Lakes beneath the ice sheet: The occurrence, analysis, and future exploration of Lake Vostok and other Antarctic subglacial lakes

Airborne geophysics has been used to identify more than 100 lakes beneath the ice sheets of Antarctica. The largest, Lake Vostok, is more than 250 km in length and 1 km deep. Subglacial lakes occur because the ice base is kept warm by geothermal heating, and generated meltwater collects in topographic hollows. For lake water to be in equilibrium with the ice sheet, its roof must slope ten times more than the ice sheet surface. This slope causes differential temperatures and melting/freezing rates across the lake ceiling, which excites water circulation. The exploration of subglacial lakes has two goals: to find and understand the life that may inhabit these unique environments and to measure the climate records that occur in sediments on lake floors. The technological developments required for in situ measurements mean, however, that direct studies of subglacial lakes may take several years to happen

Modelling mixing and circulation in subglacial Lake Vostok, Antarctica

Lake Vostok, isolated from direct exchange with the atmosphere by about 4 km of ice for millions of years, provides a unique environment. This inaccessibility raises the importance of numerical models to investigate the physical conditions within the lake. Using a three-dimensional numerical model and the best available geometry, we test different parameter settings to define a standard model configuration suitable for studying flow in this subglacial lake. From our model runs we find a baroclinic circulation within the lake that splits into three different parts: Along a topographic ridge in the northern part of Lake Vostok, bottom water masses are transported eastward, diverging away from the ridge. In the lakes surface layer, the flow in these two vertical overturning cells has opposite directions. In the southern part of the lake, where freezing occurs across about 3,500 km^2, two opposing gyres split the water column vertically. The general flow isstronger in the southern basin with horizontal velocities in the order of 1 mm/s. The strongest upwelling, found in the eastern part of this basin, is about 25 μm/s. We estimate the lower limit of the overturning timescale to be about 2.5 years vertically and 8.6 years horizontally. The basal mass loss of ice from the ice sheet floating on the lake is 5.6 mm/year (equivalent to a fresh water flux of 2.78 m^3/s, or a basal ice loss of 0.09 km^3/year). This imbalance indicates either a constant growth of the lake or its continuous (or periodical) discharge into a subglacial drainage system

Physical, chemical and biological processes in Lake Vostok and other Antarctic subglacial lakes

Over 70 lakes have now been identi®ed beneath the Antarctic ice sheet. Although water from none of the lakes has been sampled directly, analysis of lake ice frozen (accreted) to the underside of the ice sheet above Lake Vostok, the largest of these lakes, has allowed inferences to be made on lake water chemistry and has revealed small quantities of microbes. These ®ndings suggest that Lake Vostok is an extreme, yet viable, environment for life. All subglacial lakes are subject to high pressure (,350 atmospheres), low temperatures (about -3 8C) and permanent darkness. Any microbes present must therefore use chemical sources to power biological processes. Importantly, dissolved oxygen is available at least at the lake surface, from equilibration with air hydrates released from melting basal glacier ice. Microbes found in Lake Vostok's accreted ice are relatively modern, but the probability of ancient lake-¯oor sediments leads to a possibility of a very old biota at the base of subglacial lakes

The Dating of Ice-Core Archives

International audienceThe wealth of testimony about past variations in our climate and environment found in deep ice cores in Antarctica and Greenland is acknowledged well beyond the limits of glaciological research. Uniquely, both local climate variations and global atmospheric composition can be reconstructed from a single archive: the ice. Effective use of the information provided by the glacial archives requires dating as precisely as possible of these various records. To do this, the specific characteristics of ice need to be considered

Phase lag of Antarctic and Greenland temperature in the Last Glacial and link between CO2 variations and Heinrich events

Proceedings of the 6th international conference on paleoceanography [ICP IV] held august 23-28, 1998 in Lisbon, Portugal. ISBN: 978-0-306-46293-1; 443 p

Two-million-year-old snapshots of atmospheric gases from Antarctic ice

Over the past eight hundred thousand years, glacial-interglacial cycles oscillated with a period of one hundred thousand years ('100k world'1). Ice core and ocean sediment data have shown that atmospheric carbon dioxide, Antarctic temperature, deep ocean temperature, and global ice volume correlated strongly with each other in the 100k world2-6. Between about 2.8 and 1.2 million years ago, glacial cycles were smaller in magnitude and shorter in duration ('40k world'7). Proxy data from deep-sea sediments suggest that the variability of atmospheric carbon dioxide in the 40k world was also lower than in the 100k world8-10, but we do not have direct observations of atmospheric greenhouse gases from this period. Here we report the recovery of stratigraphically discontinuous ice more than two million years old from the Allan Hills Blue Ice Area, East Antarctica. Concentrations of carbon dioxide and methane in ice core samples older than two million years have been altered by respiration, but some younger samples are pristine. The recovered ice cores extend direct observations of atmospheric carbon dioxide, methane, and Antarctic temperature (based on the deuterium/hydrogen isotope ratio δDice, a proxy for regional temperature) into the 40k world. All climate properties before eight hundred thousand years ago fall within the envelope of observations from continuous deep Antarctic ice cores that characterize the 100k world. However, the lowest measured carbon dioxide and methane concentrations and Antarctic temperature in the 40k world are well above glacial values from the past eight hundred thousand years. Our results confirm that the amplitudes of glacial-interglacial variations in atmospheric greenhouse gases and Antarctic climate were reduced in the 40k world, and that the transition from the 40k to the 100k world was accompanied by a decline in minimum carbon dioxide concentrations during glacial maxima