Could subglacial Lake Vostok survive the buildup of the Antarctic ice sheet

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Could subglacial Lake Vostok survive the buildup
of the Antarctic ice sheet?

• Frank PATTYN
• Department of Geography,
• Vrije Universiteit Brussel,
• Brussels, Belgium

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Overview

• Background
• The subglacial lake effect and Lake Vostok
• Advance of an ice cap over a slippery spot
• Grounding line advance over a preglacial lake
• Similarities and dissimilarities with other
  Antarctic subglacial lakes
• Conclusions

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N. Duxbury et al.JGR 106 (E1), 2001

• If Lake Vostok existed as a preglacial lake (15
  Ma ago) it survived ice sheet growth and remained
  stable under the Antarctic ice cover
• As long as lake gt 53 m deep
• Lake Vostok considered as closed system, which is
  dynamically inconsistent, as closure must have
  happened between initiation and development of
  ice sheet

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M. SiegertJGR 109 (E02007), 2004

• Ice would ground in Lake Vostok during buildup,
  and lake could not survive
• Water flow beneath ice sheet is controlled by
  hydraulic potential gradient
• If surface slope gt 1/10 basal slope, water can
  flow uphill
• Steep margin existed during ice sheet buildup
  close to Lake Vostok (DeConto Pollard, 2003)
• So, water was expelled from lake due to high
  subglacial hydraulic potential gradient

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F. PattynJGR 109 (E11004), 2004

• Mechanism for survival of Lake Vostok during
  buildup
• Above models do not include interaction between
  ice sheet and lake water surface (pre- and sub-)
  Slippery spot
• Examined with a 3D higher-order ice-sheet model

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3D higher order ice sheet model
Ice-sheet modeling based on 3 conservative
equations. Assuming constant ice density
Mass
Momentum
Energy
Constitutive eq.
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Momentum force balance
Higher-order model including vertical
shearing, longitudinal and transverse stress
gradients
Pattyn, 2003, JGR Solid Earth
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Subglacial lake effect
Modeled domain Pattyn et al., JGLAC, in press.
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Basal boundary condition
ß2 8
Siegert (1999)
ß2 0
Vostok Station
Lake Vostok slippery spot
RADARSAT
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Surface velocity (color, white contours) surface
topography (black dashed)
DIAGNOSTIC EXPERIMENTS
DNL No Lake ice flow in direction of steepest
surface slope
Local ice divide
DLE With Lake ice flow is also flux dependent
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Effect of varying basal friction on the velocity
and surface elevation of an ice mass
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Advance of an ice cap over a slippery spot

• Rectangular domain of 1500 x 1500 km
• Advance of ice sheet determined by surface mass
  balance equation

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(No Transcript)
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Cross sectional view in time NO LAKE
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Cross sectional view in time LAKE
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Surface slope evolution across the lake
Subglacial hydraulic potential gradient remains
low in case of lake
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Grounding line advance over a preglacial lake

• Criterion of hydraulic potential gradient is
  valid as long as lake is completely sealed
• During ice sheet advance glacier terminus might
  be calving in the lake
• Ice tongues or shelves are much thinner than
  sheets, so complete grounding is not likely

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Alternative explanation

• Doran et al. (2003) Lake Vida, Dry Valleys,
  Antarctica
• Ice sealed lake covered by 19m of lake ice
• If Lake Vostok existed as a preglacial lake it
  would shift to an ice-sealed lake before being
  overridden by glaciers

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Similarities and dissimilarities with other
Antarctic subglacial lakes

• Astrolabe subglacial basin at present devoid of
  water, although similar mechanism could apply
• Advance of ice sheet occurred much later in time
  than at Lake Vostok
• Antarctic ice sheet was bigger and climate
  cooler, so maybe there existed no preglacial lake
• Furthermore, much more dynamism of Antarctic ice
  sheet edge in recent Cenozoic (no stable
  configuration compared to Lake Vostok)

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Grounding line problem

• Grounding line dynamics are not yet understood
  (Vieli Payne 2005)
• Plays a decisive role in dynamics of advance of
  ice sheets in preglacial lakes or even oceans
• Problem of calving
• ASPI IPY
• ISMIP (ice sheet model intercomparison project)

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Conclusions

• If Lake Vostok existed as a preglacial lake (gt15
  Ma BP), it could have survived mid-Miocene
  glaciation
• Interaction of ice sheet with water surface leads
  to a flattening of ice/air interface of ice sheet
• This keeps subglacial hydraulic potential
  gradients low, so water can remain in subglacial
  cavity
• But problem of grounding line migration not
  fully understood