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Geochemistry of Contrasting Stream Types, Taylor Valley, Antarctica

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Geochemistry of Contrasting Stream Types, Taylor Valley, Antarctica Geochemistry of contrasting stream types, Taylor Valley, Antarctica Russell S. Harmon1,†, Deborah L. Leslie2, W. Berry Lyons3, Kathleen A. Welch4, and Diane M. McKnight4 1 Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina 27695, USA 2 Department of Earth Sciences, University of Memphis, Memphis, Tennessee 38152, USA 3 School of Earth Sciences and Byrd Polar and Climate Research Center, Ohio State University, Columbus, Ohio 43210, USA 4 Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado 80309, USA ABSTRACT INTRODUCTION of the MCM-LTER project in 1993 coincided with a period of sustained summer cooling and The McMurdo Dry Valley region is the Located at 76°30′ to 78°30′ S latitude and low streamfows that were associated with the largest ice-free area of Antarctica. Ephemeral 160° to 164° E longitude in the central Trans- effect of the Antarctic ozone hole on atmo- streams fow here during the austral summer, arctic Mountains between the East Antarctic Ice spheric dynamics over the continent (Doran transporting glacial meltwater to perennially Sheet and the Ross Sea coast of Victoria Land et al., 2002; Walsh, 2009). This period of cool- ice-covered, closed basin lakes. The chemistry in Antarctica (Fig. 1A), the McMurdo Dry Val- ing was interrupted by warm, sunny conditions of 24 Taylor Valley streams was examined over ley region is a polar desert on the western edge in the summer of 2001–2002, when substantial the two-decade period of monitoring from of McMurdo Sound that comprises the larg- fooding occurred throughout the McMurdo 1993 to 2014, and the geochemical behavior of est ice-free area of Antarctica. Here, a set of Dry Valley region. That summer marked the end two streams of contrasting physical and biolog- E-W–trending valleys extends across an area of of the cooling trend and a return to the previ- ical character was monitored across the seven ∼4800 km2 as a mosaic of Paleozoic–Mesozoic ous pattern of strong inter-annual variation in weeks of the 2010–2011 fow season. Four spe- bedrock outcrops, glaciers, mostly closed basin streamfow observed during the 1970s (Gooseff – cies dominate stream solute budgets: HCO3 , lakes, and open expanses of barren, frozen pat- et al., 2017a). 2+ + – 2– 2+ + Ca , Na , and Cl , with SO4 , Mg , and K terned ground covered by Quaternary glacial, The MCM-LTER project has monitored the present in signifcantly lesser proportions. All lacustrine, and alluvial deposits (McKelvey and water quality of many streams in Taylor Val- streams contain dissolved silica at low con- Webb, 1959; Green et al., 1988). This landscape ley over an extended period that covers the centrations. Across Taylor Valley, streams are lacks vascular plants but, despite its unusually full range in fow conditions observed over characterized by their consistent anionic geo- harsh hyper-arid polar climate, supports robust the entire 50-year record of the Onyx River chemical fngerprint of HCO3 > Cl > SO4, but aquatic ecosystems dominated by microbial (Fig. 1C). For this reason, it is timely to ana- there is a split in cation composition between mats and phytoplankton with soil ecosystems lyze that valuable geochemical record to obtain 14 streams with Ca > Na > Mg > K and 10 hosting a variety of microscopic organisms a more detailed understanding of the chemical streams with Na > Ca > Mg > K. (Powers et al., 1998). dynamics of Antarctic streams, which will also Andersen Creek is a frst-order proglacial The U.S. National Science Foundation serve as a baseline against which to compare stream representative of the 13 short streams established a McMurdo Long-Term Ecological future changes. Because the ecological structure that fow <1.5 km from source to gage. Von Research site (the MCM-LTER project) at Tay- and function of the lakes and coastal ocean into Guerard is representative of 11 long streams lor Valley in 1993 that has the long-term objec- which McMurdo Dry Valley region streams dis- 2–7 km in length characterized by exten- tive of understanding the terrestrial and aquatic charge depend on the hydrological connectivity sive hyporheic zones. Both streams exhibit processes operating in this polar desert ecosys- between glaciers and permanent closed basin a strong daily cycle for solute load, tempera- tem. Taylor Valley (Fig. 1B) extends some 35 km lakes (Gooseff et al., 2011), it is also essential to ture, dissolved oxygen, and pH, which vary in a NE-SW orientation from the Ross Sea coast understand the geochemistry of these seasonal in proportion to discharge. A well-expressed to the terminus of the Taylor Glacier at the streams at different temporal scales. Therefore, diurnal co-variation of pH with dissolved southwestern edge of the polar plateau. Numer- this study examined the long-duration/low- oxygen is observed for both streams that ous ephemeral streams develop here each austral frequency stream chemistry record of streams refects different types of biological control. summer, where they transport glacial meltwater of contrasting character in Taylor Valley and The relative consistency of Von Guerard com- across expanses of barren ground to three peren- made higher frequency measurements of two position over the summer fow season refects nially ice-covered, closed basin lakes. streams of contrasting character over the sum- chemostatic regulation, where water in tran- Since the inception of the MCM-LTER proj- mer of 2010–2011 to obtain a detailed temporal sient storage introduced during times of high ect, there have been major climate changes record for a single fow season. Thus, data from streamfow has an extended opportunity for in the McMurdo Dry Valley region that have this study contribute to the temporal and spatial water-sediment interaction, silicate mineral driven large, inter-annual variations in stream- understanding of the geochemical dynamics dissolution, and pore-water exchange. fow. Measurement of fow for the Onyx River, of McMurdo Dry Valley region streams that is the longest river in the McMurdo Dry Valley required to establish a baseline against which Russell S. Harmon http://orcid.org/0000-0003- region located in Wright Valley (Fig. 1A), began to assess the impacts of global climate change 1967-3611 in 1970 and today is the longest environmental going forward. As the climate in Antarctica †[email protected]. record of the region (Fig. 1C). The beginning continues to warm and glacial ice melts more GSA Bulletin; January/February 2021; v. 133; no. 1/2; p. 425–448; https://doi.org/10.1130/B35479.1; 14 fgures; 6 tables; 1 supplemental fle. published online 1 July 2020 For permission to copy, contact [email protected] 425 © 2020 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/133/1-2/425/5202617/425.pdf by University of Colorado Boulder user on 26 May 2021 Harmon et al. face fows that determine solute accumulation is necessary to predict future behavior. A BACKGROUND B The McMurdo Dry Valley region’s climate is characterized by a mean annual air temperature in valley bottoms varying from –21 °C to –18 °C, which during the summer can rise daily to 10 °C at some locations, and between 2–50 cm annual precipitation that falls mostly as snow (Doran et al., 2002; Fountain et al., 2010). There is a slight climate gradient inland from cloudy, wetter, and colder conditions near the coast toward drier and warmer conditions inland. Most McMurdo Dry Valley region glaciers are polar alpine glaciers, but a few like Taylor Glacier at the southwestern end of Taylor Valley are outlet glaciers of the East Antarctic Ice Sheet. The larg- est alpine glaciers descend only short distances into the valley from the surrounding mountains because sublimation and melting exceed snow accumulation below 1500 m in all seasons (Chinn, 1985). Local relief within the McMurdo Dry Val- ley region is <3000 m, and the landscape is ) 3 C considered to have been geomorphologically m 6 Onyx River (Wright Valley) stable over the past few million years (Denton et al., 1993). Exposed lithologies consist of a pre-Ordovician metasedimentary basement sequence composed of schists, hornfels, and marble; a younger group of granite and granite gneiss intrusions of lower Paleozoic age; and the overlying mid-Paleozoic to mid-Mesozoic Beacon Sandstones that have been intruded by the Jurassic Ferrar Dolerites (McKelvey and Webb, 1959). Valley foors are covered with moraines and a thin patchy cover of Quater- nary glacial, lacustrine, and alluvial sediments Onyx River Annual Flow (x10 Onyx River that are remarkably similar across the region and occasional cinder cones of the McMurdo Volcanic Group (McKelvey and Webb, 1959; Denton et al., 1989). A texturally coarse and Figure 1. (A) Location map of the McMurdo Dry Valley region of Antarctica. (B) Map of heterogeneous alluvial soil derived from marine Taylor Valley showing the positions of major glaciers, central closed basin lakes, and the sediments, paleo-lake beds, valley wall collu- two streams that are the focus of this study: (1) Andersen Creek and (2) Von Guerard. (C) vium, and the weathering of bedrock glacial till Histogram of total annual fow of the Onyx River in Wright Valley, the longest river in the covers ∼95% of valley foors (McCraw, 1967; McMurdo Dry Valley region and on the Antarctic continent. The dark gray bars indicate Bockheim, 2002). This soil, mapped as about the years of the long-term geochemical analysis presented in this study; the light gray bars half shallowly ice-cemented and half dry-frozen indicate the years prior to the McMurdo Long-Term Ecological Research (MCM-LTER) (Bockheim et al., 2007), is strongly cryoturbated program, when fow measurements were made by the New Zealand Antarctic program, and (Bockheim and McLeod, 2008).
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