Lecture 21: Ice Core Records

Orbital-Scale Changes in CO2 and CH4 Ocean sediments tell us ice-rafted debris, 18O records from the foraminifera shells (indicating ice volume and ocean temperature)Ice cores tell us two greenhouse gases (CO2 and CH4)

Ice Core and Instrumental CO2 and CH4 MeasurementsAtmospheric CO2 is ~2000 years younger than the ice layersMid-18th century: 280 ppm Early 20th century: 300 ppm 1958: 315 ppmNow: ~381 ppm (in 2006)

Orbital-Scale Changes in CH4Six cycles since the last interglacial periodMaxima: 550-700 ppbMinima: 350-450 ppb23000 years/cyclePeak methane values match peaks of monsoonsChanges in methane levels are caused by changes in summer monsoon in the tropicsHeavy monsoon rainfall more bogs more vegetation decay more CH4Vostok Ice in Antarctica

Orbital-Scale Changes in CO2Maxima: 280-300 ppmMinima: 180-190 ppmVostok Ice in AntarcticaFour 100,000-year cycles23,000-year cycle not prominentMajor CO2 cycles match marine 18O (ice volume) cycles in an overall senseWhich is driving which?Low accuracy in dating in Antarctica Difficulties:Dust reacts with CO2 bubbles in Greenland

This lecture was prepared on 1/23/2005 (Sunday).

Took me 5 hours (from 8:00pm to 1:00am)