Atlantic “Branch Waters” (BW) Fram Strait (FSBW) and Barents Sea (BSBW)General AW Circulation SchemesTracers of Atlantic WaterCFCsCs and IPathways and “Ages” (transit time?)Routes in the ArcticHow AW varies in the ArcticThe Arctic Ocean Boundary CurrentDetails still unclearChanging AWAtlantic Layer warming in 1990s (collation/model by Karcher et al., 2003)AW warming spreads also into Western ArcticAW warming .. slow to reach Canada BasinChanging Atlantic InflowHow unique is this warming?Do these warmings agree??Do these warmings agree??Atlantic Water zigzags AOS94Mixing and Double Diffusion in T-S Space“T-S Zigzags” in the ArcticChukchi Borderland Atlantic Water CirculationAtlantic WaterAtlantic “Branch Waters” (BW) Fram Strait (FSBW) and Barents Sea (BSBW)FSBW – temperature maxBSBW - inflexion ptATLANTIC LAYER- temperature > 0 deg C- FSBW and BSBW- usually between 200-1000min water column- Tmax usually between 200 and 500m depthBarents SeaSt. Anna TroughYPYP= Yermak PlateauFram StraitSpitsbergenScandinaviaGreenlandFSBW- enters through FS, surface cools (cf first picture),(may melt ice, may freeze).FSBW TRANSFORMED tosubsurface TmaxAlong SLOPEmay be capped with ice melt,or perhaps shelf watersAt St ANNABSBW outflow mostly comesin at depth, into FSBW core,below it (maybe above)AW does not really subduct below Arctic SurfaceWaters. Instead they areformed from AW.General AW Circulation SchemesAagaard, 1989- topographically steered boundary current along slopes and ridges- interior flow weak, dominated by eddies(based on current meters)Rudels et al, 1994- mixing off St Anna- cyclonic (anti-clockwise) circulation(based on T-S and tracers)Tracers of Atlantic WaterTEMPERATURE-SALINITY- presence of Tmax- form in TS space- following a warming (see later)- also dissolved oxygen??- Delta O18?? (not really)- N:P ratios (perhaps)CHEMICAL TRACERS- usually atmospheric source- mixed into surface water, and thenisolated from the atmosphereCFCs (ChloroFluoroCarbons)- solvents from 1960s onwards- CCl4 (“carbon-tet”) is oldestthen CFC11, CFC12 and newest CFC113- atmospheric concentrations KNOWN- use presence or ratios to give ageBomb Tritium- atomic bomb tests 1950s- surface layer of tritium (isotope of H)- decays to Helium-3 (half-life ~ 12.4 yrs)Cs and I from Nuclear Reprocessing- on-going, - concentrations KNOWN- use presence or ratios to give ageNON-CONSERVATIVE (weakness and strength)CONSERVATIVE - but mixing importantJGR, 2000CFCsHighLowHighJGR, 1999Cs and ISmith et al., 1999HighLowHighHighLowHigh.. “ages” much higher than from advection speeds,possibly due to CFC mixing modelPathways and “Ages”(transit time?)HighLowHighHighLowHighLowSmethie et al., 2000Smith et al., JGR, 1999Routes in the ArcticAW circulation very different to PW circulation- AW follows topography (with exceptions?)- PW follows ice ??Jones et al., 2001, Polar ResearchHow AW varies in the ArcticJGR, 2005EWG data 1948-199345-year mean of Temperature in each boxDoes AW cool as it progresses??- if so, why?What else might be happening?Boxes numbered in order ofour best guess at time sinceFram StraitThe Arctic Ocean Boundary Current- mean flow weak, but with strong eddies- topography following- equivalent barotropic (i.e. velocity well correlated at all levels)- NOT SEASONALLY VARYING- current ~ 50 km widefound over ~ 500-3000m isobaths- centered over ~ 1700m isobathThe Arctic Ocean Boundary Current~ 5 cm/s~ 2 cm/s~ 2 cm/sTransports – large uncertainties!!, but consistent with inputsAdvection speeds a few cm/s, consistent with Tmax translation, faster than CFC ages. (? Mixing?)Flow split by Ridge – one branch N along Lomonosov Ridge, – one branch into Canadian BasinSome waters cross ridge S of 88NSmall exchange of Deep Waters (CBDW/EBDW –Canadian/Eurasian Basin Deep Water)Woodgate et al., 2001, DSRBUT STILL DON’T KNOW= what “type” of current it is- equivalent barotropic jet?(Killworth and Hughes, 2002)= what drives it- “Neptune” – interaction of eddies and topography (Holloway, 1987)- Potential Vorticity forcing (Karcheret al., 2007)- Windstress from Greenland Sea (Nost and Isachsen, 2003)From Woodgate and Steele, 2006, NSF proposalDetails still unclearChanging AWQuadfasel et al., Nature, 1991DSR, 19931990 Rossiya tourist cruise,XBT sectionSignificant Warming of AWAtlantic Layer warming in 1990s(collation/model by Karcher et al., 2003)‘80‘84‘87‘91‘93‘95‘96‘99Modelled (full fields) and observed (circles) AW core temperatures in various yearsWarmer since 1990s, ... but slight cooling following the warming ... USE THIS AS TRACER!!AW warming spreads also into Western ArcticWoodgate et al, 2001, NSF proposalTmax from submarine cruisesSee warming, but data very sparseAW warming .. slow to reach Canada BasinShimada et al., 2004, GRLTmax from submarine cruisesSee warming, but data very sparseChanging Atlantic Inflow2005How unique is this warming?JGR, 2005EWG data 1948-1993Temperature at AW depths in Box 3Have been previous warm periodsJClim, 2004Normalised anomalies of AW Core Temperature(Real data, especially sparse real data can bevery very messy)Do these warmings agree??Swift et al, 2005Polyakov et al., 2004JClim, 2004SAT – surface Arctic Air Temperature (area?)HIce – ice thickness at station in KaraWTM – 10m water temperature at station Mike (66N, 2E)NAlt SST – North Atlantic Sea Surface TempWhat are the mechanisms??Do these warmings agree??Swift et al, 2005Polyakov et al., 2004AO,courtesyI.RigorGRL, 2006- in 2000s,hydrography at NP “returning to pre-1990s state”- may relate to AO(magenta ~ red marks)1993 Larsen - 1 deg warmer on the Mendeleev Ridge- inversions in temperature and salinityCarmack et al, ‘95, and McLaughlin et al, ‘96The Warming of the 1990sAtlantic Water zigzags AOS94Line up/ Nest all throughthe Arctic - ~ 5,000kmAngles of the Zigzags match double diffusive theoryCarmack et al, 1997Salinity (psu)Potential Temperature (deg C)Mixing and Double Diffusion in T-S SpaceTEMPERATURESALINITYMechanical mixing in TS space creates straight lines between water massesTEMPERATURESALINITYIn double diffusive processes,heat diffuses faster than salt.So, in TS space resultant waters are not on a straight line between the parent water massesTheories for formation, and for growing to a large amplitude steady state(Turner, Ruddick, Toole, Georgi, McDougall, Walsh, Carmack, Rudels, May … )Salt fingeringRegime Warm Salty / Cold Freshunstable in