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3 Cross-sectional profile of the Antarctic ice sheet based on BEDMAP bed topography (Lythe et al. 2001) and surface topography from Liu et al. (1999). Inset: Location of profile end points. SOURCE: Lythe, M. B., D. G. Vaughan, and C. BEDMAP: A new ice thickness and subglacial topographic model of Antarctica, Journal of Geophysical Research B: Solid Earth, 106 (B6): pp. 11335-11351 (2001). Reproduced with permission of American Geophysical Union. SOURCE: G. Clarke, committee member.
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Antarctica is renowned for its extreme cold; yet surprisingly, there is
liquid water at the base of the Antarctic ice sheet several kilometers
beneath the surface. The exploration of these subglacial aquatic
environments is in its initial stages, and many fundamental questions
about these environments can only be answered by entering and sampling
t...
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AMPS has now been serving Antarctic scientific and logistical needs for over a decade. This mesoscale NWP system currently centers on a real-time implementation of the WRF model optimized for Antarctica. While AMPS was developed with the priority mission of supporting NSF forecasting, over the years it has expanded to a spectrum of applications. Th...
Citations
... The longest existing record of ice stream monitoring, however, covers only ~50 years and is based on satellite imagery Rignot et al., 2019). In addition to this, the subglacial environments are among the least accessible regions on Earth and, therefore, represent one of the last physical frontiers of glaciological research (Hobbie et al., 2007). ...
Palaeo ice-sheet reconstructions are considered a key approach to increase our understanding of past climate change and how this impacts on the cryosphere. These reconstructions have shown that ice sheets can have a relatively fast response to climate and ocean forcing mechanisms. This has raised concerns about the future stability of ice sheets in a warming world, especially those that are marine-based or marine-terminating, such as the Greenland and Antarctic Ice Sheets. However, predictions of ice sheets stability are complex and their long-term accuracy remains a major weakness in climate change science.
Palaeoglaciological reconstructions offer one critical approach to improve our understanding of how ice sheets respond to climatic drivers over full glacial cycles or through dynamic periods of ice sheet history. As such, palaeo-ice sheets act as useful analogues for helping to determine the important drivers that can influence ice sheets in the future. This study examines the southern margins of two former ice sheets: the British-Irish ice Sheet (BIIS) and the Newfoundland Ice Sheet (NIS). These are located on opposite sides of the North Atlantic Ocean but at similar latitudes. Both ice sheets were grounded below sea level, were drained by ice streams and had extensive marine margins potentially exposed to changes in large-scale ocean and atmospheric circulation. Therefore, they represent good analogues for modern marine-terminating ice sheets.
New marine geophysical and sediment data were analysed across the Celtic Sea shelf, between Ireland and the UK, which was occupied by the Irish Sea Ice Stream (ISIS), the largest outlet of the BIIS. Geomorphological mapping shows a large meltwater drainage system, including tunnel valleys, beneath the central axis of the former ISIS. This evidence implies significant and erosive meltwater release, potentially influencing the rapid retreat across the shelf. At this stage (~25 cal BP), the ISIS was also retreating close to the southern Irish coastline. Some 30 km off the coast, a relatively large grounding-zone wedge was formed, together with a sequence of morainic ridges, which are capped by glacimarine laminated and massive muds. These features show a stepped retreat of the ISIS margin towards to the coastline. The difference in behaviour of the retreating ice sheet near the present-day coast compared to that in the central axis was probably governed by topographical and geological controls, including variations in water depth and the presence of bedrock outcrops acting as pinning points.
On the other side of the Atlantic Ocean, new data on the southern shelf of Newfoundland were analysed. Here, fjords served as outlets for sediment-laden meltwater draining the former NIS. Intense and widespread calving occurred across the NIS marine margin following its extension to the shelf edge. When the ice sheet reached the present-day coastline, it stabilised at the mouth of the fjords and formed a series of moraines that record a still-stand of the ice margin. The combination of new and extant data suggest that the still-stand occurred between 16.3 ka cal BP and 15 ka cal BP. Stratified glacimarine sediments accumulated at the mouth of the fjords during a period of prevailing cold-water conditions when relative sea level was ~30 m higher than today.
Comparison between the two study areas shows different topographic settings and asynchronous ice-sheet behaviour during the last deglaciation. The onset of retreat between the two ice sheets is around 10 ka apart. A comparison of the results against existing proxy data from the North Atlantic Ocean highlighted that deglaciation of both shelves was initiated in the absence of ocean warming, when eustatic sea level was at a minimum. Internal glaciological factors were therefore most likely responsible for the demise of both marine sectors. This demonstrates that marine-terminating ice margins can internally trigger their own demise in very different glaciological settings and within overall cold conditions. Such information provides additional data for ice sheet numerical models that investigate links between rate and pattern of retreat and the drivers of ice sheet variability.
... The discovery of active lake and drainage systems beneath the Antarctic Ice Sheets [80] highlighted the need to avoid biological or chemical contamination in accessing and sampling the subglacial realm, and in the following year a committee of the US National Academy of Sciences published a comprehensive report with guidelines for addressing the issue [81]. The technology for sterile sampling of the subglacial aquatic environment has already been developed, including the coring of soft sediment beneath an ice sheet to a depth of 1-3 m through a clean access hole [82]. ...
Mounting evidence from models and geological data implies that the Antarctic Ice Sheet may behave in an unstable manner and retreat rapidly in response to a warming climate, which is a key factor motivating efforts to improve estimates of Antarctic ice volume contributions to future sea-level rise. Here, we review Antarctic cooling history since peak temperatures of the Middle Eocene Climatic Optimum (approx. 50 Ma) to provide a framework for future initiatives to recover sediment cores from subglacial lakes and sedimentary basins in Antarctica's continental interior. While the existing inventory of cores has yielded important insights into the biotic and climatic evolution of Antarctica, strata have numerous and often lengthy time breaks, providing a framework of 'snapshots' through time. Further cores, and more work on existing cores, are needed to reconcile Antarctic records with the more continuous 'far-field' records documenting the evolution of global ice volume and deep-sea temperature. To achieve this, we argue for an integrated portfolio of drilling and coring missions that encompasses existing methodologies using ship- and sea-ice-/ice-shelf-based drilling platforms as well as recently developed seafloor-based drilling and subglacial access systems. We conclude by reviewing key technological issues that will need to be overcome.
... The general approach described here, specifically using the natural levels of microbiota in the ice as the benchmark for cleanliness, was adopted as a recommended strategy in a recent U.S. National Research Council report (Hobbie et al. 2007) outlining how to responsibly explore subglacial aquatic environments. The concept we introduced for creating a clean pathway in the environment itself within which samples are collected was essential to developing best sampling procedures for our application, especially since forward contamination was a concern. ...
Ice-sealed lakes, potentially home to novel microbiota and microbial processes, can provide a window into isolated and geologically ancient systems. These habitats are earth analogs for extraterrestrial systems that have yet to be sampled, though potentially harbor, or have harbored life at some time during their past. They are also small-scale models of the numerous sub-glacial lake systems, which have been identified across Antarctica and in Iceland. Methods are needed to sample these ecosystems with environmental stewardship in mind, in which human impact on the ecosystem is mitigated before and during sampling. This report describes an entry and sampling approach that was executed at Lake Vida, East Antarctica, a permanently ice-sealed lake that has never been sampled. Best practice sampling procedures were developed with emphasis on mitigating introduction of trace organics or microbiota to the ecosystem. The conceptual approach is transferable to other isolated pristine aquatic ecosystems on Earth and elsewhere.
... Our use of an AUV to address these issues of spatial variability in the summertime ice-ocean boundary layer is an outgrowth of a similar study using an AUV of wintertime lead convection described by Morison and McPhee (1998). They successfully used the Autonomous Conductivity Temperature Vehicle (ACTV) in the winter Lead Experiment of March andApril 1992 (LeadEx Group, 1993) to observe under-ice horizontal profiles of temperature, salinity, and turbulent fluxes under and around freezing leads. ...
... The first location was within about 250 m of the ice cliffs of Courtauld Glacier, where Autosub could navigate beneath the cover of sea ice and deeper iceberg keels, in some cases needing to take avoidance action against their presence (McPhail, 2007). The sea floor is relatively rough in both images shown in Figure 2. The Autosub vehicle is flying about 30 m above the sea floor and parallel to the ice cliffs of the tidewater glacier at a range of about 100 m for the data shown in Figure 2a. ...
... Access to the sub ice shelf cavity is possible from the edge of the ice shelf. However, due to the vastness of some of the ice shelves and difficulties with navigating in such an environment, exploration of the sub ice shelf cavity from the ice shelf edge is currently only a very limited possibility and carries significant operational risk (see for example failed mission 383 of Autosub 2 beneath the Fimbulisen Ice Shelf: McPhail, 2006;Strutt, 2006). Access further away from the ice shelf edge and to the grounded part is therefore limited currently to narrow ice boreholes. ...
Towards Integrated Management of Transboundary River Basins over the WorldAntarctic Subglacial Lakes and Waters: The Challenge to Protect a Hidden ResourceProgressive Development of International Groundwater Law: Awareness and CooperationThe Role of Key International Water Treaties in the Implementation of the Convention on Biological DiversityThe European Union Water Framework Directive, a Driving Force for Shared Water Resources ManagementTransfer of Integrated Water Resources Management Principles to Non-European Union Transboundary River BasinsImplementation of the Water Framework Directive Concepts at the Frontiers of Europe for Transboundary Water Resources ManagementImplementation of the European Union Water Framework Directive in Non-EU Countries: Serbia in the Danube River BasinBasic Problems and Prerequisites Regarding Transboundary Integrated Water Resources Management in South East Europe: The Case of the River Evros/Maritza/MeriçReferencesFurther Reading
Demonstrating that the detected microbial diversity in non-aseptically drilled deep ice cores is truly indigenous is challenging because of potential contamination with exogenous microbial cells. The NEEM Greenland ice core project provided a first-time opportunity to determine the origin and extent of contamination throughout drilling. We performed multiple parallel cultivation and culture-independent analyses of five decontaminated ice core samples from different depths (100 m to 2051m), the drilling fluid and its components Estisol and Coasol and the drilling chips collected during drilling. We created a collection of diverse bacterial and fungal isolates (84 from the drilling fluid and its components, 45 from decontaminated ice and 66 from drilling chips). Their categorization as contaminants or intrinsic glacial ice microorganisms was based on several criteria, including phylogenetic analyses, genomic fingerprinting, phenotypic characteristics, presence in drilling fluid, chips and/or ice. Firmicutes and fungi comprised the dominant group of contaminants among isolates and cloned rRNA genes. Conversely, most Proteobacteria and Actinobacteria originating from the ice were identified as intrinsic. This study provides a database of potential contaminants useful for future studies of NEEM cores and can contribute towards developing standardized protocols for contamination detection and ensuring the authenticity of the microbial diversity in deep glacial ice. This article is protected by copyright. All rights reserved.
Antarctic subglacial lakes are thought to be extreme habitats for
microbial life and may contain important records of ice sheet history
and climate change within their lake floor sediments. To find whether or
not this is true, and to answer the science questions that would follow,
direct measurement and sampling of these environments are required. Ever
since the water depth of Vostok Subglacial Lake was shown to be >500
m, attention has been given to how these unique, ancient, and pristine
environments may be entered without contamination and adverse
disturbance. Several organizations have offered guidelines on the
desirable cleanliness and sterility requirements for direct sampling
experiments, including the U.S. National Academy of Sciences and the
Scientific Committee on Antarctic Research. Here we summarize the
scientific protocols and methods being developed for the exploration of
Ellsworth Subglacial Lake in West Antarctica, planned for 2012-2013,
which we offer as a guide to future subglacial environment research
missions. The proposed exploration involves accessing the lake using a
hot-water drill and deploying a sampling probe and sediment corer to
allow sample collection. We focus here on how this can be undertaken
with minimal environmental impact while maximizing scientific return
without compromising the environment for future experiments.
