Subglacial Lake Research Articles

Variability in the ice sheet elevations over Antarctica derived from repetitive SARAL/AltiKa radar altimeter data (2013–2016)

Changes in surface elevations of polar ice sheets are the result of changes in ice dynamics and surface mass balance. Here, we present intra- and inter-annual elevation changes over the Antarctic ice sheet using the AltiKa radar altimeter’s 40 Hz geophysical data record products for the period 2013–2016. Slope corrections were applied on the elevations using a digital elevation model (DEM) available from NASA’s ice, cloud and land elevation satellite (ICESat). Comparison of elevations from AltiKa and ICESat’s DEM yielded correlation, bias and root-mean-square-deviation values of the order of 0.99, −2.88 and 23.04 m, respectively, indicating the first-level accuracy of a former dataset. Further comparison of Airborne Topographic Mapper dataset with AltiKa derived elevation yielded 0.4 m root-mean-square-deviation over a part of Vostok subglacial lake. The intra-annual change indicates that for GY2 (glaciological year), GY3 and GY4, number of negative elevation change points exceeded the number of positive elevation change points during the Antarctic austral summer period (December–February). Inter-annual elevation changes were negative during 2013–2014 and positive during 2014–2015 over east Antarctica, whereas in west Antarctica negative elevation changes were observed for both periods.

Sentinel-3 Delay-Doppler altimetry over Antarctica

Abstract. The launch of Sentinel-3A in February 2016 represented the beginning of a new long-term series of operational satellite radar altimeters, which will provide Delay-Doppler altimetry measurements over ice sheets for decades to come. Given the potential benefits that these satellites can offer to a range of glaciological applications, it is important to establish their capacity to monitor ice sheet elevation and elevation change. Here, we present the first analysis of Sentinel-3 Delay-Doppler altimetry over the Antarctic ice sheet, and assess the accuracy and precision of retrievals of ice sheet elevation across a range of topographic regimes. Over the low-slope regions of the ice sheet interior, we find that the instrument achieves both an accuracy and a precision of the order of 10 cm, with ∼98 % of the data validated being within 50 cm of co-located airborne measurements. Across the steeper and more complex topography of the ice sheet margin, the accuracy decreases, although analysis at two coastal sites with densely surveyed airborne campaigns shows that ∼60 %–85 % of validated data are still within 1 m of co-located airborne elevation measurements. We then explore the utility of the Sentinel-3A Delay-Doppler altimeter for mapping ice sheet elevation change. We show that with only 2 years of available data, it is possible to resolve known signals of ice dynamic imbalance and to detect evidence of subglacial lake drainage activity. Our analysis demonstrates a new, long-term source of measurements of ice sheet elevation and elevation change, and the early potential of this operational system for monitoring ice sheet imbalance for decades to come.

New Estimates of Ice and Oxygen Fluxes Across the Entire Lid of Lake Vostok From Observations of Englacial Radio Wave Attenuation

AbstractOver deep Antarctic subglacial lakes, spatially varying ice thickness and the pressure‐dependent melting point of ice result in distinct areas of melting and freeze‐on at the ice‐water interface, that is, at the lake lid. These ice mass fluxes drive lake circulation and, because basal Antarctic ice contains air clathrate, affect the input of oxygen to the lake, with implications for subglacial life. Inferences of rates of melting and freeze‐on, that is, accretion rates, from radar layer tracking and geodesy are limited in spatial coverage and resolution. Here we develop a new method to estimate accretion rate, and the resulting oxygen input at a lake lid, using airborne radar data over Lake Vostok together with ice‐temperature and chemistry data from the Vostok ice core. Because the lake lid is a coherent reflector of known reflectivity (at our radar frequency), we can infer depth‐averaged radio wave attenuation in the ice, with a spatial resolution of ~1 km along flight lines. Spatial variation in attenuation depends mostly on variation in ice temperature near the lid, which in turn varies strongly with ice mass flux at the lid. We model ice temperature versus depth with ice mass flux as a parameter, thus linking that flux to observed depth‐averaged attenuation. The resulting map of melt and accretion rates independently reproduces features known from earlier studies but now covers the entire lid. We find that freeze‐on is dominant when integrated over the lid, with an ice imbalance of 0.05 to 0.07 km3/year, which is robust against uncertainties.

Software-Defined Radar Systems for Polar Ice-Sheet Research

Polar research using ice-penetrating radars will benefit from the development of smaller and more flexible systems. In this paper, we present the development progression for a series of compact and frequency-reconfigurable ice-penetrating radars based on software-defined radio (SDR) technology and platforms. The Ice Radar series we developed consists of three systems, each based on a different SDR platform that afforded additional capability as we progressed. Detailed descriptions of system structure and performance are provided for each ice radar. We present laboratory measurements to support system capabilities, and provide results of field experiments at Subglacial Lake Whillans in West Antarctica for one of the systems. Finally, we discuss ongoing research of ice-penetrating radar development that utilize SDR technology.

Design Parameters of Hot-Water Drilling Systems

Currently, hot-water drill systems are actively used to observe ocean cavities under ice shelves, detect the effects of climate change on glaciers, retrieve sub-ice seabed samples, study the internal ice structure with video imaging, log temperatures, measure deformations within ice, determine basal sliding velocity, provide clean access to subglacial lakes, and many other scientific applications. The main parameters of hot-water drilling systems in any configuration are flow rate, delivery pressure, and temperature of the delivered water. The controlled outcome variables are the diameter of the drilled borehole, rate of penetration, power and fuel consumption for ice melting, and refreezing rate of the borehole. The independent variables while drilling are the current/target depth and the temperature of the ice. The paper aims to present a design procedure for hot-water drilling parameters that are necessary to choose appropriate equipment and tools at the planning stage.

Patchy Lakes and Topographic Origin for Fast Flow in the Recovery Glacier System, East Antarctica

The Recovery subglacial basin, with its largest glacier Recovery Glacier, has been identified as potentially the biggest contributor to future sea level rise from East Antarctica. Subglacial lakes along the main trunk have been detected from satellite data, with four giant lakes (Recovery Lakes A, B, C, and D) located at the onset of the fast ice flow (≥15 m/yr) and multiple smaller lakes along the glacier. The presence of subglacial water potentially plays a key role in the control of fast ice flow of Recovery Glacier. We present new insights on the Recovery Lakes from airborne radar data collected in 2013 and 2015. Using an adjusted classification scheme, we show that a single large area consisting of smaller lakes connected by likely saturated sediment, referred to as Lake AB, exists in the originally proposed area of the Recovery Lakes A and B. We estimate that the current size of Lake AB is ∼4,320 km2. Water likely leaks from the western shore of Lake AB lubricating the bed initiating fast ice flow at this location. The difference in the outlines of Lake AB and the Lakes A and B previously derived from surface features suggested that a larger paleolake existed here in the past. From our data, we find Recovery Lake C to be dry; we attribute fast ice flow originating from this area to be due to a topographic step and thus an increase in ice thickness rather than enhanced lubrication at the bed.

Prospects for metazoan life in sub-glacial Antarctic lakes: the most extreme life on Earth?

AbstractAbout 400 subglacial lakes are known from Antarctica. The question of whether life unique of subglacial lakes exists has been paramount since their discovery. Despite frequent evidence of microbial life mostly from accretion ice, subglacial lakes are characterized by physiologically hostile conditions to metazoan life, as we know it. Pure water (salinity ≤0.4–1.2%), extreme cold (−3°C), high hydrostatic pressure, areas of limited or no oxygen availability and permanent darkness altogether require physiological adaptations to these harsh conditions. The record of gene sequences including some associated with hydrothermal vents does foster the idea of metazoan life in Lake Vostok. Here, we synthesize the physico-chemical environment surrounding sub-glacial lakes and potential sites of hydrothermal activity and advocate that the physico-chemical stability found at these sites may be the most likely sites for metazoan life to exist. The unique conditions presented by Lake Vostok may also offer an outlook on life to be expected in extra-terrestrial subglacial environments, such as on Jupiter's moon Europa or Saturn's moon Enceladus.

The 2017 catastrophic subsidence in the Dålk Glacier, East Antarctica: unmanned aerial survey and terrain modelling

ABSTRACTWe describe and interpret a catastrophic subsidence in the Dålk Glacier, East Antarctica, occurred in the morning of 30 January 2017. We analysed a dataset of high-resolution aerial photographs and video records captured ten days before, one hour after, and ten days after the event by unmanned aerial systems (UASs) as well as UAS-derived digital elevation models (DEMs). We reconstructed a subsidence mechanism as follows: An englacial cavern measuring about 885,000 m3 with a thin roof existed before the event. There was a channel of the surface and near-subsurface meltwater flow from the Boulder Lake to the Prydz Bay passing nearby the cavern. About a day before the event, an intensive meltwater flow began from the Boulder Lake. The meltwater accumulated on the cavern rooftop leading to its initial collapse. In several days, the meltwater completed the process of subsidence and collapse of the cavern. The event led to the formation of an ice depression about 40,000 m2 in size and up to 43 m deep. Our results demonstrate that ice-surface hydrological processes can cause rapid, deep subsidences of large areas in glaciers, without involving englacial water outbursts from subglacial lakes as well as subglacial geothermal or volcanic activity.

The Neoproterozoic “Blood Falls” in Tarim Craton and Their Possible Connection With Snowball Earth

AbstractBlood Falls refers to the outflow of iron‐rich brine plumes under the Taylor Glacier in Antarctica, which have distinctive blood‐like red color. It was proposed that during the Cryogenian, Fe oxides of terrestrial origin accumulated under glaciers via a mechanism similar to the modern Blood Falls, although reports of iron deposits of such novel origin are lacking in literature. The Quruqsay iron formation is hosted in Neoproterozoic glacial sequences in the northern margin of the Tarim Craton in NW China and consist of 15 lenticular iron orebodies. The iron ores are mainly composed of fine Fe‐oxide aggregate and clastics, with the latter sometimes occurring as dropstones indicating glacial fluvial deposition. The hematite minerals show positive Ce and Y anomalies but lack positive Eu anomalies, with flat shale‐normalized rare Earth elements patterns. The hematite minerals also display remarkably negative εNd values and close‐to‐0 δ56Fe values, which collectively indicate that iron was sourced from continents rather than mid‐ocean ridge hydrothermal vents. Additionally, δ18O values of the hematite are consistent with the large ice‐volume during the Snowball Earth event. Evidence from the Quruqsay iron deposit suggest oxidation of terrestrial sub‐glacier iron‐bearing discharge in oceans of extensive glaciation, correlating with the predicted Blood Falls‐type iron deposits in the Neoproterozoic. The Quruqsay iron formation is a unique hematite‐rich iron deposit implying that subglacial lakes can be a significant repository for Fe2+ and that the volume of the Neoproterozoic glaciers may be much higher than the current glacier.

Missing Evidence of Widespread Subglacial Lakes at Recovery Glacier, Antarctica

Recovery Glacier reaches far into the East Antarctic Ice Sheet. Recent projections point out that its dynamic behavior has a considerable impact on future Antarctic ice loss (Golledge et al., 2017, https://doi.org/10.1002/2016GL072422). Subglacial lakes are thought to play a major role in the initiation of the rapid ice flow (Bell et al., 2007, https://doi.org/10.1038/nature05554). Satellite altimetry observations have even suggested several actively filling and draining subglacial lakes beneath the main trunk (B. E. Smith et al., 2009, https://doi.org/10.3189/002214309789470879). We present new data of the geometry of this glacier and investigate its basal properties employing radio‐echo sounding. Using ice sheet modeling, we were able to constrain estimates of radar absorption in the ice, but uncertainties remain large. The magnitude of the basal reflection coefficient is thus still poorly known. However, its spatial variability, in conjunction with additional indicators, can be used to infer the presence of subglacial water. We find no clear evidence of water at most of the previously proposed lake sites. Especially, locations, where altimetry detected active lakes, do not exhibit lake characteristics in radio‐echo sounding. We argue that lakes far upstream the main trunk are not triggering enhanced ice flow, which is also supported by modeled subglacial hydrology.

A mini‐corer for precision sampling of the water‐sediment interface in subglacial lakes and other remote aqueous environments

AbstractRecent interest in Antarctic subglacial lakes has seen the development of bespoke systems for sampling them. These systems are considered pristine environments potentially harboring undisturbed sedimentary sequences and ecosystems adapted to these cold oligotrophic environments in the absence of sunlight. The water/sediment interface is considered a prime location for the detection of microbial life and so is of particular interest. This article describes the development of a small corer to capture and retain a short core that includes the water/sediment interface specifically to address the question of whether life exists in these lakes. This apparatus was developed as part of the UK led project to access, measure, and sample subglacial Lake Ellsworth. In addition to addressing the constraints of coring in this difficult environment, the results of subsequent testing suggest that this corer can be applied to sampling sediments in other environments and would be particularly useful in low energy environments when the water‐sediment interface is indistinct or unconsolidated.

Evidence for the long-term sedimentary environment in an Antarctic subglacial lake

Lakes beneath the Antarctic Ice Sheet are of fundamental scientific interest for their ability to contain unique records of ice sheet history and microbial life in their sediments. However, no records of subglacial lake sedimentation have yet been acquired from beneath the interior of the ice sheet, and understanding of sediment pathways, processes and structure in subglacial lake environments remains uncertain. Here we present an analysis of seismic data from Subglacial Lake Ellsworth, showing that the lake bed comprises very fine-grained sediments deposited in a low energy environment, with low water- and sediment-fluxes. Minimum sediment thickness is 6 m, the result of prolonged low sedimentation rates. Based on the few available analogues, we speculate this sediment age range is a minimum of 150 ka, and possibly >1 Ma. Sediment mass movements have occurred, but they are rare and have been buried by subsequent sedimentation. We present a new conceptual model of subglacial lake sedimentation, allowing a framework for evaluating processes in subglacial lake environments, and for determining future lake access locations and interpreting subglacial lake samples.

Subglacial water storage and drainage beneath the Fennoscandian and Barents Sea ice sheets

Subglacial hydrology modulates how ice sheets flow, respond to climate, and deliver meltwater, sediment and nutrients to proglacial and marine environments. Here, we investigate the development of subglacial lakes and drainage networks beneath the Fennoscandian and Barents Sea ice sheets over the Late Weichselian. Utilizing an established coupled climate/ice flow model, we calculate high-resolution, spatio-temporal changes in subglacial hydraulic potential from ice sheet build-up (∼37 ka BP) to complete deglaciation (∼10 ka BP). Our analysis predicts up to 3500 potential subglacial lakes, the largest of which was 658 km2, and over 70% of which had surface areas <10 km2, comparable with subglacial lake-size distributions beneath the Antarctic Ice Sheet. Asynchronous evolution of the Fennoscandian Ice Sheet into the flatter relief of northeast Europe affected patterns of subglacial drainage, with up to 100 km3 more water impounded within subglacial lakes during ice build-up compared to retreat. Furthermore, we observe frequent fill/drain cycles within clusters of subglacial lakes at the onset zones and margins of ice streams that would have affected their dynamics. Our results resonate with mapping of large subglacial channel networks indicative of high-discharge meltwater drainage through the Gulf of Bothnia and central Barents Sea. By tracking the migration of meltwater drainage outlets during deglaciation, we constrain locations most susceptible to focussed discharge, including the western continental shelf-break where subglacial sediment delivery led to the development of major trough-mouth fans. Maps of hydraulic potential minima that persist throughout the Late Weichselian reveal potential sites for preserved subglacial lake sediments, thereby defining useful targets for further field-investigation.

Velocity increases at Cook Glacier, East Antarctica, linked to ice shelf loss and a subglacial flood event

Abstract. Cook Glacier drains a large proportion of the Wilkes Subglacial Basin in East Antarctica, a region thought to be vulnerable to marine ice sheet instability and with potential to make a significant contribution to sea level. Despite its importance, there have been very few observations of its longer-term behaviour (e.g. of velocity or changes at its ice front). Here we use a variety of satellite imagery to produce a time series of ice front position change from 1947 to 2017 and ice velocity from 1973 to 2017. Cook Glacier has two distinct outlets (termed East and West), and we observe the near-complete loss of the Cook West Ice Shelf at some time between 1973 and 1989. This was associated with a doubling of the velocity of Cook West Glacier, which may also be linked to previously published reports of inland thinning. The loss of the Cook West Ice Shelf is surprising given that the present-day ocean climate conditions in the region are not typically associated with catastrophic ice shelf loss. However, we speculate that a more intense ocean climate forcing in the mid-20th century may have been important in forcing its collapse. Since the loss of the Cook West Ice Shelf, the presence of landfast sea ice and mélange in the newly formed embayment appears to be important in stabilizing the glacier front and enabling periodic advances. We also show that the last calving event at the larger Cook East Ice Shelf resulted in the retreat of its ice front into a dynamically important portion of the ice shelf and observe a short-lived increase in velocity of Cook East between 2006 and 2007, which we link to the drainage of subglacial Lake Cook. Taken together, these observations suggest that the velocity, and hence discharge, of Cook Glacier is highly sensitive to changes at its terminus, but a more detailed process-based analysis of this potentially vulnerable region requires further oceanic and bathymetric data.

Governance of the Exploration of Subglacial Antarctica

Subglacial lakes, and their surrounding aqueous environments, are known to be viable yet extreme habitats for microbial life that may hold records of climate change spanning hundreds of thousands of years. Since the detection of Lake Vostok in 1996 plans have been developed to access, sample and monitor these unique environments. Critical to these plans is assurance that contamination and disturbance is minimized in all aspects of the activity. Precisely how this is achieved has been a matter of international debate for many years culminating in the formulation of a ‘Code of Conduct’ to guide responsible scientific exploration and stewardship of these pristine systems by the Scientific Committee on Antarctic research. The Code of Conduct was first introduced to the Antarctic Treaty Consultative Meeting in 2011, influencing planning for three exploration programmes. In May 2018, following several recent and operational advances, Antarctic Treaty Parties agreed to its use and dissemination, ensuring that subglacial lakes exploration and access is undertaken in a responsible, defensible and fact-based manner. As our knowledge of subglacial lakes improves, so too will our appreciation of their scientific value and potential vulnerability. In other regions of Antarctica where value and vulnerabilities are high, Antarctic Specially Protected Areas and Antarctic Specially Managed Areas ensure long-term protection whilst allowing scientific access and study. Such governance models will be applicable to the conservation and protection of subglacial lake systems as scientific understanding of their form and functioning advances.

Desert cyanobacteria under space and planetary simulations: a tool for searching for life beyond Earth and supporting human space exploration

AbstractThe astonishing capability of life to adapt to extreme conditions has provided a new perspective on what ‘habitable’ means. On Earth extremophiles thrive in hostile habitats, such as hot and cold deserts or Antarctic sub-glacial lakes considered as Earth analogues of Mars and icy moons of Jupiter and Saturn. Recently desert cyanobacteria were exposed to ground-based simulations of space and Martian conditions and to real space and Martian conditions simulated in low Earth orbit using facilities attached outside the International Space Station. When exposure to such conditions does not exceed repair capabilities, more data are available regarding the physico-chemical constraints that life can withstand. When the accumulated damage exceeds the survival potential, the persistence of biomarkers contributes to the search for life elsewhere. Knowledge concerning the endurance of desert cyanobacteria under space and Martian conditions contributes to the development of life support systems.

Glaciological characteristics in the Dome Fuji region and new assessment for “Oldest Ice”

Abstract. A key objective in palaeo-climatology is the retrieval of a continuous Antarctic ice-core record dating back 1.5 Ma. The identification of a suitable Antarctic site requires sufficient knowledge of the subglacial landscape beneath the Antarctic Ice Sheet. Here, we present new ice thickness information from the Dome Fuji region, East Antarctica, based on airborne radar surveys conducted during the 2014/15 and 2016/17 southern summers. Compared to previous maps of the region, the new dataset shows a more complex landscape with networks of valleys and mountain plateaus. We use the new dataset as input in a thermokinematic model that incorporates uncertainties in geothermal heat flux values in order to improve the predictions of potential ice-core sites. Our results show that especially the region immediately south of Dome Fuji station persists as a good candidate site for obtaining an old ice core. An initial assessment of basal conditions revealed the existence of what appears to be subglacial lakes. Further radar data analysis shows overall high continuity of layer stratigraphy in the region. This indicates that extending the age–depth information from the Dome Fuji ice core to a new ice-core drill site is a viable option.

Low Energy Subsurface Environments as Extraterrestrial Analogs.

Earth’s subsurface is often isolated from phototrophic energy sources and characterized by chemotrophic modes of life. These environments are often oligotrophic and limited in electron donors or electron acceptors, and include continental crust, subseafloor oceanic crust, and marine sediment as well as subglacial lakes and the subsurface of polar desert soils. These low energy subsurface environments are therefore uniquely positioned for examining minimum energetic requirements and adaptations for chemotrophic life. Current targets for astrobiology investigations of extant life are planetary bodies with largely inhospitable surfaces, such as Mars, Europa, and Enceladus. Subsurface environments on Earth thus serve as analogs to explore possibilities of subsurface life on extraterrestrial bodies. The purpose of this review is to provide an overview of subsurface environments as potential analogs, and the features of microbial communities existing in these low energy environments, with particular emphasis on how they inform the study of energetic limits required for life. The thermodynamic energetic calculations presented here suggest that free energy yields of reactions and energy density of some metabolic redox reactions on Mars, Europa, Enceladus, and Titan could be comparable to analog environments in Earth’s low energy subsurface habitats.

Dynamics of an outburst flood originating from a small and high-altitude glacier in the Arid Andes of Chile

Glacial lake outburst floods (GLOFs) are common where highly dynamic temperate glaciers exist, since seasonal changes in ice-conduit dynamics can start rapid lake drainages. Lakes dammed by cold-based glaciers, however, are less common and GLOFs from these glaciers have been rarely reported. Understanding both the origin and the failure mechanisms of lakes dammed by cold-based glaciers and subsequent flood processes is essential for territorial planning. We study a remarkable GLOF triggered by the failure of a subglacial lake in the Manflas Valley, Arid Andes of Chile, in 1985 providing insights into the lake’s origin, clarifying the failure mechanism and modelling the GLOF event-related dynamics. To identify the factors that contributed to the lake formation and failure, we analysed remotely sensed images, meteorological and topographic data. The GLOF dynamics were reconstructed using empirical (LAHARZ and MSF) and physical models (RAMMS). The obtained results were compared with field data of flow extent, depth and velocity. We show that the failed lake (4 × 106 m3) formed in a low-slope (≤ 10°) area and that extreme (≥ 90th percentile) annual precipitation before the GLOF contributed to the lake filling and probably to the dam collapse. The lake likely drained rapidly after mechanical failure of the ice-dam producing a high energy sediment-laden flow. We show the challenges of modelling large flows over long distances (dozens of kilometres) especially when flows change between Newtonian and Non-Newtonian phases. A GLOF can still endanger the Manflas Valley since a remnant of the lake of about 220.000 m3 exists and economic assets are located along the1985 GLOF path.

Gravito-topographic signal of the Lake Vostok area, Antarctica, with the most recent data

By using SatGravRET2014 gravito-topography model, based also on satellite GRACE and GOCE data, we computed and plotted the gravity disturbances, the Marussi tensor of the second derivatives of the disturbing potential, the gravity invariants and their specific ratio, the strike angle and the virtual deformations for the Lake Vostok (LV) area in Antarctica. This set of gravity “aspects” provides more detailed and clearer information than the traditional gravity anomalies. Maps with the bedrock topography from Bedmap 2 are added. Some of our estimates and results confirm independent findings of other specialists, some results presented here are new. LV is divided not only into its N and S parts by a ridge, but also to E and W parts. A tension across LV has a prevailing direction E-W. We identified at least three candidates for subglacial lakes south of the lakes 90 E and Sovetskaya. In the gravity aspects this area looks like a basin, where the mentioned lakes might be just a remnant of a large bowl; the orientation of this basin is the same as that of LV; the size comparable to LV. A subglacial connection between all the mentioned lakes is possible and documented via the gravity aspects, namely by the virtual deformations.