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?