1. Antarctic Circumpolar Current
Philip Sontag

2. Thermohaline Circulation; “Mix-Master”
Circulation below major wind-driven currents
Density distribution – flow patterns
Tuggweiler & Samuels 1995 Strong ACC upwelling short circuit vertical mixing in low, mid latitudes

3. Antarctic Fronts

4. Convergence Divergence Patterns
The Antarctic currents are wind driven. Strong west winds with maximum speed near 50◦S drive the currents, and the north-south gradi- ent of wind speed produces convergence and divergence of Ekman transports.
Ekman transports diverge, pulling Circumpolar Atlantic Deep Water to the surface south of the Polar Front, which helps drive the deep circulation

5. Antarctic Circumpolar Current
Geostrophic
Driven by prevailing westerly winds
Balance of surface and bottom stresses
Potential Vorticity and Bottom Topography
Geostrophic balance = N-S direction interior flow, E-W pressure gradient
below 2500 m
Extending to bottom ocean =speeds of 3-9 cm/s
shallow ridges, plateaus of southern oceans current curves equatorward
as it moves deeper water, moves curves poleward

6. Antarctic Polar Ice, Bottom Water Formation (600S)
Penetrative barrier – Albedo – Positive Feedback
Polynas
Origin, Shallow Weddel and Ross Seas
Stability of stratified ocean
Transport to western basin
Decrease CO2 uptake
Driven by Halocline
Melting, formation of ice
Sources: 1) Surface waters -> Continental Shelf 2) Remnants of Circumpolar deep waters
Ross Sea (saltiest waters)
Total Antarctic Bottom Water production rate is about Sv 1 Sv=106 m3 s−1
Ice albedo = 30-40% -> 95% directly after snow fall
Polynas -> significant sensible heat loss, as much as 250 W/m2 in winter
Ice free areas -> 5-15% in winter, doubled in summer
Ice thickening and reducing -> analagous to formation and dissipation of thermocline
Reversal of sign in the thermal expansion coefficent at 4C
Density of seawater greater than 24.7 psu increases in during temp decrease until freezing
Halocline 50 to 200 m -> fresher lighter water cooled to freezing point
Ice forming, melting causes halocline

7. Eddies 20 km diameter –> jets
Primary mechanism for generating interface displacement
Divergence in Ekman transport
Sheered along flanks of jets

8. Eddies and Jets, Ocean Storms
Focusing of eddies into narrow jet
ACC -> 2 to 3 narrow jets, sharp fronts
Meridional gradients of potential vorticity (PV)
Strong along Eastward
Weaker along Westward
Eastward and westward flow arise from local PV mixing
“PV staircase”
Merge and split, yet persistent
“Barrier” or “Blender”
Strong PV = weak horizontal mixing
Weak PV = strong horizontal mixing
Traditionally, ACC jets viewed as circumpolar features with strong horizontal gradients
Eddies accelerating and decelerating jets locally – locally variability allows jet to manuever around local topography
Structure of jets maintains eddy field
“Barrier” = weak exchange cross jet exchange

9. Drake Passage Along line of constant longitude Drake Passage:
Major Variability in Transport
Typical current speeds are around 10 cm/s with speeds of up to 50 cm/s near some fronts. Although the currents are slow, they transport much more water than western boundary currents because the flow is deep and wide.
Max transport, late winter, early spring

10. Implications for Primary Production
Spring Bloom in New Zealand Waters
cold rivers of water that have branched off from the Antarctic Circumpolar Current flow north past the South Island and converge with warmer waters flowing south past the North Island.

11. Melting of Antarctic Shelves
Warm circumpolar water can override continental slope front
Redirection of currents, movement of warm waters into ice-shelf cavity
Increase in surface stress in southeastern
Ozone depletion and increase in greenhouse gases
Increase in zonal ACC transport
“Eddy-Saturated Regime”
0.5°C increase

12. References
Hellmer, H. H., F. Kauker, et al. (2012). Twenty-first-century warming of a large Antarctic ice-shelf cavity by a redirected coastal current. 485:
Knauss, J. A., Ed. (1997). Introduction to Physical Oceanography. Long Grove, IL, Waveland Press, Inc.
NASA/MODIS Rapid Response/Jeff Schmaltz. Caption Credit: Rebecca Lindsey, NASA Earth Observatory.
Orsi, A. H., G. C. Johnson, et al. (1999). Circulation, mixing, and production of Antarctic Bottom Water. 43:
Rintoul, S. R. and J. L. Bullister (1999). A late winter hydrographic section from Tasmania to Antarctica. 46:
Stewart, R. H. (2008). Introduction To Physical Oceanography, Department of Oceanography Texas A & M University.
Thompson, A. F. (2008). The atmospheric ocean: eddies and jets in the Antarctic Circumpolar Current. 366:
U.S. Geological Survey First published in the Encyclopedia of Earth March 30, 2010; Last revised Date June 11, 2012; Retrieved December 6,