Removal Ice from Ice Shelves 2

Ice shelf
circulation
patterns

Little et al 2009 Simulated:

temp ocean beneath shelf

melt rate pattern

circulation / ocean flow in mixed layer

Mixed
Layer

Top 10-20 m water immediately beneath ice shelf

= responding to melt & mixing etc

Circulation in mixed layer

ocean flow directly beneath ice shelf

  1. Flow along
    base ice shelf

i.e. from g.l. seaward as ice shelf shallows

  1. Flow deflected
    to one side

due to Coriolis force

∴ Water exits along ice shelf margin & sometimes melting occurs here too

Why melting along ice shelf margin?

Melting along ice shelf margin despite low temps & surface f.p.

How? Fast flow can heighten melt rates

Not only temp dictating melt rates...

Why melting may not be sustained

As melt proceeds: Thin, cold freshwater layer grows below ice-ocean interface

∴ Shields ice from heat/salt effects & inhibits melt

Unless cold water = mixed away

To sustain
high melt rates: Holland & Jenkins 1999

Warm (salty) water is not enough

Turbulence = required to:

  1. Mix cold freshwater away from ice-ocean interface
  1. Entrain warm water into mixed layer
    (to maintain heat supply)

Fast flow @ ice-ocean interface
= required to drive turbulence

(otherwise it shields ice from melt)

Effect of shelf melting on ice sheets

Different ocean temps beneath shelf yield different:

Goldberg
et al 2012 Study

Does it mattter WHERE melting occurs ?

  1. Coupled ice-ocean model - glued so interact
  1. Varied ocean temps - interior layers 0 - 1.8°C
  1. Observed how grounded ice loss changes
  1. Melt rates
  1. Grounding line retreat extent
  1. Sea level contribution

Unexpected findings: Grounding line retreat varies

Expected findings: Melt rates = higher when temps higher

Disproportionate
g.l. retreat

0 - 0.6°C = Small retreat g.l.

1.2 - 1.8 °C = Larger g.l. retreat (15-20 km.)

Sea level contribution

Reflects grounded ice volume loss

Small rise loss grounded ice

for cold - medium warm experiments (0, 0.6, 1.2 °C)

Massive increase loss grounded ice

for v. warm scenerio (1.2 - 1.8°C)

What's distinct about 1.8°C scenerio?

✓ Melting location
= important

x No signif difference overall ice shelf loss/melt

Melting strongest in top W margin

∴ Buttressing lost from W margin ice shelf

Coriolis causes pile up mixed layer flow at W margin

Focussed eat & fast flow melted through margin