1. Lecture 21: Ice Core Records
This lecture was prepared on 1/23/2005 (Sunday).
Took me 5 hours (from 8:00pm to 1:00am)

2. Orbital-Scale Changes in CO2 and CH4
Ocean sediments tell us
ice-rafted debris,
δ18O records from the foraminifera shells (indicating ice volume and ocean temperature)
Ice cores tell us two greenhouse gases (CO2 and CH4)

3. Ice Core and Instrumental CO2 and CH4 Measurements
Mid-18th century: 280 ppm
Early 20th century: 300 ppm
1958: 315 ppm
Now: ~381 ppm (in 2006)
Atmospheric CO2 is ~2000 years younger than the ice layers

4. Orbital-Scale Changes in CH4
Vostok Ice in Antarctica
Six cycles since the last interglacial period
Maxima: ppb
Minima: ppb
23000 years/cycle
Peak methane values match peaks of monsoons
Changes in methane levels are caused by changes in summer monsoon in the tropics
Heavy monsoon rainfall  more bogs more vegetation decay  more CH4

5. Orbital-Scale Changes in CO2
Vostok Ice in Antarctica
Major CO2 cycles match marine δ18O (ice volume) cycles in an overall sense
Four 100,000-year cycles
23,000-year cycle not prominent
Which is driving which?
Maxima: ppm
Difficulties:
Low accuracy in dating in Antarctica
Minima: ppm
Dust reacts with CO2 bubbles in Greenland