Fe and Nutrients in Coastal Antarctic Streams: Implications for Marine Primary

Production in the Ross Sea

THESIS

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

the Graduate School of the Ohio State University

Sydney A. Olund, B.S.

Graduate Program in Earth Sciences

The Ohio State University

2017

Thesis Committee:

Dr. W. Berry Lyons, Advisor

Dr. Yu-Ping Chin

Dr. Michael Durand

Sydney Olund

2017

ABSTRACT

The Southern Ocean (SO) has been an area of much biogeochemical interest due to the role of Fe limitation for primary production. Primary production is associated with increased carbon sequestration, making it important to characterize and quantify the fluxes of Fe and other nutrients to the ocean. Water samples were collected in the

McMurdo Dry Valleys, Antarctica (MDV) from four subaerial streams flowing into the

Ross Sea. They were analyzed for macronutrients (N, P, Si) and Fe to determine the potential impact of terrestrial water input on the biogeochemistry of coastal oceanic waters. Our stream data yield an average filterable composition of N3P1 Si100Fe0.8, which is substantially different from the planktonic composition as demonstrated by empirical measurements, and suggests that these streams are a potential source of Fe and P, relative to N and Si, to coastal phytoplankton communities.

The behavior and potential colloidal/nanoparticulate speciation of the Fe in these streams was investigated through analysis of three physiochemical forms of Fe - environmentally active Fe (acid-soluble/no filtration), filterable Fe (filtered through 0.4

µm), and dissolved Fe (filtered through 0.2 µm). It has been suggested that the dissolved

ii fraction is mainly nanoparticulate and represents a more bioavailable form of Fe, as compared with colloids and particles. Overall, the combined average annual flux from two MDV streams is approximately 240 moles fFe yr-1, which is consistent with previously predicted values. The dissolved fraction of Fe (<0.2 µm) was between 18% and 27% percent of the fFe, meaning the fFe pool is mostly colloidal. While the Fe flux from these streams is several orders of magnitude less than aeolian and iceberg sources, terrestrial streams are expected to become a more significant source of Fe to the Ross

Sea. As the Antarctic climate warms, ice-free regions similar to the MDV should increase in extent and glacier melt. This study questions how, and in what quantities, Fe is solubilized and transported from the landscape into the SO to better inform predictions of Fe fluxes following continued warming

iii

ACKNOWLEDGEMENTS

First and foremost, I would like to thank Dr. Berry Lyons for providing the opportunity to experience the wonders of Antarctic fieldwork, the encouragement to

“do good things”, and the guidance I needed to succeed in my graduate career. I will be forever grateful for the experiences you provided me during these past two years. I’d like to give a huge thanks to Elsa Saelens for assisting with fieldwork and being my Antarctic confidant throughout our adventures on the ice and in the lab. Thank you to the 2015-

16 LTER field crew for introducing me to “the dude” and providing fieldwork assistance, conversation, laughs, and advice. A special thanks to Adam Wlostowski, for letting me tag along on an impromptu helicopter tour of the Dry Valleys and for being a model of scientific enthusiasm that encouraged me to keep questioning and learning throughout the past year and a half. Thank you to Chris Jaros and Christa Torrens for answering my many flow-related questions, and specifically for the use of Chris’s flow model outputs.

Thank you to the Trace Element Research Lab, especially Anthony Lutton, for help and support with my Fe analyses. Thanks to Kathy Welch for teaching me everything from how to use a pipette to how to communicate science effectively. Your assistance with lab work, field work, presentations of data, and life have been invaluable to me. Thanks to

Sue Welch for your help with nutrient analyses, SEM analyses, and feedback on

iv presentations. Thanks to Chris Gardner for your straightforward and extremely helpful review on multiple posters and talks. Thank you to Melisa Diaz for being a great friend, office mate and science coach. Thank you to my committee for providing feedback on this research. Thank you to NSF ANT 1115245 for funding support, to ASC for logistical support, and to PHI for helicopter support. Lastly, thank you to my family for your love and support. You mean the world to me.

VITA

April 25, 1992……………………………………………. Born – Evanston, Illinois

May 2014…………………………………………………… B.S. Geology and Earth Systems,

Environment, and Society, University of

Illinois at Urbana-Champaign

August 2015 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

ACKNOWLEDGEMENTS.……….………………………………….….…………………………………………….....iv

VITA……………………………………..………………………….………………….………………………………………...vi

LIST OF TABLES………………………..….………………………….…..….……………….…………………..……….ix

LIST OF FIGURES…….………………………..….………..….…………………..…………………….…………..…...xi

1 INTRODUCTION..………………………..………………..….………………………………………………….………1

1.1 Rationale for work..….…….……..….………………………..….……………………………….…..1

2 STUDY AREA.. ……………………….………..….………………………..……………..………………………..……6

2.1 Site Description….…………………………………………………………...….………………………..6

3 METHODS……....……….………………..….………………….…..….………………………….………..…………11

3.1 Cleaning. ………………………..….………..…..……………….…………..….….………….……….11

3.2 Sampling….……………………….……………..……………………………...….……………………..11

3.3 Processing…...………………..….………………………..….…………….…………….……………..12

3.4 Analysis………………..…….………………………..….………………….………………………...... 12

4 RESULTS…..….…………….……………..….………………………..….………………………………….………….15

vii 4.1 Fe and nutrients along stream transects and partial diels…………..….….……….15

4.2 Hysteretic behavior in Commonwealth….………………………..………………..……..…18

4.3 Nutrient Stoichiometry……………….….…..………..….…………………….………...…..…..20

4.4 Physiochemical forms of Fe. ………………………..….…….……………………………….….21

4.5 Fe flux. ………………………..….…………….……………………..…....….……………….………...22

5 DISCUSSION….…..….………………………..….…………………….……………..….………………………..….23

5.1 Fe and nutrient ratios in terrestrial stream and the Southern Ocean…....…….23

5.2 Comparison to previously studied fluxes……….………………………..………………….25

5.3 Potential impacts of climate change on streamflow in the MDVs.…...... 26

5.4 Fate of Fe in the Southern Ocean…..………….………………………………………………..27

6 CONCLUSIONS……………………………………………………………………………………………………………29

6.1 Summary of research……………………….…………....…….………………………………….…29

6.2 Future work……………………………………………………………….………….…………………...29

7 REFERENCES CITED…………………….……………………………………………………….…………………….31

APPENDIX A: TABLES AND FIGURES…………………………..………………………….………………………39

APPENDIX B: MAJOR CATIONS AND MAJOR ANIONS.……….………………………….…….………..73

APPENDIX C: TITRATION ALKALINITY AND pH……………..………………………………………………..80

viii

LIST OF TABLES

Table 1. Precision and accuracy of major ion and nutrient data….…………………………………40

Table 2. Precision and accuracy for three Fe analyses using inductively coupled plasma………………………………………………………………………………………………………………………….41

Table 3. Previously calculated Fe fluxes from various sources to the Southern

Ocean…………………………………………..…………………………………………………………….…………...…..42

Table 4. Stream characteristics of coastal MDV streams………………...... ………………….43

Table 5. Annual discharge for the Commonwealth, Wales, Garwood, and Miers

Streams……………………………………………………………………………………………………….……………....44

Table 6. Average Fe concentrations in four coastal MDV streams……………..…..……………..46

Table 7. Average Fe flux from Commonwealth and Wales…..…………..….………………………..47

Table 8. Ratios of average molar concentrations of filterable (< 0.4 µm) nutrients N, P, Si, and Fe for 3 streams………………………..……..….………………………..….………………………..…………48

Table 9. Major cation concentrations for all samples collected……………………………………..74

Table 10. Major anion concentrations for all samples collected……………………………………77

ix Table 11. Titration alkalinity for several samples collected along Commonwealth, Wales,

Garwood and Miers between November 2015 - January 2016……………………………………..81

LIST OF FIGURES

Figure 1. Coastal streams in the McMurdo Dry Valleys, Antarctica………………………….……48

Figure 2. Sampling locations at Commonwealth Stream, Taylor Valley, Antarctica…..…...49

Figure 3. Sampling locations at Wales Stream, Taylor Valley, Antarctica………………..………50

Figure 4. Sampling locations at Garwood Stream, Garwood Valley, Antarctica………………51

Figure 5. Sampling locations at Miers Stream, Miers Valley, Antarctica. ……………………....52

Figure 6. Fe concentrations along Commonwealth Stream…….………..….……………………….53

Figure 7. Fe concentrations along Wales Stream.……………..….………………………..…………….54

Figure 8. Fe concentrations along Miers Stream.. ………………………..………………..….…………55

Figure 9. Fe concentrations along Garwood Stream. ………………………..….………………………56

Figure 10. Hysteretic behavior of Fe in Commonwealth Stream….…………..….………………..57

Figure 11. Soluble reactive phosphorus (SRP) concentrations along Commonwealth…...58

Figure 12. N as NO3- concentrations along Commonwealth…………...... …………….………….59

Figure 13. Si concentrations along Commonwealth….…………..….………………………..………..60

Figure 14. Soluble reactive phosphorus (SRP) concentrations along Wales……….……..….61

Figure 15. N as NO3- concentrations along Wales….………………………..….……………..………..62

Figure 16. Si concentrations along Wales……..…………………………………..….………..…………….63 xi Figure 17. N as NO3- concentrations along Miers….……………………..….…………..…..………..64

Figure 18. Si concentrations along Miers………………..………………………..….………………..…….65

Figure 19. N as NO3- concentrations along Garwood….……………………..….……………..….…66

Figure 20. Si concentrations along Garwood.……………..….………………………..….……………….67

Figure 21. Commonwealth hydrograph during the transect sampling on December 24th,

2015 from 9:55-14:10…………………………..….………………………..….…………………………………....68

Figure 22. Commonwealth hydrograph during the partial diel sampling on January 1st,

2016 from 12:40-16:15…………………………..….……………………..…..….………………………..…..….69

Figure 23. Concentration-discharge plot of nutrients collected at the delta of

Commonwealth on December 24th... ………………………..…….………..….……………………..…..70

Figure 24. Concentration-discharge plot of major cations collected at the delta of

Commonwealth on December 24th………………………..….……………………..….……..……..….….71

xii

1. INTRODUCTION

1.1 Rationale for Work

Nutrient limitation in the oceans is important to understand because primary production can lead to the sequestration of carbon via burial in marine sediments. As such, an increase in macro or micronutrients could increase the marine biological uptake of CO2. Oceanic circulation is primarily responsible for the distribution of nutrients in

Earth’s oceans, and upwelling has created a high macronutrient (N, P) environment for phytoplankton in the surface waters of the Southern Ocean (Moore et al., 2013). These macronutrients are derived mainly from the remineralization of sinking organic matter, which is brought to the surface of the Southern Ocean via strong upwelling currents

(Moore et al., 2013). Typically, nitrate is the limiting nutrient in the surface waters of the ocean (mid and low latitudes), and because of this, high nitrate waters should have high phytoplankton biomass. Instead, the Southern Ocean is characterized as ‘high-nitrate low-chlorophyll’, where primary productivity is limited by the micronutrient iron (Fe) instead of by macronutrients (Martin et al., 1990; Moore et al., 2013).

One of the earliest investigations into Fe limitation in the Southern Ocean compared the geochemistry of the productive coastal waters of Antarctica to the lower productivity off-shore waters, and revealed that Fe concentrations in the coastal waterswere 50-60

1 times higher than off-shore waters (Martin, et al., 1990). The Fe-rich coastal waters were associated with 30 times more C-fixation (Martin et al., 1990). Additionally, a number of

Fe fertilization experiments have shown that the uptake of CO2 increases substantially with increased availability of Fe (Watson, et al., 2000). Itwas noted, however, that such fertilization experiments only yielded a temporary biological response to increased Fe, and that transport of fixed carbon to depth is required for long-term carbon sequestration from this enhanced primary productivity (Watson et al., 2000). More recently, a review on metal uptake by phytoplankton throughout the global oceans showed that diatoms from the Southern Ocean have a lower Fe quota than some diatoms isolated from coastal and oligotrophic environments, which may be a strategy that has developed to cope with the Fe-limited waters in the Southern Ocean (Twinning and Baines, 2017).

Due to the importance of Fe in the biological fixation of CO2 in the Southern

Ocean, several sources and fluxes of Fe to the Southern Ocean have been postulated, and these fluxes have been estimated. The largest estimated contributions come from icebergs (Raiswell, 2011). A recent study showed increased chlorophyll-a levels in the wake of a 50-km iceberg (termed “giant icebergs”) (Duprat, et al., 2016). It is thought that half of the iceberg discharge into the Southern Ocean comes from giant icebergs

(>18 km) (Duprat, et al., 2016). Other sources of Fe include aeolian dust deposition

(Edwards and Sedwick, 2001), diffusion from oceanic sediments (Gerringa et al., 2012), and subglacial melt direct from the continent (Death et al., 2014). Several studies have

2 argued that the occurrence of off-shore phytoplankton blooms are due to inputs from the shelf sediments (Dulaiova et al., 2009) or sub-glacial melt (Gerringa et al., 2012) and these sources can provide the necessary Fe for the bloom to proceed.

Recent work has demonstrated that stream flow from ice-free areas of

Antarctica, such as the McMurdo Dry Valleys (MDV), is a potential source of filterable Fe

(<0.4 m, termed fFe) to the Southern Ocean, with the potential to provide a mean of

10.6 g, or 0.19 mol fFe/L (Lyons et al., 2015). While this concentration, when converted to a per area basis yield, is small in comparison to other estimated sources of iron into the Southern Ocean, climate change, and subsequent glacier retreat, cryospheric loss, and increased melt could likely enhance increased streamflow, leading to a higher flux of

Fe from this source in the future (Lyons et al., 2015). This study aims to further quantify the terrestrial stream input of Fe to the Southern Ocean. This work builds from the early work of Lyons et al. (2015), and specifically seeks to:

1. Identify the sources and character of Fe in four MDV streams that discharge

directly into the Southern Ocean (SO). When studying the biogeochemistry of

Fe, it’s important to distinguish between the various Fe fractions – particulate,

colloidal, nanoparticulate and aqueous – due to the relationship between

physiochemical form and bioavailability. This is complicated by the fact that the

standard operational definitions of these fractions do not truly separate each

chemical form (Raiswell and Canfield, 2012; Raiswell, 2011). In this study, we

defined three fractions of Fe: environmentally-active Fe (eFe) which is non-

3 filtered, weak acid-soluble Fe (Lyons et al., 1990); filterable Fe (fFe), which is the

fraction that passed through a 0.4 m filter, and probably includes colloidal,

nanoparticulate, and perhaps some dissolved species of Fe; and dissolved Fe

(dFe), which is the fraction that passes through a 0.2 m filter and is expected to

contain mostly nanoparticles and truly dissolved or aqueous species (Raiswell

and Canfield, 2012). While nanoparticles are not as bioavailable as the truly

aqueous species, they are considered labile due to their high solubility and

reactivity (Raiswell and Canfield, 2012; Raiswell, 2011).

2. Compare nutrient stoichiometry in streams to published phytoplankton

stoichiometry in the Ross Sea/Southern Ocean. The Redfield Ratio, 16N:1P,

represents the molar stoichiometry of macronutrient uptake of marine

phytoplankton. This ratio has been expanded to include iron (Ho et al., 2003;

Quigg et al., 2003) and silicon (Brzezinski et al., 2003) to the following generally

accepted stoichiometry for marine phytoplankton of 16N:1P:60Si:0.0075Fe.

Initial N:P ratios of 16:1 have been shown to vary spatially in the upper ocean,

and Martiny et al. (2013) described a latitude-dependent pattern, where cold,

nutrient-rich high-latitude waters, such as the Ross Sea/Southern Ocean,

exhibited a ratio of 13N:1P. The work below compares stream water

nutrient/micronutrient stoichiometry to the known phytoplankton ratios in order

to determine how they compare, and if Antarctic stream input has the potential

to influence the biogeochemistry of the coastal ocean.

4 3. Quantify the flux of Fe to the Ross Sea. As ice-free areas increase in Antarctica,

quantifying the mass flux of Fe from terrestrial sources will become more

important. In the initial work of Lyons et al., (2015) on the McMurdo Dry Valley

streams, most of the streams sampled flow into closed-basin lakes, not directly

into the marine environment. In this work, we focused on four streams that

discharge directly into the Ross Sea.

2. STUDY AREA

2.1 Site Description

The McMurdo Dry Valleys area (MDV), a polar desert, is the largest ice-free region in Antarctica, with an ice-free area in the central and south MDV of 3800 km2

(Levy, 2013). This study focuses on four glacial meltwater streams in three of the valleys that make up the MDV region: Commonwealth Stream, Wales Stream, Miers Stream, and Garwood Stream (Figures 1-5). The first two streams are in the easternmost region of Taylor Valley, and the last two streams are in the southern portion of the region in

Miers and Garwood Valley (Figure 1). All of these streams discharge into the Southern

Ocean and flow over glacial drift deposits from both local alpine glaciers and the

East/West Antarctic Ice Sheets. The valley floors and fixed stream channels consist of glacial deposits of material from lithologies all around the McMurdo region – the Beacon

Supergoup sandstone, and the Ferrar Dolerite, the older early Paleozoic crystalline basement and the McMurdo Volcanics (Hall and Denton, 2000). The McMurdo Volcanic component occurs in the highest amounts in the youngest tills in the eastern portions of most of these valleys, and was transported by the West Antarctic Ice Sheet (WAIS) during its advance at the Last Glacial Maximum.

6 Each stream is contained within a fixed channel, but they have diverse geomorphologies, both between the streams and within each stream (table 4).

Commonwealth Stream is marked by three major changes in geomorphology. In the west, nearest the meltwater source, the Commonwealth Glacier, it is relatively flat, but rapidly cuts down into a steep valley through buried ice thought to have been left by the advance of the WAIS during the last glacial maximum (Hall & Denton, 2000; Levy et al.,

2013). This change occurs 1.75 km downstream of the glacier, producing a thermokarst feature by the downcutting and loss of this buried glacial ice. Near its outlet (3.2 km downstream), Commonwealth Stream forms a wide, braided delta, a common characteristic in most of the streams sampled in this study (Figure 2). Except for its first 2 km, where it is much narrower and steeper, Wales Stream maintains a wider bed (up to

130 m wide) and moderate slope for all of its length (Figure 3). Garwood Stream, in

Garwood Valley, has prominent meanders, which are likely due to additional flow from drainage of Lake Colleen, located behind Garwood Glacier (Levy et al., 2013). Like

Commonwealth Stream, Garwood has a steep v-shaped stream bed, and prominent thermokarst formed in what is thought to be WAIS ice deposited during the Last Glacial

Maximum (Levy et al., 2013). However, it differs from Commonwealth in its outlet morphology, as it is marked by several ponds of varying size rather than a simple delta.

Some of the larger ponds have ice covers, and most of the ponds may be connected to the ocean and incur tidal induced mixing (Figure 4). The southernmost stream sampled is in Miers Valley. Miers Valley is unusual in the MDV as it has a flow-through lake with

7 two inflowing streams (Adams and Upper Miers) and one outflowing stream (Lower

Miers). Adams Stream, which is the longer of the two inflowing streams, has relatively steep slopes and large boulders near the terminus of Adams glacier, which leads to the development of small rapids. Further downstream, Adams is heavily bifurcated due to the decrease in slope. The entirety of the Upper Miers is similarly bifurcated and flat, forming a “wetlands” area prior to entering the lake. The Miers outflowing stream has a more persistent stream channel and typically accommodates higher flows than either of the two inflowing streams (Figure 5). Buried ice is a prominent feature throughout the

MDV (Fountain et al., 2014). As noted above, it is attributed to the advance of the Ross

Sea Ice sheet (grounded Ross Sea ice shelf, fed by the West Antarctic Ice Sheet) into these valleys during the LGM, where it was buried by glacial drift, as well as by later lacustrine and fluvial deposits (Hall and Denton, 2000; Levy et al., 2013). This buried ice probably contributes some meltwater to both Commonwealth Stream and Garwood

Stream.

The MDV streams flow from 4-10 weeks during the austral summer and some have been regularly sampled by the McMurdo Dry Valleys Long-Term Ecological

Research program (MCM-LTER) since 1993 (McKnight et al., 1999). Many of the streams in Taylor Valley, including Commonwealth, have been gauged routinely by the MCM-LTER program. Flow data are collected approximately every 30 minutes throughout the flow season with a network of stream gauges and Campbell CR10 dataloggers (McKnight et al., 1999). Among the streams investigated in this study, Commonwealth Stream is the

8 only stream with a long-term flow record (23 seasons). Miers Stream and Garwood

Stream were gauged by New Zealand scientists before the MCM-LTER was established, and therefore have only partial records: 1990-91 and 1988-91, respectively. Recently, the

MCM-LTER project began to gauge Miers on a regular basis (i.e. starting 2015). A summary of the annual average discharge for these three streams can be found in Table

5. In the absence of gauged measurements, flow values for Wales Stream were determined by a model using measured temperature variations on the valley floor and adiabatic lapse rate vs. elevation on the Wales Glacier (Jaros, 2002). The model values have compared favorably to streamflow measurements in the Fryxell basin portions of

Taylor Valley. The model results have proven to be quite useful in providing annual flow variations to what has been qualitatively observed from other glacial streams on the

Southeastern portion of Taylor Valley (Lyons et al., 2012).

All of these seasonally ephemeral streams experience large daily and seasonal variations in flow due to the position of the sun relative to the glacier, albedo changes from snowfall events, summer katabatic wind events, as well as with changes in temperature (McKnight et al., 1999; Nylen et al., 2004). No groundwater or overland flow input have been observed in these streams. For these streams, the primary water- rock interactions and related solute production occur in the area immediately below and alongside the stream channel, the hyporheic zone (Gooseff et al., 2002). The depth of the hyporheic zone increases up to 60 cm throughout the austral summer as the active permafrost layer melts (McKnight et al., 1999). In general, MDV stream solutes are

9 derived from chemical weathering and salt dissolution of materials within the streambed and the hyporheic zone (Nezat et al., 2001; Gooseff et al., 2002; Welch et al.,

2010) or directly from glacial melt (Lyons et al., 2003). There is also potential dissolution and chemical weathering of aeolian materials either within the stream channels or in cryoconites on the glacier surfaces during the melt season (Lyons et al., 2003). Fe, in particular, is thought to be derived primarily from chemical weathering within the hyporheic zone. Lyons et al. (2015) discussed the importance of high water-rock ratios for the introduction of fFe into MDV streams and that dissolution of aeolian material did not account for the observed fFe concentrations. In addition, organic matter within and along the edges, and in the hyporheic zones may induce redox reactions (Krause et al.,

2011; McKnight et al., 2004), impacting the solubility of Fe in these systems. Thus, the streams with greater hyporheic zone areas and longer water residence times are expected to have higher concentrations of fFe. Streams in eastern Taylor Valley have low

N:P, while streams in western Taylor Valley have high N:P and are P-limited (Welch et al.,

2010). This is a result of the different ages and lithologies of the tills throughout Taylor

Valley, as the more abundant McMurdo Volcanic debris in the eastern portions of the valleys contain more P than the western tills (Barrett et al., 2007).

3. METHODS

3.1 Cleaning

Fe samples were collected and filtered into Nalgene HDPE bottles that were soaked in a 1% HCl solution and rinsed three times with ultra-pure water. Major ion (Li,

Na, K, Mg, Ca, SO4, F, Cl, Br), Nutrient (NO3- and NO2-, soluble reactive phosphate, or

SRP, and NH4) and dissolved Si or H4SiO4 samples were collected and filtered into

Nalgene HDPE bottles that were soaked in de-ionized ultrapure (DI) water (18.2 M) and rinsed three times with ultra-pure water.

3.2 Sampling

Stream water samples were collected in Taylor Valley, Garwood Valley, and Miers

Valley during a month of the flow season from December 24th, 2015 to January 22nd,

2016. Samples were collected along the length of each stream from just below the glacial stream source to the mouth of the stream as it discharges into the ocean. In addition, samples were also collected close to the mouth of the stream over a 4 or 5-hr time interval. The bottles were rinsed 3 times with stream water prior to sample collection and the sample collector stood downstream and wore clean vinyl gloves to minimize contamination.

3.3 Processing

Stream water samples were filtered within 24 hours of collection. Major ion, nutrient, and H4SiO4 samples were filtered through 0.4 m Whatman Nuclepore polycarbonate membrane filters. DOC samples were filtered through Whatman glass microfiber filters of 0.7 m pore size (grade GF/F) that had been combusted for four hours at 450 C. Iron samples were separated into three aliquots and processed differently: (1) one aliquot was left unfiltered (termed “environmentally active” Fe, or eFe by Lyons et al. (1990)); (2) one was filtered through a 0.4 m Whatman Nuclepore filter (filterable Fe, or fFe); and (3) one was filtered through a 0.2 m Poretics filter (dissolved Fe, or dFe). In previous work, filtrates through 0.2 m filter have been described as containing colloidal, nanoparticulate, and aqueous species. However, these filtrates are mainly nanoparticulate (Raiswell and Canfield, 2012). For the sake of brevity, and as described in the literature, we have termed this fraction “dissolved Fe”.

The filtered samples for major ions, nutrients, H4SiO4, DOC, and all iron fractions were stored chilled at approximately 4 C until analysis. All DOC and iron samples were acidified by the addition of 0.1% J.T. Baker Ultrex HCl. The nutrient and H4SiO4 samples, the preserved iron samples, and several cation samples that were not analyzed on

McMurdo Station were sent back to The Ohio State University for analysis.

3.4 Analysis

12 Major ion analyses (including nitrate and phosphate) were done by ion chromatography (IC) on the Dionex DX-120 (Sunnyvale, CA) in McMurdo or at The Ohio

State University (major cations for Miers, n=8). The details of analysis have been described elsewhere in Welch et al., 2010. However, a Thermo IonPac AS14A analytical column was used for the anion analysis in this study instead of the Dionex IonPac AS14 analytical column described in Welch et al. (2010). Nutrient (NO3- and NO2-, SRP, NH4) and H4SiO4 analyses were measured on a Skalar San++ Automated Wet Chemistry

Analyzer at The Ohio State University. When nitrate concentrations were compared between the Skalar and the IC, it appeared the samples had undergone some analyte loss between the time they were analyzed on the IC in McMurdo, and when they were analyzed on the Skalar at The Ohio State University (~90 days). Therefore, only the IC measurements were used to quantify nitrate concentrations. The SRP concentrations were comparable between the two instruments, so Skalar measurements were used to quantify phosphate. DOC analyses were done at McMurdo Station on the Shimadzu

TOC-V which uses an acidification and sparging method to remove any inorganic carbon from the sample and a 680 C combustion catalytic oxidation method to detect non- purgeable organic carbon (NPOC). 3-5 injections of 150 L were done for each sample. All

DOC measurements were at or below the lowest standard (0.2 ppm), which is near the detection limit. Therefore, DOC data were not included in data analyses.

The three aliquots for iron were analyzed differently according to their processing/filtration method. Unfiltered samples, or eFe, were analyzed on the Perkin

13 Elmer Optima 4300 DV inductively coupled plasma optical emission spectrometer (ICP-

OES), samples filtered through 0.4 m filters, or fFe, were analyzed on the

Thermofinnigan Element 2 inductively coupled plasma sector field mass spectrometer

(ICP-SFMS), and samples filtered through 0.2 m filters, or dFe, were analyzed on the

PerkinElmer NexION inductively coupled plasma dynamic reaction cell mass spectrometer (ICP-DRC-MS) with methane as the reaction cell gas (Tanner and Bandura,

2003). For all Fe analyses, samples were measured in triplicate and the mean value was used for the final concentration in each. A wavelength of 234.349 nm was used in all ICP-

OES measurements and a weight of 56 amu was used in all mass spectrometry measurements. However, multiple wavelengths and masses were monitored to check for consistency. Accuracy and precision for all analyses can be seen in Tables 1 and 2.

Titration alkalinity and pH were determined on samples collected from various locations along Commonwealth, Wales, Miers, and Garwood during annual monitoring sampling by the MCM-LTER Stream Team. Titration alkalinity was performed with the use of either

0.1 N or 0.01 N HCl on samples of 15 mL. Precision is estimated to be less than 2% difference between duplicate measurements. Alkalinity values range from 200 – 1700 M and the data can be found in Appendix C. pH was determined using a Beckman pHi 265 portable meter shortly after sample collection, during the filtering process. pH data range from 6.6 – 8.3 and can be found in Appendix C.

4. RESULTS

4.1 Fe and nutrients along stream transects and during partial diels

This study focused on changes in several analytes throughout space (spatially- distributed, or sampling downstream) and time (temporally-distributed, or sampling at the delta). The analytes include major ions (Li, Na, K, Mg, Ca, SO4, F, Cl, Br), various physiochemical forms of Fe (environmentally-active (eFe), filterable (fFe), and dissolved

(dFe)), and nutrients (NO3-, soluble reactive phosphate, or SRP, and H4SiO4). The results of the above analyses are summarized below.

Stream transects

The eFe and fFe concentrations in Commonwealth range between 1.2 - 23 M and between 0.03 – 0.37 M, respectively (Figure 6). The eFe and fFe concentrations in Wales range between 0.27 – 138 M and 0.01 – 0.29 M, respectively (Figure 7). The eFe and fFe concentrations in Miers range between 0.44 – 11 M, and 0.001 - 0.3 M respectively

(Figure 8). The eFe and fFe concentrations in Garwood range between 4.2 – 10.5 M and

0.22-0.29 M, respectively (Figure 9).

The NO3-, SRP, and H4SiO4 concentrations in Commonwealth range between 1.7

– 4.4 M, 0.3 – 3.4 M, and 23 – 95 M, respectively (Figures 11-13). The NO3-, SRP and

H4SiO4 concentrations in Wales range between below the detection limit (BDL) <0.71

15 M– 6.6 M, 0.3 – 2.4M, and 34 – 142 M, respectively (Figures 14-15). The NO3-, SRP and

H4SiO4 concentrations in Miers range between below the detection limit (BDL) <0.71 M

– 0.09 M, below the detection limit (BDL) <0.17 – 0.33 M and 8.6 – 58 M, respectively

(Figures 16-17). Only two out of nine of the Miers samples were above the detection limit for SRP. The NO3- and H4SiO4 concentrations in Garwood range 1.1 – 1.2 M and 27

– 36 M, respectively (Figures 18-19). The SRP concentrations in all Garwood samples were below the detection limit (0.17 M).

Generally, Fe and nutrient concentrations increase downstream in all of the streams sampled. A few exceptions include NO3- in Miers Stream (Figure 16), which decreases after passing through Lake Miers, and a decrease in eFe near the deltas of

Garwood and Wales. Previous studies on Lake Miers have demonstrated that it behaves as a “sink” for NO3- and other solutes, due either to biological uptake or potentially due to density-driven mixing, which is intensified by recent warming and subsequent isotherm deepening (Fair, 2014). The cause for the eFe decrease is probably due to particle settling as the flow speed decreases as it approaches the delta or removal within the hyporheic zone, both of which become more dominant features in the hydrologic landscape near the stream outlets. Flow data with fine temporal resolution are not available in these streams, but our field notes indicate an apparent decrease in flow midway through the Wales transect, which would have aided suspended load deposition.

Stream partial diels

16 The eFe, fFe, cFe, and dFe concentrations in Commonwealth range between 230 -

320 M, 0.2 – 2 M, 0.06 – 1.8 M, and 0.1 – 0.2 M, respectively. The eFe, fFe, cFe, and dFe concentrations in Wales range between 2.4 – 46 M, 0.1 – 0.2 M, 0.07- 0.17 M, and 0.03

– 0.5 M, respectively. The eFe and fFe concentrations in Miers range were between 6 –

12 M, and 0.24 - 0.25 M respectively.

The NO3-, SRP and H4SiO4 concentrations in Commonwealth range between 1.9

– 2.2 M, 1.7-2.2 M and 36 – 47 M, respectively. The NO3-, SRP and H4SiO4 concentrations in Wales range between 4.5 - 11 M, 1.9 – 2.4 M and 130 - 144 M, respectively. The H4SiO4 concentrations in Miers range between 43 – 47 M.

Typically, the concentration ranges are narrower during these partial diels than in the transect sampling. This is expected, given the consistent location of diel sampling.

The average concentrations observed during the diels were similar concentrations as those observed in the terminal transect samples, except for Commonwealth. In comparison to the highest eFe concentration observed in the Commonwealth transect

(23 M), the diel eFe concentrations were about an order of magnitude higher, ranging from 230 to 320 M. These higher concentrations during the diel are probably attributed to variations in flow (5 L/s on average during the transect and 190 L/s on average during the diel).

To test this hypothesis, nutrient and major cations data were plotted on a log/log concentration-discharge plot (Figures 23-24). The trendlines for these data follow the equation y=mxb, where the value of b indicates how the solute concentration changes

17 with different flows. Negative b values indicate dilution (discharge increases, concentration decreases), positive b values indicate rapid dissolution (discharge increases, concentration increases), and b values equal to 0 indicate pure chemostasis

(constant concentration across discharge values that vary several orders of magnitude).

Chemostasis and dilution behavior have both been observed in MDV streams

(Wlostowski et al., 2016). Nitrate was the only analyte that exhibited fairly chemostatic behavior (b=0.08), while the others, both nutrients and major cations, exhibited slight to extreme dilution behavior (b= -0.16 to -3.5). It should be noted, though, that these data were collected during the peak of one hydrograph, and therefore the discharge does not vary by a large magnitude. Nonetheless, in the case of fFe, concentrations varied up to an order of magnitude across only a 2x variability in discharge.

4.2 Hysteretic behavior in Commonwealth

Figure 10 shows concentration-discharge plots (C/Q plot) of the Commonwealth diel, which can be used to identify the dominant flow component supplying different solutes during a single hydrographic event. Evans and Davies (1998) used a three- component model – surface event water (CSE), soil water (CSO), and groundwater (CG) – to create six hysteresis C/Q plots with different dominant flow components. Two of those plots exhibit negative concavity (low concentrations at very low flows) and are thus characterized by a weak groundwater influence (CSE and CSO > CG). These hysteresis loop patterns are especially relevant in the McMurdo Dry Valleys, because

18 permafrost prevents the development of groundwater there (CG=0). It has been assumed that these types of patterns in the Taylor Valley streams are due to hyporheic zone influence (Fortner, et al., 2013). The dominant flow component, either CSE or CSO in this case, is shown by an increase in solute concentration either during the rising limb or the falling limb of the hydrograph. In CSE-dominated streams, solute concentrations increase during the hydrograph’s rising limb due to rapid dissolution along the streambed from that initial pulse of water. In CSO-dominated streams, solute concentrations increase during the falling limb due to the draining of solute-rich water from the hyporheic zone.

While figure 10 shows a fairly irregular pattern, the following relationships can be observed: 1. For the eFe “loop”, concentrations increase during the major increase in flow and 2. For the fFe and dFe “loops”, concentrations decrease during the major increase in flow and increase during the falling limb of the hydrograph. This suggests that eFe is particle-associated while the fFe fraction is likely derived from water:rock interactions in the hyporheic zone and may be undergoing dilution as flow increases. By plotting multiple analytes in this way, one can use hysteresis loops to assess the dominant source for each analyte during one hydrographic event, rather than the dominant flow component overall. Unfortunately, these plots could not be replicated for the other streams at this time due to the absence of the necessary flow data. The hydrograph for this event can be found in Figure 22.

19 4.3 Nutrient Stoichiometry

Data from Ho et al. (2003) and Brzezinski et al. (2003) were used to extend the

Redfield Ratio to include Fe and Si, respectively. Samples utilized in Ho et al. (2003) were either filtered through 0.5 m or 0.8 m filters before chemical analysis by ICP-SFMS, and therefore the Fe measured most likely resembles our fFe, physiochemically. Using this information, therefore, the extended Redfield Ratio for marine phytoplankton is

16N:1P:60Si:0.0075Fe. The nutrient stoichiometry for Commonwealth, Wales and

Garwood were evaluated to understand the potential that increased flow into the Ross

Sea could have on the biogeochemistry of phytoplankton communities in the Ross Sea.

Molar concentrations of filterable (<0.4 m) nutrients – Fe, N, P, and Si – were normalized to P or N and compared to the stoichiometric ratios of marine phytoplankton -

16N:1P:60Si:0.0075Fe (Brzezinski et al., 2003; Ho et al., 2003).

In Commonwealth Stream, NO3- concentrations have an average of 2 M, SRP concentrations have an average of 2 M, Si concentrations have an average of 42 M, and fFe concentrations have an average of 0.75 M. When normalized to SRP, Commonwealth has an average nutrient stoichiometry of 1N:1P:21Si:0.38Fe. In Wales Stream, NO3- concentrations have an average of 7 M, SRP concentrations have an average of 2 M, Si concentrations have an average of 140 M, and fFe concentrations have an average of

0.15 M. When normalized to SRP, Wales has an average nutrient stoichiometry of

3N:1P:61Si:0.07Fe. In Garwood (n=1), the NO3- concentration is 1 M; the SRP concentration is below the detection limit (<0.17 M); the Si concentration is 36 M; and

20 the fFe concentration is 0.3 M. When normalized to an SRP value of 0.17M, Garwood has an average nutrient stoichiometry of 6N:1P:210Si:2Fe.

When compared to the expanded phytoplankton ratio, it is clear that these streams are a potential important source of Fe (Fe:P >> 0.0075; Fe:N>>0.0005) and P

(N:P<<16), where Fe:P ratios are up to 2 orders of magnitude higher and N:P ratios are up to 16 times lower (Table 8). Even more compelling are the stream dFe:P ratios, which are still higher than phytoplankton uptake ratios of Fe:P as the dFe:P ratios for

Commonwealth and Wales are 0.01 and 0.04, respectively.

4.4 Physiochemical forms of Fe

We calculated the fraction of each physiochemical form of Fe present in

Commonwealth Stream and Wales Stream (Table 6). As previously mentioned, eFe, fFe, and dFe are the unfiltered, <0.4 M, and <0.2 M fractions, respectively. The “colloidal” fraction, or cFe, was not directly measured, but instead determined by subtraction (cFe = fFe – dFe). For Commonwealth, fFe makes up 0.28% of the acid-soluble Fe, and cFe and dFe make up 82% and 18% of the filterable fraction, respectively. For Wales, fFe makes up 1.25% of the acid-soluble Fe, and cFe and dFe make up 73% and 27% of the filterable fraction, respectively. This is consistent with predictions and findings in the literature that the filterable fraction is mainly colloidal (Boye et al., 2010; Raiswell and Canfield,

2012).

21 4.5 Fe flux

Table 7 gives a summary of the Fe fluxes described below. For Commonwealth

Stream, the average concentration of the diel samples for each physiochemical form of

Fe was multiplied by either the mean annual discharge and the 2015-2016 annual discharge. For Wales Stream, the average concentrations were multiplied by the model- estimated flow to produce Fe fluxes into the Ross Sea. The calculations could not be done for the other streams because there are no long-term discharge data for them and the more recent gauged data are currently unavailable. The average annual (1993-2016) fluxes of eFe, fFe, cFe, and dFe for Commonwealth are 83,000 mol/yr, 232 mol/yr, 192, mol/yr, and 40 mol/yr, respectively. The average annual (1990-2013) fluxes of eFe, fFe, cFe, and dFe for Wales are 12 mol/yr, 0.15 mol/yr, 0.11 mol/yr, and 0.04 mol/yr, respectively. The 2015-2016 flux of eFe, fFe, cFe, and dFe for Commonwealth are

200,000 mol/yr, 551 mol/yr, 455 mol/yr, and 95 mol/yr, respectively. The 2015-2016 annual discharge was more than double the mean annual discharge for Commonwealth, leading to above average Fe fluxes to the Ross Sea during that year. On average, Taylor

Valley streams contribute a combined flux of 84,440 mol eFe/yr, 243 mol fFe/yr, 200 mol cFe/yr, and 43 mol dFe/yr to the SO. While the Fe fluxes for Commonwealth are 1-2 orders of magnitude larger than the Wales Fe fluxes, the fraction of fFe in Wales is about

5 times higher than that of Commonwealth, suggesting Wales could be a more important source of bioavailable Fe.

5. DISCUSSION

5.1 Fe and nutrient ratios in terrestrial streams and the Southern Ocean

The similarity between the nutrient stoichiometry in marine waters and phytoplankton composition was striking when it was first observed by Alfred Redfield in

1958 (Redfield, 1958). Recently, interest in primary productivity in the Southern Ocean

(SO) has revealed variability in nutrient uptake ratios, which may be due to various chemical and biogeochemical factors. These factors include micro/macronutrient and light availability, cell size, and temperature (Moore et al., 2013; Klunder et al., 2014), and these factors can effect nutrient uptake and, hence, nutrient ratios in the phytoplankton in interrelated ways. For example, some sites in the Drake Passage show higher N uptake, relative to Si and P, with increased dFe concentrations. However, these sites also had a larger percentage of large (>5000 m3) diatoms compared with sites in the Weddell

Sea, which showed no relationships with dFe and nutrient uptake (Klunder et al., 2014).

Thus, increased N uptake appeared to be driven by both micronutrient availability (Fe) and cell size.

Different phytoplankton species can also play a role in nutrient uptake in the ocean. In an analysis of nutrient uptake in the Ross Sea, Arrigo et al. (1999) identified variable nutrient uptake ratios between two dominant phytoplankton in the Ross Sea –

23 Phaeocystis antarctica, a colony-forming haptophyte, and diatoms. Phaeocystis antarctica were more efficient in utilizing PO4, fixing up to 56% more CO2 than per mol PO4 ( Arrigo et al., 1999). Since MDV streams exhibited higher P:N ratios than the Redfield P:N ratio, and are therefore a source of P relative to N to the coastal Ross

Sea, it would follow that, given everything else being equal, this could greatly favor

Phaeocystis antarctica growth in the coastal phytoplankton community relative to diatoms. Further work is necessary to support this claim.

Metal uptake by phytoplankton has also been studied using several methods, including culture experiments, bulk particulate ratios, and observations of seawater nutrient concentration following increases in primary productivity. In a recent review of these approaches, Twinning and Baines (2017) determined metal quotas (normalized to nutrients) for phytoplankton throughout the global oceans. They found that Zn was as abundant or more abundant than Fe in marine phytoplankton, which suggests that Zn has the potential to be co-limiting with Fe in the Southern Ocean (Twinning and Baines,

2017). The general metal abundance for the Southern Ocean is Zn>Ni>Cd=Cu>Fe>Co

(Twinning and Baines, 2017). There have been a few recent investigations of dissolved trace metals (fMe) in MDV streams, and in general, they show a metal abundance of

Fe>Zn>Cu>Co=Ni>Cd (Green et al., 1986; Fortner, et al., 2013). This suggests MDV streams would be a more important source of Fe relative to Zn for phytoplankton in the coastal Ross Sea. However, zinc measurements have not been performed in MDV

24 streams since 1985, and may be slightly different due to advances in analytical methods and instrumentation.

5.2 Comparison to previously studied fluxes

The fFe concentrations measured in this study are comparable to the average fFe concentrations previously determined by Lyons et al. (2015) (Table 6). The authors found that subaerial streams are currently a very minor source of fFe to the coastal ocean compared with aeolian sources and icebergs that have been estimated to currently provide several orders of magnitude more fFe and dFe. These data presented within support this notion. Dulaiova et al. (2009) calculated an Fe demand of 1.1 – 4 × 105 mol

Fe for a 22,500 km2 phytoplankton bloom in the Drake Passage. Using the residence time for dFe in coastal waters of approximately 4 days from Dulaiova et al. (2009), a range of 4-10 weeks in the MDV glacier streamflow season, and our mean dFe flux from

Commonwealth and Wales Streams, the flux could only account for the Fe demand of

0.14 – 1.23 km2 of this expansive bloom or 0.0006-0.0056% of the Fe demand. This also assumes that all dFe is both bioavailable and utilized. In another study of primarily

Phaeocystis Antarctica bloom in the Pine Island Polynya, it was estimated that 7 + 5 × 10-

6 mol Fe m-2 d-1 was needed to sustain the growth (Gerringa et al., 2012). This bloom lasted 73 days, and spanned up to 16,890 km2 (Arrigo and van Dijken, 2003). Using this information, the dFe flux from Taylor Valley streams could provide the necessary Fe for just 0.09 km2 – 0.2 km2 of the bloom. Clearly, terrestrial stream input of dFe would be a

25 very minor source to large events such as these, but it is important to note that our estimates of the average daily flux of dFe only include that which is provided by

Commonwealth and Wales. Future studies of other coastal streams around Antarctica will help to truly quantify the magnitude of dFe sourced from terrestrial streams. In addition, future climate warming should be expected to increase this source of Fe, as warming summer temperatures will greatly enhance the melting of coastal glaciers.

5.3 Potential impacts of climate change on stream flow in the MDV

Several landscape and hydrological changes are expected to occur in the Dry

Valleys as greenhouse gas concentrations increase and warming continues (Fountain et al., 2014; Lyons et al., 2015). These changes include higher annual discharge from increased glacial melt, the deepening of the active permafrost layer, the melting of buried glacier ice and ice-cored morainal materials which would lead to larger hyporheic zones, and greater hydrological connectivity of the landscape. Indeed, there has been an increase in flow in Commonwealth observed, where in the last 15 years, 2001-2016, the annual flows have been higher than the first 8 years of the MCM-LTER record, 1993-2001

(http://mcmlter.org). Some of the most vulnerable locations for landscape change lie along the relatively warm coast and include those that are underlain by buried ice, which we observed throughout Commonwealth and Garwood, and to some extent,

Miers (Fountain et al., 2014; table 4). One of the most important influences in determining the dFe concentrations in these streams is likely the deepening of the active

26 layer, and subsequent broadening of the hyporheic zones. As noted in the hysteretic behavior of the various physiochemical forms of Fe in Commonwealth (figure 10), the hyporheic zone (i.e. active zone of chemical weathering) is an important source of dFe and fFe because of the high water:rock ratios within the hyporheic zone and its importance in promoting redox reactions that can reduce Fe3+ to more soluble Fe2+

(McKnight et al., 2004). In addition, the retreat of coastal glaciers could lead to more exposed (subaerial) surface providing additional sources of Fe. Thus, larger hyporheic zones could lead to increased dFe and fFe concentrations in these streams. These increases on the Fe fluxes from the terrestrial environment (increased melt, larger hyporheic zones) that will be produced by warming temperatures could possibly provide a small, but potentially important, negative feedback for climate change by increasing

CO2 drawdown by iron fertilization of the nearby coastal ocean.

5.4 Fate of Fe in the Southern Ocean

Upon its entry to the Ross Sea, dFe will either become oxidized and scavenged onto sinking particles, will remain in the photic zone with the potential to become further solubilized via photochemical reduction or complexation by ligands, or be rapidly taken up by phytoplankton (Death et al., 2014; Dulaiova et al., 2009; Klunder et al.,

2014; Raiswell and Canfield, 2012; Raiswell, 2011). On average, scavenging and sinking are thought to be the most dominant export of nanoparticles and colloids (Raiswell and

Canfield, 2012), and will likely be even more important at the stream-ocean interface

27 where rapid sedimentation occurs. As such, much of the Fe carried into the Southern

Ocean via MDV streams will likely be removed to depth. The fraction of Fe that remains in the photic zone could be photochemically reduced and/or chelated by ligands.

Photochemical reduction, especially in conjunction with Fe-binding ligands, can lead to increased bioavailability via partial breakdown of the ligand, and subsequent ligand-to- metal charge transfer (Barbeau et al., 2001). This may be an especially important process for the Fe chemistry in the Southern Ocean during the austral summer, where 24 hours of sunlight coincides with increased nutrient delivery via terrestrial streams. In addition, several studies have shown that Fe-complexing ligand concentrations in unfiltered (2-12 nM) and filtered (0.72 + 0.23 nM, <0.2 m) seawater are in excess of dFe concentrations in the Southern Ocean (Boye et al., 2001; Nolting et al., 1998). These processes, photochemical reduction and solubilization, aid in the transformation of Fe to more bioavailable forms, which have been shown, in one study, to be taken up at rates with

1000-fold variability (Lis et al., 2015). Lis et al. (2015) describes this variability as a bioavailability envelope, with dissolved, unchelated Fe at the fast end and chelated Fe at the slow end. Further research into the shallow coastal waters of the Ross Sea and at the stream-ocean interface will be necessary to determine the actual fate of Fe flowing from the MDV streams.

6. CONCLUSIONS

6.1 Summary of Research

1. The Commonwealth and Wales Streams supply approximately 84,400 mol eFe/yr,

240 mol fFe/yr, 200 mol cFe/yr, and 40 mol dFe/yr to the Coastal Ross Sea. This is

several orders of magnitude smaller than the estimated fluxes for other aeolian

and iceberg sources.

2. Future warming can be expected to make terrestrial streamflow a more

significant source of Fe.

3. Based on our operationally defined physiochemical forms, the pool of fFe in MDV

streams is approximately 73-82% colloidal and 18-27% dissolved.

4. MDV streams are a potential source of Fe and P, relative to N and Si, to coastal

phytoplankton communities.

6.2 Future Work

The work in this study can be expanded upon by applying similar analyses to greater spatial and temporal extent. Some of this additional work would require installation of stream gauges and dataloggers throughout the MDV where coastal streams exist. Some further questions include:

29 1. What are the Fe and nutrient fluxes for the other MDV streams that discharge

into the Southern Ocean (Miers, Garwood, Marshall)?

2. After entering the ocean, how much of the fFe and dFe will be complexed by

ligands? And how much is bioavailable?

3. What is the ultimate source of Fe in MDV streams, specifically with respect to

oxidation and reduction dynamics of Fe (oxyhydr)oxides?

4. What is the microbiome of the hyporheic zone in the MDV streams and how does

it affect the biogeochemistry of Fe?

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APPENDIX A: TABLES AND FIGURES

39 Table 1. Precision and accuracy of major ion and nutrient data. Precision was calculated as the average relative standard deviation (RSD) of duplicate samples (n) above the detection limit. Accuracy was calculated from the results of the 2015 USGS inter- laboratory comparison study.

Analyte % difference (prec.) % difference (acc.) Major ions Cl- (n=11) 0.6 <8 2- SO4 (n=11) 7 <4 Na+ (n=10) 0.2 <2 K+ (n=10) 0.3 <3 Mg2+ (n=10) 0.8 <6 Ca2+ (n=10) 0.6 <8 Nutrients on IC - N as NO3 (n=5) 11 <8 Nutrients on Skalar 3- PO4 (n=6) 3.4 <13 Si as H4SiO4 (n=6) 0.3 N/A

40 Table 2. Precision and accuracy for three Fe analyses using inductively coupled plasma.

The limit of quantification was used in place of detection limit (LoQ = Meanblank + 10 *

SDblank). Precision was determined using the relative standard deviation of the duplicates

(n=7 for ICP-OES, n=5 for ICP-SFMS, n=2 for ICP-DRC-MS). Accuracy was determined using the USGS trace metal reference standard from 2015. Accuracy for the ICP-SFMS is not shown here because it went under repair before accuracy measurements were taken.

Analytical method LoQ (µM) % difference % difference (acc.) (prec.) ICP-OES (eFe) 0.07 1.3 2.5 ICP-SFMS (fFe) 0.01 3.4 N/A ICP-DRC-MS (dFe) 0.003 1.2 2.0

41 Table 3. Previously calculated Fe fluxes from various sources to the Southern Ocean (SO).

The aeolian and iceberg sources from Raiswell et al. (2008) quantify that which passes through a 0.2 µm filter and is extractable with a buffered ascorbate solution. The aeolian source from Edwards and Sedwick (2001) is that which passes through a 0.2 µm filter.

The subglacial meltwater source of Fe is that which passes through a 0.45 µm filter. The

MDV stream source of Fe is that which passes through a 0.45 µm filter. Source Fe flux to SO (Tg yr-1) Physiochemical form Aeolian deposition 1 – 1.3 × 10-2 nanoparticulate + (Raiswell et al., 2008) aqueous; extractable Aeolian wet deposition 2.9 × 10-4 nanoparticulate + (Edwards and Sedwick, 2001) aqueous Icebergs 6.1 – 12 × 10-2 nanoparticulate + (Raiswell et al., 2008) aqueous Subglacial meltwater 0.9 – 9 × 10-2 colloidal + (Death et al., 2014) nanoparticulate + aqueous MDV Terrestrial streams 1.2 × 10-5 colloidal + (Lyons et al., 2015) nanoparticulate + aqueous

42 Table 4. Stream characteristics of coastal MDV streams. Elevation measurements for

Adams and Miers inflow streams suggested that these streams flow uphill, and were therefore not included here.

Stream name Length (km) Width (m) Gradient (%) Thermokarst Commonwealth 4.2 3-100 2.7 Yes Wales 5.3 5-130 6.3 No Garwood 10 -- 3.2 Yes Adams 2.1 -- -- No Miers – inflow 1.4 -- -- No Miers – outflow 9.3 -- 3.6 Some

43 Table 5. Annual discharge (×103 m3) for the Commonwealth, Wales, Garwood, and Miers

Streams. Wales discharge was determined with a predictive flow model based on temperature data and adiabatic lapse rate calculations (Jaros, 2002). For the

Commonwealth, Garwood, and Miers Streams, some days did not record a measurement every 15 minutes, yielding a lower total discharge for that day, and subsequently, that year. n|N = days with missing data | number of days in the flow season.

Commonwealth n|N Wales Garwood Miers 1989-90 ------1900 -- 1990-91 -- -- 187 83 489 1991-92 -- -- 125 -- -- 1992-93 -- -- 68 -- -- 1993-94 115 3|61 68 -- -- 1994-95 62 4|65 25 -- -- 1995-96 135 3|82 26 -- -- 1996-97 115 8|65 27 -- -- 1997-98 95 3|90 30 -- -- 1998-99 157 2|74 36 -- -- 1999-00 101 1|75 18 -- -- 2000-01 99 2|83 16 -- -- 2001-02 1272 2|86 273 -- -- 2002-03 218 2|73 32 -- -- 2003-04 203 4|76 61 -- -- 2004-05 478 5|94 102 -- -- 2005-06 395 4|83 91 -- -- 2006-07 191 3|70 100 -- -- 2007-08 135 3|74 54 -- -- 2008-09 618 5|85 257 -- --

Continued 44 Table 5, Continued.

Commonwealth n|N Wales Garwood Miers 2009-10 199 7|83 74 -- -- 2010-11 652 10|103 158 -- -- 2011-12 266 18|81 100 -- -- 2012-13 201 26|57 79 -- -- 2013-14 465 28|65 ------2014-15 205 15|90 ------2015-16 734 6|59 ------Average 309 -- 87 991 489

45 Table 6. Average Fe concentrations in four coastal MDV streams. Environmentally-active

Fe (eFe) is the concentration of Fe in samples that were unfiltered and acidified.

Filterable Fe (fFe) is the concentration of Fe in samples that were filtered (0.4 µm) and acidified. Dissolved Fe (dFe) is the concentration of Fe in samples that were filtered (0.2

µm) and acidified. Colloidal Fe (cFe) is the difference between the fFe concentration and dFe concentration (cFe = fFe – dFe). Only samples collected at the outlet of each stream were used to calculate average. For comparison, the average fFe concentration in some coastal and closed-basin MDV streams from Lyons, et al. (2015) is included.

eFe (µM) fFe (µM) cFe (µM) dFe (µM) Commonwealth (n=6) 270 0.75 0.62 0.13 Wales (n=6) 12 0.15 0.11 0.04 Garwood (n=1) 4.2 0.29 -- -- Miers (n=7) 7.9 0.24 -- -- MDV streams (Lyons et al., -- 0.19 -- -- 2015) (n=143)

46 Table 7. Average Fe flux from Commonwealth and Wales. Flux was calculated by multiplying the average Fe concentration and the average annual discharge or the 2015-

2016 annual discharge for each stream (see tables 5 &6).

eFe fFe cFe dFe (mol/yr) (mol/yr) (mol/yr) (mol/yr) Commonwealth 2015-16 198,000 550 460 95 Avg. (1993-2016) 83,400 230 190 40 Wales 2015-16 ------Avg. (1990-2013) 1040 13 9.6 3.5

47 Table 8. Ratios of average molar concentrations of filterable (< 0.4 µm) nutrients N, P, Si, and Fe for 3 streams. Nutrients are normalized to P, unless the P concentration was below the detection limit (0.17 µM), in which case ratios are normalized to the detection limit. Only samples collected at the outlet of each stream were used to calculate average. - 3- fFe N as NO3 P as PO4 Si n Commonwealth 0.38 + 0.12 1 + 0.03 1 21 + 2 6 Wales 0.07 + 0.01 3 + 0.37 1 61 + 2 6 Garwood 2 6 1 210 1 Phytoplankton 0.0075† 16† 1† 60 + 6‡ (Ho et al., 2003†, Brzezinski et al., 2003‡)

48 Figure 1. Coastal streams in the McMurdo Dry Valleys, Antarctica

Commonwealth

McMurdo Sound Wales

Garwood

Miers

49 Figure 2. Sampling locations at Commonwealth Stream, Taylor Valley, Antarctica

50 Figure 3. Sampling locations at Wales Stream, Taylor Valley, Antarctica

51 Figure 4. Sampling locations at Garwood Stream, Garwood Valley, Antarctica

52 Figure 5. Sampling locations at Miers Stream, Miers Valley, Antarctica

53 Figure 6. Fe concentrations along Commonwealth Stream. Environmentally-active Fe

(eFe) is the concentration of Fe in samples that were unfiltered and acidified. Filterable

Fe (fFe) is the concentration of Fe in samples that were filtered (0.4 µm) and acidified.

Error bars reflect the relative standard deviation (RSD) of duplicate samples (n=7 for eFe, n=5 for fFe). RSD (%) is often smaller than the data point.

24 0.5

0.4 18

0.3 12 0.2

6 0.1 eFe concentration (µM) fFe concentration (µM) 0 0.0 0.0 1.1 2.2 3.3

Distance (km) eFe fFe

54 Figure 7. Fe concentrations along Wales Stream. Environmentally-active Fe (eFe) is the concentration of Fe in samples that were unfiltered and acidified. Filterable Fe (fFe) is the concentration of Fe in samples that were filtered (0.4 µm) and acidified. Error bars reflect the relative standard deviation (RSD) of duplicate samples (n=7 for eFe, n=5 for fFe). RSD (%) is often smaller than the data point.

160 0.3

120 0.2

0.1 40 fFe concentration (µM) eFe concentration (µM) 0 0.0 0.0 1.4 2.8 4.2

Distance (km) eFe fFe

55 Figure 8. Fe concentrations along Miers Stream. Environmentally-active Fe (eFe) is the concentration of Fe in samples that were unfiltered and acidified. Filterable Fe (fFe) is the concentration of Fe in samples that were filtered (0.4 µm) and acidified.

12 0.6 LAKE MIERS 8

4 0.3

0 fFe concentration (µM) eFe concentration (µM)

-4 0.0 0 4 8 12 Distance (km) eFe - Miers eFe - Adams fFe - Adams fFe - Miers

56 Figure 9. Fe concentrations along Garwood Stream. Environmentally-active Fe (eFe) is the concentration of Fe in samples that were unfiltered and acidified. Filterable Fe (fFe) is the concentration of Fe in samples that were filtered (0.4 µm) and acidified. Error bars reflect the relative standard deviation (RSD) of duplicate samples (n=7 for eFe, n=5 for fFe). RSD (%) is often smaller than the data point.

12 0.3

8 0.2

4 0.1 eFe concentration (µM) fFe concentration (µM) 0 0.0 0.0 2.5 5.0 Distance (km)

eFe fFe

57 Figure 10. Hysteretic behavior of eFe, fFe, and dFe in Commonwealth Stream. Error bars reflect the relative standard deviation (RSD) of duplicate samples (n=7 for eFe, n=5 for fFe, n=2 for dFe). RSD (%) is often smaller than the data point.

350 4.0

175 2.0

0 0.0 fFe concentration (µM) eFe concentration (µM) 140 175 210 Discharge (L/s) eFe fFe

0.21 ) µM

0.14

dFe concentration ( 0.07 140 175 210 245 Discharge (L/s) dFe

58 Figure 11. Soluble reactive phosphate concentrations along Commonwealth. Error bars reflect the relative standard deviation (RSD) of duplicate samples (n=6). RSD (%) is often smaller than the data point.

SRP concentration (µM) 0 0.0 1.1 2.2 3.3 Distance (km)

59 - Figure 12. N as NO3 concentrations along Commonwealth. Error bars reflect the relative standard deviation of duplicate samples (n=5).

3 concentration (µM) - 3

NO 1 0.0 1.1 2.2 3.3 Distance (km)

60 Figure 13. Si concentrations along Commonwealth. Error bars (relative standard deviation) smaller than data points.

120

40 Si concentration (µM) 0 0.0 1.1 2.2 3.3 Distance (km)

61 Figure 14. Soluble reactive phosphate concentrations along Wales Stream. Error bars reflect the relative standard deviation (RSD) of duplicate samples (n=6). RSD (%) is often smaller than the data point.

3 ) µM

SRP concentration ( 0 0.0 1.4 2.8 4.2 Distance (km)

62 - Figure 15. N as NO3 concentrations along Wales. Error bars reflect the relative standard deviation of duplicate (RSD) samples (n=5). RSD (%) is often smaller than the data point.

4 concentration (µM) - 3

NO 0 0.0 1.4 2.8 4.2 Distance (km)

63 Figure 16. Si concentrations along Wales. Error bars (relative standard deviation) smaller than data points.

150

100

Si concentration (µM) 0 0.0 1.4 2.8 4.2 Distance (km)

64 - Figure 17. N as NO3 concentrations along Garwood. Error bars reflect the relative standard deviation of duplicate samples (n=5).

1.5

1.0

0.5 concentration (µM) - 3

0.0 0.0 2.5 5.0 N as NO Distance (km)

65 Figure 18. Si concentrations along Garwood. Error bars (relative standard deviation) smaller than data points.

0 0.0 2.5 5.0 Si concentration (µM) Distance (km)

66 - Figure 19. N as NO3 concentrations along Miers. Error bars reflect the relative standard deviation (RSD) of duplicate samples (n=5). RSD (%) is often smaller than the data point.

8 LAKE MIERS

4 concentration (µM) - 3

N as NO 0 0 4 8 12 Distance (km) Adams Miers

67 Figure 20. Si concentrations along Miers. Error bars (relative standard deviation) smaller than data points.

LAKE MIERS 40

Si concentration (µM) 0 0 4 8 12 Distance (km) Adams Miers

68 Figure 21. Commonwealth hydrograph during the transect sampling on December 24th,

2015 from 9:55-14:10. Sample collection times correspond to red triangles.

7 Discharge (L/s)

0 9:15 10:45 12:15 13:45 15:15

Time (24h)

69 Figure 22. Commonwealth hydrograph during the partial diel sampling on January 1st,

2016 from 12:40-16:15. Sample collection times correspond to red triangles.

250

200

150

Discharge (L/s) 100

50 12:00 14:00 16:00 18:00 Time (24h)

70 Figure 23. Concentration-discharge plot of nutrients collected at the delta of

Commonwealth on December 24th. Data is plotted on log-log axes and trendlines follow the general equation y=mxb. Negative and positive b values indicate dilution and dissolution trends, respectively.

1000

eFe: y = 630x-0.16 100

Si: y = 750x-0.55 10

- 0.08 NO3 : y = 1.3x 1 Concentration (µM) fFe: y = 6E+07x-3.5 dFe: y = 2.9x-0.59 0 10 100 1000 Discharge (L/s) fFe eFe dFe Nitrate Si

71 Figure 24. Concentration-discharge plot of major cations collected at the delta of

Commonwealth on December 24th. Data is plotted on log-log axes and trendlines follow the general equation y=mxb. Negative/positive b values indicate dilution/dissolution trends.

1000 Na: y = 2100x-0.21

100

K: y = 140x-0.19 Ca: y = 2800x- 10 Si: y = 750x-0.55 Mg: y = 6600x-0.96

Concentration (µM) 1

0 Li: y = 0.57x-0.24 10 100 1000 Discharge (L/s) Mg Na Ca K Si Li

APPENDIX B: MAJOR CATIONS AND MAJOR ANIONS

73 Table 9. Major cation concentrations for all samples collected.

Li (µM) Na (µM) K (µM) Mg (µM) Ca (µM) Commonwealth transect - 12/24 CW1 0.11 283 25 83 213 CW2 0.09 254 24 67 172 CW3 0.09 235 23 68 174 CW4 0.10 273 27 81 206 CW5 0.12 338 30 92 215 CW6 0.14 428 36 113 240 CW7 0.69 4,300 203 900 571 CW8 0.26 1,400 78 92 118 diel – 1/1 CW1 0.17 721 52 56 97 CW2 0.18 807 56 49 83 CW3 0.16 755 54 46 80 CW4 0.16 735 54 38 70 CW5 0.15 671 52 36 71 CW6 0.16 698 51 36 68 Wales transect – 12/29 W1 0.13 323 25 57 290 W2 -- 127 20 36 178 W3 -- 141 24 41 215 W4 0.16 213 36 54 274 W5 0.25 414 64 93 351 W6 0.36 665 86 139 403 W7 0.43 760 99 158 427 W8 0.55 915 113 189 444 diel – 1/6 W1 0.51 905 108 192 490 W2 0.53 930 111 201 492

Continued 74 Table 9, Continued Li (µM) Na (µM) K (µM) Mg (µM) Ca (µM) W3 0.56 953 114 201 490 W4 0.57 930 108 206 500 W5 0.59 1000 120 203 493 W6 0.56 1010 123 210 516 Garwood transect – 12/31 G1 0.14 200 38 35 242 G2 0.13 197 38 34 249 G3 0.18 226 48 39 305 Marshall 1.0 8,530 326 730 765 1/31 Miers inflow transect – 12/28 M1 -- 60 13 12 175 M2 0.08 85 22 19 221 M3 0.10 96 26 21 240 Adams transect – 12/28 A1 0.22 472 53 124 961 A2 0.14 284 47 88 811 A3 0.15 280 41 64 542 Miers outflow transect – 12/28 M4 0.13 136 30 30 303 M5 0.14 256 37 37 336 M6 0.32 901 71 97 472 Miers diel – 1/22 M1 0.23 632 47 69 365 M2 0.26 635 48 72 375 M3 0.28 647 49 72 376 M4 0.28 660 51 73 378 M5 0.30 674 52 74 379 M6 0.30 679 53 74 381 Continued

75 Table 9, Continued Li (µM) Na (µM) K (µM) Mg (µM) Ca (µM) M7 0.29 681 53 74 380 Von Guerard transect – 1/9 VG1 -- 132 40 51 331 VG2 -- 165 45 60 352 VG3 -- 192 53 63 369 VG4 2.2 232 60 72 383 diel – 1/9 VG1 1.7 225 58 70 388 VG2 1.8 238 62 74 407 VG3 1.8 233 57 78 420 VG4 0.48 202 52 78 421 VG5 0.60 209 53 83 445 VG6 0.85 222 54 88 469 VG7 0.86 200 50 73 401 VG8 0.72 198 51 68 372 VG9 0.99 228 59 72 399 VG10 1.15 234 57 77 418 Andersen Creek diel – 1/22 AC1 -- 104 22 26 112 AC2 -- 102 22 27 110 AC3 -- 88 19 23 103 AC4 -- 90 20 23 91 AC5 -- 77 17 19 81 AC6 -- 80 17 20 84 AC7 -- 98 21 24 101 AC8 -- 117 25 29 122 AC9 -- 137 30 33 137 AC10 -- 114 26 28 120 “--“ indicates sample was below the detection limit.

Table 10. Major anion concentrations for all samples collected. - 2- F (µM) Cl (µM) Br (µM) NO3 (µM) SO4 (µM) Commonwealth transect - 12/24 CW1 2.6 324 -- 0.89 52 CW2 2.9 296 -- 0.38 49 CW3 2.3 283 -- 0.64 45 CW4 2.9 330 -- 0.70 50 CW5 2.9 345 -- 0.84 40 CW6 3.4 361 -- 1.0 36 CW7 12 5760 5.7 -- 272 CW8 12 317 -- 0.91 48 diel – 1/1 CW1 6.1 239 -- 0.42 34 CW2 6.0 232 -- 0.51 33 CW3 6.2 295 -- 0.43 39 CW4 5.6 247 -- 0.45 32 CW5 4.9 219 -- 0.45 28 CW6 5.4 227 -- 0.45 27 Wales transect – 12/29 W1 3.3 344 -- 0.77 41 W2 3.2 128 -- -- 24 W3 3.3 132 -- -- 23 W4 4.6 159 -- 0.27 26 W5 6.3 227 -- 0.62 33 W6 7.9 416 -- 1.1 50 W7 8.4 481 -- 1.3 56 W8 9.9 635 -- 1.5 64 diel – 1/6 W1 10 586 -- 1.9 69 W2 12 608 -- 1.0 69 Continued 77 Table 10, Continued - 2- F (µM) Cl (µM) Br (µM) NO3 (µM) SO4 (µM) W3 10 634 -- 2.4 74 W4 9.6 623 -- 1.5 73 W5 11 643 -- 1.2 71 W6 12 723 -- 1.8 74 Garwood transect – 12/31 G1 4.2 129 -- 0.27 46 G2 4.3 130 -- 0.25 46 G3 5.8 133 -- 0.27 49 Marshall 26 8760 2.1 0.91 700 1/31 Miers inflow transect – 12/28 M1 2.2 36 -- 0.77 22 M2 3.1 49 -- 1.0 25 M3 3.0 54 -- 1.0 27 Adams transect – 12/28 A1 4.6 650 0.94 1.5 4.6 A2 3.7 460 -- 0.96 3.7 A3 2.2 36 -- 0.77 2.2 Miers outflow transect – 12/28 M4 4.4 100 -- -- 4.4 M5 5.1 180 -- 0.38 5.1 M6 15 750 0.79 0.55 15 Miers diel – 1/22 M1 13 554 -- -- 83 M2 12 550 -- -- 82 M3 11 553 -- -- 83 Continued 78 Table 10, Continued - 2- F (µM) Cl (µM) Br (µM) NO3 (µM) SO4 (µM) M4 14 557 -- -- 85 M5 13 561 -- -- 84 M6 12 572 -- -- 84 M7 12 564 -- -- 86 Von Guerard transect – 1/9 VG1 4.9 131 -- -- 23 VG2 4.9 150 -- -- 27 VG3 4.3 162 -- -- 29 VG4 5.0 185 -- -- 30 diel – 1/9 VG1 6.9 181 -- -- 38 VG2 6.0 190 -- -- 38 VG3 7.5 191 -- -- 35 VG4 6.5 174 -- -- 38 VG5 6.8 180 -- -- 38 VG6 6.5 187 -- -- 40 VG7 4.6 173 -- -- 34 VG8 5.8 168 -- -- 30 VG9 5.7 185 -- -- 32 VG10 5.0 187 -- -- 31 Andersen Creek diel – 1/22 AC1 4.1 128 -- -- 58 AC2 3.5 118 -- -- 56 AC3 3.4 106 -- -- 52 AC4 2.9 97 -- -- 54 AC5 3.3 105 -- -- 57 AC6 3.2 114 -- -- 62 AC7 3.8 93 -- -- 47 AC8 4.0 94 -- -- 51 AC9 3.7 116 -- -- 64 AC10 3.5 137 -- -- 73 “--“ indicates sample was below the detection limit. 79

APPENDIX C: TITRATION ALKALINITY AND pH

80 Table 11. Titration alkalinity for several samples collected along Commonwealth, Wales,

Garwood and Miers between November 2015 - January 2016. During each stream visit, samples may be collected at one of several standard sampling locations. Approximate location for each sample is indicated in the second column.

Sample Approx. location alkalinity (µM) pH Commonwealth 24 Nov 2015 near delta 290 7.5 4 Dec 2015 near delta 160 6.6 8 Dec 2015 near delta 350 6.6 22 Dec 2015 near delta 170 6.6 19 Jan 2016 near delta 180 7.6 Wales 21 Jan 2016 near delta 1400 6.8 Garwood 29 Dec 2015 mid-way below glacier 690 7.4 13 Jan 2016 mid-way below glacier 780 7.1 Adams 15 Nov 2015 near glacier 710 --- 10 Dec 2015 near glacier 570 8.3 15 Dec 2015 near glacier 680 7.4 29 Dec 2015 near glacier 1200 7.8 13 Jan 2016 near glacier 670 7.1 28 Jan 2016 near glacier 1200 7.2 Miers - inflow 10 Dec 2015 -- 950 8.1 15 Dec 2015 -- 450 7.2 29 Dec 2015 -- 430 7.4 13 Jan 2016 -- 350 7.5 28 Jan 2016 -- 1300 7.0

Continued

81 Table 11, Continued Sample Approx. location alkalinity (µM) pH Miers - outflow 10 Dec 2015 just below lake Miers 950 8.2 15 Dec 2015 just below lake Miers -- 7.8 29 Dec 2015 just below lake Miers 760 7.4 13 Jan 2016 just below lake Miers 800 7.2 28 Jan 2016 just below lake Miers 600 7.3