The meandering and spiraling pathway of the Antarctic Circumpolar Current and climate variations

39 Pages·2017·42.23 MB·English

The meandering and spiraling pathway of the
Antarctic Circumpolar Current and climate
variations
Lynne Talley, Matthew Mazloff, Veronica Tamsitt
Southern Ocean Workshop, NCAR Mesa Lab
April 10, 2017
Tamsitt, V., H. Drake, A.K. Morrison, L.D. Talley, C.O. Dufour, A.R. Gray, S.M. Griffies, M.R. Mazloff,
J.L. Sarmiento, J. Wang, and W. Weijer, 2017. Spiraling up: the pathways of the global deep waters
to the surface of the Southern Ocean. Nature Communications, in revision.
Talley, L.D. and M. Mazloff, 2017. Topographic effects on the southern Antarctic Circumpolar
Current and winter sea ice extent. (in GRL purgatory, perhaps sending to JGRO after revision.)
Take-home
§ ACC has standing meanders
§ These affect interaction with the cryosphere
§ One large one: inward and upward spiral (set by S.
America and Ant. Peninsula)
§ Affects where warm water reaches shelves and
hence ice shelves
§ Standing meanders on scale of basins (set by
topographic obstructions and ridges)
§ Affects ACC southern front location and
maximum winter sea ice
§ Causes poleward heat transport in ocean (does
this affect the atmosphere?? Amundsen Sea Low?)
§ Wind stress curl forcing + topography is essential
for understanding how circulation and ice changes
Questions
» Why do Antarctic ice shelf decline and sea ice
growth/decline have their peculiar nonzonal spatial
patterns?
» Why does Antarctic winter sea ice have its peculiar
pentagonal spatial pattern?
» Why does the southern side of the ACC (the sea ice
edge) have the shape that it does? (topography ->
standing meanders)
» Can we partially explain the standing meander pattern of
the ACC using linear vorticity balance?
» What circulation changes are observed, how are these
related to wind, and how does these affect ice?
Outline
§ Ice season duration trend pattern
§ Winter sea ice pattern and southern ACC
fronts
§ Pattern of spiral circulation, standing
meanders of the ACC southern fronts and
the linear vorticity balance with wind stress
curl, beta, and topography
§ Hydrographic property changes and likely
relationship to strengthening winds and
wind stress curl
The Southern Ocean overturning: first step towards 3-D with
differences between ocean basins.
Now it’s time to get much more specific about the 3-D flows!
(new schematic on its way? Group work this week?)
Deep water inflow
Deep waters rise to sea surface
in and south of ACC
Formation of AABW and
thermocline waters
Talley (Oceanography, 2013)
After Schmitz who was After Gordon
A look at the ACC’s
standing meander pattern
and the spatial structure of:
shelf temperature and ice shelf melt
sea ice
sea ice duration trend
Ice sheet mass loss and proximity to warm ocean water
Potential temperature at γN = 28.05 (NADW -
LCDW isopycnal)
Orsi and Whitworth (WHP atlas, 2005)
Paolo et al. (2015)
• Inward (and upward) spiral of warm North Atlantic Deep Water (Tamsitt talk)
• Topographic constraints on cold-warm boundaries, especially at Ross and Weddell
Gyres, which extend MUCH farther north than they should based on where
continental boundaries lie
• -> Ridges are acting as boundaries (equivalent BT flow)
Antarctic winter (September) sea ice
Antarctic sea ice trend: spatial structure
Trend in sea ice duration: Trend in sea ice
1979–2006 duration:1979-2010
Stammerjohn et al. (2008)
Antarctic sea ice trend: spatial structure
Trend in sea ice concentration: Trend in sea ice
1979 – 2016 duration:1979-2010