Transcript Alley's 'Wally Was Right: Predictive Ability of the North

Alley’s ‘Wally Was Right:
Predictive Ability of the North
Atlantic “Conveyor Belt”
Hypothesis for Abrupt Climate
Change’
Jake Leech
29 Aug 08
Bestiary
Wally’s Arguments
• Greenland proxies all show abrupt
climate change
• Greenland data matches Europe data
• Data matches expectations from North
Atlantic SST changes
• MOC switching is possible
• Data shows ocean circulation changes
Ice core data
Hemispheric See-Saw
Modelled climate patterns seem to match Voelker data set
See Saw in Data
Response of MOC to
freshwater
Sea Ice and Seasonality
Wally’s data
• Young, surface waters are depleted in
Cd and C-12, and enriched in C-14
• SH water is “older”
• During cold periods, NH sediments are
“older”
Jean’s Data
• Benthic forams have heavier oxygen
isotopes in colder water and saltier
water, and therefore in denser water.
• Density profiles can be used to
reconstruct geostrophic flow through the
Florida Straits, which shows changes in
MOC.
Jerry’s Data
• Water is stripped of Pa and Th before
entering the North Atlantic
• Thorium is stripped out of the water
within 20-40 years, before being
exported
• Protactinium is stripped out of the water
within 100-200 years, after being
exported.
Jerry’s Data vs. Forams
Caveats
• Background state is important.
• Freshwater forcing? Cooling events and
freshwater pulses are correlated, but
which causes which?
• 1500 year oscillation?