Климат, лед, вода, ландшафты

Climate, ice, water, landscapes

Рудой Алексей Николаевич

Location for direct access to subglacial Lake Ellsworth. J. Woodward et al.

Эту статью прислал мне только что один из исполнителей работ и её авторов Джон Вудуэрд с котором я познакомился на недавнем Конгрессе ИНКВА в Берне. После открытия подлёдного озера Восток в Антарктиде, на пороге достижения самого озера буровым снарядом возник ряд серьёзных экологических проблем. Одним из способов для решения таких проблем Научным комитетом по исследованию Антарктики (SCAR) было предложено выбрать аналогичное, но меньших размеров, подлёдное озеро в качестве модельного, и провести на этом озере комплекс работ, результаты которых помогли бы решить проблемы, связанные с проникновением в более крупные подледниковые озёра. В качестве такого модельного озера было выбрано, в числе других, и озеро Эллсворт в Западной Антарктиде.
В статье представлена детальная характеристика физико-географических обстановок этого подледникового озера, включающая и результаты батиметрических и комплексных геофизических работ.
Размеры озера Эллсворт составляет 14,7 км х 3,1 км, площадь - 28,9 км2. Глубины озера меняются вдоль длинной оси от 52 м до 156 м, объем воды определён в 1,37 км3. В статье предложены результаты геофизических и геохимических исследований, выполненных авторами на озере в сезоны 2007/8 и 2008/9 годов. - Алексей Рудой.
 
 
Animation of Subglacial Lake Behavior

Location for direct access to subglacial Lake Ellsworth: An assessment of geophysical data and modeling
J. Woodward,1 A. M. Smith,2 N. Ross,3 M. Thoma,4,5 H. F. J. Corr,2 E. C. King,2 M. A. King,6 K. Grosfeld,5 M. Tranter,7 and M. J. Siegert3
Received 10 February 2010; revised 19 April 2010; accepted 28 April 2010; published 2 June 2010.
Elsuopt
[1] Subglacial Lake Ellsworth has been proposed as a candidate for direct measurement and sampling, to identify microbial life and extract sedimentary climate records. We present a detailed characterization of the physiography of this subglacial lake from geophysical surveys, allowing bathymetry and geomorphic setting to be established. Lake Ellsworth is 14.7 km × 3.1 km with an area of 28.9 km2. Lake depth increases downlake from 52 m to 156 m, with a water body volume of 1.37 km3. 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.
1. Introduction
[2] Since the discovery that subglacial Lake Vostok possessed a water column of over 500 m [Kapitsa et al., 1996], microbiologists have regarded subglacial lakes as viable habitats for life, which may involve unique adaptations. Additionally, palaeoclimatologists have suggested subglacial lakes may contain records of ice sheet and climate history within sediments on their floors. To identify life in subglacial lakes and to understand the climate history within their sediment records requires direct measurements and sampling. Recent gravity and seismic measurements over Lake Vostok have improved understanding of 3D bathymetry and sediment distribution [Filina et al., 2008], but to
date, no subglacial lake has been accessed.
[3] In 2003 the Subglacial Antarctic Lake Environments (SALE) programme of the Scientific Committee on Antarctic Research (SCAR) suggested an appropriate first access site would be one of the relatively small subglacial lakes [Priscu et al., 2003]. As a consequence of this assessment, subglacial Lake Ellsworth in West Antarctica was offered as an excellent candidate for direct measurement and sampling [Siegert et al., 2004; Vaughan et al., 2007]. To evaluate the suitability of this lake and determine the prime location for direct access,  information on the lake’s bathymetry and the physical processes operating within the lake are necessary.
[4] During the 2007/8 and 2008/9 seasons subglacial Lake Ellsworth was subject to a detailed ground‐based geophysics campaign, involving towed radar, seismics, GPS and stake measurements. Here we present results outlining the physiography of the lake and its subglacial surroundings. We then present model simulations of lake water circulation and model prediction of basal mass balance. This information is integrated to provide the most suitable location for lake access and to assess the potential risks associated with the concentration of dissolved gasses within the lake.
2. Geophysical Data Collection
 
lake22.1. Radar Surveys
[5] Radio‐echo sounding (RES) lines totaling ∼740 km were collected in a grid over Lake Ellsworth and the surrounding area (Figure 1) using a ground‐based, 1.7 MHz pulsed radar. The ice sheet surface elevation was determined using kinematic GPS with differential correction from the Midlake GPS base station (Figure 1). Ice‐bed reflection travel times were converted to ice thickness using a mean radio‐velocity in the ice column of 0.168 m ns−1. Estimated RMS errors in ice thickness based on crossover analysis of RES surveys over the lake are ±6.4 m. Surface elevation and ice thickness measurements were then used to construct a Digital Elevation Model (DEM) of the basal topography of the lake catchment (Figure 1). 
2.2. Seismic Surveys
[6] Five seismic reflection lines, spaced ∼1.4 km apart and aligned perpendicular to the long axis of the lake were completed (Figure 1). With the exception of Profile D, all lines covered the full lake width and part of the surrounding bed. Data were detected using 48 geophones at 10 m spacing. Shot spacing was 240 m, producing single‐fold seismic reflection profiles. Data processing included a normal moveout correction and migration.
1School of Applied Sciences, Northumbria University, Newcastleupon‐
Tyne, UK.
2British Antarctic Survey, Natural Environment Research Council,
Cambridge, UK.
3School of Geosciences, University of Edinburgh, Edinburgh, UK.
4Commission for Glaciology, Bavarian Academy of Sciences,
Munich, Germany.
5Alfred Wegener Institute for Polar and Marine Research,
Bremerhaven, Germany.
6School of Civil Engineering and Geosciences, Newcastle University,
Newcastle‐upon‐Tyne, UK.
7School of Geographical Sciences, University of Bristol, Bristol, UK.
Copyright 2010 by the American Geophysical Union.
0094‐8276/10/2010GL042884
Кстати, немного странную и безадресную, хотя и интересную статью  я обнаружил в поисковом Яндексе. Я размещаю эту статью вот здесь.

18.08.2011 07:52 2434
 

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