Life Cycle of Sea-IceInternal Structure of Sea IceBrine Volume and SalinityImpacts of Sea-ice on the OceanImpacts of Sea-ice on the AtmosphereHeat balance Sea Ice MotionSea-ice motionSea-ice motionSea-ice motionSea-ice motionSea-ice thicknessArctic Sea-ice Change - extentArctic Sea-ice Change - ThicknessChanging AGE of Sea IceLife Cycle of Sea-IceSea-water~ 35 psuFrazil, or grease ice- small crystalsThickensNilasThickensIce FloesCalm ConditionsRough ConditionsPancake IceThickensThickening:- thermodynamic = congelation ice- mechanical = (finger rafting)= ridgingFIRST-YEAR ICE~ 4-10 psuflat and ridged1-2 m thick unridgedMULTI-YEAR ICE~ 1-4 psuThermodynamic equilibrium thickness ~ 3mRidges ~ 10-25m, keels maybe 50m!ThickensRotten Ice- surface melt pondsMeltsIce Melt~ 4 psuDistillationeffectInternal Structure of Sea Iceaway 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 C100psu 145psu 216psuPictures from AWIBrine Volume and SalinityFrom Thomas and Dieckmann 2002, Science .... adapted from papers by Hajo EichenOceanImpacts 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, etc35psuSTART10psuS increasesFREEZEFreshSaltierMELTWindImpacts of Sea-ice on the AtmosphereICE PRESENCE- albedo change- Ocean-Atmos momentum barrier- Ocean-Atmos heat barrierWater SkySea SmokeHeat balance From N. UntersteinerS=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 OceanM=Melt (snow and ice)P=PrecipitationT=Atmospheric Heat Transferq = Atmospheric moisture transferice albedo feedbackSea Ice MotionOLD RULE OF THUMBIce (Northern Hemisphere) moves with - speed about 2% of surface wind- about 45deg to the right of the windGeostrophicWIND = 20 m/sICE ~ 20cm/s,5 deg to rightSurfaceWIND = 10 m/sICE ~ 20 cm/s,~45 deg to rightquite 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 windRigor et al, 2002, Response of Sea Ice to the Arctic Oscillation, J ClimateSea-ice motionRIGOR ET AL 2002Infer Sea ice motion from Sea Level Pressure and Buoy tracksRigor et al, 2002, Response of Sea Ice to the Arctic Oscillation, J ClimateSea-ice motionThorndike and Colony, 1982, Sea Ice Motion in Response to Geostrophic Winds, JGRLong termIce Drift =Winds + OceanRigor et al, 2002, Response of Sea Ice to the Arctic Oscillation, J ClimateSea-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 atmosphereBeaufort Gyre (AC) ► stronger, biggerLess ice swept out with TransPolar driftMore stored in Beaufort Gyre(less Atlantic Influence)(Cold Phase)Rigor et al, 2002, Response of Sea Ice to the Arctic Oscillation, J ClimateSea-ice motionHIGH AOLower 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 ChukchiLOW AOHigher SLP ►more anticyclonic atmosphereBeaufort Gyre (AC) ► stronger, biggerLess ice swept out with TransPolar driftMore stored in Beaufort Gyre- more convergence, more ridgingYears to exit through Fram StraitrecirculatesrecirculatesSea-ice thicknessData from CREL, from the SHEBA experiment, western ArcticHow to define it?- mean- mode- maximum- average?How to measure it?Ice thickness distributionArctic Sea-ice Change- extent200220042003September Sea ice concentration anomalies relative to 1979-2000, pink=median of 1979 to 2000YearSept ice extent(million sq km)19752005199076Washington State ~ 185,000 sq kmTexas ~ 670,000 sq kmAlaska ~1,700,000 sq kmGRL, 2005Arctic Sea-ice Change- ThicknessGRL, 1999BUT – seasonal cycle- aliasing due to submarine tracksArctic Climate Impacts Assessment (ACIA) Report 2004Temperature Change 2003 - 1954Alaska+2°CGreenlandSiberia+2°C–1°C??Increasing Arctic Air Temperature(links to Sea ice?)Chapman and Walsh, 1999; updatedJones et al, 1999; updatedCourtesy of I. RigorChanging AGE of Sea IceSeptember1981September2002GRL,