Taylor Glacier Research Articles

Reconstructing the evolution of Lake Bonney, Antarctica using dissolved noble gases

Lake Bonney (LB), located in Taylor valley, Antarctica, is a perennially ice-covered lake with two lobes, West Lake Bonney (WLB) and East Lake Bonney (ELB), which are separated by a narrow ridge. Numerous studies have attempted to reconstruct the evolution of LB because of its sensitivity to climatic variations and the lack of reliable millennial-scale continental records of climate in this region of Antarctica. However, these studies are limited by the availability of accurate lacustrine chronologies. Here, we attempt to better constrain the chronology of LB and thus, the evolution of past regional climate by estimating water residence times based on He, Ne and Ar concentrations and isotopic ratios in both WLB and ELB.3He and 4He excesses up to two and three orders of magnitude and 35–150 times the atmospheric values are observed for WLB and ELB samples, respectively. In comparison, while measured 40Ar/36Ar ratios are atmospheric (∼295.5) in ELB, WLB samples display 40Ar/36Ar ratios of up to ∼315 reflecting addition of radiogenic 40Ar. Both 4He and 40Ar excesses clearly identify the addition of subglacial discharge (SGD) from underneath Taylor Glacier into WLB at depths of 25m and 35m. He isotopic ratios suggest that He excesses are predominantly crustal (>93%) in origin with small mantle contributions (<7%). These crustal 4He and 40Ar excesses are used together with basement rock production rates of these isotopes to derive first-order approximations of water residence times for both lobes. Numerous factors capable of affecting water residence times are evaluated and corrected 4He and 40Ar water ages are used to place further constrains into the reconstruction of both WLB and ELB history. Combined 4He and 40Ar ages in WLB suggest maximum water residence times of ∼250kyrs BP. These results support the presence of remnant water from proglacial lakes that existed during Marine Isotope Stage 7 (160–240kyrs) in WLB, in agreement with previous studies. In comparison, 4He ages in ELB are much younger (<27kyrs BP) and display a complex evolutionary history that is very different from WLB. 4He ages also suggest that the ELB ice cover formed significantly earlier (∼1.5kyrs BP) than previously reported. The timing of these hydrologic changes in ELB appears to correspond to regional and global climatic events that are recorded in both the Taylor Dome ice-core record as well as in other Dry Valley Lakes.

Pedological Iron/Al Extracts, Clast Analysis, and Coleoptera from Antarctic Paleosol 831: Evidence of a Middle Miocene or Earlier Climatic Optimum

An unusual and remarkable find of fossilized Coleoptera exoskeletons, soil organics/plant roots, and microbes—recovered from an alpine-age paleosol in moraine at New Mountain near the Taylor Glacier in the Antarctic Dry Valleys—provides evidence for an ameliorative Early to middle Miocene Climatic Optimum (MMCO). Compared with the microbial analysis of other nearby and somewhat younger paleosols (sites 827–829) in nearby moraine deposits at both New Mountain and Aztec Mountain (sites that are known to contain bacteria and fungi), paleosol horizons at the alpine-age site (831) contain prolific fossil evidence of either an expanded MMCO or an earlier Early Miocene/Oligocene age. Together with fossil filamentous forms of either algae or fungi and bacteria, these Coleoptera exoskeletons make up part of a higher-altitude tundra ecosystem distantly related to a many-fold increase in terrestrial pollen and woody plants that inhabited the Dry Valley Coast ∼15 Ma or earlier. While the age of the 831 paleosol as discussed elsewhere is impossible to assess with precision, the presence of a mix of subround/subangular sands—a high percentage carrying V-shaped percussion cracks—signals significant aqueous transport, with the sediment believed to have been deposited before the transition from warm/wet to cold/dry ice. In addition, fossilized organics—including salt-encrusted earth, roots, and clay/mineral coatings on both sands and biogenic specimens—suggest at least an early cold/semihumid environment conducive to weathering, probably mediated by microbe activity. Other chemical indices reported previously are here analyzed with extractable Fe/Al, which suggests greater antiquity, possibly Early Miocene or Oligocene.

Isotopic constraints on marine and terrestrial N2O emissions during the last deglaciation.

Nitrous oxide (N2O) is an important greenhouse gas and ozone-depleting substance that has anthropogenic as well as natural marine and terrestrial sources. The tropospheric N2O concentrations have varied substantially in the past in concert with changing climate on glacial-interglacial and millennial timescales. It is not well understood, however, how N2O emissions from marine and terrestrial sources change in response to varying environmental conditions. The distinct isotopic compositions of marine and terrestrial N2O sources can help disentangle the relative changes in marine and terrestrial N2O emissions during past climate variations. Here we present N2O concentration and isotopic data for the last deglaciation, from 16,000 to 10,000 years before present, retrieved from air bubbles trapped in polar ice at Taylor Glacier, Antarctica. With the help of our data and a box model of the N2O cycle, we find a 30 per cent increase in total N2O emissions from the late glacial to the interglacial, with terrestrial and marine emissions contributing equally to the overall increase and generally evolving in parallel over the last deglaciation, even though there is no a priori connection between the drivers of the two sources. However, we find that terrestrial emissions dominated on centennial timescales, consistent with a state-of-the-art dynamic global vegetation and land surface process model that suggests that during the last deglaciation emission changes were strongly influenced by temperature and precipitation patterns over land surfaces. The results improve our understanding of the drivers of natural N2O emissions and are consistent with the idea that natural N2O emissions will probably increase in response to anthropogenic warming.

Microclimate and mass fluxes of debris-laden ice surfaces in Taylor Valley, Antarctica

AbstractThis study investigates the microclimate and hydrology of debris-laden ice surfaces in the Taylor Valley, Antarctica, in early summer, focusing on the onset of melt. Measurements of energy and mass fluxes were made on an outwash fan and in moraines near the terminus of Taylor Glacier. The surface microclimate was strongly controlled by absorbed solar radiation, with a low albedo of 0.17. Seasonal warming of the substrate led to an abrupt shift in thermal and hydrological patterns as temperatures exceeded freezing point. Within a week the Bowen ratio switched from 2.05 to 0.48 and mass losses to the atmosphere increased four-fold from 0.39 to 1.6 mm d-1. Melt onset also produced complex ground temperature patterns with strong diurnal damping below the freezing front. These patterns were caused by phase changes in the freezing front, coupled with an abundant water supply from local runoff. Of secondary importance to the surface energy balance and mass fluxes was the effect of local winds on boundary layer characteristics. This resulted in larger mass losses during the more turbulent, warmer and drier down-valley flows.

Radiometric 81Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica.

We present successful (81)Kr-Kr radiometric dating of ancient polar ice. Krypton was extracted from the air bubbles in four ∼350-kg polar ice samples from Taylor Glacier in the McMurdo Dry Valleys, Antarctica, and dated using Atom Trap Trace Analysis (ATTA). The (81)Kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean absolute age offset of 6 ± 2.5 ka. Our experimental methods and sampling strategy are validated by (i) (85)Kr and (39)Ar analyses that show the samples to be free of modern air contamination and (ii) air content measurements that show the ice did not experience gas loss. We estimate the error in the (81)Kr ages due to past geomagnetic variability to be below 3 ka. We show that ice from the previous interglacial period (Marine Isotope Stage 5e, 130-115 ka before present) can be found in abundance near the surface of Taylor Glacier. Our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available, greatly enhancing their scientific value as archives of old ice and meteorites. At present, ATTA (81)Kr analysis requires a 40-80-kg ice sample; as sample requirements continue to decrease, (81)Kr dating of ice cores is a future possibility.

Influence of debris-rich basal ice on flow of a polar glacier

AbstractAt Taylor Glacier, a cold-based outlet glacier of the East Antarctic ice sheet, observed surface speeds in the terminus region are 20 times greater than those predicted using Glen’s flow law for cold (–17°C), thin (100 m) ice. Rheological properties of the clean meteoric glacier ice and the underlying deformable debris-rich basal ice can be inferred from surface-velocity and ablation-rate profiles using inverse theory. Here, with limited data, we use a two-layer flowband model to examine two end-member assumptions about the basal-ice properties: (1) uniform softness with spatially variable thickness and (2) uniform thickness with spatially variable softness. We find that the basal ice contributes 85–98% to the observed surface velocity in the terminus region. We also find that the basal-ice layer must be 10–15 m thick and 20–40 times softer than clean Holocene-age glacier ice in order to match the observations. Because significant deformation occurs in the basal ice, our inverse problem is not sensitive to variations in the softness of the meteoric ice. Our results suggest that despite low temperatures, highly deformable basal ice may dominate flow of cold-based glaciers and rheologically distinct layers should be incorporated in models of polar-glacier flow.

Acoustic in-ice positioning in the Enceladus Explorer project

AbstractThe Enceladus Explorer project is a preparatory study for a future space mission to Saturn’s moon, Enceladus. Its ultimate goal is to probe liquid-water pockets below the ice surface of Enceladus for signatures of life. A probe could be based on the IceMole concept, which melts curved trajectories through the ice. In the Enceladus Explorer project, a specialized IceMole probe for a terrestrial test scenario is in development. The goal of this exploratory study is to probe water from a liquid crevasse close to Blood Falls at Taylor Glacier, Antarctica. To navigate such a probe it is essential to be able to determine its position and monitor its trajectory. Part of the navigation system is the in-ice acoustic positioning system. For this, the head of the IceMole is equipped with acoustic sensors, which receive signals from synchronized acoustic emitters situated at the ice surface. Based on the measured propagation times, the speed of sound in ice and the positions of the emitters at the surface, the position of the IceMole can be determined by trilateration techniques. Here we present the developed acoustic positioning system, which is designed to track the in-ice melting probe up to distances of 100 m in glacier ice. Results from full-system tests in water and a first field test on Morteratschgletscher, Switzerland, are discussed.

A new large-diameter ice-core drill: the Blue Ice Drill

AbstractThe Blue Ice Drill (BID) is a large-diameter agile drill system designed by the Ice Drilling Design and Operations group of the University of Wisconsin–Madison to quickly core-clean 241 mm diameter ice samples from near-surface sites. It consists of a down-hole motor/gear reducer rotating a coring cutter and core barrel inside an outer barrel for efficient cuttings transport in solid ice. A variable-frequency drive and custom control box regulates electrical power to the drill. Torque reaction is accomplished on the surface via handles attached to a torsion stem. Core recovery is achieved with either core dogs in the sonde or with a separate core recovery tool. All down-hole tools are suspended on a collapsible tripod via ropes running on a capstan winch. The BID is operated by a minimum of two people and has been used successfully during two seasons of coring on a blue ice area of Taylor Glacier, Antarctica. An updated version of the drill system, BID-Deep, has been designed to recover cores to depths up to 200 m.

Long-term trends in the population size and breeding success of emperor penguins at the Taylor Glacier colony, Antarctica

The population size of emperor penguins at the land-based Taylor Glacier colony was monitored over 54 years from 1957 to 2010 by intermittent ground counts from 1957 to 1975 and annual photographic counts from 1988 to 2010 of males attending the colony in winter and chicks in early summer. The breeding population in the early years averaged 3,684 ± 492 pairs compared with 2,927 ± 320 pairs from 1988–2010, a reduction of 20.5 %. The exact timing and magnitude of the change is unknown because there was a 13-year gap between the end of the historical counts and start of the contemporary counts. From 1954 to 2010 no real or inferred warming event that may have been linked to the decrease was evident at Australia’s Mawson station, 95 km from Taylor Glacier colony. From 1988 to 2010, variation in breeding population size and breeding success were not related to variation in the distance between the colony and open water. In this period, the number of pairs breeding fluctuated annually and overall showed signs of a gradual decrease. The Taylor Glacier colony is one of only three emperor penguin colonies where populations have been monitored in winter over the long term. Given the threat of climate warming to the future of this ice-dependent species it is imperative that the annual monitoring programme at Taylor Glacier continues well into the future.

Debris-Rich Basal Ice as a Microbial Habitat, Taylor Glacier, Antarctica

Two ∼4 m vertical sequences of basal ice were collected from tunnels dug into the northern lateral margin of Taylor Glacier, McMurdo Dry Valleys, Antarctica. In both cases the basal sequences exhibit two contrasting ice facies groups; clean (debris-free) and banded dispersed (debris-rich). Debris-rich ices exhibit elevated CO2 and depleted O2 concentrations compared to the clean facies. Bacterial cell numbers, respiration rates, and nutrient concentrations are highest in debris-rich layers. Together, our geochemical and biological data indicate that microbial heterotrophic respiration is likely occurring in situ within the basal ice matrix at ambient temperatures near −15°C. This implies that the basal ice zone of polar glaciers and larger ice sheets is a viable subglacial microbial habitat and active biome of significant volume that has not previously been considered.

Characterizing microbial diversity and the potential for metabolic function at -15 °c in the Basal ice of taylor glacier, antarctica.

Measurement of gases entrapped in clean ice from basal portions of the Taylor Glacier, Antarctica, revealed that CO2 ranged from 229 to 328 ppmv and O2 was near 20% of the gas volume. In contrast, vertically adjacent sections of the sediment laden basal ice contained much higher concentrations of CO2 (60,000 to 325,000 ppmv), whereas O2 represented 4 to 18% of the total gas volume. The deviation in gas composition from atmospheric values occurred concurrently with increased microbial cell concentrations in the basal ice profile, suggesting that in situ microbial processes (i.e., aerobic respiration) may have altered the entrapped gas composition. Molecular characterization of 16S rRNA genes amplified from samples of the basal ice indicated a low diversity of bacteria, and most of the sequences characterized (87%) were affiliated with the phylum, Firmicutes. The most abundant phylotypes in libraries from ice horizons with elevated CO2 and depleted O2 concentrations were related to the genus Paenisporosarcina, and 28 isolates from this genus were obtained by enrichment culturing. Metabolic experiments with Paenisporosarcina sp. TG14 revealed its capacity to conduct macromolecular synthesis when frozen in water derived from melted basal ice samples and incubated at −15 °C. The results support the hypothesis that the basal ice of glaciers and ice sheets are cryospheric habitats harboring bacteria with the physiological capacity to remain metabolically active and biogeochemically cycle elements within the subglacial environment.

Nutrient and population dynamics in a subglacial reservoir: a simulation case study of the Blood Falls ecosystem with implications for astrobiology

AbstractSubglacial ecosystems have recently become of interest within the astrobiological community, as they represent a potentially habitable location in otherwise uninhabitable environments. We used data from Blood Falls, particularly the periodic discharge from the subglacial reservoir beneath Taylor Glacier, Antarctica, to construct an ecosystem model of the putative subglacial microbial community residing there using system dynamics modelling. The model results were, for the most part, within an order of magnitude of the geochemical field data. Productivity was quite low, at 6.4×10−5g carbon l−1yr−1. Based on the results, we draw the following conjectures for the search for life on Mars: A similar ecosystem would require a continual supply of oxidized iron for energy and generate significant amounts of reduced iron as a waste product, be relatively resilient to temporary disturbances, and, thermodynamically, would require at least 0.003 kJ mol l−1of energy to survive at that level of productivity. These results may help to better identify the constraints and boundaries of ecosystems in extreme environments, on Earth and other planetary bodies.

Draft Genome Sequence of Paenisporosarcina sp. Strain TG-14, a Psychrophilic Bacterium Isolated from Sediment-Laden Stratified Basal Ice from Taylor Glacier, McMurdo Dry Valleys, Antarctica

The psychrophilic bacterium Paenisporosarcina sp. TG-14 was isolated from sediment-laden stratified basal ice from Taylor Glacier, McMurdo Dry Valleys, Antarctica. Here we report the draft genome sequence of this strain, which may provide useful information on the cold adaptation mechanism in extremely variable environments.

Draft Genome Sequence of Paenisporosarcina sp. Strain TG-20, a Psychrophilic Bacterium Isolated from the Basal Ice of Taylor Glacier

We report the draft genome sequence of Paenisporosarcina sp. strain TG-20, which is 4.12 Mb in size and consists of 4,071 protein-coding genes and 76 RNA genes. The genome sequence of Paenisporosarcina sp. TG-20 may provide useful information about molecular adaptations that enhance survival in icy subsurface environments.

Seismic multiplet response triggered by melt at Blood Falls, Taylor Glacier, Antarctica

Meltwater input often triggers a seismic response from glaciers and ice sheets. It is difficult, however, to measure melt production on glaciers directly, while subglacial water storage is not directly observable. Therefore, we document temporal changes in seismicity from a dry‐based polar glacier (Taylor Glacier, Antarctica) during a melt season using a synthesis of seismic observation and melt modeling. We record icequakes using a dense six‐receiver network of three‐component geophones and compare this with melt input generated from a calibrated surface energy balance model. In the absence of modeled surface melt, we find that seismicity is well‐described by a diurnal signal composed of microseismic events in lake and glacial ice. During melt events, the diurnal signal is suppressed and seismicity is instead characterized by large glacial icequakes. We perform network‐based correlation and clustering analyses of seismic record sections and determine that 18% of melt‐season icequakes are repetitive (multiplets). The epicentral locations for these multiplets suggest that they are triggered by meltwater produced near a brine seep known as Blood Falls. Our observations of the correspondingp‐wave first motions are consistent with volumetric source mechanisms. We suggest that surface melt enables a persistent pathway through this cold ice to an englacial fracture system that is responsible for brine release episodes from the Blood Falls seep. The scalar moments for these events suggest that the volumetric increase at the source region can be explained by melt input.

In situ cosmogenic radiocarbon production and 2‐D ice flow line modeling for an Antarctic blue ice area

Radiocarbon measurements at ice margin sites and blue ice areas can potentially be used for ice dating, ablation rate estimates and paleoclimatic reconstructions. Part of the measured signal comes from in situ cosmogenic 14C production in ice, and this component must be well understood before useful information can be extracted from 14C data. We combine cosmic ray scaling and production estimates with a two‐dimensional ice flow line model to study cosmogenic 14C production at Taylor Glacier, Antarctica. We find (1) that 14C production through thermal neutron capture by nitrogen in air bubbles is negligible; (2) that including ice flow patterns caused by basal topography can lead to a surface 14C activity that differs by up to 25% from the activity calculated using an ablation‐only approximation, which is used in all prior work; and (3) that at high ablation margin sites, solar modulation of the cosmic ray flux may change the strength of the dominant spallogenic production by up to 10%. As part of this effort we model two‐dimensional ice flow along the central flow line of Taylor Glacier. We present two methods for parameterizing vertical strain rates, and assess which method is more reliable for Taylor Glacier. Finally, we present a sensitivity study from which we conclude that uncertainties in published cosmogenic production rates are the largest source of potential error. The results presented here can inform ongoing and future 14C and ice flow studies at ice margin sites, including important paleoclimatic applications such as the reconstruction of paleoatmospheric 14C content of methane.

Elevated East Antarctic outlet glaciers during warmer-than-present climates in southern Victoria Land

We document Plio-Pleistocene changes in the level of Taylor Glacier, an outlet glacier in southern Victoria Land that drains Taylor Dome on the periphery of the East Antarctic Ice Sheet (EAIS). Chronologic control comes from 3He cosmogenic-nuclide analyses of 27 boulders sampled from drifts and moraines in Kennar Valley, a small hanging valley that opens onto a peripheral lobe of Taylor Glacier in the Quartermain Mountains. Assuming a constant boulder-erosion rate of 10 cm Myr −1, our preferred age model spans the last 3.1 Myr and calls for stepped ice recession from a local highstand ~ 200 m above the present base of Taylor Glacier at the mouth of Kennar Valley. The texture and sedimentology of all mapped moraines and drifts indicate deposition from cold-based ice, analogous with the modern Taylor Glacier at the mouth of Kennar Valley. The Kennar Valley glacial record shows an uncharacteristic relationship with average global temperatures, exhibiting higher-than-present ice levels during globally warm periods, including the Pliocene climatic optimum (~ 3.1 Ma) and Marine Oxygen Isotope Stage (MIS) 31 (~ 1.07 Ma). The Kennar Valley record also suggests that the rate of ice-surface lowering accelerated after the mid-Pleistocene transition at ~ 0.9 Ma. Correlation of our moraine record with published reports for fluctuations of Taylor Glacier elsewhere in the Quartermain Mountains, and with a dated moraine record from Ferrar Glacier (a second outlet for Taylor Dome), reveals similar ice-surface changes, highlighting minor, but widespread ice recession in southern Victoria Land since the mid- to late-Pliocene. Our record for minimal variability in the East Antarctic Ice Sheet contrasts with recent data from nearby marine cores that call for dynamic fluctuations in the volume of grounded ice in the Ross Embayment, and significant reduction of the West Antarctic Ice Sheet (WAIS) during warmer-than-present intervals. Taken together, these records from the Ross Embayment call for considerable variation in the response of marine-based West Antarctic ice and terrestrial East Antarctic outlet glaciers during Plio-Pleistocene time.

Aluminum extracts in Antarctic paleosols: Proxy data for organic compounds and bacteria and implications for Martian paleosols

Pyrophosphate-extractable Al has been used to establish the presence of organically-complexed compounds in middle latitude and tropical soils and paleosols on Earth. As proxy data used to establish the presence of organic molecules and trace movement within profiles, it has proved an accurate indicator of downward translocation in Spodosols (podzols). Antarctic paleosols, dating from Middle to Early Miocene age (15–20 Ma), are mineralic weathering profiles lacking A and B horizons. These profiles exhibit pavement/Cox/Cz/Cu horizons, largely with sandy silt textures, little clay, and exceedingly low concentrations of organic matter. Recent chemical investigations of 33 soil samples from the New Mountain and Aztec Mountain areas near the Inland Ice, adjacent to the Taylor Glacier, show that pyrophosphate-extractable Al concentrations vary in phase with organic carbon as determined by loss-on-ignition. While Al-extract concentrations in selected samples are low (< 0.15%), increasing values above nil approximately correlate positively with increases in bacterial populations of several common phylum, the extreme high numbers with more advanced biota including fossil Coleoptera. Available data suggest Al p extracts may target samples which may have undergone minor chelation, and which over long periods of time might have a cumulative weathering effect resulting in the accumulation of small concentrations of organic matter. As such, Al p extracts may prove useful in targeting the presence of life once in situ investigations of paleosols begin on Mars.

Sublimation and surface energy budget of Taylor Glacier, Antarctica

AbstractTaylor Glacier, an outlet of the East Antarctic ice sheet, flows through the Transantarctic Mountains and terminates in the Dry Valleys. Understanding how this glacier fluctuates is important for studies of glacial geology, paleoclimate, ice dynamics and ecology. Sublimation is the primary mass-loss process for most of the glacier. Four years of specific balance measurements from the ablation zone show sublimation rates up to 40 cm a−1. We used data from an array of weather stations as inputs to a model for latent heat flux and hence sublimation rate. Calculated and measured ablation rates agree to within uncertainties, indicating that wind speed and vapour pressure gradient (a function of temperature and humidity) are the governing variables, as expected from theory. Measurements and model results together allowed us to examine the spatial and temporal variations of sublimation on the glacier. On average, sublimation is about two times faster in summer than winter. Rapid sublimation occurs during storms and katabatic wind events, but such periods contribute less to the annual total than do slow, persistent losses. Spatially, sublimation reaches a maximum midway along the glacier, where descending surface air currents are focused by the topography of the aptly named tributary, Windy Gully.

Spatial variations in the geochemistry of glacial meltwater streams in the Taylor Valley, Antarctica

AbstractStreams in the McMurdo Dry Valleys, Antarctica, flow during the summer melt season (4–12 weeks) when air temperatures are close to the freezing point of water. Because of the low precipitation rates, streams originate from glacial meltwater and flow to closed-basin lakes on the valley floor. Water samples have been collected from the streams in the Dry Valleys since the start of the McMurdo Dry Valleys Long-Term Ecological Research project in 1993 and these have been analysed for ions and nutrient chemistry. Controls such as landscape position, morphology of the channels, and biotic and abiotic processes are thought to influence the stream chemistry. Sea-salt derived ions tend to be higher in streams that are closer to the ocean and those streams that drain the Taylor Glacier in western Taylor Valley. Chemical weathering is an important process influencing stream chemistry throughout the Dry Valleys. Nutrient availability is dependent on landscape age and varies with distance from the coast. The streams in Taylor Valley span a wide range in composition and total dissolved solids and are surprisingly similar to a wide range of much larger temperate and tropical river systems.