Fe and Nutrients in Coastal Antarctic Streams: Implications for Primary

Journal of Geophysical Research: Biogeosciences

RESEARCH ARTICLE Fe and Nutrients in Coastal Antarctic Streams: Implications 10.1029/2017JG004352 for Primary Production in the Ross Sea Key Points: Sydney Olund1,2 , W. Berry Lyons1 , Susan A. Welch1 , and Kathy A. Welch2 • Two Antarctic streams supply an average annualﬂux of 240 moles of 1School of Earth Sciences, Ohio State University, Columbus, OH, USA,2Byrd Polar Research Center, Ohio State University, ﬁlterable Fe to phytoplankton communities in the coastal Ross Sea Columbus, OH, USA • The average stoichiometry of these

coastal streams was N3P1Si100Fe0.8, suggesting an important source of Fe AbstractThe Southern Ocean (SO) has been an area of biogeochemical interest due to the presence of and P relative to Si and N macronutrients (N, P, and Si) but lack of the expected primary production response, which is thought to be • Climate change and subsequent melt in this region is expected to increase primarily due to Fe limitation. Because primary production is associated with increased drawdown of the Feflux from these terrestrial, atmospheric CO2, it is important to quantify thefluxes of Fe and other nutrients into the SO. Here we present coastal streams data from subaerial streams thatflow into the Ross Sea, a sector of the coastal SO. Water samples were collected in the McMurdo Dry Valleys, Antarctica, and analyzed for macronutrients and Fe to determine the Supporting Information: potential impact of terrestrial water input on the biogeochemistry of coastal oceanic waters. The •Supporting Information S1 physiochemical forms of Fe were investigated through analysis of three operationally defined forms: •Table S1 •Table S2 acid-dissolvable Fe (nofiltration),filterable Fe (<0.4μm), and dissolved Fe (<0.2μm). The combined average •Table S3 flux from two McMurdo Dry Valley streams was approximately 240 moles offilterable Fe per year. The •Table S4 dissolved fraction of Fe made up 18%–27% of thefilterable Fe. The stream data yield an averagefilterable •Table S5 stoichiometry of N3P1Si100Fe0.8, which is substantially different from the planktonic composition and Correspondence to: suggests that these streams are a potential source of Fe and P, relative to N and Si, to coastal phytoplankton S. Olund, communities. While the Feflux from these streams is orders of magnitude less than estimated eolian and [email protected] iceberg sources, terrestrial streams are expected to become a more significant source of Fe to the Ross Sea in the future. Citation: Olund, S., Lyons, W. B., Welch, S. A., & Welch, K. A. (2018). Fe and nutrients in coastal Antarctic streams: Implications 1. Introduction for primary production in the Ross Sea. 1.1. Rationale Journal of Geophysical Research: Biogeosciences,123, 3507–3522. https:// It is important to understand nutrient distribution in the ocean because primary production can lead to CO2 doi.org/10.1029/2017JG004352 uptake and the subsequent sequestration of carbon via burial in marine sediments (Marinov et al., 2008; Moore et al., 2013). The distribution of nutrients in Earth’s oceans is primarily driven by ocean circulation, Received 29 DEC 2017 Accepted 11 NOV 2018 upwelling, and proximity to terrestrial sources, and these factors have created a high macronutrient (N and Accepted article online 23 NOV 2018 P) environment in the surface waters of the Southern Ocean (Moore et al., 2013). Typically, nitrate is the Published online 12 DEC 2018 limiting nutrient in the surface waters of the ocean (middle and low latitudes), and because of this, high-nitrate waters are expected to have high phytoplankton biomass (Moore et al., 2013). Work over the past decade has clearly demonstrated, however, that the micronutrient (Fe) is very important throughout various ocean locations in controlling marine primary production (Tagliabue et al., 2017). The Southern Ocean is characterized ashigh-nutrient low-chlorophyll, where primary productivity is limited by Fe instead of by macronutrients (Cassar et al., 2007; 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 offshore waters and revealed that Fe concentrations in the coastal waters were 50–60 times higher than the less productive offshore waters (Martin et al., 1990). The Fe-rich coastal waters produced 30 times more Cfixation (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 (e.g., Watson et al., 2000). It was noted, however, that such fertilization experiments only yielded a temporary biological response to increased Fe and that transport ofﬁxed carbon to depth is required for long-term carbon sequestration from this enhanced primary productivity (Watson et al., 2000). Several studies have conﬁrmed the earlier investigations on the importance of Fe in helping to drive primary production in Antarctic waters (Arrigo & van Dijken, 2003;

©2018. American Geophysical Union. Bertrand et al., 2015; Cassar et al., 2007; De Jong et al., 2012; Fennel et al., 2003; Smetacek et al., 2012; All Rights Reserved. Tagliabue & Arrigo, 2005), as well as having an impact on the structure of the pelagic ecosystem (Hare

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Table 1 et al., 2007; Meyerink et al., 2017). More recently, a review of metal uptake Previously Calculated Fe Fluxes From Various Sources to the SO by phytoplankton throughout the global oceans showed that diatoms Feflux to SO from the Southern Ocean have a lower Fe quota than some diatoms Source (Gg/year) isolated from coastal and oligotrophic environments, which may be a Eolian deposition (Raiswell et al., 2016) ~1 strategy that has developed to cope with low Fe concentrations Eolian wet deposition (Edwards & Sedwick, 2001) 2.9 × 10 1 (Twining & Baines, 2013). Icebergs (Raiswell et al., 2016) 180–1,400 Subglacial meltwater (Death et al., 2014) 9–90 Due to this importance of Fe in influencing the biologicalfixation of CO2, MDV Terrestrial streams (Lyons et al., 2015) 1.2 × 10 2 several sources of Fe to the Southern Ocean have been investigated and Maritime Antarctic terrestrial streams dFe 1–100 theirfluxes estimated. To date, the largest estimated contributions come Maritime Antarctic terrestrial streams aFe 100–1,000 from icebergs (Raiswell, 2011). A recent study demonstrated increased (Hodson et al., 2017) chlorophyllalevels in the wake of a 50-km iceberg (termedgiant icebergs; Note. The eolian and iceberg sources from Raiswell et al. (2016) quantify Duprat et al., 2016). Other significant sources of Fe include eolian dust that which passes through a 0.2-μmfilter and is extractable with a buf- fered ascorbate solution. The eolian source from Edwards and Sedwick deposition (Edwards & Sedwick, 2001), diffusion from shelf (2001) is that which passes through a 0.2-μmfilter. The subglacial melt- sediments/porewaters (de Baar et al., 1995), convection and mixing from water source of Fe is that which passes through a 0.45-μmfilter. The deeper waters (Marsay et al., 2017; Tagliabue et al., 2014), hydrothermal MDV stream source of Fe is that which passes through a 0.45-μmfilter. MDV = McMurdo Dry Valleys; SO = Southern Ocean. sources (Tagliabue et al., 2010), the melting of sea ice (Bhattachan et al., 2015; de Jong et al., 2013; Winton et al., 2016), and subglacial melt direct from the continent (Death et al., 2014). Several studies have argued that the occurrence of offshore phytoplankton blooms are due to inputs from shelf sediments (Dulaiova et al., 2009; de Jong et al., 2013) or subglacial melt (Gerringa et al., 2012), and these sources were shown to provide the necessary Fe for the bloom to proceed. Clearly from the summation of all these studies, there are multiple sources of Fe to the Southern Ocean, and there is a need to better quantify all the contributions of Fe as well as determine the bioavailability of these sources (Tagliabue et al., 2017). Recent work has demonstrated that subaerial streamflow from ice-free areas of Antarctica, such as the McMurdo Dry Valleys (MDV), is a potential source offilterable Fe (<0.4μm, termed fFe) to the Ross Sea, with the potential to provide a mean of 0.19μmol fFe/L (Lyons et al., 2015). While this concentration, when converted to a yield on a per area basis, is small compared to other estimated sources of iron into the Southern Ocean (Table 1), climate warming, and subsequent cryospheric loss and glacier retreat could create more ice-free area (Lee et al., 2017). In addition, this increased melt could enhance streamflow, leading to a largerflux of Fe from this source in the future (Lyons et al., 2015). Recent work in other ice-free areas of the Antarctic has also clearly shown that glacier meltwater streams can contribute significantly high concentrations offilterable Fe (i.e., dissolved, colloidal, and nanoparticulate) to the marine environment surrounding the continent, enhancing the coastal water Fe concentrations (Hodson et al., 2017; Kim et al., 2015; Monien et al., 2017). This study aims to further quantify the terrestrial stream input of Fe to the McMurdo Sound. The work presented builds from the work of Lyons et al. (2015) and specifically seeks to 1. identify the physiochemical form of Fe in four MDV streams that discharge directly into the coastal Ross Sea. It is important to distinguish between the various Fe fractions—particulate, colloidal, nanoparticulate, and dissolved—due to the relationship between physiochemical form and potential bioavailability. This is complicated by the fact that the standard operational definitions of these fractions do not truly separate each chemical form and that different operational definitions occur in the literature (Raiswell, 2011; Raiswell & Canfield, 2012). In this study, we defined three fractions of Fe: a. aDFe—acid dissolvable Fe, which is unfiltered dissolvable Fe (as defined by acidification with dilute HCl for 60+ days; b. fFe—filterable Fe, which is colloidal, nanoparticulate, and soluble Fe that passes through a 0.4-μmfilter; c. dFe—dissolved Fe, which is colloidal, nanoparticulate, and soluble Fe that passes through a 0.2-μmfilter; 2. compare nutrient stoichiometry in streams to published phytoplankton stoichiometry in the Ross Sea/Southern Ocean. The traditional RedfieldRatio, 16N:1P, has been used since the 1950s to better understand the 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 generally accepted stoichiometry for marine phytoplankton of 16N:1P:60Si:0.0075Fe. The initial N:P ratio of 16:1 has been shown to vary spatially in the upper ocean, and Martiny et al. (2013) described a latitude-

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Figure 1.Four coastal streams in the McMurdo Dry Valleys, Antarctica.

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 dominant local phytoplankton ratios from the literature to determine how they compare and if stream input has the potential to influence the biogeochemistry of the Antarctic coastal ocean; 3. quantify theflux of Fe to the Ross Sea. As ice-free areas increase in Antarctica, quantifying the massflux of Fe from terrestrial sources will become more important. In the initial work of Lyons et al. (2015) on the MDV streams, most of the streams sampledflow 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.

1.2. Study Area The MDV area, a polar desert, is the largest ice-free region in Antarctica, with an area in the central and south MDV of 3,800 km2(Levy, 2013). Our work 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 (Figure 1). All of these streams discharge directly into the McMurdo Sound, the southernmost extent of the Ross Sea, andflow over glacial drift deposited from both local alpine glaciers and the East/West Antarctic Ice Sheets. The valleyfloors andfixed stream channels consist of deposits from all the bedrock lithologies that are observed in the McMurdo region—the Beacon Supergoup sandstone, the Ferrar Dolerite, the older early

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Table 2 Paleozoic crystalline basement igneous and metamorphic rocks, and the Stream Characteristics for Four McMurdo Dry Valleys Streams McMurdo Volcanics (Hall & Denton, 2000). The McMurdo Volcanic Stream name Length (km) Gradient (%) Thermokarst component occurs in the highest amounts in the youngest tills in the east- Commonwealth 4.2 2.7 Yes ern portions of these valleys and was transported by the West Antarctic Ice Wales 5.3 6.3 No Sheet (WAIS) during its advance during the Last Glacial Maximum. Garwood 10 3.2 Yes Streams in the MDV can have varying lengths, gradients, and bedforms Adams 2.1 — No Miers—inflow 1.4 — No (McKnight et al., 1999; Wlostowski et al., 2016; Table 2). Several streams Miers—outflow 9.3 3.6 Some (Commonwealth, Garwood, and Lower Miers) are marked by the presence of thermokarst where the stream cuts down, often dramatically, through buried ice found throughout the MDV (Fountain et al., 2014). 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 andfluvial deposits (Hall & Denton, 2000; Levy et al., 2013). This buried ice probably contributes some meltwater to both Commonwealth Stream and Garwood Stream, where it is most prominent. All of these seasonally ephemeral streamsflow from 4 to 10 weeks during the austral summer and experience large daily and seasonalflow variations due to the position of the sun relative to the glacier, albedo changes from snowfall and dust deposition events, summer katabatic wind events, and changes in temperature (McKnight et al., 1999; Nylen et al., 2004). The stream channels are bounded by permafrost, which limits groundwater input and, due to the dry, desert-like conditions in the MDV, most of the snow that falls on the valleyfloor is rapidly sublimated, so there is no overlandflow. 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). These zones extend further into the bank (i.e., laterally) during theflow season, as well (Gooseff et al., 2002). In general, MDV stream solutes are derived from chemical weathering and salt dissolution of materials within the streambed and the hyporheic zone (Barrett et al., 2007; Fortner et al., 2013; Gooseff et al., 2002; Maurice et al., 2002; Nezat et al., 2001; Welch et al., 2010) or directly from snow/ice melt of the glaciers (Lyons et al., 2003). There is also potential dissolution and chemical weathering of eolian materials 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 eolian material did not account for the observed fFe concentrations (Deuerling et al., 2014). 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. Recent work on Svalbard has clearly demonstrated the importance of hyporheic zone exchange andfloodplain weathering in the production offilterable Fe in proglacial streams there (Hodson et al., 2016).

2. Materials and Methods 2.1. Cleaning Fe samples were collected andﬁltered into Nalgene HDPE (High Density Polyethylene) bottles that were

soaked in a 1% HCl solution and rinsed three times with ultrapure water. Nutrient (NO3 and NO2 , soluble + reactive phosphate or SRP, and NH4) and dissolved Si or H4SiO4samples were collected andﬁltered into Nalgene HDPE bottles that were soaked in deionized ultrapure water (18.2M) and rinsed three times with ultrapure water.

2.2. Sampling Stream water samples were collected in Taylor Valley, Garwood Valley, and Miers Valley from 24 December 2015 to 22 January 2016. Samples were collected along the length of each stream from just below the glacier source to the mouth of the stream as it discharged 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 collection bottles were rinsed three times

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with stream water prior to sample collection and the sample collector stood downstream and wore clean vinyl gloves to minimize contamination.

2.3. Processing

Stream water samples werefiltered within 24 hr of collection. Nutrient and H4SiO4samples werefiltered through 0.4-μm Whatman Nuclepore polycarbonate membranefilters. DOC (dissolved organic carbon) samples werefiltered through Whatman glass microfiberfilters of 0.7-μm pore size (grade GF/F) that had been combusted for 4 hr at 450 ° C. Iron samples were separated into three aliquots and then acidified to a pH of approximately 2 by the addition of 0.1% J.T. Baker Ultrex HCl. The three aliquots were processed differently as follows: (1) One aliquot was left unfiltered (we term this fraction acid-dissolvable Fe or adFe); (2) one was filtered through a 0.4-μm Whatman Nucleporefilter (filterable Fe or fFe); and (3) one wasfiltered through a 0.2-μm Poreticsfilter (dissolved Fe or dFe). Due to the various methods used to isolate different fractions of Fe, there is a lack of continuity in the literature with the naming of all these Fe fractions. Our methods for the first fraction, adFe, most closely resemble what other groups have calledtotal dissolvable Fe(Gerringa et al., 2012; Schroth et al., 2014). In addition,filtrates through 0.2-μmfilter have been described as containing colloidal, nanoparticulate, and aqueous species. For the sake of brevity, and as previously described in the literature, we have termed this fractiondissolved Fe.

Theﬁltered samples for nutrients, H4SiO4, DOC, and all iron fractions were stored chilled at approximately 4 ° C in the dark until analysis. All DOC samples were acidiﬁed by the addition of 0.1% J.T. Baker Ultrex HCl. All the

acidiﬁed iron samples, as well as the cation, nutrient and H4SiO4samples that were not analyzed at the Crary Laboratory on McMurdo Station were sent back to The Ohio State University for analysis.

2.4. Analysis Nitrate and phosphate were analyzed by ion chromatography (IC) on the Dionex DX-120 (Sunnyvale, CA) in McMurdo or at The Ohio State University. 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, and NH4) and H4SiO4 analyses were also 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 that the samples had undergone some loss of nitrate 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). Thus, only the data from the IC analysis were used to quantify nitrate concentrations. Where SRP data were above the detection limit on the IC (n= 1), SRP concentrations were comparable between the two methods, so Skalar measurements were used to quantify phosphate. DOC analyses were done within a few days of collection at McMurdo Station using 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 nonpurgeable organic carbon. Three tofive injections of 150μl were done for each sample. All DOC measurements were at or below the lowest standard (0.2 ppm or 17μM), which is near the detection limit. Therefore, DOC data will not be discussed. The three aliquots for iron were analyzed differently due to instrument availability and equipment repairs: (1) Unfiltered samples, or adFe, were analyzed on the Perkin Elmer Optima 4300 DV inductively coupled plasma optical emission spectrometer; (2) samplesfiltered through 0.4-μmfilters, or fFe, were analyzed on the Thermofinnigan Element 2 inductively coupled plasma sectorfield mass spectrometer; and (3) samples filtered through 0.2-μmfilters, or dFe, were analyzed on the PerkinElmer NexION inductively coupled plasma dynamic reaction cell mass spectrometer with methane as the reaction cell gas (Tanner & Bandura, 2003). For all Fe analyses, samples were measured in triplicate and the mean value was used for thefinal concentration. A wavelength of 234.349 nm was used in all inductively coupled plasma optical emission spectrometer 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. Precision and accuracy can be found in Table S5. Stream pH was determined on samples collected from various locations along Commonwealth, Wales, Miers, and Garwood during annual monitoring sampling by the McMurdo Dry Valleys Long-Term Ecological Research (MCM-LTER) Stream Team; pH was measured using a Beckman pHi 265 portable

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meter shortly after sample collection, during theﬁltering process. The pH data range from 6.6 to 8.3, with an average of 7.3. Alkalinity was measured by titration and was also calculated from the difference in the charge balance between anions and cations (Welch et al., 2010). Alkalinities in these streams range from ~160 to 1,400μM.

2.5. Discharge Measurements Many of the streams in Taylor Valley have been gauged routinely by the MCM-LTER program for 24 years or more. Flow data are collected approximately every 30 min throughout theflow season with a network of stream gauges and Campbell CR10 data loggers (McKnight et al., 1999). Among the streams investigated in this study, Commonwealth Stream is the only stream with a long-termflow 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: 1990–1991 and 1988–1991, respectively. Recently, the MCM-LTER project began to gauge Miers on a regular basis (i.e., starting 2015). Wales Stream has never been gauged. In the absence of gauged measurements,flow values for Wales Stream were determined by a model, which uses a linear regression between source glacier area and seasonal discharge of gauged streams to determine a seasonal yield parameter. The source glacier area is weighted using temperature variations on the valley floor and adiabatic lapse rate versus elevation on the Wales Glacier (Jaros, 2002). The model values have compared favorably to streamflow measurements in the Fryxell basin portions of Taylor Valley (Jaros, 2002). In addition, the model results have proven to be quite useful in providing annualflow variations to what has been qualitatively observed from other glacial streams on the southeastern portion of Taylor Valley (Lyons et al., 2012).

3. Results 3.1. Fe and Nutrients in Stream Transects and During Partial Diels This study focused on changes in space (spatially distributed or sampling downstream) and time (temporally distributed or sampling at the delta). 3.1.1. Stream Transects

The NO3 , SRP, and H4SiO4concentrations in Commonwealth range between 1.7–4.4, 0.3–3.4, and 23–95μM, respectively. The NO3 , SRP, and H4SiO4concentrations in Wales range between below the detection limit (BDL)<0.71–6.6, 0.3–2.4, and 34–142μM, respectively. The NO3 , SRP, and H4SiO4concentrations in Miers range between BDL<0.71–0.09μM, BDL<0.17–0.33μM, and 8.6–58μM, respectively (Figures 2 and

S1–S3). Only two out of nine of the Miers samples were above the detection limit for SRP. The NO3 and H4SiO4concentrations in Garwood range 1.1–1.2μM and 27–36μM, respectively. The SRP concentrations in all Garwood samples were BDL (0.17μM). The adFe and fFe concentrations in Commonwealth range between 1.2 and 23μM, and 0.03 and 0.37μM, respectively. The adFe and fFe concentrations in Wales range between 0.27 and 138μM, and 0.01 and 0.29μM, respectively. The adFe and fFe concentrations in Miers range between 0.44 and 11μM, and 0.001 and 0.3μM, respectively. The adFe and fFe concentrations in Garwood range between 4.2 and 10.5μM, and 0.22 and 0.29μM, respectively (Figure S3). Generally, Fe and nutrient concentrations increase downstream in all of the streams sampled (Figures 2 and

S1–S3). A few exceptions include NO3 in Miers Stream (Figure S2), which decreases after passing through Lake Miers and a decrease in adFe near the deltas in both Garwood and Wales (Figure S3). Previous studies

on Lake Miers have demonstrated that the lake behaves as asinkfor bioactive constituents such as NO3 and other solutes, due to biological uptake and dilution of inflow water can also occur through density-driven mixing, which has been intensified by recent warming and subsequent isotherm deepening (Fair, 2014). The decrease in adFe observed in Miers Stream is probably due to particle settling as theflow decreases upon entering the lake (Green et al., 1986). The adFe lost in Garwood and Wales may also be related to decreases in streamflow as the water approaches the wide delta after exiting from a much narrower channel. Flow data withfine temporal resolution are not available in these streams, but ourfield notes indicate an apparent decrease inflow midway through the Wales transect, which would have led to deposition of the suspended load.

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Figure 2.Si concentrations along Commonwealth, Wales, Garwood, and Miers. Error bars (relative standard deviation) smaller than data points.

3.1.2. Stream Partial Diels The adFe, fFe, and dFe concentrations in Commonwealth range between 230 and 320μM, 0.2 and 2μM, and 0.1 and 0.2μM, respectively. The adFe, fFe, and dFe concentrations in Wales range between 2.4 and 46μM, 0.1 and 0.2μM, and 0.03 and 0.05μM, respectively. The adFe and fFe concentrations in Miers range were between 6 and 12μM, and 0.24 and 0.25μM, respectively.

The NO3 , SRP, and H4SiO4concentrations in Commonwealth range between 1.9 and 2.2μM, 1.7 and 2.2μM, and 36 and 47μM, respectively. The NO3 , SRP, and H4SiO4concentrations in Wales range between 4.5 and 11μM, 1.9 and 2.4μM, and 130 and 144μM, respectively. The H4SiO4concentrations in Miers range between 43 and 47μM. Typically, the concentration ranges are narrower during these partial diels than in the transect sampling. This is expected, given the location consistency of diel sampling. The average concentrations observed during the diels were similar to concentrations observed in the terminal transect samples, except for Commonwealth. In comparison to the highest adFe concentration observed in the Commonwealth transect (23μM), the diel adFe concentrations were about an order of magnitude higher, ranging from 230 to 320μM. These higher concentrations during the diel are attributed to large variations inﬂow (5 L/s on average during the transect and 190 L/s on average during the diel). To test this hypothesis, nutrient data were plotted on a log/log concentration-discharge (C-Q) plot (Figure 3; Godsey et al., 2009). The trend lines for these data follow the equationC=aQb, where the value ofbindicates

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Figure 3.Concentration-discharge plot of nutrients collected at the delta of Commonwealth on 24 December. Data are plotted on log-log axes and trendlines follow the general equationy=mxb. Negative and positivebvalues indicate dilution and dissolution trends, respectively. Error bars (relative standard deviation) smaller than data points for all nutrients (note that error bars are approximately the same size as the symbol for NO3 ).

how the solute concentration changes with differentﬂows. Negativebvalues indicate dilution (discharge increases and concentration decreases), positivebvalues indicate rapid dissolution (discharge increases and concentration increases), andbvalues equal to 0 indicate pure chemostasis (constant concentration across discharge values that vary several orders of magnitude; Godsey et al., 2009; Wlostowski et al., 2016). Chemostasis and dilution behavior have both been observed in long-term ﬂow versus electrical conductivity data from MDV streams (Wlostowski et al., 2016). Nitrate was the only analyte that exhibited close to chemostatic behavior (b= 0.08), while the others exhibited slight to extreme dilution behavior (b= 0.16 to 3.5). It should be noted, though, that these data were collected during a portion of one daily hydrograph, and the discharge did not vary by a large amount. Nonetheless, in the case of fFe, concentrations varied up to an order of magnitude across only a 2× variability in discharge.

3.2. Nutrient Stoichiometry Data from Ho et al. (2003) and Brzezinski et al. (2003) were used to include Fe and Si in the nutrient stoichiometry relationship. The marine plankton samples utilized in Ho et al. (2003) were eitherfiltered through 0.5- or 0.8-μmfilters before chemical analysis by inductively coupled plasma sectorfield mass spectrometer, and therefore, the Fe measured most likely resembles our fFe, physiochemically. Using this information, therefore, an extended Redfield Ratio for marine phytoplankton is 16N:1P:60Si:0.0075Fe. The nutrient stoichiometry of the Commonwealth, Wales, and Garwood stream waters was evaluated to understand the potential that increasedflow into the Ross Sea could have on the biogeochemistry of phytoplankton communities in the Ross Sea. Molar concentrations offilterable (<0.4μm) 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 averaged 2μM, SRP concentrations averaged 2μM, Si concentrations averaged 42μM, and fFe concentrations averaged 0.75μM. When normalized to SRP,

Commonwealth stream water has an average stoichiometry of 1N:1P:21Si:0.38Fe. In Wales Stream, NO3 concentrations averaged 7μM, SRP concentrations averaged 2μM, Si concentrations averaged 140μM, and fFe concentrations averaged 0.15μM. When normalized to SRP, Wales stream water has an average

stoichiometry of 3N:1P:61Si:0.07Fe. In Garwood (n= 1), the NO3 concentration was 1μM; the SRP concentration was BDL (<0.17μM); the Si concentration was 36μM; and the fFe concentration was 0.3μM. Normalized to an SRP detection limit of 0.17μM, Garwood had an average stoichiometry of 6N:1P:210Si:2Fe. Recent work in the coastal waters of the Ross Sea, north of Taylor Valley found that the mean N:P:Si ratio in the surface mixed layer was observed to be 21.5:1:63 (Mangoni et al., 2017). Thus, these coastal streams with their enhanced P (relative to N) concentrations may be very consequential in affecting macronutrient stoichiometry during the austral summer.

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Table 3 3.3. Physiochemical Forms of Fe Average Fe Concentrations in Four Coastal MDV Streams We calculated the fraction of each physiochemical form of Fe present in adFe (μM) fFe (μM) dFe (μM) Commonwealth Stream and Wales Stream (Table 2). As previously men- Commonwealth (n= 6) 270 0.75 0.13 tioned, adFe, fFe, and dFe are the unfiltered,<0.4-μm, and<0.2-μm Wales (n = 6) 12 0.15 0.04 fractions, respectively. For Commonwealth, fFe makes up 0.28% of the Garwood (n = 1) 4.2 0.29 — acid-soluble Fe, and dFe makes up 18% of thefilterable fraction Miers (n= 7) 7.9 0.24 — MDV streams (n= 143; — 0.19 — (Table 3). For Wales, fFe makes up 1.25% of the acid-dissolvable Fe, and Lyons et al., 2015) dFe makes up 27% of thefilterable fraction (Table 3). Note. Acid-dissolvable Fe (adFe) is the concentration of Fe in samples that were unfiltered and acidified. Filterable Fe (fFe) is the concentration of Fe 4. Discussion in samples that werefiltered (0.4μm) and acidified. Dissolved Fe (dFe) is the concentration of Fe in samples that werefiltered (0.2μm) and acidi- 4.1. Fe Concentrations—A Comparison to Previous Work fied. Only samples collected at the outlet of each stream were used to calculate average. For comparison, the average fFe concentration in some As noted in Table 3, the mean fFe values for Miers, Garwood, and Wales are coastal and closed-basin MDV streams from Lyons et al. (2015) is included. similar to what was reported previously for the Taylor Valley streams and MDV = McMurdo Dry Valleys. the Onyx River in Wright Valley to the north (Lyons et al., 2015). The fFe for Commonwealth samples, however, are 4 times higher than those reported by Lyons et al. (2015). Lyons et al. (2015) evaluated all reported, previously published fFe concentrations from Antarctic streams and determined that the Taylor Valley stream values were similar to values observed in other subaerial streams along the Victoria Land coast. The mean fFe value from a maritime Antarctic stream was lower than those reported here, at 0.06μM (Hodson et al., 2010). Recent reported discharge-weighted fFe concentrations in three periglacial streams in Svalbard were slightly higher at 0.49, 0.44, and 0.43μM (Hodson et al., 2016) but were slightly lower in outlet glacier streams from Greenland at 0.02–0.18μM (Statham et al., 2008). In addition, the dFe concentrations from these Svalbard streams were similar to or lower than what has been reported for Greenland glacier melt (Bhatia et al., 2013). This variability is not surprising, as fFe and dFe should vary based on rock type, water residence time andflow rate, and redox conditions. Waters deriving from subglacial sources may be expected to have higher values (Hawkings et al., 2014). The fFe concentrations in the MDV streams are much higher than would be expected based off of equilibrium

calculations with a Fe-oxyhydroxide phase in these circumneutral pH and O2-rich stream waters. Lyons et al. (2015) argued that the source of the fFe in these waters is from rock-water interactions in the hyporheic zones of these streams (Gooseff et al., 2002; Maurice et al., 2002), which are regions with high chemical weathering rates (Nezat et al., 2001). Research has also clearly demonstrated that within the hyporheic zones of the Taylor Valleys streams, especially ones with long water residence times, denitrification can occur (Koch et al., 2011; McKnight et al., 2004). These suboxic regions could also be loci of the reduction of Fe3+to more soluble Fe2+. Needless to say, the hyporheic zones are the primary source of the initial soluble Fe entering these streams, either through direct solubilization by chemical weathering or through redox-induced reactions that lead to the conversion of Fe3+to Fe2+. Once hyporheic exchange occurs and the water is subaerial, Fe2+in the water is exposed to sunlight 24 hr/day during the austral summer. This is a significant environmental feature because photoreduction and cold temperatures could play an important role in maintaining the iron in the fFe and/or dFe forms (Schlosser et al., 2012; Sivan et al., 1998). Work in the Southern Ocean during iron enrichment experiments has definitively demonstrated that Fe2+can persist for times longer than expected, strongly suggesting that Fe3+reduction was a major process occurring (Croot et al., 2001, 2008). On-ship experiments using Southern Ocean water have also shown that the concentration of Fe2+had a linear relationship with irradiance with ultraviolet B (280–315 nm) light, which produces higher concentra- Table 4 tions than other wavelengths (Rijkenberg et al., 2005). We expect that 3+ Average Fe Fluxes From Commonwealth and Wales photoreduction of Fe may play an important role in the physiochemical adFe fFe cFe dFe form and speciation of Fe in these streams during the austral summer. Stream Year (Mol/yr) (Mol/yr) (Mol/yr) (Mol/yr) The DOC concentrations in these streams are very low (<0.17μM), and we have no data to suggest that organic associations of Fe play a significant Commonwealth 2015–2016 198,000 550 460 95 Avg. 83,400 230 190 40 role in its transport. (1993–2016) Wales 2015–2016 — — — — 4.2. Fe Fluxes From MDV Streams Avg. 1040 13 9.6 3.5 Table 4 gives a summary of our Fefluxes. For Commonwealth Stream, the (1990–2013) average concentration of the diel samples for each physiochemical form of

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Fe was calculated by using both the measured mean annual discharge over a long-term interval (23–26 years) and the annual discharge for 2015–2016, the year the samples were obtained. For Wales Stream, the average concentrations were multiplied by the model-estimatedflow developed for Taylor Valley, discussed previously, to produce Fefluxes into the coastal Ross Sea. The calculations could not be done for the other two streams because there are no long-term discharge data for them, and the more recent gauged data are currently unavailable. Based on the stream discharge data from 1993 to 2016 and the Fe measurements from our study, the average annualfluxes of adFe, fFe, cFe, and dFe for Commonwealth are 83,000, 232, 192, and 40 mol/year, respectively. The 2015–2016flux of adFe, fFe, cFe, and dFe for Commonwealth are 200,000, 551, 455, and 95 mol/year, respectively. The 2015–2016 annual discharge was more than double the mean annual discharge for Commonwealth, leading to above average Fefluxes to the coastal Ross Sea during that year. For Wales, the stream discharge data from 1990 to 2013 and the Fe measurements from this study yield average annualfluxes for adFe, fFe, cFe, and dFe are 12, 0.15, 0.11, and 0.04 mol/year, respectively. Based on these calculations, the two Taylor Valley streams contribute a combined meanflux of 84,440-mol adFe per year, 243-mol fFe per year, 200-mol cFe per year, and 43-mol dFe per year to the Ross Sea/McMurdo Sound (Table 4). It should be noted that stream discharge varies greatly from year to year depending on the atmospheric temperature, cloud cover, and amount of surface debris blown onto the contributing glaciers (McKnight et al., 1999). While the Fefluxes for Commonwealth are 1–2 orders of magnitude larger than the Wales Fefluxes, the fraction of fFe in Wales is about 5 times higher than that of Commonwealth, suggesting Wales could be a more important source of potentially bioavailable Fe. Lyons et al. (2015) argued that subaerial streams in MDV are currently a very minor source of fFe to the coastal ocean compared to eolian sources and icebergs. These latter two sources have been estimated to provide several orders of magnitude more fFe and dFe than the streams. The data presented by us support this notion. Dulaiova et al. (2009) calculated a Fe demand of 1.1–4×105-mol Fe for a 22,500-km2phytoplankton 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 dFeflux from Commonwealth and Wales Streams, the stream input could only account for the Fe demand of 0.14– 1.23 km2of 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 a primarilyPhaeocystis antarcticabloom in the Pine Island Polynya, it was estimated that 7 ± 5 × 10 6-mol Fe per square meter per day was needed to sustain the growth (Gerringa et al., 2012). This bloom lasted 73 days and spanned up to 16,890 km2(Arrigo & van Dijken, 2003). Using this information, the dFeflux from Taylor Valley streams could provide the necessary Fe for just 0.09–0.2 km2of the bloom. Clearly, terrestrial stream input of dFe would be a very minor source to such large events as these, but it is important to note that our estimates of the average dailyflux of dFe only include that which is provided by Commonwealth and Wales. In addition, there is evidence to suggest that these blooms can be sustained on recycled Fe in the absence of large grazers (Croot et al., 2004; Klunder et al., 2014). In that case, the required Feflux may be lower than previously estimated. Although our work in the MDV show that the total Feflux from streams represent a small fraction of Fe compared to eolian input or icebergs other studies of coastal streams from maritime Antarctica demonstrate that terrestrial streams can contribute significant quantities of dFe and acid-soluble Fe to the Southern Ocean (Hodson et al., 2017) and may be increasingly important as the ice cover melts. Hodson et al. (2017) estimated the contribution of dissolved Fe from surface runoff was approximately 2 orders of magnitude higher than the contributions from icebergs (6 to 81 kg·km2·a1and 0–1.2 kg·km 2·a1) while estimates of acid soluble Feflux in suspended sediments from glacial streams was up to 1,000-fold greater than icebergs. 4.3. Fe and Nutrient Ratios in Terrestrial Streams and the Southern Ocean When compared to the phytoplankton ratio, it is clear that MDV streams could be an important source of Fe (Fe:P>>0.0075; Fe:N>>0.0005) and P (N:P<<16) relative to N and Si, where Fe:P ratios are up to 2 orders of magnitude higher, and N:P ratios are up to 16 times lower than both the phytoplankton and the coastal Ross Sea mixed layer water ratios (Table 5). 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. Recently, interest in primary productivity in the Southern Ocean has revealed variability in nutrient uptake ratios that are not strictly Redfield like. This variation may be due to many biogeochemical or physical

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Table 5 Ratios of Average Molar Concentrations of Filterable Nutrients for Three Streams and Marine Phytoplankton 3 Stream fFe N as NO3 PasPO4 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 (Ho et al., 2003, Brzezinski et al., 2003) 0.0075a 16a 1a 60 + 6b Phytoplankton uptake from Southern Ocean (Takeda, 1998) — 12 1 26 1 Note. Nutrients are normalized to P, unless the P concentration was below the detection limit (0.17μM), in which case ratios are normalized to the detection limit. Only samples collected at the outlet of each stream were used to calculate average. aHo et al. (2003). bBrzezinski et al. (2003).

factors, including micronutrient/macronutrient and light availability, cell size, phytoplankton species, and temperature (Arrigo et al., 1999; de Baar et al., 1997; Klunder et al., 2014; Moore et al., 2013) that can all affect nutrient uptake and, hence, nutrient concentrations 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 higher percentage of large (>5,000μm3) diatoms compared to sites in the Weddell Sea, which showed no relationships between dFe and nutrient uptake (Klunder et al., 2014). Thus, increased N uptake appeared to be driven by both micronutrient availability (Fe) and cell size (Klunder et al., 2014). 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—P.antarctica, a colony-forming haptophyte, and

diatoms.P.antarcticawere more efficient in utilizing PO4,fixing up to 56% more CO2 per mole 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, increased stream input into the coastal ocean would greatly favor P.antarcticagrowth in the coastal phytoplankton community relative to diatoms. Further work is necessary to support this claim, but increased meltwaterfluxes could have important consequences on species composition as well as primary production rates.

4.4. Bioavailability of Particulate Fe Numerous studies have attempted to quantify the amount of Fe associated with particulate matter in polar/glacier environments that could be solubilized and hence be potentially bioavailable. A number have looked at suspended material and/or glacialflourassociated with glacier meltwater/runoff (Hopwood et al., 2014; Monien et al., 2017; Schroth et al., 2014), while others have investigated eolian materials associated with either sea or glacier ice in Antarctica (Bhattachan et al., 2015; Deuerling et al., 2014; Kim et al., 2015; Lannuzel et al., 2016; Winton et al., 2016). In some cases, both adissolvedand atotal dissolvablefraction were defined. However, not all the methodological procedures used to do this are the same, and therefore, directly comparing these results is difficult. For the sake of simplicity, we compare the studies that measured the released fFe after the solids were either submerged in water or after the ice associated with the particles melted, allowing solid-liquid water interactions to occur. In these cases, the percentage of total Fe present that issolublein water is usually very low—from 0.1% for glacial streams in Greenland (Hopwood et al., 2014) to 0.0004% for glacier particulates from the MDV (Deuerling et al., 2014). The actual concentrations themselves—from 20–1,680 nM in McMurdo Sound sea ice (Winton et al., 2016) to 2.6–29.2 nM in King George Island snow (Kim et al., 2015)—are however biogeochemically significant and obviously could be important additions of bioavailable Fe into polar coastal regions. There is clearly a difficulty in quantifying these studies into a more regional picture due to the various sources of materials, variable grain sizes, and the lack of consistency in the procedures (Hopwood et al., 2014; Schroth et al., 2014; Winton et al., 2014). For example, we have demonstrated above that the largest fraction of Fe entering the coastal Ross Sea/McMurdo Sound from the streams is the acid-dissolvable Fe (adFe), yet we do not know what percentage of it is biologically available.

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4.5. Fate of Fe in Coastal Waters of Antarctica 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, 2011; Raiswell & Canfield, 2012). On average, scavenging and sinking are thought to be the most dominant export of nanoparticles and colloids (Raiswell & Canfield, 2012) and will likely be even more important at the freshwater-saltwater interface where rapid sedimentation can occur. Although much of the work examining freshwater fFe removal entering a marine environment has been done in temperate settings (Boyle et al., 1977), there have been a few studies done in polar regions. Schroth et al. (2014) demonstrated that over 85% of the soluble Fe from glacier runoff was lost byflocculation of colloidal material during estuarine mixing in Alaska. Kim et al. (2015) found that a large fraction of Fe supplied into the coastal zone of King George Island, Antarctica settles out before being biologically utilized. Zhang et al. (2015) also observed extensive removal of fFe as glacier melt enters an estuary in Svalbard. Hopwood et al. (2016) have shown that in-fjord processes remove large amounts of Fe from Greenland glacier melt. On the other hand, one study has argued that in Arctic Ocean water, the Feflocs that form in estuarine waters have lower settling velocities than previously thought, due, in part, to their different sizes and shapes, and that a greater understanding of the mechanisms offloc formation in the environment of glacier meltwater entering cold, polar oceans is needed (Markussen et al., 2016). Nonetheless, probably much of the Fe carried into the McMurdo Sound via MDV streams is likely to be removed close to its entering location. 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; Croot et al., 2001, 2008). This could be an important process for the Fe biogeochemistry in the coastal Southern Ocean during the austral summer, where 24 hr 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) andfiltered (0.72 ± 0.23 nM,<0.2μm) seawater are in excess of dFe concentrations in the Southern Ocean (Boye et al., 2001; Croot & Heller, 2012; Nolting et al., 1998). This process, photochemical reduction and solubilization, aid in the transformation of Fe to more bioavailable forms, which have been shown to be taken up at rates with 1,000-fold variability (Lis et al., 2015). Lis et al. (2015) describe this variability as a bioavailability envelope, with dissolved, unchelated Fe at the fast end and chelated Fe at the slow end. Further research into shallow coastal waters like the McMurdo Sound and at the stream-ocean interface will be necessary to determine the actual fate of Feflowing from subaerial streams like those in the MDV.

4.6. Potential Impacts of Climate Change on Stream Flow in the MDV Several landscape and hydrological changes are expected to occur in the ice-free areas of Antarctica as greenhouse gas concentrations increase and warming continues. Changes in MDV will 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 (Fountain et al., 2014). These changes would in turn lead to larger hyporheic zones, and greater hydrological connectivity of the landscape, increasing the potential for rock-water interaction and subsequent solubilization and transport of Fe. Indeed, there has been an increase inflow in Commonwealth stream observed in the last 15 years (2001–2016), where the annualflows have been higher than thefirst 8 years of the total MCM-LTER record, 1993–2001 (http://mcmlter.org). Some of the most vulnerable locations for landscape change lie along the relatively warm coastal valleys, and include those that are underlain by buried ice, which include Taylor, Garwood, and to some extent, Miers Valleys (Fountain et al., 2014). One of the most important influences in determining the dFe concentrations in these streams is likely the deepening of the active layer, and subsequent broadening of the hyporheic zones. In addition, the retreat of coastal glaciers could lead to more exposed (subaerial) surface providing additional sources of Fe, leading to increased dFe and fFe loads in these streams. When considering the entire Antarctic continent, most of the current impact of warming and glacier retreat is in West Antarctica and the Antarctic Peninsula region (Harig & Simons, 2015). These changes have already impacted both the coastal marine and terrestrial ecosystems there with changes in primary production, biomass, and biodiversity (Amesbury et al., 2017; Montes-Hugo et al., 2009). In the Peninsula region, the

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glacier ice loss is27 ± 2 Gt/year, with the acceleration of loss at5 ± 1 Gt/year2between 2003 and 2014 (Harig & Simons, 2015). In the northern portion of the Antarctic Peninsula, glaciers appear to be more sensitive to temperature than precipitation increases, and hence, as temperatures warm, more glacier melt will occur (Davies et al., 2014). This is the region that Lyons et al. (2015) suggested might have increased subaerial waterflow and hence input of Fe into the coastal ocean. In fact, Lee et al. (2017) have recently suggested that by the turn of the century, ice-free areas in Antarctic ice could expand by over 17,000 km2, most of which will be in the Peninsula region. This increase in glacier loss and meltwater generation will impact the N, P, and Si budgets as well (Corbett et al., 2017). Needless to say, enhanced glacier melting will increase nutri- entfluxes from Antarctica, as has been previously highlighted in Greenland (Hawkings et al., 2014). These enhancedfluxes could provide a small but potentially significant negative feedback on climate change by

increasing coastal primary production and CO2drawdown.

5. Conclusions The Commonwealth and Wales Streams supply approximately 84,400-mol adFe per year, 240-mol fFe per year, and 40-mol dFe per year to the Coastal Ross Sea. This is several orders of magnitude smaller than the estimatedﬂuxes for other eolian and iceberg sources. Based on our operationally deﬁned physiochemical forms, the pool of fFe in MDV streams is approximately 18–27% dissolved. MDV streams are not only a potential stoichiometry potential source of Fe but also a source of P, N, and Si, to coastal phytoplankton communities. The stoichiometric of the 0.4-μm input of these nutrients in MDV stream water is different than the observed in marine phytoplankton, indicating a major source of Fe and P, relative to N and Si. Future climate warming, especially in the Peninsula region of Antarctica and the Victoria Land coast, can be expected to enhance the glacier retreat, ice/permafrost loss, and subsequent nutrient export to the coastal ocean.

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