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Journal ArticleDOI

A comment on the Equation of State and the freezing point equation with respect to subglacial lake modelling

TL;DR: In this paper, the most common formulations of the EOS and the EOFP applied in numerical ocean and lake models during the past decades are discussed and the impact of the recent and selfconsistent Gibbs thermodynamic potential formulation on subglacial lake modelling.
About: This article is published in Earth and Planetary Science Letters.The article was published on 2010-05-15 and is currently open access. It has received 16 citations till now. The article focuses on the topics: Subglacial lake & Lake Vostok.

Summary (1 min read)

1 Introduction

  • In the following the authors briefly review different representations of EoS and EoFP used in ocean modelling, before they discuss the relevance of their improved formulations for the modelling of subglacial lakes.
  • Finally the authors present updated results of subglacial lake modelling studies, with respect to the revised EoS and EoFP.

1.1 Equation of State ( EoS)

  • Water depth and potential temperature dependence of isopycnals (Feistel, 2003; Jackett et al., 2006) .
  • The black solidus line shows the depth-dependent freezing point of fresh water (Feistel, 2003; Jackett et al., 2006) , the red solidus line indicates the linearized form of the freezing point equation adjusted for Lake Vostok.

The

  • The dashed line connects the isopycnal's vertices and indicates the line of maximum density (LoMD).
  • Here the authors only present the updated results with respect to the revised EoS and EoFP with otherwise identical configurations.
  • In Table 1 the authors present updates of the most relevant results and their uncertainties for Lake Vostok and Lake Concordia published in the aforementioned studies.
  • Malte.Thoma@awi.de (Malte Thoma), also known as Email address.

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Citations
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Journal ArticleDOI
TL;DR: In this paper, the authors summarize the scientific protocols and methods being developed for the exploration of Ellsworth Subglacial Lake in West Antarctica, planned for 2012-2013, which they offer as a guide to future subglacial environment research missions.
Abstract: 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.

153 citations


Cites background from "A comment on the Equation of State ..."

  • ...However, below the LOMD, where overburden pressure is “high” relative to the Pc, any heated water will rise through buoyancy [Thoma et al., 2010]....

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Journal ArticleDOI
TL;DR: Woodward et al. as mentioned in this paper used geophysical data and modeling information to confirm that Lake Ellsworth is ideal for direct access and propose an optimal drill site, and the likelihood of dissolved gas exchange between the lake and the borehole is also assessed.
Abstract: Ellsworth is 14.7 km ×3 .1 km with an area of 28.9 km 2 . Lake depth increases downlake from 52 m to 156 m, with a water body volume of 1.37 km 3 . The ice thickness suggests an unusual thermodynamic characteristic, with the critical pressure boundary intersecting the lake. Numerical modeling of water circulation has allowed accretion of basal ice to be estimated. We collate this physiographic and modeling information to confirm that Lake Ellsworth is ideal for direct access and propose an optimal drill site. The likelihood of dissolved gas exchange between the lake and the borehole is also assessed. Citation: Woodward, J., A. M. Smith, N. Ross, M. Thoma, H. F. J. Corr, E. C. King, M. A. King, K. Grosfeld, M. Tranter, and M. J. Siegert (2010), Location for direct access to subglacial Lake Ellsworth: An assessment of geophysical data and modeling, Geophys. Res. Lett., 37, L11501, doi:10.1029/ 2010GL042884.

115 citations


Cites methods from "A comment on the Equation of State ..."

  • ...The model has recently been improved by an updated equation of state and a revised equation for the freezing point temperature, according to the Gibbs thermodynamic potential [Thoma et al., 2010]....

    [...]

Journal ArticleDOI
TL;DR: In this article, an improved three-dimensional full-Stokes ice flow model with a nonlinear rheology was employed to simulate the basal mass balance at the lake-ice interface, and a newly developed coupler to exchange boundary conditions between the two individual models.
Abstract: . Subglacial lakes in Antarctica influence to a large extent the flow of the ice sheet. In this study we use an idealised lake geometry to study this impact. We employ a) an improved three-dimensional full-Stokes ice flow model with a nonlinear rheology, b) a three-dimensional fluid dynamics model with eddy diffusion to simulate the basal mass balance at the lake-ice interface, and c) a newly developed coupler to exchange boundary conditions between the two individual models. Different boundary conditions are applied over grounded ice and floating ice. This results in significantly increased temperatures within the ice on top of the lake, compared to ice at the same depth outside the lake area. Basal melting of the ice sheet increases this lateral temperature gradient. Upstream the ice flow converges towards the lake and accelerates by about 10% whenever basal melting at the ice-lake boundary is present. Above and downstream of the lake, where the ice flow diverges, a velocity decrease of about 10% is simulated.

38 citations


Cites background or methods from "A comment on the Equation of State ..."

  • ...The horizontal resolution (0.025◦×0.0125◦, about 0.7× 1.4 km), the number of vertical layers (16), as well as the horizontal and vertical eddy diffusivities (5 m2/s and 0.025 cm2/s, respectively) are adopted from a model of subglacial Lake Concordia (Thoma et al., 2009a)....

    [...]

  • ...Previous subglacial lake simulations of Lake Vostok (Thoma et al., 2007, 2008a; Filina et al., 2008), Lake Concordia (Thoma et al., 2009a), or Lake Ellsworth (Woodward et al., 2009) used a prescribed average heat conduction into the ice (QIce = dT /dz×2.1 W/(K m)), based on borehole temperature…...

    [...]

  • ...…spherical coordinates and has been applied successfully to ice-shelf cavities (e.g.,Grosfeld et al., 1997; Williams et al., 2001; Thoma et al., 2006) as well as to subglacial lakes (Williams, 2001; Thoma et al., 2007, 2008a,b; Filina et al., 2008; Thoma et al., 2009a,b,c; Woodward et al., 2009)....

    [...]

  • ...The horizontal resolution (0.025◦×0.0125◦, about 0.7× 1.4 km), the number of vertical layers (16), as well as the horizontal and vertical eddy diffusivities (5 m2/s and 0.025 cm2/s, respectively) are ad pted from a model of subglacial Lake Concordia (Thoma et al., 2009a)....

    [...]

  • ...The strength of the mass transport is between those modelled for Lake Vostok and those for Lake Concordia (Thoma et al., 2009a), and hence reasonable for subglacial lakes....

    [...]

Journal ArticleDOI
TL;DR: In this article, repeated measurements of surface height profiles around Vostok station using kinematic GNSS observations on a snowmobile allow the quantification of surface surface height changes at 308 crossover points.
Abstract: Height changes of the ice surface above subglacial Lake Vostok, East Antarctica, reflect the integral effect of different processes within the subglacial environment and the ice sheet. Repeated GNSS (Global Navigation Satellite Systems) observations on 56 surface markers in the Lake Vostok region spanning 11 years and continuous GNSS observations at Vostok station over 5 years are used to determine the vertical firn particle movement. Vertical marker velocities are derived with an accuracy of 1 cm/yr or better. Repeated measurements of surface height profiles around Vostok station using kinematic GNSS observations on a snowmobile allow the quantification of surface height changes at 308 crossover points. The height change rate was determined at 1 ± 5 mm/yr, thus indicating a stable ice surface height over the last decade. It is concluded that both the local mass balance of the ice and the lake level of the entire lake have been stable throughout the observation period. The continuous GNSS observations demonstrate that the particle heights vary linearly with time. Nonlinear height changes do not exceed ±1 cm at Vostok station and constrain the magnitude of spatiotemporal lake-level variations. ICESat laser altimetry data confirm that the amplitude of the surface deformations over the lake is restricted to a few centimeters. Assuming the ice sheet to be in steady state over the entire lake, estimates for the surface accumulation, on basal accretion/melt rates and on flux divergence, are derived.

30 citations

Journal ArticleDOI
TL;DR: In this paper, the authors simulate the Vostok Subglacial Lake area with a coupled full Stokes 3D ice-flow model and a 3D lake-circulation model and show that basal lubrication at the bottom of the ice sheet has a significant impact not only on the ice flow above the lake itself, but also on the vicinity and far field.
Abstract: Several hundred subglacial lakes have been identified beneath Antarctica so far. Their interaction with the overlying ice sheet and their influence on ice dynamics are still subjects of investigation. While it is known that lakes reduce the ice-sheet friction towards a free-slip basal boundary condition, little is known about how basal melting and freezing at the lake/ice interface modifies the ice dynamics, thermal regime and ice rheology. In this diagnostic study we simulate the Vostok Subglacial Lake area with a coupled full Stokes 3-D ice-flow model and a 3-D lake-circulation model. The exchange of energy (heat) and mass at the lake/ice interface increases (decreases) the temperature in the ice column above the lake by up to 10% in freezing (melting) areas, resulting in a significant modification of the highly nonlinear ice viscosity. We show that basal lubrication at the bottom of the ice sheet has a significant impact not only on the ice flow above the lake itself, but also on the vicinity and far field. While the ice flow crosses Vostok Subglacial Lake, flow divergence is observed and modelled. The heterogeneous basal-mass-balance pattern at the lake/ice interface intensifies this divergence. Instead of interactive coupling between the ice-flow model and the lake-flow model, only a single iteration is required for a realistic representation of the ice/water interaction. In addition, our study indicates that simplified parameterizations of the surface temperature boundary condition might lead to a velocity error of 20% for the area of investigation.

28 citations

References
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01 Jan 1999
TL;DR: In this article, a repeat-pass Synthetic Aperture Radar (SAR) interferometry was used to measure the ice motion over Lake Vostok in the Russian Arctic.
Abstract: Ice motion over Lake Vostok is measured using repeat-pass Synthetic Aperture Radar (SAR) interferometry.

13 citations

Frequently Asked Questions (1)
Q1. What are the contributions in "A comment on the equation of state and the freezing point equation with respect to subglacial lake modelling" ?

This article aims three tasks: Then the authors describe the impact of the recent and self-consistent Gibbs 12 thermodynamic potential-formulation of the EoS and the EoFP on subglacial lake 13 modeling. Finally, the authors show that the circulation regime of subglacial lakes covered 14 by at least 3000 m of ice, in principle, is independent of the particular formula15 tion, in contrast to lakes covered by a shallower ice sheet, like e. g., subglacial Lake 16 Ellsworth. However, as modeled values like the basal mass balance or the distri17 bution of accreted ice at the ice-lake interface are sensitive to different EoS and 18 EoFP, the authors present updated values for subglacial Lake Vostok and subglacial Lake 19 Concordia.