1. L. Padman, R. Muench, A. Orsi; Presentation OS41H-06 at the AGU Ocean Sciences Meeting, Portland OR, January 2004 Observations of Dense Off-Slope Flow With Energetic Tidal Forcing Laurence Padman 1, Robin Muench 1 Alejandro Orsi 2, Arnold Gordon 3 1 Earth & Space Research, Seattle WA 2 Texas A&M, College Station TX 3 Lamont-Doherty Earth Observatory, NY

2. L. Padman, R. Muench, A. Orsi; Presentation OS41H-06 at the AGU Ocean Sciences Meeting, Portland OR, January 2004 Setting for AnSlope; the NW Ross Sea Ant. Slope Current Warm inflows Cold outflows Dense outflows off the shelf Shallow banks –– 1000 m isobath

3. L. Padman, R. Muench, A. Orsi; Presentation OS41H-06 at the AGU Ocean Sciences Meeting, Portland OR, January 2004 AnSlope Cruise#1 (Feb-Apr 2003): track and station locations Ross Ice Shelf Drygalski Trough Focus Region

4. L. Padman, R. Muench, A. Orsi; Presentation OS41H-06 at the AGU Ocean Sciences Meeting, Portland OR, January 2004 Antarctic Slope Front  Mean current flow is along the shelf break (into screen).  Warm deep water (MCDW) gets onto shelf.  Cold, dense water escapes from shelf.  “Dense Plume”: contributes to AABW }  Mixing

5. L. Padman, R. Muench, A. Orsi; Presentation OS41H-06 at the AGU Ocean Sciences Meeting, Portland OR, January 2004 Tidal Environment Mean tidal speed  |U|  (cm s -1 )  |U|  > 50 cm s -1 along break; Spring currents ~ 2  |U|  ; Diurnal, topo vorticity waves – short space scales; – strong cross-slope currents; RossTIM model validated w. current meters and ADCP. RossTIM model Yo-yo CTD/CMiPS 

6. L. Padman, R. Muench, A. Orsi; Presentation OS41H-06 at the AGU Ocean Sciences Meeting, Portland OR, January 2004 Hydrographic variability T S T-S CTD/CMiPS Locations Plume on slope HSSW CTD-179/180 CTD-181

7. L. Padman, R. Muench, A. Orsi; Presentation OS41H-06 at the AGU Ocean Sciences Meeting, Portland OR, January 2004 Hypothesis... A combination of small- and micro-scale processes associated in large part with tidal currents influence the flux and T-S properties of dense water moving seaward over the Ross Sea shelf break. Test using... - Tidal currents derived from models and observations; - Small-scale and microscale field data; - Moored, time-series current observations.

8. L. Padman, R. Muench, A. Orsi; Presentation OS41H-06 at the AGU Ocean Sciences Meeting, Portland OR, January 2004 Yo-yo CTD/CMiPS sequence, ~900 m isobath Alongslope tidal current (cm s -1 ) Cross-slope tidal current (cm s -1 ) Cross-slope tidal displacement (km) CTD/CMiPS CTDs 179 &180 (thick benthic plumes), coincident with: - max. offshore disp. - max. westward flow (augments ASF)

9. L. Padman, R. Muench, A. Orsi; Presentation OS41H-06 at the AGU Ocean Sciences Meeting, Portland OR, January 2004 Pressure Thermistor (x2) Conductivity Cell CMiPS Overview P max = 3500 m; Internal recording; Sample rate=512 Hz; Resolution ~1-10 cm; Requires monotonic descent at moderate speed: no large vessel heave on CTD cable. (Good in ice.) CTD-Mounted Microstructure Profiling System (CMiPS)

10. L. Padman, R. Muench, A. Orsi; Presentation OS41H-06 at the AGU Ocean Sciences Meeting, Portland OR, January 2004 Plume structure on slope CTD-180 CMiPS LSDW HSSW Interface ~10 cm thick! Density T T z T K z  0.004 m 2 s -1 F H  10 3 W m -2

11. L. Padman, R. Muench, A. Orsi; Presentation OS41H-06 at the AGU Ocean Sciences Meeting, Portland OR, January 2004 Mixing on sill Density T T z T K z  0.003 m 2 s -1 F H  250 W m -2 MCDW LSDW HSSW HSSW warms by ~0.05 o /day CTD-181 CMiPS (on sill)

12. L. Padman, R. Muench, A. Orsi; Presentation OS41H-06 at the AGU Ocean Sciences Meeting, Portland OR, January 2004 High frequency internal waves? EK-500: 38 kHz 10 min.

13. L. Padman, R. Muench, A. Orsi; Presentation OS41H-06 at the AGU Ocean Sciences Meeting, Portland OR, January 2004 Summary of near-frontal structures ASF (outer edge of “V”) has along-slope speeds of ~50 cm s -1 : This front is very sharp (2-5 km?); Tidal cross-slope advection ~10-20 km; “Plume” thickness:  100 m; “Plume” outflow at sill: ~50 cm s -1 ; Interface at top of plume very sharp (~10 cm); Mixing rates at top of plume: K z >10 -3 m 2 s -1. Tidal advection (  |U|  ~50 cm s -1 ) brings Warm Water onto outer shelf where it can mix directly with HSSW. 

14. L. Padman, R. Muench, A. Orsi; Presentation OS41H-06 at the AGU Ocean Sciences Meeting, Portland OR, January 2004 Tidal rectification (Lagrangian) ~10 km/day 15 days of particle tracking Start

15. L. Padman, R. Muench, A. Orsi; Presentation OS41H-06 at the AGU Ocean Sciences Meeting, Portland OR, January 2004 Preliminary conclusions... 1.Tides are a significant source of cross-slope advection of water masses in AABW source region in the NW Ross Sea. Tides here are both irritating noise and fascinating signal. 2.Benthic stirring/mixing by tides contributes to reduction of HSSW signal as plume flows over the sill. 3.Comparisons to major AABW source region in Weddell Sea.