Taylor Glacier Research Articles

Microbial assemblages and associated biogeochemical processes in Lake Bonney, a permanently ice-covered lake in the McMurdo Dry Valleys, Antarctica

BackgroundLake Bonney, which is divided into a west lobe (WLB) and an east lobe (ELB), is a perennially ice-covered lake located in the McMurdo Dry Valleys of Antarctica. Despite previous reports on the microbial community dynamics of ice-covered lakes in this region, there is a paucity of information on the relationship between microbial genomic diversity and associated nutrient cycling. Here, we applied gene- and genome-centric approaches to investigate the microbial ecology and reconstruct microbial metabolic potential along the depth gradient in Lake Bonney.ResultsLake Bonney is strongly chemically stratified with three distinct redox zones, yielding different microbial niches. Our genome enabled approach revealed that in the sunlit and relatively freshwater epilimnion, oxygenic photosynthetic production by the cyanobacterium Pseudanabaena and a diversity of protists and microalgae may provide new organic carbon to the environment. CO-oxidizing bacteria, such as Acidimicrobiales, Nanopelagicales, and Burkholderiaceae were also prominent in the epilimnion and their ability to oxidize carbon monoxide to carbon dioxide may serve as a supplementary energy conservation strategy. In the more saline metalimnion of ELB, an accumulation of inorganic nitrogen and phosphorus supports photosynthesis despite relatively low light levels. Conversely, in WLB the release of organic rich subglacial discharge from Taylor Glacier into WLB would be implicated in the possible high abundance of heterotrophs supported by increased potential for glycolysis, beta-oxidation, and glycoside hydrolase and may contribute to the growth of iron reducers in the dark and extremely saline hypolimnion of WLB. The suboxic and subzero temperature zones beneath the metalimnia in both lobes supported microorganisms capable of utilizing reduced nitrogens and sulfurs as electron donors. Heterotrophs, including nitrate reducing sulfur oxidizing bacteria, such as Acidimicrobiales (MAG72) and Salinisphaeraceae (MAG109), and denitrifying bacteria, such as Gracilimonas (MAG7), Acidimicrobiales (MAG72) and Salinisphaeraceae (MAG109), dominated the hypolimnion of WLB, whereas the environmental harshness of the hypolimnion of ELB was supported by the relatively low in metabolic potential, as well as the abundance of halophile Halomonas and endospore-forming Virgibacillus.ConclusionsThe vertical distribution of microbially driven C, N and S cycling genes/pathways in Lake Bonney reveals the importance of geochemical gradients to microbial diversity and biogeochemical cycles with the vertical water column.

Deformation, Strength and Tectonic Evolution of Basal Ice in Taylor Glacier, Antarctica

AbstractObservation and measurements of ice structure and deformation made in tunnels excavated into the margin of Taylor Glacier, a polythermal glacier in the McMurdo Dry Valleys of Antarctica, reveal a complex, rapidly deforming basal ice sequence. Displacement measurements in the basal ice, which is at a temperature of −18°C, together with the occurrence of cavities and slickenslides, suggest that sliding or rapid deformation in thin zones of high shear occurs at structural discontinuities within the basal zone. Strain measurements show that the highest strain rates occur in ice with average debris concentrations of 26% followed by ice with debris concentrations of around 12%. The lowest strain rates occur in clean bubbly ice that has very low debris concentrations (<0.02%). Deformation within the basal ice sequence is dominated by simple shear but disrupted by folding which results in shortening of the debris‐bearing ice followed by attenuation of the folds due to progressive simple shear which generates predominantly laminar basal ice structures. About 60% of glacier surface velocity can be attributed to deformation within the 4.5 m thick sequence of basal ice that was monitored for this study, and 15% of motion can be attributed to sliding or very localized shear. The combination of high debris concentrations and high strain rates in the debris‐bearing ice results in high rates of abrasion and the production of striated and facetted clasts typical of temperate glaciers, even though the basal ice is at a temperature of −18°C.

Meteorological drivers of melt at two nearby glaciers in the McMurdo Dry Valleys of Antarctica

Abstract We study the meteorological drivers of melt at two glaciers in Taylor Valley, Antarctica, using 22 years of weather station observations and surface energy fluxes. The glaciers are located only 30 km apart, but have different local climates; Taylor Glacier is generally drier and windier than Commonwealth Glacier, which receives more snowfall due to its proximity to the coast. Commonwealth Glacier shows more inter-annual melt variability, explained by variable albedo due to summer snowfall events. A significant increase in surface melt at Commonwealth Glacier is associated with a decrease in summer minimum albedo. Inter-annual variability in melt at both glaciers is linked to degree-days above freezing during föhn events, occurring more frequently at Taylor Glacier. At Taylor Glacier melt occurs most often with positive air temperatures, but föhn conditions also favour sublimation, which cools the surface and prevents melt for the majority of the positive air temperatures. At Commonwealth Glacier, most of the melt instead occurs with sub-zero air temperatures, driven by strong solar radiative heating. Future melt at Taylor Glacier will likely be more sensitive to changes in föhn events, while Commonwealth Glacier will be impacted more by changes in near coastal weather, where moisture inputs can drive cloud cover, snowfall and change albedo.

Using ice core measurements from Taylor Glacier, Antarctica, to calibrate in situ cosmogenic 14C production rates by muons

Abstract. Cosmic rays entering the Earth's atmosphere produce showers of secondary particles such as protons, neutrons, and muons. The interaction of these particles with oxygen-16 (16O) in minerals such as ice and quartz can produce carbon-14 (14C). In glacial ice, 14C is also incorporated through trapping of 14C-containing atmospheric gases (14CO2, 14CO, and 14CH4). Understanding the production rates of in situ cosmogenic 14C is important to deconvolve the in situ cosmogenic and atmospheric 14C signals in ice, both of which contain valuable paleoenvironmental information. Unfortunately, the in situ 14C production rates by muons (which are the dominant production mechanism at depths of >6 m solid ice equivalent) are uncertain. In this study, we use measurements of in situ 14C in ancient ice (>50 ka) from the Taylor Glacier, an ablation site in Antarctica, in combination with a 2D ice flow model to better constrain the compound-specific rates of 14C production by muons and the partitioning of in situ 14C between CO2, CO, and CH4. Our measurements show that 33.7 % (±11.4 %; 95 % confidence interval) of the produced cosmogenic 14C forms 14CO and 66.1 % (±11.5 %; 95 % confidence interval) of the produced cosmogenic 14C forms 14CO2. 14CH4 represents a very small fraction (<0.3 %) of the total. Assuming that the majority of in situ muogenic 14C in ice forms 14CO2, 14CO, and 14CH4, we also calculated muogenic 14C production rates that are lower by factors of 5.7 (3.6–13.9; 95 % confidence interval) and 3.7 (2.0–11.9; 95 % confidence interval) for negative muon capture and fast muon interactions, respectively, when compared to values determined in quartz from laboratory studies (Heisinger et al., 2002a, b) and in a natural setting (Lupker et al., 2015). This apparent discrepancy in muogenic 14C production rates in ice and quartz currently lacks a good explanation and requires further investigation.

Organic matter distribution in the icy environments of Taylor Valley, Antarctica

Glaciers can accumulate and release organic matter affecting the structure and function of associated terrestrial and aquatic ecosystems. We analyzed 18 ice cores collected from six locations in Taylor Valley (McMurdo Dry Valleys), Antarctica to determine the spatial abundance and quality of organic matter, and the spatial distribution of bacterial density and community structure from the terminus of the Taylor Glacier to the coast (McMurdo Sound). Our results showed that dissolved and particulate organic carbon (DOC and POC) concentrations in the ice core samples increased from the Taylor Glacier to McMurdo Sound, a pattern also shown by bacterial cell density. Fluorescence Excitation Emission Matrices Spectroscopy (EEMs) and multivariate parallel factor (PARAFAC) modeling identified one humic-like (C1) and one protein-like (C2) component in ice cores whose fluorescent intensities all increased from the Polar Plateau to the coast. The fluorescence index showed that the bioavailability of dissolved organic matter (DOM) also decreased from the Polar Plateau to the coast. Partial least squares path modeling analysis revealed that bacterial abundance was the main positive biotic factor influencing both the quantity and quality of organic matter. Marine aerosol influenced the spatial distribution of DOC more than katabatic winds in the ice cores. Certain bacterial taxa showed significant correlations with DOC and POC concentrations. Collectively, our results show the tight connectivity among organic matter spatial distribution, bacterial abundance and meteorology in the McMurdo Dry Valley ecosystem.

A Multi-Technique Analysis of Surface Materials From Blood Falls, Antarctica

Aperiodic discharge of brine at Blood Falls forms a red-tinged fan at the terminus of Taylor Glacier, Antarctica. Samples from this discharge provide an opportunity for mineralogical study at a Martian analogue study site. Environmental samples were collected in the field and analyzed in the laboratory using Fourier transform infrared, Raman, visible to near-infrared, and Mössbauer spectroscopies. Samples were further characterized using microprobe and inductively coupled plasma optical emission spectroscopy for chemistry, and x-ray diffraction, scanning electron microscopy, and transmission electron microscopy for mineralogy, crystallography, and chemistry. The mineralogy of these samples is dominated by the carbonate minerals calcite and aragonite, accompanied by quartz, feldspar, halide, and clay minerals. There is no strong evidence for crystalline iron oxide/hydroxide phases, but compositionally and morphologically diverse iron- and chlorine-rich amorphous nanospheres are found in many of the samples. These results showcase the strengths and weaknesses of different analytical methods and underscore the need for multiple complementary techniques to inform the complicated mineralogy at this locale. These analyses suggest that the red color at Blood Falls arises from oxidation of dissolved Fe2+ in the subglacial fluid that transforms upon exposure to air to form nanospheres of amorphous hydroxylated mixed-valent iron-containing material, with color also influenced by other ions in those structures. Finally, the results provide a comprehensive mineralogical analysis previously missing from the literature for an analogue site with a well-studied sub-ice microbial community. Thus, this mineral assemblage could indicate a habitable environment if found elsewhere in the Solar System.

Comparison of ground-based and airborne transient electromagnetic methods for mapping glacial and permafrost environments: Cases from McMurdo Dry Valleys, Antarctica

The transient electromagnetic (TEM) method is a non-invasive geophysical tool well-suited for subsurface imaging in cold and polar regions, where common targets are associated with strong contrasts in electrical resistivity. By imaging the electrical properties of the subsurface, the TEM methods can discriminate between geological units such as frozen ground (permafrost), fresh/saline groundwater systems, and bedrock/glacier ice. In this study, we compare TEM data acquired with ground-based and airborne TEM systems. We demonstrate the mapping capabilities of these two approaches in high latitude polar environments with datasets from Taylor Glacier, Lake Vanda, and Canada Glacier in the McMurdo Dry Valleys of Antarctica. The results show a high consistency between the airborne and ground-based TEM data, both with a high resolution and a deep penetration depth down to hundreds of meters due to the resistive background material, which makes both approaches capable of mapping hydrological systems and identifying the base of glaciers. The airborne TEM approach offers an unmatched spatial data coverage in difficult terrain and a far improved lateral resolution compared to the static ground-based system. The ground-based TEM system offers the possibility for using larger transmitter coils and longer stacking times and therefore has potential for reaching deeper penetration depths. The ground-based TEM approach is hence a valuable tool that can provide consistent imaging results while also being far more accessible in terms of cost and field logistics compared to an airborne TEM campaign.

Wintertime Brine Discharge at the Surface of a Cold Polar Glacier and the Unexpected Absence of Associated Seismicity

AbstractA subglacial groundwater system beneath Taylor Glacier, Antarctica, discharges hypersaline, iron‐rich brine episodically at the glacier surface to create Blood Falls. However, the triggering mechanism for these brine release events is not yet understood. Identifying which fracture processes are observed seismically can help us better characterize the hydrological system at Taylor Glacier, and more generally, provide us with a broader understanding of englacial hydrologic activity in cold glaciers. We document wintertime brine discharge using time‐lapse photography. Subfreezing air temperatures during the brine discharge indicate that surface melt‐induced hydrofracture is an unlikely trigger for brine release. Further, we analyze local seismic data to test a hypothesis that fracturing generates elevated surface wave energy preceding and/or coinciding with brine release events. Our results show no discernible elevated Rayleigh wave activity prior to or during Blood Falls brine release. Instead, we find a pattern of seismic events dominated by a seasonal signal, with more Rayleigh events occurring in the summer than the winter from the Blood Falls source area. We calculate that the volumetric opening of cracks that would generate Rayleigh waves at our detection limits are of similar size to myriad cracks in glacier ice, lake ice, and frozen sediment in the terminus area. We therefore propose that any fracturing coincident with brine release activity likely consists of a series of smaller opening events that are masked by other seismicity in the local environment.

Charting the “Bloody” Brine Flows from an Antarctic Glacier

Photographs and field observations yield a more complete historical record of the ebbs and flows of the so-called Blood Falls on Taylor Glacier.

Draft Genome Sequence of Shewanella sp. Strain BF02_Schw, Isolated from Blood Falls, a Feature Where Subglacial Brine Discharges to the Surface of Taylor Glacier, Antarctica

ABSTRACTWe report the sequencing, assembly, and draft genome of Shewanella sp. strain BF02_Schw. The assembly contains 5,304,243 bp, with a GC content of 41.43%.

Recent advances in Quaternary paleoclimate research using Antarctic blue ice

<p indent="0mm">Remarkable scientific discoveries have been made from the studies of ice cores drilled in polar ice sheets and mountain ice caps. These samples serve as the most accurate archives of the past atmospheric composition thus far. Two milestone achievements of ice cores include a continuous record of atmospheric greenhouse gas concentrations over the past eight glacial cycles (800 ka) and the discovery of abrupt climate change events on millennial timescale, both made possible by deep drilling in polar ice sheets. Yet, this conventional approach of deep drilling is faced with challenges from prohibitive logistical and operational cost and limited sample supply, particularly with greater depth. To address these challenges, shallow coring in blue ice areas has emerged as an appealing alternative. Two significant advances have been recently achieved from blue ice studies. Ice older than <sc>800 ka</sc> from the Allan Hills Blue Ice Area was discovered and the trapped gases inside the ice allow, for the first time, for the direct observation of atmospheric carbon dioxide concentrations (pCO₂) before <sc>800 ka.</sc> The data show no long-term decline in atmospheric pCO₂, and consequently, the Mid-Pleistocene Transition is not the result of cooling resulting from a decreasing pCO₂. Moreover, large-volume samples retrieved by a large-diameter ice drill (“Blue Ice Drill”) in the Taylor Glacier Blue Ice Area allow for novel geochemical analyses such as the radiocarbon (¹⁴C) content of methane (CH₄). The ¹⁴C of CH₄ trapped in the Taylor Glacier ice suggests that old carbon reservoirs were not responsible for the deglacial rise of CH₄ in the last glacial cycle. Another example of new geochemical methods enabled by the unprecedented sample availability offered by the blue ice areas is the elemental ratios of xenon, krypton, and nitrogen which are sensitive to the mean ocean temperature (MOT). Taylor Glacier ice samples dating back to the penultimate glacial period record <sc>1.1±0.3°C</sc> warmer-than-modern MOT values at <sc>129 ka</sc>, near the end of the penultimate deglaciation. Despite these advances, several challenges and limits remain. First, to accurately establish a chronology for the blue ice samples requires methods of absolute dating, which have considerable uncertainties at present. A precise chronology can be established via timescale synchronization with existing deep ice cores only when the blue ice is younger than <sc>800 ka.</sc> Second, the original deposition site of the blue ice field is not always known, complicating the interpretations of climate proxies that are sensitive to depositional environments such as the stable water isotopes of the ice. Third, glacial flows disrupt the chronology of the ice and could lead to the incomplete and biased preservation of climate signals. In light of these issues and shortcomings, stratigraphically continuous ice cores cannot be fully replaced by temporally discrete samples from the blue ice areas, although blue ice records hold the potentials to provide snapshots of the critical intervals of the Quaternary climate. Future progress in blue ice research may be made in three directions: (1) The prospecting of new blue ice fields and identification of blue ice areas containing the climate records of key understudied intervals; (2) numerical simulations of glacial dynamics to better the interpretation of blue ice records; and (3) the development of novel analytical techniques that reveal new climate information.

Microbial Species-Area Relationships in Antarctic Cryoconite Holes Depend on Productivity.

The island species–area relationship (ISAR) is a positive association between the number of species and the area of an isolated, island-like habitat. ISARs are ubiquitous across domains of life, yet the processes generating ISARs remain poorly understood, particularly for microbes. Larger and more productive islands are hypothesized to have more species because they support larger populations of each species and thus reduce the probability of stochastic extinctions in small population sizes. Here, we disentangled the effects of “island” size and productivity on the ISAR of Antarctic cryoconite holes. We compared the species richness of bacteria and microbial eukaryotes on two glaciers that differ in their productivity across varying hole sizes. We found that cryoconite holes on the more productive Canada Glacier gained more species with increasing hole area than holes on the less productive Taylor Glacier. Within each glacier, neither productivity nor community evenness explained additional variation in the ISAR. Our results are, therefore, consistent with productivity shaping microbial ISARs at broad scales. More comparisons of microbial ISARs across environments with limited confounding factors, such as cryoconite holes, and experimental manipulations within these systems will further contribute to our understanding of the processes shaping microbial biogeography.

The influence of environmental microseismicity on detection and interpretation of small-magnitude events in a polar glacier setting

AbstractGlacial environments exhibit temporally variable microseismicity. To investigate how microseismicity influences event detection, we implement two noise-adaptive digital power detectors to process seismic data from Taylor Glacier, Antarctica. We add scaled icequake waveforms to the original data stream, run detectors on the hybrid data stream to estimate reliable detection magnitudes and compare analytical magnitudes predicted from an ice crack source model. We find that detection capability is influenced by environmental microseismicity for seismic events with source size comparable to thermal penetration depths. When event counts and minimum detectable event sizes change in the same direction (i.e. increase in event counts and minimum detectable event size), we interpret measured seismicity changes as ‘true’ seismicity changes rather than as changes in detection. Generally, one detector (two degree of freedom (2dof)) outperforms the other: it identifies more events, a more prominent summertime diurnal signal and maintains a higher detection capability. We conclude that real physical processes are responsible for the summertime diurnal inter-detector difference. One detector (3dof) identifies this process as environmental microseismicity; the other detector (2dof) identifies it as elevated waveform activity. Our analysis provides an example for minimizing detection biases and estimating source sizes when interpreting temporal seismicity patterns to better infer glacial seismogenic processes.

Subglacial brine flow and wind-induced internal waves in Lake Bonney, Antarctica

AbstractBrine beneath Taylor Glacier has been proposed to enter the proglacial west lobe of Lake Bonney (WLB) as well as from Blood Falls, a surface discharge point at the Taylor Glacier terminus. The brine strongly influences the geochemistry of the water column of WLB. Year-round measurements from this study are the first to definitively identify brine intrusions from a subglacial entry point into WLB. Furthermore, we excluded input from Blood Falls by focusing on winter dynamics when the absence of an open water moat prevents surface brine entry. Due to the extremely high salinities below the chemocline in WLB, density stratification is dominated by salinity, and temperature can be used as a passive tracer. Cold brine intrusions enter WLB at the glacier face and intrude into the water column at the depth of neutral buoyancy, where they can be identified by anomalously cold temperatures at that depth. High-resolution measurements also reveal under-ice internal waves associated with katabatic wind events, a novel finding that challenges long-held assumptions about the stability of the WLB water column.

Spatial pattern of accumulation at Taylor Dome during Marine Isotope Stage 4: stratigraphic constraints from Taylor Glacier

Abstract. New ice cores retrieved from the Taylor Glacier (Antarctica) blue ice area contain ice and air spanning the Marine Isotope Stage (MIS) 5–4 transition, a period of global cooling and ice sheet expansion. We determine chronologies for the ice and air bubbles in the new ice cores by visually matching variations in gas- and ice-phase tracers to preexisting ice core records. The chronologies reveal an ice age–gas age difference (Δage) approaching 10 ka during MIS 4, implying very low snow accumulation in the Taylor Glacier accumulation zone. A revised chronology for the analogous section of the Taylor Dome ice core (84 to 55 ka), located to the south of the Taylor Glacier accumulation zone, shows that Δage did not exceed 3 ka. The difference in Δage between the two records during MIS 4 is similar in magnitude but opposite in direction to what is observed at the Last Glacial Maximum. This relationship implies that a spatial gradient in snow accumulation existed across the Taylor Dome region during MIS 4 that was oriented in the opposite direction of the accumulation gradient during the Last Glacial Maximum.

Silicate weathering in antarctic ice-rich permafrost: Insights using magnesium isotopes

This study reports that substantial chemical weathering occurs at subzero temperatures in ice-and-salt-rich permafrost in the McMurdo Dry Valleys, Antarctica. Chemical weathering is documented in a 30.0-m core collected in Beacon Valley by measuring the ionic composition, pH, and Mg isotopes of water extracted from thawed ice-rich sediment. Evidence of rock weathering is revealed by coinciding increases in the Mg isotopic composition and pH values. The primary factor that controls weathering is the salt content that leads to unfrozen brine; this is most apparent in the upper 7.0 m where salt content is high, temperatures rise above −21 °C and modeled unfrozen water reaches up to 4.0% of ice-content. In the upper 7.0 m, up to 60% of soluble Mg in the thawed permafrost ice is sourced from Ferrar Dolerite (δ26Mg = −0.22 ± 0.07‰) weathering, resulting in δ26Mg values ranging from of −0.82 ± 0.05‰ to −0.64 ± 0.05‰. Below 7.0 m, temperatures remain below −21 °C, unfrozen water is less than 2.0% of ice-content, and on average, 5% of soluble Mg is sourced from dolerite weathering with δ26Mg values ranging from −1.05 ± 0.05‰ to −0.76 ± 0.05‰. Regions of the core that are modeled to have no unfrozen water show little or no evidence of chemical weathering and relatively constant δ26Mg values close to Taylor Glacier and Beacon Valley snowfall values (–0.93 ± 0.06‰). This study demonstrates that significant chemical weathering occurs at subzero temperatures in permafrost where liquid brines form.

Is the Noble Gas‐Based Rate of Ocean Warming During the Younger Dryas Overestimated?

AbstractNoble gases in ice cores enable reconstructions of past mean ocean temperature. A recent result from the clathrate‐containing WAIS Divide Ice Core showed tight covariation between ocean and Antarctic temperatures throughout the last deglaciation, except for the Younger Dryas interval. In the beginning of this interval, oceans warmed at 2.5 °C/kyr—three times greater than estimates of modern warming. If valid, this challenges our understanding of the mechanisms controlling ocean heat uptake. Here we reconstruct mean ocean temperature with clathrate‐free ice samples from Taylor Glacier to test these findings. The two records agree in net temperature change over the Younger Dryas, but the Taylor Glacier record suggests sustained warming at the more modest rate of 1.1 ± 0.2°C/kyr. We explore mechanisms to explain differences between records and suggest that the noble gas content for the Younger Dryas interval of WAIS Divide may have been altered by a decimeter‐scale fractionation during bubble‐clathrate transformation.

Microbial diversity of an Antarctic subglacial community and high-resolution replicate sampling inform hydrological connectivity in a polar desert.

Antarctic subglacial environments host microbial ecosystems and are proving to be geochemically and biologically diverse. The Taylor Glacier, Antarctica, periodically expels iron-rich brine through a conduit sourced from a deep subglacial aquifer, creating a dramatic red surface feature known as Blood Falls. We used Illumina MiSeq sequencing to describe the core microbiome of this subglacial brine and identified previously undetected but abundant groups including the candidate bacterial phylum Atribacteria and archaeal phylum Pacearchaeota. Our work represents the first microbial characterization of samples collected from within a glacier using a melt probe, and the only Antarctic subglacial aquatic environment that, to date, has been sampled twice. A comparative analysis showed the brine community to be stable at the operational taxonomic unit level of 99% identity over a decade. Higher resolution sequencing enabled deconvolution of the microbiome of subglacial brine from mixtures of materials collected at the glacier surface. Diversity patterns between this brine and samples from the surrounding landscape provide insight into the hydrological connectivity of subglacial fluids to the surface polar desert environment. Understanding subice brines collected on the surfaces of thick ice covers has implications for analyses of expelled materials that may be sampled on icy extraterrestrial worlds.

Crystal structure of a transcription factor, GerE (PaGerE), from spore-forming bacterium Paenisporosarcina sp. TG-14

In cold and harsh environments such as glaciers and sediments in ice cores, microbes can survive by forming spores. Spores are composed of a thick coat protein, which protects against external factors such as heat-shock, high salinity, and nutrient deficiency. GerE is a key transcription factor involved in spore coat protein expression in the mother cell during sporulation. GerE regulates transcription during the late sporulation stage by directly binding to the promoter of cotB gene. Here, we report the crystal structure of PaGerE at 2.09 Å resolution from Paenisporosarcina sp. TG-14, which was isolated from the Taylor glacier. The PaGerE structure is composed of four α-helices and adopts a helix-turn-helix architecture with 68 amino acid residues. Based on our DNA binding analysis, the PaGerE binds to the promoter region of CotB to affect protein expression. Additionally, our structural comparison studies suggest that DNA binding by PaGerE causes a conformational change in the α4-helix region, which may strongly induce dimerization of PaGerE.

Rock glaciers in Pearse Valley, Antarctica record outlet and alpine glacier advance from MIS 5 through the Holocene

Rock glaciers and buried ice are common in the McMurdo Dry Valleys, Antarctica. In central Taylor and Pearse valleys rock glaciers cover at least 10% of the valley walls and occur at elevations of 300–800 m above sea level. We investigate the origin and geomorphology of a ~1.5 km2 rock glacier in northern Pearse Valley, the westernmost extension of Taylor Valley. The rock glacier is cored by sporadic deposits of clean ice that are covered by sand-rich, stratified sediments and dissected by five glacial meltwater streams. Ground-penetrating radar data indicate that the clean buried ice ranges from 1 to 14 m thick and contains dipping sediment-rich bands. Water stable isotopes from five cores extracted from the buried ice support multiple ice sources: (1) recent ice from alpine glaciers and (2) ancient, stagnant ice from East Antarctic outlet Taylor Glacier. The eastern half of the rock glacier lies directly downslope from alpine Fountain Glacier, which is actively feeding ice, sediments and water to the rock glacier via ~1 km-long ice falls. The buried ice in this section of the rock glacier is relatively heavy isotopically and similar to Fountain Glacier (δ18O of −36‰ to −32‰). The ice that cores the western half of the rock glacier is isotopically light and similar to Taylor Glacier (δ18O of −43‰ to −40‰). The last documented advance of Taylor Glacier that was sufficient to reach the rock glacier position occurred during Marine Isotope Stage 5 (70–125 ka), implying long-term preservation of the ice. The age and origin of buried ice in Pearse Valley has implications for rock glaciers throughout the Antarctic. Rock glaciers (1) are potentially long-term archives of glacial ice with complex depositional histories and (2) could be used to map previous advances of both outlet and alpine glaciers.