Water beneath Ice sheets

Sources

Basal melting due to ice sheet flow

frictional heating during sliding

Geothermal heating

due to heatflux from Earth's core

Surface melt reaches bed

via crevasses/moulin etc

Subglacial
water impact

Small amounts melt - limited RSL contribution

Influence on ice flow - can contribute signif to RSL rise

Ice velocities increase due to subglacial water

Flows into ablation zone /ocean ∴ mass loss increased

Acceleration sea level rise driver

Ice flow acceleration at IS margins

= possible driver

Antarctica Mass Loss Mechanism

Little surface melting

Mostly fast flow velocities

& discharge into ocean via ice streaming

Subglacial water Antarctica

Vast lakes

Streams (& sometimes channels)

Lake
Vostok

= largest freshwater lake on Earth

Beneath ~ 4km ice in EAIS

Cored 2.2
miles Z

did not penetrate bottom

microbes isolated from atmos for Myr

could be useful / dangerous

Discovered from sonar soundings in 50s

Observing water beneath ice sheets

  1. Surface roughness

Ice surface - rough texture normally

expression of uneven topog ice flows over

Smooth & flat
surface above lake

WHen ice flows over lake,

ice surface = smooth & flat

since lake surface ∴ ice bed = flat

  1. Ice penetrating radar

Airborne surveys - radar penetrates ice surface

Radargram
exhibits:

Long flat reflector
@ 4 km Z

= surface of Lake Vostok

Hyperbola (curve) either side

= freeze on of ice

accreted basal ice on Lake Vostok

Lake Vostok Water

Source: Basal melting

subglacial melting causing water to [ool / collect

Removal: Accretion of ice onto base of ice flow

Water carried to other parts of ice shet

Residence time ~ 13 kyr

Freeze-on Hyperbola

Ice flows into lake & accretion focussed there at bottom

Freeze-on occurs rapidly

Accretion doesn't occur elsewhere

Freezing releases heat (latent)

Heat warms base a little

Hence accretion doesn't occur elsewhere

since base of ice very cold

∴ will freeze liquid as soon as exposed to it

flowing over cold bedrock for ~kyr

Thwaites
Glacier

Amongst fastest & largest glaciers in world

Important - could dictate sealevel contribution of Antarctica in next 100 years

Hyperbola found either side Lake Vostok on radargram

Water flow beneath IS

Water that is not ponded beneath ice sheets

1. Concentrated channels

= huge channels with large water throughput

2. Distributed cavity networks

= small, distributed network of cavities

streams travel parallel to eachother

Drainage network - influences flow velocity

influences sensitivity ice flow to water input