Elemental Cycling in a Flow-Through Lake in the Mcmurdo Dry Valleys, Antarctica

Elemental Cycling in a Flow-Through Lake in the McMurdo Dry Valleys, Antarctica:

Lake Miers

THESIS

Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in

the Graduate School of The Ohio State University

Alexandria Corinne Fair

Graduate Program in Earth Sciences

The Ohio State University

2014

Master’s Examination Committee:

Dr. W. Berry Lyons, Advisor

Dr. Anne E. Carey

Dr. Yu-Ping Chin

Alexandria Corinne Fair

2014

ABSTRACT

The ice-free area in Antarctica known as the McMurdo Dry Valleys has been monitored biologically, meteorologically, hydrologically, and geochemically continuously since the onset of the MCM-LTER in 1993. This area contains a functioning ecosystem living in an extremely delicate environment. Only a few degrees of difference in air temperature can effect on the hydrologic system, making it a prime area to study ongoing climate change. The unique hydrology of Lake Miers, i.e. its flow- through nature, makes it an ideal candidate to study the mass balance of a McMurdo Dry

Valley lake because both input and output concentrations can be analyzed. This study seeks to understand the physical and geochemical hydrology of Lake Miers relative to other MCMDV lakes. Samples were collected from the two inflowing streams, the outflowing stream, and the lake itself at 11 depths to analyze a suite of major cations (Li+,

+ + + 2+ - - - 2- - - Na , K , Mg , Ca ), major anions (Cl , Br , F , SO4 , ΣCO2), nutrients (NO2 , NO3 ,

+ 3- NH4 , PO4 , Si), trace elements (Mo, Rb, Sr, Ba, U, V, Cu, As), water isotopes (δD,

δ18O), and dissolved organic carbon (DOC). The lake acts as a sink for all constituents

+ - 3- analyzed, but by amounts varying from ~10% (DOC, NH4 , and NO2 ) to PO4 at nearly

100%, indicating this lake may be P-limited. Cl-, a typically conservative element, was only 79% retained, which could be due to the late season sample collection, hyperheic zone influences, or other factors. The hyperheic zone’s role in lake and stream

geochemistry was analyzed with a 24-hour sampling event. The positive relationships between stream flow and solute concentrations indicate that the delta in Miers Valley plays a role in controlling stream geochemistry and future work could help to explain this relationship. Lake depth profiles of trace elements U, V, Cu, and As decrease relative to

Cl in the deepest part of the lake, while non-reducing trace elements show increases with

2- depth. SO4 and dissolved O2 lake depth profiles decrease from 53 μM and 22.3 mg/L to

18 μM and 1.8 mg/L, respectively, at depth, indicating that the lake bottom is under reducing and near anoxic conditions. Lake depth profiles show that, while the

“biological pump” may be a factor controlling lake chemistry, it is masked by the stronger signal of diffusion from the lake bottom sediments and requires future work to understand fully. The “age” of Lake Miers was calculated with a diffusion model to be

84 years, which agrees with other estimates of 100-300 years. The diffusion of solutes from the lake bottom and the redox conditions at depth are two major processes controlling the geochemistry of Lake Miers, and future work can help determine their extent and relationship with other processes.

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ACKNOWLEDGMENTS

I would like to thank a lot of people for their assistance in the completion of this document. The MCM-LTER Stream Team at University of Colorado, Boulder, including

Devin Castendyk, Chris Jaros, and Adam Wlostowski, and the Limno group at Montana

State University helped with sample collection and processing, and especially Chris Jaros and his help with stream discharge data. I would also like to thank Kelsey Bisson for staying up all night with me in the field, for analyzing DOCs and alkalinities, and for being a great support along the way. I am grateful to Holly Hughes at Kiowa Lab, UCB for running the nutrient samples. Dr. John Olesik, and especially Anthony Lutton, provided enormous help with analyzing my trace element samples. Thank you to Deb

Leslie for her help with my isotope samples, and to Kelsey Dailey and Sue Welch for their help with my iron analysis. Thank you to Chris Gardner for your help with my computer-related questions. Thank you to Kathy Welch for your patience, advice, ion analysis, help with figures, answering all of my numerous questions, and for being someone who could always help with whatever problem I was facing. Thank you to my committee for you time and feedback. A huge thank you to my advisor, Dr. W. Berry

Lyons, for being incredibly patient with me, and pushing me to get to this point. His knowledge and guidance have been critical to my graduate career. I would lastly like to thank the NSF grant ANT 1115245 for funding and PHI helicopters and ASC for logistical support during field work.

VITA

June 15, 1900 ...... Born — Columbus, Ohio

May 2012 ...... B.S. Anthropological Sciences and

Chemistry, The Ohio State University

August 2012 to present ...... Graduate Research and Teaching Associate,

School of Earth Sciences, The Ohio State

University

Fields of Study

Major Field: Earth Sciences.

Table of Contents ABSTRACT ...... ii ACKNOWLEDGMENTS ...... iv VITA ...... v LIST OF TABLES ...... viii LIST OF FIGURES ...... ix CHAPTER 1: INTRODUCTION ...... 1 1.1 Rationale for Work ...... 2 1.1.1 End-Member Example of MCM Lakes ...... 2 1.1.2 Climate Change Impacts ...... 3 1.2 Flow-Through vs Closed-Basin ...... 4 1.2.1 Mass Balances ...... 4 1.2.2 Test Bioreactor Hypothesis ...... 4 1.2.3 Future Scenarios for Closed-Basin Lakes ...... 5 1.3 Objectives of Work ...... 6 CHAPTER 2: STUDY AREA ...... 7 2.1 Site Description ...... 7 2.1.1 Miers Valley...... 7 2.1.2 Summary of Previous Work on Lake Miers ...... 8 CHAPTER 3: METHODS ...... 14 3.1 Bottle Preparation ...... 14 3.2 Sample Collection ...... 15 3.2.1 Streams ...... 15 3.2.2 Lakes ...... 17 3.3 Methodology ...... 18 3.3.1 Major Ions and Alkalinity ...... 18 3.3.2 Nutrients and Silica ...... 18 3.3.3 Trace Elements...... 18 3.3.4 DOC ...... 19 3.3.5 Water Isotopes ...... 20

3.3.6 Precision and Accuracy...... 20 3.4 Hydrologic Measurements ...... 21 CHAPTER 4: RESULTS AND DISCUSSION ...... 22 4.1 Streams ...... 22 4.1.1 Input ...... 23 4.1.2 Output ...... 24 4.1.3 Comparison to other MCM Streams ...... 25 4.1.4 Comparison to Previous Stream Work ...... 26 4.1.5 Minor and Trace Element Data ...... 27 4.1.6 Hydrology and Geochemical Fluxes ...... 29 4.1.7 Relationship of Discharge to Concentration ...... 32 4.2 Lake Miers ...... 34 4.2.1 Comparison to other MCM Lakes ...... 35 4.2.2 Analyte Profiles normalized to Cl...... 36 4.2.3 Comparison to Previous Trace Element Work ...... 37 4.2.4 Comparison to Past measurements ...... 39 4.3 Processes Controlling the Biogeochemistry of Lake Miers ...... 41 4.3.1 “Age” of Lake ...... 41 4.3.2 Biological Limnology of Lake Miers ...... 43 4.3.3 The Role of Biogeochemistry in Controlling Solute Distribution ...... 45 4.3.5 Role of Diffusion ...... 49 4.3.6 Lake Miers as a “Bioreactor” ...... 49 CHAPTER 5: CONCLUSIONS ...... 52 5.1 Summary of Research ...... 52 5.2 Future Work ...... 52 REFERENCES CITED ...... 54 APPENDIX A: TABLES AND FIGURES ...... 61 APPENDIX B: STREAM DATA ...... 111 APPENDIX C: LAKE DATA ...... 118

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LIST OF TABLES

Table 1: Standards for Trace Element Analysis...... 62

Table 2: Precision, Accuracy, and Detection Limit of Analyses...... 63

Table 3: Summary of Green et al. 1988 Data for Adams and Miers Streams...... 64

Table 4: Influxes of all measured analytes into Lake Miers...... 65

Table 5 Data Used in Age-of-Lake Calculation...... 66

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LIST OF FIGURES

Figure 1 Map of the McMurdo Dry Valleys...... 67

Figure 2 Map of Miers Valley...... 68

Figure 3 Ternary Plots of Cations and Anions in MCMDV Lakes and Streams...... 69

- 2+ Figure 4 Plot of HCO3 vs. Ca with 2:1 line in Miers Valley Streams...... 70

Figure 5 Scatter plot of Adams Discharge vs Miers Discharge...... 71

Figure 6 Flow Measurements from Adams Stream During 24-Hour Sampling...... 72

Figure 7 Hydrograph of Na...... 73

Figure 8 Hydrograph of Cl...... 74

- Figure 4.7 Hydrograph of NO3 ...... 75

Figure 10 Hydrograph of Ba...... 76

Figure 11 Delta in Miers Valley...... 77

Figure 12 Plot of Miers:Hoare Surface Cl Over Time...... 78

Figure 13 Depth Profile of Cl in Lakes Miers and Hoare...... 79

Figure 14 Plot of Miers:Hoare Surface Ca Over Time...... 80

Figure 15 Depth Profile of Ca/Cl in Lake Miers...... 81

Figure 16 Depth Profile of K/Cl in Lake Miers...... 82

Figure 17 Depth Profile of Mg/Cl in Lake Miers...... 83

Figure 18 Depth Profile of Na/Cl in Lake Miers...... 84

2- Figure 19 Depth Profile of SO4 /Cl in Lake Miers...... 85

- Figure 20 Depth Profile of HCO3 /Cl in Lake Miers...... 86

+ Figure 21 Depth Profile of NH4 /Cl in Lake Miers...... 87

Figure 22 Depth Profile of DOC/Cl in Lake Miers...... 88

Figure 23 Depth Profile of Si/Cl in Lake Miers...... 89

Figure 24 Depth Profile of F/Cl in Lake Miers...... 90

Figure 25 Depth Profile of Rb/Cl in Lake Miers...... 91

Figure 26 Depth Profile of Sr/Cl in Lake Miers...... 92

Figure 27 Depth Profile of Ba/Cl in Lake Miers...... 93

Figure 28 Depth Profile of As/Cl in Lake Miers...... 94

Figure 29 Depth Profile of U/Cl in Lake Miers...... 95

Figure 30 Depth Profile of V/Cl in Lake Miers...... 96

Figure 31 Depth Profile of Mo/Cl in Lake Miers...... 97

Figure 32 Depth Profile of Cu/Cl in Lake Miers...... 98

Figure 33 Depth Profile of Cl Over Time in Lake Miers...... 99

Figure 34 Depth Profile of Na in Lake Miers...... 100

Figure 35 Depth Profile of PPR in Lake Miers...... 101

Figure 36 Depth Profile of Chlorophyll-A in Lake Miers...... 102

Figure 37 Depth Profile of O2 in Lake Miers...... 103

- Figure 38 Depth Profile of SO4 in Lake Miers...... 104

+ Figure 39 Depth Profile of NH4 in Lake Miers...... 105

Figure 40 Depth Profile of DOC in Lake Miers...... 106

- Figure 41 Depth Profile of NO2 in Lake Miers...... 107

Figure 42 Depth Profile of Fe+ in Lake Miers...... 108

Figure 43 Depth Profile of δ18O in Lake Miers...... 109

Figure 44 Depth Profile of δD in Lake Miers...... 110

CHAPTER 1: INTRODUCTION

The perennially ice-covered lakes of the McMurdo Dry Valleys (MCMDV),

Antarctica have been an intellectual curiosity since their identification by the British

Antarctic Expedition in 1911 and have been scientifically studied since the early 1960s

(Angino et al. 1962). The biogeochemistry of these lakes has been investigated in detail since the 1980s in order to understand geochemical behavior in these systems (Green et al. 1988), to describe their climatic and evolutionary histories (Lyons et al. 2005), and to use them as analogies to water bodies on other planetary systems (Wharton et al. 1995).

In this work, I describe the geochemistry and chemical mass balance of one of the least investigated lakes in the MCMDV—Lake Miers. This work on Lake Miers is significant in that it represents the first examination of several chemical elements/compounds in the lake and streams that enter and exit the lake, and it adds detail to the description of the physiochemical processes that control lake chemistry. Lake Miers is the only major

“flow-through” lake (as opposed to closed-basin) in the McMurdo region. Its biogeochemical behavior may serve as an important predictor of the behavior of the closed-basin lakes in the MCMDV future climate scenarios of climate warming and increased glacier melt, which suggest that the closed-basin lakes will eventually become

“flow-through” lake systems.

1.1 Rationale for Work 1.1.1 End-Member Example of MCM Lakes The McMurdo Dry Valley Long Term Ecological Research (MCM-LTER)

Project, funded by the US National Science Foundation, established the MCMDV as a study site in 1993, and climatological, hydrological, biogeochemical, and ecological data have been collected continuously for the past 21 years (MCM-LTER Database). The primary geographical focus of the MCM-LTER was initially Taylor Valley and the lakes, streams, glaciers, and soils therein (Fountain et al., 1999). Long-term monitoring of environmental variables in Taylor Valley has provided important new insights in how the ecology of this polar desert reacts to, by temperate standards, subtle climatic changes.

Recently, MCM-LTER investigations have expanded into other valleys, including Miers

Valley, but in the 21 years since the MCM-LTER’s inception, little work had focused on

Lake Miers and Miers Valley. Previous lake sampling by LTER personnel typically includes 2 – 4 lake profiles of each of the four Taylor Valley lakes. These researchers collect samples at specific water depths every year for biogeochemical parameters

2- including major cations (Ca, Na, Mg, K) and anions (Cl, SO4 , ΣCO2), dissolved organic

- + 3- carbon (DOC), and major nutrient species (NO3 , NH4 , PO4 ). These previous analyses have shown a large degree of variation in terms of total dissolved solids (TDS) and ionic ratios in the Taylor Valley lakes (Lyons et al., 1998). The surface waters of the lakes also change in chemical composition due to variations in discharge. In addition, each lake shows variation within its water column with generally increasing concentrations of ions from the shallow to the deeper waters. In Taylor Valley, the TDS concentration is highest in the west lobe of Lake Bonney and is lowest in Lake Hoare. These salinity

differences have influences on the ecosystems within the lakes (Priscu, 1995). In 2011 –

2012, Lake Miers was added to the annual sampling regime to compare a flow-through lake to the closed-basin systems in Taylor Valley. Lake Miers has the lowest TDS concentrations of any lakes in the MCMDV (Spigel and Priscu 1998). This low salinity makes Lake Miers an important end-member of the MCMDV lakes and it may have very different biogeochemical behavior than the other lakes.

1.1.2 Climate Change Impacts One of the important features of the MCMDV lakes is their sensitivity to small variations in climate (Doran et al., 2002; Foreman et al., 2004). An air temperature change of only a few degrees can significantly affect the hydrologic system of the valleys by increasing glacier melt (Doran et al., 2002). In the closed-basin lakes, increases and decreases in water inflows cause the lakes to change in size. On the other hand, colder austral summers lead to decreased lake volumes. Spigel and Priscu (1998) suggest that the outflowing stream of Lake Miers also acts to regulate the depth and volume of the lake, but prevents it from increasing past a specific depth. This annual fluctuation in closed-basin level in the Taylor Valley presents a problem when analyzing long-term data. Because lake samples are taken from the surface and measured in meters below the ice cover, the year-to-year comparisons of lake depth profiles are difficult. For Lake

Miers, this problem still exists, but only during times of very low lake volume. As long as the outflow stream is flowing, the assumption has been made that the volume of Lake

Miers is constant (Spigel and Priscu, 1998). In addition, because the closed-basin lakes only lose water through sublimation of the ice cover, solutes can concentrate in these

lakes as freezing-on of water occurs at the bottom of the ice covers. The flux of solutes into the lakes also varies with discharge from glacier melt. These processes make it difficult to determine solute mass fluxes through time as elemental residence times vary from year to year and may not be solely related to input.

1.2 Flow-Through vs Closed-Basin 1.2.1 Mass Balances Determination of the mass balance of a lake system allows the biogeochemical behavior of the system to be studied and described. Mass balance calculations on Lake

Miers will determine whether it is gaining, losing, or in equilibrium with respect to many different chemical constituents within the lake waters. Of the MCMDV lakes, Lake

Miers is ideally suited to a mass balance study because its inflow and outflow can be measured and the chemical fluxes can be determined. Sampling of the outflow of Lake

Miers also allows residence times of dissolved constituents and water to be calculated better than previous studies have done. When the fluxes are calculated for all analyzed chemical species, comparisons can be drawn to see if similar factors are controlling their behavior.

1.2.2 Test Bioreactor Hypothesis All of the lakes in the MCMDV have pelagic and most have benthic ecosystems within them (Lawson et al., 2004). These ecosystems utilize nutrients (i.e. N, P), carbon, and other dissolved species. Due to the perennial ice cover on the MCMDV lakes, the only substantial input of solutes/compounds to the lakes is through inflowing streams.

Measurement of concentrations of solutes in the stream inflow and in the lakes at various depths can provide insight into the hydrological, physical, biological, and geochemical cycling taking place in the lake. Chloride can be used as a conservative species (i.e. it reacts neither biologically nor geochemically in this extremely fresh water system), and, with elemental:Cl ratios, trends of different elemental species can be determined. Those

Cl- normalized species showing similar depth profiles may have similar behavior and respond to similar biogeochemical processes. Through these methods of delineating the lake profiles and establishing the fluxes of elements by comparison of inflow and outflow stream flux measurements, an understanding of the processes within the lake can be better established.

1.2.3 Future Scenarios for Closed-Basin Lakes During the time of the MCM-LTER, the volumes of the Taylor Valley lakes have varied, but have been increasing for the past decade (P. Doran, personal communication).

These lakes respond to the summer air temperatures above 0°C, as they are fed by glacial meltwater. Modeling has predicted increased warming of 1 – 2°C by 2050 (Rowlands et al. 2012). MCM-LTER scientists (McKnight et al., personal communication) have hypothesized that if the warming trend continues, lake levels will continue to rise until other MCMDV lakes overflow their basins and develop outflowing streams. If this comes to pass, knowledge of the hydrological and geochemical dynamics of Lake Miers will be extremely significant in predicting how the closed-basin lakes will change.

1.3 Objectives of Work Because Lake Miers is the least studied of the MCMDV lakes, a comparison of its elemental concentrations to those of the closed-basin lakes is a worthy first step in understanding the geochemistry of these systems. The flow-through aspect of Lake

Miers makes possible mass balance calculations to determine the fate of elements within the stream-lake system. This will be evidenced by differences in mean annual geochemical storage budgets, residence times, mixing processes, and element deposition and uptake compared to the Taylor Valley closed-basin lakes. Mass balance and residence time calculations conducted on Lake Miers quantify the effect the hydrologic regime has on the geochemical cycling of major and minor elements. The primary hypotheses of this research project are as follows:

1. The Lake Miers concentration of not only major ions, but also minor and trace

elements, will be lower than in the closed-basin systems in MCMDV.

2. The surface water of Lake Miers will exhibit characteristics similar to the closed-

basin systems, but its bottom waters will show evidence of biological and

geochemical “processing” as evidenced through the ‘biological pump’ concept of

bioactive elemental removal in surface water and bottom water increases in these

elements.

3. Residence times of bioactive elements in Lake Miers will be much shorter than

previous estimates of those in closed-basin lakes due to either hydrologic transport

(i.e. flow-through) or biological removal.

CHAPTER 2: STUDY AREA

2.1 Site Description 2.1.1 Miers Valley

Ice free areas compose only 2% of Antarctica and the MCMDV are the largest ice-free region on the continent (Levy 2012). Miers Valley is one of the MCMDV, located between 78º06’ and 78º07’S and 163º44’ and 164º12’E in Southern Victoria

Land, Antarctica (Figure 1). Miers Valley extends from the Royal Society Range in the west, to McMurdo Sound 11 km away in the east. (Clayton-Greene et al. 1988). The valley floor lies between 80 – 150 m above sea level (Clayton-Greene et al. 1988). The extremely low humidity and mean annual temperature of approximately -20ºC keep the precipitation to less than 3 cm per year (Fountain et al., 2010). Katabatic winds from the polar plateau reach speeds as high as 60 ms-1 and help to keep the valleys clear of any snow that is deposited (Nylen et al., 2004). The hydrologic cycle of the MCMDV is driven by glacier melt which flows into fixed stream channels which, in turn, flows into perennially ice-covered lakes (McKnight et al., 1999). There is no overland flow and groundwater is also not a significant contribution to the hydrologic system of the

MCMDV due to the shallow depth of the permafrost (average depth of ~50 cm)

(Fountain et al., 1999; McKnight et al., 1999).

The surficial materials on the valley floor consist primarily of lacustrine sediments, which include calcite, gypsum, and aluminosilicate minerals. A major

component of the surface materials in the western end of the valley is marble derived from the nearby basement complex (Clayton-Greene et al 1988). In addition, many of the Miers Valley rocks exhibit calcite coatings on their unexposed side, a relic from the

Glacial Lake Trowbrigde, which occupied Miers Valley between 23 and 10 Ka years BP

(Clayton-Greene et al. 1988). The presence of fragments of kenyte and other basaltic material from Ross Island implies that Miers Valley was blocked by the West Antarctic

Ice Sheet during the Last Glacial Maximum (LGM) (Clayton-Greene et al. 1988).

2.1.2 Summary of Previous Work on Lake Miers Lake Miers is located in the western portion of Miers Valley (Figure 2). It is fed by two glacial meltwater streams: Adams and Miers. Adams Stream, the southerly of the two inflowing streams, is 2 km long and flows from the eastern face of Adams Glacier into the western edge of Lake Miers. Miers Stream is the northerly of the two inflowing streams. It is 1 km long and flows from the eastern face of Miers Glacier to the western edge of Lake Miers (Bell, 1967). Miers River, the sole outflowing stream, is 8 km long and flows from the eastern edge of Lake Miers into the Ross Sea (Green et al. 1988). In addition to the water input from the streams during the 4 – 12 week flow season, a minimal amount of snowfall can accumulate on the frozen lake surface, and can be later input into moat along the lake edge during the austral summer to contribute to the lake’s volume (Bell 1967). The ice cover on the lake also undergoes a cycle of water freeze from below and ablation at the surface to maintain 3 – 6 m of ice (Bell, 1967; Spigel and

Priscu, 1998). The thickness of the ice cover varies from year to year as the climate

varies (Chinn 1993), but unlike the Taylor Valley lakes, there are few data depicting the ice cover variations on Lake Miers.

The earliest investigation of Lake Miers by Bell in 1964 resulted in the first publication specifically about Lake Miers. Bell (1967) had three primary research objectives: to investigate debris buildup on the lake ice, to investigate the temperature profile of the lake, and to investigate the biology, chemistry, and physics of the lake. Bell

(1967) concluded that there were three possible mechanisms for rocks and debris that accumulate atop the ice cover and, in some places, form cones on the lake ice. These include aeolian deposition of fine-grained material, previous glacial deposition from the

Miers and Adams Glaciers, and freeze-thaw of lake surface ice freezing to the lake bed

(Bell 1967). Later, Clayton-Greene et al. (1988) suggested that the debris cones were the result of glacial damming of Glacial Lake Trowbridge by ice tongues of the McMurdo

Sound from the east. The cone shapes are the result of the blocking of sunlight and therefore the lack of heat absorption and ice melt over many years (Bell 1967). The surrounding exposed ice surface melts much faster than that covered by this debris, creating large debris-covered cones of ice (Bell 1967).

As noted above, Lake Miers is the freshest of the MCMDV lakes. Because Lake

Miers is a flow-through lake, turbulent horizontal flow can exist in the surface water between 3.5 m and 6.5 m below the ice cover (Spigel & Priscu 1998). Although it is the freshest lake, chemical and physical gradients exist in Lake Miers. The temperature increases with depth to a maximum of 5ºC (Bell 1967). As in most freshwater lakes, this temperature gradient maintains the stability of the water column, unlike the other lakes of the MCMDV in which the salinity controls water column stability (Spigel & Priscu

1998). Several of sources of heat to maintain this profile have been postulated, including biological activity, chemical heating, hot springs, solar radiation, and a high geothermal gradient (Bell 1967). Bell (1967) concluded that the most likely were geothermal heat, hot springs, and/or solar radiation. A negative temperature gradient at all four measuring locations in the bottom 30 cm of the lake was enough evidence to rule out geothermal heat as the source (Bell 1967). Due to the lack of surrounding volcanic activity, the horizontally near uniform temperatures across the length of the lake, a hot springs heating source was also deemed unlikely (Bell 1967). More recent evaluations indicate that this gradient is indeed due to solar heating (Spigel and Priscu 1998).

Interfingering of inflowing stream water can take place between 8 m and 12 m depths due to higher ion concentrations, and therefore the mixing downward of higher density water (Bell 1967). Thermohaline convection cells have also been observed between 15 m and 20 m, but the physical stability of the lake exists even with these thermohaline convection cells present (Bell 1967). The thermohaline cells cause vertical mixing as inflowing water combines with lake water, and density currents created by salt exclusion from freezing processes during lake ice formation cause sinking and mixing

(Spigel & Priscu 1998). Previously measured profiles of step functions in conductivity and temperature indicate that the convection cells also correspond to fluorescence variations (Spigel and Priscu 1998). The depth for peak primary productivity lies around

8m (Green et al. 1998), and the primary productivity is likely associated with the thermohaline convection cells, as seen in other MCMDV lakes (Bell 1967, Spigel and

Priscu 1998).

The geochemistry of Miers Valley and Lake Miers has been studied in the past by many researchers beginning with Bell (1967) and including Green et al. (1988). Bell

(1967) compared the ionic ratios measured in Lake Miers with those commonly found in hot springs in other parts of the world and found the K/Na, (Ca+Mg)/(Na+K), and

HCO3/Cl molar ratios differed from hot spring sources. The ionic ratios more closely resembled the range associated with rivers and dilute ground water (Bell 1967). Bell’s geochemical analyses of Lake Miers provided an early time point with which to compare more recent values. He made measurements at 14 depths from two locations on the lake surface and measured major cations, anions, temperature, and conductivity (Bell 1967).

- - + He noted the absence of NO3 and NO2 at depth with the presence of NH4 and concluded the bottom of the lake is anaerobic (Bell 1967). He also observed high

- concentrations of Si, Ca, HCO3 , and Mg in the deepest part of the lake and suggested these ions are diffusing into the lake from the sediments in the lake bed. Bell (1967) also suggested the lake bed may also show deposits of calcite (CaCO3) and gypsum

(CaSO4•2H2O) as are seen on the valley floor east of Lake Miers, but was unable to obtain a sample for verification. He did note that the Ca(HCO3)2 concentrations were near saturation at depth (Bell 1967).

Green et al. (1988) also studied the geochemistry of Lake Miers and suggested

2- that SO4 reduction is ongoing in the bottom waters of Lake Miers and that sulfide is being lost through mineral formation. Green et al. (1988) also made geochemical measurements, specifically looking at major cation and anion concentrations of the lake and of the inflowing streams. They also measured a series of transition metal elements

(Fe, Mn, Co, Ni, Cu, Zn, Pb, and Cd) (Green et al., 1986). They did not analyze the

geochemistry of the outflowing stream. Calcium carbonate deposition was suggested as a major process contributing to the geochemistry of Lake Miers, due to high mole fractions

- of Ca and HCO3 in the inflowing water and residence time considerations (Green et al.,

1988). On a Gibbs plot, Lake Miers and its associated streams show ion concentrations closest to the “rock dominance” category, whereas other MCMDV lakes fall into the evaporation or atmospheric precipitation dominance categories, suggesting differences in the geochemical cycling (Green et al. 1988). More recent work has demonstrated that

Taylor Valley streams have a wide variety of geochemical patterns (Welch et al. 2010), but the work of Green et al. (1988) clearly demonstrated that CaCO3 dissolution within the glacier-channel watersheds must be a dominant process. Bell (1967) determined the bottom waters of Lake Miers were anaerobic. The water age of Lake Miers has been calculated by Bell (1967) to be on the order of 100 years and by Green et al. (1988) to be at least 267 years. Both of these estimates are based upon the chloride concentrations in the lake and (in Green et al.’s case) in the stream input and assume that the chloride is conservative within the lake. Lyons et al. (1999) have argued that Cl- ages calculated with only one year of inflow data can be erroneous as the Cl- input can vary greatly from year to year. These age estimates are much lower than those from the other lakes of the

MCMDV, which are on the order of thousands of years, and strongly suggest that the flow-through nature of Lake Miers makes it very different than the MCM closed-basin lakes.

The first biological measurements in Lake Miers are from Parker et al. (1982) when chlorophyll-a and the mass of organisms in the water column were determined.

Since the onset of the MCM-LTER, chlorophyll-a, primary production, and bacteria production have been measured sporadically (MCM-LTER Database).

CHAPTER 3: METHODS 3.1 Bottle Preparation Nalgene LDPE bottles of 60 mL and 120 mL were either pre-washed at The Ohio

State University before being shipped to McMurdo Station or washed in Crary Lab. All pre-washed bottles were shipped closed, dry, and sealed in Ziploc bags, which were, in turn, placed in plastic bins for shipment to Antarctica. Bottles washed in Crary Lab and at Ohio State were washed following the same procedures. 60 mL Nalgene bottles used for cation samples were rinsed three times with 18-MΩ, or deionized (DI) water and allowed to air dry with their lids loosely closed. 60 mL bottles used for anion samples and 120 mL bottles used for nutrient samples were rinsed with 1% (v/v) lab grade hydrochloric acid three times and then with DI water three times. 120 mL bottles and caps used for trace metal samples were soaked in 1% (v/v) ultra clean grade nitric acid for at least 48 hours before being rinsed with 1% (v/v) ultra clean grade nitric acid three times and with DI water three times. Borosilicate glass scintillation vials used to collect stable isotope samples were not pre-rinsed. They were left in factory-clean conditions.

Alkalinity samples were collected in three time DI-rinsed 120 mL Nalgene bottles in the field. An aliquot of the water was then transferred to three time DI-rinsed 20 mL Fisher

HDPE scintillation vials within 24 hours of collection in Crary Lab. Dissolved organic carbon (DOC) samples were collected in 120 mL amber bottles. The bottles and lids were soaked in 1% (v/v) hydrochloric acid for four hours and then rinsed three times with

DI water in Crary Lab. Nitrile gloves were worn at all times during bottle rinsing, soaking, packing, and other handling.

Bottles for lake sampling at depth are 1 L amber Nalgene bottles. Each bottle is used only for a specific depth of Lake Miers. Before collection, the bottles were rinsed three times with DI water and allowed to dry with their lids loosely closed.

3.2 Sample Collection 3.2.1 Streams Miers Valley contains three streams, all of which were sampled during the 2012 –

2013 season. The two glacier-derived streams flowing from a glacier into the lake are referred to as upstream. They are named, from south to north, Adams Stream and Miers

Stream. The lake-derived stream flowing from the lake into the ocean is referred to as downstream and called Miers River. The three streams in Miers Valley were sampled on

30 December 2012; 11 January 2013; 18 – 19 January 2013; and 2 February 2013.

Sample kits were put together, each consisting of one washed bottle for cations, one washed bottle for anions, one washed bottle for nutrients, one washed bottle for

DOC, one vial for water isotopes, one washed bottle for trace elements, one washed bottle for titration alkalinity, one syringe (either 20, 30, or 60 mL), two syringe-tips, 0.45

μm Whatman filters, and two pairs of nitrile gloves. All of these materials were placed into a gallon-size Ziploc bag. Each sample kit was used at a single sample location. All of the sample kits were packed into backpacks and carried from the helicopter landing site to the sample location. Upon arrival at the sample location, one sample kit was opened to begin sample collection. Gloves were worn by both the person collecting the

water, and the person uncapping, holding, and capping the sample bottle/vial. As soon as the bottle was filled with water and capped, it was placed back into the Ziploc bag for cleanliness and transport. For the cation, anion, nutrients, and DOC samples, water was collected with a syringe from the flowing water and filtered through a syringe-tip filter into the sample bottle. This process was repeated until the cation, anion, nutrients, and

DOC bottles were full. For the stable isotope sample, water was collected via syringe, but the filter was not used when dispelling water. The stable isotope vials were rinsed three times with sample water. Care was taken to empty the rinse water at least 0.5 m downstream of the sample location. The stable isotope vials were filled completely with sample water from the syringe until the meniscus was above the bottle lip. After capping the vial, it was inverted to ensure no air bubble was captured in the vial. If an air bubble was present, the vial was emptied and refilled until no air bubble remained. For the whole water, and trace metals samples, the bottles were submerged, open-end first, into the flowing water, then inverted to allow water to flow into the bottles. They were then removed from the flowing water and immediately capped. All capped bottles were replaced in the Ziploc bag and repacked into backpacks for transport. At the same time the bottles were being filled, pH and temperature measurements were taken in situ downstream from the sample water extraction location using a Beckman pHi 265 pH meter. In some cases, a conductivity measurement was also taken with a YSI Model 30 conductivity meter.

Upon return to Crary Lab, all samples were labeled and placed in storage at 4°C except the nutrients samples, which were stored at -20°C. Aliquots for titration alkalinity analysis of 15 mL were taken from each whole water sample and placed in 20 mL pre-

washed Fisher HDPE scintillation vials which were also stored at 4°C. Trace element samples were filtered in Crary Lab through 0.4 μm Nuclepore filters, then acidified to a pH of less than 3 with 1% (v/v) ultra clean grade nitric acid and stored at 4°C. DOC samples were also acidified upon return to Crary Lab to a pH of less than 3 with 1% (v/v) hydrochloric acid.

3.2.2 Lakes A hole was drilled and melted out in the ice cover of Lake Miers to allow water samples to be collected, as is the MCM-LTER limno team’s method (MCM-LTER

Database). The hole was later covered by a hut to prevent aerial contamination and for ease of sampling. Before sampling each time, the thin ice cover which had formed over the hole was broken and scooped out to create a clear and clean sampling hole. Lake

Miers was sampled at ten depths by lowering a Niskin bottle into the hole in the ice cover. Water from 5, 7, 9, 11, 13, 15, 16, 17, 18, and 19 m was then collected in 1 L

Nalgene bottles. The Niskin bottle was inverted five times before filling the sample bottles with water to ensure a homogeneous water sample. Water isotope samples were collected in 20 mL unwashed borosilicate scintillation vials with no head space as described above for the streams. The sample bottles were then transported back to a field camp laboratory where they were filtered through 0.4 μm Nuclepore filters. All filter towers and filters were pre-rinsed three times with DI water before each sample was filtered. A new filter was used for each depth sample. After filtration, aliquots of sample were taken for nutrients analysis, anions, cations, and DOC. Each of these samples was placed in a pre-washed bottle, as described above, appropriate for each sample type. DOC

samples were acidified to a pH of less than 3 with 1% (v/v) hydrochloric acid. All samples were stored at 4°C until transport to Crary Lab where the nutrient samples were moved to -20°C storage. Nitrile gloves were worn at all times when handling uncapped samples.

3.3 Methodology 3.3.1 Major Ions and Alkalinity Cation and anion samples were stored at 4°C in Crary Lab until analysis via

- - - 2+ 2+ + + 2- Dionex DX-300 ion chromatograph. Standards for Cl , Br , F , Ca , Mg , Na , K , SO4 were made from a stock solution. The standards chosen were based upon previous years of data from the same sample sites. Analysis procedures of the major ions were followed according to Welch et al. (1996; 2010). Alkalinity samples were transported back to

Ohio State for analysis according to Welch et al. (2010).

3.3.2 Nutrients and Silica Nutrient samples were collected in 120 mL Nalgene bottles which were pre- washed as described earlier. Upon return to Crary Lab, the nutrient samples were frozen and stored at -20°C until transport back to the University of Colorado, Boulder for analysis.

3.3.3 Trace Elements Water samples for trace metals were collected in 120 mL Nalgene bottles that were pre-washed with nitric acid as described earlier. Blank samples were also created

by filling nitric and DI rinsed bottles with DI water to assess the cleanliness of the washing and sampling procedure. Upon return to Crary Lab, the water samples, including the blank samples, were filtered with 0.4 μm Nucleopore filters in a filter tower. The filter tower was rinsed with nitric acid and DI water in the same manner as the bottles. After filtration, the samples were acidified to 2% (v/v) with trace metal grade nitric acid. The samples were then stored at 4°C and shipped back to Ohio State for analysis on the Thermo Finnigan Element 2 high resolution inductively coupled plasma mass spectrometer (ICP-MS).

Standards were prepared for the metals Mo, Sr, Ba, Rb, U, V, Cu, and As. Each metal had a different range of standards based upon expected concentrations (Table 1).

Five solutions of standards were made, each containing all of the metals analyzed to simulate matrix effects. Multiple isotopes of metals were analyzed whenever possible to avoid spectral overlap. Each element analyzed in high resolution (Rb, Sr, Mo, Ba, and U) was measured with 10 repetitions for a total integration time of 1.3 seconds. Elements measured in medium resolution (V and Cu) were measured with 10 repetitions for a total integration time of 2.5 seconds. As was measured in high resolution with 10 repetitions for a total integration time of 25 seconds. A check standard was run after every 5 samples to monitor instrument drift.

3.3.4 DOC Water samples for dissolved organic carbon analysis were stored at 4°C until analysis via Shimadzu TOC-V according to standard procedure recommended by the manufacturer.

3.3.5 Water Isotopes Water isotope samples were stored at 4°C until transported back to Ohio State for analysis via Picarro Cavity Ringdown Spectrometer according to methods of Maruyama and Tada (2014) and Leslie (2014).

3.3.6 Precision and Accuracy The precisions of the measurements of the above mentioned analytes are shown in

Table 2. In addition, our laboratory has taken part in the USGS “Round Robin” exercise where we analyze a certified major cation and anion standard provided by them. We also have analyzed NIST-1643e and TMDA-64.2 trace element reference standards along with our trace element samples. The accuracy of our measurements compared to these reference materials is also shown in Table 2. Detection limits are also shown in Table 2.

Accuracy was calculated as percent difference of average measured value from a known check standard. NIST-1643e was used as a check standard for all trace elements except U, where TMDA-64.2 was used. Major ion analysis used SPEX mix 2 and 3 multi ion as a check standard. Other analyses did not have a check standard, so accuracy could not be determined. Precision was calculated as average percent difference from 2 replicate runs of 3 – 4 samples for major ion analysis. For trace element and isotope analysis it was calculated as the greatest percent difference between the average of 5 replicates and any other one. Detection limit was determined for the trace elements as three times the standard deviation, and for the other analytes by blank values.

3.4 Hydrologic Measurements A gauge was installed at Adams Stream by the MCM-LTER stream team in 2011

– 2012. The gauge automatically reads the flow rate, temperature, and conductivity of the stream every 15 minutes throughout the flow season (MCM-LTER Database).

During a 24 hour sampling period, a portable Baski flume was installed at 1630 on

January 18, 2012 in the Miers Inflow. A reading was taken approximately every hour to provide a flow rate. Combination of these two values provides a total inflow into the lake, and therefore a total outflow under the assumption that the lake depth remains constant over time (Spigel and Priscu 1998). An in situ pH and temperature measurements were also taken at most sampling sites while samples were collected.

These were measured slightly downstream (between 0.5 m and 3 m) from the water sample collection location to avoid contamination. Additionally, specific conductivity was measured at some sampling sites, either as direct conductivity or specific conductivity depending upon temperature.

CHAPTER 4: RESULTS AND DISCUSSION

During the flow season of 2013 – 2013, the concentrations of several analytes were measured in the inflowing and outflowing streams of Lake Miers, and in the lake itself at specific depths. These analytes include major cations and anions (Li, Na, K, Mg,

Ca, SO4, F, Cl, Br), nutrients (NO2, NO3, NH4, PO4, Si), trace elements (Rb, Sr, Ba, Mo,

U, V, Cu, As), dissolved organic carbon (DOC) and water isotopes (δ18O and δD). The results of the total data set are in Appendix B (stream data) and Appendix C (lake data) and are summarized here.

4.1 Streams The two inflowing steams and the outflowing stream were each sampled about 16 times on 5 separate days throughout the flow season. The first sample was taken on 30

December 2012 and the last sample was taken on 2 February 2013. On 18 – 19 January

2013 a sample was taken every other hour for a full 24 hours. Each sample was analyzed for major cations and anions, nutrients, δ18O and δD isotopes, and dissolved organic carbon (DOC). Many samples were also analyzed for trace elements including Sr, Rb,

Mo, Ba, V, U, Cu, and As. Flow measurements were also taken in Adams Stream and during the 24-hour sampling for Miers Stream. These data are summarized below.

Because of the very low concentrations of the ion data for the 2 February, 2013 Adams

Stream sample, it is considered suspect, and not included in the discussion, but the data are provided in Appendix B.

4.1.1 Input The total volume of water that flowed into Lake Miers through Adams Stream over the 2012 – 2013 season was measured at 3.73E08 L. The total volume of water that flowed into Lake Miers through Miers Stream over the 2012 – 2013 season was estimated at 1.56E08 L. As noted above, unlike the Taylor Valley streams and the Onyx River in

Wright Valley, little information exists with which to compare these annual discharges.

Green et al (1988) estimated inflowing volume of water into Lake Miers from streams,

M1 and M2 (i.e. Adams and Miers) to be 3.07E07 L and 2.5E07 L, respectively, during the 1983-1984 flow season. The 83 – 84 flow year in the Onyx was a very high flow year, whereas the 12 – 13 flow year was not (MCM-LTER Database). There are no other data to compare the two flow regimes (i.e. Miers and Onyx), but this might hint that these streams are not responding to similar climatic drivers as the 12 – 13 flow in Lake Miers was almost an order of magnitude higher than in 83 – 84. Major Cations: The Na concentrations range 183 – 740 μM in both inflowing streams with a mean of 360 μM in

Adams Stream and 586 μM in Miers Stream. The K concentrations range 35 – 88 μM in both inflowing streams with a mean of 43 μM in Adams Stream and 73 μM in Miers

Stream. The Mg concentrations range 35 – 153 μM in both inflowing streams with a mean of 80 μM in Adams Stream and 122 μM in Miers Stream. The Ca concentrations range 395 – 1195 μM in both inflowing streams with a mean of 688 μM in Adams Stream and 763 μM in Miers Stream. Major Anions: The Cl concentrations range 79 – 854 μM in both inflowing streams with a mean of 354 μM in Adams Stream and 371 μM in Miers

Stream. The titration alkalinity ranges 0.75 – 1.86 meqL-1 with means of 1.08 and 1.36

2- for Adams and Miers Streams, respectively. The SO4 concentrations range 44 – 239

μM in both inflowing streams with a mean of 106 μM in Adams Stream and 150 μM in

Miers Stream. The Br concentrations were below detection limit of 40 μM in all stream samples.

4.1.2 Output The total estimated volume of water that flowed out of Lake Miers through Miers

River was 5.29E08 L. The output is assumed to be equal to the inflow. A stream gage was not in place to measure outflow during the time of this sampling. Therefore, the assumption that outflow = inflow is based on the work of Spigel and Priscu (1998) who argue that Lake Miers does not increase size above a certain threshold that it is at present.

The mean concentrations of all analyzed constituents are lower in the outflowing stream than in either inflowing stream. Major Cations: The Na concentrations range 104 – 127

μM in the outflowing stream with a mean of 123 μM. The K concentrations range 23 –

29 μM in the outflowing stream with a mean of 27 μM. The Mg concentrations range 27

– 36 μM in the outflowing stream with a mean of 33 μM. The Ca concentrations range

298 – 384 μM in the outflowing stream with a mean of 370 μM. Major Anions: The Cl concentrations range 73 – 80 μM in the outflowing stream with a mean of 77 μM. The

2- SO4 concentrations range 28 – 33 μM in the outflowing stream with a mean of 31 μM.

The Br concentrations were below the detection limit of 40 μM for all outflowing stream samples.

4.1.3 Comparison to other MCM Streams Both the inflow and outflow streams in Miers Valley can be geochemically described as follows: cations – Ca > Na > Mg > K, and anions – HCO3 > Cl > SO4. On a ternary plot for cations (Figure 3), these streams plot as some of the highest Ca2+ enriched streams of all MCM, with the outflow stream being one of the most Ca2+ dominated.

They have a much higher proportions of Ca2+, and a substantially lower Mg/Ca molar ratio compared to the mean global river value (Welch et al. 2010). In this respect, they closely resemble the geochemistry of the streams from the western Lake Hoare basin in

- Taylor Valley that also drain through marble debris (Welch et al. 2010). On a HCO3 vs

Ca2+ plot they fall slightly below the 2:1 line suggesting an excess of Ca2+ besides what is being derived from CaCO3 weathering (Figure 4). Although it is clear that the dissolution of the local marble bedrock is a major process controlling the chemistry of

Adams and Miers Streams, they both also have mean dissolved Si concentrations (115 and 174 μM) that are in the highest ~20% of all MCM streams, suggesting a significant occurrence of aluminosilicate mineral weathering in the stream channels (Welch et al.

- 2010). Finally, these inflow streams are at the high end of NO3 concentrations reported in MCM streams, and have some of the highest concentrations of soluble reactive phosphate reported for the Taylor Valley streams (Welch et al., 2010). Concentrations of

- 3- NO3 and PO4 in MCM streams are related to both landscape position, and the distribution of photosynthetic algal mats in the streams (Barrett et al. 2007). In Taylor

- Valley, the highest NO3 is in the westernmost streams in the oldest landscape surfaces, while the highest phosphate levels are in the easternmost streams that sit in the youngest

- aged tills. The source of the NO3 to Adams and Miers Stream is likely from the

accumulation of atmospherically deposited N over time, both within the stream channels and deltas close to the lake itself and on the glaciers. It is unclear what the source of the phosphate is, especially because the western Lake Hoare basin streams draining similar lithologic material have much lower concentrations than the Miers inflowing streams.

- 3- Nonetheless, the very low NO3 /PO4 (i.e. inorganic N:P) ratios entering the lake would lead to the conclusion that Lake Miers is N-limited (Priscu 1995). To date, the only documented N-limited lake in the MCMDV is Lake Fryxell. Experiments and field observations have demonstrated that all other lakes in MCMDV are P-limited (Priscu

1995; Barrett et al., 2007).

4.1.4 Comparison to Previous Stream Work Green et al. (1988) were the first to conduct any detailed geochemical analyses of

Adams and Miers Streams when they analyzed 8 and 7 samples, respectively, during the

1983 – 1984 austral summer. Their data are shown in Table 3. In general, these data all show a similar geochemical pattern to the results presented here, with cations – Ca > Na

> Mg = K and anions – HCO3 > Cl > SO4. The major difference is that there appears to have been an increase in Mg relative to K over this time period, and the mean concentrations of all major solutes are higher in 2012 – 2013. The increased Mg could be due to enhanced weathering of the local carbonate bedrock, and the higher solute concentrations perhaps to higher inundation of the delta area surrounding the two streams as they enter the lake, thereby having higher rock:water ratios and increased water exposure to reactive mineral surfaces (Green et al., 1988). These authors had previously recognized that Ca2+ had a higher relative contribution to the total cation concentration

than other MCM streams, and that the high Na:Cl ratios could not be due to these two ions being from a marine aerosol or halite dissolution source alone. Green et al. (1988) attributed these high Na:Cl ratios to the dissolution of mirabilite (i.e. Na2SO4•10H2O) which is abundant in both Miers and Garwood Valleys (to the north of Miers Valley).

These authors also concluded that the observed high proportion of Ca2+ and the high

Ca/Mg molar ratio both suggested that the dissolution of CaCO3 was a major process contributing to the geochemistry of these streams. The data presented herein certainly substantiate earlier work.

4.1.5 Minor and Trace Element Data All Miers Valley inflow and outflow stream data are given in Appendix B.

Unlike the major element data, with a few exceptions, there has been little systematic attempt to generate minor and trace element data for MCM streams over the length of the

MCM-LTER program. The data that do exist were collected only from a few streams and over a very limited temporal period, usually as part of “process” studies, and not as part of the monitoring program (MCM-LTER Database). In addition to these short term, and spatially limited, MCM-LTER related works, there are also only a few non-LTER related investigations in which one or more minor/trace element concentrations were measured in MCM streams. Minor Elements: Over the length of the MCM-LTER, F- has been measured in Taylor Valley streams and the Onyx River (LTER Database). The F- concentrations from these streams have a mean value of 5.1 μM. These previous stream compilations compare well to the mean values of 6.3, 8.9, and 3.8 μM for Adams Stream,

Miers Stream and Miers River, respectively. The Taylor Valley stream Li data were

initially summarized by Lyons and Welch (1997) with a mean stream value of 0.17 μM, compared to the means of 0.45, 0.52, and 0.31 μM for Adams Stream, Miers Stream, and the Miers River, respectively. Rubidium, strontium, and barium were measured in a number of Taylor Valley streams by Witherow (2009). The mean Rb concentration in the Taylor Valley streams was 10 nM, compared to the mean values of 21, 28, and 9 nM for the three Miers streams. The mean Sr concentration in the Taylor Valley streams was

647 nM, while the three Miers stream values were 2040, 2230, and 885 nM. Witherow

(2009) found the mean Ba concentration in Taylor Valley to be 12 nM, compared to 8,

13, and 3 nM for the three Miers Valley streams. Trace Elements: Henderson et al.

(2006) have a few U measurements from the Onyx River (in Wright Valley) and three non-Blood Falls associated streams in Taylor Valley. The mean U concentration is 0.3 nM, compared to 2, 11, and 1.4 nM for the three Miers streams presented within. Fortner et al. (2012) analyzed two streams (Andersen Creek and Canada Stream) in Taylor

Valley through a hydrographic cycle and found mean concentrations of 1.0 nM and ND

(non-detectable) for Mo, 12.7 and 4.8 nM for V, 2.5 and 1.1 nM for Cu, and a range of

ND and <0.2 – 8.9 nM for As for these two streams draining the Canada Glacier in central Taylor Valley. The Miers Valley stream means for Mo were 8, 8, and 1.4 nM; for

V were 23, 44, and 20 nM; for Cu were 2.2, 2.3, and 1.1 nM; and for As were 1.2, 1.5, and 0.6 nM.

In summary, the concentrations of minor and trace elements in the Miers and

Adams Streams have the following relationship to the Taylor Valley streams and the

Onyx River, Wright Valley: U >> Mo > Sr ≥ F, Rb = Ba, V, Cu, and As. The Miers

River relationship to the Taylor Valley and the Onyx River is: U > Li > Sr = F, Rb, Mo,

Cu ≤ As < Ba. The higher Sr and F concentrations, and possibly U, in Adams and Miers

Streams can possibly be explained because of the dissolution of the marble-carbonate materials over which streams are flowing, as Sr and F have higher concentrations in carbonate than aluminosilicates sedimentary rocks (Li, 2000). However, the Mo, Rb, and

Li concentrations are lower in carbonate rock than the aluminosilicate sediments, and average continental crust, and the higher concentrations of these elements in the Miers

Valley streams compared to the Taylor Valley ones are problematic, and merit further investigation. Water Isotopes: The means of δ18O and δD of the Miers Streams are approximately -25 – -26 ‰ and -203 – -212 ‰ which is much heavier than the Taylor

Valley stream values (Gooseff et al. 2006). Because there are no published values for the glaciers producing the meltwaters for these streams, we cannot differentiate between a heaver isotopic source of glacier ice melt or a substantial loss of the 16O isotope via evaporation as the streams flow through the drainage into the lake.

4.1.6 Hydrology and Geochemical Fluxes Adams Stream is gauged and its discharge was recorded every 15 minutes during the 2012 – 2013 flow season. The gauge measures the height of the water in a known cross-section channel indirectly via pressure, the specific conductivity, and the water temperature (MCM-LTER Database). The stream flow in the 2012 – 2013 season was recorded from 1115 local, December 12, 2012 to 2345 local, February 5, 2013. The last recorded non-zero flow measurement was at 2015 local, February 3, 2013. During the

24-hour sampling period on January 18 and 19, 2013, a Baski flume was temporarily installed in Miers Stream to record its discharge. Measurements were made

approximately every hour for 24 hours. Within the 24-hour sampling period, measurements of the discharges of both inflowing streams were made simultaneously.

Because the glacial melt depends primarily upon local air temperature and radiation, the two inflowing streams should have related discharges. When the inflow discharges are plotted against each other in a scatter plot (Figure 5), a best-fit line can be drawn with an equation of y=0.3129x+0.2434 and an R2 value of 0.8183. Using this formula, an estimation of the discharge of Miers Stream can be calculated for the entire flow season where x=discharge of Adams Stream and y=discharge of Miers Stream. The best-fit line does not go through zero due to a difference in the methods used to measure the discharge of each stream. Miers Stream’s discharge was measured via Baski flume which required a visual read of the water height. Adams Stream’s discharge was measured via stream gauge installed earlier in the season and located farther up-valley.

Those measurements were recorded indirectly and were not corrected for freezing conditions which produced erroneous zero flow measurements. The gauge recorded zero-flow measurements during the 24-hour sampling period when flow did exist. This means that a zero-flow measurement from the Miers Stream and a zero-flow measurement from the Adams Stream do not mean the same thing (during the 24-hour sampling period) and a best-fit line through (0,0) would not be the best option to correlate these stream discharge values.

For the 24-hour sampling period, 3.95E05 L of water flowed into Lake Miers from Adams Stream and 3.11E05 L of water flowed into Lake Miers from Miers Stream.

This is a small amount compared to the 3.73E08 L of water that flowed from Adams

Stream and an estimated 1.52E08 L that flowed from Miers Stream into Lake Miers over

the 65 days of measured flow. The total outflow of water from Lake Miers to Miers

River can be estimated by adding the two inflows together. The lake depth is controlled by the outflowing stream, meaning that as long as the lake level is at least high enough for Miers River to flow, the lake level is at a maximum (Spigel and Priscu 1998).

Because the volume of Lake Miers is not apparently changing, the volume of water entering the lake must be equal to the volume of water exiting the lake. Therefore, an estimate of the total discharge of Miers River can be achieved by summing the total discharges of both inflowing streams. The estimate of the total volume of water outflowing from Lake Miers through the Miers River during the 65 measured days of the

2012 – 2013 season was 5.25E08 L. With the total discharge of each of the three streams, a seasonal flux can be calculated for all analytes by finding the difference between total input and output. By multiplying the total annual flow in each stream by the average concentration of analyte in each stream, a total mass of analyte flowing into and out of the lake can be calculated. A total lake flux can then be calculated by subtracting the mass flowing out from the mass flowing in. There is a positive influx into

Lake Miers for all analytes examined in this study (Table 4). The percent retained in the lake can be calculated by dividing the flux difference by the total input (Table 4). The percent retention differed for each analyte and ranges from 10% to nearly 100%. Those

- + analytes with the lowest retention include NO2 , NH4 , and Li. Those analytes with the

- 3- highest retention include NO3 , PO4 , and Mo.

Based on data collected over the time period of this study and the assumption that the water budget of the lake is in balance (i.e. input = output), the lake is a net “sink” for all of the ions measured (Table 4). The removal of major and minor elements, in moles,

are as follows: Si >>Ca > Na > Cl >> SO4 > Mg > K > NO3 >> F > Sr > PO4 > Li; and for the trace elements: Rb > V > Ba ≥ Mo > U > Cu ≥ As. In general, the sequence closely resembles the relative concentrations of the incoming streams noted above.

These calculations suggest that Cl- is not conservative in the Lake Miers system.

Because there is no mechanism in this very fresh system to remove Cl- actively, and hence there is no reason to think Cl- is non-conservative, there must be other mechanisms and processes at work to explain our calculated balances.

Explanations that could explain this discrepancy include: 1) incoming streams

(Adams and Miers) had abnormally high concentrations during our sampling interval

(perhaps due to the draining of the hyperheic zones associated with the delta sediments),

2) lake water has a very long (i.e. longer than perhaps a melt season) residence time, so there is a net gain of solutes on a short term basis, 3) some of the inflow water is more dense than the surface water in the lake, allowing it to sink and mix with depth, and therefore the lake is indeed gaining solutes.

4.1.7 Relationship of Discharge to Concentration The typical flow season in the MCMDV begins in November and continues into late January or early February and last 4 – 12 weeks (McKnight et al., 1999). The maximum flow recorded in Adams Stream during the 2012 – 2013 season was >978.46

L/s. The greatest flow recorded during the 24-hour sampling period between January 18 and 19 was 27.75 L/s. The 24-hour sampling took place at the end of the flow season when flow was lower than in December. The late season timing of the 24-hour sampling, the overcast conditions, and low temperatures resulted in very low flow and very little

variation in flow (Figure 6). The geochemical variation in this low-flow case may not be indicative of higher-flow situations. Most of the major ions, trace elements, and nutrients analyzed show the same trends when plotted in hydrograph form (Figures 7 – 10). The lowest concentration of each analyte occurs at high, but not typically the highest, flow.

With more meltwater from the glacier creating higher discharge in the streams, the concentration of analyte does not increase linearly. As the flow increases to the maximum flow, the concentration of analyte increases (Figures 7 – 10). This phenomenon is likely due to increases interaction between water and delta surface/subsurface as the flow enters the lake. As a greater delta area is wetted, more analytes are dissolved into the streamwater. The large delta between the Adams and

Miers Streams is untypical of the geomorphology of streams in Taylor Valley and the

Onyx River (Figure 11). After the streamflow peaks for the day and begins to decrease, the analyte concentrations maintain a fairly constant value, and even in some cases continue to increase. This pattern may be attributed to loss via freezing and salt exclusion, thereby increasing concentrations in the remaining liquid water, and/or the draining of the aforementioned large hyporheic zone of the delta. Once the lowest flow is reached and the discharge begins to increase again in the rising limb, the concentration of the analytes shows little to no increase (Figures 7 – 10). As stated earlier, these hydrographs may not be typical of the stream behavior during higher flow in the early and mid-season. Future work should examine the variation of solutes during a diel cycle at higher flow regimes. In addition, the interaction of streamwater with the extensive delta system needs to be further investigated in order to better quantify solute gain in this portion of the stream system.

4.2 Lake Miers Three lake profiles were taken during the 2012 – 2013 season on November 13,

2012; December 12, 2012; and January 2, 2013. Major cations, anions, trace elements, and Si were analyzed for only the first two profiles of the season. Nutrients and DOC were analyzed for all three profiles. Water isotopes were analyzed for only the second two profiles of the season. The major ion profiles generally have a trend of increasing

2- concentration with increasing depth, but vary from early to mid-season. SO4 is an exception to the increasing with depth trend. Major Cations: The Na concentrations increase from 183 μM and 118 μM at the surface to 278 μM and 269 μM at depth in the first and second lake profiles, respectively. The K concentrations increase from 38 μM and 26 μM at the surface to 81 μM and 81 μM at depth in the first and second lake profiles, respectively. The Mg concentrations increase from 47 μM and 27 μM at the surface to 100 μM and 97 μM at depth in the first and second lake profiles, respectively.

The Ca concentrations increase from 471 μM and 307 μM at the surface to 1024 μM and

1061 μM at depth in the first and second lake profiles, respectively. Major Anions: The

Cl concentrations increase from 124 μM and 79 μM at the surface to 173 μM and 171 μM

2- at depth in the first and second lake profiles, respectively. The SO4 concentrations decrease from 48 μM and 29 μM at the surface to 22 μM and 18 μM at depth in the first

- and second lake profiles, respectively. Nutrients: The NO2 concentrations decrease from

4 μM, 8 μM, and 1 μM at the surface to below the detection limit of 0.7 μM at 18 m, 15

3- m, and 11 m for the first, second, and third lake profile, respectively. The PO4 concentration is only above the detection limit of 0.6 μM at a few depths in the three lake

profiles, and a pattern is not obvious. The Si concentrations increase with depth from

152 μM and 61 μM at the surface to 408 μM and 424 μM at depth. The dissolved organic carbon (DOC) concentrations in the first lake profile show some fluctuation. The surface

DOC concentration is 37 μM, which increases then decreases in the middle of the lake with a low of 16 μM at 13 m depth and a high of 95 μM at 19 m depth. In the second lake profile, the DOC concentration increases from 14 μM at the surface to 55 μM at depth. The majority of constituents analyzed exhibited concentration increasing with depth. The exceptions to this were the DOC and several of the trace metals, which showed more complicated profiles.

4.2.1 Comparison to other MCM Lakes Lake Miers is the freshest lake in the MCMDV and the data from Lake Miers can be compared to the freshest closed-basin lake in Taylor Valley, Lake Hoare. Since the beginning of the LTER in 1993, the TDS in both Lake Miers and Lake Hoare have fluctuated, but Lake Miers has never been less than ten times fresher than Lake Hoare in the surface waters (Figures 12 and 13). The ion concentrations in Lake Miers have the following relationships: cations – Ca > Na > K > Mg, and anions – Cl > SO4 > HCO3.

These are similar to the ion relationships seen in the streams in Miers Valley. The only other water in the MCMDV with Ca as the dominant cation is the hypolimnion of Lake

Vanda (Witherow and Lyons 2011). The other lakes have Na dominance (Lyons et al.,

1998). This difference in cation dominance between Lake Miers and Lake Hoare has existed since the LTER began sampling in 1993 – 4 and is likely due in part to the high amounts of marble in the streambeds in Miers Valley (Figure 14) (MCM-LTER

Database). Lake Miers also differs greatly from the Taylor Valley lakes in its anion

- assemblage. It is the only lake to have HCO3 as the majority of anions present and with a very small percentage of Cl-. Lake Hoare is the most similar to Miers with

- - approximately equal parts HCO3 and Cl , while East and West Lake Bonney have only

- ~4% HCO3 .

4.2.2 Analyte Profiles normalized to Cl Depth profiles of various analytes can be easily compared after normalization to

Cl-. Cl is a conservative species, as mentioned above, and therefore a normalization of other solutes to Cl- gives insight into how other species react to both physical and biogeochemical processes. Major Cations/Cl-: Ca, K, and Mg all show a nearly constant profile from the surface to ~11 – 13 m depth. After 11 – 13 m, however, Ca, K, and Mg increase relative to Cl (Figures 15 – 17). Na shows this, but with a little more variation

- 2- above 11 – 13 m (Figure 18). Major Anions/Cl : The SO4 concentration normalized to

Cl decreases slightly from 0.37 at the surface to 0.30 at 15 m. Before 15 m, the normalized concentration decreases dramatically to 0.1 – 0.13 at depth (Figure 19).

- HCO3 normalized to Cl, however, steadily increases from 0.6 – 1.0 at the surface to 2.3 –

- + 2.4 at depth (Figure 20). Nutrients/Cl : The profile of NH4 normalized to Cl is a constant value of ~10 from the surface to 18 m depth. At the very bottom (19 m),

+ however, the NH4 /Cl value increases to 164 (Figure 21). The later profile of DOC/Cl is similar, but less dramatic. The values from surface to 15 m are between 0.15 and 0.18.

After 15 m, however, the value increases to 0.32 at the bottom (Figure 22). The Cl normalized profile of Si shows a constant value of 0.7 – 0.9 between the surface and 13

m. After 13 m, the value increases to 2.4 – 2.5 at depth (Figure 23). Minor and Trace

Elements/Cl-: F/Cl shows a slight increase from surface to lake bottom (Figure 24).

When normalized to Cl, the Rb, Sr, Ba, and As profiles all show fairly constant values from surface to 11 m, with the exception of Ba which shows a slight decrease from surface to 11 m. Below 11 m, all of these trace elements increase to the bottom of the lake (Figures 25 – 28). U and V normalized to Cl both decrease slowly from surface to

15 m, then decrease at a higher rate from 15 m to the lake bottom (Figures 29 and 30).

Mo is below detection limit in waters above 13 m depth, below which Mo/Cl peaks and then decreases to the lake bottom (Figure 31).

4.2.3 Comparison to Previous Trace Element Work Minor Elements: The F concentrations increase from 5 μM and 2 μM at the surface to 11 μM and 11 μM at depth in the first and second lake profiles, respectively.

Witherow and Lyons (2011) analyzed the concentrations of Li, Rb, Sr, and Ba in the water column of Lake Hoare. The Li concentrations are below the detection limit at the surface and increase to 0.4 μM and 0.3 μM at depth in the first and second lake profiles, respectively. The Rb concentrations increase from 16 nM and 10 nM at the surface to 29 nM and 33 nM at depth in the first and second lake profiles, respectively. The strong

Li:Cl and Rb: Cl relationships seen in Lake Hoare suggest that Li and Rb are both conservative and primarily the result of chemical weathering and/or salt dissolution

(Witherow and Lyons 2011). These relationships were not as strong in Lake Miers. A

Li:Cl scatter plot of Lake Miers with a trendline has an R2 value of 0.3762 and a Rb:Cl scatter plot of Lake Miers with a trendline has an R2 value of 0.6295. In Lake Miers, the

Sr concentration increases from 1360 nM and 790 nM at the surface to 2700 nM and

2710 nM at depth in the first and second lake profiles, respectively. In Lake Hoare, the

Sr is being removed through precipitation of CaCO3, but the concentrations of Sr are undersaturated with respect to strontianite and celestite, so those removal pathways are unlikely (Witherow and Lyons 2011). The Ba concentrations increase from 8 nM and 4 nM at the surface to 14 nM and 16 nM at depth in Lake Miers. Lake Hoare approaches equilibrium with the mineral barite (BaSO4) at depth, suggesting that this may be a primary removal mechanism of Ba (Witherow and Lyons 2011). Trace Elements: Green et al. (1986) measured the concentration of eight trace elements in Lake Hoare, including

Fe, Mn, Co, Ni, Cu, Zn, Pb, and Cd. They saw little to no increase for any mental in the bottom waters of Lake Hoare. In Lake Miers, the Cu concentrations are highest at the 7 m depth in both the first and second lake profiles, increasing from 3 nM and 2 nM at the surface to 4 nM and 6 nM at 7 m, then decreasing to 2 nM and 0.4 nM at depth, respectively. Lake Hoare shows Cu decreasing at depth, but not until 24 m (Green et al.

1986). The Mo concentration is below the detection limit at the surface until 11 – 15 m, below which it has a concentration of 7 nM at 16 m and 6 nM at 13 m in the first and second lake profiles, respectively. At these depths the Mo concentrations then decrease and are not detected at depth for in either profile. The U concentrations increase from 1.9 nM and 1 nM at the surface to 2.1 nM and 2 nM at 13 m in the first and second lake profiles, respectively. After these peak concentrations mid-depth, the U decreases to 0.7 nM and 0.4 nM at depth. The V concentrations follows the same pattern described for the U concentrations, beginning with an increase from 36 nM and 22 nM at the surface to

44 nM at 11 m and 42 nM at 13 m and then decreasing to 9 nM and 4 nM at depth for the

first and second lake profiles, respectively. The As concentrations are highest at 19 m depth for the first and second lake profiles, respectively, increasing from 0.9 nM and 0.5 nM at the surface to 2 nM and 2 nM at depth, respectively. Water Isotopes: δ18O and δD were the most negative in the earliest lake profile, but only the surface waters were analyzed during that time. For the second and third lake profiles, the δ18O became more depleted from -25.28 and -25.78 at the surface to -28.22 and -27.08 at depth, respectively.

The δD also became more depleted with depth, decreasing from -205.23 and -208.70 at the surface to -224.95 and -217.36 at depth, respectively.

4.2.4 Comparison to Past measurements Figure 33 shows the Cl- profiles from the earliest work of Bell (1967), that of

Green et al. (1988), and tor the long-term monitoring data of the MCM-LTER program.

These data, as noted in the figure, are plotted with the 16 m depth as the reference point.

This has been done to correct for any potential lake depth change over this ~50 year period. 16 m was chosen as the reference point because some years have data only extending to 16 m depth. There is no evidence that the lake has been larger than it is today, but it could have been smaller (Spigel and Priscu, 1998). Although these Cl- concentrations are low for MCMDV lakes, the variations are not due to analytical uncertainty (i.e. the precision of the measurement), which, at most, is ~2%, (Welch et al.,

2010). The larger variations at any particular depth could be due to spatial variations within the lake where the samples were obtained (i.e. variation in the melt hole through the ice), Niskin bottle mis-firing, or even contamination. The latter two are unlikely, but we cannot rule them out completely.

The pre-LTER data show almost constant Cl- concentration with depth at values

~0.16 mM. The LTER 97 – 98 profile is also similar to the Bell and Green et al. data

(Figure 33). In general, the rest of the MCM-LTER data show lower, more dilute concentrations in the surface, and in many years, throughout the water column. The

“spikey” profiles in 08 – 09 and especially 10 – 11 certainly reflect some type of problem with either collection or processing of the samples. The only definitive thing that can be said about this time series is that the surface waters in post-1997 have decreased in their

Cl- content. Because the 1990s were very low stream flow years in Taylor Valley (Doran et al., 2002), it is not surprising that in the years since the large flow year of 2000 – 01 to the 2012 – 13, the surface water of the lake should have lower (>3x) Cl- concentrations.

This is similar to what has been observed in the surficial waters of Lake Hoare (Welch et al., 2010).

The large fluctuations of Cl- observed at depth are much more perplexing. The

1964 – 65 profile (from Bell) and perhaps the 2010 – 11 data show much higher Cl- values at the deepest depth. Yet, as noted above, the 83 – 84 (Green et al., 1988), and the

96 – 97 and 09 – 10 LTER data show much lower values. These variations should be due to premature Niskin bottle release (i.e. collection of water at shallower depths by mistake), or the depth of the bottles itself was not measured correctly. Interestingly, the

Bell #1 profile at depth matches up very well with the 11 – 12 and both 12 – 13 profiles, the most recent measurements. Future work will have to resolve this issue.

4.3 Processes Controlling the Biogeochemistry of Lake Miers 4.3.1 “Age” of Lake Many of the ion profiles and the ion:Cl profiles illustrate the importance of diffusion from the sediments of solutes into the lake. This was first suggested by Bell

(1967) using his data collected in 1964. He also argued that, based on the temperature decrease very close to the sediment-water interface, it was possible that the lake had desiccated to complete dryness in the recent past. Lakes in Taylor and Wright Valleys have greatly fluctuated over time, with high stands during the LGM and, in the cases of

Lake Vanda, Lake Fryxell, and possibly Lake Hoare, have decreased dramatically from

2.5 – 4 Kyr ago and all of them increased in size between 1200 to 600 years ago (Wilson,

1964; Lyons et al. 1999). The east lobe of Lake Bonney has also been much lower in the recent past with data suggesting that low levels began to rise to above the sill depth (~13 m) that separates the two lobes of the lake at ~200 years ago (Doran et al. 2014). Bell

(1967) estimated that the refilling event at Lake Miers began ~100 years ago, but he pointed out that this was a “very crude” determination. He also mentioned that Lake

Bonney had increased ~10 m from the beginning of the twentieth century until 1964, work that has been confirmed by Chinn (1993) and the MCM-LTER group (P. Doran, A.

Fountain, personal communication).

We have used the diffusion model for Lake Fryxell of Lawrence and Hendy

(1985) to constrain the “age” of Lake Miers. (“Age” essentially means the beginning of the refilling event.) The model calculated the age of the diffusion cell:

ℎ2−ℎ2 푡 = 2 1 4퐷(ln 퐶1−ln 퐶2)

Where: t = age of the diffusion event

D = diffusion coefficient of a particular ion

C1 = concentration of the ion at the beginning of diffusion

C2 = concentration of the ion at some h or height in the water column

h1,2 = depth in the water column at C1 and C2

In this calculation we have used Na+ as the element of interest, as has been previously used by both Lawrence and Hendy (1985) and Lyons et al. (1999) for similar calculations on Lake Fryxell. The diffusion coefficient for Na+ at 0°C was taken from Li and Gregory (1974) and the “electroneutrality D” was used by assuming Na+ was

- diffusing along with Cl (Lawrence and Hendy, 1985). C2 was taken to be at 11 m at the point where the current Na+ diffusion cell is terminated by lake mixing and flushing

+ (Figure 34). We have assumed that the C1 concentration of Na was that of seawater in equilibrium with mirabilite (Marion and Kargel, 2008). Mirabilite (Na2SO4•H2O) is an abundant salt in both Miers and Garwood Valleys, and previous work has demonstrated that it has been derived from a marine source probably during the LGM when the advancing West Antarctic Ice Sheet pushed seawater into those valleys (Clayton-Greene et al., 1988). Using these values (Table 5), we obtain an age of 84 years, which is similar to Bell’s (1967) crude calculations of 100 years. The value of C1 does not greatly influence these calculation. For example, if we assume that the initial Na+ value was that in equilibrium with hydrohalite, the calculated diffusion age would be within a few years.

Green et al. (1988) compared the Cl- flux into the lake to the total Cl- within the lake (Cl-

= age) and determined the lake to be 270 years old. It is reassuring, however, that the age presented here is similar to that determined by Bell (1967) and to Green et al. (1988), and fits the overall notion of lake level rises over the past century in the MCM region (Hood

et al. 1998; Bomblies et al. 2001); Doran et al. 2014). This age of refilling connects

Lake Miers to the general Late Pleistocene – Holocene evolutionary histories of the other

MCM lake in that Lake Miers had a very large high stand from the LGM (23 – 18 Ka) until the Lake Pleistocene (13 – 14 Ka) where its size was reduced enough to precipitate evaporates (Clayton-Greene et al. 1988). Although there are no data at present to determine the volume of the lake throughout the Holocene, our calculations and those of previous work here suggest the lake was completely drawn down until ~100 – 300 years ago. The higher stand during the LGM was due to the advance of the West Antarctic Ice

Sheet (WAIS) blocking the easternmost part of Miers Valley as the WAIS advanced north from its current position. Evidence from both Taylor Valley and Wright Valley suggest the lakes there fluctuated in size throughout the Holocene (Hall et al. 2002;

Smith and Friedman, 1993; Wagner et al., 2006). Based on the similarities of these lakes’ dynamics in the Late Pleistocene and in the past few hundred years, it is probable that the size of Lake Miers also fluctuated in similar fashion during the Holocene.

4.3.2 Biological Limnology of Lake Miers Parker et al. (1982) were the first to investigate the biological components of

Lake Miers. They measured the chlorophyll-a (chl-a) maximum at 19 m depth and it approached 4 μg/L. The maximum volume of biological mass was found by direct counting to be just below the ice cover. They did not measure primary production. They also noted that the lake was devoid of higher level consumers, but found ciliates acting as herbivores in the system. They described Lake Miers as in an oligotrophic-mesotrophic tropic state. Primary production (PPR) was measured twice and chl-a was determined on

three occasions in 2012 – 13 by the Priscu Group’s “limno team” (MCM-LTER

Database). Those profiles are shown in Figures 35 and 36. In this study, the earliest PPR measurements of the season show relatively high PPR with maxima just below the ice cover at 5 m, at a mid-depth of 11 – 12 m, and again at depth (Figure 35). The later PPR determination from December, 2012 yielded much lower and relatively constant values of

~0.75 μg C/L, but with a maximum of almost double at 17 m. This decrease in PPR may be due, at least in part, to changes in the color of the lake ice covering through the austral summer (J. Priscu, personal communication). The chl-a profiles also demonstrate higher concentrations just under the ice-cover and the highest values just above the sediment- water interface (Figure 36). These values are higher than those measured from 2009 –

2012 in both the surface water and at depth (MCM-LTER Database). This chl-a maximum at great depth confirms the earlier of Parker et al. (1982), and along with the high PPR there, suggest that microbes are very active at this depth in biogeochemical processing within the lake. The relationship of biological parameters, the redox state, and potential diffusional flux of bio-active compounds is probably not coincidental. Priscu

(1995) has clearly demonstrated the importance of the diffusion of nutrients from below redox gradients in the water columns of all the Taylor Valley lakes, and the data presented here imply that the diffusion of materials from the sediments may also have important consequences in Lake Miers. In general, the highest chl-a values are observed very early in the austral summer and decrease over time except at the deepest depth of the lake (Figure 36). This loss may be due to settling and deposition of the phytoplankton, or consumption via the ciliate herbivores, or a combination of the two. The increase at 19 m in December and January suggest water column loss via settling is significant.

4.3.3 The Role of Biogeochemistry in Controlling Solute Distribution One of the important biogeochemical processes taking place in Lake Miers is sulfate reduction. This process is occurring at or below the sediment-water interface as there is dissolved O2 present in the bottom waters (~19 m), but only at a concentration of

1.6 – 1.8 mg/L. The O2 profile resembles that of sulfate with a decrease of 19 mg/L from

11 m to 19 m in December, 2012 (Figure 37). The sulfate profile indicates reduction of sulfate in the sediment (Figure 38). Parker et al. (1982) also observed a decrease in O2 approaching the bottom of the lake, and speculated that the sediments were anoxic (as did

Bell from the 1964 data). Green et al. (1988) suggested, via mass balance considerations, that 70% of the sulfate entering Lake Miers is lost through sulfate reduction, and suggested that sulfate reduction could also be taking place in the deepest portion of the water column, not just in the sediments.

Clearly sulfate reduction and the anoxic conditions in the sediments, and at least sub-oxic conditions in the bottommost water column, have profound impacts on the geochemistry of the other redox sensitive solutes in the lake water. In 1984, the

2- concentration of SO4 was measured to be 28 μM at 18.5 m depth in Lake Miers (Green

2- et al., 1988). During the 2012-2013 season, we measured SO4 to be 18 μM in the

2- bottom-most water. Extrapolating this rate of SO4 loss, into the future, the bottom-most portion of Lake Miers could be anoxic by ~2050.

Nutrients: The oxidized inorganic nitrogen concentrations change through the austral summer with the highest concentrations occurring in the upper portions of the water column after streams begin to flow (Figure 41). The concentrations vary

inconsistently below ~12 m, but this is probably due in part to the very low concentrations of < 5 μM. The surface water becomes depleted between mid-December to early January due to biological uptake during the height of the austral summer. The

+ NH4 concentrations are very low throughout the water column through the season except below 16 m, with the highest concentrations closest to the sediment-water interface late

+ in the melt season (Figure 39). This relatively high NH4 close to the sediment-water interface is related to the suboxic conditions at these depths, or at least at the sediment- water interface, as noted above. Dissolved phosphate is mostly at or below detection in the Lake Miers water. There are detectable concentrations at 9 m depth, but only after stream flow commenced. Any phosphate in the water column is rapidly taken up by primary producers. There could be some phosphate regenerated at depth through either the mineralization of organic matter or the dissolution of Fe oxides/hydroxides, but the concentrations are extremely low. The dissolved organic carbon concentrations in Lake

Miers are very low, only reaching values of ~83 μM at depth (Figure 40), and they are much lower than the concentrations in the Taylor Valley lakes (McKnight et al., 1991).

These lower DOC concentrations may reflect the young age of the lake, the lack of cryconcentration, and its flow-through behavior. This lack of chemical constituent buildup is the case with the major cations and anions. The concentration of DOC increases with depth and is probably related to the higher biomass and production rates, and hence, organic matter remineralization that is occurring there. However, we cannot rule out that another source of DOC to the bottom waters is diffusion from the sediments, as is clearly the case in Lake Fryxell (McKnight et al., 1991).

Trace Elements: Dissolved Fe2+ is below detection except at ~7m after initial stream inflow and at the deepest portion of the lake sampled (Figure 42). These data suggest that the production of dissolved Fe2+ in the bottom of the water column or its diffusion from the sediments increases through the austral summer. These values at

2+ depth are low and thus may indicate that most of the Fe present is sequestered as FeS2 by the production of sulfide via sulfate reduction. As, Mo, U, and V form soluble oxyanion complexes in oxygenated waters that can be reduced to more insoluble species.

For example, Mo has been utilized in marine sediments as an indication of reducing conditions (Crusius et al., 1996). V and U show similar profiles, in increasing with depth to ~11 – 15 m, then decreasing to very low values close to the sediment-water interface, suggesting either removal in the sub-oxic bottom water, and/or diffusion into the sediments. Mo concentrations remain undetectable until 13 – 16 m where they reach a maximum and then decrease with depth. The reason for the mid-water maximum is not known as it is slightly above both chlorophyll-a and primary production maxima. The decrease with depth close to the sediment-water interface is related either to reduction and removal or diffusion into the sediments or both. The As is much different than those other oxyanions forming metals and metalloids in that dissolved As increases with depth and then, in the December limno run case, decreases very close to the sediment-water interface. We did not discern if the dissolved As present is As5+ or As3+, but based on the

3+ low O2 concentrations, some of the As below 16 m could be As . The maximum total dissolved As concentration occurs very close to the chlorophyll-a maximum and the increases could be related to biological processes. Cu and Fe were the only two transition metals measured in this study. The dissolved Cu profiles show an upper water column

maximum, constant values between ~8 – 15 m, then a decrease with depth. The decrease could be related to biological uptake, sulfate reduction and removal, or diffusion into the sediments. In Lake Fryxell and Lake Hoare, Cu is readily removed in the sulfidic portion of the water columns of these lakes (Green et al., 1986;1989). These authors also point out that Cu also can be scavenged out of solution by metal oxides and biogenic particles.

The process involved in Cu removal in Lake Miers may involve all of the above mentioned ones and awaits future work.

Water Isotopes: In general, both δ18O and δD become lighter with depth (Figures

43 and 44). Of all the MCM lakes, only Lakes Fryxell and Hoare have similar profiles

(Gooseff et al., 2006). One of the previous interpretations of this type of profile (i.e. getting lighter with depth) is that the “younger” water in the tops of the lakes has more evaporative loss of stream water recently than when the lakes began to fill (Gooseff et al.,

2006). The surface waters of Lake Miers have some of the most enriched δD and δ18O values observed in the MCM. It has been demonstrated previously that longer streams tend to have more enriched values, due to longer travel times and, hence, more potential time for evaporitic loss of the lighter isotope (Gooseff et al., 2006). Green et al. (1988) argued, based on differences in the Na:Cl ratio of stream water and surface water that both the Adams and Miers Glacier have recently retreated, allowing for longer stream flow paths, and increased salt dissolution of mirabilite (e.g. input of Na+ relative to Cl-).

Although we cannot prove or disprove Green et al.’s 1988 hypothesis, the δD and δ18O data could be used to support their idea. The same temperature rise that initiated the retreat of Miers and Adams Galciers could have led to the melting the ice cover on Lake

Miers. This exposure to sunlight would have led to evaporation of the lake water with a

preference for the lighter isotopes, leaving behind a heavier ratio in the now bottom waters of Lake Miers. When the temperature again rose and the ice cover on Lake Miers refroze, the surface waters would fill with lighter water that had been subjected to less evaporation. Unlike the streams in Taylor Valley, there are no ice data for Adams and

Miers Glaciers. Isotopic values from the glacier ice itself would help to test this idea that the heavier values in the surface waters of the lake are due to evaporitic loss of glacier melt waters during stream transport.

4.3.5 Role of Diffusion Diffusion of solutes from the lake bed into the water column can be observed by looking at many of the ion profiles normalized to Cl-. All of the major ion:Cl depth profiles show increases in ratios in the bottom of the lake from ~11 m to depth, while the surface ratios remain fairly constant. (Figures 15 – 18). This shows that there is a source of ions at depth, unrelated to the stream inflow or outflow, which is contributing to the concentrations. Green et al. (1988) suggested that mirabilite and CaCO3 dissolution were both ongoing processes taking place at depth in Lake Miers. Bell (1967) also suggested that gypsum dissolution is likely occurring under anaerobic conditions.

4.3.6 Lake Miers as a “Bioreactor” In the initial planning of this project, I hypothesized that I would see the removal of bioactive elements in the upper waters of the lake and their accumulation in the lower waters. This progress occurs in temperate lakes where photosynthetic organisms extract nutrients and micronutrients in the euphotic zone, the organisms or their detritus sink, and

the elements and compounds are bacterially remineralized at depth. This cycle is referred to as the “biological pump.” In most temperate lakes, this is a seasonal process as wind mixing and density driven water turnover re-establish the distribution of bioactive materials in the Fall/Winter period (Judd et al., 2005). There is little mixing and no density driven turnover the MCM lakes (Spigel and Priscu, 1998). Lake Miers is a flow through system with very low TDS, in part because much of the salt concentrated through ice development through cryoconcentration is lost through surface water flushing into the

Miers River. Therefore, we originally thought the processes observed in temperate lakes of the concentration of bioactive materials at depth would be easily observed in Lake

Miers. The results presented within demonstrate a much more complicated picture of the processes controlling solute composition of the lake. The input/output flux data indicate that the lake may be a sink for all the measured analytes, and yet this “removal” signal is not observed in the lake profiles. As noted above, the advection of dense water to depth may aid in the gain of solutes to the lake.

Besides the “flushing” or transport of water through the lake in the top ~10 m, chemical diffusion of dissolved components from, and changing redox conditions in, the sediments, and in the lower few meters of the lake waters play important roles in controlling the overall biogeochemical profiles within the lake. These processes are clearly more important than the transfer of bioactive material vertically within the lake system. The legacy of previous lake conditions, i.e. its desiccation to dryness in the recent past, has overprinted current processes that are taking place. This has been demonstrated for all the other MCM lakes (Wilson, 1964; Priscu, 1995; Lyons et al.,

2000; Doran et al., 2014). The previous climatic history and its impact on the local

hydrological system have had profound impacts on all these lakes, and this work has established that the same is true for Lake Miers.

As noted by both Bell (1967) and Spigel and Priscu (1998), the salinity gradient in Lake Miers supports its current density stratification. Spigel and Priscu (1998) demonstrated clearly there had been a considerable warming of the mid-lake waters since

Bell’s (1967) observations in 1964. The work herein demonstrates that this warming has continued. Although surface water can be mixed to depths of ~12.4 m, below 8.5 m the temperature increased (Spigel and Priscu, 1998). Our work demonstrates that the 4°C isotherm has now dropped to a depth of ~6 m in 2012 – 2013. This overall increase of temperature within the lake should act to destabilize stratification, and could eventually lead to more mixing of the water column. How this temperature profile may change the potential input of dense streamwater to depth remains to be investigated. Spigel and

Priscu (1998) described step-like function of both temperature and TDS with depth that represented thermohaline convection cells, and these cells are mixing depth increments within the lake. Clearly, the on-going monitoring of Lake Miers by the MCM-LTER will lead to a better, more complete understanding of these processes, and enable the prediction of the future physical and biogeochemical state of the lake. From this initial study, it is clear that a much better and more comprehensive understanding of the physical limnology of Lake Miers is needed before the biogeochemistry of the lake can be described.

CHAPTER 5: CONCLUSIONS 5.1 Summary of Research 1. The concentrations of all major ions and minor and trace elements are lower in

Lake Miers than in other MCMDV lakes. This is likely due to the flushing of

solutes out of the lake through the outflowing stream, and to the relatively young

age of the lake.

2. A “bioreactor” in Lake Miers is not easily seen. While the surface water is

similar to other MCMDV closed-basin lakes, the lower depths of the lake are

dominated by chemical diffusion and redox conditions, which mask any potential

“bioreactor” signal.

3. Lake Miers is a sink for all major ions, and minor and trace elements analyzed in

this study. However, this may be misleading given the extremely low flow used

to make these calculations. Future work will either confirm or deny this.

5.2 Future Work There are many aspects of the physical, hydrological, and biogeochemical cycling of Lake Miers that could benefit from future work, including but not limited to:

3-  the source of PO4 to the Miers Valley streams and Lake Miers

 the source of elevated Rb, Mo, and Li concentrations in Miers Valley streams and

Lake Miers compared to Taylor Valley streams and lakes

 the variation of solutes during a diel cycle at flow regimes higher than those

examined herein.

 the interaction of streamwater with the extensive delta system in Miers Valley

 the Cl depth profile concentration variation through time in Lake Miers

 the processes controlling Cu removal from Lake Miers

 the heat budget of Lake Miers and how the greater temperature of the bottom

waters compared to surface waters may affect the chemical stratification of the

lake

This suggested future work will contribute to the understanding of the geochemical, physical, biological, and hydrological processes occurring in Lake Miers. More comprehensive mass balances are needed in order to determine if Lake Miers is a “sink” for fluvial elemental inputs.

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APPENDIX A: TABLES AND FIGURES

Table 1: Standards Used for Trace Element Analysis. Units for all concentrations are in nM. Std 1 Std 2 Std 3 Std 4 Std 5 NIST 1643e TMDA-64.2 Mo 0.03 0.13 1.3 26 130 129 303 Sr 0.3 14 143 2850 14300 377 722 Ba 0.22 0.91 9.1 182 910 405 210 Rb 0.35 1.5 15 293 1460 17 36 U 0.0063 0.028 0.28 6.3 28.4 n/a 59.4 V 0.29 1.33 13.3 245 1325 76 56.5 Cu 0.047 0.197 1.97 39.3 197 36.5 423 As 0.04 0.167 1.67 33.4 167 82.5 217

Table 2 Precision, Accuracy, and Detection Limits of all analytes (Calculations for nutrients obtained from H. Hughes, Kiowa, UC Boulder) Detection limits given in μM for nutrients, ions, Si, and DOC, and nM for trace elements; ND=not determined Precision (% Diff) Accuracy (% Diff) Detection Limit

- NO2 1.5 ND 0.06

- - NO2 + NO3 1.3 ND 0.11

+ NH4 1.0 ND 0.50

3- PO4 2.7 ND 0.03 Mo 3.0 0.8 8.2 Rb 1.9 5.5 1.8 Sr 2.9 1.6 24 Ba 1.9 0.8 1.1 U 26 11 0.67 V 4.0 3.6 2.9 Cu 5.1 14 0.47 As 3.4 9.5 0.41 Li 7.9 6.5 0.29 Na 0.50 3.9 8.7 K 2.2 3.7 1.0 Mg 0.52 1.5 4.1 Ca 0.34 6.3 2.5 F 5.2 3.3 1.1 Cl 1.0 0.6 5.6 Br n/a 1.0 0.5

SO4 0.48 0.3 2.1 Si 1.0 ND 1.1 DOC 11.4 ND 8.3 δD 4.4 ND ND δ18O 3.9 ND ND

Table 3: Major Solute Data from 1983 – 84 (mean values in μM) (Green et al. 1988)

Stream Ca Mg Na K HCO3 SO4 Cl M1 347 23 135 28 758 31 65 (Adams) M2 400 21 100 22 825 25 58 (Miers)

Table 4: Lake flux and percent retention in Lake Miers 2012 – 2013 Season (all masses in moles) Adams Miers In Miers Out Flux % Retained

Mo 3.00 1.45 0.66 3.8 85.2 Sr 7.62 3.59 4.105 710.47 63.4 Rb 7.65 4.37 4.17 7.85 65.3 Ba 3.13 2.07 1.2 3.99 76.9 U 0.76 1.77 0.66 1.86 73.9 V 8.57 6.81 8.99 6.39 41.5 Cu 0.73 3.67 5.33 0.57 51.5 As 0.4 0.24 0.27 0.38 58.5 Na 1.44E05 9.16E04 6.50E04 1.71E05 72.4 K 1.70E04 1.13E04 1.45E04 1.38E04 48.8 Ca 2.69E05 1.19E05 1.96E05 1.93E05 49.6 Mg 3.15E04 1.91E04 1.76E04 3.30E04 65.1 Cl 1.40E05 5.81E04 4.07E04 1.58E05 79.5

SO4 4.18E04 2.46E04 1.66E04 5.00E04 75.0

NO2 34.6 24.3 52.1 6.85 11.6

NO3 5110 2820 1660 7860 97.9

NH4 284 115 357 42.35 10.6

PO4 83.8 75.2 10.3 148.75 93.6 Si 4.03E07 2.95E07 3.20E07 3.78E07 54.2 F 2360 1390 1990 1760 47.0 Li 167 82.1 164 85.13 34.2 DOC 3730 1690 4850 571 10.5

Table 5: Values used to calculate age of Lake Miers via diffusion model

2 D (cm /s) C1 (g/L) C2 (mg/L) h1 (m) h2 (m)

8.2E-06 46 5.92 0 9

Wright Valley Taylor Valley

Miers Valley

Figure 1: Map of McMurdo Dry Valleys

Miers Stream

Lake Miers

Delta

Adams Stream

Miers River

McMurdo Sound

Figure 2: Map of Miers Valley

Lake Miers 100% 0% Miers Streams

Lake Hoare

Hoare Streams Mg % Na + K % Lake Fryxell 50% Fryxell Streams 50% East Lake Bonney

East Lake Bonney Streams West Lake Bonney

West Lake Bonney Streams 0% 100% 0% 50% 100% Ca %

Lake Miers 100% Miers Streams 0%

Lake Hoare

Hoare Streams Alk % SO4 % Lake Fryxell 50% Fryxell Streams 50% East Lake Bonney

East Lake Bonney Streams West Lake Bonney

West Lake Bonney Streams 0% 100% 0% 50% 100% Cl % Figure 3: Ternary plots of cations (top) and anions (bottom) of five MCMDV lakes and their associated streams.

2.5

1.5 Alk (mN) Alk 1

0.5

0 -0.1 0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 Ca (mM)

Figure 4: Plot of measured Alkalinity vs Ca2+ from Miers Valley streams with a 2:1 line

15 y = 0.3129x + 6.8937 R² = 0.8183

Miers Stream Discharge (L/s) Stream Miers Discharge 5

0 0 10 20 30 Adams Stream Discharge (L/s)

Figure 5: Plot of Miers vs Adams Discharge Over 24 Hours

30 Discharge (L/s) Discharge 20

Date and Time

Figure 6: Discharge in Adams Stream During 24-hour Sampling

0.8

0.6

0.4

Concentratioin (mM) Concentratioin 0.2 Rising Limb

Falling Limb

0 0 5 10 15 20 Discharge (L/s)

Figure 7: Hydrograph of Na concentrations in Miers Stream from 1600 18 January 2013 to 1400 19 January 2013

0.5

0.4

0.3

0.2 Concentration (mM) Concentration

0.1 Rising Limb

Falling Limb 0 0 5 10 15 20 Discharge (L/s)

Figure 8: Hydrograph of Cl concentrations in Miers Stream from 1600 18 January 2013 to 1400 19 January 2013

0.024

0.018

0.012

Rising

Concnetration (mM) Concnetration 0.006 Limb Falling Limb

0 0 5 10 15 20 L/s

- Figure 9: Hydrograph of NO3 concentrations in Miers Stream from 1600 18 January 2013 to 1400 19 January 2013

0.018

0.012

0.006 Concentration (mM) Concentration Rising Limb

Falling Limb 0 0 5 10 15 20 Discharge (L/s)

Figure 10: Hydrograph of Ba concentrations in Miers Stream from 1600 18 January 2013 to 1400 19 January 2013

Miers Glacier

Miers Valley Delta

Lake Miers

Figure 11: Delta in Miers Valley

0.1

0.09

0.08

0.07

0.06

0.05

0.04

0.03

0.02

0.01

0 Molar Ratio of Cl in Lake Miers:Cl in Lake Miers:Clin Hoare Lake Ratio in Cl of Lake Molar 1992 1997 2002 2007 2012 Year

Figure 12: Plot of the molar ratio of the surface water concentrations of Cl in Lake Miers to Lake Hoare over time

Average Concentration (mM) 0.1 1 10 100 1000 0

10 Depth (m) Depth 20

Miers 1994-2013 avgd

Hoare 1993-2013 avgd 30 Figure 13: Depth Profile of average Cl concentrations with error bars representing one standard deviation for Lakes Miers and Hoare

1.2

0.8

0.6 Hoare

0.4

0.2 Molar Ratio of Ca in Lake Miers:Ca in Lake Lake in Lake in Miers:Ca Ratio Ca of Molar 0 1992 1997 2002 2007 2012 Year

Figure 14: Plot of the ratio of the concentrations of Ca in the surface water of Lake Miers to Lake Hoare over time

Molar Ratio of Ca:Cl 0.00 2.00 4.00 6.00 8.00 0

10 Depth (m) Depth

Figure 15: Depth Profiles of Ca normalized to Cl in Lake Miers

Molar Ratio of K:Cl 0 0.2 0.4 0.6 0

10 Depth (m) Depth

Figure 16: Depth Profiles of K normalized to Cl in Lake Miers

Molar Ratio of Mg:Cl 0 0.5 1 0

10 Depth (m) Depth

20 Figure 17: Depth Profiles of Mg normalized to Cl in Lake Miers

Molar Ratio of Na:Cl 1.3 1.4 1.5 1.6 1.7 0

10 Depth (m) Depth

Figure 18: Depth Profiles of Na normalized to Cl in Lake Miers

Molar Ratio of SO4:Cl 0 0.1 0.2 0.3 0.4 0.5 0

10 Depth (m) Depth

2- Figure 19: Depth Profile of SO4 normalized to Cl in Lake Miers

Molar Ratio of HCO3:Cl 0 1 2 3 0

10 Depth (m) Depth

- Figure 20: Depth Profile HCO3 of normalized to Cl in Lake Miers

+ Molar Ratio of NH4 :Cl 0 50 100 150 200 0

10 Depth (m) Depth

+ Figure 21: Depth Profile of NH4 normalized to Cl in Lake Miers

Molar Ratio of DOC:Cl 0 0.2 0.4 0.6 0

10 Depth (m) Depth

Figure 22: Depth Profile of DOC normalized to Cl in Lake Miers

Molar Ratio of Si:Cl 0 1 2 3 0

10 Depth (m) Depth

Figure 23: Depth Profile of Si normalized to Cl in Lake Miers

Molar Ratio of F:Cl 0 0.02 0.04 0.06 0.08 0

10 Depth (m) Depth

Figure 24: Depth Profile of F normalized to Cl in Lake Miers

Molar Ratio of Rb:Cl 0 0.0001 0.0002 0.0003 0

10 Depth (m) Depth

Figure 25: Depth Profile of Rb normalized to Cl in Lake Miers

Molar Ratio of Sr:Cl 0 0.005 0.01 0.015 0.02 0

10 Depth (m) Depth

Figure 26: Depth Profile of Sr normalized to Cl in Lake Miers

Molar Ratio of Ba:Cl 0 0.00005 0.0001 0

10 Depth (m) Depth

Figure 27: Depth Profile of Ba normalized to Cl in Lake Miers

Molar Ratio of As:Cl 0 0.000005 0.00001 0.000015 0

10 Depth (m) Depth

Figure 28: Depth Profile of As normalized to Cl in Lake Miers

Molar Ratio of U:Cl 0 0.000005 0.00001 0.000015 0.00002 0

10 Depth (m) Depth

Figure 29: Depth Profile of U normalized to Cl in Lake Miers

Molar Ratio of V:Cl 0 0.0001 0.0002 0.0003 0.0004 0

10 Depth (m) Depth

Figure 30: Depth Profile of V normalized to Cl in Lake Miers

Molar Ratio of Mo:Cl

0 0.00002 0.00004 0.00006 0

10 Depth (m) Depth

Figure 31: Depth Profile of Mo normalized to Cl in Lake Miers

Molar Ratio of Cu:Cl 0 0.00002 0.00004 0.00006 0

10 Depth (m) Depth

Figure 32: Depth Profile of Cu normalized to Cl in Lake Miers

12 1964-1965 1983-1984 10 1994-1995 1996-1997 8 1997-1998

6 2008-2009 2009-2010 4 2010-2011 2011-2012 2 2012-2013 1 2012-2013 2 Concentration (mM)

0 Level Relative to 16 m Depth (m) Depth m 16 to Relative Level 0.000 0.100 0.200 0.300 -2

-4

Figure 33: Cl depth profiles over time in Lake Miers (1964-1965 data from Bell 1967; 1983-1984 data from Green et al. 1988; 2012-2013 data from this study; all other data from MCM-LTER Database)

Na (mM)

0 0.1 0.2 0.3 0

10 Depth (m) Depth

Figure 34: Depth Profile of Na in Lake Miers

100

PPR (μg C/L) 0 1 2 3 4 5 0

10 Depth (m) Depth

Figure 35: Depth Profile of PPR in Lake Miers

101

Chlorophyll-A (μg/L) 0 2 4 6 8 0

10 Depth (m) Depth

Figure 36: Depth Profile of Chl-A in Lake Miers

102

Dissolved Oxygen (mg/L)

0 10 20 30 0

Depth (m) Depth 10

Figure 37: Depth Profile of O2 in Lake Miers

103

2- SO4 Concentration (mM)

0 0.02 0.04 0.06 0

10 Depth (m) Depth

2- Figure 38: Depth Profile of SO4 in Lake Miers

104

+ NH4 Concentration (μM)

0.00 20.00 40.00 60.00 80.00 0

10 Depth (m) Depth

+ Figure 39: Depth Profile of NH4 in Lake Miers

105

DOC Concentration (mM)

0 0.05 0.1 0.15 3.5

5.5

7.5

9.5

11.5

Depth (m) Depth 13.5

15.5

17.5

19.5

21.5

Figure 40: Depth Profile of DOC in Lake Miers

106

NO2 Concentration (μM) 0.00 1.00 2.00 3.5

5.5

7.5

9.5

11.5

Depth (m) Depth 13.5

15.5

17.5

19.5

21.5

Figure 41: Depth Profile of NO2 in Lake Miers

107

Fe Concentration (μM) 0 0.1 0.2 0.3 0.4 0

10 Depth (m) Depth

Figure 42: Depth Profile of Fe+ in Lake Miers

108

δ18O Ratio -29.0 -28.0 -27.0 -26.0 -25.0 0

8 Depth(m)

Figure 43: Depth Profile of δ18O in Lake Miers

109

δD Ratio -230.0 -220.0 -210.0 -200.0 0

6 Depth(m) 8

Figure 44: Depth Profile of δD in Lake Miers

110

APPENDIX B: STREAM DATA

111

112

113

114

115

116

117

APPENDIX C: LAKE DATA

118

119

Ions were not measured for L3 at any depth.

120

Nutrients (μM) μM Isotopes 18 Sample NO2 NO3 + NO2 NH4 PO4 Si DOC δ O δD L3 13m

121

Metals (nM)

Sample Rb Sr Mo Ba U V Cu As

L1 5m 16 1357

L1 15m 22 2346

L1 16m 24 2534 7.3 12 1.5 23 2.1 1.9 L1 17m 26 2607 4.3 12 1.2 18 1.5 1.8 122 L1 18m 29 2693

L1 19m NM NM NM NM NM NM NM NM L2 5m 9.7 792

L2 7m 13 1167

L2 9m 16 1439

L2 11m 17 1606

L2 19m 33 2713

Metals were not measured for L3 at any depth.