The first step toward accomplishing this project should be core drilling of the first 50 m below the bottom of the existing borehole. In this case further drilling of 50 m of accreted ice will reduce the remaining ice thickness to 80 m, which still exceeds, by a factor of 3, the minimum allowed thickness (25 m) established and agreed at the Lake Vostok workshop held in Cambridge in 1995. With this in mind, the RAE planned to do this drilling in hole 5G from 3,623 m depth to about 3,673 m depth as fast as possible. Many specialist scientists have requested this segment of the core for study. This part of the project leaves sufficient ice below the bottom of borehole 5G to perform this aspect.
This plan was presented by Dr. Lukin, Head of the RAE, at the first meeting of the Subglacial Antarctic Lake Exploration Group of Specialists (SALEGOS), held in Bologna, Italy, in November 2001 with the hope of quick approval. SALEGOS was formed by SCAR in 2000 on a recommendation of the Workshop on Subglacial Lakes held in 1999 in Cambridge to deal with everything connected with Lake Vostok. Dr. Lukin proposed the plan to retrieve an additional 50 m of suspected accreted lake ice from the Vostok borehole in the 2002-2003 field season as part of a general project to enter the lake (Kennicut, 2001).
The plan was supported by the results of a glaciological study described by Lipenkov (private commun., 2001):
The vertical seismic profiling experiments (Masolov et al., 2001) and the borehole temperature measurements (Salamatin, 2000) performed repeatedly in the hole 5G-1 to the bottom at 3,623 m suggest that the thickness of the remaining ice that separates the hole from sub-ice water is 130-140 m, corresponding to a total thickness of the ice sheet of 3,750-3,760 m. From ground-based radar sounding (Popov et al., 2000), the ice sheet thickness in the vicinity of the hole is 3,775 ± 15 m, corresponding to 140-170 m of remaining ice.
The lower layer of the accreted ice is characterized by exceptionally large ice crystals (from 10-100 cm and larger). The high crystalline quality, as revealed by recent X-ray diffraction measurements of these crystals (Montagnat et al., 2001), indicates that lake ice is not plastically deforming under in situ conditions. This result supports earlier assumptions that accreted ice in the vicinity of Vostok Station is blocked by the lake edge (Lipenkov and Barkov, 1998). In addition, low lattice distortion (low dislocation density) of these crystals rules out significant diffusion of the drilling fluid through the ice lattice.
Given that the lake ice is formed by slow freezing of a mixture of frazil ice plus host water (Souchez et al., 2000), one can expect polycrystalline ice with crystal sizes not exceeding some millimeters immediately after freezing. Crystal growth should therefore occur after initial freezing and during the long annealing time while lake ice remains at a temperature close to the melting point. It is considered that the abnormal grain growth is probably at the origin of the structure of lake ice with exceptionally large and high crystalline quality grains typically characterized by well ordered grain boundaries (Montagnat et al., 2001).
Both well ordered (low-energy) grain boundaries and very large crystal size (extremely low vein density factor) make the permeability of accreted ice to drilling fluid very unlikely. We should therefore not fear for the long-term contamination of sub-ice water due to drilling fluid intrusion from the borehole bottom, at more than 80 m above the lake surface.
After reviewing and discussing background material for the proposal of the "Russian plan to deepen the Vostok hole'', "... the group agreed that the scientific justification for further drilling of 50 m of accreted ice was adequate to endorse this deepening to get additional accreted lake ice for coordinated international studies. However, the group did not feel that the necessary glaciological experts were present for a valid technical and environmental judgment to be made, and that an independent assessment of the drilling plan was needed in order to judge the safety of the proposed deepening of the Vostok borehole. The convener will correspond with geophysical and glaciological experts on this issue and request their input on the safety aspects of the plan for deepening the borehole. If at all possible this issue will be resolved intersessionally, and if not this item will be placed on the agenda for further consideration for the proposed spring 2002 meeting of the group'' (Kennicut, 2001).
What happened next is outlined in the following letter from the convener of the group, John Priscu, Professor of Ecology at Montana State University (U.S.A.), to the President of SCAR, Dr. Rutford in April 2002, about a month and a half before the next meeting of SALEGOS.
The RAE presented plans at our last SALEGOS meeting to retrieve an additional 50 m of accretion ice from the deep Vostok borehole during the 20022003 season. Details of this plan are outlined in the SALEGOS report from meeting I (Bologna, Italy, 29-30 November 2001). The group agreed that the scientific justification was adequate to endorse a deepening of the Vostok borehole to provide additional accreted lake ice for coordinated international studies. However, the group did not feel that appropriate experts were present for a valid technical and environmental judgment to be made. I, as convener, was tasked with obtaining statements from geophysical and glaciological experts concerning environmental issues. I presented five experts (only four responded) with the Russian plan to deepen the Vostok borehole by another 50 meters. The letter sent to each expert read as follows.
You may know that the Russian program is planning on taking another 50 m of accretion ice from borehole 5G (leaving 80 m between the bottom of the borehole and the ice-water interface). SCAR has requested that SALEGOS provide recommendations concerning the scientific and environmental issues that surround such a venture. There was a unanimous consensus that more accretion ice, particularly the very clear ice below 3,608 m, will have important scientific ramifications. However, the environmental issues remain unresolved. I was tasked by the Group of Specialists to obtain the judgment of experts on this issue. In this respect, would you please send me your formal evaluation of the environmental issues that you feel may result from increasing the depth of the 5G borehole? Specific items you should address (but are not limited to) are:
(1) What is the probability of drilling fluid permeating the additional 80 m, thus contaminating the lake water?
(2) What is the probability that the same mechanical properties of the accretion ice previously collected (the clear ice between 3,608 and 3,623 m) exist to the lake water interface?
The response from each individual is attached (because several experts requested to remain anonymous I imposed anonymity on all). Based on the advice and comment from these recognized specialists and discussions among the Group of Specialists, we are unable to arrive at a consensus on the risk of contaminating the lake during a deepening of the existing hole. This is primarily due to a lack of adequate information about the properties of the ice to be drilled and an inability to quantitatively predict ice behavior at these great depths and unusual conditions. One expert suggests that based on experience with drilling-induced hydrofracturing that any fracture once initiated would propagate long distances. Grain boundary percolation of contaminants also raises concerns about lake contamination, as the expectation is that increasingly warm temperatures will be encountered as the lake surface is approached. Other experts propose various preventive activities that might reduce the risk of lake contamination. While recognizing that the Russians are world leaders in ice drilling, the general consensus of other experts is that additional assessment would be needed before the risk of lake contamination can be adequately determined. The precautionary approach would seem prudent but we defer to SCAR to determine what the next steps might be. I suggest that the SCAR Executive convene a meeting in Shanghai to discuss these issues in detail and develop clear and tractable guidelines that can be presented to the Russian program.
The proposed drilling at Vostok Station to deepen the borehole by 50 m in 20022003 was thus postponed until 2003-2004 due to the absence of a clear answer as to whether the borehole can be deepened by another 50 m, because the anonymous experts were uncertain about the potential for contamination of the lake. The XXVIth Consultative Meeting of the Antarctic Treaty agreed in 2003 with the "Russian proposal''. "It was like a competition to be first to the Moon. We have abided by the rules of the game within the international Antarctic Treaty'', said Dr. Lukin, Head of the RAE, to the Russian News Agency "RIA Novosti'' on 13 May 2004.
Dr. Lukin advised that the first 50 m of the Vostok borehole would be drilled in 2004-2005, leaving about 80 m of the ice. In 2005-2006, another 50 m of ice would be drilled and "The lake waters will be reached in 2006 or 2007'' ("RIA Novosti'', 13 May 2004).
Now, at the end of January 2006, we know that this plan was partly completed. A new stage of drilling at Vostok Station began in December 2005 and ended in the middle of January 2006 with 27.5 m of the core taken to the surface. Each round of drilling took about 6 hours and brought to the surface about 1.5 m of the core, increasing the depth of the hole from 3,623 m to 3,650 m. This does not represent a big step, but nonetheless a very important one. Part of this core was sent to Europe for study.
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