X AABW formation sites; O Potential Monitoing sites

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) southern ocean meridional overturning circulation ACC 140 Sv Antarctic Intermediate Water, [AAIW] Ice shelve/ ocean Circumpolar Deep Water SOMOC, 50 Sv a Antarctic Bottom water [AABW] 140 million m3/sec 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 S q s0 O2 q 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 temperature [differencing the top and bottom temperature data]: bottom temperature decreases as the temperature gradient increases. large dT/dz ‘warm’ bottom q Cold 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. High salinity bottom water Low salinity bottom water Barotropic tide removed

Escape may have something to do with the tides #2 #1 #4 #3

#1 #3 #2 #4

Monitoring? Mixed BW Avalanches HSBW 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 Generally <1500-m fresher plume Generally >1500-m

X AABW formation sites; O Potential Monitoing sites