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The Geochemistry of Englacial Brine from Taylor Glacier, Antarctica

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The Geochemistry of Englacial Brine from Taylor Glacier, Antarctica RESEARCH ARTICLE The Geochemistry of Englacial Brine 10.1029/2018JG004411 From Taylor Glacier, Antarctica Key Points: W. Berry Lyons1,2 , Jill A. Mikucki3 , Laura A. German1,2, Kathleen A. Welch1,2,4 , • Englacial brine was extracted from 1,2 1,2 5 6,7 Taylor Glacier, Antarctica, using Susan A. Welch , Christopher B. Gardner , Slawek M. Tulaczyk , Erin C. Pettit , clean‐entry techniques Julia Kowalski8 , and Bernd Dachwald9 • This is the first direct sampling of recently discovered subglacial brines 1School of Earth Sciences, The Ohio State University, Columbus, OH, USA, 2Byrd Polar and Climate Research Center, The beneath Taylor Valley, Antarctica 3 • Ohio State University, Columbus, OH, USA, Department of Microbiology, University of Tennessee, Knoxville, Knoxville, TN, Geochemistry suggests that brine is 4 5 of marine origin and has been USA, Now at Institute of Arctic and Alpine Research, University of Colorado Boulder, Boulder, CO, USA, Earth & Planetary 6 subsequently altered by chemical Sciences Department, University of California, Santa Cruz, CA, USA, CNMS Department of Geosciences, University of weathering products Alaska Fairbanks, Fairbanks, AL, USA, 7Now at College of Earth Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA, 8AICES and Faculty of Georesources and Materials Engineering, RWTH Aachen University, Aachen, Germany, 9Faculty of Aerospace Technology, FH Aachen University of Applied Sciences, Aachen, Germany Correspondence to: W. B. Lyons, ‐ [email protected] Abstract Blood Falls is a hypersaline, iron rich discharge at the terminus of the Taylor Glacier in the McMurdo Dry Valleys, Antarctica. In November 2014, brine in a conduit within the glacier was penetrated and sampled using clean‐entry techniques and a thermoelectric melting probe called the Citation: fi Lyons, W. B., Mikucki, J. A., IceMole. We analyzed the englacial brine sample for lterable iron (fFe), total Fe, major cations and anions, German, L. A., Welch, K. A., Welch, S. nutrients, organic carbon, and perchlorate. In addition, aliquots were analyzed for minor and trace A., Gardner, C. B., et al. (2019). The elements and isotopes including δD and δ18O of water, δ34S and δ18O of sulfate, 234U, 238U, δ11B, 87Sr/86Sr, geochemistry of englacial brine from δ81 Taylor Glacier, Antarctica. Journal of and Br. These measurements were made in order to (1) determine the source and geochemical evolution Geophysical Research: Biogeosciences, of the brine and (2) compare the chemistry of the brine to that of nearby hypersaline lake waters and 124, 633–648. https://doi.org/10.1029/ previous supraglacially sampled collections of Blood Falls outflow that were interpreted as end‐member 2018JG004411 brines. The englacial brine had higher Cl− concentrations than the Blood Falls end‐member outflow; Received 19 JAN 2018 however, other constituents were similar. The isotope data indicate that the water in the brine is derived Accepted 25 OCT 2018 from glacier melt. The H4SiO4 concentrations and U and Sr isotope suggest a high degree of chemical Accepted article online 2 FEB 2019 weathering products. The brine has a low N:P ratio of ~7.2 with most of the dissolved inorganic nitrogen in Published online 28 MAR 2019 + the form of NH4 . Dissolved organic carbon concentrations are similar to end‐member outflow values. Our results provide strong evidence that the original source of solutes in the brine was ancient seawater, which has been modified with the addition of chemical weathering products. 1. Introduction The subglacial environment of major ice sheets has become of important scientific interest (e.g., Laybourn‐Parry & Wadham, 2014; Siegert et al., 2011, 2016). Yet little direct evidence exists on the ecology and biogeochemistry of these environments and the processes that control them. Although there have been both modeling efforts (Wadham et al., 2008) and the analyses of refrozen subglacial waters (Christner et al., 2006; Priscu et al., 1999; Royston‐Bishop et al., 2005; Siegert et al., 2003), to date only a few direct samplings and analyses have occurred, most recently along the Whillans Ice Stream in West Antarctica (Achberger et al., 2016; Christner et al., 2014; Michaud et al., 2016; Mikucki et al., 2016; Purcell et al., 2014; Skidmore et al., 2010). Geophysical and remote sensing investigations have demonstrated that Antarctic subglacial aquatic environments are diverse. Subglacial lakes range in size from over 10,000 km2, such as Lake Vostok, to lakes less than 1 km2. Observations include lakes and ponds connected in series by subglacial streams, allowing movement of water between lakes at timescales less than a year, saturated sediments that act as deformable beds under flowing glacier ice, and, undoubtedly, groundwater‐type systems (Ashmore & Bingham, 2014; Fricker et al., 2014; Kyrke‐Smith & Fowler, 2014; Mikucki et al., 2015; Siegert, 2016; Wright & Siegert, 2012). All of these subglacial aquatic systems remain poorly understood due to the lack of direct sampling—the logistical challenges associated with drilling through hundreds of meters of ice presents a fi ‐ ‐ ©2019. American Geophysical Union. signi cant barrier. Differences in water residence times, water rock ratios, refreezing at the water ice All Rights Reserved. interface, basal geologic conditions, and biological processes could produce water chemistries that vary LYONS ET AL. 633 Journal of Geophysical Research: Biogeosciences 10.1029/2018JG004411 greatly (Wadham et al., 2010). Besides the obvious ecological interest in these subglacial environments, they can be extremely important in regard to glacier dynamics as well (i.e., Siegfried et al., 2016; Stearns et al., 2008). Although it is not clear currently how the brine affects the movement of Taylor Glacier, the hypersa- line nature of the Taylor Glacier subglacial system keeps the water from freezing and thus could impact gla- cier dynamics (Hubbard et al., 2004). Polythermal glaciers in the Arctic are known to release subglacial waters, particularly at the start of the melt season. These waters have long been studied to better understand the biogeochemistry below ice. Because glaciers in the Antarctic that terminate on land are primarily cold based, there is limited opportunity for the surface collection of any released subglacial materials. Blood Falls, the system we describe here, is cur- rently the only known exception. In addition to the interest in subglacial environments on Earth, the subglacial brine that we describe within this paper is of great interest from a planetary geobiological perspective as well. Pluto has just become the seventh body in our solar system thought to harbor an “ocean” beneath an ice cover (Nimmo et al., 2016). The existence of subcryospheric “oceans” on such bodies within our solar system including Enceladus, Titan, and Europa has generated great interest (e.g., Mitri et al., 2014; Postberg et al., 2011), while most recently evidence of subglacial water has been detected below the ice of the South Polar Layered Deposits on Mars (Orosei et al., 2018). Whether these subcryospheric oceans can sustain life today is a major question in astrobiology and planetary exploration. Interest in the subglacial waters on Earth is also at least partially driven by examining the lifeforms in these environments and describing the structure and function of the ecosystems present. For example, in the recent Scientific Committee on Antarctic Research Horizon Scan exercise, one of the questions posed was “How do subglacial systems inform models for the development of life on Earth and elsewhere?” (Kennicutt et al., 2015). It has been demonstrated that the geochemistry of the subglacial environment influences the microbial diversity in these systems (Mitchell et al., 2013) and that coupled biogeochemical processes can allow microbial growth (Mikucki et al., 2009). The McMurdo Dry Valleys are the largest ice‐free region in Antarctica and represent a location where both the West Antarctic Ice Sheet (WAIS) and East Antarctic Ice Sheet (EAIS) have advanced and retreated throughout the Pleistocene (Denton et al., 1989). The Taylor Glacier, which terminates in Taylor Valley (Figure 1), is one of the easternmost portions of the EAIS. Blood Falls, a hypersaline, iron‐rich subglacial flow, discharges at the terminus of Taylor Glacier in the westernmost portion of Taylor Valley (Mikucki et al., 2009). The source of this discharge is believed to be a subglacial aquifer (Mikucki et al., 2015) several kilometers upstream that flows toward the terminus until it is connected to the sur- face through a perennial englacial fracture (Badgeley et al., 2017). In this paper we describe for the first time, the biogeochemical composition of this hypersaline subglacial environment acquired through direct clean‐entry sampling techniques. 1.1. Description of the Taylor Glacier Subglacial Brine System Blood Falls was first described chemically by Black et al. (1965). These authors concluded that the existence of the subglacial brine had “far‐reaching consequences” and acknowledged that the extent and origin of the brine were important scientific questions. Taylor Glacier is described as frozen to its bed and surface melt water does not penetrate to the base (Fountain et al., 1999). Robinson (1984) first hypothesized that subgla- cial brine may be sealed below the lower several kilometers of Taylor Glacier, causing what was described as polythermal glacier behavior. Using ice‐penetrating radar, Hubbard et al. (2004) detected a zone 3–6km
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