PERMEABILITY OF LAKE ICE IN THE TAYLOR VALLEY, ANTARCTICA: FROM PERMEAMETER DESIGN TO PERMEABILITY UPSCALING
A Thesis
Presented in Partial Fulfillment of the Requirements for the Degree of Master of Science in the Graduate School of The Ohio State University
By
Kelly Patrick Carroll, B.S.
*****
The Ohio State University 2008
Master’s Examination Committee:
Dr. Anne E. Carey, Advisor Approved by
Dr. W. Berry Lyons ______Advisor Dr. Garry D. McKenzie Graduate Program in Geological Science
ABSTRACT
Research on lake ice permeability in the McMurdo Dry Valleys, Antarctica required the
design and construction of a novel multi-support, field based, gas permeameter. The
permeameter’s simple design allows rapid, precise, and non-destructive permeability
measurements in a harsh polar environment. The research goals using the multi-support
gas permeameter (MSGP) are to (1) determine lake ice physical hydrology through the
investigation of primary permeability, (2) how permeability affects the mechanics and
physics of fluid and gas transport through lake ice, (3) describe any variable nature of lake ice permeability, (4) scale up permeability to different sections of the lakes, and (5)
document the change in permeability during the austral spring. The multi-support gas
permeameter is of original design, however, a tip seal system utilizing the developments
of a laboratory-based permeameter by Tidwell and Wilson (1997) was incorporated. The
tip seal design has five interchangeable components, with inner seal radii of 0.15cm,
0.31cm, 0.63cm, 1.27cm, and 2.54cm, and outer radii twice the inner, which allows
multiple gas diffusion depths, thus permitting permeability measurements over a wide
variety of ice thickness and formation. The system delivers a positive pressure of 0–
100kPa of compressed laboratory grade nitrogen (N2) gas into the tip seal interface that is
in direct contact with the ice being tested. The volumetric flow rate, absolute injection
ii pressure, barometric pressure, and temperature of the N2 gas penetrating the ice are
recorded manually from a digital readout. The permeability is then calculated using a modified version of Darcy’s Law. Spot primary permeability measurements were used to scale permeability readings up to the entire lakes’ surface areas. The two lakes are
influenced by different environmental conditions including source of wind (continental or
marine influence), amount of sunlight (ablation rate), and ice conditions (annual and
perennial ice lasting approximately 7–10 years).
Measurements were made at locations around the lakes with different
environmental conditions. Measurements were made on a small scale (nine sample
points per 81cm2 area) and were repeated weekly over a four-week period from early to
late austral spring. By understanding the heterogeneity in smallest of scales at the
different sampling sites (and through any temporal changes), the lakes' permeability
heterogeneity could be factored out and scaled up to reflect the primary permeability of
the entire lake as a single, homogenous system. Data analysis revealed little difference in
surficial primary permeability over a large spatial area, regardless of ice type sampled or
the environmental conditions encountered. Although slight trends of permeability variability were noticed, the ice is intrinsically semi-permeable on the primary level.
Average primary permeability of void spaces between ice crystals was at approximately
10-13 to 10-14 m2 for all in situ measurements. Observation revealed that although there was little difference in primary permeability of lake ice in general, it is very permeable
iii due to secondary structures (fractures, bubbles, and lenses) contained within the ice column. This study dealt exclusively with the primary permeability and could not quantitatively constrain the secondary, and therefore, the overall permeability of the lakes.
Laboratory determinations of ice core permeability from selected sampling locations confirmed the surficial permeability values, analyzed the primary permeability throughout the ice column, and attempted to characterize the secondary permeability, which seems to control the lakes’ overall permeability. This research provides material property data about ice as a porous medium, thereby defining and constraining the mechanics and physics of fluid and gas transport through ice, and enhances understanding of the mechanics and the physics of lake ice cover.
iv ACKNOWLEDGMENTS
I wish to thank my advisor Dr. Anne Carey for her suggestion of and support throughout every aspect of this research project. I sincerely thank Dr. W. Berry Lyons
and Kathy Welch of The McMurdo Dry Valleys Long-Term Ecological Research
Program for facilitating many aspects of my research and the extensive knowledge given
to me of working in the Taylor Valley, Antarctica.
I thank Dr. Vincent Tidwell of the Sandia National Laboratory for his assistance
on the multi-support gas permeameter and use of his laboratory based system tip seals. I
wish to sincerely thank Dr. Polly Penhale of National Science Foundation’s Office of
Polar Programs for enabling my inclusion on the 2006 McMurdo Dry Valleys Long Term
Ecological Program’s field deployment team. I thank the assistance of Dr. Ed Adams and
Steven Jeppsen of the Civil Engineering Department at the Montana State University in testing the multi-support gas permeameter. I thank Brent Johnson, Lonnie Thompson and
Ellen Mosley-Thompson, and Victor Zagorodnov for assistance in ice core permeability testing at The Ohio State University’s Byrd Polar Research Center. I would also like to acknowledge the Antarctic field assistance of Becky Pierce and Mary Holozubeic of
Raytheon Polar Services.
I would also like to acknowledge the years of support from Dr. Seth Rose of
Georgia State University and for cementing my interest in hydrogeology.
v
This project could not have been accomplished without Jennifer Fisher and
Amy Szabo and their continued encouragement, assistance, and friendship during all
phases of this research project.
vi VITA
November 4, 1969……....……….….Born – Los Angeles, California
2004……………….……………..…..B.S. Geology (Environmental Concentration), Georgia State University, Atlanta, GA.
2003 –2006……………………….…Hydrological Technician, United States Geological Survey, Georgia Division
2005 – present……...... ……Graduate Teaching and Research Associate, The Ohio State University
FIELDS OF STUDY
Major Field: Geological Science
vii TABLE OF CONTENTS
Page Abstract…………………………………………………………………………………....ii Acknowledgments…………………………………………………………………………v Vita………………………………………………………………………………………vii List of Figures……………………………………………………………...……………...x List of Tables…………………………………………………………………………….xii List of Equations……………………………………………………………………...…xiii
Chapters:
1. Introduction………………………………………………………………………..1
1.1 Permeability Ranges in Ice….……………….………………………………..9
2. Field Area Description………………………………………………………..….10
2.1 Lake Description…………….………………….……………………………12 2.2 Solar Radiation Input……….…………………….………………………….13 2.3 2006 Seasonal Weather…….……….………………………………………..14 2.4 Lake Ice Characteristics.…….…………………………………………….....22
3. Methods…………………………………………………………………………..26
3.1 Permeameter Design………………..……………………………………..…25 3.2 Permeameter Calibration…………..………………………………...………33 3.3 Permeability Sampling Domains…………..…………………………...……35 3.4 Permeability Calculation…………………………………………..…………41
4. Results……………………………………………………………………………44
4.1 Lake Hoare Permeability……………..……………………………………...44 4.2 Lake Fryxell Permeability………..………………………………………….49 4.3 Lake Fryxell Crash Site Permeability………………………………..………51 4.4 Laboratory Ice Core Permeability……..……………………....……………..52
viii
5. Discussion………………………………………………………………………..54
5.1 Formation and Development of Secondary Structures that Affect Permeability…………………………...………………………..……55 5.2 Interpretation of Permeability Graphs………………………………...……..58 5.3 Lake Hoare and Lake Fryxell Spatial Permeability Variability………..….....59 5.4 Permeability Variability within Ice Types…………………...…..………….61 5.5 Variability of Permeability due to Solar Radiation Input…...…..………..…63 5.6 Permeability Variability through Temporal Domain...………………..…….67 5.7 Lake Fryxell Crash Site Permeability…..…………………………………....72 5.8 Laboratory Investigation of Primary Permeability………………….....…….74 5.9 Permeability Upscaling………………………………………….…….……..76 5.10 Limitations of the Multi-Support Gas Permeameter….………….…....……79 5.11 Recommendations for Future Work…...…...………………………….…...81 5.12 Conclusions………………………………………………………………....82
Appendix:
A Primary Permeability Measurements…………...………...….……………..…84 B GPS Coordinates ……………………………………………………………...93 C Sampling Location Descriptions….…………………………..……………….95
List of References…………………………………………………………………….101
ix LIST OF FIGURES
Figure Page
1.1 Wreckage of NSF Bell 212 Helicopter on Lake Fryxell…………..…………...….3
1.2 81cm2 spatial sampling grid………………………………………………...... ….7
1.3 Permeability Ranges in Ice………………………………………………..………9
2.1 Map of Lake Hoare and Lake Fryxell…………………………………………....11
2.2 Plot of Lake Hoare incoming shortwave radiation (2006)…………………….…15
2.3 Plot of Lake Hoare incoming shortwave radiation (sampling period)……….…..16
2.4 Plot of Lake Fryxell incoming shortwave radiation (2006)………………….…..18
2.5 Plot of Lake Fryxell incoming shortwave radiation (sampling period)…….……19
2.6 Plot of air temperature at Lake Hoare (sampling period)………………….…….20
2.7 Plot of air temperature at Lake Fryxell (sampling period)……………...... …….21
2.8 Map of predominate wind directions for Lake Hoare and Lake Fryxell...………22
2.9 Ice types at Lake Hoare………………………………………………………….23
3.1 Multi-support gas permeameter………………………………………………….30
3.2 Tip seal internal parts……………………………………………………………32
3.3 Plot of permeameter precision test………………..……………………………..33
3.4 Plot of steady gas flow test……………………………………………………....34
3.5 81cm2 spatial sampling grid……………….…………………………………...... 36
x 3.6 Lake Fryxell crash site sampling locations………………………………...…….37
3.7 Lake Hoare sampling locations…………………………………………………..39
3.8 Lake Fryxell sampling locations……………………………………………...….40
5.1 Fracture and bubble formation at Site #410…………………………...….…..…57
5.2 Plot of primary permeability of all measurements at Lake Hoare……………….59
5.3 Plot of primary permeability of moat ice at Lake Fryxell…………………...…..61
5.4 Plot of moat and center ice primary permeability at Lake Hoare………………..62
5.5 Plot of moat and center ice primary permeability at Lake Fryxell……...... 62
5.6 Plot of Lake Hoare primary permeability NW and SW (early)……...... …....…..65
5.7 Plot of Lake Hoare primary permeability NW and SW (late)…..……...………..66
5.8 Plot of Lake Hoare primary permeability through time series……………..……67
5.9 Plot of Lake Hoare primary permeability NW and NW (early/late)…………….69
5.10 Plot of Lake Hoare primary permeability SW and SW (early/late)……….…….70
5.11 Plot of Lake Fryxell crash site primary permeability…………...……………….73
5.12 Plot of ice core primary permeability……………………………………...…….75
5.13 Plot of upscaled Lake Hoare primary permeability……………………...………77
5.14 Plot of Lake Hoare and Lake Fryxell primary permeability……………………..79
5.15 Ice temperature records from Lake Hoare (1985-1988)………..………………..81
xi
LIST OF TABLES
Table Page
4.1 Primary permeability averages for LHX1………………………………………..46
4.2 Primary permeability averages for LHX2………………………………………..47
4.3 Primary permeability averages for LHX3………………………………………..48
4.4 Primary permeability averages for LHX4………………………………………..49
4.5 Primary permeability averages for LFX1………………………………………..50
4.6 Primary permeability averages for LFX2………………………………………..51
4.7 Primary permeability averages for LFCS………………………………………..52
5.1 Lake Hoare time series t-test………………………….………………………….71
xii
LIST OF EQUATIONS
Equation Page
1 Modified Darcy’s Law……………………………………………………...... …...6
2 Modified Darcy’s Law………………………………………………………...…41
3 Sutherland’s Gas Viscosity……………..………………………………………..42
xiii
CHAPTER 1
INTRODUCTION
Ice cover on lakes provides an important physical barrier to gas exchange,
sediment mixing, chemical input, and radiation, essential for biological processes.
Knowledge of lake ice physical and hydrological parameters will help in determining the
exchange of radiation fluxes between the ice and the atmosphere and in modeling fluid
transport through the ice (Karanovic, 2005). Essential to deriving the radiation budget and modeling fluid transport is a clear understanding of the permeability of ice. Many studies of the formation of pore space in ice (Adams et al., 1998; Fritsen, et al., 1998), permeability of sea ice (Fretag et al., 2003), snow and firn (Albert et al., 2000), and frozen soils (Seyfried et al., 1997) have been conducted; there have been no studies conducted on the permeability of high-latitude lake ice.
The Antarctic Dry Valleys are among the coldest and driest environment on Earth
(Priscu, 1998). The fragile biological communities existing there are primarily of microbiota, and lack higher order animals and plants (Moorhead et al., 1998). Because of this absence of higher order life, the Dry Valleys provide a rare area for the study of ecological processes (Moorhead et al., 1998). The McMurdo Dry Valley (MCM) lakes ecosystem is controlled by the variability of light infusion due to seasonal changes in ice cover and thickness but otherwise have stable physical and chemical characteristics, but 1 do vary in different lakes in the valley (Moorhead et al., 1998). Variability of light effects photosynthesis in the water column and in sediment layers that are contained within the ice (Fritsen et al., 1998; Simmons et al. 1993; James et al., 1998). The variable ice permeability of these lakes directly effects the overall radiation budget and transportation of natural and anthropogenic substances to the water column, and specifically, to the ecosystem itself.
Permeability is defined as the capacity of a porous medium for transporting a fluid (Bates et al., 1984). In this study the terms primary and secondary permeability will be used extensively. Primary permeability, in this study, refers to the interconnectivity void space present between the individual ice crystals of the lake ice in question.
Secondary permeability refers to macro-scale formations contained within the ice column such as fractures, lenses, exsolution gas bubbles, ice blisters, and melt water pools. The unit of permeability used throughout this study is the SI unit of m2.
In January 2003, a National Science Foundation Bell 212 helicopter crashed onto the frozen surface of Lake Fryxell in the Taylor Valley (77° 36’ 41.09824” S, 163° 06’
47.22831” E) (Alexander et al., 2003) (Figure 1.1).
2
Figure 1.1 Bell 212 79U Wreckage at Lake Fryxell. Source: Alexander et al., 2003
As a result of the crash, approximately 731 liters of diesel fuel oil, engine oil, and
hydraulic fluid spilled. The area of the crash is characterized by a series of flat ice ridges approximately one meter high surrounded by troughs from previous years melt pools.
The various fluids spread out and percolated throughout the ice. Cleanup operations delayed due to local weather conditions, and did not commence until January 21, 2003 and were completed on February 2, 2003 (Alexander et al., 2003). At the end of recovery operations, it was believed that approximately 45% to 50% of the hydrocarbons were recovered. The values means that approximately 350 liters were not recovered and had entered the ice and water column of the lake (Alexander et al., 2003). Because the Dry
Valleys are an environmentally protected site and contained within the Long Term
Ecological Research (LTER) area, an environmental assessment was needed to understand the mobility of the hydrocarbons and the possible damage to the fragile
3 ecosystem of Lake Fryxell.
Karanovic (2005) developed a time dependent, one-dimensional flow model of
the remaining hydrocarbons of the Lake Fryxell crash site. This model simulated the
hydrocarbon transport from the surface of the ice cover to a depth of approximately 0.5
meters into the water column. Due to the lack of field data, the ice material property of
permeability was assumed in this model to be homogenous and isotropic (Karanovic,
2005). Transport testing showed results were highly dependent upon the value chosen for
the ice permeability. The ice in the Dry Valley lakes is very heterogeneous and can
change significantly on spatial, seasonal, and daily time scales. A permeability input is needed to allow a more accurate simulation. Although this model was used to describe the flow of hydrocarbons through lake ice at a specific site, it can be utilized as a model to describe the transport of fluids through high latitude lake ice in general.
Ice permeability measurements and ice core extraction were conducted at Lake
Hoare and Lake Fryxell in Taylor Valley between October 29, 2006 to December 4,
2006. These lakes were chosen for differences in their ice characteristics (oral communication, Priscu, 2006). Generally, both lakes are composed of a moat ice cover that refreezes annually, a center ice that remains frozen throughout the year, and transition ice connecting the moat and center ice. The moat ice is a smooth ice surface, approximately 6-8 meters thick during the winter, which recedes during the austral spring and summer. The austral spring is defined as the months of October through November and the austral summer as the months of December through February. The center ice is characterized by major surface fractures in an undulating ridge and trough system.
4 Variable permeability of the moat and center ice is caused by radiative ablation, eolian deposited sand, and the in flow of relatively warmer streamwater, which produce fractures and bubbles in the ice column.
The multi-support gas permeameter (MSGP) was of original design, however, a tip seal system was devised on the developments of Tidwell and Wilson (1997). The tip seal design has five interchangeable diameters that allow multiple gas diffusion depth, thus permitting permeability measurements over a wide variety of ice thickness and formation.
The system delivered a positive pressure between 0-100kPa of compressed laboratory grade N2 gas into a tip-seal interface in contact with the ice being tested.
Steady gas flow is an important factor in maintaining constant diffusion geometry beneath the tip seal. To accomplish this gas flow was measured at a time interval of 0,
30, 60, 120, 240, and 300 seconds to identify the average time to achieve a steady gas flow. The flow rate, injection pressure, and temperature of the N2 gas that penetrates the ice were recorded manually from a digital readout. The primary permeability was then calculated using a modified version of Darcy’s Law (Goggin et al., 1988, Equation 1).
5 (Q Pμ(T)) k ()Q ,P,P ,r,r = 1 1 p 1 1 0 i o ⎛ ⎛ ⎞ ⎞ ro 2 2 ⎜ 0.5riGo⎜ ⎟ P1 − P0 ⎟ ⎝ ⎝ ri ⎠ ⎠
Equation 1. Modified Darcy’s Law (Goggin et al., 1988)
Where:
k is permeability
Q1 is gas flow
P1 is gas injection pressure
P0 is atmospheric pressure
T is gas temperature
ri is radius of the inner seal
ro is radius of the outer seal
μ is gas viscosity as a function of temperature
Go is a geometric ratio
Permeability is valid through the range of 10-15 to 10-9 (oral communication,
Tidwell, 2006). If k was below 10-15, the measurement were discarded due to the probably that turbulence is controlling the reading.
The sampling consisted of specific sampling points on the moat and center ice of both lakes. The exact spots, using GPS waypoints, were re-sampled throughout October and November 2006 using temporally and spatially created domains.
6 Measurements were made during through the early (late October – early
November) and late (mid-November) austral spring to investigate any variable in primary
permeability. These temporal domains were selected because of changing environmental
conditions and ice morphology typically seen during this time period.
To describe the variability and be able to upscale permeability, a spatial domain
system will be employed. An 81cm2 grid system was sub-divided into nine cells of 3cm2
and used as the ice conditions allowed at each sampling site (Figure 1.2). These
measurements were designed to describe the variability of permeability on small scales; however, the average of the nine measurements can be used to describe the permeability of the sampling location.
3cm
3cm
9cm
Figure 1.2 81cm2 sampling grid utilized during all permeability sampling, when applicable.
7 To support the permeability measurements, ice cores were drilled at various spots
on both lakes and transported back to The Ohio State University’s Byrd Polar Research
Center for further analysis. This was done to show any primary permeability variability throughout the length of the uppermost ice column (approximately 1 to 1 ½ meters), and to verify field measurements in a temperature and radiation controlled environment.
This research provides material property data about ice as a porous medium and thus helps define and constrain the mechanics and physics of fluid and gas transport through ice. The research herein on permeability determinations of Taylor Valley lake ice and ice cores will enhance understanding of the mechanics and the physics of lake ice cover. The air permeameter was of original design; however, certain parts were built upon concepts of previously designed systems. This novel air permeameter for fieldwork provides an ability to determine permeability over many orders of magnitude. The research upscales permeability measurements for the ice being tested. The hydrological research improved understanding the biogeochemistry of lakes, provide data for ground- truth remote sensing studies, improve inputs to existing models, and enhance understanding of Dry Valley as possible analogues to extraterrestrial ice surfaces.
The overall goal of this research was to determine surficial ice permeability and its variability throughout an austral spring on Taylor Valley lakes. The specific objectives to be accomplished were:
1. To design and build a portable, field-based air permeameter.
2. To measure the primary permeability of ice on Lake Hoare and Lake Fryxell in
8 the Taylor Valley through the development of temporal and special domains.
3. To develop methods to upscale permeability.
Specifically, this research set out to (1) determine lake ice physical hydrology through the investigation of primary permeability, (2) determine how permeability affects the mechanics and physics of fluid and gas transport through lake ice, (3) describe any variable nature of lake ice permeability, (4) scale up permeability to different sections of the lakes, and (5) document the change in permeability during the austral spring.
1.1 Permeability Ranges in Ice
Permeability in ice ranges over many magnitudes. Figure 1.3 illustrates the permeability of ice as compared to geologic strata.
Figure 1.3 Permeability of ice as compared to geologic strata. The permeability for glacial ice spans the entire range to due the changing density of ice at depth and secondary structures contained within a glacier. Lake ice range is taken from permeability measurements conducted within this study. Source: Sea Ice: Freitag, et al., 2003; Firn: Rick, et al., 2004
9
CHAPTER 2
FIELD AREA DESCRIPTION
The McMurdo Dry Valleys of southern Victoria Land (76°30’–78°20S, 160°–
164°E) compose the largest ice-free portion of the Antarctic continent. Taylor Valley
(77°37.25’S, 162°53’E), an area approximately 400km2, is located within the McMurdo
Dry Valleys. Taylor Valley, which lies at the eastern most extent of the East Antarctic
Ice Sheet, has three main lakes, Lake Bonney, Lake Hoare, and Lake Fryxell, which are fed by meltwater from a large number of alpine glaciers. These lakes range in size from
1km2 to 5.5km2. The valley is enclosed by two mountain ranges, Asgard Range on the northern edge and Kukri Hills on the southern edge (Figure 2.1).
10
Figure 2.1 Map of the Taylor Valley showing Lake Hoare and Lake Fryxell and streams. Source: K. Carroll
Taylor Valley receives very little precipitation (<10cm yr-1) because of the
precipitation shadow of the Transantarctic Mountains and the warm, dry fohn winds
descending from the polar plateau (Wharton et al., 1992). The average temperature of
the winter (April-September) and summer seasons (October-March) vary widely from
year to year (Dana et al., 2002). During 2006, the winter season average temperature was
-31.8°C and -11.5°C during the summer (www.mcmlter.org). Taylor Valley has a 6–10
week period during the austral summer when streams flow into the lakes of the valley
(Dana et al., 2002). The lakes in Taylor Valley have a perennial ice cover of 2m–6m
thickness over liquid water (Wharton et al., 1992). The evaporation rate of the ice is
approximately 35 cm yr-1, is highly dependent on local weather conditions, and is the primary mode of water loss from the lakes (Wharton et al., 1992, Clow et al., 1988).
Glacial till is common along the valley floor (Clow et al., 1988).
11 The McMurdo Dry Valleys are unusual in that they have a large system of meromitic lakes enclosed in singular hydrological basins. The extreme weather conditions (extremely low precipitation rates and very cold temperatures) create an environment where summer ablation and direct melt cannot exceed the amount of winter freezing (Chinn, 1993).
The surrounding ice-free rocks create an area of extremely low albedo compared to other coastal regions, and thereby increases surface temperatures by 5°C to 7°C in the austral summer and decreases temperatures by 5°C in the winter (Chinn, 1993).
Although most lakes in the McMurdo Dry Valleys have streamwater inputs from melting glaciers, the enclosed lakes of the McMurdo Dry Valleys have no outflow.
Because of this, many of the lakes contained within the valley have unusually highly stratified temperature and salinity levels (Chinn, 1993).
The stream inflows have a profound impact on the thickness of ice levels of these lakes. While the ablation rate seems to be relatively consistent from year to year, the amount of annual streamwater contribution has remarkable variability from year to year
(Chinn, 1993).
2.1 Lake Description
Lake Hoare
Lake Hoare is the second inland lake from McMurdo Sound (77° 37’ 52.9” S,
162° 50’ 43.8” E) at approximately 3.62 km long and 1.60 km at its widest point. The lake elevation is 73m MSL. As previously described, it is enclosed by two sets of hills with large topographical gradients, on the north and south edges, and by a 20m high 12 tongue of the Canada Glacier on the eastern end, and Lake Chad on its western flank.
Weather is primarily controlled by “up-valley” winds descending off the polar plateau during the austral summer and relatively calm or strong fohn winds during the winter.
Lake Fryxell
Lake Fryxell is a large lake near the mouth of the Taylor Valley to McMurdo
Sound (77° 36’ 23.0” S, 163° 07’ 07.6” E). It is approximately 5 km long and 2 km wide, with a lake elevation of 17m MSL. The same north-south features enclose the lake as with Lake Hoare except the topological gradient is much less steep. The lake is bordered by a tongue of the Canada Glacier on its western end and open valley to the east. Compared to Lake Hoare, the weather here has a greater marine influence due to its proximity to McMurdo Sound.
2.2 Solar Radiation Input
The principle factor controlling the removal of ice is sublimation caused by energy inputs above and below the ice cover. Ablation is the primary mechanism of removal of ice from the surface. Heat energy input to the liquid water column from glacial melt streamwater accounts for the majority of ice loss from the bottom of the ice column. Surface ablation rates are variable at both Lake Hoare and Lake Fryxell because of differing setting within the Taylor Valley.
Lake Hoare is enclosed tightly by both the Asgard Range on the north and Kukri
Hills on the south (and bordered by the Canada Glacier on the east and open area, Lake
Chad on the west) shield a majority of the ice surface from direct solar radiation input in
13 the early spring and increases to a more moderate solar input later in the austral spring.
Lake Hoare can have extensive cloud cover during the austral spring. This aids in a
lower mean solar flux input to this portion of the valley (Clow et al., 1988). During the
field season of October – November 2006 no portion of the ice cover was exposed to
continuous solar input. The first 14 days of sampling, Lake Hoare’s ice cover was
entirely shrouded by a thin layer of snow (increasing albedo, and reducing ablation).
Lake Fryxell is located in the much more open eastern end of the Taylor Valley.
While the lake is still enclosed by the same mountains on the north and south sides, the
lake receives a larger solar radiation input than Lake Hoare in the early austral spring.
Sublimation rates, historically, have been measured at approximately 35cm yr-1
(Clow et al., 1988; Chinn, 1993). With average daily rates that peak 2–3mm day-1 in summer, and 0–1mm day-1 in the winter. Sublimation rates are primarily controlled by solar radiation input during the austral summer and wind during the winter (Clow et al.,
1988).
2.3 2006 Seasonal Weather
Solar Shortwave Radiation – Lake Hoare
The environmental setting of Lake Hoare protects the ice from abundant direct
solar heating throughout the early to late austral spring. This shading slows ablation rates
(the dominate cause of ice mass loss in the spring and summer), reduces summer ice crystal changes, and retards the melting of moat and center ice-melt pools. As noted, during the 2006 field season the entire lake ice cover was blanketed with a thin layer of snow at Lake Hoare. On November 4, 2006, a low-pressure front accumulated 2–5cm of 14 snow and again blanketed the ice cover of the lake. This snow cover increased the local albedo and assisted in retarding the ablation rate. The northern shore of the lake receives much less direct solar input (~4.5 non-continuous hours) than the south side (~9 non- continuous hours) due to a sun angle that varies from 11.5° to 35.5°during this time of the year. Diurnal effects of this angle can change the total solar flux by as much as a factor of 3 (Clow et al., 1988).
Figure 2.2 Lake Hoare Shortwave Radiation Input (2006) Source: www.mcmlter.org
15 Measurements from the Lake Hoare Meteorological Station (77° 1.45324 S, 162°
54.02422067 E, 77.1m MSL) reflect this eastern shore shading due to its location. Figure
2.2 shows the shortwave radiation input (SW) for the year 2006. The SW input peak in the middle of the 2005 and 2006 austral summer, conversely, is minimal during the austral polar night.
Figure 2.3 Lake Hoare Shortwave Radiation Input during Sampling Period 2006. Source: www.mcmlter.org
16 During the 2006 field season, SW input was at its minimum during the early sampling
period (late October – early November) and increased as the austral spring progressed,
from a minimum of 3.60Wm2 on October 25, 2006 to a maximum of 760.0Wm2 on
November 28, 2006 (Figure 2.3). This dynamic range of SW input changed many ice characteristics, due to ablation and temperature isostasy, as the season progressed (as discussed later in this chapter).
Solar Shortwave Radiation – Lake Fryxell
Lake Fryxell receives more SW radiation input than Lake Hoare due to a broadening of the valley on the east and west ridges. During the sampling period at Lake
Fryxell (November 7 – November 11), as with Lake Hoare, was also a thin covering of snow that helped retard the onset of higher ablation rates. Figure 2.4 shows the SW input for the sampling period from the Lake Fryxell Metrological Station (77° 10.6 S, 163°
10.1766 E, at an elevation of 19m MSL).
17
Figure 2.4 Lake Fryxell Shortwave Radiation Input (2006). Source: www.mcmlter.org
During the 2006 field season, SW input was at its minimum during the early austral spring (October – early November) and increased as the austral spring progressed, seeing a minimum of 3.60Wm2 on October 25, 2006 to a maximum of 762.0Wm2 on November
28, 2006 (Figure 2.5).
18
Figure 2.5 Lake Fryxell Shortwave Radiation Input during Sampling Period 2006. Source: www.mcmlter.org
Temperature
The temperatures in the McMurdo Dry Valleys are very dynamic and are influenced by many environmental parameters. The temperature is strongly controlled by the geographical placement of the valley and winds the valley experiences (Figure 2.8).
Temperature gradients usually follow an alpine standard (the higher in elevation, the lower the air temperature), however, this is not the case in most of the Dry Valleys. In a
19 study of climate statistics in the McMurdo Dry Valleys, Doran et al (2002) found that a
14-year (1987–2000) average mean air temperature was -17.7°C (max temp 9°C/min
temp -60.2°C) for Lake Hoare and -20.2°C (max temp 10.0°C/min temp –45.4°C) for
Lake Fryxell. The average air temperature for 2006 for Lake Hoare was -19.0°C and -
22.0°C for Lake Fryxell, a year slightly warmer than average. During the sampling period of October 25, 2006 through December 4, 2006 the average mean daily temperatures for Lake Hoare was -10.1°C (max temp 1.4°C/min temp -26.5°C) and
-10.0°C (max temp 1.8°C/min temp -28.2°C) for Lake Fryxell (Figures 2.6–2.7).
Figure 2.6 Lake Hoare Air Temperature (+3m). Source: www.mcmlter.org
20
Figure 2.7 Lake Fryxell Air Temperature (+3m). Source: www.mcmlter.org
21
Figure 2.8 Lake Hoare Predominate Wind Directions. Source: Clow et al,. 1988
Environmental datasets for the McMurdo Dry Valleys are available at www.mcmlter.com.
2.4 Lake Ice Characteristics
The ice in both lakes sampled have similar characteristics. For this study, three types of ice were sampled and labeled as moat ice, transitional ice, and center ice (Figure
2.9).
22
Figure 2.9 Ice Types at Lake Hoare. Source: K. Carroll
Moat ice is an annual ice layer that ranges between 0–6m thick. This layer of ice follows the perimeter of each lake and is on average approximately 10–30m wide. Since this ice melts each austral summer and refreezes each winter, the exact placement varies from year to year. Once the moat ice melts, the center ice (which remains frozen all year) will position itself with the last major movement due to wind (Adams et al., 1988). This placement will determine the boundaries of the new moat ice as the ice refreezes.
The moat ice is a flat surface (with the exception of ablation “cups” that form as the austral spring commences) that varies from clean (non-fractured) ice but is dominated by a series of vertical fractures. These fractures can be 10–15cm to sub-millimeter wide.
Almost the entire ice cover of the moat ice has exsolution gas bubbles that exist 5–10cm below the surface.
23 The center ice is characterized by a series of undulating ridge and troughs that run
parallel with the long axis of the lake. These ridges and troughs repeat approximately
every 10m for more than a kilometer in distance. The troughs have a “cleaner”
appearance because of melting and refreezing of the ice each year. The ridge ice has an
uneven and irregular surface consisting of solid ice in the spring which becomes spheres
of individual ice crystals 0.25 to 0.5m tall as the austral spring and summer progress.
Theses spheres are structurally weak and prevented measurement using the MSGP later
in the austral spring.
The transitional ice is a layer ~10m wide that has characteristics of both the moat
ice and center ice. From the outside perimeter in occurs a gradual transition between structures of the moat ice (flatter with fractures and bubbles) along an inclined surface to
form the first ridge (in a gradual ramping gradient). The transitional ice surface characteristics were such that measurements could not be made on it because of its very uneven surface character. This unevenness prevented the MSGP from making a tight seal
with the ice causing a free-flow condition with the N2.
Lake Hoare 2006 Spatial Ice Characteristics
During the 2006 austral spring, the lake ice at Lake Hoare was similar to the
conditions described above. The moat ice was 10–15m wide around the perimeter with
the exception of the western margin (proximate to the Canada Glacier) because of the 1–
2m high snow drifts there. The transitional ice was about 10m wide between the moat
and center ice. The center ice was approximately 1 km wide and just over 2 km long.
The center ice was filled with the ridges and troughs (each ridge and trough has about a
24 20m frequency) running parallel with the east-west axis of the lake, however, the ridges
and troughs are neither continuous, nor interconnected. The center ice was spotted with
large boulders (up to a meter in diameter) and gravel to silt size, eolian transported
sediments in the troughs, as well as, one large one mound (4m high) covered by
sediments near the eastern margin of the center ice.
Lake Fryxell 2006 Spatial Ice Characteristics
During the 2006 austral spring, the ice characteristics were similar to those
observed at Lake Hoare. The two major difference was that the eastern and western
margins of the lake the transitional ice was more extensive than at Lake Hoare, as well as,
the ridge and trough system had a much wider frequency and covered a much larger
spatial area. These areas had center ice widths over a ½ km wide followed by larger
ridge and troughs. The interior of the lake had a ridge and trough system that was spatially similar to Lake Hoare (east to west trending), however, as noted, there were
much wider and spaced farther apart.
25
CHAPTER 3
METHODS
3.1 Permeameter Design
A variety of laboratory and field based gas permeameter’s have been designed
and used to investigate the physical properties of strata, soils, and man-made substances.
However, no known permeameter has been designed for use on lake ice, especially for
use in remote, field-based polar environments. The goals of this research required the
development of a permeameter for investigating the primary permeability of ice, through
an efficient design, and to provide accurate and quantitative measurements. For the goals
of this project to be met, a novel multi-support gas permeameter (MSGP) was designed,
tested, and used on Lake Hoare and Lake Fryxell in the Taylor Valley, Antarctica.
These requirements warranted original modifications of previously created
systems. The MSGP design was based on an automated lab-based permeameter created
by Dr. Vincent Tidwell of Hydrogeology Division, Sandia National Laboratories
(Tidwell et al., 1997). Dr. Tidwell’s system was designed for use on rocks and geologic
strata, not ice. However, the basic principles were such that different media could be
substituted and the overall concept of his system could be adapted to the goals of this
product. The novel design of his system was a set of interchangeable “tip seals” that
would give the ability of measure permeability over a range of 1x10-15 to 1x10-10 m2.
26 Since the object was to capture the primary permeability in snap shots at different sampling locations throughout the season the MSGP had to have the ability to detect slight changes in permeability, as well as, have small measurement error. The design of
Dr. Tidwell’s fit the basic criteria needed but his design is a laboratory-based system and this research required a MSGP to be used in a remote field setting.
There are three basic concepts of gas permeameter in use in permeability studies: a pressure decay permeameter, a high-volume permeameter, and a low volume steady state permeameter (Tidwell et al., 1997). The basic concept in permeameter operation is to inject a fluid into a sampling medium through sealed contact with the media being tested, and observe various measurements of the fluid, such as, flow rate and pressure, and then use those values to calculate permeability.
The MSGP had to meet basic design criteria; the permeameter must be portable, have portable and reliable power, subsections with double redundancy, be non-evasive to the sampling medium, and sample different types of ice surfaces and operate over a large scale of different permeability values.
Transportation of equipment through the physical environment of the Taylor
Valley required any design be made portable. The MSGP was designed to fit and be transported on a banana sled, a standard sled used in polar environments, and to be transported by human power. To accomplish this, the permeameter had to be quickly disassembled and reassembled and transported in a large stainless steel Coleman cooler for protection during transportation. All sections could be disassembled and assembled with standard hand tools at the sampling site.
27 The power requirements for the MSGP were that it be field transportable and
replenishable. The MSGP required only two exchangeable batteries, one 9V battery to power the electronics and one CR-2032 lithium cell battery to power the digital barometer. The options were chosen because of their portability. To extend battery life all electronics were contained in a waterproof housing that assisted in retaining warmth emitted by the equipment.
Because of the novel subsystems of the MSGP and the requirement to have back- up sections in the design to ensure redundancy if needed. These include analogue versions of digital gauges, back-up gas lines and pneumatic connectors, and spare silicone seals for the tip-seal assembly. The back-up systems were not employed at
anytime during sampling.
The environment of Taylor Valley and the possible changing ice characteristics of
the lakes required the MSGP to be able to sample various ice surfaces and over a possible
large range of permeability. This was accomplished by the tip seal design of Dr. Tidwell
and the rocker and stability plate, both discussed in detail below.
The MSGP is composed of four basic sections; gas handling, rocker and stability
platform, electronics, tip seals (Figure 3.1). The purpose of the gas handling section is to
supply, regulate, and deliver a known quantity of gas to the tip seal interface for insertion
into the ice. The MSGP uses laboratory grade nitrogen (N2) gas (“B” size cylinder for
field use (~17.2 liters) and “A” size cylinder for laboratory use (~43.9 liters)). Nitrogen was chosen because of its purity and low humidity. Gas injection was controlled by a standard two-stage pressure regulator running at a continuous ~27kPa (4PSI) or ~70kPa
(10PSI) flow as indicated by the pressure regulator gauge exclusively unless noted. The
28 gas is delivered to the electronics section and the tip seals via two 24-inch copper inner and aluminum outer flexible “pigtail-type” ¼ inch gas lines. The gas lines are connected to the tip seals using aircraft quality ¼ inch quick-disconnect male fittings (Swagelok
Model SS-QM2-D-400).
The rocker and stability platform allows positioning of the tip seal over the sampling point with sufficient down force to make an airtight seal with the ice surface.
The assembly consisted of a ½ inch aluminum mounting plate with seven-inch diameter hole. The plate sits directly on the ice surface. The rocker assembly is a T-shaped mount connected to a two-ton hydraulic jack (NAPA Model NLE5201037) on one end and a male (threaded) bolt on the other. The bolt was designed to screw on the different tip seals. The bottle jack provided the force upwards and is transferred downward to the tip seal by a ½ inch thick aluminum rocker plate.
29
Figure 3.1 Multi-Support Gas Permeameter showing subsections. Source: K Carroll
The electronics section was composed of two individual units. The first was a one NIST traceable unit (a US based rating standard on repeatability of measurements) that measured absolute gas pressure (0-1 MPa), volumetric and mass gas flow (0-20 standard liters per minute (slpm)), and gas temperature (°C) manufactured by Alicat
Scientific (Alicat Series M Gas Flow Meter). The second unit was a NIST digital barometer (Control Company 4198).
The Alicat gas flow meter was chosen because of its ability to operate in wide temperature range, measure accurately under low to moderate gas flow conditions, powered by one 9V battery, and could be specially calibrated for use with N2 gas. The accuracy of the unit was rated at ±0.8% of reading (readings were accurate to two
30 significant figures) and could maintain that accuracy over its entire scale of measurable range.
The barometer was chosen because of its NIST traceable calibration and its ability to measure atmospheric pressure between 400-1070 kPa (accurate to ±8 kPa) to handle the atmospheric extremes that could be experienced in Antarctica. The unit was calibrated daily from altimeter readings reported from aircraft flying locally in the Taylor
Valley. This calibration was also compared to the input gas pressure reading on the gas flow meter (which measured atmospheric pressure if no input gas pressure was applied).
The tip seal assembly, originally designed by Dr. Tidwell, was the heart of the multi support capacity of this system. The actual tip seals that Dr. Tidwell used for his laboratory-based permeameter were used and no modifications were made. Tidwell et al., (1997) describe the construction and operations as:
Gas is directed into the rock sample via the tip seal. A series of specially designed tip seals, the diameter of which defines the sample support, are used to establish a known boundary condition on the rock surface. Tip seal sizes in current use have inner radii (ri) of 0.15, 0.31, 0.63, 1.27, and 2.54 cm and an outer radii (ro) measuring twice the inner. Critical to precise measurement is a consistent and known tip seal geometry under compressed conditions. For this reason, each of the tip seals is equipped with an internal spring-driven guide to maintain a constant inner seal diameter. Beyond this characteristic, slight variations in design among the five tip seals is necessitated because the degree of tip seal deformation increases with decreasing tip seal width (ro-ri). Specifically, an immobile outer guide is required by the 0.15, 0.31, and 0.63cm ri tip seals but not for the larger two seals. Tip seal thickness and hardness must also be varied. For the 0.63, 1.27, and 2.54 cm tip seals, silicone rubber (Dow Corning HS III RTV) molded into a 1.6 cm thick ring is used to establish the seal between the injection nozzle and the rock surface, while a thinner (0.5 cm) seal made of a harder silicone rubber (Dow Corning HS 630) is used for the 0.15 and 0.31 cm tip seals.
31 Redundant seals were made at The Ohio State University using the same silicone types used in the original design. For the remainder of this paper the tip seals will be referred to as: TS1, TS2, TS3, TS4, and TS5 (0.15, 0.31, 0.63, 1.27, and 2.54 cm respectively). The tip seal design is illustrated in Figure 3.2.
Figure 3.2 Schematic of an MSGP tip seal. A molded ring of silicone rubber is used to form the seal with the rock surface while a spring loaded inner guide and immobile outer guide (0.63 cm ri and smaller) constrain the shape of the seal under compression. A similar design is employed for each of the five tip seals. Figure in Tidwell et al., 1997
During the sampling season the ice conditions encountered required two minor alterations to the MSGP. The stability platform was modified by removing approximately 5 inches of aluminum from the sides to reduce its footprint and weight on the ice, and four bolts were added on the underside to provide additional lateral stability.
The large size stability platform was designed to provide enough weight for it to be stable while on the ice surface, but in practice proved to be too large to remain stable, thus
32 dictating the modifications. The other exclusion was with the 0.62cm tip seal. This tip seal could not be calibrated during the in situ calibration experiments.
3.2 Permeameter Calibration
The MSGP underwent a series of tests both in a laboratory setting (a -7 °C lab at the Byrd Polar Research Center) and repeated in situ at Lake Hoare. These tests included a precision test to insure that all tip seals measured the same permeability on fracture and bubble free moat ice at Lake Hoare (site #407), a steady gas flow test to determine the period in which the gas pressure/flow/temperature stabilized, a test to determine at which input gas pressure converted from a laminar to turbulent flow, and head loss calibration when the tip seal was sealed with an impermeable surface (1/2 inch thick Plexiglas).
Figure 3.3 Tip Seal Precision Test
33 The precision test was conducted at two gas pressure inputs (4 PSI and 10 PSI).
TS1, TS2, and TS4 were consistent in the measurement at the two input pressures. The
TS3 did not seal at either pressure, and TS5 showed turbulent flow at 10 PSI (Figure 3.3).
The steady gas flow test was conducted to determine the amount of time to achieve steady gas flow. The measurement showed that all tip seals (with the exception of TS3) achieved a steady gas flow by 100 seconds at ~28 and 70kPa. Throughout the sampling season, the gas was allowed to maintain this steady state at ~28kPa to conserve the amount of gas used (Figure 3.4).
Figure 3.4 MSGP Steady Gas Flow Test.
34 The test to determine the laminar/turbulent flow boundary condition was
conducted also at site #407. It was observed that all tip seals either could not seal or the
gas flow reading entered into an error condition (turbulent flow) at pressure above
103kPa. At gas input pressures above 103kPa, the back pressure was to large to maintain
a tight seal with the ice surface, this caused seal flutter resulting in a gas flow reading that
was too large for the gas flow meter to read (>250slpm). Because of this, no site was
sampled at a pressure higher than 70kPa.
The head loss test was conducted inside a laboratory at the Lake Hoare camp
using an impermeable medium, a piece of ½ inch thick Plexiglas™. Connection of a
manometer (Meriam Instruments 350 Series Smart Manometer) to the output port of the
tip seals, which allowed the gas flow to become static (because of the impermeable medium), the measured difference from input gas pressure (minus atmospheric pressure)
subtracted from the measured pressure at the output would reveal in pressure loss in the
system. At a pressure of ~28kPa the average loss measured was 0.03%, and 0.008% at
~70kPa.
3.3 Permeability Sampling Domains
The permeability sampling was conducted at sampling points on the moat,
transition, and center ice of both lakes. The exact spots, using GPS waypoints (Garmin
GPSMAP 76CX), were re-sampled throughout October and November 2006. Temporal
domains are labeled late spring and early spring, and describe any changes in
permeability through time. Due to camp personnel allocations and time constraints, only
one 7-day sampling period was conducted at Lake Fryxell.
35 To describe the variability and be able to upscale permeability, a spatial domain system was employed. An 81cm2 grid system was sub-divided into nine cells of 3cm2 and used during sampling where the ice surface permitted (Figure 3.5).
These measurements were able to describe any variability of permeability on small scales; however, the average of the nine measurements can be used to describe the permeability of the whole sampling point. To maintain consistency, the grid was placed with cardinal reference points. 3cm
3cm
9cm
Figure 3.5 81cm2 sampling grid.
To validate the permeability measurements, 25 ice cores were drilled using a
Kovacs™ Enterprises Mark II ice corer from 12 sampling locations on both lakes.
Laboratory permeability determinations on these ice cores were measured to verify surficial primary permeability and to also measure the primary permeability vertically in
36 the ice column. The 9cm diameter ice cores varied in length from 13cm to 62cm long.
The ice core permeability was measured on the surface, at ~5cm, and repeating every
~10cm down the ice core (as applicable). This testing was conducted in a -7°C cold lab
at The Ohio State University’s Byrd Polar Research Center during August and September
2007.
The in situ sampling was conducted at both Lake Hoare and Lake Fryxell using
straight line transects on both moat and center ice, with the exception of the Lake Fryxell
crash site which was done in a 8-point radial pattern sampling pattern centered on the
middle of the crash site (Figure 3.6).
Figure 3.6 Lake Fryxell Crash Site sampling locations.
The sampling on Lake Hoare consisted of four straight line transects. Three transects sampled moat/transitional ice on the northeast (LHX1), northwest (LHX2), and
37 the southwest side (LHX4) of the lake and one transect sampled the center ridge and
trough ice (LHX3). The center, eastern, and southeastern portions of the lake were not
sampled because of difficulty transporting the equipment long distances and snowdrift
encountered on the eastern margin.
At Lake Fryxell two approximate straight-line transects were sampled on moat
and transitional ice (LFX1 and LFX2). No center ice was sampled, with the exception of
the crash site, because of time constraints of being at Lake Fryxell.
Figures 3.7 and 3.8 illustrate the sampling locations on both Lake Hoare and Lake
Fryxell.
The sampling location on all transects was chosen arbitrarily on a USGS
quadrangle map before sampling commenced. It was predetermined which transects would contain moat/transitional or center ice but the exact spot was chosen in the fashion mentioned above. This method was employed as to not weigh any sampling location with predetermined structures contained the ice.
38
Figure 3.7 Lake Hoare Sampling Transects.
39
Figure 3.8 Lake Fryxell Sampling Transects.
40 3.4 Permeability Calculation
Permeability is calculated using a modified version of Darcy’s Law (Goggin et al., 1988, Equation 13) (Equation 2).
(Q Pμ(T)) k ()Q ,P,P ,r,r = 1 1 p 1 1 0 i o ⎛ ⎛ ⎞ ⎞ ro 2 2 ⎜ 0.5riGo⎜ ⎟ P1 − P0 ⎟ ⎝ ⎝ ri ⎠ ⎠
Equation 2. Modified Darcy’s Law (Goggin et al.,, 1988)
Where:
2 ke is permeability (m )
Q1 is gas flow (sccm)
P1 is gas injection pressure (PSIA)
P0 is atmospheric pressure (hPa)
T is gas temperature
ri is radius of the inner seal (cm)
ro is radius of the outer seal (cm)
μ(T) is gas viscosity as a function of temperature (Pa/sec)
Go is a geometric ratio
41 The parameters of Q1, P1, P0, and T are measured directly using the electronics subsection
of the MSGP.
Gas viscosity is determined using a Sutherland’s standard engineering formula
(Crane, 1998) (Equation 3):
3/2 µ = µo(a/b)*(T/To)
a = 0.555To + C
b = 0.555T + C
Where:
µ = viscosity in centipoise at input temperature T
µo = reference viscosity for N2 in centipoise at reference
temperature To (0.01781)
T = input temperature in degrees Rankine
To = reference temperature for N2 in degrees Rankine
(540.99)
C = Sutherland's constant for N2 (111)
Equation 3. Sutherland’s Gas Viscosity
The geometric ratio (Go) is a single, analytically derived; dimensionless number
to deal with complexities associated with the flow field geometry of the tip seals (Tidwell
et al., 1997). For this study, the geometry used is G0(r0/ri)=G0(2)=5.03.
42 All measured parameters were calculated and converted in a Excel spreadsheet and the SI unit of m2 is used for all permeability measurements.
43
CHAPTER 4
RESULTS
Contained within this chapter are the results of field and laboratory surficial primary lake ice permeability (k) measurements. Field measurements were made using the MSGP on both Lake Hoare and Lake Fryxell during the austral spring 2006.
Laboratory measurements, using ice cores extracted during the early austral summer
2006, were made in August and September 2007. In totality, 351 spots were sampled for permeability (244 at Lake Hoare and 107 at Lake Fryxell). With an injection pressure between 28kPa and 7kPa, and allowing the gas flow rate to become steady after a minimum of 100 seconds, each permeability measurement was obtained using the 81cm2 grid, when applicable. Ice column depth was calculated from the MCM LTER bathymetry maps. Moat ice column was assumed to be equal to bathymetry, while ridge and trough ice columns are known to be ~6-8 meters thick (Adams et al., 1999).
Measurements from all sampling locations are in Appendix A.
4.1 Lake Hoare Permeability
The ice sampled at Lake Hoare was a combination of moat, transitional, and center ridge and trough ice. The measurements were conducted over a period of 15 days.
A change of ice conditions in late November 2006 prevented the use of the MSGP in
44 obtaining a longer temporal data set (discussed in “Limitations of the MSGP” in
Discussion chapter.
Sampling at Lake Hoare consisted of four transects (LHX1, LHX2, LHX3, and
LHX4) which provided a range of environmental conditions and ice characteristics and
allowed analysis of any variability in permeability measurements (Figure 3.8). The
transect locations were selected to reflect differences in solar radiation input, structures
contained within the ice, ice surface morphology, and analysis of anticipated temporal
variation in solar radiation. Three of the four transects consisted of moat and transitional
ice and one transect of center ice; each transect had four individual sampling locations.
Nine samples were obtained at each location using the 81cm2-sampling grid. One
transect sampled the center (ridge and trough) ice and consisted of two sampling locations at each ridge and corresponding trough.
Lake Hoare Transect One (LHX1)
Lake Hoare Transect One was located on the northeastern side moat ice, and trended east/west for approximately 1km. The four individual sampling locations (Site
412, 410, 408, and 407), chosen for their ice characteristic diversity, ranging from sites that contained no fractures or bubble structures to sites with low to heavy plume shape bubbles residing approximately 5cm below the surface of the ice. The ice columns’ depths ranged from less than 1m to nearly 8m thick. Transects that flanked the northern margin of the lake (LHX1 and LHX2) were exposed to considerably less sunlight than
transects on the southern side of the lake (LXH3 and LXH4).
45 The average primary permeability at all sites during the 15 days of sampling
ranged from a low of 1.03x10-13 m2 to a high of 8.56x10-14 m2. This variability was due
to differences in albedo, ice temperature, and tip seal gas diffusion depth. The averages
for the nine measurements are listed in Table 4.1.
Site/Date 412 410 408 407
10 / 2 9 / 2 0 0 6 1. 0 5 x 10 -13 1. 2 1x 10 -13 1. 0 3 x 10 -13 1. 6 7 x 10 -13
11/03/2006 7.90x10-14 2.21x10-14 8.56 x10-14 Error
11/ 14 / 2 0 0 6 2 . 12 x 10 -13 2.02x10-13 2.01x10-13 2.70 x10-13
Table 4.1 Primary permeability averages for LHX1. Site 407 (11/03/2006) data were discarded due to error in gas temperature as a result of battery failure. All sites on 11/03/2006 were sampled using tip seal #2, all others used tip seal #1.
Lake Hoare Transect Two (LHX2)
Lake Hoare Transect Two was located on the northwestern side moat and
transitional ice, and trended east/west for approximately 2km. The four individual
sampling locations (Site 413, 414, 415, and 416) consisted of various ice characteristics
that contained heavy plume shape bubbles residing approximately 5cm below the surface,
a large ice blister, and large arrays of vertical and horizontal fractures ranging from
<1mm to larger than 5cm wide. The ice columns depth of this transect, at ~8m–10m thick, was thicker than LHX1.
The average primary permeability at all sites on LHX2 during the 15 days of sampling ranged from a low of 1.76x10-13 m2 to a high of 9.80x10-14 m2. This variability
46 was due to changes, as with LHX1, in albedo, ice temperature, and tip seal gas diffusion
depth. The average for the nine measurements within each sample site is listed in Table
4.2.
Site/Date 413 414 415 416
10/ 30/ 2006 9.80x10-14 1. 7 7 x 10 -13 1. 7 8 x 10 -13 1. 7 6 x 10 -13
11/ 13 / 2 0 0 6 1. 9 8 x 10 -13 1. 9 6 x 10 -13 2.11x10-13 2.12x10-13
Table 4.2 Primary permeability averages for LHX2. Site 413 on 10/30/2006 was sampled using tip seal #2; all others used tip seal #1.
Lake Hoare Transect Three (LHX3)
Lake Hoare Transect Three was located on the southwestern side moat and
transitional ice, which trended east/west for approximately 500m. The four individual
sampling locations (Site 421, 422, 423, and 424) consisted of various ice characteristics
that contained heavy plume shape bubbles residing approximately 5cm below the surface,
a large ice blister, and large array of vertical, interconnecting fractures less than 1mm
wide. The ice columns depth on LHX3 was much shallower than the northern transects,
ranging from 0.5m to 2m deep. As noted above, this transect received an additional 2-3
hours of direct sunlight than the other transects at Lake Hoare.
The average primary permeability determined for each site along this transcript on
each of the 5 days of sampling ranged from a low of 1.57x10-13 m2 to a high of 9.02x10-14 m2. As with other transects, the variability was due to changes in albedo, ice temperature,
47 and tip seal gas diffusion depth. The average for the nine measurements within each sample site is listed in Table 4.3.
Site/Date 421 422 423 424
10/ 30/ 2006 1.6 2x10-13 1. 6 3 x 10 -13 1. 5 7 x 10 -13 2.25 x10-13
11/ 13 / 2 0 0 6 9 . 0 2 x 10 -14 2.35x10-13 1. 6 3 x 10 -13 8.41x10-14
Table 4.3 Primary permeability averages for LHX3. Site 421 and 424 on 11/13/2006 was sampled using tip seal #2; all others used tip seal #1.
Lake Hoare Transect Four (LHX4)
Lake Hoare Transect Four, trending east/west for approximately 1.5km, was located on the northern margin ridge and trough center ice. At each of the four individual sampling locations (Site 417, 425, 427, and 429), one set of measurements was taken on a ridge and another on the southern lateral corresponding trough. Each ridge was approximately 1–1.5m above the trough. The ridge ice was bubble and fracture free but had irregular rough surfaces. Because of the surface irregularities, site 429 could not be sampled. The ice columns’ depth on LHX4 was assumed to be 6–8m thick with approximately 20m of liquid water below.
The average primary permeability on the ridges at all sites ranged from a low of
1.62x10-13 m2 to a high of 1.98x10-13 m2. In the troughs, permeability ranged from a low of 1.60x10-13 m2 to a high of 2.21x10-13. The average measurements for all sites on both days are listed in Table 4.4.
48
Site/Date 417R 417T 425R 425T
11/ 5 / 2 0 0 6 1. 6 2 x 10 -13 1. 6 5 x 10 -13 1. 6 4 x 10 -13 1. 6 0 x 10 -13
11/06/2006 427R 427T 429R 429T
1. 9 8 x 10 -13 2.12x10-13 No Data No Data
Table 4.4 Primary permeability averages for LHX4 ridge and trough. All sites used tip seal #1.
4.2 Lake Fryxell Permeability
The ice sampled at Lake Fryxell consisted of three moat ice transects (LFX1,
LFX2, and LFX3), and the site of the NSF Bell 212 helicopter crash in January 2003
(LFCS). LFX3 was planned but never sampled because large snowdrifts along the margin of the Canada Glacier prevented access to the transect. The ice surface at Lake
Fryxell had 2–5cm deep snow cover when sampling commenced. This snow cover was removed using a soft bristle hand broom, which did not alter the ice surface. Of the 107 measurements conducted on Lake Fryxell ice, the average primary k measured was
1.55 x10-13m2.
As with transects at Lake Hoare, the ice sampled at Lake Fryxell was a combination of moat, transitional, and center trough ice (crash site); measurements were obtained using the same sampling procedures and spatial grid. The measurements were conducted over a period of 7 days.
49 Lake Fryxell Transect One (LFX1)
Lake Fryxell Transect One was located on the northwestern side moat ice, which
trended east/west for approximately 2km. Six individual sampling locations (Site
720,721,722,723,724, and 725) consisted of various ice characteristics that were
encountered on Lake Hoare, ranging from sites that contained no fractures or bubble
structures to sites with low to heavy plume shape bubbles residing approximately 5cm below the surface of the ice. The ice columns depth ranged from less than 1m to 6–8 meters thick.
The average primary permeability throughout all sites ranged from a low of
1.44x10-13 m2 to a high of 4.73x10-14 m2. The averages of the measurements for each site
on all days are listed in Table 4.5.
Site/ Date 720 721 722 723
11/ 0 7 / 2 0 0 6 1. 4 4 x 10 -13 2.30x10-13 1. 9 4 x 10 -13 1. 9 1 x 10 -13
724 726
11/ 0 7 / 2 0 0 6 1. 8 3 x 10 -13 4.73x10-14
Table 4.5 Primary permeability averages for LFX1. Site 726 was sampled using tip seal #2; all others used tip seal #1.
Lake Fryxell Transect One (LFX2)
Lake Fryxell Transect Two was located on the northern margin in a north/south
trending moat feature created by a sediment island. This transect was shorter than all
other transects at ~200m. Three sampling locations (Site 726,727, and 728) included ice 50 with various ice characteristics, including large diameter bubbles (2-4cm), extensive
horizontal fracturing, and clear bubble and fracture free ice. The ice columns’ depths
ranged from less than 1m to 6 meters thick.
The average for the nine measurements within each sample site is listed in Table 4.6.
Site/ Date 726 727 728
11/ 10 / 2 0 0 6 2 . 2 9 x 10 -14 9.85x10-14 2.19x10-14
Table 4.6 Primary permeability averages for LFX2. All sites used tip seal #2.
4.3 Lake Fryxell Crash Site Permeability (LFCS)
The Lake Fryxell Crash Site sampling site was located in an ellipsoidally shaped
trough created by the impact of the Bell 212 crash. Eight sampling locations in a radial
fashion from the center on the crash zone were chosen. A few centimeters below its
surface the ice had small sediment layers which had been deposited initially by eolian
transport onto the surface of the ice. Over time, the sediment sank into the ice cover, ice
ablation left liquid water in its path. This water refroze, trapping the sediment below the surface. During the sampling period, the sediment was shallow, indicating that the deposition had been recent, since sediment will continue to travel downward (because of its decreased albedo), leaving larger amounts of refrozen water above them. Small pieces
of aircraft exterior paint were also found in the ice. No visual signs of hydrocarbons
were present. The average primary permeability for each of the sites sampled at the
LFCS crash site are listed in Table 4.7.
51
Site/ Date A4 A10 B4 7 B57
11/08/ 2006 2.04x10-13 2.24x10-13 2.07x10-13 2.03x10-13
C12 D 6 E41 F10
11/08/ 2006 2.07x10-13 2.00x10-13 2.03x10-13 2.05x10-13
Table 4.7 Primary permeability averages for LFCS. Numbers after site locations indicate distance in feet from center marker of the crash zone. All sites used tip seal #1.
4.4 Laboratory Measurements of Ice Core Permeability
Ice cores from sampling sites at Lake Hoare and from the Lake Fryxell crash site
were tested for a primary permeability along the vertical axis using the same methods that
were used during the in situ testing. However, rather than using the spatial grid used
during in situ testing, the sampling method utilized identified five spots sampled per depth (the geometric pattern was square box with a center sample) approximately 3cm inside the outer perimeter of the ice core.
Upon extraction from the lake, the ice cores were wrapped in plastic storage bags, labeled, and then stored outside, in the shade, inside a large Styrofoam FreezeSafe™ container. The ice cores were transferred to McMurdo Station via helicopter and stored in a -20°C freezer at the Crary Lab. Approximately half the cores were shipped with dry ice via commercial aircraft to the Byrd Polar Research Center (BPRC) at The Ohio State
University, where they were stored at -20°C. The remaining ice cores were shipped via surface vessel from McMurdo Station to Pt. Hueneme, California before being shipped
52 via FedEx to BPRC. The ice cores were cut and prepared using a ice core band saw, and tested in a -6°C cold room at BPRC. The average primary permeability for the LFCS showed no apparent variability through depth. Results from individual measurements are tabulated in Appendix A.
53
CHAPTER 5
DISCUSSION
The goals of this study were manifold: to understand the ice’s role in the atmosphere/biosphere exchange of gases, to understand any spatial or temporal variation of the lake ice’s physical properties, to determine an average in situ permeability for use in flow and transport models, to provide a range of permeability to compare with parameters used in a one dimensional hydrocarbon flow model by Karanovic 2005, and to develop a method to upscale the permeability to a lake-wide permeability scale. While this study focused on determining the primary permeability, the overall permeability is greatly influenced by secondary structures, such as fractures and bubbles, contained within the ice column increasing the overall permeability.
Over 350 individual measurements of primary permeability were made on Lake
Hoare’s and Lake Fryxell’s ice surface. These locations were arbitrarily selected to sample the variety of the ice’s physical and environmental conditions to which the lakes are subject. Overall, the primary permeability measurements made of lake ice show that the surface of the ice column is intrinsically semi-permeable. All permeability measurements fell within the range of 10-13 to 10-14 m2, a range similar to the intrinsic permeability of sandstone. These determinations of Dry Valley wet-based lake ice permeability are important because of the ice’s ability to transfer atmospheric elements
54 and nutrients to the microbial communities present under the ice column in the liquid
water. Priscu et al. (1995) and others contend that the ice is an essential feature
influencing the biological activity in the lake water below and contained within the ice.
The term, primary permeability, refers to the void space and its interconnectivity between
individual hexagonal ice crystals that make up the different types of ice present at both
lakes.
In this study, variability in primary permeability will be contrasted by difference
in space, time, and the environmental parameters inherent to the lakes. This discussion
will be followed by development of a model for upscaling the individual measurements
in order to understand the primary permeability of the entire lake. Next, a discussion of
any variability with depth measured in laboratory measurements on ice cores extracted
from the lake and returned to the laboratory will show a vertical profile of the ice that
was not performed as part of the in situ research. Finally, this study will discuss the
limitations of the MSGP designed for this project.
5.1 Formation and Development of Secondary Structures that Affect
Permeability
Permeability of ice cover on the Dry Valley lakes is dominated by a variety of structures within the ice (e.g., bubbles, water lenses and fractures) that are responsible for secondary permeability in the ice, similar to fluid flow through fractures in geologic strata. Each structure alters and affects the secondary permeability by increasing the interconnectivity of the pore space between ice crystals. These secondary structures influence the heat flux, the transmission and absorption of light, and the mass transport of
55 elements from the atmosphere and directly affect the biogeochemical processes that occur in and out of the cryosphere and hydrosphere of the lake (Fritsen et al., 1998).
During the austral fall and winter ice is formed from the top down by a freezing
process at the liquid water/ice interface, while at the same time, ablation acts to remove
the ice from above. Bubble formations contained within the ice are a product of gas
exsolution and are captured in the ice at its boundary with the liquid water (Carte, 1961
and Bari et al., 1974). Adams et al. (1998, p. 282) explain the process of bubble
formation:
As the ice front advances downward, the solid phase rejects dissolved gasses thereby increasing the supersaturation level of the liquid at the interface until, in presence of a nucleate, a critical value for bubble formation is reached. A consequence of bubble formation is that supersatuaration of adjacent liquid is lowered. Size, number, and shape are to large degree a function of ice growth rate. As the growth increases, the number of bubbles also increases, but the size decreases.
Adams et al. (1998) go on to describe the bubble formations encountered from the
bottom of the ice column upwards. They describe the morphology found within the
lowest 2m of the ice as vertically oriented cylinders approximately 20cm long, followed
by layers of clear ice and cylindrical fractures around 10cm in diameter, which are
formed by trapped liquid water that expands during freezing. Following this process,
sand and gravel size particles, which had been delivered by eolian transport, are then
moved downward through the ice as the ice melts. This eolian-transported sediment
increases the ice ablation rate and leaves liquid water in the ice column as it progresses
downward. The sediments collects at approximately 2m below the ice surface and acts as
the boundary point in which light radiating through the ice column no longer has a
56 significant influence. At this sediment layer, found 2–3m below the ice surface, a liquid
water aquifer forms during the late austral spring and summer.
In the uppermost layer of the ice, Adams et al. (1998) describe a morphology of
bubble structure that is generally smaller than bubbles found at lower levels, have a tear
drop appearance, and are distinctly frosted on the upper surface. It is this morphology,
plus fracturing, that is responsible for the slight variations in permeability noticed in this
study. This bubble formation and fractures are illustrated in Figure 5.1, taken from
sampling site #410 on Lake Hoare.
Figure 5.1. Fracture and bubble formation from Site #410 on Lake Hoare. This photograph indicates the heterogeneity that is encounter on a small spatial scale.
Fractures in the ice are common features for both the moat ice and troughs of center ice. This fracturing results from the expansion of molecules during the state
change from liquid water to a solid during the freezing period in the fall. The fractures
57 encountered on both Lake Hoare and Lake Fryxell range in size from less than a
millimeter to greater than 20cm, although fractures this large were only rarely observed.
When fractures larger than 1–2mm were encountered during sampling, the MSGP could
not seal and the result, therefore, was recorded as no data, essentially describing a
condition of infinite permeability at that particular location. The lateral extent of fractures encountered could be tens of meters long and would intersect with many other
fractures ranging in all sizes.
5.2 Interpretation of Permeability in Graphs
This study uses a single method to interpret the reoccurrence of permeability data
through the use of “clustering.” Permeability plots are one-dimensional and do not have
a value for the X-axis, with the exception of Figure 5.8 and Figure 5.12. This allows the
values of k to be plotted vertically, using a thin horizontal line for each individual
permeability measurement. The clustering visually observed then gives an indication of
solid or thicker areas and indicates a denser range the individual permeability
measurements occur; the thin dashes indicate a less dense occurrence. This method of
plotting is used exclusively in this chapter.
58
5.3 Lake Hoare and Lake Fryxell Spatial Permeability Variability
Figure 5.2 Primary permeability of all k measurements obtained at Lake Hoare. To show where the largest clusters of k measurements occur, the graph above uses a thin horizontal line. Solid clusters indicate a higher density of k values measured as highlighted inside the oval.
This study of primary permeability at Lake Hoare was conducted from late-
October to mid-November 2006. The average permeability determined from the 177 measurements made is 1.63x10-13 m2 (Figure 5.2). Figure 5.2 is plotted with all
permeability measurements stacked (no x-axis value), which indicates the variability
present on the smallest spatial scale, an which would be an expected result considering
the nature and abundance of ice structures at the centimeter scale, but the cluster of data
(solid darker areas) indicates the range of permeability values commonly measured. 59 Through the use of the mean of samples all measurements during the sampling period the
heterogeneity at the smallest scale can be factored out as the spatial scale becomes larger
using the statistical mean of all permeability values. This is the basis for using single,
small-scale spot measurements and upscaling, through the use of the mean, those
measurements to understand the ice at a lake size scale.
Lake Fryxell’s permeability similar to that of Lake Hoare for the same reasons as
explained above. The average permeability at Lake Fryxell,1.90x10-13 m2, closely
resembles that of Lake Hoare’s moat ice and the Lake Fryxell crash site average,
~2.00x10-13 m2, is a proxy for the ridge and trough ice (Figure 5.3). Although there are physical and environmental differences between the two lakes, the same characteristics, such as ablation rate, sediment deposit, and internal ice temperature gradients, are present at both lakes. These factors form, alter, and decay the ice, affecting primary permeability, and structures contained within the ice, affect secondary permeability.
60
Figure 5.3 Lake Fryxell moat ice permeability. The largest clusters of k measurements occur, the graph above uses a thin horizontal line. Solid clusters indicate a higher density of k values measured.
5.4 Permeability Variability within Ice Types
A comparison of the different types of ice (moat/transitional versus ridge and trough ice) shows that the same clustering of data is observed at both Lake Hoare and
Lake Fryxell (Figures 5.4 and 5.5).
61
Figure 5.4. Moat ice and ridge and trough ice permeability measurements at Lake Hoare. The average k value shows similarity between the types of ice sampled.
Figure 5.5. Lake Fryxell moat and crash site permeability measurements. The average k value shows show the similarity between the types of ice sampled.
62 Although there is slight difference in the average permeability, the value it is not
significant in describing any profound difference in the ice types sampled. This
difference between moat and center ice, on the order 0.5x10-13 m2, does not indicate a
large change in the permeable nature of the moat ice. The slight increase in permeability is expected due to a slight increase in porosity from the larger amount of secondary structures in the moat ice. The position of the moat ice changes on an annual basis, depending on the position of the permanent center ice after the last major wind storm before the moat refreezes during the austral fall. The moat ice has more internal bubble structures than does the center ice, due to the larger latent heat content, which is essential for bubble formation. This influx of heat is generated from annual glacier meltwater runoff into the lake and absorption of solar radiation (Adams et al., 1998). Within the ridge and trough ice, the main latent heat input is less influential because of the relative thicker ice columns present. However, trough ice (which melts and refreezes annually) would have a higher latent heat content due to incoming solar flux and eolian sediment present.
5.5 Variability of Permeability due to Solar Radiation Input
The physical location of Lake Hoare within Taylor Valley results in different parts of the lake to receive different solar radiation input. During the austral spring, the sun is above the horizon 24 hours a day. The Asgard Range, however, provides the northern margins of the lake with a substantial amount of shade. Due to the sun angle during the early part of the sampling period, the northwestern transect received ~5–6 hours of sunlight per day, while the southwestern transect received an additional 2–3
63 hours of direct solar input because of less shading. Later in the austral spring, both the
northwestern and southwestern sides of the lake received additional direct solar input
when the sun angle increased to allow sunlight over the Kukri Hills.
Solar radiation input to the ice column plays a major role in ice surface alteration
throughout the austral spring and summer by directly ablating the ice and by heating any sediment that is present on the surface. When sampling commenced at Lake Hoare in late October, the lake had a small layer of snow covering the ice, which increased the albedo and protected the ice surface from ablation. However, within days after removal of the snow, ablation cups (concave melting about 10 cm in diameter) started to form on the moat ice and center ice troughs.
Because of the different physical location of the transects the northwestern
transect receives less direct sunlight than the southwestern transect. Because of this these
two transects were used to test for possible variability due to this difference in solar input.
Both transects were measured in early austral spring (labeled “early” on plots) and in the
late austral spring (labeled “late” on plots).
64
Figure 5.6 Permeability measurements in late October on different transects receiving different solar input.
Figure 5.6 shows that in general there was slightly greater permeability measured on the southwestern transect. This side of the lake receives more sunlight than does the northwestern shadier side of the lake. This greater permeability is deemed to be due to two factors. The first factor is the greater direct sunlight, warming on the southwestern portion of the lake, causes the ice there to ablate at a higher rate, exposing secondary permeability features. Secondly, the northwestern side of the lake receives less sunlight than the southwestern side, however, the snow cover on Lake Hoare during this time increased the albedo, lowering any additional latent heat input into the ice, thereby reducing the ablation rate for both transects.
65
Figure5.7. Permeability measurements in mid-November on different transects receiving different solar input.
Measurements made later at the same locations (in mid-November) showed generally lower permeability (Figure 5.7). This decrease in permeability is likely due to the snow cover on the lake ice during this time, which increased the albedo, lowered any additional latent heat input into the ice, and refroze any water of the surface ice that had melted earlier in the austral spring.
Prior to the initiation of glacial meltwater input to the lake in late December, direct solar absorption is the primary factor controlling the permeability. By late
November, dramatic changes in ice characteristics were visibly noticeable, which is discussed later in this chapter.
66 5.6 Permeability Variability in Temporal Domain
The data show an increase of the primary permeability at Lake Hoare at different locations when observing the data through time (Figure 5.8).
Figure 5.8. Time series of Lake Hoare primary permeability measured at all locations over a period of 16 days from October 30, 2006 to November 14, 2006. The label “A” indicates the tight cluster of lower permeability in the early austral spring, and the label “B” indicates the same cluster of increased permeability in the late austral spring. The variation noticed in the middle of the plot indicates the permeability increasing due to higher ablation rate. The cluster of low permeability measurements on day 5 is due to snow cover from a recent small fall that increased the albedo and allowed refreezing of the surface layer of the ice.
The time series plot shows the progression of increased permeability throughout
the austral spring. Figure 5.8 indicates that early in the austral spring permeability was
67 similar at all points measured at Lake Hoare (labeled A in Figure 5.8). The variability in this time period is due to sample points experiencing different environmental conditions
(exposure to sunlight and snow cover).
The permeability values in Figure 5.8 in the late austral spring (labeled B) also indicate consistent values and show increased permeability when compared to the early austral spring measurements. This increase, as noted above, is due to ablation caused by the increasing amount of direct solar exposure as the sun angle increased. This is especially important to the parts of the northern margin of the lake, which receive as much sunlight as the southern portion.
The variability between the early and latest periods in austral spring shows a marked increased in permeability followed by decrease. This indicates the effect that sunlight has on the surficial layer of the ice. Ablation of the ice changes the permeability quite rapidly by exposing the bubble formations contained in the upper two meters of ice.
This exposure allows secondary permeability to increase rapidly and thereby increasing the overall permeability of the ice. The decreased permeability seen around day five is caused by a snowfall, which occurred on November 4, 2006, which shielded the ice surface by increasing the albedo, retarding the ablation rate, and allowed a refreeze of the ice surface to occur.
68
Figure 5.9. k measurements during the early and late austral spring on the northwestern transect (shady side).
At Lake Hoare there was an increase in permeability from late-October to mid-
November (Figure 5.9). This is due to the increasing direct solar input to the ice, which sublimated the ice down to the secondary bubble features present in the uppermost meter of the ice column. Figure 5.10 shows decrease in permeability through time, expected due to the snow cover present retarding the ablation of the ice.
69
Figure 5.10. k measurement made in the early and late austral spring on the southwestern transect (sunny side).
A t-Test: Two-Sample Assuming Equal Variances test was conducted to investigate a null hypothesis that the same mean value for permeability between 64 permeability measurements made at Lake Hoare during the early austral spring and 64 measurements made at the same locations in the late spring existed.
Results indicate that the P value =3.61x10-16 and |t| =9.38 is greater than the
critical value of 1.978 for a 2-tailed test, so we reject the null hypothesis that the means
are equal, and conclude the different sampling times have different mean permeability
(Table 5.1). The alpha used in this test was 0.05. 70
t-Test: Two-Sample Assuming Equal Variances
Early Austral Spring Late Austral Spring Mean 1.4921E-13 2.08912E-13 Variance 2.28966E-27 3.05025E-28 Observations 64 64 Pooled Variance 1.29734E-27 Hypothesized Mean 0 df 126 t Stat -9.376391075 P(T<=t) two-tail 3.60721E-16 t Critical two-tail 1.978970576
Table 5.1 t-Test: Two-Sample Assuming Equal Variances test was conducted to investigate a null hypothesis that the same mean value for permeability at Lake Hoare during the early and late austral spring. The null hypothesis was reject because the |t| state value is greater than the t critical two-tail value. α=0.05.
In summary, there was a slight increase in permeability for Lake Hoare ice
through the time when measurements were performed. The variability seen is attributed
to an increased sublimation of snow cover, and ablation of ice. The uppermost ice
surface has many inverted tear drop shape ice bubbles which are present within 5cm of
the surface in late-October; with in increase of direct solar radiative input, causing
ablation later in the austral spring, allow these secondary structures become closer to the
surface of the ice (which would increase the connectivity of void space), falling within
the effective range of the MSGP, and increasing the ice’s primary permeability through
time.
71 5.7 Lake Fryxell Crash Site Permeability
One of the major goals of this study was to provide the material parameter of
single value of ice permeability for use in time-dependent, one-dimensional flow and
transport model for the lake ice cover. Sensitivity testing showed transport results were
highly dependent upon the value of this material parameter (Karanovic, 2005).
To this end, a comprehensive investigation of lake ice primary permeability was
conducted at the site of the January 2003 NSF Bell 212 helicopter crash on Lake Fryxell.
As explained in the methods chapter, a radial transect was developed, emanating from the center of the crash zone. The site was located in a trough created by the impact of the
crash. The ice in this zone is subject to repeated melting and refreezing each season.
During the period of testing the ice was still frozen but had shown signs that melting had
already started to occur. By late-November the ice in the crash zone deteriorated to a thin
veneer of frozen ice with 0.5 m liquid water pools underneath.
Permeability measurements made during mid-November were similar at all points
tested in the crash zone (Figure 5.11). This observation showed that little variation was
seen in this site, and a value of 2.06x10-13 m2 could be used as the model’s primary
permeability measurement for a period prior to the austral summer.
72
Figure 5.11. Lake Fryxell Crash Site permeability. Data shows low variability of the eight sites sampled with the crash zone.
However, observation of the ice conditions in late-November showed rapid melting occurred during this period. As the crash occurred in the month of January, a time of the maximum melting, the permeability values most likely would have been greater than those measured in November, increasing the ability of hydrocarbons to be transported into the ice column.
Prior to the commencement of clean-up operations in January 2003, personnel arriving at the crash sight within 72 hours of the incident noticed that a significant amount of aviation fuel had already been transported into the ice column. Post-crash studies show that hydrocarbons did penetrate through ice column into the water column
73 below. In later assessments and field studies, it was determined that the organisms present in the water column readily metabolized the hydrocarbons, and that bioremediation could be used successfully for future fuel spills on wet-based lakes in the
Dry Valleys (Foreman et al., 2006). The initial observation that a significant amount of fuel had been absorbed indicates the extreme nature of the secondary permeability features of these lakes.
During the extraction of ice cores for this project, most core holes filled with water up to the hydrostatic level of the lake within seconds after the ice core was removed. Squyres et al. (1991) encountered liquid water at 2.1 m below the ice surface at Lake Hoare during the month of November. They found that the holes could not be pumped dry, indicating the ice was very permeable. Adams et al. (1999) also encountered this phenomenon during later studies of bubble morphology on wet-based
Dry Valleys lakes.
5.8 Laboratory Investigation of Primary Permeability
During late-November through early-December, 25 ice cores, from 12 sampling sites, were extracted from the previously used sampling locations at Lake Hoare and Lake
Fryxell. Of these 25 ice cores, twelve were tested for their permeability. This testing included measuring the primary permeability down the length of the core (starting at 5cm below the surface and continuing every 10cm, unless ice quality (brittleness) prevented this) to investigate any change in permeability in the upper 1.5m of the ice column. The ice cores were tested using the same methods and equipment used in field. However,
74 instead of the 100-second wait time, a visual inspection of steady gas flow on the Alicat gas flow meter was used to determine steady gas conditions.
Figure 5.12 shows the results of three of the eight ice cores extracted from the moat ice of Lake Hoare.
Figure 5.12. Laboratory results of Lake Hoare moat ice cores. The three ice cores represented show results consistent with the 12 ice cores that were measured.
The data indicate little permeability variation with depth in these ice cores. This result can be attributed to the lack of vertical or lateral force present within the ice column, due
75 to its shallow depth (2-6m), did not act to compact or deform the ice crystals contained within.
5.9 Permeability Upscaling
The need for permeability upscaling derives from the disparity of the scale at which permeability is measured and the scale of system for analysis (Tidwell et al.,
1999). The concept of permeability upscaling is this: by using multiple small-scale measurements from different sampling sites, the lakes’ heterogeneity could be factored out and scaled up to reflect the primary permeability of the entire lake as a single, homogenous system through use of the samples’ mean permeability. Darcy’s Law is assumed to hold at all scales in a heterogeneous system (Hassanizadeh et al., 2005).
Therefore, data analysis can reveal slight differences in surficial primary permeability in different ice types and ice exposed to different environmental conditions over large spatial areas on small scales. Through measuring permeability in all ice types the various environmental conditions encountered, and plotting all measurements, the sampled mean of all permeability values could be used as a scaled up primary permeability value for the entire system, eliminating the heterogeneity on the smallest of scales.
Tidwell and Wilson (1999) describe the key concepts needed for permeability upscaling, including: (1) all measurements, regardless of sample support, are made subject to consistent boundary conditions and the same flow geometry; (2) measurements are nondestructive, thus allowing all data to be collected from the same physical sample;
(3) dense sampling grids are employed to provide detailed spatial information on the permeability field; and (4) measurements are precise, subject to small and consistent
76 measurement error. By acquiring data in this manner, sampling artifacts that can
aggravate quantification of permeability upscaling are minimized or eliminated. For this
study, these conditions were accomplished through the use of the sample spatial domain
size (3cm x 3cm grid); through use of the multi-support capacity of the tip seals, and by
basing the MSGP design on a theoretically and empirically proven system.
At Lake Hoare, the average primary permeability measured was 1.63x10-13 m2 and a high density of measurements fell within a range centered on ~2.00x10-13 m2 (Figure
5.13).
Figure 5.13. Permeability measurements showing the mean at 1.63x10-13 m2 at Lake Hoare. The upscaled primary permeability of Lake Hoare is obtained as the mean of all sample measurements.
77 The cluster of data points shown in Figure 5.13 can be equivalent to the average primary
permeability encountered at any spatial point, during any time period, and within any ice type. Although changes in permeability may vary on small scales on the vertical plane due to sublimation uncovering secondary features, the primary permeability of the ice
crystal remains constant on a horizontal plane. Because of this, the heterogeneity can be
factored out as the spatial scale increases while using the sample mean allows the lakes’
ice column to be considered a single homogenous system.
When a comparison of the total permeability measurements at Lake Hoare and
Lake Fryxell is made, the sampled mean of all permeability measurements is similar.
This further indicates that regardless of all physical and environmental factors present,
the upscaled permeability is similar at approximately 2.00x10-13 m2 (Figure 5.15).
Limitations to this upscaling method exist. Most permeability upscaling
experiments are done either through the use of mathematical modeling or through an
automated process in a laboratory setting that allows the collection of extensive data
points. With the increase in data, the variance of any sampled data set decreases. In this
study, 351 total measurements were used to calculate an upscaled value. Due to nature of
conducting field based testing in a physically challenging environment while the medium
that is being analyzed is changing over time no more measurements were able to be
collected.
78
Figure 5.14. Comparison of all k measurements indicates clustered data that can be used to determine a single primary permeability value.
5.10 Limitations of the Multi-support Gas Permeameter
Operation of the MSGP during the period of late-October to mid-November met the operational goal set during the design phase of this project. The primary goal was to measure primary permeability accurately and precisely by injecting known quantities of fluid into sample medium. However, due to changes in ice characteristics observed at all locations at both Lake Hoare and Lake Fryxell in the early austral summer, the MSGP was unable to continue at measuring surficial primary permeability once there was a large amount of ice melt. During late November, the injection of the N2 gas through the tip
seals would physically alter the surface of the ice being tested by melting it. During this
79 time, when the gas was applied to any ice type, some of the ice underneath the inner tip
seal would melt, and the melted area corresponded to an area consistent with the inner
radius. Initially it seemed that the metal of the N2 tank, gas lines, or the tip seals
themselves were increasing the temperature of the gas prior to its contact with the
sampling medium through the absorption of radiant heat. To test this, procedures were employed to resolve this issue by shielding all parts of the MSGP in a protective cooler between sampling locations. The second attempt at resolution was to sample only during the coldest times of the day (3:00am to 5:00am) and only to measure sample points that were (and had been) located out of the path of direct sunlight. Finally, to test the idea that ambient warming of the equipment was plausible, the tip seal and all equipment was stored in constant shade for 24 hours and then permeability measurements were made on ice that had been shaded by a large boulder that prevented the ice from receiving any direct sunlight. None of these procedures prevented the ice underneath the tip seals from melting.
The cause of the ice melt was determined to be the friction created when the pressurized N2 gas came in contact with ice. This small amount of heat created was not
critical during periods when the ice’s potential energy was much lower, but in late
November the ice column had become isothermal at a temperature just below 0C°
allowing the phase change to occur. This near melt isothermal condition occurs
consistently in mid to late November each year, as indicated by a three-year study using
thermocouples at Lake Hoare (Figure 5.15) (Fritsen et al., 1998).
80
Figure 5.15. Ice temperature records from 1985 to 1988 in Lake Hoare. Source: Fritsen et al., 1999.
When the ice on the lakes became isothermal near its melting point, the internal energy created by the operation of MSGP rendered the system incapable of measuring primary permeability. This process suspended any further measurements using the
MSGP.
5.11 Recommendations for Future Work
To gain a better understanding of lake ice in the McMurdo Dry Valleys, an
MSGP should be incorporated into an investigation of the permeability of the entire ice column by excavation of a pit an repeated measurements in the vertical profile. This would allow a better understanding of any permeability changes; not only from the energy input at the surface, but what affect that glacial meltwater input has on the lower margins of the ice column near the ice/water interface.
81 Any change to climate in the McMurdo Dry Valleys would likely have a
significant effect on the perennial ice covered lakes. A multiyear study, using the same methods employed in this study, could be used to track yearly changes to permeability of
the ice column. Using a differential GPS system that would allow relocation to the same
spots repeatedly, measurements could be conducted at the same locations in future seasons, over multiple field seasons.
Although this study was limited to measurements of the surficial primary permeability of lake ice, the MSGP could be used on a host of different sample supports, including geological strata, glacial ice, sea ice, firn, and hard pack snow cover. Because
of the range of measurements (10-9 to 10-15 m2) with the MSGP, its portability,
nondestructive nature, and repeatability of measurements, would the MSGP could be
used in almost any field setting to give rapid investigations of permeability in a variety of
Earth materials.
5.12 Conclusions
This research study investigated the primary permeability of lake ice on two lakes, Lake Hoare and Lake Fryxell, in Taylor Valley, Antarctica. To accomplish the stated goals of this research, a novel multi-support gas permeameter was created for use in a harsh polar environment. The information obtained through this investigation was:
(1) all lake ice, regardless of type, environmental condition, and through the austral
spring was semi-permeable on a intrinsic scale, (2) the ice showed little variation in
primary permeability, (3) an average permeability value of 2.03x10-13 m2 was determined
and can be used in the hydrocarbon flow model developed by Karanovic 2005, (4) the
82 average permeability value of Lake Hoare of 1.63x10-13 m2 was determined as the mean, using samples upscaling method, and (5) little variation in intrinsic permeability exists in a vertical profile of the uppermost meter of the ice column through the testing of ice cores extracted.
83
APPENDIX A
PRIMARY PERMEABILITY MEASURMENTS
84 Primary Permeability Measurements
Lake Hoare Permeability
LHX1
10/29/2006
Grid Loc Site #412 Site #410 Site #408 Site #407 1 1.04E-13 1 1.07E-13 1 1.07E-13 1 1.64E-13 2 1.03E-13 2 1.07E-13 2 1.04E-13 2 1.65E-13 3 1.11E-13 3 1.94E-13 3 1.05E-13 3 1.68E-13 4 1.06E-13 4 1.08E-13 4 1.04E-13 4 1.65E-13 5 1.04E-13 5 1.45E-13 5 1.03E-13 5 1.65E-13 6 1.06E-13 6 1.03E-13 6 9.71E-14 6 1.66E-13 7 1.04E-13 7 1.19E-13 7 1.03E-13 7 1.69E-13 8 1.03E-13 8 1.04E-13 8 1.05E-13 8 1.69E-13 9 1.03E-13 9 1.03E-13 9 1.01E-13 9 1.71E-13 Avg 1.05E-13 Avg 1.21E-13 Avg 1.03E-13 Avg 1.67E-13
11/03/2006
Grid Loc Site #412 Site #410 Site #408 Site #407 1 1.51E-14 1 2.12E-14 1 2.50E-14 1 Not Sampled 2 1.01E-13 2 2.67E-14 2 9.41E-14 2 3 7.98E-14 3 2.09E-14 3 9.30E-14 3 4 8.74E-14 4 2.08E-14 4 9.33E-14 4 5 8.82E-14 5 2.07E-14 5 9.33E-14 5 6 8.55E-14 6 No data 6 9.31E-14 6 7 8.50E-14 7 No data 7 9.28E-14 7 8 8.45E-14 8 No data 8 9.30E-14 8 9 8.46E-14 9 No data 9 9.27E-14 9 Avg 7.90E-14 Avg 2.21E-14 Avg 8.56E-14 Avg
85 11/14/2006
1 2.12E-13 1 2.05E-13 1 2.01E-13 1 2.68E-13 2 2.12E-13 2 2.05E-13 2 2.08E-13 2 2.67E-13 3 2.13E-13 3 2.04E-13 3 2.02E-13 3 2.80E-13 4 2.11E-13 4 2.02E-13 4 2E-13 4 2.65E-13 5 2.13E-13 5 1.99E-13 5 1.99E-13 5 No data 6 2.12E-13 6 1.94E-13 6 1.98E-13 6 No data 7 2.11E-13 7 2.02E-13 7 No data 7 No data 8 2.14E-13 8 2.03E-13 8 No data 8 No data 9 2.13E-13 9 2.03E-13 9 No data 9 No data Avg 2.12E-13 Avg 2.02E-13 Avg 2.01E-13 Avg 2.70E-13
86
LHX2
10/30/2006
Grid Loc Site #413 Site #414 Site #415 Site #416 1 1.52E-13 1 1.78E-13 1 1.78E-13 1 1.71E-13 2 9.06E-14 2 1.8E-13 2 1.78E-13 2 1.78E-13 3 8.95E-14 3 1.69E-13 3 1.79E-13 3 1.78E-13 4 9.32E-14 4 1.79E-13 4 1.78E-13 6 1.77E-13 5 8.97E-14 5 1.79E-13 5 1.78E-13 5 1.76E-13 6 error 6 No data 6 1.8E-13 4 1.77E-13 7 8.87E-14 7 No data 7 1.78E-13 7 1.76E-13 8 9.2E-14 8 No data 8 1.78E-13 8 1.76E-13 9 8.83E-14 9 No data 9 1.77E-13 9 1.75E-13 Avg 9.8E-14 Avg 1.77E-13 Avg 1.78E-13 Avg 1.76E-13
11/13/2006
Grid Loc Site #413 Site #414 Site #415 Site #416 1 2.01E-13 1 1.95E-13 1 2.17E-13 1 2.12E-13 2 2.04E-13 2 1.92E-13 2 2.13E-13 2 2.12E-13 3 1.94E-13 3 1.97E-13 3 2.11E-13 3 2.13E-13 4 1.96E-13 4 1.93E-13 4 2.07E-13 4 2.11E-13 5 1.97E-13 5 1.95E-13 5 2.08E-13 5 2.13E-13 6 1.99E-13 6 1.97E-13 6 2.08E-13 6 2.12E-13 7 1.98E-13 7 1.93E-13 7 2.06E-13 7 2.11E-13 8 1.96E-13 8 1.98E-13 8 2.2E-13 8 2.14E-13 9 1.97E-13 9 1.99E-13 9 2.11E-13 9 2.13E-13 Avg 1.98E-13 Avg 1.96E-13 Avg 2.11E-13 Avg 2.12E-13
87 LHX3
11/01/2006
Grid Loc Site #421 Site #422 Site #423 Site #424 1 1.62E-13 1 1.61E-13 1 1.56E-13 1 2.86E-13 2 1.61E-13 2 1.62E-13 2 1.56E-13 2 2.87E-13 3 1.61E-13 3 1.65E-13 3 1.57E-13 3 2.86E-13 4 1.64E-13 4 1.63E-13 4 1.58E-13 4 1.59E-13 5 1.61E-13 5 1.62E-13 5 1.56E-13 5 2.53E-13 6 No data 6 1.62E-13 6 No data 6 2.91E-13 7 No data 7 1.63E-13 7 No data 7 1.55E-13 8 No data 8 1.63E-13 8 No data 8 1.55E-13 9 No data 9 1.63E-13 9 No data 9 1.55E-13 Avg 1.62E-13 Avg 1.63E-13 Avg 1.57E-13 Avg 2.25E-13
11/04/2006
Grid Loc Site #421 Site #422 Site #423 Site #424 1 8.88E-14 1 3.1E-14 1 9.2E-14 1 8.62E-14 2 8.83E-14 2 2.14E-14 2 8.42E-14 2 8.42E-14 3 8.69E-14 3 2.14E-14 3 1.97E-13 3 8.38E-14 4 8.83E-14 4 2.08E-14 4 1.63E-13 4 8.35E-14 5 8.7E-14 5 2.08E-14 5 1.83E-13 5 8.44E-14 6 8.8E-14 6 2.14E-14 6 1.83E-13 6 8.33E-14 7 9.22E-14 7 2.12E-14 7 1.83E-13 7 8.39E-14 8 8.91E-14 8 2.13E-14 8 1.94E-13 8 8.36E-14 9 1.04E-13 9 3.25E-14 9 1.85E-13 9 8.35E-14 Avg 9.02E-14 Avg 2.35E-14 Avg 1.63E-13 Avg 8.41E-14
88 LHX4
11/05/2006 – 11/06/2006
Spot Site #417R Site #417T Site #425R Site #425T 1 1.59E-13 1 1.65E-13 1 1.58E-13 1 1.63E-13 2 1.59E-13 2 1.63E-13 2 1.62E-13 2 1.58E-13 3 1.71E-13 3 1.64E-13 3 1.72E-13 3 1.58E-13 4 1.58E-13 4 1.68E-13 Avg 1.64E-13 4 1.57E-13 Avg 1.62E-13 Avg 1.65E-13 5 1.58E-13 6 1.58E-13 7 1.62E-13 8 1.62E-13 9 1.63E-13 Avg 1.60E-13
Site #427R Site #427T Site #429R Site #429T 1 1.98E-13 1 2.26E-13 1 No data 1 No data 2 1.98E-13 2 1.96E-13 2 No data 2 No data Avg 1.98E-13 3 2.25E-13 3 No data 3 No data 4 2E-13 4 No data 4 No data Avg 2.12E-13 5 No data 5 No data 6 No data 6 No data 7 No data 7 No data 8 No data 8 No data 9 No data 9 No data Avg No data Avg No data
89 Lake Fryxell Permeability
LFX1
11/07/2006
Grid Loc Site #720 Site #721 Site #722 Site #723 1 2.58E-14 1 1.94E-13 1 1.9E-13 1 2.02E-13 2 1.1E-13 2 1.91E-13 2 1.89E-13 2 1.95E-13 3 9.19E-14 3 1.94E-13 3 2.21E-13 3 2.05E-13 4 9.04E-14 4 1.92E-13 4 1.93E-13 4 2.09E-13 5 1.91E-13 5 1.9E-13 5 1.91E-13 5 2.04E-13 6 2.1E-13 6 1.92E-13 6 1.89E-13 6 1.75E-13 7 1.93E-13 7 5.25E-13 7 1.91E-13 7 1.77E-13 8 1.92E-13 8 1.93E-13 8 1.91E-13 8 1.74E-13 9 1.92E-13 9 1.94E-13 9 1.92E-13 9 1.75E-13 Avg 1.44E-13 Avg 2.3E-13 Avg 1.94E-13 Avg 1.91E-13
Site #724 Site #725 1 1.8E-13 1 No data 2 1.81E-13 2 1.94E-14 3 1.84E-13 3 7.99E-14 4 1.83E-13 4 2.22E-14 5 1.84E-13 5 3.26E-14 6 1.82E-13 6 1.98E-14 7 1.83E-13 7 1.99E-14 8 1.83E-13 8 1.97E-14 9 1.85E-13 9 1.65E-13 Avg 1.83E-13 Avg 4.73E-14
90
LFX2
11/10/2006
Grid Loc Site #726 Site #727 Site #728 1 2.24E-14 1 9.1E-14 1 2.06E-14 2 2.22E-14 2 9.04E-14 2 2.21E-14 3 2.29E-14 3 9.12E-14 3 2.15E-14 4 2.29E-14 4 9.2E-14 4 2.17E-14 5 2.39E-14 5 1.02E-13 5 2.37E-14 Avg 2.29E-14 6 1.3E-13 Avg 2.19E-14 7 1.06E-13 8 9.41E-14 9 9.03E-14 Avg 9.85E-14
LFCS
11/08/2008
Site Site Site Site a4 2.13E-13 a10 2.54E-13 b47 2.08E-13 b57 2.08E-13 a4 2.09E-13 a10 2.08E-13 b47 2.05E-13 b57 2.03E-13 a4 1.96E-13 a10 2.08E-13 b47 2.07E-13 b57 2.02E-13 a4 1.98E-13 Avg 2.24E-13 b47 2.07E-13 b57 1.99E-13 Avg 2.04E-13 Avg 2.07E-13 Avg 2.03E-13
c12 2.12E-13 d6 2.02E-13 e41 2.02E-13 f10 2.12E-13 c12 2.04E-13 d6 2E-13 e41 2.04E-13 f10 2.08E-13 c12 2.04E-13 d6 1.99E-13 e41 2.02E-13 f10 2.03E-13 Avg 2.07E-13 d6 1.99E-13 e41 2.05E-13 f10 2.02E-13 Avg 2E-13 Avg 2.03E-13 f10 2.01E-13 f10 2.02E-13 Avg 2.05E-13
91 Laboratory Ice Core Permeability
LH4071A LH4121A LH4161A LH4251AR
5 CM 2.26E-13 6 CM 2.19E-13 5 CM 2.08E-13 8 CM 2.23E-13 2.14E-13 2.19E-13 2.1E-13 2.15E-13 2.13E-13 2.18E-13 2.27E-13 No data 2.28E-13 2.17E-13 2.15E-13 2.14E-13 2.6E-13 2.38E-13 2.15E-13 2.15E-13 15 CM 2.32E-13 16 CM 2.2E-13 15 CM 2.08E-13 18 CM 2.32E-13 2.2E-13 2.23E-13 2.07E-13 2.34E-13 2.18E-13 2.19E-13 2.16E-13 2.31E-13 2.18E-13 2.19E-13 2.21E-13 2.30E-13 2.2E-13 2.2E-13 2.09E-13 2.30E-13 26 CM 2.22E-13 28 CM 2.42E-13 2.21E-13 2.42E-13 2.41E-13 2.33E-13 2.24E-13 2.39E-13 2.22E-13 2.43E-13 36 CM 2.44E-13 38 CM 2.28E-13 2.15E-13 2.40E-13 2.14E-13 2.21E-13 2.2E-13 2.45E-13 2.24E-13 2.27E-13
LH4261AR LH4271BT CS1A CS1B
21 CM 2.11E-13 5 CM 9.56E-14 5 cm 8.41E-14 5cm 8.50E-14 2.16E-13 9.18E-14 8.15E-14 8.20E-14 2.12E-13 1.1E-13 8.33E-14 8.74E-14 2.07E-13 1.05E-13 8.76E-14 9.17E-14 2.07E-13 9.38E-14 8.6E-14 8.72E-14 30 CM 2.17E-13 18 CM 8.5E-14 16 cm 9.62E-14 20 cm 9.00E-14 2.45E-13 8.76E-14 9.16E-14 8.58E-14 2.25E-13 1.05E-13 8.59E-14 8.98E-14 2.77E-13 8.93E-14 8.77E-14 1.02E-13 2.86E-13 8.79E-14 9.63E-14 8.46E-14 37 CM 2.17E-13 28 cm No data 31 cm 8.69E-14 35 cm 1.02E-13 2.33E-13 1.02E-13 8.45E-14 8.90E-14 2.22E-13 1.17E-13 8.59E-14 1.05E-13 2.16E-13 No data 8.89E-14 9.41E-14 2.15E-13 8.98E-14 9.21E-14 8.91E-14 47 CM 2.16E-13 38 CM 9.27E-14 41 cm 8.79E-14 45 cm 1.15E-13 2.35E-13 9.04E-14 9.05E-14 8.61E-14 2.21E-13 9.54E-14 8.75E-14 8.41E-14 2.18E-13 9.99E-14 8.65E-14 No data 2.15E-13 1.04E-13 8.82E-14 8.43E-14 51 cm 8.82E-14 8.68E-14 8.51E-14 8.54E-14 8.67E-14
92
APPENDIX B
GLOBAL POSITIONING SYSTEM COORDINATES
93
GPS Coordinates
Transect/WYPT Latitude Longitude Elevation Transect/WYPT Latitude Longitude Elevation LHX1 407 S77 37 25.5 E162 54 11.3 257 ft LHX3 421 S77 38 22.4 E162 47 10.8 228 ft LHX1 408 S77 37 36.0 E162 52 41.9 252 ft LHX3 422 S77 38 23.5 E162 47 34.5 237 ft LHX1 410 S77 37 38.2 E162 52 22.8 254 ft LHX3 423 S77 38 22.8 E162 47 43.8 232 ft LHX1 412 S77 37 45.7 E162 51 25.5 253 ft LHX3 424 S77 38 22.2 E162 47 49.6 229 ft
LHX2 413 S77 37 51.2 E162 51 04.4 235 ft LHX4 417 S77 38 07.0 E162 49 25.1 226 ft LHX2 414 S77 37 52.9 E162 50 43.8 217 ft LHX4 425 S77 37 37.0 E162 53 07.4 224 ft LHX2 415 S77 37 59.0 E162 50 09.5 232 ft LHX4 427 S77 38 01.5 E162 50 06.2 276 ft LHX2 416 S77 38 05.8 E162 49 17.6 231 ft LHX4 429 S77 38 00.3 E162 50 10.5 221 ft
LF CRASH S77 36 21.0 E163 07 31.2 72 ft
LFX1 720 S77 36 58.8 E163 04 12.0 61 ft LFX2 726 S77 36 14.1 E163 09 12.6 75 ft LFX1 721 S77 36 44.4 E163 05 27.8 74 ft LFX2 727 S77 36 15.2 E163 09 29.8 73 ft LFX1 722 S77 36 34.4 E163 05 52.9 74 ft LFX2 728 S77 36 16.8 E163 09 47.9 73 ft LFX1 724 S77 36 08.9 E163 09 00.9 75 ft LFX1 723 S77 35 55.9 E163 10 24.2 73 ft LFX1 725 S77 36 23.0 E163 07 07.6 59 ft
94
APPENDIX C
SAMPLE LOCATION DESCRIPTIONS
95 Sample Location Descriptions
LHX1 (Northeast moat and transitional ice)
Site #407 – Very clear ice, with no bubbles, horizontal or vertical fractures present. Lake
bathymetry is ~4 meters. Moat ice.
Site #408 – Ice has considerable Hoarfrost, many 1-2mm diameter bubbles within 5cm of
surface, and no fractures. Lake bathymetry very shallow (<1m). Moat ice.
Site #410 – Ice has bubbles (4-5mm diameter) within 5cm of surface. No fractures
present. Lake bathymetry is ~8 meters. Moat ice.
Site #412 – Ice has considerable bubbling directly under surface. No fractures. Lake
bathymetry is ~12 meters. Transitional ice.
LHX2 (Northwest moat ice)
Site #413 – Large plume bubbles located ~10cm below surface. Site has five large (3-
6cm) vertical fractures converging. Lake bathymetry is ~8 meters.
Site #414 – Moat/transitional ice boundary. Ice has many bubbles (4-5mm diameter) within 5cm of surface transitional to saturated bubbles in transitional ice. One N-S fracture (<1cm). Lake bathymetry is ~12 meters.
Site #415 – Heavy bubble formation with many (<1cm) vertical and horizontal fractures.
Lake bathymetry is ~8 meters.
Site #416 - Heavy bubble formation with many (<1cm) vertical and horizontal fractures.
Lake bathymetry is ~8 meters.
96
LHX3 (Southwest moat ice)
Site #421 – Many bubbles present (1-2mm diameter). Two converging (<1mm)
fractures. Lake bathymetry is ~4 meters.
Site #422 – Very shallow (<0.5m). No bubbles present. Four small perpendicular
vertical fractures cross.
Site #423 – Moat/transition ice boundary. One vertical fracture (<1mm) and many
bubble ~5cm below surface. Lake bathymetry ~2 meters.
Site #424 – Very shallow (<0.5m). Hoarfrost and vertical fractures (~1cm).
LHX4 (North ridge and trough ice)
Site #417 Ridge – Ridge ~1m above trough. Rough surface, no bubbles or fractures present. Lake bathymetry is ~25 meters.
Site #417 Trough – Ice is clear. No fractures or bubbles near surface.
Site #425 Ridge – Similar features to #417. Lake bathymetry is ~25 meters.
Site #425 Trough - Similar features to #417. Lake bathymetry is ~25 meters.
Site #427 Ridge – Similar features to #417. Lake bathymetry is ~25 meters.
Site #427 Trough - Similar features to #417. Lake bathymetry is ~25 meters.
Site #429 Ridge – Ice surface is very poor and could not collect data.
Site #429 Trough – Ice surface is very poor and could not collect data.
97
LFX1 (Northwestern moat ice)
Site #720 – Heavy vertical fractures ranging in size of <1mm to >1cm. Plume bubbles
~5cm below the surface. Lake bathymetry is ~12 meters.
Site #721 – Very shallow (<1m) ice. Moderate bubble formation of 1-2mm, numerous
vertical fractures <1mm.
Site #722 – Very rough surface with clear, bubble and fracture free ice below.
Moat/transitional ice boundary. Lake bathymetry is ~12 meters.
Site #723 – Very low amount of bubbles and vertical fracturing that did not reach the
surface. Lake bathymetry is ~15 meters.
Site #724 – Two large +1cm fractures, low bubble formation, rough surface. Lake
bathymetry is ~13 meters.
Site #725 – Very shallow (<0.5), adjacent to the shoreline. Low bubble formation but
heavy vertical fracturing (<1mm).
LFX2 (N/S trending transect, north central moat ice)
Site #726 – Very little bubbles, but bubbles are very large (2-4cm diameter). Site has
horizontal and vertical fractures. Lake bathymetry is ~9 meters.
Site #727 – Very shallow ice (<0.2m) with heavy horizontal fracturing (below surface)
and low bubble formation.
Site #728 – Clear ice surface with a open lens 5-6cm below surface filled with snow.
Moat/transition ice. Lake bathymetry is ~10 meters.
98
LFX3 (Southwestern moat ice)
Abandoned – This site could not be reached due to very deep snowdrifts abutting up to
the Canada Glacier.
LFCS (Western trough)
Site #a4 – 2cm x 10cm sediment lens ~2-3cm below ice surface. Two vertical fractures
(~1mm).
Site #a10 – Surface is honeycomb shape (ablation) with very small bubbles (1-2mm)
below surface.
Site #b47 - Surface is honeycomb shape (ablation) with small (2-3cm diameter) sediment
layer below surface.
Site #b57 – Bubble and fracture free, however, there are thin snow lenses below surface.
Site #c12 - Surface is honeycomb shape (ablation) with very small bubbles (1-2mm) and
a small (2-3cm diameter) sediment layer below surface.
Site #d6 - Ice is similar to site #c12.
Site #e41 – Ice is clear with the exception of a large snow filled bubble (5cm diameter)
below surface.
Site #f10 – Sediment layers are at the surface of the ice. Below are numerous small
bubbles.
(NOTE: Bathymetry at the crash site is ~13 meters. All numbers following site letter correspond to feet from center point of crash zone.)
99
Ice Core Description
Core LH4071A (LH Site #407) - 30cm long, tested at 5cm and 15cm. Moat ice.
Core LH4121A (LH Site #412) – 49cm long, tested at 6cm, 16cm, 26cm, and 36cm.
Moat ice.
Core LH4161A (LH Site #416) – 36cm long, tested at 5cm and 15cm. Moat ice.
Core LH4251A (LH Site #425R) – 59cm long, tested at 8cm, 18cm, 28cm, 38cm, and 48 cm. Center ridge ice.
Core LH4261A (LH Site #426R) – 61cm long, tested at 21cm, 30cm, 37cm, and 47cm.
Center ridge ice.
Core LH4271B (LH Site #427T) – 58cm long, tested at 5cm, 18cm, 28cm, and 38cm.
Center trough ice.
Core CS1A (LF Crash site 5m southwest of center point) – 59cm long, tested at 5cm,
16cm, 31cm, 41cm, and 51cm.
Core CS1B (LF Crash site 28m southwest of center point) – 62cm long, tested at 5cm,
20cm, 35cm, and 45cm.
100
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