life cycle of sea-ice - polar science...
TRANSCRIPT
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Life Cycle of Sea-IceSea-water~ 35 psu
Frazil, or grease ice- small crystals
Thickens Nilas
Thickens Ice Floes
Calm Conditions
Rough Conditions
Pancake Ice
Thickens
Thickening:- thermodynamic = congelation ice- mechanical = (finger rafting)
= ridging
FIRST-YEAR ICE~ 4-10 psu
flat and ridged1-2 m thick unridged
MULTI-YEAR ICE~ 1-4 psu
Thermodynamic equilibrium thickness ~ 3m
Ridges ~ 10-25m, keels maybe 50m!
Thickens
Rotten Ice- surface melt ponds
Melts
Ice Melt~ 4 psu
Distillationeffect
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Internal Structure of Sea Ice
away from surface, long crystals as congelation ice
(frozen on from below)
Brine Channels within the ice(~width of human hair)
Brine rejected from ice (4-10psu), but concentrates in brine channels
(small volume but VERY HIGH SALINITIES)-6 deg C -10 deg C -21 deg C
100psu 145psu 216psuPictures from AWI
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Brine Volume and Salinity
From Thomas and Dieckmann 2002, Science .... adapted from papers by Hajo Eichen
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Ocean
Impacts of Sea-ice on the OceanICE FORMATION and PRESENCE
- brine rejection- Ocean-Atmos momentum barrier
- Ocean-Atmos heat barrier- ice edge processes (e.g. upwelling)- keel stirring (i.e. mixing, but < wind)
MELTING ICE- stratification (fresher water)
(cf. distillation as ice moves from formation region)
- transport of sediment, etc
35psu
START
10psu
S increases
FREEZE
Fresh
Saltier
MELT
Wind
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Impacts of Sea-ice on the AtmosphereICE PRESENCE- albedo change
- Ocean-Atmos momentum barrier- Ocean-Atmos heat barrier
Water Sky
Sea Smoke
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Heat balance
From N. Untersteiner
S=Shortwave radiation from sun(reflects off clouds and surface)
albedo= how much radiation reflects from surfacealbedo of ice ~ 0.8
albedo of water ~ 0.04 (if sun overhead)
L=Longwave radiation(from surface and clouds)
F=Heat flux from Ocean
M=Melt (snow and ice)P=Precipitation
T=Atmospheric Heat Transferq = Atmospheric moisture transferice albedo feedback
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Sea Ice MotionOLD RULE OF THUMBIce (Northern Hemisphere) moves with - speed about 2% of surface wind- about 45deg to the right of the wind
GeostrophicWIND = 20 m/s
ICE ~ 20cm/s,5 deg to right
SurfaceWIND = 10 m/s
ICE ~ 20 cm/s,~45 deg to right
quite a fast ice speed – see next plots (NB 50cm/s ~ 1 knot ~ 1 mph)
THORNDIKE AND COLONY 1982- speed 1% of geostrophic wind- 5 deg to right of wind
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Rigor et al, 2002, Response of Sea Ice to the Arctic Oscillation, J Climate
Sea-ice motion
RIGOR ET AL 2002Infer Sea ice motion from Sea Level Pressure and Buoy tracks
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Rigor et al, 2002, Response of Sea Ice to the Arctic Oscillation, J Climate
Sea-ice motion
Thorndike and Colony, 1982, Sea Ice Motion in Response to Geostrophic Winds, JGR
Long termIce Drift
= Winds + Ocean
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Rigor et al, 2002, Response of Sea Ice to the Arctic Oscillation, J Climate
Sea-ice motionHIGH AOLower SLP ►more cyclonic atmosphereBeaufort Gyre (AC) ► weaker, smallerMore ice swept out with TransPolar drift
(more Atlantic Influence)(Warm Phase)
LOW AOHigher SLP ►more anticyclonic atmosphere
Beaufort Gyre (AC) ► stronger, biggerLess ice swept out with TransPolar drift
More stored in Beaufort Gyre(less Atlantic Influence)
(Cold Phase)
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Rigor et al, 2002, Response of Sea Ice to the Arctic Oscillation, J Climate
Sea-ice motionHIGH AO
Lower SLP ►more cyclonic atmosphereBeaufort Gyre (AC) ► weaker, smallerMore ice swept out with TransPolar drift
- less convergence of sea ice (i.e. less ridging, ice thinner)- longer transit from Chukchi
LOW AOHigher SLP ►more anticyclonic atmosphere
Beaufort Gyre (AC) ► stronger, biggerLess ice swept out with TransPolar drift
More stored in Beaufort Gyre- more convergence, more ridging
Years to exit through Fram Strait
recirculates
recirculates
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Sea-ice thickness
Data from CREL, from the SHEBA experiment, western Arctic
How to define it?- mean- mode
- maximum- average?
How to measure it?
Ice thickness distribution
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Arctic Sea-ice Change- extent
2002 20042003
September Sea ice concentration anomalies relative to 1979-2000, pink=median of 1979 to 2000
Year
Sep
t ice
ext
ent
(milli
on s
q km
)
1975 20051990
7
6
Washington State ~ 185,000 sq kmTexas ~ 670,000 sq kmAlaska ~1,700,000 sq km
GRL, 2005
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Arctic Sea-ice Change
- Thickness
GRL, 1999
BUT – seasonal cycle- aliasing due to submarine tracks
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Arctic Climate Impacts Assessment (ACIA) Report 2004
Temperature Change 2003 - 1954
Alaska+2°C
Greenland
Siberia+2°C
–1°C
?
?
Increasing Arctic Air Temperature(links to Sea ice?)
Chapman and Walsh, 1999; updated
Jones et al, 1999; updated
Courtesy of I. Rigor
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Changing AGE of Sea Ice
September1981
September2002
GRL, 2004