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
coastal polynya NADW
X AABW formation sites;
O Potential Monitoing sites
suggest open ocean
entrainment into slope
dense shelf water; ice shelf water
AABW and slope plumes
are part of the O(50Sv)
ACC 140 Sv southern ocean meridional
Antarctic Bottom water
ACC = Antarctic Circumpolar Current
Orsi, Smethie, Bullister
Orsi, Jacobs, Gordon, Visbeck, GRL 2001
q s0 O2
Plume speeds [geostrophic,
ref to 50-m current meters]
Weddell Monitoring 1999-2001
M3, 63.52°S, 41.79°W, at approximately 4635 db.
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
Cold bottom q ‘warm’ bottom q
Salty events: during cold periods of May-July 99&01
Increased output from WSBW-3?
M3 From Boda MA thesis, 2003
Ross Sea [AnSlope]
Bathymetry well resolved by multi-beam: no incised canyons
Section across continental margin at AnSlope
[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
HSBW Avalanches LSBW
• 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.
• 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
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?
fresher plume Generally >1500-m