Southern Ocean Paleoceanography: Lessons from Sediments

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Southern Ocean PaleoceanographyLessons from
Sediments

• Will Howard
• Antarctic Cooperative Research Centre
• University of Tasmania

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Preview

• Overall paleo view of S.O.
• Some of what weve learned, and how we think we
  know it.
• Operational issues linkages
• IMAGES Science Plans
• Links to CLIVAR via IGBP/PAGES

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Framework Past 250,000 years
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What did this look like in the past?
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Basic approach (Sea-ice example)
From Armand (2000)
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Last Glacial Sea-ice Snapshot
Sea-ice edges, fronts, Isotherms, iceberg tracks
all shift equatorward
From Armand (2000)
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Particle fluxes shift (increase in SubAA,
decrease so. of PFZ
Anderson et al. (1998)
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0
500
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Deep-water circulation in glacial intervals?
The view from paleo ?14C Longer residence times
for deep waters
Sikes et al., 2000 also Goldstein et al. 2001
EPSL show older S.O. waters at 1125 m in Drake
Passage from deep solitary corals
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Conflict in tracers

• More sluggish circulation (or reduction of NADW
  admixture)
• d13C
• ?14C
• Nd isotopes

Similar circulation (or continuation of NADW
admixture) Pa/Th Ba/Ca Cd/Ca
More vigorous circulation Grain size (at
Chatham Rise Hall et al. 2001)
Problem in comparing tracers - state vs.
rate proxies
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Paleocurrent example from the N. Atlanticare
there S.O. equivalents e.g.Kerguelen Plateau?
Bianchi et al. 1999
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Higher frequency/abrupt changes
South Atlantic ice-rafting Kanfoush et al, 2001
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South Atlantic SST Sachs et al, 2001
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Abrupt cooling at 8,000 years BP
Core at 45S, So. Tasman Rise C. Samson Ph.D,
U.Tasmania 1998
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Other centennial-scale records

• Palmer Deep, Ant. Peninsula (Domack, Leventer,
  Dunbar and others)
• Adelie Drift (DunbarLeventer) Mertz Drift
  (Harris)

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Carbon cycle constraints
The challenge to carbon cycle research
Age (ka)
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Biological pump at the deglaciation
Planktonic-benthic gradient increased at LGM
Core at 45S, So. Tasman Rise C. Samson Ph.D,
U.Tasmania 1998
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Biological pump at the deglaciation
Planktonic-benthic gradient at minimum on
deglaciation
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Solubility pump
Alkalinity pumps
Biological pump
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Subantarctic model CO2 vs. Vostok
Observations
Model
Shackleton (2000) time scale
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IMAGES S.O. Targets
IMAGES Southern Ocean Working Group Report See
http//images.pclab.ifg.uni-kiel.de/start.html
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S.O. Core coverage
Links to Ocean Drilling Program national
programs Links to mooring programs (e.g. JGOFS)
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Main findings

• Distinct, coupled Southern Ocean variations
  linked to orbital forcing, ice volume CO2
• Warming/cooling cycles lead NH responses on
  orbital and suborbital time scales
• SH terrestrial ecosystems track SO SST
• Subantarctic carbon sink intensified in glacials
• Deep-water circulation changes still
  controversial as tracers disagree

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More main findings

• Fronts and isotherms shift northward along with
  sea-ice edges (e.g. Armand, Howard, others)
• Particle fluxes intensify in Subantarctic,
  decrease south of (modern) PFZ in glacials
  (Anderson)
• Stratification increase in polar waters in
  glacials, but N-isotope tracers conflict with
  other tracers (Francois)

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Main challenges/questions

• Zonal asymmetries?
• Reconciling deep-water paleotracers (esp.
  geoochemical vs. advective)
• Finding cores of appropriate resolution and
  composition in areas that intercept bottom
  water pathways esp. continental slope/rise
  environments.
• Finding marine cores of centennial resolution