipitation (Dansgaard,
1964).
Deuterium excess factors for ice cores and surface samples are shown in Table 2, and statistical comparisons are shown in Table 3. For all the sample sets, the deuterium excess factors are larger than the global average. This finding is consistent with high altitude isotope stations elsewhere in the Swiss Alps (11.6‰ and 12.7‰ in 1983 and 1984, respectively, at
Grimsel Station, elevation 1950 m) (IAEA, 2008). In general, these higher values for d suggest 40
a larger fraction of moisture recycling from evaporation of local sources. When plotted with depth in the ice cores, there is no clear seasonal variation (or other clear variation) in deuterium excess. The excess factors do not show large variations. At α=0.001 significance level, none of the differences in deuterium excess are statistically significant. Although the deuterium excess factors reveal information about the evaporative source of the regional precipitation, the data do not suggest the sources for the two adjacent glaciers are different. A difference in precipitation source may not be used to explain isotopic differences between Zwillingsgletscher and
Grenzgletscher.
6.1.2c. Ablation: Solar Radiation
Microclimate ablation effects include the amount of incoming solar radiation, which is dependent on latitude, aspect, and shading. Increased short wave solar radiation results in increased melting in the top several centimeters of snow (Zhou et al., 2001) and increased fractionation as meltwater has depleted isotope values (Souchez and Lorrain, 1991). If enough energy is available, solid-vapor transitions may also occur, causing further fractionation.
Evaporation during the day, however, is often offset by deposition from water vapor during the night. Using Spatial Analyst tools in ArcMap, the annual solar radiation was estimated for the accumulation areas using a uniform sky model (Figure 23).
The mean annual solar radiation values for the accumulation areas have the same order of magnitude, but are higher for Grenzgletscher. High solar radiation may increase surface melting in the Grenzgletscher accumulation area, resulting in heavier isotopic compositions as meltwater with lighter isotopes percolates downward. However, the refreezing of this meltwater may have the opposite effect (Zhou et al., 2001).
41
Figure 23. Annual solar radiation for the accumulation zones of Zwillingsgletscher (left) and Grenzgletscher (right). Calculations are based on a digital elevation model, 45.9 ° latitude, and a uniform sky model (diffuse proportion=0.3). Red indicates high solar radiation, blue indicates low solar radiation.
Difficulties arise in attempting to quantify the impact of solar radiation on surface melting and eventually on isotopic composition in ice cores, because the energy available to melt ice in a glacier is a result of not only incoming shortwave (solar) radiation, but also albedo, net longwave radiation (a result of air and surface emissivity and temperature), sensible heat, and latent heat (Paterson, 1994; pp.303-307). Glacier models that incorporate solar energy and mass balance (e.g.Rupper and Roe, 2008) are required to accurately predict the amount of ablation in relation to solar radiation and a given set of conditions. Higher solar radiation in Grenzgletscher
(a result of shading and aspect) may increase δ18O values in ice cores. This effect, therefore, does not help explain why the Grenzgletscher ice core was isotopically lighter than the
Zwillingsgletscher cores. 42
6.1.2d. Ablation: Wind Erosion
Because winter snow is drier and lighter than summer snow, erosive wind loss preferentially removes winter precipitation. In such exposed areas, most of the net accumulation is from summer precipitation. Winter precipitation is isotopically lighter than summer precipitation, so wind erosion often results in heavier isotopic compositions (Eichler et al.,
2000). High, exposed areas, such as Colle Gnifetti in the upper part of the Grenzgletscher accumulation area, are subject to this effect. Stichler and Schoterrer (2000) suggest that the erosive loss of light winter snow results in a ~3.5‰ increase in δ18O from what would be expected based on the elevation lapse rate alone. In such exposed areas, most accumulation is from summer precipitation. Below Colle Gnifetti, most of the Grenzgletscher accumulation area is not as exposed to wind. Given the location of the ice cores, the possible presence of seasonal variation (discussed below) and discussions from Rüegg, et al (2008), it is unlikely that the ice in the cores originated in Colle Gnifetti. Instead, the ice in all three cores most likely originated as precipitation in areas little affected by wind erosion. Isotopic differences between the cores are unlikely to be explained by wind erosion of snow in the accumulation areas.
6.1.2e. Microclimate Effects: Summary
In attempting to explain the lighter isotopic composition in the Grenzgletscher core, most microclimate factors do not appear significant. Storm tracks and the source of precipitation in the accumulation areas are similar, and extensive wind erosion is not likely in the source area for any of the ice cores in this study. Solar radiation differences and the resultant surface melting, though difficult to quantify, may enrich Grenzgletscher in heavy isotopes, and do not explain why core 3 is 4.8‰ lower δ18O. Avalanching above Grenzgletscher, however, may contribute 43
high elevation precipitation with 1.8‰ lower δ18O than in the rest of the accumulation zone. A summary of possible isotopic effects is shown in Table 4 .
Table 4. Summary of Isotopic Effects in the Accumulation Areas
Effect Net Effect on δ18O Elevation The Grenzgletscher accumulation area is higher decrease δ18O in Grenzgletscher by up to 1.1 ‰ than the Zwillingsgletscher accumulation area. Accumulation The orientations of storm tracks relative to the two no large effect expected accumulation areas are similar Avalanching A large, steep slope adjacent to the accumulation area may introduce higher elevation precipitation to decrease δ18O in Grenzgletscher by up to 1.8 ‰ Grenzgletscher Precipitation Source Deuterium excess factors are not significantly different between glaciers, suggesting similar no large effect expected sources. Solar Radiation Mean annual solar radiation is higher for the increase δ18O in Grenzgletscher by an unknown amount Grenzgletscher accumulation area. Wind Erosion The source areas for the ice in both cores are not no large effect expected strongly impacted by wind erosion. Total Expected lower δ18O in Grenzgletscher by up to 2.9 ‰ Observed lower δ18O in Grenzgletscher by ~ 4.8 ‰ 18 Difference lower δ O in Grenzgletscher by ~ 1.9 ‰
6.2 Age and Flow Rates
6.2.1. Age
As shown in the previous discussions, elevation and microclimate differences between the accumulation zones of Zwillingsgletscher and Grenzgletscher are alone not significant enough to account for the ~4.8‰ difference in δ18O observed in the ice cores. Although they do 44
not necessarily reflect differences in physical and chemical properties between the glaciers, the ages of ice in the cores may explain the remainder of the isotopic difference between the cores.
Age differences may be small scale (seasonal) or larger scale (annual to decadal climate variation).
Seasonal variation in the isotopic composition of precipitation is the result of temperature dependent fractionation. In order for seasonal variation to be observed in ice cores, accumulation from both summer and winter must be preserved. The plots of stable isotopic ratios in the ice cores (Figure 9) show a wave-like variation with depth. This variation is on the order of 41‰ for δD and 6‰ for δ18O. In the GNIP database, the closest high elevation isotope station to the study area is Grimsel, located at 1950 m (see Figure 32 in Appendix B). Grimsel precipitation data show a 6.3‰ seasonal variation for δ18O (Figure 36, Appendix B), although seasonal variation will be suppressed in the GNIP database because only monthly means are reported (IAEA, 2008). The hydrological yearbook of Switzerland (FOEN, 2008) reports seasonal variation of δ18O around 7-10‰ for the three closest precipitation stations to the study area (Figure 32). Rüegg, et al (2008) report seasonal variations of up to 10‰ δ18O for three cores in the ablation zone of Grenzgletscher. The magnitude of seasonal variation in this study is consistent with seasonal isotopic variation in nearby precipitation and ice cores.
Seasonal variation is most apparent in core 2 (down glacier in Zwillingsgletscher).
Approximately two annual cycles appear in the ~3 m core. The presence of seasonal variation in cores 2 and 3 suggest that both summer and winter accumulation are preserved. The uppermost part of the Grenzgletscher accumulation zone is a high, exposed saddle called Colle Gnifetti.
Numerous studies in this area have determined that there is dominant erosive loss of light, dry winter precipitation in this area due to wind exposure (Döscher et al., 1995; Eichler et al., 2000; 45
Haeberli et al., 1983; Smiraglia et al., 2000). Low accumulation rates and absent winter accumulation have been reported. The source of the ice in core 3 is therefore located somewhere below Colle Gnifetti in a less wind exposed area, which supports the previous discussion on erosion having a limited effect on the isotopes in core 3. Approximately one annual cycle is preserved in core 3 (see Figure 9).
In order to determine if seasonality is present in the surface samples, histograms of δ18O are shown in Figure 24. A seasonal isotopic distribution should be bimodal, with peaks for winter and summer. The actual distribution in the surface samples suggests that winter and summer accumulation is represented by the ice in the samples, but when plotted with easting (i.e. distance along the flow line) there is no obvious seasonal trend (Figure 25), most likely due to sampling frequency.
The seasonal differences alone do not account for the isotopic differences between
Zwillingsgletscher and Grenzgletscher. Although the magnitude of seasonal variation (~6‰
δ18O) is larger than the difference in the means for cores from the two glaciers, the seasonal curves are still offset. In other words, when the ―summer‖ accumulation (highest δ values) is compared between glaciers, and the ―winter‖ accumulation (lowest δ values) is compared between glaciers, there is still ~4-6‰ difference in δ18O in the cores, and ~1‰ difference in δ18O in the surface samples (Table 9 in Appendix A). This offset is also apparent in Figure 9. 46
Core 1
15 Zwillingsgletscher Surface
10 16 14 5 12 10 0
8
9 8 6 5 7
- - - - -
24 23 22 21 19 18 17 16 15 14 13 12 11 10 20
25
------6 4 Core 2 2 15
0
9 8 7 6 5 4 3
------
25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
------10 - δ18O Grenzgletscher Surface 5 8
0 7
8 7 6 5 9
- - - -
- 6
25 24 23 21 20 19 18 17 16 15 14 13 12 11 10 22
------5 4 Core 3 3 15 2 1 10
0
9 7 6 5 4 3 8
------
25 23 22 20 19 17 16 15 14 13 12 10 24 21 18 11
------5 -
δ18O
0
8 7 6 5 9
- - - - -
25 24 23 21 20 19 18 17 16 15 14 13 12 11 10 22
------δ18O Figure 24. Histograms of δ18O (‰) in surface samples and ice cores. 47
0.0 406450 406500 406550 406600 406650 406700 406750 -5.0
-10.0 (‰)
-15.0
VSMOW O
18 -20.0 δ
-25.0 Zwillings Zwillings Ave -30.0
0.0 406960 406980 407000 407020 407040 407060 407080 -5.0
-10.0 (‰)
-15.0
VSMOW O
18 -20.0 δ
-25.0 Grenz Grenz Ave -30.0
Figure 25. δ18O (‰) for surface samples plotted against Easting (UTM zone 32T), which approximates distance along the flow line. Average values indicate the average δ18O when the isotope ratio was measured in multiple sections from the same surface sample.
Although seasonal differences do not explain the differences in mean isotopic composition, they may provide a clue to the age of the ice collected in each ice core. While moving to greater depth in the accumulation zone, annual snow layers become thinner by viscous deformation. If the annual accumulation rate and annual layer thickness in an ice core are known, the age of the ice may be estimated (Schwerzmann et al., 2006).
Because annual layer thinning is a function of depth, a simple kinematic model of glacier flow may be used to quantitatively describe thinning. Eichler et al. (2000) use the kinematic ice- flow model of Nye (1963): 48
t (11) in which t is the age of a layer y distance below the surface. The absolute ice thickness is H and
λ0 is the initial annual layer thickness. Although this model does not take into account a dynamical ice-flow law, it has been successfully applied to time-scale estimations down to 2/3 H
(Eichler et al., 2000). Using a given absolute ice depth and initial accumulation rate for the two glaciers, the age of the ice in the cores may be estimated based on the current thickness of the annual layers. From the discussion of microclimate above, the annual accumulation rates for
Grenzgletscher and Zwillingsgletscher may be assumed to be the same, as long as the area of accumulation for Grenzgletscher is below Colle Gnifetti.
For purposes of comparison, λ0=2.7 m w.e. was used for both glaciers, based on ice core data from Eichler et al. (2000), which is similar to rates obtained by other authors (see Table 10 in Appendix A). The effective annual layer thickness in the ice cores (λE) was estimated from peak to peak (summer to summer) in the isotopes (Figure 9). The annual thickness of ice in the cores was converted to meters water equivalent using a density of 0.9 g/cm3. For core 2
(Zwillingsgletscher), λE = 1.4 m w.e., and for core 3 (Grenzgletscher), λE = 1.7 m w.e.
Absolute ice thickness, H, is estimated based on surface and bedrock elevations reported by Eisen et al. (2009). Surface and bedrock elevations were interpolated using ArcMap 9.3, and the difference between the interpolated layers was taken as the ice thickness, as shown in Figure
26. The estimated ice thicknesses are 290 m at core 1, 215 m at core 2, and 330 m at core 3.
Ages of the ice estimated using these H values in Nye’s ice flow model (Eq. 11) are shown in
Figure 27. Probable ages are 52 years for core 2 and 56 years core 3. These ages are consistent with those determined by other authors. Using an average flow velocity and distance traveled 49
along the flow path, Rüegg et al. (2008) estimated that ice sampled from Grenzgletscher roughly in the vicinity of core 3 was 30-150 years old, which was consistent with measured grain size.
The ages calculated in the current study should, however, still be considered rough estimates because Nye’s flow model (Eq. 11) does does incorporate flow dynamics and includes parameters (annual accumulation and absolute ice thickness) that were not directly measured in this study.
Figure 26. Ice thickness (m) in the confluence region of Zwillingsgletscher and Grenzgletscher with ice core locations. White squares indicate surface samples. Light contours show surface elevation.
50
Figure 27. Estimated ages of ice in core 2 (Zwillingsgletscher) and core 3 (Grenzgletscher) based on the ice flow model of Nye (1963). Lines reflect uncertainty in ice thickness.
The general observation may be made that the ice in the Grenzgletscher core is apparently older than the ice in Zwillingsgletscher by ~4 years. This age difference may be insignificant within inherent uncertainty in the analysis, or it may be larger, up to 10-15 years, depending on the true values for annual layer thickness, accumulation rate, and ice thickness.
6.2.2. Flow Rates
Age estimates may be used to get a sense of relative flow velocity. Along flow lines visible in aerial photographs, core 2 is ~3300 m from the ELA, and core 3 is ~3500 m from the
ELA. These are the minimum travel distances. The maximum travel distances are ~4500 m and
~7500 m, based on the distance from the sample site to the head wall along flow lines. In Figure
28, velocities for the two glaciers are plotted based on the maximum and minimum possible flow distances for each glacier. Velocities in the range 60-120 m/yr are in agreement with Rüegg et 51
al. (2008) (50-150 m/yr for Grenzgletscher). The calculated velocities are also supported by the movement of a specific boulder in the medial moraine between the July 2009 field season and a return trip in May 2010. Survey measurements indicate 78 m of movement in 10 months, corresponding to a velocity of approximately 90 m/yr. The magnitude of the velocity difference between the two glaciers depends on the source area for the ice (i.e. distance traveled).
Assuming that the ice in core 3 has traveled farther than the ice in core 2, the ice in
Grenzgletscher is traveling more rapidly than the ice in Zwillingsgletscher.
160
140
120
100 Core 2 Core 3 80
60 Velocity(m/yr) 40
20
0 3000 4000 5000 6000 7000 8000 Distance Traveled (m)
Figure 28. Estimated velocity for Zwillingsgletscher and Grenzgletscher. Estimates based on age of ice in cores (Figure 27) (52 yr for Zwillingsgletscher and 56 yr for Grenzgletscher) and flow distances of 3500-7500 m for Grenzgletscher and 3300-4500 m for Zwillingsgletscher.
6.2.3. Isotopes and Ages of Ice in Cores
As a result of varying flow distances and velocities, the ice sampled from Grenzgletscher is ~4 years older. The age difference between the ice cores could explain part of the isotopic difference between the glaciers (~4.8 ‰ in δ18O) if there is climatic variation on the order of this 52
time range with temperature changes large enough to produce a significant change in the isotopic content of precipitation.
Climate data from four Swiss weather stations are shown Figure 29. The only high elevation station is Saentis (2490 m a.s.l.), but Lugano and Geneve are the two closest stations to the study area (see Figure 32). For each station, the interannual variability of the mean annual air temperature can be as large as ~2-3°C over the last 100 years. Using Eq. 9 for the local relationship between temperature and δ18O (IAEA, 2008), a temperature change of 2°C corresponds to ~0.9 -1.4‰ change in δ18O.
Short-term climate variation may therefore contribute partially to the isotopic differences between ice cores in the two glaciers. In other words, the lighter isotopic composition of the
Grenzgletscher core may simply be the result of a colder winter. In order to account for the
4.8‰ difference in δ18O, it is necessary to assume elevation-dependent fractionation in the precipitation and microclimates for the two glaciers (up to 2.9‰, see Table 4), as well as temperature variation between the times of precipitation (up to1.4‰).
Flow velocities for the two glaciers may be similar, but Grenzgletscher likely has a higher velocity. This finding has important implications for the flow dynamics of the glacier system as a whole. The higher flow velocity of the main valley glacier may be due to glacier geometry (size, shape, slope), as well as physical properties that affect flow (grain size, fabric, etc.).
53
Figure 29. Long term climate from 5 Swiss weather stations. Annual average temperatures are shown from 1900-2004. Data and graphs from (ECA&D, 2010) 54
6.3 Solutes, Dust Content, Bubble Density
In addition to the isotopes, seasonal variation appears in the solutes, dust content, and bubble density in the ice cores. When plots of isotopes, bubble density, dust content, and total anion concentration are displayed side-by-side (Figure 30), some correlation is apparent between the parameters measured with depth in the ice cores. No such correlation was discovered in cores from the Grenzgletscher ablation zone and Colle Gnifetti in a previous study by Rüegg et al. (2008). The seasonality of dust, bubble density, and solute concentrations has been well established, however, in the literature as described below. The correlation provides some support for the annual layer thicknesses described above based on variations in the isotopes.
Such a multi-parametric approach is employed by Eichler et al. (2000).
Figure 30. Measurements from core 2 with depth showing possible seasonal correlation. ―Summer‖ conditions are indicated around 1.00 and 2.75 m depth. ―Winter‖ corresponds to low δ18O around 2.00 m.
55
6.3.1. Solute Concentrations
As water refreezes during recrystallization, nearly all solutes are preferentially rejected by the ice, resulting in very low solute concentrations. Leaching also occurs as precipitation or meltwater from the surface percolates downward though snow and firn, entraining dust and aerosols (Souchez and Lorrain, 1991; pp. 65-66). These leaching and flushing processes lead to lower solute concentrations in ice that is down glacier or has experienced more deformation and recrystallization. The low solute concentrations in the core from Grenzgletscher (core 3) offer support for longer travel distances for that ice. Although both cores from Zwillingsgletscher are roughly along the same flow path, the core further downstream (core 2) may have lower chloride and nitrate concentrations because it has experienced more melting, freezing, and flushing.
The effect of progressively increasing flushing of solutes is seen in the solute concentrations of the surface samples (Figure 15). When plotted against easting (approximately distance along flow line), the concentrations of individual analytes generally decrease from right
(up-glacier) to left (down-glacier).
A seasonal variation is apparent in cores 2 and 3, but the data are scattered in core 1. The same lack of a clear signal was also observed in the isotopes of core 1. Seasonal variation in solutes is due to variations in the source of the solutes during the course of a year (for example, increased agricultural activities during summer months increases certain solutes such as ammonium), and vertical transport of solutes to high-alpine sites that varies seasonally (Eichler et al., 2000). In particular, sulfate records are often used to provide seasonal signals and define annual variation (Smiraglia et al., 2000). In Figure 14, the peaks in sulfate in core 2 may be seasonal. The seasonal variation in solute concentration offers support for seasonal variation in the isotopes. 56
6.3.2 Dust Content
Estimated dust concentrations in this study are more in the range suggested for Saharan dust fall events (0.01-0.1 mg/cm3) in Grenzgletscher ice cores (Haeberli et al., 1983). In studies of ice cores from Colle Gnifetti, Wagenbach, et al. (1996) identified Saharan dust events by peaks in Ca2+, corresponding peaks in δ18O and deuterium excess, and yellow-red meltwater filters. One peak in Ca2+ is interpreted as a Saharan dust fall in the late 1950s. The ice collected in this study originated during that time period. It is unlikely the dust in this study is from a
Saharan dust event, however, because the dust concentrations from both glaciers, which are separated in age by ~4 years, have the same order of magnitude.
Instead of indicating a specific event, dust content in the ice cores (plotted with depth in
Figure 16) shows a possible seasonal variation that coincides with the seasonal variation in isotopes. The absolute concentrations reported are not entirely reliable (see Results section), but the variation in dust concentration with depth in the cores is useful. Higher dust concentrations are expected in the summer (with higher δ18O and δD) (Wagenbach et al., 1996) due to lack of snow covering the soil (Dams and Jonge, 1976). This effect was observed in the field, when gusts of wind entrained large amounts of dust from the valley sides. During the winter, these valley slopes and walls are covered with snow, preventing removal by wind. The alignment of the seasonal variation with the isotopic composition supports the presence of annual layers present in the cores as opposed to single precipitation events.
6.3.3 Bubble Density
Air bubbles are created in glacier ice during the firnification of snow. When the interconnecting air passages between grains are sealed off, firn becomes glacier ice with air 57
bubbles (Paterson, 1994; pp. 6-10). The high bubble density and small bubble size (less than 5 mm) observed in the ice cores are typical of englacial ice (Hubbard et al., 2000).
In general, ice from core 3 (Grenzgletscher) exhibits higher bubble density. Cores 1 and
2 (Zwillingsgletscher) exhibit comparable bubble density, although the bubbles are much more elongated in core 1. Reduced bubble density may be caused by near surface or englacial processes. Near the surface, freezing and percolating meltwater in the surface snowpack, cracks, or firn may result in fewer air bubbles being trapped. Within the glacier, deformation-generated and grain-boundary melting and refreezing can reduce bubble density (Hubbard et al., 2000).
Lower bubble density in the Zwillingsgletscher cores may suggest more meltwater or warmer conditions during firnification. Bands of clear, bubble-free ice in core 2 support this hypothesis.
If the Grenzgletscher ice originated from very cold, dry snow, it should have higher bubble density. Cold, dry snow is consistent with the higher elevation (by up to more than 400 m) of the
Grenzgletscher accumulation zone relative to the Zwillingsgletscher accumulation zone.
According to Rüegg et al. (2008), bubble density is not related to primary stratification, but is instead the result of foliation. Foliation is the result of deformation of inhomogeneities further up glacier. The elongation of bubbles in core 1 strongly suggests deformation. The variation of bubble density with depth with roughly the same periodicity as the variation in stable isotopes, however, suggests that bubble density is at least somewhat related to primary stratification. In terms of the significance of bubble density, Rüegg et al. (2008) point out that strain rate increases with bubble density (Hooke, 1973). In addition, higher strain rate may increase deformation and lead to further bubble formation in the weaker zones of high bubble density. If bubble-rich ice is dominant throughout Grenzgletscher, the soft ice would contribute to increased strain rate (Souchez and Lorrain, 1991; p. 85). 58
6.4 Ground Penetrating Radar
The antiformal shapes of high-reflectivity onset 10-20 m below the glacier surface
(Figure 20) generally mimic the wave ogives visible on the Zwillingsgletscher surface and in aerial photographs. Part of the 775-m GPR transect covered the ogives pictured in Figure 6. The subsurface pattern does not necessarily correspond exactly to the wave ogives visible at the surface, but the wavy onset of reflectivity suggests that ogive-forming processes influence the glacier ice at least in the upper 10-20 m.
Mechanisms for the formation of ogives are still a topic of debate. Goodsell, et al. (2002) suggest that band ogives (light and dark bands) are due to different amounts of foliation, most likely caused by longitudinal extension above and compression and shearing below an ice fall.
Wave ogives, as suggested by Nye (1958), form during steady ice flow that is stretched due to increased velocity as it passes through an ice fall. The ice that passes through the ice fall and is stretched during the summer is more exposed to ablation, resulting in a wave trough below the ice fall. Annual waves due to velocity changes are usually the largest, although waves may also be generated by changes in other parameters along the flow line, including channel width and mass balance (Waddington, 1986).
Although formed by different mechanisms, both band ogives (Fisher, 1962) and wave ogives are related to ice falls where there is a zone of rapid ice acceleration. The wave ogives observed on Zwillingsgletscher are the result of rapid acceleration through an ice fall. In order to determine if and how ogive-related structures produce antiformal zones of high and low reflectivity, it is necessary to understand causes of reflectivity in the ice subsurface.
The strength of reflections in a GPR survey is a function of the difference in dielectric permittivity between two points in the subsurface. The interfaces of different materials across 59
which there is a change in permittivity (ε) produce reflection. Stronger reflections are produced by larger contrasts in permittivity. In the top 50 m of Zwillingsgletscher, ice, water, and sediment may be present. As shown in Figure 31, near the melting point there is a contrast between the permittivity values of ice and water. Sediment will have permittivity values lower than water. GPR reflections will therefore occur at the contacts between ice, water, and sediment. Based on a center frequency of 200 MHz and a velocity of 0.16 m/ns, vertical resolution is about 0.2 m (λ/4). Pockets of sediment or liquid water with high reflectivity separated by at least 0.2 m will be seen as separate on the GPR profile. More closely-spaced layers of high reflectivity will still be observed on the profile, but not as distinct layers.
Figure 31. Steady state permittivity εs of pure polycrystalline ice and pure water as functions of temperature T. From (Petrenko and Whitworth, 1999).
In the frequency range in this study, ice below the melting point is transparent to electromagnetic waves (Paterson, 1994; pp.73-74). The relatively transparent zone in the upper
10-20 m of Zwillingsgletscher suggests cold ice without pockets of water, which is consistent with measurements taken of surface samples and ice cores (-2 to -5°C in upper 0-3 m). 60
A GPR study conducted using a 100 MHz antenna in the ogived region of Bas Glacier d’Arolla (25 km northeast of the study area) by (Goodsell et al., 2002) produced a profile with similar antiformal zones of high reflectivity. The authors in that study interpreted the zones of high reflectivity as foliated zones that correspond to the dark, highly foliated band ogives.
Reflectivity was due to ―changes in ice properties across foliation boundaries.‖
Another study, conducted at 40 MHz by Eisen, et al. (2009), suggests that areas of low backscatter within GPR profiles of Grenzgletscher correspond to a tongue of cold ice that extends up to 400 m laterally and almost 200 m deep at its center. These authors explain that the cold ice is below the pressure melting point, so the liquid-water content is greatly reduced and less backscatter is observed. This hypothesis was supported by thermistor data that show the cold-temperate-transition-surface (CTS) at or near the depth of the onset of high reflectivity.
Eisen, et al. (2009) deduce that scattering is due to liquid-water inclusions, as opposed to boulders or sediments, because such materials were not encountered during drilling. The proposed mechanism for the cold layer requires the following steps: (1) a cold layer originates high in the accumulation area, (2) this layer is covered by temperate ice further down glacier, (3) at some point in the ablation area, the overlying temperate ice is removed by ablation, and (4) the underlying ice is heated from below due to strain heating and the geothermal heat flux.
A direct comparison between these studies and the new GPR survey is complicated by the use of different frequencies :100 MHz in Goodsell et al. (2002) and 40 MHz in Eisen et al.
(2009). The correlation between transparency and temperatures below the pressure melting point
(Eisen et al., 2009) may or may not be valid at the higher frequencies (200 MHz) used in the new survey. If the correlation is valid, the GPR profiles of the Zwillingsgletscher subsurface 61
suggest that a layer of cold ice (10-20 m thick) overlies waves of warmer ice at the pressure melting point.
One explanation for the wave-like surface between warmer ice and the overlying cold ice involves the depth of influence of air temperatures. In temperate glaciers, ice is at the pressure melting point throughout, except in a cold surface layer, about 15 m thick, that varies in response to seasonal changes in surface temperature (Paterson, 1994; pp.9, 186). If the troughs on the ice surface are aligned with the troughs in the onset of reflectivity, it is likely that the cold ice layer is the result of air temperatures below 0°C. Where there are crests in the glacier surface caused by ogives, the influence of cold air temperatures will not be as deep. Ogives therefore influence the subsurface thermal structure of the glacier. The temperature contrast has implications for the internal ice dynamics of the system, because strain rate depends on ice viscosity, which is a function of temperature (Eq. 3 and 4).
7. CONCLUSION
Based on the results of ice cores, surface samples, and GPR profiles of Zwillingsgletscher and Grenzgletscher, glacier modeling may be improved by incorporating the geometry and chemical and physical properties of the tributaries in complex glacier systems. Such models could have multiple applications, such as predicting glacier response under future climate scenarios, reconstructing paleoclimate using geomorphologic evidence of past glacier extent, and understanding modern glacier responses. In order to improve glacier models, it is essential to study the physical and chemical properties of tributary glaciers.
In this study, ice properties between two adjacent glaciers were determined from shallow cores (~3m) and surface samples (<0.5 m). Stable water isotopes from cores in a tributary 62
glacier (Zwillingsgletscher) and a main valley glacier (Grenzgletscher) show a ~4.8‰ difference in mean δ18O. Multiple factors may contribute to this difference. First, the accumulation zones of the two glaciers are at different elevations. Using a local elevation lapse rate, the higher elevation of the Grenzgletscher accumulation zone may account for ~1.1‰ difference in δ18O.
Microclimates for the two glaciers are similar, but avalanching from the steep slope adjacent to
Grenzgletscher may contribute high elevation precipitation with ~1.8‰ lower δ18O. Interannual variation in climate may also explain isotopic differences. Isotopically light ice may simply reflect precipitation during a colder winter. Interannual temperature variability on the order of 2-
3°C may account for ~0.9-1.4‰ difference in δ18O. The sum of all these effects (4.3‰) approaches the isotopic variation observed between tributary and main valley glaciers.
Spatial variability between adjacent glaciers is the focus of this study. Notably, spatial variability in ice properties also occurs within an individual glacier, suggesting that one or two shallow cores are not necessarily representative of the overall glacier. For example, the influence of avalanching in a core depends on the proximity of its source area to valley walls. In order to draw definitive conclusions about the properties of a particular glacier, data from many more cores should be collected.
From the few cores collected, seasonal variation in δ with depth permitted the estimation of annual layer thickness, and using a kinematic flow model (Nye, 1963), ages of the ice and velocities of the respective glaciers were calculated. A lower flow velocity is observed in the tributary glacier (~63-87 m/yr), than in the main valley glacier (~61-134 m/yr). This difference may be due to lower temperatures, fewer ice crystals with favorable c-axis orientations, or possibly increased grain size and decreased grain-boundary sliding. Channel shape and size also influence the velocity. It is important to note that several assumptions were made in determining 63
the relative velocities of the two glaciers, including the annual accumulation rate and absolute ice thickness. The effective annual layer thickness in the cores was also estimated using only 1-2 annual cycles. Solutes and dust concentrations in the ice cores offer support for seasonal layering in the isotopes. To achieve more reliable age estimates, however, longer cores (and hence longer records) should be obtained to observe a more definite annual layer thickness.
Dating by 210Pb methods (e.g., Gäggeler et al., 1983) should also be incorporated into future studies to confirm relative ice ages. More information on grain size and c-axis orientation is needed in order to better constrain flow dynamics.
Support for annual layer thicknesses (and age and velocity calculations) is provided by seasonal variation in solute concentrations in the ice cores. In the depths examined in this study
(0-3 m), however, solute concentrations between glaciers are not dramatically different. Deeper cores that have been less influenced by leaching due to meltwater and precipitation would be required to check for any significant differences between the two glaciers. A significant difference in solute concentrations could potentially affect strain rates due to the lower eutectic temperatures of solutes and melting at grain boundaries. Salt-rich solutions between ice crystals will increase sliding at grain boundaries. Higher bubble density in the core from Grenzgletscher is consistent with a higher elevation source area and firnification occurring in colder, drier conditions. Increased strain rate due to higher bubble density supports a higher strain rate for
Grenzgletscher, consistent with velocity estimates.
In addition to measuring ice properties near the surface, ground penetrating radar was used to determine subsurface properties. Using a 200 MHz antenna, GPR data show evidence for a complex thermal structure in the tributary glacier. The wave-like onset of reflectivity 10-20 m below the surface is likely related to ogives. Ogives are formed as ice accelerates rapidly 64
through an ice fall, leaving crests and troughs. A layer of cold ice with low reflectivity mimics the shape of wave ogives, indicating the depth of the influence of cold air temperatures. Below the cold layer, ice is at the pressure melting point, and pockets of water result in high reflectivity.
The subsurface thermal structure in Zwillingsgletscher has implications for other tributary glaciers. Ice falls often form at the confluence of tributary glaciers, where the steep gradient is a natural result of increased mass balance (Anderson et al., 2006b). Because the thermal properties that influence strain rates in tributary glaciers are influenced by ice falls, it is important to include the results of tributary ice falls in studies of ice flow in complex glacier systems.
Much of this research focused on explaining isotopic differences between cores from the two glaciers. Although stable water isotopes may not have a direct influence on strain rate (see
Equations 3-6), they are often ―tracers‖ that indicate changes in other properties that do impact strain rate. Some of these properties may include solutes, dust content, and bubble density, all of which are incorporated into the softness parameter, A, in Glen’s Flow Law (Eq. 3).
Temperature, (indirectly observed using GPR) is also incorporated in the softness parameter (Eq.
4) and influences strain rate. All of these parameters determine the internal ice dynamics of a glacier and how it responds to changes in climate. This study has shown that tributary glaciers can exhibit different physical and chemical properties from the main valley glacier as a result of elevation and microclimate differences between the accumulation areas, and geomorphologic differences such as channel shape and ice falls. These differences, as well as tributary geometry and mass balance, should be incorporated into numerical models of glacier advance and retreat. 65
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9. APPENDIX A: ADDITIONAL TABLES
Table 5.Shape Factors (F) for shear stress in glacier ice* (W=half-width/thickness at the center line).
Cross-sectional Channel Shape W Parabola Semi-ellipse Rectangle 1 0.445 0.5 0.558 2 0.646 0.709 0.789 3 0.746 0.799 0.884 4 0.806 0.849 ∞ 1.000 1.000 1.000 *From (Paterson, 1994; p. 103)
Table 6.UTM Coordinates (Zone 32T) of Ice Cores and Surface Samples
Glacier Point Easting Northing Elevation (m) Glacier Point Easting Northing Elevation (m) Zwillingsgletscher Core 1 406571 5090718 2550 Grenzgletscher Core 3 407055 5090846 2553 Core 2 406693 5090445 2584 Zwillingsgletscher S1 406609 5090648 2564 Grenzgletscher S31 407074 5090887 2555 S2 406600 5090662 2564 S32 407067 5090906 2557 S3 406595 5090673 2562 S33 407054 5090933 2556 S4 406592 5090685 2564 S34 407054 5090954 2553 S5 406586 5090697 2562 S35 407040 5090961 2551 S6 406578 5090706 2557 S36 407021 5090969 2549 S7 406572 5090720 2556 S37 407014 5090984 2544 S8 406568 5090729 2554 S38 407001 5091000 2543 S9 406561 5090734 2557 S39 406988 5091018 2545 S10 406553 5090740 2553 S40 406972 5091036 2545 S11 406559 5090749 2553 S12 406556 5090756 2551 S13 406553 5090766 2551 S14 406542 5090784 2553 S15 406534 5090791 2550 S16 406521 5090805 2545 S17 406513 5090815 2551 S18 406499 5090824 2550 S19 406495 5090837 2550 S20 406484 5090844 2550 S21 406475 5090856 2544 S22 406616 5090638 2572 S23 406625 5090624 2569 S24 406636 5090608 2569 S25 406646 5090595 2572 S26 406652 5090585 2576 S27 406666 5090568 2576 S28 406669 5090547 2579 S29 406679 5090516 2577 S30 406702 5090474 2581 *Data obtained using a Garmin 60CSX handheld GPS unit. 71
Table 7.Published Elevation Lapse Rates
(‰ δ18O / 100 m) Area Authors -0.2 Switzerland (Schürch et al., 2003) -0.2 Swiss Alps (Stichler and Schotterer, 2000) -0.24 French and Italian Alps (Dray et al., 1998) -0.25 Italian Alps (Zuppi and Bortolami, 1982) -0.26 Central Switzerland (Siegenthaler and Oeschger, 1980) -0.28 Global (excl. extreme high elevations) (Poage and Chamberlain, 2001)
Table 8.Accumulation Zone Elevations (from DEM)
Elevation of Accumulation Zone (m) Minimum Maximum Mean Zwillingsgletscher 3239 3774 3492 Grenzgletscher 3246 4209 3704 Difference: 7 435 213 X lapse rate: 0‰ 1.1‰ 0.6‰
Table 9.Comparison of δ18O for “Winter” (lowest ¼) and “Summer” (highest ¼)
18 Statistically Significant Comparison of Mean δ OVSMOW of Top and Bottom Quarter Difference (‰) p-value α=0.01 α=0.001 Ice Cores Main glacier and Tributary, up glacier Lowest 1/4 Winter -4.88 6.19E-12 yes yes Core 2 vs Core 3 Highest 1/4 Summer -5.49 1.37E-07 yes yes Main glacier and Tributary, down glacier Lowest 1/4 Winter -6.76 9.23E-14 yes yes Core 1 vs Core 3 Highest 1/4 Summer -4.42 9.90E-08 yes yes Tributary, up glacier and Tributary, down glacier Lowest 1/4 Winter -1.87 0.0000 yes yes Core 1 vs Core 2 Highest 1/4 Summer 1.07 0.0636 no no Main glacier and Tributary, both cores Lowest 1/4 Winter -5.22 5.56E-13 yes yes Cores 1,2 vs Core 3 Highest 1/4 Summer -5.12 2.47E-12 yes yes Surface Samples Surfaces of Main glacier and tributary Lowest 1/4 Winter -0.64 0.1444 no no S1-S30 vs S31-S40 Highest 1/4 Summer -1.46 0.0398 no no
72
Table 10.Annual Accumulation Rates for Grenzgletscher Region
Annual Accum. Area Authors Comments (m w.e.) Wind-protected slopes and 2-3 Upper Grenz (Suter et al., 2001) basins Calculated from ice-core data 2.7 Upper Grenz (Eichler et al., 2000) + 18 (NH4 and δ O) 1.9 Upper Grenz (Eichler et al., 2000) Based on 210Pb dating From (Döscher, 1996; Gäggeler 2 Upper Grenz (Eichler et al., 2000) et al., 1997) Reflects 10% of mean annual 0.2-0.6 Colle Gnifetti (Eisen et al., 2003) precipitation Low accumulation due to wind 0.3 Colle Gnifetti (Eichler et al., 2000) erosion 0.2 to 1.1 Colle Gnifetti (Lüthi and Funk, 2000)
0.278 Colle Gnifetti (Smiraglia et al., 2000)
(Döscher et al., 1995; Only 15% of precipitation at 0.32-0.37 Colle Gnifetti Gäggeler et al., 1983) this altitude 0.55 Colle Gnifetti (Haeberli et al., 1983) Some years larger (0.65 m w.e.) Mean precipitation rate from Col du Grand St 2.4 (Eichler et al., 2000) closest (50 km) high elevation Bernard weather station (2469 m a.s.l.) 73
Table 11.Core Sample Field Measurements
Section Depth Core Depth Core radius (cm): 2.827 Section Sample Ave. Section Density Isotope Chem. Core Start End Start End Caliper Caliper Caliper Thickness Weight Lab # Number Number Caliper Volume (g/cm3) Sample Sample (cm) (cm) (m) (m) (mm) (mm) (mm) (cm) (g) (mm) (cm3) 1 1.1 1.1.1 0.0 5.1 0.00 0.05 51.51 48.31 47.5 49.11 4.91 123.29 95 0.771 1 2 7151 1.1.2 5.1 10.2 0.05 0.10 53.01 51.51 52.05 52.19 5.22 131.04 118.6 0.905 3 4 7152 1.1.3 10.2 15.2 0.10 0.15 53.7 53.5 53.47 53.56 5.36 134.47 124 0.922 5 6 7153 1.1.4 15.2 20.3 0.15 0.20 48.81 47.7 45.49 47.33 4.73 118.84 109 0.917 7 8 7154 1.1.5 20.3 21.0 0.20 0.21 THIN SECTION 1.1.6 21.0 23.5 0.21 0.23 18.76 18.73 17.72 18.40 1.84 46.21 44.4 0.961 DUST SAMPLE 1.1.7 23.5 28.6 0.23 0.29 47.77 49.38 47.9 48.35 4.84 121.39 113.4 0.934 9 10 7155 1.1.8 28.6 33.7 0.29 0.34 52.15 52.31 51.95 52.14 5.21 130.90 121.6 0.929 11 12 7156 1.1.9 33.7 38.7 0.34 0.39 46.27 48.68 47.53 47.49 4.75 119.24 110 0.922 13 14 7157 1.1.10 38.7 43.8 0.39 0.44 45 45.85 45.08 45.31 4.53 113.76 105.3 0.926 15 16 7158 1.1.11 43.8 44.5 0.44 0.44 THIN SECTION 1.1.12 44.5 47.0 0.44 0.47 21.64 21.27 21.06 21.32 2.13 53.54 51.2 0.956 DUST SAMPLE 1.1.13 47.0 52.1 0.47 0.52 47.22 46.73 46.56 46.84 4.68 117.59 109 0.927 17 18 7159 1.1.14 52.1 57.2 0.52 0.57 51.59 52.28 53.36 52.41 5.24 131.59 123.8 0.941 19 20 7160 1.1.15 57.2 62.2 0.57 0.62 50.67 50.69 50.4 50.59 5.06 127.01 117.3 0.924 21 22 7161 1.1.16 62.2 67.3 0.62 0.67 50.9 49.72 49.8 50.14 5.01 125.89 119 0.945 23 24 7162 1.1.17 67.3 67.9 0.67 0.68 THIN SECTION 1.1.18 67.9 70.5 0.68 0.70 17.66 17.7 18.5 17.95 1.80 45.08 41.9 0.930 DUST SAMPLE 1.1.19 70.5 75.6 0.70 0.76 45.22 45.56 46.17 45.65 4.57 114.62 108 0.942 25 26 7163 1.1.20 75.6 80.6 0.76 0.81 46.56 46.58 46.35 46.50 4.65 116.74 108.2 0.927 27 28 7164 1.1.21 80.6 88.3 0.81 0.88 75.19 75.12 75.17 75.16 7.52 188.71 168.2 0.891 29 30 7165 1.2 1.2.1 0.0 5.1 0.88 0.93 50.5 49.3 50.88 50.23 5.02 126.11 112.3 0.891 31 32 7166 1.2.2 5.1 10.2 0.93 0.98 49.99 43.76 43.65 45.80 4.58 114.99 99.7 0.867 33 34 7167 1.2.3 10.2 15.2 0.98 1.04 54.6 52.88 53.57 53.68 5.37 134.78 122.5 0.909 35 36 7168 1.3 1.3.1 0.0 10.2 1.04 1.14 79.32 78.12 75.27 77.57 7.76 194.76 220.4 1.132 37 38 7169 1.4 1.4.1 0.0 0.6 1.14 1.14 THIN SECTION 1.4.2 0.6 8.3 1.14 1.22 79.73 78.2 79.04 78.99 7.90 198.32 175.2 0.883 39 40 7170 1.5 1.5.1 0.0 5.1 1.22 1.27 35.63 44.39 42.06 40.69 4.07 102.17 75.8 0.742 41 42 7171 1.6 1.6.1 0.0 5.1 1.27 1.32 fractured 81.3 DUST SAMPLE 1.6.2 5.1 12.7 1.32 1.40 fractured 116.2 43 44 7172 1.6.3 12.7 20.3 1.40 1.47 fractured 93.4 45 46 7173 1.6.4 20.3 22.9 1.47 1.50 fractured 47 48 7174 1.7 1.7.1 0.0 7.6 1.50 1.57 72.71 72.21 73.02 72.65 7.26 182.40 159.1 0.872 49 50 7175 1.7.2 7.6 8.9 1.57 1.59 THIN SECTION 1.7.3 8.9 20.3 1.59 1.70 169.6 171.6 170.8 170.67 17.07 428.50 51 52 7176 1.8 1.8.1 0.0 5.1 1.70 1.75 51.55 51.1 51.07 51.24 5.12 128.65 118.2 0.919 53 54 7177 1.8.2 5.1 7.6 1.75 1.78 24.37 24.67 23.56 24.20 2.42 60.76 55.4 0.912 55 56 7178 1.8.3 7.6 12.7 1.78 1.83 70.26 72.03 72.89 71.73 7.17 180.09 168.3 0.935 57 58 7179 1.9 1.9.1 0.0 3.8 1.83 1.87 41.07 45.25 41.06 42.46 4.25 106.61 82.1 0.770 59 60 7180 1.10 1.10.1 0.0 2.5 1.87 1.89 26.16 29.41 25.05 26.87 2.69 67.47 57.5 0.852 THIN SECTION 1.10.2 2.5 7.6 1.89 1.94 48.1 48.27 57.41 51.26 5.13 128.70 111.2 0.864 61 62 7181 1.10.3 7.6 15.2 1.94 2.02 87.48 82.29 78.45 82.74 8.27 207.74 186.4 0.897 63 64 7182 1.11 1.11.1 0.0 7.6 2.02 2.10 67.75 66.85 72 68.87 6.89 172.91 147.5 0.853 65 66 7183 1.11.2 7.6 10.2 2.10 2.12 THIN SECTION 1.11.3 10.2 20.3 2.12 2.22 79.05 79.84 78.35 79.08 7.91 198.55 184 0.927 67 68 7184
74
Table 11. Core Sample Field Measurements (cont.)
Section Depth Core Depth Core radius (cm): 2.827 Section Sample Ave. Section Density Isotope Chem. Core Start End Start End Caliper Caliper Caliper Thickness Weight Lab # Number Number Caliper Volume (g/cm3) Sample Sample (cm) (cm) (m) (m) (mm) (mm) (mm) (cm) (g) (mm) (cm3) 2 2.1 2.1.1 0.0 5.0 0.00 0.05 47.29 45.52 46.77 46.53 4.65 116.82 88.6 0.758 69 70 7185 2.1.2 5.0 10.0 0.05 0.10 47.08 45.75 45.08 45.97 4.60 115.42 99.9 0.866 71 72 7186 2.1.3 10.0 15.0 0.10 0.15 44.78 46.06 44.38 45.07 4.51 113.17 104.2 0.921 73 74 7187 2.1.4 15.0 15.5 0.15 0.16 THIN SECTION 2.1.5 15.5 18.0 0.16 0.18 18.15 17.21 16.56 17.31 1.73 43.45 41.1 0.946 DUST SAMPLE 2.1.6 18.0 23.0 0.18 0.23 50.81 51.3 49.97 50.69 5.07 127.28 118.4 0.930 75 76 7188 2.1.7 23.0 28.0 0.23 0.28 50.74 49.34 50.29 50.12 5.01 125.85 119.1 0.946 77 78 7189 2.1.8 28.0 33.0 0.28 0.33 50.87 51.22 49.98 50.69 5.07 127.27 117.8 0.926 79 80 7190 2.1.9 33.0 38.0 0.33 0.38 50.92 52.9 50.8 51.54 5.15 129.40 120.1 0.928 81 82 7191 2.1.10 38.0 38.5 0.38 0.39 THIN SECTION 2.1.11 38.5 41.0 0.39 0.41 17.67 19.01 18.09 18.26 1.83 45.84 42 0.916 DUST SAMPLE 2.1.12 41.0 43.0 0.41 0.43 29.04 28.65 29.66 29.12 2.91 73.10 68.8 0.941 83 84 7192 2.1.13 43.0 55.0 0.43 0.55 126.11 125.7 126.09 125.97 12.60 316.27 285.3 0.902 85 86 7193 2.2 2.2.1 0.0 5.1 0.55 0.60 58.07 47.57 51.33 52.32 5.23 131.37 108.3 0.824 87 88 7194 2.2.2 5.1 10.2 0.60 0.65 52.06 58.95 52.21 54.41 5.44 136.60 117.5 0.860 89 90 7195 2.2.3 10.2 15.2 0.65 0.70 46.35 46.73 46.39 46.49 4.65 116.72 105 0.900 91 92 7196 2.2.4 15.2 20.3 0.70 0.75 52.41 51.2 51.24 51.62 5.16 129.60 120.9 0.933 93 94 7197 2.2.5 20.3 21.6 0.75 0.77 THIN SECTION 2.2.6 21.6 24.1 0.77 0.79 21.56 21.4 23.26 22.07 2.21 55.42 51.2 0.924 DUST SAMPLE 2.2.7 24.1 29.2 0.79 0.84 44.48 44.49 44.46 44.48 4.45 111.67 104.4 0.935 95 96 7198 2.2.8 29.2 34.3 0.84 0.89 51.4 51.39 50.72 51.17 5.12 128.47 120 0.934 97 98 7199 2.2.9 34.3 39.4 0.89 0.94 43.54 44.11 44.3 43.98 4.40 110.43 103.2 0.935 99 100 7200 2.2.10 39.4 45.7 0.94 1.01 63.15 62.28 63.98 63.14 6.31 158.52 146.6 0.925 101 102 7201 2.3 2.3.1 0.0 8.9 1.01 1.10 63.66 81.61 71.78 72.35 7.24 181.65 160.7 0.885 103 104 7202 2.4 2.4.1 0.0 5.1 1.10 1.15 50.87 48.92 46.18 48.66 4.87 122.16 104.9 0.859 105 106 7203 2.4.2 5.1 6.4 1.15 1.16 THIN SECTION 2.4.3 6.4 8.9 1.16 1.19 19.21 20.15 20.34 19.90 1.99 49.96 48.4 0.969 DUST SAMPLE 2.4.4 8.9 14.0 1.19 1.24 49.99 49.71 51.06 50.25 5.03 126.17 117.4 0.930 107 108 7204 2.4.5 14.0 19.1 1.24 1.29 50.1 50.18 49.31 49.86 4.99 125.19 115.2 0.920 109 110 7205 2.4.6 19.1 34.3 1.29 1.44 131.98 129.55 131.25 130.93 13.09 328.72 296.3 0.901 111 112 7206 2.5 2.5.1 0.0 5.1 1.44 1.49 47.39 46.18 46.48 46.68 4.67 117.21 98.7 0.842 113 114 7207 2.5.2 5.1 10.2 1.49 1.54 51.39 51.33 52.04 51.59 5.16 129.52 118.5 0.915 115 116 7208 2.5.3 10.2 11.4 1.54 1.55 THIN SECTION 2.5.4 11.4 14.0 1.55 1.58 19.96 19.91 19.41 19.76 1.98 49.61 46.8 0.943 DUST SAMPLE 2.5.5 14.0 19.1 1.58 1.63 47.59 49.63 47.67 48.30 4.83 121.26 113.8 0.938 117 118 7209 2.5.6 19.1 27.9 1.63 1.72 77.4 77.23 76.79 77.14 7.71 193.68 177.7 0.918 119 120 7210 2.5.7 27.9 33.0 1.72 1.77 52.68 53.4 50 52.03 5.20 130.63 107.8 0.825 121 122 7211 2.5.8 33.0 34.3 1.77 1.78 THIN SECTION 2.5.9 34.3 36.8 1.78 1.81 21.55 22.67 20.74 21.65 2.17 54.37 51 0.938 DUST SAMPLE 2.5.10 36.8 48.3 1.81 1.92 102.04 97 100.32 99.79 9.98 250.54 221.6 0.884 123 124 7212 2.6 2.6.1 0.0 5.1 1.92 1.97 49.96 45.78 45.95 47.23 4.72 118.58 100.8 0.850 125 126 7213 2.6.2 5.1 10.2 1.97 2.02 50.92 51.05 53.09 51.69 5.17 129.77 120 0.925 127 128 7214 2.6.3 10.2 11.4 2.02 2.04 THIN SECTION 2.6.4 11.4 14.0 2.04 2.06 16.07 15.92 16.86 16.28 1.63 40.88 38 0.929 DUST SAMPLE 2.6.5 14.0 20.3 2.06 2.12 72.04 69.45 69.68 70.39 7.04 176.73 166.9 0.944 129 130 7215 2.6.6 20.3 27.9 2.12 2.20 68 67.67 67.65 67.77 6.78 170.16 157.8 0.927 131 132 7216 2.7 2.7.1 0.0 5.1 2.20 2.25 54.93 55.21 54.76 54.97 5.50 138.01 118.2 0.856 133 134 7217 2.7.2 5.1 10.2 2.25 2.30 54.35 54.97 54.54 54.62 5.46 137.14 112 0.817 135 136 7218 2.7.3 10.2 15.2 2.30 2.35 50.05 51.46 49.95 50.49 5.05 126.76 117.1 0.924 137 138 7219 2.7.4 15.2 16.5 2.35 2.37 THIN SECTION 2.7.5 16.5 19.1 2.37 2.39 22.37 22.49 22.43 22.43 2.24 56.32 51.6 0.916 DUST SAMPLE 2.7.6 19.1 30.5 2.39 2.51 112.55 106.49 116.43 111.82 11.18 280.76 259.9 0.926 139 140 7220 2.8 2.8.1 0.0 5.1 2.51 2.56 66.67 71.17 71.16 69.67 6.97 174.91 153.8 0.879 141 142 7221 2.8.2 5.1 10.2 2.56 2.61 73.12 68.93 70.67 70.91 7.09 178.03 170.9 0.960 143 144 7222 2.8.3 10.2 12.7 2.61 2.63 16.48 16.01 15.99 16.16 1.62 40.57 32.2 0.794 DUST SAMPLE 2.8.4 12.7 20.3 2.63 2.71 66.93 72.23 67 68.72 6.87 172.54 155 0.898 145 146 7223 2.8.5 20.3 25.4 2.71 2.76 47.12 46.41 47.58 47.04 4.70 118.10 105.5 0.893 147 148 7224 2.8.6 25.4 26.7 2.76 2.77 THIN SECTION 2.8.7 26.7 31.8 2.77 2.82 58.49 57.93 57.38 57.93 5.79 145.46 135.8 0.934 149 150 7225 2.8.8 31.8 43.2 2.82 2.94 81.56 81.46 80.83 81.28 8.13 204.08 189.7 0.930 151 152 7226 2.9 2.9.1 0.0 5.1 2.94 2.99 21.36 22.28 23.09 22.24 2.22 55.85 49.8 0.892 DUST SAMPLE 2.9.2 5.1 6.4 2.99 3.00 THIN SECTION 2.9.3 6.4 11.4 3.00 3.05 47.99 48.84 48.72 48.52 4.85 121.81 114 0.936 153 154 7227 2.9.4 11.4 17.8 3.05 3.12 78.65 71.97 72.12 74.25 7.42 186.41 170.9 0.917 155 156 7228 75
Table 11. Core Sample Field Measurements (cont.)
Section Depth Core Depth Core radius (cm): 2.827 Section Sample Ave. Section Density Isotope Chem. Core Start End Start End Caliper Caliper Caliper Thickness Weight Lab # Number Number Caliper Volume (g/cm3) Sample Sample (cm) (cm) (m) (m) (mm) (mm) (mm) (cm) (g) (mm) (cm3) 3 3.1 3.1.1 0.0 5.1 0.00 0.05 37.07 46 46.36 43.14 4.31 108.32 59.5 0.549 189 190 7245 3.1.2 5.1 10.2 0.05 0.10 43.16 42.39 42.15 42.57 4.26 106.87 94.6 0.885 191 192 7246 3.1.3 10.2 11.4 0.10 0.11 THIN SECTION 3.1.4 11.4 14.0 0.11 0.14 19.93 19.84 22.44 20.74 2.07 52.06 43.8 0.841 DUST SAMPLE 3.1.5 14.0 20.3 0.14 0.20 98.93 97.8 96.63 97.79 9.78 245.52 220.1 0.896 193 194 7247 3.2 3.2.1 20.3 25.4 0.20 0.25 52.94 55.24 54.48 54.22 5.42 136.13 124.3 0.913 195 196 7248 3.2.2 25.4 30.5 0.25 0.30 54.82 53.94 53.43 54.06 5.41 135.74 123.3 0.908 197 198 7249 3.2.3 30.5 35.6 0.30 0.36 53.65 53.52 53.26 53.48 5.35 134.27 122.6 0.913 199 200 7250 3.2.4 35.6 36.8 0.36 0.37 THIN SECTION 3.2.5 36.8 41.9 0.37 0.42 23.61 22.45 22.23 22.76 2.28 57.15 51.7 0.905 DUST SAMPLE 3.2.6 41.9 47.0 0.42 0.47 53.36 53.43 53.03 53.27 5.33 133.76 120.4 0.900 201 202 7251 3.2.7 47.0 52.1 0.47 0.52 51.58 53.81 53.44 52.94 5.29 132.93 116.8 0.879 203 204 7252 3.2.8 52.1 57.2 0.52 0.57 47.16 48.84 47.88 47.96 4.80 120.42 106 0.880 205 206 7253 3.2.9 57.2 58.4 0.57 0.58 THIN SECTION 3.2.10 58.4 61.0 0.58 0.61 16.82 18.08 17.2 17.37 1.74 43.60 39.2 0.899 DUST SAMPLE 3.2.11 61.0 66.0 0.61 0.66 54.1 54.19 54.74 54.34 5.43 136.44 118.2 0.866 207 208 7254 3.2.12 66.0 73.7 0.66 0.74 95.5 95.51 96.07 95.69 9.57 240.26 208 0.866 209 210 7255 3.3 3.3.1 0.0 5.1 0.74 0.79 58.16 50.66 51.98 53.60 5.36 134.58 121.9 0.906 211 212 7256 3.3.2 5.1 10.2 0.79 0.84 47.1 47.07 47.97 47.38 4.74 118.96 102 0.857 213 214 7257 3.3.3 10.2 15.2 0.84 0.89 50.07 44.69 45.07 46.61 4.66 117.03 104.6 0.894 215 216 7258 3.3.4 15.2 16.5 0.89 0.90 THIN SECTION 3.3.5 16.5 19.1 0.90 0.93 21.34 18.1 18.31 19.25 1.93 48.33 45.7 0.946 DUST SAMPLE 3.3.5 19.1 27.9 0.93 1.02 91.93 92.64 93.55 92.71 9.27 232.76 212 0.911 217 218 7259 3.4 3.4.1 0.0 5.1 1.02 1.07 57.34 51.93 52.26 53.84 5.38 135.19 124.4 0.920 219 220 7260 3.4.2 5.1 10.2 1.07 1.12 85.84 81.99 50.58 72.80 7.28 182.79 181.2 0.991 221 222 7261 3.5 3.5.1 0.0 5.1 1.12 1.17 52.16 51.48 50.46 51.37 5.14 128.97 118.8 0.921 223 224 7262 3.5.2 5.1 6.4 1.17 1.18 THIN SECTION 3.5.3 6.4 8.9 1.18 1.21 18.29 17.89 17.42 17.87 1.79 44.86 42.9 0.956 DUST SAMPLE 3.5.4 8.9 14.0 1.21 1.26 51.83 52.29 54.19 52.77 5.28 132.49 122.5 0.925 225 226 7263 3.5.5 14.0 20.3 1.26 1.32 55.17 51.82 51.6 52.86 5.29 132.73 123.9 0.934 227 228 7264 3.6 3.6.1 0.0 5.1 1.32 1.37 76.7 75.72 73.1 75.17 7.52 188.74 172 0.911 229 230 7265 3.6.2 5.1 10.2 1.37 1.42 69.61 69.05 67.24 68.63 6.86 172.32 159.2 0.924 231 232 7266 3.7 3.7.1 0.0 7.6 1.42 1.50 51.81 54.05 53.65 53.17 5.32 133.50 120.4 0.902 233 234 7267 3.7.2 7.6 15.2 1.50 1.57 50.53 50.94 51.3 50.92 5.09 127.86 117.8 0.921 235 236 7268 3.7.3 15.2 22.9 1.57 1.65 66.52 67.74 66.25 66.84 6.68 167.81 156.3 0.931 237 238 7269 3.7.4 22.9 30.5 1.65 1.73 61.64 60.55 59.8 60.66 6.07 152.31 138.2 0.907 239 240 7270 3.8 3.8.1 0.0 2.5 1.73 1.75 21.85 19.07 15.95 18.96 1.90 47.60 41.7 0.876 DUST SAMPLE 3.8.2 2.5 3.8 1.75 1.77 THIN SECTION 3.8.3 3.8 8.9 1.77 1.82 59.7 59.27 59.87 59.61 5.96 149.67 143.8 0.961 241 242 7271 3.8.4 8.9 14.0 1.82 1.87 61.43 60.59 60.52 60.85 6.08 152.77 141.5 0.926 243 244 7272 3.8.5 13.97 19.05 1.87 1.92 59.5 61.01 60.72 60.41 6.04 151.67 136.6 0.901 245 246 7273 3.8.6 19.05 27.94 1.92 2.01 66.82 68.89 58.53 64.75 6.47 162.56 127.8 0.786 247 248 7274 3.9 3.9.1 0 7.62 2.01 2.08 67.76 61.29 60.6 63.22 6.32 158.72 138.5 0.873 249 250 7275 3.9.2 7.62 15.24 2.08 2.16 62.12 63.23 62.15 62.50 6.25 156.92 138.2 0.881 251 252 7276
76
Table 12.Core Stable Water Isotopes and Anion Concentrations
Section Sample Core δD (‰) δ18O (‰) Anions (μg/L) Core Lab # d (‰) Number Number Depth (m) (+/- 1.0) (+/- 0.16) Flouride Chloride Nitrate Phosphate Sulfate Total 1 1.1 1.1.1 0.05 7151 -90.4 -12.98 13.43 2687 376 3063 1.1.2 0.10 7152 -88.7 -13.15 16.47 612 295 48 574 1529 1.1.3 0.15 7153 -96.3 -13.94 15.26 624 386 126 691 1827 1.1.4 0.20 7154 -96.8 -13.30 9.59 751 544 176 859 2330 1.1.5 0.21 1.1.6 0.23 1.1.7 0.29 7155 -100.6 -14.45 14.96 971 417 90 541 2019 1.1.8 0.34 7156 -104.2 -14.93 15.20 797 320 58 513 1688 1.1.9 0.39 7157 -105.7 -14.62 11.29 709 234 15 280 1238 1.1.10 0.44 7158 -102.9 -15.04 17.44 302 163 266 731 1.1.11 0.44 1.1.12 0.47 1.1.13 0.52 7159 -102.1 -14.91 17.15 279 171 235 685 1.1.14 0.57 7160 -106.0 -14.84 12.75 375 221 33 347 976 1.1.15 0.62 7161 -97.9 -14.41 17.38 436 154 230 820 1.1.16 0.67 7162 -102.4 -14.65 14.77 989 111 31 166 1297 1.1.17 0.68 1.1.18 0.70 1.1.19 0.76 7163 -98.8 -14.79 19.54 148 82 131 361 1.1.20 0.81 7164 -100.1 -14.57 16.46 313 111 161 585 1.1.21 0.88 7165 -88.0 -13.31 18.52 586 100 50 167 903 1.2 1.2.1 0.93 7166 -107.1 -14.87 11.86 367 142 509 1.2.2 0.98 7167 -107.3 -15.04 12.99 153 63 126 342 1.2.3 1.04 7168 -103.5 -14.76 14.64 243 107 187 537 1.3 1.3.1 1.14 7169 -99.0 -14.32 15.61 565 194 391 1150 1.4 1.4.1 1.14 1.4.2 1.22 7170 -93.8 -13.36 13.09 566 138 255 959 1.5 1.5.1 1.27 7171 -95.5 -13.54 12.78 2788 295 3083 1.6 1.6.1 1.32 1.6.2 1.40 7172 -96.1 -13.96 15.57 917 142 27 216 1302 1.6.3 1.47 7173 -95.9 -13.53 12.33 852 44 226 1122 1.6.4 1.50 7174 -93.9 -13.52 14.27 1875 277 233 2385 1.7 1.7.1 1.57 7175 -98.3 -14.28 16.00 218 73 85 376 1.7.2 1.59 1.7.3 1.70 7176 -98.0 -13.72 11.77 776 149 166 1091 1.8 1.8.1 1.75 7177 -111.6 -15.71 14.13 726 101 827 1.8.2 1.78 7178 -110.8 -15.18 10.72 1466 312 1778 1.8.3 1.83 7179 -104.0 -13.55 4.44 1081 271 1352 1.9 1.9.1 1.87 7180 -102.0 -13.83 8.62 531 286 817 1.10 1.10.1 1.89 1.10.2 1.94 7181 1782 113 157 2052 1.10.3 2.02 7182 -111.0 -15.80 15.43 1553 72 100 1725 1.11 1.11.1 2.10 7183 -106.5 -15.42 16.92 353 176 529 1.11.2 2.12 1.11.3 2.22 7184 -116.0 -16.27 14.21 822 197 247 1266 Ave -100.9 -14.4 14.1 829.8 187.6 65.4 279.7 1272.2 StDev 6.6 0.8 3.0 652.2 122.1 50.9 175.0 724.3
77
Table 12.Core Stable Water Isotopes and Anion Concentrations (cont.)
Section Sample Core δD (‰) δ18O (‰) Anions (μg/L) Core Lab # d (‰) Number Number Depth (m) (+/- 1.0) (+/- 0.16) Flouride Chloride Nitrate Phosphate Sulfate Total 2 2.1 2.1.1 0.05 7185 -123.0 -18.01 21.13 589 235 36 294 1154 2.1.2 0.10 7186 -123.9 -17.45 15.73 421 157 249 827 2.1.3 0.15 7187 -125.8 -17.62 15.19 245 264 259 768 2.1.4 0.16 2.1.5 0.18 2.1.6 0.23 7188 -122.1 -16.67 11.30 286 164 285 735 2.1.7 0.28 7189 -124.9 -16.46 6.74 282 86 174 542 2.1.8 0.33 7190 -124.6 -17.08 12.02 86 48 78 212 2.1.9 0.38 7191 -125.6 -16.71 8.05 223 128 161 512 2.1.10 0.39 2.1.11 0.41 2.1.12 0.43 7192 -125.8 -17.27 12.42 137 75 163 375 2.1.13 0.55 7193 -126.0 -17.65 15.17 5 603 103 204 915 2.2 2.2.1 0.60 7194 146 46 238 430 2.2.2 0.65 7195 -120.3 -16.23 9.51 2 197 16 173 388 2.2.3 0.70 7196 -116.8 -16.13 12.24 88 8 192 288 2.2.4 0.75 7197 -115.6 -16.43 15.80 110 20 452 582 2.2.5 0.77 2.2.6 0.79 2.2.7 0.84 7198 -109.2 -15.45 14.44 4 67 31 1944 2046 2.2.8 0.89 7199 -106.7 -14.81 11.78 125 38 2254 2417 2.2.9 0.94 7200 -104.0 -14.32 10.55 5 147 60 1922 2134 2.2.10 1.01 7201 -99.1 -14.20 14.50 5 334 126 502 967 2.3 2.3.1 1.10 7202 -102.3 -14.29 12.02 234 481 715 2.4 2.4.1 1.15 7203 -93.0 -14.70 24.60 3 184 312 499 2.4.2 1.16 2.4.3 1.19 2.4.4 1.24 7204 -116.7 -16.19 12.79 2 110 240 352 2.4.5 1.29 7205 -113.8 -15.74 12.09 95 88 183 2.4.6 1.44 7206 -121.7 -16.23 8.10 2 180 39 166 387 2.5 2.5.1 1.49 7207 -121.6 -16.76 12.50 1 177 97 275 2.5.2 1.54 7208 -121.7 -16.45 9.88 148 43 191 2.5.3 1.55 2.5.4 1.58 2.5.5 1.63 7209 -121.9 -16.77 12.28 109 107 216 2.5.6 1.72 7210 -123.9 -15.61 0.98 241 1686 1927 2.5.7 1.77 7211 -124.3 -17.24 13.65 87 89 176 2.5.8 1.78 2.5.9 1.81 2.5.10 1.92 7212 -126.2 -17.17 11.16 251 130 381 2.6 2.6.1 1.97 7213 -125.3 -17.24 12.66 3 114 121 238 2.6.2 2.02 7214 -126.2 -16.75 7.83 62 83 145 2.6.3 2.04 2.6.4 2.06 2.6.5 2.12 7215 -120.8 -15.31 1.69 67 47 114 2.6.6 2.20 7216 -118.7 -15.47 5.08 3 115 72 190 2.7 2.7.1 2.25 7217 -114.6 -13.94 -3.04 3 144 108 255 2.7.2 2.30 7218 -105.6 -14.34 9.15 4 138 99 163 404 2.7.3 2.35 7219 -102.9 -14.60 13.90 5 114 35 551 705 2.7.4 2.37 2.7.5 2.39 2.7.6 2.51 7220 -93.4 -14.99 26.54 7 201 284 492 2.8 2.8.1 2.56 7221 -89.7 -12.88 13.31 6 411 142 975 1534 2.8.2 2.61 7222 -98.4 -14.10 14.39 7 753 195 1547 2502 2.8.3 2.63 0.00 2.8.4 2.71 7223 -71.7 -10.57 12.85 3 113 191 307 2.8.5 2.76 7224 -69.4 -10.19 12.15 6 80 278 364 2.8.6 2.77 2.8.7 2.82 7225 -78.6 -11.31 11.90 9 81 508 598 2.8.8 2.94 7226 -72.4 -9.97 7.37 8 130 101 606 845 2.9 2.9.1 2.99 2.9.2 3.00 2.9.3 3.05 7227 -81.7 -11.22 8.07 8 614 620 1242 2.9.4 3.12 7228 -88.5 -12.23 9.31 6 430 614 1050 Ave -110.2 -15.2 11.4 4.7 215.2 96.3 36.0 448.9 717.7 StDev 17.1 2.1 5.5 2.2 166.0 71.0 556.2 630.6 78
Table 12.Core Stable Water Isotopes and Anion Concentrations (cont.)
Section Sample Core δD (‰) δ18O (‰) Anions (μg/L) Core Lab # d (‰) Number Number Depth (m) (+/- 1.0) (+/- 0.16) Flouride Chloride Nitrate Phosphate Sulfate Total 3 3.1 3.1.1 0.05 7245 -160.4 -22.10 16.44 4 237 230 471 3.1.2 0.10 7246 -160.1 -22.01 15.96 3 179 244 426 3.1.3 0.11 3.1.4 0.14 3.1.5 0.20 7247 -161.4 -21.72 12.39 2 142 198 342 3.2 3.2.1 0.25 7248 -154.3 -21.87 20.63 2 82 59 181 324 3.2.2 0.30 7249 -163.1 -22.00 12.90 1 53 62 200 316 3.2.3 0.36 7250 -168.1 -23.22 17.66 49 56 199 304 3.2.4 0.37 3.2.5 0.42 3.2.6 0.47 7251 -157.7 -22.55 22.70 2 42 34 173 251 3.2.7 0.52 7252 -157.1 -21.98 18.70 46 37 244 327 3.2.8 0.57 7253 -153.4 -21.01 14.72 30 33 262 325 3.2.9 0.58 3.2.10 0.61 3.2.11 0.66 7254 -149.0 -20.30 13.39 53 172 225 3.2.12 0.74 7255 -145.2 -19.74 12.69 29 6 148 183 3.3 3.3.1 0.79 7256 -145.1 -20.02 15.03 85 151 236 3.3.2 0.84 7257 -140.3 -18.15 4.90 69 151 220 3.3.3 0.89 7258 -139.9 -18.76 10.18 27 12 144 183 3.3.4 0.90 3.3.5 0.93 3.3.5 1.02 7259 -138.3 -19.25 15.66 85 177 262 3.4 3.4.1 1.07 7260 -137.9 -19.69 19.62 244 117 361 3.4.2 1.12 7261 -135.8 -19.30 18.58 134 118 252 3.5 3.5.1 1.17 7262 -134.6 -18.28 11.64 61 335 396 3.5.2 1.18 3.5.3 1.21 3.5.4 1.26 7263 -133.7 -18.68 15.77 245 314 559 3.5.5 1.32 7264 -132.0 -18.43 15.46 217 211 428 3.6 3.6.1 1.37 7265 -130.5 -17.80 11.90 306 171 477 3.6.2 1.42 7266 -130.4 -18.96 21.28 96 309 405 3.7 3.7.1 1.50 7267 -130.3 -16.20 -0.70 59 6 550 615 3.7.2 1.57 7268 -130.1 -17.60 10.68 37 125 162 3.7.3 1.65 7269 -129.9 -17.71 11.80 45 147 192 3.7.4 1.73 7270 -131.6 -18.77 18.53 185 211 396 3.8 3.8.1 1.75 3.8.2 1.77 3.8.3 1.82 7271 -132.6 -18.72 17.17 420 1012 309 1741 3.8.4 1.87 7272 -134.3 -17.86 8.55 11 177 20 101 309 3.8.5 1.92 7273 -137.7 -19.20 15.88 143 123 266 3.8.6 2.01 7274 -139.1 -19.28 15.15 54 105 159 3.9 3.9.1 2.08 7275 -141.1 -18.70 8.49 171 5 126 302 3.9.2 2.16 7276 -147.5 -19.18 5.95 133 154 287 Ave -143.2 -19.7 14.1 3.6 123.0 111.8 200.0 365.7 StDev 11.7 1.7 5.0 3.4 94.2 284.3 90.6 274.5
79
Table 13.Core Dust Content and Bubble Density
Core Dust Content Bubble Density Section Sample Core Depth Filter Dust Conc. Area Density Number Number Number (m) Number (mg) (mg/cm3) (cm2) (cm-2) 1 1.1 1.1.5 0.21 120 0.79 152.8 1 1.1 1.1.6 0.23 1 1.50 0.032 1 1.1 1.1.11 0.44 132 0.79 168.1 1 1.1 1.1.12 0.47 5 2.30 0.043 1 1.1 1.1.17 0.68 95 0.79 121.0 1 1.1 1.1.18 0.70 3 2.00 0.044 1 1.4 1.4.1 1.14 110 0.79 140.1 1 1.6 1.6.1 1.32 4 1.90 * 1 1.7 1.7.2 1.59 150 0.79 191.0 1 1.10 1.10.1 1.89 2 2.10 0.031 1 1.11 1.11.2 2.12 58 0.28 205.1 Ave 1.98 0.038 111 0.70 163.0 StDev 0.34 0.007 32 0.21 31.6 2 2.1 2.1.4 0.16 189 0.79 240.6 2 2.1 2.1.5 0.18 9 -2.90 * 2 2.1 2.1.10 0.39 83 0.79 105.7 2 2.1 2.1.11 0.41 12 2.00 0.044 2 2.2 2.2.5 0.77 117 0.99 118.8 2 2.2 2.2.6 0.79 17 2.00 0.036 2 2.4 2.4.2 1.16 191 0.99 193.9 2 2.4 2.4.3 1.19 7 2.80 0.056 2 2.5 2.5.3 1.55 140 0.99 142.1 2 2.5 2.5.4 1.58 14 2.20 0.044 2 2.5 2.5.8 1.78 132 0.99 134.0 2 2.5 2.5.9 1.81 8 6.50 * 2 2.6 2.6.3 2.04 167 0.99 169.5 2 2.6 2.6.4 2.06 23 1.00 0.024 2 2.7 2.7.4 2.37 171 0.99 173.6 2 2.7 2.7.5 2.39 13 2.00 0.036 2 2.8 2.8.3 2.63 20 2.20 0.054 2 2.8 2.8.6 2.77 110 0.99 111.7 2 2.9 2.9.1 2.99 6 2.50 0.045 2 2.9 2.9.2 3.00 72 0.38 187.1 Ave 2.09 0.04 137 0.89 157.7 StDev 0.52 0.01 42 0.19 42.9 3 3.1 3.1.3 0.11 172 0.99 174.6 3 3.1 3.1.4 0.14 18 3.40 0.065 3 3.2 3.2.4 0.37 240 0.99 243.6 3 3.2 3.2.5 0.42 21 1.00 0.017 3 3.2 3.2.9 0.58 412 0.99 418.2 3 3.2 3.2.10 0.61 10 1.70 0.039 3 3.3 3.3.4 0.90 306 0.99 310.6 3 3.3 3.3.5 0.93 16 1.90 0.039 3 3.5 3.5.2 1.18 322 0.99 326.8 3 3.5 3.5.3 1.21 22 1.00 0.022 3 3.8 3.8.1 1.75 19 2.40 * 3 3.8 3.8.2 1.77 237 0.79 301.8 Ave 1.80 0.037 282 0.95 295.9 StDev 0.98 0.01875 84 0.08 82.0 *Outliers not included in results. Grayed bubble density data shows probable core location. 80
10. APPENDIX B: ADDITIONAL FIGURES
Figure 32. Locations of isotope stations near the study area (star). Elevations: Sion (482 m), Grimsel (1950 m), Locarno (379 m). Data available from FOEN (2008).
Figure 33. Seasonality in δ18O from three Swiss precipitation stations, 1998-2007 (FOEN, 2008). For locations of stations, see Figure 32. Locations of isotope stations near the study area (star). Elevations: Sion (482 m), Grimsel (1950 m), Locarno (379 m). Data available from FOEN (2008). 81
18 Total Anions 40 16 Chloride 35 14 30 12 Core 1, n=34 25 Core 1, n=34 10 Core 2, n=44 Core 2, n=44 20 8 Core 3, n=32 Core 3, n=32 15 6 10
4
Frequency of Measurement of Frequency Frequency of Measurement of Frequency 2 5
0 0 0 300 600 900 1200 1500 1800 2100 2400 2700 3000 3300 3600 0 300 600 900 1200 1500 1800 2100 2400 2700 3000 3300 3600 Total Anion Concentration (μg/L) Chloride Concentration (μg/L) 20 12 Sulfate Nitrate 18
10 16
14 8 Core 1, n=34 Core 1, n=34 12 Core 2, n=44 Core 2, n=44 6 10 Core 3, n=32 Core 3, n=32 8
4 6 Frequency of Measurement of Frequency Frequency of Measurement of Frequency 4 2 2
0 0 0 75 150 225 300 375 450 525 600 675 750 825 900 975 1050 0 75 150 225 300 375 450 525 600 675 750 825 900 975 1050 Nitrate Concentration (μg/L) Sulfate Concentration (μg/L) Figure 34. Histograms of anion concentrations of ~5cm sections of ice cores from Zwillingsgletscher (core 1, n=34 and core 2, n=44) and Grenzgletscher (core 3, n=32). Total Anions includes chloride, nitrate, sulfate and negligible fluoride and phosphate. 82
30 40 Total Anions Nitrate 35 25 30 20 Zwillingsgletscher, n=71 25 Zwillingsgletscher, n=71 Grenzgletscher, n=35 15 20 Grenzgletscher, n=35
15 10
10 Frequency of Measurement ofFrequency 5 Measurement of Frequency 5
0 0 0 300 600 900 1200 1500 1800 2100 2400 2700 3000 3300 3600 0 75 150 225 300 375 450 525 600 675 750 825 900 975 1050 Total Anion Concentration (μg/L) Nitrate Concentration (μg/L)
50 30 45 Chloride Sulfate 25 40 35 20 30 Zwillingsgletscher, n=71 Zwillingsgletscher, n=71
25 Grenzgletscher, n=35 15 Grenzgletscher, n=35 20 10 15
10 Frequency of Measurement of Frequency Frequency of Measurement of Frequency 5 5
0 0 0 300 600 900 1200 1500 1800 2100 2400 2700 3000 3300 3600 0 75 150 225 300 375 450 525 600 675 750 825 900 975 1050 Chloride Concentration (μg/L) Sulfate Concentration (μg/L)
Figure 35. Histograms of anion concentrations of ~15 cm sections of surface samples (<50 cm depth) from Zwillingsgletscher (n=71) and Grenzgletscher (n=35). Total Anions includes chloride, nitrate, sulfate and negligible amounts of fluoride and phosphate. 83
Figure 36. Seasonal variation at Grimsel (1950 m). Parameters are shown by month (1=Jan, etc.), using monthly averages for the period 1970- 1992. GNIP data from IAEA (2008).
84
Figure 37. Long term variation at Grimsel (1950 m) from 1966-1992. Annual data are averages calculated from monthly data points. GNIP data from IAEA (2008).