U23B-01 INVITED 

Subglacial plumbing mapped from space: water transfer, water volumes and implications for ice dynamics

* Fricker, H A (hafricker@ucsd.edu), Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0225, United States

Over the last two years, pivotal studies using satellite data have demonstrated that subglacial water can move rapidly and in large volumes beneath the Antarctic ice sheet. Movement is documented over long distances (10s of km), and persists under the fast-flowing ice streams all the way to the grounding line, where subglacial water reaches the Southern Ocean. It has been shown that subglacial lakes may have a role in initiating fast ice stream flow in the upper glacier catchments. The studies have provided a glimpse at a previously unidentified process occurring under the Antarctic ice sheet and point to a renewed appreciation of the importance of subglacial hydrology and how it relates to ice stream dynamics. Mapping subglacial water distribution and movement in Antarctica is of critical importance to the characterization of the ice sheet system and its potential for change. Monitoring subglacial outflows from the ice sheet margins is also important for quantifying freshwater flux to the ocean and understanding ice-ocean interactions. Such lakes have the potential to harbor unique life-forms. Discovery of lakes close to the grounding line, where there are no downstream lakes, provides an opportunity for exploration without the risk of contaminating other lakes.

U23B-02 INVITED 

The Geomorphic and Potential Climatic Impact of Subglacial-Lake Outbursts

* Marchant, D R (marchant@bu.edu), Department of Earth Sciences, Boston University, 685 Commonwealth Ave, Boston, MA 02215, United States

Subglacial water flow has been linked to changes in ice-sheet elevation and enhanced ice-stream flow. In addition to these important effects, significant bedrock erosion could arise from the catastrophic release of one or more subglacial lakes. If sufficient meltwater reaches the Southern Ocean, then such outburst floods might additionally trigger ecological change at a variety of scales. In the Transantarctic Mountains, an ancient 50+ km- long network of bedrock channels, collectively termed the Labyrinth, emerges from beneath the margin of the East Antarctic Ice Sheet (Wright Upper Glacier). Three distinct surfaces are noted, with upper- and intermediate- elevation surfaces reflecting direct erosion beneath wet-based ice, and a lower-elevation surface exhibiting anastomosing channels, some as much as 600 m wide and 250 m deep, that require incision from fast-flowing subglacial meltwater. ⁴⁰Ar/³⁹Ar analyses of volcanic tephra on the Labyrinth show that the channels are relict, with the last major subglacial flood occurring sometime between 14.4 Ma and 12.4 Ma. A similar, mid- Miocene age has been assigned to buried channels observed in the central Ross Embayment. Meltwater draining through the Labyrinth ultimately flowed into the Ross Sea, a region now critical for ocean turnover and deep-water formation and one shown in modeling studies to be sensitive to freshwater influx. Given an East Antarctic Ice Sheet larger-than-present during the mid Miocene with melting margins offshore in the Ross Embayment, the Ross Sea may have been preconditioned such that a significant influx of freshwater could have exceeded threshold conditions and led to changes in sea-ice extent, near-surface ocean salinity, and regional ocean circulation. These discoveries suggest that subglacial meltwater floods likely play a major role in modifying polar landscapes and regional ocean circulation.

U23B-03 INVITED 

Towards Estimating the Salinity of Subglacial Lakes from Aerogeophysical Data

* Studinger, M (mstuding@ldeo.columbia.edu), Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, United States

Subglacial lakes are now being recognized as an integral part of the global cryosphere and the global climate system. Knowledge of the physical, chemical and biological processes operating within these features is crucial for addressing questions about the presence and functioning of life in subglacial lakes. However, little is known about the prevailing in situ environmental conditions. Existing airborne ice-penetrating radar and laser altimeter data over large subglacial lakes can be used to estimate the salinity without penetrating the lakes. The underlying assumption for estimating the salinity from aerogeophysical data is that the ice sheet above large subglacial lakes is in hydrostatic equilibrium and the hydrological potential of the lake surface is constant. Because the flexural support of the ice near the shoreline reduces the load and thus the ice overburden pressure the data analysis has to be restricted to regions several ice thicknesses away from the shoreline allowing this analysis only over the largest know subglacial lakes. In order to estimate the salinity from aerogeophysical data several effects have to be included in a refined calculation of the hydrological potential: 1) A firn layer has to be included in the calculation of ice thickness from radar wave travel times. Because the velocity v of electromagnetic waves in firn is faster than in ice (v_firn > v_ice) a firn correction has to be added to the preliminary ice thickness estimates. Including a firn layer will impact the ice overburden pressure estimate by changing the total ice thickness estimate and reducing the load by a near surface layer with lower density. 2) Lateral changes in the radar wave velocity for the deeper section of the ice sheet have to be accounted for. 3) The vertical density structure of the ice ρ_ice = ρ_ice(z) has to be included in the calculation of the ice overburden pressure pice. The water density is a function of the salinity, temperature, and pressure, i.e. ρ_water = ρ_water(S, T, p_ice). It is important to note that the horizontal and vertical variations in all parameters that impact salinity estimates cannot be neglected. Many of the unknown parameters involved in the salinity estimate can be predicted at least within certain boundaries. I will present a strategy towards estimating the salinity of subglacial lakes from aerogeophysical data, that carefully balances the unknown parameters involved in the calculation. http://pubs.usgs.gov/of/2007/1047/ea/of2007-1047ea032.pdf

U23B-04 INVITED 

Microbial evolution and adaptation in subglacial environments

* Lanoil, B (brian.lanoil@ucr.edu), Univeristy of California, Department of Environmental Sciences Geology 2217, Riverside, CA 92521, United States

Recent discoveries of ancient, huge subglacial lakes in Antarctica, transport of enormous volumes of water from the surface of the Greenland ice sheet through giant cracks extending through nearly 4000 m of ice, and other astounding features of polar regions underscores the lack of knowledge regarding the physical and chemical aspects of these widespread environments, to say nothing of their microbiology. In fact, until recently subglacial environments were thought to be completely abiotic. However, many recent studies indicate the presence of widespread, abundant, and active microbial assemblages in subglacial environments. Surprisingly, the composition of these assemblages appears to be quite similar in subglacial environments around the world. I will discuss these similarities and potential reasons for this similarity, and ongoing and future studies to provide clearer insights into the mechanisms of evolution and adaptation to these environments.

U23B-05 

In-Situ Examination of Ice Stratrigraphy and Organic Material in the Lake Vostok Borehole

* Lane, A L (arthur.l.lane@jpl.nasa.gov), Jet Propulsion Laboratory, California Inst. of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099, United States Bhartia, R

Behar, A E (alberto.behar@jpl.nasa.gov), Jet Propulsion Laboratory, California Inst. of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099, United States Conrad, P G), Jet Propulsion Laboratory, California Inst. of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099, United States Hug, W F (W.Hug@photonsystems.com), Photon Systems, Inc., 1512 Industrial Park Street, Covina, CA 91722, United States

Investigation of microbial and biochemical content in the deep ice cores from Lake Vostok has excited the scientific and public community and led to consideration of very low metabolic rate, long time period biochemical processes at near water-freezing temperatures. Our laboratory team has been involved in considerations of potential future opportunities to investigate Lake Vostok utilizing deep UV fluorescence and UV Raman instrumentation to locate and classify organic material in the oldest (deepest) meteoric ice (3300 m depth region) and in the differing regions of the accretion ice above the roof of the lake water. We have designed a probe that may be able to be inserted into the existing Vostok 5G drill hole and could provide high spatial imaging of the borehole wall along with examination of possible organic material imbedded within the ice near the wall. The drill fluid utilized by the Vostok drill team and still present in the hole limits the sensitivity and capabilities for detection of in-situ material. It appears that the same fluid will not affect visible light examination of the structures and stratigraphy of the ice layers. UV fluorescence data from several Vostok ice cores (3308, 3562 and 3564 m depth) that are resident at the U.S. National Ice Core Laboratory (USGS-Denver) will be presented and discussed, as well as the case for a new approach to examining the bio-cleanliness of instrumentation that might eventually be inserted for examination of the Lake and sediment bed.

U23B-06 

Exploration of Antarctic Subglacial Aquatic Environments: Environmental and Scientific Stewardship

* White, J W (james.white@colorado.edu), University of Colorado, INSTAAR Campus Box 450, Boulder, CO 80309, United States Hobbie, J E), Marine Biological Laboratory, Ecosystems Center, 7 MBL Street, Woods Hole, MA 02543, United States Baker, A), Technical Administrative Services, PO Box 620433, Littleton, CO 80162, United States Clarke, G), The University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4, Canada Doran, P T), University of Illinois at Chicago, Earth and Environmental Sciences, MC 186 845 W Taylor Street, Chicago, IL 60607, United States Karl, D), University of Hawaii at Manoa, School of Ocean and Earth Science, 1000 Pope Road, Honolulu, HI 96822, United States Methe, B), The Institute for Genomic Research, 9712 Medical Center Drive, Rockville, MD 20850, United States Miller, H), Alfred-Wegener-Institute for Polar and Marine Research, Building D-2880 Columbusstrasse, Bremerhaven, D 27568, Germany Mukasa, S B), University of Michigan Department of Geological Sciences, 2534 CC Little Building, Ann Arbor, MI 48109, United States Race, M), SETI Institute, 505 N Whisman Road, Mountain View, CA 94043, United States Vincent, W), Departement de Biologie, Universite Laval, Pavillon Alexandre-Vachon, Quebec, G1K 7P4, Canada Walton, D), British Antarctic Survey, High Cross Maddingly Road, Cambridge, CB3 0BT, United Kingdom Uhle, M), National Research Council, 500 Fifth Street, Washington, DC 20001, United States

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 the water. Accordingly, the management of subglacial aquatic environments requires responsible environmental stewardship while allowing field research. As of early 2007, no one has yet drilled into a lake but entry within the next one or two years is likely. Thus, the challenge is to determine the best way of drilling into, extensively sampling, and monitoring these environments. While general guidelines for research in Antarctica are provided in the Antarctic Treaty, currently no clear protocols or standards for minimizing contamination have been established. At the request of the National Science Foundation (NSF), the National Research Council convened a committee to develop a set of environmental and scientific protection standards needed to responsibly explore the subglacial lake environments in Antarctica. Specifically, the committee was asked to define levels of cleanliness for equipment or devices entering subglacial aquatic environments, develop a sound scientific basis for contamination standards, and recommend the next steps needed to define an overall exploration strategy. This talk will present the findings of that committee. The committee included U.S. and international scientists, and gathered information from the global scientific community. Although a U.S. scientific advisory body produced this study, the committee hopes that its multinational makeup will be recognized and that the recommendations in this report will serve as a basis for broad international discussion about environmental stewardship for the exploration of subglacial aquatic environments. http://nationalacademies.org/prb

Author(s) (2007), Title, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract #####-##.