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Sea Ice (Ice shelf --> what? (= Floating extension of grounded ice,…
Sea Ice
Ice shelf
--> what?
=
Floating extension of grounded ice
Attached to land
Floating
Thick
- 100m or more
Meteoric ice
- glacial ice
Internal forces
drive flow
i.e. gravity/internal stresses
What is
sea ice ?
Freely floating
Marine ice
- frozen seawater
Thin
- 2 m or less (usually < 1 m)
Flow driven by
winds & ocean currents
Internal forces may be important if very thick
Sea ice formation
Air is cooler than ocean at high latitudes
Wind turbulence drives heat transfer
Frazil ice begins to form
= thin sub-mm ice layer
∴ Ocean temp lowered to surface freezing point
= -1.9°C due
to salt content
Polynya
= open stretch of water surrounded by ice
where one would expect sea ice to be yet there is NOT
i.e. area of unfrozen sea within the ice pack
Ice growth processes
= dictated by ocean surface conditions
i.e. calm or rough ?
Processes causing thickening of frazil ice --> sea ice pack
Sea ice formation = self limiting
As sea ice thickens (& snow atop)
Insulates ocean against more heatloss
∴ Ice growth slows
Temperature influence
When very thick
Only upper layers sensitive to seasonal temp cycles
Temp perturbation cannot penetrate through whole ice thickness
Monitoring
Sea Ice
Area
easy to measure
thus widely studied
visual, radar, passive microwave
Volume
Also important
Dictates
Time required for ice cover to disappear
Potential freshwater may be introduced into ocean
Similarity sea ice & ice shelf
both affected by ocean below i.e. melt / freeze
Calm ocean
Frazil -> Grease ice -> Nilas -> Congelation ice -> Sheet ice (smooth bottom)