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					Global reaching Antarctic Bottom Water [AABW] is drawn from
Antarctica’s dense shelf waters formed in restricted polynya strips,
with export to deep ocean by energetic plumes


                                                Bottom Potential Temperature
                                                NADW>1°C; AABW<1°C



                              coastal polynya                                           NADW


                                                                                        AABW


                                                                        X AABW formation sites;
                                                                        O Potential Monitoing sites




                                                                         AABW characteristics
                                                                         suggest open ocean
                                                                         pycnocline
                                                                         entrainment into slope
                                                                         plumes


  dense shelf water; ice shelf water
                                               AABW and slope plumes
                                               are part of the O(50Sv)
                                  ACC 140 Sv   southern ocean meridional
Antarctic Intermediate
Water, [AAIW]
                                               overturning circulation
                            Ice shelve/
                            ocean

 Circumpolar
 Deep Water

                                SOMOC,
                                50 Sv
   Antarctic Bottom water
                                   a
   [AABW]




                                                  ACC = Antarctic Circumpolar Current
                                          Orsi, Smethie, Bullister
                                          JGR 2002




Orsi, Jacobs, Gordon, Visbeck, GRL 2001
Active plumes

 No plumes
WeddellSea AABW
50 km
    s2                         s2
                       q   S




                           q                  S
q                                   s0   O2
                   S
         s0   O2
Plume speeds [geostrophic,
ref to 50-m current meters]
>0.15 m/s
Weddell Monitoring 1999-2001
And beyond
  M3,   63.52°S, 41.79°W, at approximately 4635 db.




                        2000



1999
                                                      2001
small dT/dz




                               Bottom intensified. The bottom
                               temperatures at M2 and M3 are linear
                               dependent on the vertical gradient of
 large dT/dz                   temperature [differencing the top and bottom
                               temperature data]: bottom temperature
                               decreases as the temperature gradient
                               increases.
               Cold bottom q                                 ‘warm’ bottom q
                                        Regional CTD
                                         Regional CTD

M2
 M2


                       M3
                        M3
      Salty events
        Salty events: during cold periods of May-July 99&01
        Increased output from WSBW-3?
                                    Warm events


                                       Cold events



     Eddy 34




                                       Along isobaths



M3             From Boda MA thesis, 2003
Ross Sea [AnSlope]




 Bathymetry well resolved by multi-beam: no incised canyons
Section across continental margin at AnSlope
                mooring array
          [see white line on station map]
Bottom tracked LADCP current for
the lower 80 meters, color coded by
salinity. High salinity is derived from
the Drygalski Trough [western most
deep trough within the Ross Sea].

• A direct relationship of bottom
speed and salinity is observed.

• Benthic slope water with high
salinity [denser] moves downslope at
approximately 20°-30° to the isobath.




                                          Barotropic tide removed
     Escape may have something to do with the tides




#1                                #2
                                                      #4
                                          #3
#1



          #3
     #2
               #4
Monitoring?
Mixed BW



 HSBW         Avalanches   LSBW




              HSSW
          Summary 1


 •   Plume thickness: 200-m
•    High and low salinity plumes, often in same plume [salty variety below fresher variety].
•    Thermobaric important [for low salinity plumes]
•    Plume speed relative to interior water column: 1 m/s
•    Ri ≈ 0.25; internal Froude ≈ 1.6 [0.5 m/s]; 6 [1.0 m/s]
•    Flow relative to isobaths: <30° to isobath; sudden downhill Avalanches.
Summary 2:
• Escape to deep ocean takes on two forms:
          1. Quasi-geostrophic flow [low angle descent relative to isobaths]
          2. Rapid downhill ‘avalanches’. Plume front has scalloped edge, breaking into
eddies.

Which is more important to deep ocean ventilation? What processes producing ‘avalanches’?




   .Ross Sea condition- no canyons
I can calculate numbers, what do you want?
   Salty plume
                 Salty plumes
                 decend fastest




fresher plume     Generally >1500-m

				
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posted:8/5/2012
language:English
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