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Removal Ice from Ice Shelves (Cold ice shelf cavity (1. Cold water…
Removal Ice from Ice Shelves
In Antarctica ice shelf loss both:
Ocean driven - from below
Atmos driven - from above
W. Antarctic
Cont Shelf
How warm
below cold?
salinity = stronger control on density in polar oceans
Above: Cold freshwater ~300-400m deep
Below: Warm salty water (up to 1.2°C)
Cold freshwater overlies warm salty water
High salinity shelf water
Formed by
sea ice formation
High salinity - reflects brine rejection
Cold - Is at surface freezing point (-1.8°C)
--> Salt depresses freezing point
Freezing
Point & Z
Freezing point decreases as depth increases
0.7°C per km increase Z
Ice Pump
= net ice transport beneath cold ice shelves
from grounding line
further along ice shelf
Melt flows upwards & freezes again in shallows
∴ Marine ice forms via ice pump & migrates oceanward
Cold ice
shelf cavity
1. Cold water enters shelf cavity @ depth
However: freezing point decreases with depth ~0.7°C/km
Melt occurs @ base ice shelf
since pressure suppresses freezing point at depth
Freshwater melt makes ambient seawater buoyant
as mixed in via turbulence
Water flows upward & freezes again in shallows
where pressure & freezing point are lower
∴
Marine ice forms on base of ice shelf via ice pump
Cold water = high salinity shelf / polar water
(n.b. Water densified as freshwater remains)
Cold & warm
ice shelves
Cold - Ross, Filchner-Ronne, Amery
Warm i.e. Amundsen, S. Greenland Bellingshausen?
Warm ice
shelf cavities
Warm water (~1°C) may enter cavity
--> well above surface freezing point
Warm water i.e. Circumpolar deepwater / Irminger water
Strong melting induced ~20-100m/yr)
when water reaches g.l.
Water never freezes
- since well above f.p.
Water may upwell out of shelf
--> if buoyancy overcomes stratification
∴ Delivering nutrients to the surface