Potential technological solution for sampling the bottom sediments of the subglacial lake Vostok: relevance and formulation of investigation goals

The subglacial Lake Vostok in Antarctic is a unique natural phenomenon, its comprehensive study involves sampling of water and bottom surface rocks. For further study of the lake, it is necessary to drill a new access well and develop environmentally safe technologies for its exploration. This article discusses existing and potential technologies for sampling bottom surface rocks of subglacial lakes. All these technologies meet environmental safety requirements and are conducive for sampling. The authors have proposed an alternative technology, using a walking device, which, due to its mobility, enables selective sampling of rocks across a large area from a single access well. The principal issues, related to the implementation of the proposed technology, are investigated within this article. This report is prepared by a team of specialists with many years of experience in drilling at the Vostok Station in Antarctic and in experimental work on the design of equipment and non-standard means of mechanization for complicated mining, geological and climatic conditions.

Melting temperature of ice and total gas content of water at the ice-water interface above subglacial Lake Vostok

It is generally assumed that the gas composition and the total gas content of Lake Vostok’s water are, to a large extent, governed by the budget of atmospheric gases entering the lake together with glacier ice melt, mostly in its northern part. Since the ice accretion that prevails in the south of the lake leads to the exclusion of gases during the freezing process, these gases can build up in the lake water. Earlier theoretical works [2, 3] have demonstrated that about 30 water residence times are required to attain equilibrium between gases in solution and those in a hydrate phase, which sets the upper bounds of concentrations of nitrogen and oxygen dissolved in sub-ice water (~2.7 g N2 L–1 and ~0.8 g O2 L–1). Here we attempt to estimate the real gas content of the lake water based on the link between the pressure melting temperature of ice and the concentration of gases dissolved in the liquid phase [2]. We use the stacked borehole temperature profile extended to 3753 m depth and the measurements of temperature of sub-ice water that entered the borehole after the second unsealing of Lake Vostok to estimate the melting temperature of ice (–2.72 ± 0.1 °C) at the ice sheet-lake interface (depth 3758.6 ± 3 m, pressure 33.78 ± 0.05 MPa). The gas content of the near-surface layer of lake that corresponds to this melting temperature is calculated to be 2.23 g.L–1, meaning that the concentration of dissolved oxygen must be as high as 0.53 g.L–1, i. e. one-two orders of magnitude higher than in any other known water bodies on our planet. The inferred gas content of sub-ice water is, by a factor of 1.6, lower than the maximal solubility of air in water in equilibrium with air hydrate, though it is still higher, by a factor of 19, than the total air content of melting glacier ice. The relatively low concentration of dissolved air in the near-surface layer of the lake revealed in this study provides a new experimental constraint for understanding the gas distribution in Lake Vostok as affected by the circulation and mixing of water beneath the ice sheet.

New large subglacial lake in Princess Elizabeth Land, East Antarctica, detected by airborne geophysical observations

Knowledge of subglacial lakes is important for understanding the stability of the Antarctica Ice Sheet (AIS) and its contribution to the global sea-level change. We designed an intensified airborne campaign to collect geophysical data in Princess Elizabeth Land (PEL), East Antarctica, during the 2015–2019 CHINARE expeditions. We developed an innovative method to build a set of evidence of a newly detected subglacial lake, Lake Zhongshan. Adaptive RES data analysis allowed us to detect the lake surface and extent. We quantified the lake depth and volume via gravity modeling. Another dataset collected at Lake Vostok provided the ground truth. The results revealed that Lake Zhongshan, located at 73°26'53"S, 80°30'39"E and ~3,603 m below surface, has an area of 328 ± 1 km2, making it the only one in PEL and the fifth largest in Antarctica. These findings are important for understanding subglacial hydrodynamics in PEL, as well as the stability of the AIS.

Device for fusion drilling with simultaneous or follow-up reaming of wells in ice

The paper deals with a new opening technology for subglacial reservoirs, which ensures environmentally friendly geological exploration. The technology is based on the results of the first openings of the subglacial Lake Vostok in Antarctica (February 2012 and January 2015). The primary goal of further studies of the subglacial Lake Vostok is to take clean samples of lake water and bottom sediments, which requires direct penetration into the lake. There is a number of conditions to be met in order to conduct further studies of the lake using a clean access well at the Vostok drilling complex. The article summarizes the main results including technological and engineering solutions protected by the patent of the Russian Federation. A detailed consideration is given to a new device for fusion drilling with simultaneous reaming of an ice hole. This device combines two technological processes: drilling due to contact melting, and an increase in the diameter of the well due to the creation of a vortex flow of a continuously heated coolant in the bottomhole zone. The thermal method of ice breaking ensures the ecological cleanliness when opening subglacial reservoirs and is a priority method that favorably differs from the existing ones. The device was named a “thermal drill reamer” (TDR). During the seasonal work of the 64th Russian Antarctic Expedition bench tests of the TDR 132/400 were carried out, the results of which confirmed that the device is capable to ensure 132 mm drilling with simultaneous reaming up to 400 mm.

Borehole multi-functional logger for geophysical high-precision monitoring in Antarctic and Greenland ice sheets and glaciers

This article presents the main aspects of the design solutions (based on the application of sensors MEMS and cantilevers), testing and applying of the multi-functional borehole logger ANTTIC (Antarctic Thermo-barometer, Inclinometer, Caliper) for geophysical high-precision monitoring (when simultaneous registering of temperature, pressure, axis inclination angle and radii of borehole cross-sections at 12 points), which is designed specifically for ultra-low temperatures and ultra-high pressures, and to determine an elliptical borehole shape and registration anisotropy factor in deep ice boreholes in the central region of Eastern Antarctica, in the areas of dome A at the Kunlun station (China) and/or of lake Vostok at the Vostok station (Russia).

Surface Mass Balance Models Vs. Stake Observations: A Comparison in the Lake Vostok Region, Central East Antarctica

The surface mass balance (SMB) is very low over the vast East Antarctic Plateau, for example in the Vostok region, where the mean SMB is on the order of 20–35 kg m-2 a-1. The observation and modeling of spatio-temporal SMB variations are equally challenging in this environment. Stake measurements carried out in the Vostok region provide SMB observations over half a century (1970–2019). This unique data set is compared with SMB estimations of the regional climate models RACMO2.3p2 (RACMO) and MAR3.11 (MAR). We focus on the SMB variations over time scales from months to decades. The comparison requires a rigorous assessment of the uncertainty in the stake observations and the spatial scale dependence of the temporal SMB variations. Our results show that RACMO estimates of annual and multi-year SMB agree well with the observations. The regression slope between modelled and observed temporal variations is close to 1.0 for this model. SMB simulations by MAR are affected by a positive bias which amounts to 6 kg m-2 a-1 at Vostok station and 2 kg m-2 a-1 along two stake profiles between Lake Vostok and Ridge B. None of the models is capable to reproduce the seasonal distributions of SMB and precipitation. Model SMB estimates are used in assessing the ice-mass balance and sea-level contribution of the Antarctic Ice Sheet by the input-output method. Our results provide insights into the uncertainty contribution of the SMB models to such assessments.

Basal melting over Subglacial Lake Ellsworth and its catchment: insights from englacial layering

Deep-water ‘stable’ subglacial lakes likely contain microbial life adapted in isolation to extreme environmental conditions. How water is supplied into a subglacial lake, and how water outflows, is important for understanding these conditions. Isochronal radio-echo layers have been used to infer where melting occurs above Lake Vostok and Lake Concordia in East Antarctica but have not been used more widely. We examine englacial layers above and around Lake Ellsworth, West Antarctica, to establish where the ice sheet is ‘drawn down’ towards the bed and, thus, experiences melting. Layer drawdown is focused over and around the northwest parts of the lake as ice, flowing obliquely to the lake axis becomes afloat. Drawdown can be explained by a combination of basal melting and the Weertman effect, at the transition from grounded to floating ice. We evaluate the importance of these processes on englacial layering over Lake Ellsworth and discuss implications for water circulation and sediment deposition. We report evidence of a second subglacial lake near the head of the hydrological catchment and present a new high-resolution bed DEM and hydropotential model of the lake outlet zone. These observations provide insight into the connectivity between Lake Ellsworth and the wider subglacial hydrological system.